Research ArticlePorogenic Behavior of Water in High-AluminaCastable Structures

Rafael Salomatildeo

Materials Engineering Department Satildeo Carlos School of Engineering University of Satildeo PauloAvenida Trabalhador Satildeo-carlense 400 Satildeo Carlos SP Brazil

Correspondence should be addressed to Rafael Salomatildeo rsalomaoscuspbr

Received 31 October 2017 Revised 30 January 2018 Accepted 26 April 2018 Published 7 June 2018

Academic Editor Marino Lavorgna

Copyright copy 2018 Rafael Salomatildeo +is is an open access article distributed under the Creative Commons Attribution Licensewhich permits unrestricted use distribution and reproduction in any medium provided the original work is properly cited

Direct casting is a processingmethod that can produce large parts of complex geometry It uses dispersions of ceramic particles inwater anda hydraulic binder for consolidation Studies on castable structures have reported the generation of a significant fraction of pores due to thepresence of water +is effect occurs because drying preserves part of the interparticle pores originally occupied by water +e fraction ofpores obtained in these cases can reach levels higher than 50 affecting the properties of the structure However the porogenic behavior ofwater in these materials was not investigated in depth In this work aqueous suspensions of calcined alumina and hydratable alumina(hydraulic binder) of different water contents (40ndash60 vol) were prepared in a paddler mixer For compositions of lower (5ndash35 vol) orhigher (66ndash80 vol) water amounts casting and curing steps were assisted by external pressure and a rotating device respectively toproduce homogeneous microstructures +e total porosity after drying was similar to the initial volumetric content of water in thecompositions when side effects such as sedimentation and air entrapment were prevented Below water content of 25 vol particlespacking flaws became the main pore generator and the hydroxylation reaction of the binder no longer occurred effectively

1 Introduction

In the process known as direct casting ceramic particles aremixed with water additives and a binder to produce a stablesuspension [1ndash5] After homogenization the system is castinto the desired shape and curing reactions harden thestructure [6 7] +e parts are then demolded and dried (insome cases further steps of thermal treatment are required)Due to its straightforwardness direct casting is widely used toproduce large parts of concrete in civil construction [5] andpieces of complex shapes of refractory materials [3 4 6 7] andrecently has been used to produce porous structures for high-temperature thermal insulation [8ndash11] Water is a key in-gredient in such processes and plays three main roles

Firstly water wets the surface of ceramic particlesforming a continuous phase amongst them (Figure 1(a))[5 12ndash15] Stable suspensions containing high solid loadscan be produced using particles of optimized size distri-bution proper dispersants to prevent agglomeration andsuitable mixing of high shear and turbulence [16ndash20] Under

favorable conditions such suspensions can present lowviscosity and excellent workability which are requirementsto facilitate the casting step and prevent the undesired en-trapment of air bubbles into the structure Secondly thepresence of water generates strong capillarity forces amongstlarge and fine particles (Figure 1(b)) [17 18 20 21] Suchforces are known as Wall effect and improve the packingefficiency of the system (compared to the same particle sizedistribution without water or application of external com-pacting forces) +irdly water is a major component of mostbinding systems for castable suspensions (Figure 1(c))[22ndash25] +e reactions amongst water and hydraulic binders(such as Portland and calcium aluminate cements hydrat-able alumina and plaster) during mixing and curing stepsproduce hydrated compounds that restrain the matrixparticle movement Colloidal binders (such as aqueoussuspensions of silica and alumina nanoparticles) andpolymeric binders (chitosan and sodium alginate) work ina similar way hardening the structure [7 19] Because allthese chemical reactions and the setting of the structures

HindawiAdvances in Materials Science and EngineeringVolume 2018 Article ID 2876851 10 pageshttpsdoiorg10115520182876851

occur in the presence of water most of the spaces it occupiesduring mixing are preserved during the curing and dryingsteps As a consequence direct casting usually producesstructures of higher porosity than other consolidatingmethods (such as pressing and slip-casting) [21 26]

+is last aspect has been recently used as an advanta-geous way to produce porous ceramics Aqueous suspen-sions of calcined alumina or silica (dense matrixes) severalinorganic porogenic agents (hydrotalcite [8] Al(OH)3[9 10] Mg(OH)2 [27] and CaCO3 [28]) and hydratablealumina were produced and directly cast using hydraulicbinders (hydratable alumina mainly) In these systems thetotal porosity levels attained after curing and drying (50ndash120degC 45ndash60) were close to the volumetric amount ofwater initially added during mixing (40ndash55) After thermaltreatment (up to 1700degC) pore content increases occurreddue to the dehydroxilationdecarbonatation of the porogenicagents and hydrated phases of the hydraulic binders+erefore the final total porosity levels of these castablesuspensions can be defined as a contribution of pores formedby water during the setting period (Figure 1(c)) and by thedecomposition of porogenic agents Based on this statementit is reasonable to assume that by controlling the wateramount in the composition the total porosity level of thestructures can be designed

For each system there is an optimum amount of water toproduce stable castable suspensions that can be determinedby means of viscosity measurements If the water content inthe casting suspensions is excessive particle sedimentationmay occur On the other hand if the total water amount inthe system is not enough to wet and spread particlesa continuous medium is not formed In both cases struc-tures of low homogeneity are produced To overcome these

aspects and study the impact of a wide variation in thewater content in physical properties of castable systemsthe present study used two strategies (1) to producesuspensions of very high solid loads (60ndash95 vol) waterwas added to the powders as a spray and the consolidationwas assisted by isostatic pressing and (2) to prevent particlesedimentation the initial setting of very low solid-load sus-pensions (20ndash55 vol) was performed in a rotating devicethat slightly agitates the liquid inside the molds beforehardening +e samples prepared by these methods werecompared to others produced in a conventional paddlermixer and static casting conditions (solid load varyingfrom 20 up to 75 vol)

2 Experimental

Raw materials calcined alumina (CA E-sy 1000 AlmatisUSA) hydratable alumina (HA Alphabond 300 AlmatisUSA) dispersant (diammonium citrate C6H14N2O7 DACSynth Brazil 030 wt dry-basis) and distilled water (from5 vol up to 80 vol) (Table 1) +e optimum dispersantcontent was previously determined and was in goodagreement with other reports [13]

Samples were prepared using three different casting andcuring methods (Table 2) (1) Static curing suspensionscontaining 25ndash80 vol of water were homogenized ina paddler mixer (PowerVisc Ika Germany 1000 rpm for 5minutes) cast under vibration as cylinders (length 70mmdiameter 16mm) and kept immobile at 60plusmn 2degC for 24 h inhigh-humidity atmosphere (2) Curing under rotation aftermixing and casting under vibration the molds containingcompositions of 45ndash80 vol of water were capped and fixedinside polyethylene spheres (diameter of 8 cm) placed

Water forms a continuousphase amongst ceramic particles

Ceramic particles

Hydraulic binders during thecuring step react with water toform hydrated compounds thathard the structure

Layer of dispersant moleculesat particlesrsquo surface preventagglomeration and improvedispersion

(a)

(c)

(b)

Water

Aggregates(DPart ge 100 microm)

Matrix (DPart lt 100 microm)Water helps to improvepacking efficiency near atthe aggregates (Wall effect)

Pores generated by waterduring the curing step

Figure 1 Roles of water in the preparation of ceramic particles suspensions (a) it is a continuous medium for particle dispersion (b) itimproves particle packing through the Wall effect and (c) it reacts with a hydraulic binder to strengthen the structure

2 Advances in Materials Science and Engineering

between two corotating cylinders (10 rpm) at 60 plusmn 2degC(Figure 2) In such an arrangement these spheres can rotatefreely in all directions and the gentile movement of the sus-pensions inside themolds prevents particle sedimentation After2h all compositions were rigid and remained static for another22h at 60plusmn2degC in high-humidity atmosphere (3) Casting

under pressure to produce samples of a very high solid loadwater (5ndash40 vol) was sprayed over the solid particlespreviously dry-mixed Afterwards these humid mixtureswere homogenized in an intensive stirrer (IKA1603600 IKAGermany) and compacted as 70mmtimes 16mm cylinders byisostatic pressing (Trexler CP360 USA 5MPa 60 s) usingflexible silicone molds +en the samples were kept immobileat 60plusmn 2degC for 24 h in high-humidity atmosphere A water-freereference sample was prepared using the same method

After the initial 24 h of curing all samples weredemolded and remained 24 h at 60plusmn 2degC and 24 h at 120plusmn4degC in a ventilated atmosphere +ese curing procedureswere used to maximize the binding effect of HA and reducethe likelihood of explosive spalling during the first drying[6 10 22 23]

Samples were measured (L length D diameter) andweighted (M mass) immediately after demolding (humidstage HS) and after drying at 120degC (dried stage DS) +eirlinear shrinkage after drying (LS ) was calculated using

LS 100 timesLHS minus LDS( 1113857

LHS1113890 1113891 (1)

+e total porosity (TP ) of the dried samples wascalculated using

Table 1 Characteristics of the raw materials tested

Physic-chemical propertiesSolid particles

Calcined alumina (CA) Hydratable alumina (HA)aComposition (wt) α-Al2O3 997 Na2O 02 Fe2O3 003 SiO2 034

CaO 003α-Al2O3 994 Na2O 005 Fe2O3 002 MgO 007

SiO2 003 CaO 002bParticles size (D50D90 μm) 1596 7631cSolid density (ρ gmiddotcmminus3) 389 272dSpecific surface area (SSAm2middotgminus1) 13 95eLOI (wt 1000degC) lt01 82aX-ray dispersive spectroscopy (EDX 720 Shimadzu Japan after calcination at 1000degC for 5 h) bDT-1202 (Dispersion Technology Inc USA) cHeliumpycnometer method (Ultrapyc 1200e Quantachrome Instruments USA) dN2 adsorption (Nova 1200e Quantachrome Instruments USA ASTM C 1069-09standard) e+ermogravimetry (TGA-Q50 TA Instruments 25ndash1000degC 5degCmiddotminminus1 heating rate and synthetic air atmosphere)

Table 2 Tested compositions

Casting and curing methodsRaw materials (volwt)

Water (W) Calcined alumina (CA) Hydratable alumina (HA) Solids load (CA+HA)Under pressure 500134 85509171 950695 95009866Under pressure 1000280 81009036 900684 90009720Under pressure 1500437 76508890 850673 85009563Under pressure 2000608 72008731 800661 80009392Under pressure static 2500794 67508557 750648 75009206Under pressure static 3000999 63008368 700634 70009001Under pressure static 35001223 58508159 650618 65008777Under pressure static 40001472 54007928 600600 60008528Static under rotation 45001748 49507671 550581 55008252Static under rotation 50002056 45007384 500559 50007944Static under rotation 55002403 40507062 450535 45007597Static under rotation 60002797 36006696 400507 40007203Static under rotation 65003247 31506278 350476 35006753Static under rotation 70003766 27005795 300439 30006234Static under rotation 75004371 22505232 250396 25005629Static under rotation 80005087 18004567 200346 20004913

Polyethylene sphere(diameter = 8 cm)

Possibilities of rotation(360deg in all directions)

Cylindrical mold(closed edgeslength 7 cminner diameter 16 cm)

Cast sample(~12 cm3)

Parallel rollers (spinning at 10 rpm)

Controlledtemperature(60degC plusmn 2degC)

Slow speedto prevent

centrifugation

Figure 2 Rotating device used to prevent particle sedimentationduring the curing step of very low solid-load suspensions

Advances in Materials Science and Engineering 3

TP 100 times 1minus4 middot MDS

π middot D2DS middot LDS middot ρSolid

1113888 11138891113890 1113891 (2)

where ρSolid is the solid density of the material (measured byHe pycnometer method in equivalent crushed samples)

+e Youngrsquos modulus (E GPa) of dried samples wasmeasured using impulse excitation of the vibration tech-nique (Sonelastic ATCP Brazil) according to the ASTME 1876-01 standard (ldquoStandard Test Method for DynamicYoungrsquos Modulus Shear Modulus and Poissonrsquos Ration byImpulse Excitation of Vibrationrdquo) Each linear shrinkagetotal porosity and elastic modulus result is the average valueof five different samples

Samplesrsquo pore size distributions and average pore size(APS) were determined by mercury intrusion porosimetry(PoreMaster 33 Quantochrome Instruments USA mercurysurface tension equal to 0480Nmiddotmminus1 contact angle of 130deg)and ranging applied pressure between 00014 and 210MPa+e fracturesrsquo cross sections of the samples were examinedby field emission scanning electron microscopy (FEG-SEM)

To understand how the workability of the suspensionscan affect particle packing and other physical properties theapparent viscosity of the suspensions (30ndash80 vol of water)was measured (Brookfield Viscosimeter VLDV-II+PROUSA) using a coaxial cylinder configuration (barrel 19mmdiameter by 65mm length and spindle 1747mm diameterby 3185mm height) During the measurements (at a shearrate of 50 sminus1 for 60 seconds) the temperature of the sus-pensions was kept at 25degCplusmn 05degC (thermal bath BrookfieldTC-550 USA) +ese parameters were previously de-termined as sufficient to achieve steady-state conditions+eshear rate of 50 sminus1 was chosen because the casting tech-niques that could be used to install this system usuallyemploy shear rates of 10ndash100 sminus1

3 Results and Discussion

31 Conventional Processing Suspensions Homogenized inPaddler Mixer and Cured Statically Samplesrsquo total porosity(TP) presented a strong linear dependence on water contentat the interval from 40 vol up to 60 vol (Figure 3) In this

range the TP values were very close to the initial volumetricamount of water in the composition It is noteworthy thatthe water amount affected poresrsquo size distribution (Figure 4)and morphology (Figures 5(a) and 5(b)) +is behavioroccurs because during the setting period of the binder thegreater the water content in the formulation the more apartparticles are in the suspension Consequently as averagespace amongst the particles in suspension increases TP andaverage pore size enhance linearly Although the mor-phology of the pores remained irregular it was possible toobserve a significant reduction in the particlesrsquo packingefficiency Such behaviors are typical from cast systemscontaining hydraulic binders such as hydratable alumina[6 7 10 29] On the other hand further increasing ordecreasing in the water content beyond or below this rangerespectively resulted in the opposite behavior with signif-icant deviations of linearity +ese unusual behaviors can beunderstood analyzing the processing conditions

Suspensions of water contents below 40 vol presentedhigh levels of apparent viscosity (η Figure 6) due to twomains effects Firstly for a same solid-liquid pair low watercontents generate denser fluids that require greater energy tobe deformed and flow [12 15 16] +erefore the denser thesuspensions the higher their apparent viscosity levels andvice-versa Secondly the high solid load reduces significantlythe spacing amongst particles and forms narrow channels ofnanometric dimension through which water must flow[17 18] Due to this the strong capillarity and attrite forcesand the constant shocks generated amongst particles restraintheir movement +e usually undesired consequence of thehigh viscosity is the entrapment of air bubbles during themixing that increases the porosity of the structure well abovethe volumetric water content in the composition Figures 7(a)and 7(b) presents the aspect of such samples at which largemillimetric voids are visible at the surface and beneath it incomparison to a defect-free one

Conversely suspensions of high water content (above 60vol) exhibited very low apparent viscosity levels anda linear dependence on the water content in the range of40ndash80 vol +is effect was reported elsewhere and is alsoexplained by means of the increase in the average spacing

0

25

50

75

100

0 10 20 30 40 50 60 70 80 90 1000

3

6

9

12

Tota

l por

osity

(TP

)

Elas

tic m

odul

us (E

GPa

)

Linear fitting for TP (40 le W le 60)R2 = 099 TP (W) = 100 W + 030

Linear fitting for E (40 le W le 60)R2 = 099 E (W) = ndash039 W + 244

Water content (W vol)

Figure 3 Effects of water content (W vol) on samplesrsquo total porosity (TP ) and flexural elastic modulus (EGPa) after conventional staticcuring and drying at 120degC for 24 h

4 Advances in Materials Science and Engineering

amongst particles and of the reduction in the wholedensity of the suspension [12 17 18] Despite the easymixing and casting the intense shrinkage observed after

drying (Figure 6) is a harmful side effect In these sus-pensions the excess of water reduced the binding effect ofhydratable alumina and favored particle sedimentation

Intr

uded

Hg

volu

me (

cm3 middotg

ndash1)

0000

0015

0030

0045

0060

001 01 1 10 100

Curing under rotation80 vol (APS = 24 microm)Static curing 40 vol(APS = 04 microm)

Curing under pressure 25 vol(APS = 007 microm)Static curing 60 vol(APS = 13 microm)

(a)

Pore diameter (microm)

00000

00025

00050

00075

00100

001 01 1 10 100

Incr

emen

tal i

ntru

sion

(cm

3 ∙gndash1

)

Curing under rotation80 vol (APS = 24 microm)Static curing 40 vol(APS = 04 microm)

Curing under pressure 25 vol(APS = 007 microm)Static curing 60 vol(APS = 13 microm)

(b)

Figure 4 (a) Continuous and (b) incremental pore size distribution for samples mixed and cured in the conventional static way containing40 vol and 60 vol of water containing 80 vol of water after curing under rotation and containing 25 vol of water cast underisostatic pressing APS average pore size

4 microm

(a)

4 microm

(b)

4 microm

(c)

4 microm

(d)

Figure 5 Microstructure of sample samples mixed and cured in the conventional static way containing (a) 40 vol and (b) 60 vol ofwater (c) containing 80 vol of water after curing under rotation (d) and containing 25 vol of water cast under isostatic pressing

Advances in Materials Science and Engineering 5

during the curing step (Figure 5(c)) +erefore as theparticles were practically free to move around during thedrying step the water withdrawal shrank the samplesreducing their total porosity Other processing methods(such as slip-casting) use this mechanism to improveparticle packing and to produce dense structures In directcasting on the other hand the poor dimension controland the generation of cracks are significant drawbacks thatmust be avoided

+e effects of water content and consequently poregeneration upon samplesrsquo flexural elastic modulus are shownin Figure 3 As observed for TP E presented an interval oflinear dependency on the water amount (40ndash60 vol) and

different behaviors for lower and higher contents +e linearrange can be understood using a simple model known asRule of the Mixtures [30] For a composite consisting of ndifferent components an estimate of its elastic modulus(EComposite) can be calculated by the sum of each individualmodulus value (Ei) multiplied by the correspondent volu-metric fraction

EComposite 1113944n

1Ei timesemptyi( 1113857 (3)

For a porous structure the elastic modulus of the voidsequals zero and (3) can be rewritten as a function of theelastic modulus and volumetric fraction of the dense part(EDense and emptyDense resp)

EPorous EDense timesemptyDense( 1113857 (4)

Unlike more sophisticated models Rule of Mixtures isa simplification of the real case because it does not considermicromechanic effects such as the effectiveness of theconnections amongst particles and average pore sizes andshapes Nevertheless it explains the influence of TP on Elevels quite well in the linear range For water contents lowerthan 40 vol and greater than 60 vol the E values dropand rise respectively following the TP level the less porousthe structure the more rigid it becomes and vice-versa [5]

32 Samples Cured under Rotation and under IsostaticPressing +e procedure of curing under rotation preventedparticle sedimentation (Figure 7(d)) and reduced dryingshrinkage (Figure 8(a)) significantly in all the water contentranges tested (45ndash80 vol) +ese effects indicate that thestructure formed during curing comprised by particleshighly spaced amongst each other was preserved by thebinding effect of hydratable alumina +ey also explain whyTP levels became linearly similar to the initial volumetricwater amount in these compositions after drying (Figure 8(b))

0

1350

2700

4050

5400

0 10 20 30 40 50 60 70 80 90 1000

3

6

9

12

Water content (W vol)

App

aren

t visc

osity

(η m

Pamiddots

at 5

0 sndash1

)

Line

ar sh

rinka

ge aft

er d

ryin

g (L

S

)

40ndash60 vol goodworkability and low

shrinkage after drying

65ndash80 vol sedimentationand significant shrinkage

after drying

5ndash35 vol poor or no workability(required external pressure) and

entrapment of air bubbles

Nonmeasurablebelow 30 vol

Linear fitting for η(40 le W le 80) R2 = 099η(W) = ndash1295W + 10452

Figure 6 Effects of water content (W vol) on compositionsrsquo apparent viscosity (η mPamiddotsminus1 measured at 50 sminus1 and 25degC) and linearshrinkage after drying (LS after 24 h at 120degC for samples cured in the conventional static way)

a)

b)

c)

d)

70 mm

70 mm

16 mm

16 mm

16 mm

5 mm

Supernatant

Precipitated particles

e)

70 mm

16 mm

Figure 7 Samples mixed and cured in the conventional static waycontaining (a) 25 vol (b) 50 vol and (c) 80 vol of water (tubecontaining sedimented suspension) (d) sample containing 80 volof water after curing under rotation (e) sample containing 25 vol ofwater cast under isostatic pressing

6 Advances in Materials Science and Engineering

0

3

6

9

12

0 10 20 30 40 50 60 70 80 90 100Water content (W vol)

Line

ar sh

rinka

ge a

er d

ryin

g (L

S

)

Curing under rotationStatic curing

Curing under pressure(nondetectable LS)

(a)

0

25

50

75

100

0 10 20 30 40 50 60 70 80 90 100Water content (W vol)

Tota

l por

osity

(TP

)

Linear fitting for TPRotation(45 le W le 80)R2 = 099 TPRotation(W) = 093W + 367

Water-free reference sample(0 2401)Curing under pressure Static curing

Curing underrotation

(b)

Figure 8 Continued

Advances in Materials Science and Engineering 7

and the increase in the average pore size (Figure 4)+e elasticmodulus values on the other hand were drastically re-duced as would be expected (the four smallest levels wereranged between 050 and 045 GPa) (Figure 8(c)) due to thelarge fraction of pores in the structures and the poor in-terconnections amongst the particles (Figure 5(c))

Such very low levels of E for samples of TP greater than50 are certainly a problem for materials that depend ex-clusively on the strengthening effect of the hydraulic bindersConcrete and mortar used in civil construction would re-quire strategies to improve mechanical properties such asfibers or steel bar reinforcement [5] On the other hand forsystems that are thermally treated after curing and drying(such as high-temperature thermal insulators eg) a sig-nificant gain of strength is expected after sintering and thehigh total porosity levels would be a technological advantage[26ndash28 31]

Compared to samples prepared by conventional staticcuring those cured under pressure presented no detectableshrinkage after drying (Figures 7(e) and 8(a)) significantlylower TP values (Figure 8(b)) and average pore size (Fig-ure 4) +ese effects relate to the high efficiency of particlepacking this shaping method produces (Figure 5(c)) and tothe extremely low volume of water added to the composi-tions In the water content range of 25ndash40 vol the TPreduction generated a huge gain of rigidity (Figure 8(c)) atwhich the greatest E value is two times higher than the bestresult achieved for conventional processing and almost threetimes than those cured under rotation +ese results suggestthat for applications where the initial green strength ismandatory curing under isostatic pressure could be a suit-able alternative to adding larger amounts of binders

For water contents below 25 vol samplesrsquo TP valuesstabilize around 25 and E levels are significantly reduced

To understand these effects it is important to observe thebehavior of the water-free reference sample Because nowater was added to this composition the TP value attainedafter compacting relates to the pores generated by packingflaws amongst the particles (248) +is residual porositycould be reduced by means of changing the particle sizedistribution of the calcined alumina matrix [16 17] butthese points are beyond the scopus of the present study Onthe other hand the rigidity of these samples is a combinationof the binding action of hydratable alumina and particlepacking [6 10 16 18] +e fact that the rigidity of the lowwater content samples is similar to the water-free one showsthe low effectiveness of the hydraulic binder in such com-positions A possible explanation for that is that there was noenough water in the system to promote full hydroxylation ofhydratable alumina [23ndash25]

4 Conclusions

Water can be a powerful porogenic agent for high-aluminastructures consolidated by direct casting In these materialschanging the volumetric amount of water in the composi-tion directly affected the physical properties of the structureattained When a conventional paddler mixer was used forhomogenization there was an intermediate water contentrange (40ndash60 vol) at which the suspensions producedpresented good workability (low apparent viscosity and nosignificant sedimentation) and low drying shrinkage In thisrange the total porosity average pore size and flexuralelastic modulus measured after drying presented a stronglinear dependency on the original water content When thewater contents were excessively increased or reducedprocessing drawbacks occurred In the diluted suspensions(65ndash80 vol of water) particle sedimentation occurred and

0

6

12

18

24

0 10 20 30 40 50 60 70 80 90 100Water content (W vol)

Elas

tic m

odul

us (E

GPa

)

Static castingCuring under rotationCuring under pressure

(c)

Figure 8 Effects of water content (W vol) on samples (a) linear shrinkage after drying (LS ) (b) total porosity (TP ) and (c) flexuralelastic modulus (E GPa) after conventional static curing curing under rotation and curing under isostatic pressure (drying performed at120degC for 24 h)

8 Advances in Materials Science and Engineering

structures of low homogeneity and high drying shrinkagewere generated For the more concentrated ones (5ndash35 volof water) on the contrary the poor workability promotedexcessive entrapment or air bubbles increasing total porosityand reducing elastic modulus +e rotating device used toprevent particle sedimentation allowed the casting andcuring of compositions containing up to 80 vol of waterwithout segregation For these samples total porosity valueswere close to the original volumetric amount of water in theformulation and their drying shrinkage was significantlyreduced compared to conventional processing Samplescured under isostatic compression and containing wateramounts between 25 and 40 vol were the strongestamongst all the compositions tested because of their lowtotal porosity and effective binding action of hydratablealumina Additional water content reductions (0ndash20 vol) onthe contrary did not further decrease the pore content +isbehavior can be explained by the interparticle packing flawsintrinsically present in this system that became the mainpore generator Besides this it is possible that the smallquantity of water present in these samples was not enough tofully hydroxilate the hydratable alumina reducing itsbinding effect

Conflicts of Interest

+e authors declare that they have no conflicts of interest

Acknowledgments

Brazilian Research Foundations FAPESP (2010-19274-5)and CNPq (4558612014-5) for supporting this study andAlmatis (Brazil USA and Germany) for kindly supplyingsamples of calcined and hydratable aluminas

References

[1] G V Givan L D Hart and G McZura ldquoCuring and firinghigh purity calcium aluminate-bonded tabular aluminacastablesrdquo American Ceramic Society Bulletin vol 54 no 8pp 710ndash713 1975

[2] A Nishikawa ldquoManufacture and properties of monolith re-fractoriesrdquo in Technology of Monolithic Refractories PlibricoCo Ltd Tokyo Japan 1984

[3] W E Lee and R E Moore ldquoEvolution of in situ refractories inthe 20th centuryrdquo Journal of the American Ceramic Societyvol 81 no 6 pp 1385ndash1410 1998

[4] F A Cardoso M D M Innocentini M M Akiyoshi andV C Pandolfelli ldquoEffect of curing time on the properties ofCAC bonded refractory castablesrdquo Journal of the EuropeanCeramic Society vol 24 no 7 pp 2073ndash2078 2004

[5] P K Mehta and P J M Monteiro Concrete MicrostructureProperties and Materials McGraw-Hill New York NY USA3rd edition 2006

[6] R Salomatildeo M R Ismael and V C Pandolfelli ldquoHydraulicbinders for refractory castables mixing curing and dryingrdquoCeramic Forum International vol 84 pp E103ndashE108 2007

[7] M R Ismael R Salomatildeo and V C Pandolfelli ldquoRefractorycastables based on colloidal silica and hydratable aluminardquoAmerican Ceramic Society Bulletin vol 86 no 9 pp 58ndash612007

[8] R Salomatildeo M O C Villas-Boas and V C PandolfellildquoPorous alumina-spinel ceramics for high temperature ap-plicationsrdquo Ceramics International vol 37 no 4 pp 1393ndash1399 2011

[9] A D V Souza C C Arruda L Fernandes M L P AntunesP K Kiyohara and R Salomatildeo ldquoCharacterization of alu-minum hydroxide (Al(OH)3) for its use as a porogenic agentin castable ceramicsrdquo Journal of the European Ceramic Societyvol 35 no 2 pp 803ndash812 2015

[10] A D V Souza L L Sousa L Fernandes P H L Cardosoand R Salomatildeo ldquoAl2O3-Al(OH)3-based castable porousstructuresrdquo Journal of the European Ceramic Society vol 35no 6 pp 1943ndash1954 2015

[11] L L Sousa A D V Souza L Fernandez V L Arantes andR Salomatildeo ldquoDevelopment of densification-resistant castableporous structures from in situ mulliterdquo Ceramics In-ternational vol 41 no 8 pp 9943ndash9545 2015

[12] G Schramm A Practical Approach to Rheology andRheometry Gebrueder HAAKE GmbH Karlsruhe Germany2nd edition 2000

[13] A R Studart V C Pandolfelli E Tervoot and L J GaucklerldquoGelling of alumina suspensions using alginic acid salt andhydroxyaluminum diacetaterdquo Journal of the American Ce-ramic Society vol 85 no 11 pp 2711ndash2718 2002

[14] F T Ramal R Salomatildeo and V C Pandolfelli ldquoWater contentand its effect on the drying behavior of refractory castablesrdquoRefractories Applications and News vol 10 no 3 pp 10ndash17 2005

[15] F S Ortega R H R Castro D Gouvea and V C Pandolfellildquo+e rheological behavior and surface charging of gelcastingalumina suspensionsrdquo Ceramics International vol 34 no 1pp 237ndash241 2008

[16] D M Roy B C Schutz and M R Silsbee ldquoProcessing andoptimized cements and concretes via particle packingrdquo Mate-rials Research Society Bulletin vol 18 no 3 pp 45ndash49 1993

[17] J E Funk and D R Dinger Predictive Process Control ofCrowded Particle Suspensions Applied to CeramicsManufacturing Kluwer Academic Publishers England 1994

[18] J E Funk and D R Dinger ldquoParticle size control for high-solids castables refractoriesrdquo American Ceramic SocietyBulletin vol 73 no 10 pp 66ndash69 1994

[19] M R Ismael R Salomatildeo and V C Pandolfelli ldquoOptimi-zation of the particle size distribution of colloidal silicacontaining refractory castablesrdquo Interceram vol 4 pp 34ndash392007

[20] R Salomatildeo and V C Pandolfelli ldquo+e PSD effect on thedrying efficiency of polymeric fibers containing castablesrdquoCeramics International vol 34 no 1 pp 173ndash180 2008

[21] J P Ollivier J C Maso and B Bourdette ldquoInterfacialtransition zone in concreterdquo Advanced Cement Based Ma-terials vol 2 no 1 pp 30ndash38 1995

[22] W Ma and P W Brown ldquoMechanisms of reaction ofhydratable aluminasrdquo Journal of the American Ceramic So-ciety vol 82 no 2 pp 453ndash456 1999

[23] F A Cardoso M D M Innocentini M F MirandaF A O Valenzuela and V C Pandolfelli ldquoDrying behavior ofhydratable alumina-bonded refractory castablesrdquo Journal of theEuropean Ceramic Society vol 24 no 5 pp 797ndash802 2004

[24] I R Oliveira and V C Pandolfelli ldquoCastable matrix additivesand their role on hydraulic binder hydrationrdquo Ceramics In-ternational vol 35 no 4 pp 1453ndash1460 2009

[25] R Salomatildeo and V C Pandolfelli ldquo+e role of hydraulicbinders on magnesia containing refractory castables calciumaluminate cement and hydratable aluminardquo Ceramics In-ternational vol 35 no 8 pp 3117ndash3124 2009

Advances in Materials Science and Engineering 9

[26] A D V Souza and R Salomatildeo ldquoEvaluation of the porogenicbehavior of aluminum hydroxide particles of different sizedistribution in castable high-alumina structuresrdquo Journal ofthe European Ceramic Society vol 36 no 3 pp 885ndash8972016

[27] R Salomatildeo A D V Souza and P H L Cardoso ldquoAcomparison of Al(OH)3 andMg(OH)2 as inorganic porogenicagents for aluminardquo InterceramndashRefractories Manual vol 4pp 193ndash199 2015

[28] R Salomatildeo V L Ferreira I R Oliveira A D V Souza andW R Correr ldquoMechanism of pore generation in calciumhexaluminate (CA6) ceramics formed in situ from calcinedalumina and calcium carbonate aggregatesrdquo Journal of theEuropean Ceramic Society vol 36 no 16 pp 4225ndash42352016

[29] R Salomatildeo M A Kawamura A D V Souza andJ Sakihama ldquoHydratable alumina-bonded suspensionsevolution of microstructure and physical properties duringfirst heatingrdquo InterceramndashRefractories Manual vol 1pp 28ndash23 2017

[30] H Ledbetter S Kim D Balzar S Crudele and W KrivenldquoElastic properties of mulliterdquo Journal of the American Ce-ramic Society vol 81 no 4 pp 1025ndash1028 1998

[31] A R Studart U T Gonzenbach E Tervoot andL J Gauckler ldquoProcessing routes to macroporous ceramicsa reviewrdquo Journal of the American Ceramic Society vol 89no 6 pp 1771ndash1789 2006

10 Advances in Materials Science and Engineering

CorrosionInternational Journal of

Hindawiwwwhindawicom Volume 2018

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Materials Science and EngineeringHindawiwwwhindawicom Volume 2018

Hindawiwwwhindawicom Volume 2018

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Analytical ChemistryInternational Journal of

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Submit your manuscripts atwwwhindawicom

between two corotating cylinders (10 rpm) at 60 plusmn 2degC(Figure 2) In such an arrangement these spheres can rotatefreely in all directions and the gentile movement of the sus-pensions inside themolds prevents particle sedimentation After2h all compositions were rigid and remained static for another22h at 60plusmn2degC in high-humidity atmosphere (3) Casting

under pressure to produce samples of a very high solid loadwater (5ndash40 vol) was sprayed over the solid particlespreviously dry-mixed Afterwards these humid mixtureswere homogenized in an intensive stirrer (IKA1603600 IKAGermany) and compacted as 70mmtimes 16mm cylinders byisostatic pressing (Trexler CP360 USA 5MPa 60 s) usingflexible silicone molds +en the samples were kept immobileat 60plusmn 2degC for 24 h in high-humidity atmosphere A water-freereference sample was prepared using the same method

After the initial 24 h of curing all samples weredemolded and remained 24 h at 60plusmn 2degC and 24 h at 120plusmn4degC in a ventilated atmosphere +ese curing procedureswere used to maximize the binding effect of HA and reducethe likelihood of explosive spalling during the first drying[6 10 22 23]

Samples were measured (L length D diameter) andweighted (M mass) immediately after demolding (humidstage HS) and after drying at 120degC (dried stage DS) +eirlinear shrinkage after drying (LS ) was calculated using

LS 100 timesLHS minus LDS( 1113857

LHS1113890 1113891 (1)

+e total porosity (TP ) of the dried samples wascalculated using

Table 1 Characteristics of the raw materials tested

Physic-chemical propertiesSolid particles

Calcined alumina (CA) Hydratable alumina (HA)aComposition (wt) α-Al2O3 997 Na2O 02 Fe2O3 003 SiO2 034

CaO 003α-Al2O3 994 Na2O 005 Fe2O3 002 MgO 007

SiO2 003 CaO 002bParticles size (D50D90 μm) 1596 7631cSolid density (ρ gmiddotcmminus3) 389 272dSpecific surface area (SSAm2middotgminus1) 13 95eLOI (wt 1000degC) lt01 82aX-ray dispersive spectroscopy (EDX 720 Shimadzu Japan after calcination at 1000degC for 5 h) bDT-1202 (Dispersion Technology Inc USA) cHeliumpycnometer method (Ultrapyc 1200e Quantachrome Instruments USA) dN2 adsorption (Nova 1200e Quantachrome Instruments USA ASTM C 1069-09standard) e+ermogravimetry (TGA-Q50 TA Instruments 25ndash1000degC 5degCmiddotminminus1 heating rate and synthetic air atmosphere)

Table 2 Tested compositions

Casting and curing methodsRaw materials (volwt)

Water (W) Calcined alumina (CA) Hydratable alumina (HA) Solids load (CA+HA)Under pressure 500134 85509171 950695 95009866Under pressure 1000280 81009036 900684 90009720Under pressure 1500437 76508890 850673 85009563Under pressure 2000608 72008731 800661 80009392Under pressure static 2500794 67508557 750648 75009206Under pressure static 3000999 63008368 700634 70009001Under pressure static 35001223 58508159 650618 65008777Under pressure static 40001472 54007928 600600 60008528Static under rotation 45001748 49507671 550581 55008252Static under rotation 50002056 45007384 500559 50007944Static under rotation 55002403 40507062 450535 45007597Static under rotation 60002797 36006696 400507 40007203Static under rotation 65003247 31506278 350476 35006753Static under rotation 70003766 27005795 300439 30006234Static under rotation 75004371 22505232 250396 25005629Static under rotation 80005087 18004567 200346 20004913

Polyethylene sphere(diameter = 8 cm)

Possibilities of rotation(360deg in all directions)

Cylindrical mold(closed edgeslength 7 cminner diameter 16 cm)

Cast sample(~12 cm3)

Parallel rollers (spinning at 10 rpm)

Controlledtemperature(60degC plusmn 2degC)

Slow speedto prevent

centrifugation

Figure 2 Rotating device used to prevent particle sedimentationduring the curing step of very low solid-load suspensions

Advances in Materials Science and Engineering 3

TP 100 times 1minus4 middot MDS

π middot D2DS middot LDS middot ρSolid

1113888 11138891113890 1113891 (2)

where ρSolid is the solid density of the material (measured byHe pycnometer method in equivalent crushed samples)

+e Youngrsquos modulus (E GPa) of dried samples wasmeasured using impulse excitation of the vibration tech-nique (Sonelastic ATCP Brazil) according to the ASTME 1876-01 standard (ldquoStandard Test Method for DynamicYoungrsquos Modulus Shear Modulus and Poissonrsquos Ration byImpulse Excitation of Vibrationrdquo) Each linear shrinkagetotal porosity and elastic modulus result is the average valueof five different samples

Samplesrsquo pore size distributions and average pore size(APS) were determined by mercury intrusion porosimetry(PoreMaster 33 Quantochrome Instruments USA mercurysurface tension equal to 0480Nmiddotmminus1 contact angle of 130deg)and ranging applied pressure between 00014 and 210MPa+e fracturesrsquo cross sections of the samples were examinedby field emission scanning electron microscopy (FEG-SEM)

To understand how the workability of the suspensionscan affect particle packing and other physical properties theapparent viscosity of the suspensions (30ndash80 vol of water)was measured (Brookfield Viscosimeter VLDV-II+PROUSA) using a coaxial cylinder configuration (barrel 19mmdiameter by 65mm length and spindle 1747mm diameterby 3185mm height) During the measurements (at a shearrate of 50 sminus1 for 60 seconds) the temperature of the sus-pensions was kept at 25degCplusmn 05degC (thermal bath BrookfieldTC-550 USA) +ese parameters were previously de-termined as sufficient to achieve steady-state conditions+eshear rate of 50 sminus1 was chosen because the casting tech-niques that could be used to install this system usuallyemploy shear rates of 10ndash100 sminus1

3 Results and Discussion

31 Conventional Processing Suspensions Homogenized inPaddler Mixer and Cured Statically Samplesrsquo total porosity(TP) presented a strong linear dependence on water contentat the interval from 40 vol up to 60 vol (Figure 3) In this

range the TP values were very close to the initial volumetricamount of water in the composition It is noteworthy thatthe water amount affected poresrsquo size distribution (Figure 4)and morphology (Figures 5(a) and 5(b)) +is behavioroccurs because during the setting period of the binder thegreater the water content in the formulation the more apartparticles are in the suspension Consequently as averagespace amongst the particles in suspension increases TP andaverage pore size enhance linearly Although the mor-phology of the pores remained irregular it was possible toobserve a significant reduction in the particlesrsquo packingefficiency Such behaviors are typical from cast systemscontaining hydraulic binders such as hydratable alumina[6 7 10 29] On the other hand further increasing ordecreasing in the water content beyond or below this rangerespectively resulted in the opposite behavior with signif-icant deviations of linearity +ese unusual behaviors can beunderstood analyzing the processing conditions

Suspensions of water contents below 40 vol presentedhigh levels of apparent viscosity (η Figure 6) due to twomains effects Firstly for a same solid-liquid pair low watercontents generate denser fluids that require greater energy tobe deformed and flow [12 15 16] +erefore the denser thesuspensions the higher their apparent viscosity levels andvice-versa Secondly the high solid load reduces significantlythe spacing amongst particles and forms narrow channels ofnanometric dimension through which water must flow[17 18] Due to this the strong capillarity and attrite forcesand the constant shocks generated amongst particles restraintheir movement +e usually undesired consequence of thehigh viscosity is the entrapment of air bubbles during themixing that increases the porosity of the structure well abovethe volumetric water content in the composition Figures 7(a)and 7(b) presents the aspect of such samples at which largemillimetric voids are visible at the surface and beneath it incomparison to a defect-free one

Conversely suspensions of high water content (above 60vol) exhibited very low apparent viscosity levels anda linear dependence on the water content in the range of40ndash80 vol +is effect was reported elsewhere and is alsoexplained by means of the increase in the average spacing

0

25

50

75

100

0 10 20 30 40 50 60 70 80 90 1000

3

6

9

12

Tota

l por

osity

(TP

)

Elas

tic m

odul

us (E

GPa

)

Linear fitting for TP (40 le W le 60)R2 = 099 TP (W) = 100 W + 030

Linear fitting for E (40 le W le 60)R2 = 099 E (W) = ndash039 W + 244

Water content (W vol)

Figure 3 Effects of water content (W vol) on samplesrsquo total porosity (TP ) and flexural elastic modulus (EGPa) after conventional staticcuring and drying at 120degC for 24 h

4 Advances in Materials Science and Engineering

amongst particles and of the reduction in the wholedensity of the suspension [12 17 18] Despite the easymixing and casting the intense shrinkage observed after

drying (Figure 6) is a harmful side effect In these sus-pensions the excess of water reduced the binding effect ofhydratable alumina and favored particle sedimentation

Intr

uded

Hg

volu

me (

cm3 middotg

ndash1)

0000

0015

0030

0045

0060

001 01 1 10 100

Curing under rotation80 vol (APS = 24 microm)Static curing 40 vol(APS = 04 microm)

Curing under pressure 25 vol(APS = 007 microm)Static curing 60 vol(APS = 13 microm)

(a)

Pore diameter (microm)

00000

00025

00050

00075

00100

001 01 1 10 100

Incr

emen

tal i

ntru

sion

(cm

3 ∙gndash1

)

Curing under rotation80 vol (APS = 24 microm)Static curing 40 vol(APS = 04 microm)

Curing under pressure 25 vol(APS = 007 microm)Static curing 60 vol(APS = 13 microm)

(b)

Figure 4 (a) Continuous and (b) incremental pore size distribution for samples mixed and cured in the conventional static way containing40 vol and 60 vol of water containing 80 vol of water after curing under rotation and containing 25 vol of water cast underisostatic pressing APS average pore size

4 microm

(a)

4 microm

(b)

4 microm

(c)

4 microm

(d)

Figure 5 Microstructure of sample samples mixed and cured in the conventional static way containing (a) 40 vol and (b) 60 vol ofwater (c) containing 80 vol of water after curing under rotation (d) and containing 25 vol of water cast under isostatic pressing

Advances in Materials Science and Engineering 5

during the curing step (Figure 5(c)) +erefore as theparticles were practically free to move around during thedrying step the water withdrawal shrank the samplesreducing their total porosity Other processing methods(such as slip-casting) use this mechanism to improveparticle packing and to produce dense structures In directcasting on the other hand the poor dimension controland the generation of cracks are significant drawbacks thatmust be avoided

+e effects of water content and consequently poregeneration upon samplesrsquo flexural elastic modulus are shownin Figure 3 As observed for TP E presented an interval oflinear dependency on the water amount (40ndash60 vol) and

different behaviors for lower and higher contents +e linearrange can be understood using a simple model known asRule of the Mixtures [30] For a composite consisting of ndifferent components an estimate of its elastic modulus(EComposite) can be calculated by the sum of each individualmodulus value (Ei) multiplied by the correspondent volu-metric fraction

EComposite 1113944n

1Ei timesemptyi( 1113857 (3)

For a porous structure the elastic modulus of the voidsequals zero and (3) can be rewritten as a function of theelastic modulus and volumetric fraction of the dense part(EDense and emptyDense resp)

EPorous EDense timesemptyDense( 1113857 (4)

Unlike more sophisticated models Rule of Mixtures isa simplification of the real case because it does not considermicromechanic effects such as the effectiveness of theconnections amongst particles and average pore sizes andshapes Nevertheless it explains the influence of TP on Elevels quite well in the linear range For water contents lowerthan 40 vol and greater than 60 vol the E values dropand rise respectively following the TP level the less porousthe structure the more rigid it becomes and vice-versa [5]

32 Samples Cured under Rotation and under IsostaticPressing +e procedure of curing under rotation preventedparticle sedimentation (Figure 7(d)) and reduced dryingshrinkage (Figure 8(a)) significantly in all the water contentranges tested (45ndash80 vol) +ese effects indicate that thestructure formed during curing comprised by particleshighly spaced amongst each other was preserved by thebinding effect of hydratable alumina +ey also explain whyTP levels became linearly similar to the initial volumetricwater amount in these compositions after drying (Figure 8(b))

0

1350

2700

4050

5400

0 10 20 30 40 50 60 70 80 90 1000

3

6

9

12

Water content (W vol)

App

aren

t visc

osity

(η m

Pamiddots

at 5

0 sndash1

)

Line

ar sh

rinka

ge aft

er d

ryin

g (L

S

)

40ndash60 vol goodworkability and low

shrinkage after drying

65ndash80 vol sedimentationand significant shrinkage

after drying

5ndash35 vol poor or no workability(required external pressure) and

entrapment of air bubbles

Nonmeasurablebelow 30 vol

Linear fitting for η(40 le W le 80) R2 = 099η(W) = ndash1295W + 10452

Figure 6 Effects of water content (W vol) on compositionsrsquo apparent viscosity (η mPamiddotsminus1 measured at 50 sminus1 and 25degC) and linearshrinkage after drying (LS after 24 h at 120degC for samples cured in the conventional static way)

a)

b)

c)

d)

70 mm

70 mm

16 mm

16 mm

16 mm

5 mm

Supernatant

Precipitated particles

e)

70 mm

16 mm

Figure 7 Samples mixed and cured in the conventional static waycontaining (a) 25 vol (b) 50 vol and (c) 80 vol of water (tubecontaining sedimented suspension) (d) sample containing 80 volof water after curing under rotation (e) sample containing 25 vol ofwater cast under isostatic pressing

6 Advances in Materials Science and Engineering

0

3

6

9

12

0 10 20 30 40 50 60 70 80 90 100Water content (W vol)

Line

ar sh

rinka

ge a

er d

ryin

g (L

S

)

Curing under rotationStatic curing

Curing under pressure(nondetectable LS)

(a)

0

25

50

75

100

0 10 20 30 40 50 60 70 80 90 100Water content (W vol)

Tota

l por

osity

(TP

)

Linear fitting for TPRotation(45 le W le 80)R2 = 099 TPRotation(W) = 093W + 367

Water-free reference sample(0 2401)Curing under pressure Static curing

Curing underrotation

(b)

Figure 8 Continued

Advances in Materials Science and Engineering 7

and the increase in the average pore size (Figure 4)+e elasticmodulus values on the other hand were drastically re-duced as would be expected (the four smallest levels wereranged between 050 and 045 GPa) (Figure 8(c)) due to thelarge fraction of pores in the structures and the poor in-terconnections amongst the particles (Figure 5(c))

Such very low levels of E for samples of TP greater than50 are certainly a problem for materials that depend ex-clusively on the strengthening effect of the hydraulic bindersConcrete and mortar used in civil construction would re-quire strategies to improve mechanical properties such asfibers or steel bar reinforcement [5] On the other hand forsystems that are thermally treated after curing and drying(such as high-temperature thermal insulators eg) a sig-nificant gain of strength is expected after sintering and thehigh total porosity levels would be a technological advantage[26ndash28 31]

Compared to samples prepared by conventional staticcuring those cured under pressure presented no detectableshrinkage after drying (Figures 7(e) and 8(a)) significantlylower TP values (Figure 8(b)) and average pore size (Fig-ure 4) +ese effects relate to the high efficiency of particlepacking this shaping method produces (Figure 5(c)) and tothe extremely low volume of water added to the composi-tions In the water content range of 25ndash40 vol the TPreduction generated a huge gain of rigidity (Figure 8(c)) atwhich the greatest E value is two times higher than the bestresult achieved for conventional processing and almost threetimes than those cured under rotation +ese results suggestthat for applications where the initial green strength ismandatory curing under isostatic pressure could be a suit-able alternative to adding larger amounts of binders

For water contents below 25 vol samplesrsquo TP valuesstabilize around 25 and E levels are significantly reduced

To understand these effects it is important to observe thebehavior of the water-free reference sample Because nowater was added to this composition the TP value attainedafter compacting relates to the pores generated by packingflaws amongst the particles (248) +is residual porositycould be reduced by means of changing the particle sizedistribution of the calcined alumina matrix [16 17] butthese points are beyond the scopus of the present study Onthe other hand the rigidity of these samples is a combinationof the binding action of hydratable alumina and particlepacking [6 10 16 18] +e fact that the rigidity of the lowwater content samples is similar to the water-free one showsthe low effectiveness of the hydraulic binder in such com-positions A possible explanation for that is that there was noenough water in the system to promote full hydroxylation ofhydratable alumina [23ndash25]

4 Conclusions

Water can be a powerful porogenic agent for high-aluminastructures consolidated by direct casting In these materialschanging the volumetric amount of water in the composi-tion directly affected the physical properties of the structureattained When a conventional paddler mixer was used forhomogenization there was an intermediate water contentrange (40ndash60 vol) at which the suspensions producedpresented good workability (low apparent viscosity and nosignificant sedimentation) and low drying shrinkage In thisrange the total porosity average pore size and flexuralelastic modulus measured after drying presented a stronglinear dependency on the original water content When thewater contents were excessively increased or reducedprocessing drawbacks occurred In the diluted suspensions(65ndash80 vol of water) particle sedimentation occurred and

0

6

12

18

24

0 10 20 30 40 50 60 70 80 90 100Water content (W vol)

Elas

tic m

odul

us (E

GPa

)

Static castingCuring under rotationCuring under pressure

(c)

Figure 8 Effects of water content (W vol) on samples (a) linear shrinkage after drying (LS ) (b) total porosity (TP ) and (c) flexuralelastic modulus (E GPa) after conventional static curing curing under rotation and curing under isostatic pressure (drying performed at120degC for 24 h)

8 Advances in Materials Science and Engineering

structures of low homogeneity and high drying shrinkagewere generated For the more concentrated ones (5ndash35 volof water) on the contrary the poor workability promotedexcessive entrapment or air bubbles increasing total porosityand reducing elastic modulus +e rotating device used toprevent particle sedimentation allowed the casting andcuring of compositions containing up to 80 vol of waterwithout segregation For these samples total porosity valueswere close to the original volumetric amount of water in theformulation and their drying shrinkage was significantlyreduced compared to conventional processing Samplescured under isostatic compression and containing wateramounts between 25 and 40 vol were the strongestamongst all the compositions tested because of their lowtotal porosity and effective binding action of hydratablealumina Additional water content reductions (0ndash20 vol) onthe contrary did not further decrease the pore content +isbehavior can be explained by the interparticle packing flawsintrinsically present in this system that became the mainpore generator Besides this it is possible that the smallquantity of water present in these samples was not enough tofully hydroxilate the hydratable alumina reducing itsbinding effect

Conflicts of Interest

+e authors declare that they have no conflicts of interest

Acknowledgments

Brazilian Research Foundations FAPESP (2010-19274-5)and CNPq (4558612014-5) for supporting this study andAlmatis (Brazil USA and Germany) for kindly supplyingsamples of calcined and hydratable aluminas

References

[1] G V Givan L D Hart and G McZura ldquoCuring and firinghigh purity calcium aluminate-bonded tabular aluminacastablesrdquo American Ceramic Society Bulletin vol 54 no 8pp 710ndash713 1975

[2] A Nishikawa ldquoManufacture and properties of monolith re-fractoriesrdquo in Technology of Monolithic Refractories PlibricoCo Ltd Tokyo Japan 1984

[3] W E Lee and R E Moore ldquoEvolution of in situ refractories inthe 20th centuryrdquo Journal of the American Ceramic Societyvol 81 no 6 pp 1385ndash1410 1998

[4] F A Cardoso M D M Innocentini M M Akiyoshi andV C Pandolfelli ldquoEffect of curing time on the properties ofCAC bonded refractory castablesrdquo Journal of the EuropeanCeramic Society vol 24 no 7 pp 2073ndash2078 2004

[5] P K Mehta and P J M Monteiro Concrete MicrostructureProperties and Materials McGraw-Hill New York NY USA3rd edition 2006

[6] R Salomatildeo M R Ismael and V C Pandolfelli ldquoHydraulicbinders for refractory castables mixing curing and dryingrdquoCeramic Forum International vol 84 pp E103ndashE108 2007

[7] M R Ismael R Salomatildeo and V C Pandolfelli ldquoRefractorycastables based on colloidal silica and hydratable aluminardquoAmerican Ceramic Society Bulletin vol 86 no 9 pp 58ndash612007

[8] R Salomatildeo M O C Villas-Boas and V C PandolfellildquoPorous alumina-spinel ceramics for high temperature ap-plicationsrdquo Ceramics International vol 37 no 4 pp 1393ndash1399 2011

[9] A D V Souza C C Arruda L Fernandes M L P AntunesP K Kiyohara and R Salomatildeo ldquoCharacterization of alu-minum hydroxide (Al(OH)3) for its use as a porogenic agentin castable ceramicsrdquo Journal of the European Ceramic Societyvol 35 no 2 pp 803ndash812 2015

[10] A D V Souza L L Sousa L Fernandes P H L Cardosoand R Salomatildeo ldquoAl2O3-Al(OH)3-based castable porousstructuresrdquo Journal of the European Ceramic Society vol 35no 6 pp 1943ndash1954 2015

[11] L L Sousa A D V Souza L Fernandez V L Arantes andR Salomatildeo ldquoDevelopment of densification-resistant castableporous structures from in situ mulliterdquo Ceramics In-ternational vol 41 no 8 pp 9943ndash9545 2015

[12] G Schramm A Practical Approach to Rheology andRheometry Gebrueder HAAKE GmbH Karlsruhe Germany2nd edition 2000

[13] A R Studart V C Pandolfelli E Tervoot and L J GaucklerldquoGelling of alumina suspensions using alginic acid salt andhydroxyaluminum diacetaterdquo Journal of the American Ce-ramic Society vol 85 no 11 pp 2711ndash2718 2002

[14] F T Ramal R Salomatildeo and V C Pandolfelli ldquoWater contentand its effect on the drying behavior of refractory castablesrdquoRefractories Applications and News vol 10 no 3 pp 10ndash17 2005

[15] F S Ortega R H R Castro D Gouvea and V C Pandolfellildquo+e rheological behavior and surface charging of gelcastingalumina suspensionsrdquo Ceramics International vol 34 no 1pp 237ndash241 2008

[16] D M Roy B C Schutz and M R Silsbee ldquoProcessing andoptimized cements and concretes via particle packingrdquo Mate-rials Research Society Bulletin vol 18 no 3 pp 45ndash49 1993

[17] J E Funk and D R Dinger Predictive Process Control ofCrowded Particle Suspensions Applied to CeramicsManufacturing Kluwer Academic Publishers England 1994

[18] J E Funk and D R Dinger ldquoParticle size control for high-solids castables refractoriesrdquo American Ceramic SocietyBulletin vol 73 no 10 pp 66ndash69 1994

[19] M R Ismael R Salomatildeo and V C Pandolfelli ldquoOptimi-zation of the particle size distribution of colloidal silicacontaining refractory castablesrdquo Interceram vol 4 pp 34ndash392007

[20] R Salomatildeo and V C Pandolfelli ldquo+e PSD effect on thedrying efficiency of polymeric fibers containing castablesrdquoCeramics International vol 34 no 1 pp 173ndash180 2008

[21] J P Ollivier J C Maso and B Bourdette ldquoInterfacialtransition zone in concreterdquo Advanced Cement Based Ma-terials vol 2 no 1 pp 30ndash38 1995

[22] W Ma and P W Brown ldquoMechanisms of reaction ofhydratable aluminasrdquo Journal of the American Ceramic So-ciety vol 82 no 2 pp 453ndash456 1999

[23] F A Cardoso M D M Innocentini M F MirandaF A O Valenzuela and V C Pandolfelli ldquoDrying behavior ofhydratable alumina-bonded refractory castablesrdquo Journal of theEuropean Ceramic Society vol 24 no 5 pp 797ndash802 2004

[24] I R Oliveira and V C Pandolfelli ldquoCastable matrix additivesand their role on hydraulic binder hydrationrdquo Ceramics In-ternational vol 35 no 4 pp 1453ndash1460 2009

[25] R Salomatildeo and V C Pandolfelli ldquo+e role of hydraulicbinders on magnesia containing refractory castables calciumaluminate cement and hydratable aluminardquo Ceramics In-ternational vol 35 no 8 pp 3117ndash3124 2009

Advances in Materials Science and Engineering 9

[26] A D V Souza and R Salomatildeo ldquoEvaluation of the porogenicbehavior of aluminum hydroxide particles of different sizedistribution in castable high-alumina structuresrdquo Journal ofthe European Ceramic Society vol 36 no 3 pp 885ndash8972016

[27] R Salomatildeo A D V Souza and P H L Cardoso ldquoAcomparison of Al(OH)3 andMg(OH)2 as inorganic porogenicagents for aluminardquo InterceramndashRefractories Manual vol 4pp 193ndash199 2015

[28] R Salomatildeo V L Ferreira I R Oliveira A D V Souza andW R Correr ldquoMechanism of pore generation in calciumhexaluminate (CA6) ceramics formed in situ from calcinedalumina and calcium carbonate aggregatesrdquo Journal of theEuropean Ceramic Society vol 36 no 16 pp 4225ndash42352016

[29] R Salomatildeo M A Kawamura A D V Souza andJ Sakihama ldquoHydratable alumina-bonded suspensionsevolution of microstructure and physical properties duringfirst heatingrdquo InterceramndashRefractories Manual vol 1pp 28ndash23 2017

[30] H Ledbetter S Kim D Balzar S Crudele and W KrivenldquoElastic properties of mulliterdquo Journal of the American Ce-ramic Society vol 81 no 4 pp 1025ndash1028 1998

[31] A R Studart U T Gonzenbach E Tervoot andL J Gauckler ldquoProcessing routes to macroporous ceramicsa reviewrdquo Journal of the American Ceramic Society vol 89no 6 pp 1771ndash1789 2006

10 Advances in Materials Science and Engineering

CorrosionInternational Journal of

Hindawiwwwhindawicom Volume 2018

Advances in

Materials Science and EngineeringHindawiwwwhindawicom Volume 2018

Hindawiwwwhindawicom Volume 2018

Journal of

Chemistry

Analytical ChemistryInternational Journal of

Hindawiwwwhindawicom Volume 2018

ScienticaHindawiwwwhindawicom Volume 2018

Polymer ScienceInternational Journal of

Hindawiwwwhindawicom Volume 2018

Hindawiwwwhindawicom Volume 2018

Advances in Condensed Matter Physics

Hindawiwwwhindawicom Volume 2018

International Journal of

BiomaterialsHindawiwwwhindawicom

Journal ofEngineeringVolume 2018

Applied ChemistryJournal of

Hindawiwwwhindawicom Volume 2018

NanotechnologyHindawiwwwhindawicom Volume 2018

Journal of

Hindawiwwwhindawicom Volume 2018

High Energy PhysicsAdvances in

Hindawi Publishing Corporation httpwwwhindawicom Volume 2013Hindawiwwwhindawicom

The Scientific World Journal

Volume 2018

TribologyAdvances in

Hindawiwwwhindawicom Volume 2018

Hindawiwwwhindawicom Volume 2018

ChemistryAdvances in

Hindawiwwwhindawicom Volume 2018

Advances inPhysical Chemistry

Hindawiwwwhindawicom Volume 2018

BioMed Research InternationalMaterials

Journal of

Hindawiwwwhindawicom Volume 2018

Na

nom

ate

ria

ls

Hindawiwwwhindawicom Volume 2018

Journal ofNanomaterials

Submit your manuscripts atwwwhindawicom

TP 100 times 1minus4 middot MDS

π middot D2DS middot LDS middot ρSolid

1113888 11138891113890 1113891 (2)

where ρSolid is the solid density of the material (measured byHe pycnometer method in equivalent crushed samples)

+e Youngrsquos modulus (E GPa) of dried samples wasmeasured using impulse excitation of the vibration tech-nique (Sonelastic ATCP Brazil) according to the ASTME 1876-01 standard (ldquoStandard Test Method for DynamicYoungrsquos Modulus Shear Modulus and Poissonrsquos Ration byImpulse Excitation of Vibrationrdquo) Each linear shrinkagetotal porosity and elastic modulus result is the average valueof five different samples

Samplesrsquo pore size distributions and average pore size(APS) were determined by mercury intrusion porosimetry(PoreMaster 33 Quantochrome Instruments USA mercurysurface tension equal to 0480Nmiddotmminus1 contact angle of 130deg)and ranging applied pressure between 00014 and 210MPa+e fracturesrsquo cross sections of the samples were examinedby field emission scanning electron microscopy (FEG-SEM)

To understand how the workability of the suspensionscan affect particle packing and other physical properties theapparent viscosity of the suspensions (30ndash80 vol of water)was measured (Brookfield Viscosimeter VLDV-II+PROUSA) using a coaxial cylinder configuration (barrel 19mmdiameter by 65mm length and spindle 1747mm diameterby 3185mm height) During the measurements (at a shearrate of 50 sminus1 for 60 seconds) the temperature of the sus-pensions was kept at 25degCplusmn 05degC (thermal bath BrookfieldTC-550 USA) +ese parameters were previously de-termined as sufficient to achieve steady-state conditions+eshear rate of 50 sminus1 was chosen because the casting tech-niques that could be used to install this system usuallyemploy shear rates of 10ndash100 sminus1

3 Results and Discussion

31 Conventional Processing Suspensions Homogenized inPaddler Mixer and Cured Statically Samplesrsquo total porosity(TP) presented a strong linear dependence on water contentat the interval from 40 vol up to 60 vol (Figure 3) In this

range the TP values were very close to the initial volumetricamount of water in the composition It is noteworthy thatthe water amount affected poresrsquo size distribution (Figure 4)and morphology (Figures 5(a) and 5(b)) +is behavioroccurs because during the setting period of the binder thegreater the water content in the formulation the more apartparticles are in the suspension Consequently as averagespace amongst the particles in suspension increases TP andaverage pore size enhance linearly Although the mor-phology of the pores remained irregular it was possible toobserve a significant reduction in the particlesrsquo packingefficiency Such behaviors are typical from cast systemscontaining hydraulic binders such as hydratable alumina[6 7 10 29] On the other hand further increasing ordecreasing in the water content beyond or below this rangerespectively resulted in the opposite behavior with signif-icant deviations of linearity +ese unusual behaviors can beunderstood analyzing the processing conditions

Suspensions of water contents below 40 vol presentedhigh levels of apparent viscosity (η Figure 6) due to twomains effects Firstly for a same solid-liquid pair low watercontents generate denser fluids that require greater energy tobe deformed and flow [12 15 16] +erefore the denser thesuspensions the higher their apparent viscosity levels andvice-versa Secondly the high solid load reduces significantlythe spacing amongst particles and forms narrow channels ofnanometric dimension through which water must flow[17 18] Due to this the strong capillarity and attrite forcesand the constant shocks generated amongst particles restraintheir movement +e usually undesired consequence of thehigh viscosity is the entrapment of air bubbles during themixing that increases the porosity of the structure well abovethe volumetric water content in the composition Figures 7(a)and 7(b) presents the aspect of such samples at which largemillimetric voids are visible at the surface and beneath it incomparison to a defect-free one

Conversely suspensions of high water content (above 60vol) exhibited very low apparent viscosity levels anda linear dependence on the water content in the range of40ndash80 vol +is effect was reported elsewhere and is alsoexplained by means of the increase in the average spacing

0

25

50

75

100

0 10 20 30 40 50 60 70 80 90 1000

3

6

9

12

Tota

l por

osity

(TP

)

Elas

tic m

odul

us (E

GPa

)

Linear fitting for TP (40 le W le 60)R2 = 099 TP (W) = 100 W + 030

Linear fitting for E (40 le W le 60)R2 = 099 E (W) = ndash039 W + 244

Water content (W vol)

Figure 3 Effects of water content (W vol) on samplesrsquo total porosity (TP ) and flexural elastic modulus (EGPa) after conventional staticcuring and drying at 120degC for 24 h

4 Advances in Materials Science and Engineering

amongst particles and of the reduction in the wholedensity of the suspension [12 17 18] Despite the easymixing and casting the intense shrinkage observed after

drying (Figure 6) is a harmful side effect In these sus-pensions the excess of water reduced the binding effect ofhydratable alumina and favored particle sedimentation

Intr

uded

Hg

volu

me (

cm3 middotg

ndash1)

0000

0015

0030

0045

0060

001 01 1 10 100

Curing under rotation80 vol (APS = 24 microm)Static curing 40 vol(APS = 04 microm)

Curing under pressure 25 vol(APS = 007 microm)Static curing 60 vol(APS = 13 microm)

(a)

Pore diameter (microm)

00000

00025

00050

00075

00100

001 01 1 10 100

Incr

emen

tal i

ntru

sion

(cm

3 ∙gndash1

)

Curing under rotation80 vol (APS = 24 microm)Static curing 40 vol(APS = 04 microm)

Curing under pressure 25 vol(APS = 007 microm)Static curing 60 vol(APS = 13 microm)

(b)

Figure 4 (a) Continuous and (b) incremental pore size distribution for samples mixed and cured in the conventional static way containing40 vol and 60 vol of water containing 80 vol of water after curing under rotation and containing 25 vol of water cast underisostatic pressing APS average pore size

4 microm

(a)

4 microm

(b)

4 microm

(c)

4 microm

(d)

Figure 5 Microstructure of sample samples mixed and cured in the conventional static way containing (a) 40 vol and (b) 60 vol ofwater (c) containing 80 vol of water after curing under rotation (d) and containing 25 vol of water cast under isostatic pressing

Advances in Materials Science and Engineering 5

during the curing step (Figure 5(c)) +erefore as theparticles were practically free to move around during thedrying step the water withdrawal shrank the samplesreducing their total porosity Other processing methods(such as slip-casting) use this mechanism to improveparticle packing and to produce dense structures In directcasting on the other hand the poor dimension controland the generation of cracks are significant drawbacks thatmust be avoided

+e effects of water content and consequently poregeneration upon samplesrsquo flexural elastic modulus are shownin Figure 3 As observed for TP E presented an interval oflinear dependency on the water amount (40ndash60 vol) and

different behaviors for lower and higher contents +e linearrange can be understood using a simple model known asRule of the Mixtures [30] For a composite consisting of ndifferent components an estimate of its elastic modulus(EComposite) can be calculated by the sum of each individualmodulus value (Ei) multiplied by the correspondent volu-metric fraction

EComposite 1113944n

1Ei timesemptyi( 1113857 (3)

For a porous structure the elastic modulus of the voidsequals zero and (3) can be rewritten as a function of theelastic modulus and volumetric fraction of the dense part(EDense and emptyDense resp)

EPorous EDense timesemptyDense( 1113857 (4)

Unlike more sophisticated models Rule of Mixtures isa simplification of the real case because it does not considermicromechanic effects such as the effectiveness of theconnections amongst particles and average pore sizes andshapes Nevertheless it explains the influence of TP on Elevels quite well in the linear range For water contents lowerthan 40 vol and greater than 60 vol the E values dropand rise respectively following the TP level the less porousthe structure the more rigid it becomes and vice-versa [5]

32 Samples Cured under Rotation and under IsostaticPressing +e procedure of curing under rotation preventedparticle sedimentation (Figure 7(d)) and reduced dryingshrinkage (Figure 8(a)) significantly in all the water contentranges tested (45ndash80 vol) +ese effects indicate that thestructure formed during curing comprised by particleshighly spaced amongst each other was preserved by thebinding effect of hydratable alumina +ey also explain whyTP levels became linearly similar to the initial volumetricwater amount in these compositions after drying (Figure 8(b))

0

1350

2700

4050

5400

0 10 20 30 40 50 60 70 80 90 1000

3

6

9

12

Water content (W vol)

App

aren

t visc

osity

(η m

Pamiddots

at 5

0 sndash1

)

Line

ar sh

rinka

ge aft

er d

ryin

g (L

S

)

40ndash60 vol goodworkability and low

shrinkage after drying

65ndash80 vol sedimentationand significant shrinkage

after drying

5ndash35 vol poor or no workability(required external pressure) and

entrapment of air bubbles

Nonmeasurablebelow 30 vol

Linear fitting for η(40 le W le 80) R2 = 099η(W) = ndash1295W + 10452

Figure 6 Effects of water content (W vol) on compositionsrsquo apparent viscosity (η mPamiddotsminus1 measured at 50 sminus1 and 25degC) and linearshrinkage after drying (LS after 24 h at 120degC for samples cured in the conventional static way)

a)

b)

c)

d)

70 mm

70 mm

16 mm

16 mm

16 mm

5 mm

Supernatant

Precipitated particles

e)

70 mm

16 mm

Figure 7 Samples mixed and cured in the conventional static waycontaining (a) 25 vol (b) 50 vol and (c) 80 vol of water (tubecontaining sedimented suspension) (d) sample containing 80 volof water after curing under rotation (e) sample containing 25 vol ofwater cast under isostatic pressing

6 Advances in Materials Science and Engineering

0

3

6

9

12

0 10 20 30 40 50 60 70 80 90 100Water content (W vol)

Line

ar sh

rinka

ge a

er d

ryin

g (L

S

)

Curing under rotationStatic curing

Curing under pressure(nondetectable LS)

(a)

0

25

50

75

100

0 10 20 30 40 50 60 70 80 90 100Water content (W vol)

Tota

l por

osity

(TP

)

Linear fitting for TPRotation(45 le W le 80)R2 = 099 TPRotation(W) = 093W + 367

Water-free reference sample(0 2401)Curing under pressure Static curing

Curing underrotation

(b)

Figure 8 Continued

Advances in Materials Science and Engineering 7

and the increase in the average pore size (Figure 4)+e elasticmodulus values on the other hand were drastically re-duced as would be expected (the four smallest levels wereranged between 050 and 045 GPa) (Figure 8(c)) due to thelarge fraction of pores in the structures and the poor in-terconnections amongst the particles (Figure 5(c))

Such very low levels of E for samples of TP greater than50 are certainly a problem for materials that depend ex-clusively on the strengthening effect of the hydraulic bindersConcrete and mortar used in civil construction would re-quire strategies to improve mechanical properties such asfibers or steel bar reinforcement [5] On the other hand forsystems that are thermally treated after curing and drying(such as high-temperature thermal insulators eg) a sig-nificant gain of strength is expected after sintering and thehigh total porosity levels would be a technological advantage[26ndash28 31]

Compared to samples prepared by conventional staticcuring those cured under pressure presented no detectableshrinkage after drying (Figures 7(e) and 8(a)) significantlylower TP values (Figure 8(b)) and average pore size (Fig-ure 4) +ese effects relate to the high efficiency of particlepacking this shaping method produces (Figure 5(c)) and tothe extremely low volume of water added to the composi-tions In the water content range of 25ndash40 vol the TPreduction generated a huge gain of rigidity (Figure 8(c)) atwhich the greatest E value is two times higher than the bestresult achieved for conventional processing and almost threetimes than those cured under rotation +ese results suggestthat for applications where the initial green strength ismandatory curing under isostatic pressure could be a suit-able alternative to adding larger amounts of binders

For water contents below 25 vol samplesrsquo TP valuesstabilize around 25 and E levels are significantly reduced

To understand these effects it is important to observe thebehavior of the water-free reference sample Because nowater was added to this composition the TP value attainedafter compacting relates to the pores generated by packingflaws amongst the particles (248) +is residual porositycould be reduced by means of changing the particle sizedistribution of the calcined alumina matrix [16 17] butthese points are beyond the scopus of the present study Onthe other hand the rigidity of these samples is a combinationof the binding action of hydratable alumina and particlepacking [6 10 16 18] +e fact that the rigidity of the lowwater content samples is similar to the water-free one showsthe low effectiveness of the hydraulic binder in such com-positions A possible explanation for that is that there was noenough water in the system to promote full hydroxylation ofhydratable alumina [23ndash25]

4 Conclusions

Water can be a powerful porogenic agent for high-aluminastructures consolidated by direct casting In these materialschanging the volumetric amount of water in the composi-tion directly affected the physical properties of the structureattained When a conventional paddler mixer was used forhomogenization there was an intermediate water contentrange (40ndash60 vol) at which the suspensions producedpresented good workability (low apparent viscosity and nosignificant sedimentation) and low drying shrinkage In thisrange the total porosity average pore size and flexuralelastic modulus measured after drying presented a stronglinear dependency on the original water content When thewater contents were excessively increased or reducedprocessing drawbacks occurred In the diluted suspensions(65ndash80 vol of water) particle sedimentation occurred and

0

6

12

18

24

0 10 20 30 40 50 60 70 80 90 100Water content (W vol)

Elas

tic m

odul

us (E

GPa

)

Static castingCuring under rotationCuring under pressure

(c)

Figure 8 Effects of water content (W vol) on samples (a) linear shrinkage after drying (LS ) (b) total porosity (TP ) and (c) flexuralelastic modulus (E GPa) after conventional static curing curing under rotation and curing under isostatic pressure (drying performed at120degC for 24 h)

8 Advances in Materials Science and Engineering

structures of low homogeneity and high drying shrinkagewere generated For the more concentrated ones (5ndash35 volof water) on the contrary the poor workability promotedexcessive entrapment or air bubbles increasing total porosityand reducing elastic modulus +e rotating device used toprevent particle sedimentation allowed the casting andcuring of compositions containing up to 80 vol of waterwithout segregation For these samples total porosity valueswere close to the original volumetric amount of water in theformulation and their drying shrinkage was significantlyreduced compared to conventional processing Samplescured under isostatic compression and containing wateramounts between 25 and 40 vol were the strongestamongst all the compositions tested because of their lowtotal porosity and effective binding action of hydratablealumina Additional water content reductions (0ndash20 vol) onthe contrary did not further decrease the pore content +isbehavior can be explained by the interparticle packing flawsintrinsically present in this system that became the mainpore generator Besides this it is possible that the smallquantity of water present in these samples was not enough tofully hydroxilate the hydratable alumina reducing itsbinding effect

Conflicts of Interest

+e authors declare that they have no conflicts of interest

Acknowledgments

Brazilian Research Foundations FAPESP (2010-19274-5)and CNPq (4558612014-5) for supporting this study andAlmatis (Brazil USA and Germany) for kindly supplyingsamples of calcined and hydratable aluminas

References

[1] G V Givan L D Hart and G McZura ldquoCuring and firinghigh purity calcium aluminate-bonded tabular aluminacastablesrdquo American Ceramic Society Bulletin vol 54 no 8pp 710ndash713 1975

[2] A Nishikawa ldquoManufacture and properties of monolith re-fractoriesrdquo in Technology of Monolithic Refractories PlibricoCo Ltd Tokyo Japan 1984

[3] W E Lee and R E Moore ldquoEvolution of in situ refractories inthe 20th centuryrdquo Journal of the American Ceramic Societyvol 81 no 6 pp 1385ndash1410 1998

[4] F A Cardoso M D M Innocentini M M Akiyoshi andV C Pandolfelli ldquoEffect of curing time on the properties ofCAC bonded refractory castablesrdquo Journal of the EuropeanCeramic Society vol 24 no 7 pp 2073ndash2078 2004

[5] P K Mehta and P J M Monteiro Concrete MicrostructureProperties and Materials McGraw-Hill New York NY USA3rd edition 2006

[6] R Salomatildeo M R Ismael and V C Pandolfelli ldquoHydraulicbinders for refractory castables mixing curing and dryingrdquoCeramic Forum International vol 84 pp E103ndashE108 2007

[7] M R Ismael R Salomatildeo and V C Pandolfelli ldquoRefractorycastables based on colloidal silica and hydratable aluminardquoAmerican Ceramic Society Bulletin vol 86 no 9 pp 58ndash612007

[8] R Salomatildeo M O C Villas-Boas and V C PandolfellildquoPorous alumina-spinel ceramics for high temperature ap-plicationsrdquo Ceramics International vol 37 no 4 pp 1393ndash1399 2011

[9] A D V Souza C C Arruda L Fernandes M L P AntunesP K Kiyohara and R Salomatildeo ldquoCharacterization of alu-minum hydroxide (Al(OH)3) for its use as a porogenic agentin castable ceramicsrdquo Journal of the European Ceramic Societyvol 35 no 2 pp 803ndash812 2015

[10] A D V Souza L L Sousa L Fernandes P H L Cardosoand R Salomatildeo ldquoAl2O3-Al(OH)3-based castable porousstructuresrdquo Journal of the European Ceramic Society vol 35no 6 pp 1943ndash1954 2015

[11] L L Sousa A D V Souza L Fernandez V L Arantes andR Salomatildeo ldquoDevelopment of densification-resistant castableporous structures from in situ mulliterdquo Ceramics In-ternational vol 41 no 8 pp 9943ndash9545 2015

[12] G Schramm A Practical Approach to Rheology andRheometry Gebrueder HAAKE GmbH Karlsruhe Germany2nd edition 2000

[13] A R Studart V C Pandolfelli E Tervoot and L J GaucklerldquoGelling of alumina suspensions using alginic acid salt andhydroxyaluminum diacetaterdquo Journal of the American Ce-ramic Society vol 85 no 11 pp 2711ndash2718 2002

[14] F T Ramal R Salomatildeo and V C Pandolfelli ldquoWater contentand its effect on the drying behavior of refractory castablesrdquoRefractories Applications and News vol 10 no 3 pp 10ndash17 2005

[15] F S Ortega R H R Castro D Gouvea and V C Pandolfellildquo+e rheological behavior and surface charging of gelcastingalumina suspensionsrdquo Ceramics International vol 34 no 1pp 237ndash241 2008

[16] D M Roy B C Schutz and M R Silsbee ldquoProcessing andoptimized cements and concretes via particle packingrdquo Mate-rials Research Society Bulletin vol 18 no 3 pp 45ndash49 1993

[17] J E Funk and D R Dinger Predictive Process Control ofCrowded Particle Suspensions Applied to CeramicsManufacturing Kluwer Academic Publishers England 1994

[18] J E Funk and D R Dinger ldquoParticle size control for high-solids castables refractoriesrdquo American Ceramic SocietyBulletin vol 73 no 10 pp 66ndash69 1994

[19] M R Ismael R Salomatildeo and V C Pandolfelli ldquoOptimi-zation of the particle size distribution of colloidal silicacontaining refractory castablesrdquo Interceram vol 4 pp 34ndash392007

[20] R Salomatildeo and V C Pandolfelli ldquo+e PSD effect on thedrying efficiency of polymeric fibers containing castablesrdquoCeramics International vol 34 no 1 pp 173ndash180 2008

[21] J P Ollivier J C Maso and B Bourdette ldquoInterfacialtransition zone in concreterdquo Advanced Cement Based Ma-terials vol 2 no 1 pp 30ndash38 1995

[22] W Ma and P W Brown ldquoMechanisms of reaction ofhydratable aluminasrdquo Journal of the American Ceramic So-ciety vol 82 no 2 pp 453ndash456 1999

[23] F A Cardoso M D M Innocentini M F MirandaF A O Valenzuela and V C Pandolfelli ldquoDrying behavior ofhydratable alumina-bonded refractory castablesrdquo Journal of theEuropean Ceramic Society vol 24 no 5 pp 797ndash802 2004

[24] I R Oliveira and V C Pandolfelli ldquoCastable matrix additivesand their role on hydraulic binder hydrationrdquo Ceramics In-ternational vol 35 no 4 pp 1453ndash1460 2009

[25] R Salomatildeo and V C Pandolfelli ldquo+e role of hydraulicbinders on magnesia containing refractory castables calciumaluminate cement and hydratable aluminardquo Ceramics In-ternational vol 35 no 8 pp 3117ndash3124 2009

Advances in Materials Science and Engineering 9

[26] A D V Souza and R Salomatildeo ldquoEvaluation of the porogenicbehavior of aluminum hydroxide particles of different sizedistribution in castable high-alumina structuresrdquo Journal ofthe European Ceramic Society vol 36 no 3 pp 885ndash8972016

[27] R Salomatildeo A D V Souza and P H L Cardoso ldquoAcomparison of Al(OH)3 andMg(OH)2 as inorganic porogenicagents for aluminardquo InterceramndashRefractories Manual vol 4pp 193ndash199 2015

[28] R Salomatildeo V L Ferreira I R Oliveira A D V Souza andW R Correr ldquoMechanism of pore generation in calciumhexaluminate (CA6) ceramics formed in situ from calcinedalumina and calcium carbonate aggregatesrdquo Journal of theEuropean Ceramic Society vol 36 no 16 pp 4225ndash42352016

[29] R Salomatildeo M A Kawamura A D V Souza andJ Sakihama ldquoHydratable alumina-bonded suspensionsevolution of microstructure and physical properties duringfirst heatingrdquo InterceramndashRefractories Manual vol 1pp 28ndash23 2017

[30] H Ledbetter S Kim D Balzar S Crudele and W KrivenldquoElastic properties of mulliterdquo Journal of the American Ce-ramic Society vol 81 no 4 pp 1025ndash1028 1998

[31] A R Studart U T Gonzenbach E Tervoot andL J Gauckler ldquoProcessing routes to macroporous ceramicsa reviewrdquo Journal of the American Ceramic Society vol 89no 6 pp 1771ndash1789 2006

10 Advances in Materials Science and Engineering

CorrosionInternational Journal of

Hindawiwwwhindawicom Volume 2018

Advances in

Materials Science and EngineeringHindawiwwwhindawicom Volume 2018

Hindawiwwwhindawicom Volume 2018

Journal of

Chemistry

Analytical ChemistryInternational Journal of

Hindawiwwwhindawicom Volume 2018

ScienticaHindawiwwwhindawicom Volume 2018

Polymer ScienceInternational Journal of

Hindawiwwwhindawicom Volume 2018

Hindawiwwwhindawicom Volume 2018

Advances in Condensed Matter Physics

Hindawiwwwhindawicom Volume 2018

International Journal of

BiomaterialsHindawiwwwhindawicom

Journal ofEngineeringVolume 2018

Applied ChemistryJournal of

Hindawiwwwhindawicom Volume 2018

NanotechnologyHindawiwwwhindawicom Volume 2018

Journal of

Hindawiwwwhindawicom Volume 2018

High Energy PhysicsAdvances in

Hindawi Publishing Corporation httpwwwhindawicom Volume 2013Hindawiwwwhindawicom

The Scientific World Journal

Volume 2018

TribologyAdvances in

Hindawiwwwhindawicom Volume 2018

Hindawiwwwhindawicom Volume 2018

ChemistryAdvances in

Hindawiwwwhindawicom Volume 2018

Advances inPhysical Chemistry

Hindawiwwwhindawicom Volume 2018

BioMed Research InternationalMaterials

Journal of

Hindawiwwwhindawicom Volume 2018

Na

nom

ate

ria

ls

Hindawiwwwhindawicom Volume 2018

Journal ofNanomaterials

Submit your manuscripts atwwwhindawicom

amongst particles and of the reduction in the wholedensity of the suspension [12 17 18] Despite the easymixing and casting the intense shrinkage observed after

drying (Figure 6) is a harmful side effect In these sus-pensions the excess of water reduced the binding effect ofhydratable alumina and favored particle sedimentation

Intr

uded

Hg

volu

me (

cm3 middotg

ndash1)

0000

0015

0030

0045

0060

001 01 1 10 100

Curing under rotation80 vol (APS = 24 microm)Static curing 40 vol(APS = 04 microm)

Curing under pressure 25 vol(APS = 007 microm)Static curing 60 vol(APS = 13 microm)

(a)

Pore diameter (microm)

00000

00025

00050

00075

00100

001 01 1 10 100

Incr

emen

tal i

ntru

sion

(cm

3 ∙gndash1

)

Curing under rotation80 vol (APS = 24 microm)Static curing 40 vol(APS = 04 microm)

Curing under pressure 25 vol(APS = 007 microm)Static curing 60 vol(APS = 13 microm)

(b)

Figure 4 (a) Continuous and (b) incremental pore size distribution for samples mixed and cured in the conventional static way containing40 vol and 60 vol of water containing 80 vol of water after curing under rotation and containing 25 vol of water cast underisostatic pressing APS average pore size

4 microm

(a)

4 microm

(b)

4 microm

(c)

4 microm

(d)

Figure 5 Microstructure of sample samples mixed and cured in the conventional static way containing (a) 40 vol and (b) 60 vol ofwater (c) containing 80 vol of water after curing under rotation (d) and containing 25 vol of water cast under isostatic pressing

Advances in Materials Science and Engineering 5

during the curing step (Figure 5(c)) +erefore as theparticles were practically free to move around during thedrying step the water withdrawal shrank the samplesreducing their total porosity Other processing methods(such as slip-casting) use this mechanism to improveparticle packing and to produce dense structures In directcasting on the other hand the poor dimension controland the generation of cracks are significant drawbacks thatmust be avoided

+e effects of water content and consequently poregeneration upon samplesrsquo flexural elastic modulus are shownin Figure 3 As observed for TP E presented an interval oflinear dependency on the water amount (40ndash60 vol) and

different behaviors for lower and higher contents +e linearrange can be understood using a simple model known asRule of the Mixtures [30] For a composite consisting of ndifferent components an estimate of its elastic modulus(EComposite) can be calculated by the sum of each individualmodulus value (Ei) multiplied by the correspondent volu-metric fraction

EComposite 1113944n

1Ei timesemptyi( 1113857 (3)

For a porous structure the elastic modulus of the voidsequals zero and (3) can be rewritten as a function of theelastic modulus and volumetric fraction of the dense part(EDense and emptyDense resp)

EPorous EDense timesemptyDense( 1113857 (4)

Unlike more sophisticated models Rule of Mixtures isa simplification of the real case because it does not considermicromechanic effects such as the effectiveness of theconnections amongst particles and average pore sizes andshapes Nevertheless it explains the influence of TP on Elevels quite well in the linear range For water contents lowerthan 40 vol and greater than 60 vol the E values dropand rise respectively following the TP level the less porousthe structure the more rigid it becomes and vice-versa [5]

32 Samples Cured under Rotation and under IsostaticPressing +e procedure of curing under rotation preventedparticle sedimentation (Figure 7(d)) and reduced dryingshrinkage (Figure 8(a)) significantly in all the water contentranges tested (45ndash80 vol) +ese effects indicate that thestructure formed during curing comprised by particleshighly spaced amongst each other was preserved by thebinding effect of hydratable alumina +ey also explain whyTP levels became linearly similar to the initial volumetricwater amount in these compositions after drying (Figure 8(b))

0

1350

2700

4050

5400

0 10 20 30 40 50 60 70 80 90 1000

3

6

9

12

Water content (W vol)

App

aren

t visc

osity

(η m

Pamiddots

at 5

0 sndash1

)

Line

ar sh

rinka

ge aft

er d

ryin

g (L

S

)

40ndash60 vol goodworkability and low

shrinkage after drying

65ndash80 vol sedimentationand significant shrinkage

after drying

5ndash35 vol poor or no workability(required external pressure) and

entrapment of air bubbles

Nonmeasurablebelow 30 vol

Linear fitting for η(40 le W le 80) R2 = 099η(W) = ndash1295W + 10452

Figure 6 Effects of water content (W vol) on compositionsrsquo apparent viscosity (η mPamiddotsminus1 measured at 50 sminus1 and 25degC) and linearshrinkage after drying (LS after 24 h at 120degC for samples cured in the conventional static way)

a)

b)

c)

d)

70 mm

70 mm

16 mm

16 mm

16 mm

5 mm

Supernatant

Precipitated particles

e)

70 mm

16 mm

Figure 7 Samples mixed and cured in the conventional static waycontaining (a) 25 vol (b) 50 vol and (c) 80 vol of water (tubecontaining sedimented suspension) (d) sample containing 80 volof water after curing under rotation (e) sample containing 25 vol ofwater cast under isostatic pressing

6 Advances in Materials Science and Engineering

0

3

6

9

12

0 10 20 30 40 50 60 70 80 90 100Water content (W vol)

Line

ar sh

rinka

ge a

er d

ryin

g (L

S

)

Curing under rotationStatic curing

Curing under pressure(nondetectable LS)

(a)

0

25

50

75

100

0 10 20 30 40 50 60 70 80 90 100Water content (W vol)

Tota

l por

osity

(TP

)

Linear fitting for TPRotation(45 le W le 80)R2 = 099 TPRotation(W) = 093W + 367

Water-free reference sample(0 2401)Curing under pressure Static curing

Curing underrotation

(b)

Figure 8 Continued

Advances in Materials Science and Engineering 7

and the increase in the average pore size (Figure 4)+e elasticmodulus values on the other hand were drastically re-duced as would be expected (the four smallest levels wereranged between 050 and 045 GPa) (Figure 8(c)) due to thelarge fraction of pores in the structures and the poor in-terconnections amongst the particles (Figure 5(c))

Such very low levels of E for samples of TP greater than50 are certainly a problem for materials that depend ex-clusively on the strengthening effect of the hydraulic bindersConcrete and mortar used in civil construction would re-quire strategies to improve mechanical properties such asfibers or steel bar reinforcement [5] On the other hand forsystems that are thermally treated after curing and drying(such as high-temperature thermal insulators eg) a sig-nificant gain of strength is expected after sintering and thehigh total porosity levels would be a technological advantage[26ndash28 31]

Compared to samples prepared by conventional staticcuring those cured under pressure presented no detectableshrinkage after drying (Figures 7(e) and 8(a)) significantlylower TP values (Figure 8(b)) and average pore size (Fig-ure 4) +ese effects relate to the high efficiency of particlepacking this shaping method produces (Figure 5(c)) and tothe extremely low volume of water added to the composi-tions In the water content range of 25ndash40 vol the TPreduction generated a huge gain of rigidity (Figure 8(c)) atwhich the greatest E value is two times higher than the bestresult achieved for conventional processing and almost threetimes than those cured under rotation +ese results suggestthat for applications where the initial green strength ismandatory curing under isostatic pressure could be a suit-able alternative to adding larger amounts of binders

For water contents below 25 vol samplesrsquo TP valuesstabilize around 25 and E levels are significantly reduced

To understand these effects it is important to observe thebehavior of the water-free reference sample Because nowater was added to this composition the TP value attainedafter compacting relates to the pores generated by packingflaws amongst the particles (248) +is residual porositycould be reduced by means of changing the particle sizedistribution of the calcined alumina matrix [16 17] butthese points are beyond the scopus of the present study Onthe other hand the rigidity of these samples is a combinationof the binding action of hydratable alumina and particlepacking [6 10 16 18] +e fact that the rigidity of the lowwater content samples is similar to the water-free one showsthe low effectiveness of the hydraulic binder in such com-positions A possible explanation for that is that there was noenough water in the system to promote full hydroxylation ofhydratable alumina [23ndash25]

4 Conclusions

Water can be a powerful porogenic agent for high-aluminastructures consolidated by direct casting In these materialschanging the volumetric amount of water in the composi-tion directly affected the physical properties of the structureattained When a conventional paddler mixer was used forhomogenization there was an intermediate water contentrange (40ndash60 vol) at which the suspensions producedpresented good workability (low apparent viscosity and nosignificant sedimentation) and low drying shrinkage In thisrange the total porosity average pore size and flexuralelastic modulus measured after drying presented a stronglinear dependency on the original water content When thewater contents were excessively increased or reducedprocessing drawbacks occurred In the diluted suspensions(65ndash80 vol of water) particle sedimentation occurred and

0

6

12

18

24

0 10 20 30 40 50 60 70 80 90 100Water content (W vol)

Elas

tic m

odul

us (E

GPa

)

Static castingCuring under rotationCuring under pressure

(c)

Figure 8 Effects of water content (W vol) on samples (a) linear shrinkage after drying (LS ) (b) total porosity (TP ) and (c) flexuralelastic modulus (E GPa) after conventional static curing curing under rotation and curing under isostatic pressure (drying performed at120degC for 24 h)

8 Advances in Materials Science and Engineering

structures of low homogeneity and high drying shrinkagewere generated For the more concentrated ones (5ndash35 volof water) on the contrary the poor workability promotedexcessive entrapment or air bubbles increasing total porosityand reducing elastic modulus +e rotating device used toprevent particle sedimentation allowed the casting andcuring of compositions containing up to 80 vol of waterwithout segregation For these samples total porosity valueswere close to the original volumetric amount of water in theformulation and their drying shrinkage was significantlyreduced compared to conventional processing Samplescured under isostatic compression and containing wateramounts between 25 and 40 vol were the strongestamongst all the compositions tested because of their lowtotal porosity and effective binding action of hydratablealumina Additional water content reductions (0ndash20 vol) onthe contrary did not further decrease the pore content +isbehavior can be explained by the interparticle packing flawsintrinsically present in this system that became the mainpore generator Besides this it is possible that the smallquantity of water present in these samples was not enough tofully hydroxilate the hydratable alumina reducing itsbinding effect

Conflicts of Interest

+e authors declare that they have no conflicts of interest

Acknowledgments

Brazilian Research Foundations FAPESP (2010-19274-5)and CNPq (4558612014-5) for supporting this study andAlmatis (Brazil USA and Germany) for kindly supplyingsamples of calcined and hydratable aluminas

References

[1] G V Givan L D Hart and G McZura ldquoCuring and firinghigh purity calcium aluminate-bonded tabular aluminacastablesrdquo American Ceramic Society Bulletin vol 54 no 8pp 710ndash713 1975

[2] A Nishikawa ldquoManufacture and properties of monolith re-fractoriesrdquo in Technology of Monolithic Refractories PlibricoCo Ltd Tokyo Japan 1984

[3] W E Lee and R E Moore ldquoEvolution of in situ refractories inthe 20th centuryrdquo Journal of the American Ceramic Societyvol 81 no 6 pp 1385ndash1410 1998

[4] F A Cardoso M D M Innocentini M M Akiyoshi andV C Pandolfelli ldquoEffect of curing time on the properties ofCAC bonded refractory castablesrdquo Journal of the EuropeanCeramic Society vol 24 no 7 pp 2073ndash2078 2004

[5] P K Mehta and P J M Monteiro Concrete MicrostructureProperties and Materials McGraw-Hill New York NY USA3rd edition 2006

[6] R Salomatildeo M R Ismael and V C Pandolfelli ldquoHydraulicbinders for refractory castables mixing curing and dryingrdquoCeramic Forum International vol 84 pp E103ndashE108 2007

[7] M R Ismael R Salomatildeo and V C Pandolfelli ldquoRefractorycastables based on colloidal silica and hydratable aluminardquoAmerican Ceramic Society Bulletin vol 86 no 9 pp 58ndash612007

[8] R Salomatildeo M O C Villas-Boas and V C PandolfellildquoPorous alumina-spinel ceramics for high temperature ap-plicationsrdquo Ceramics International vol 37 no 4 pp 1393ndash1399 2011

[9] A D V Souza C C Arruda L Fernandes M L P AntunesP K Kiyohara and R Salomatildeo ldquoCharacterization of alu-minum hydroxide (Al(OH)3) for its use as a porogenic agentin castable ceramicsrdquo Journal of the European Ceramic Societyvol 35 no 2 pp 803ndash812 2015

[10] A D V Souza L L Sousa L Fernandes P H L Cardosoand R Salomatildeo ldquoAl2O3-Al(OH)3-based castable porousstructuresrdquo Journal of the European Ceramic Society vol 35no 6 pp 1943ndash1954 2015

[11] L L Sousa A D V Souza L Fernandez V L Arantes andR Salomatildeo ldquoDevelopment of densification-resistant castableporous structures from in situ mulliterdquo Ceramics In-ternational vol 41 no 8 pp 9943ndash9545 2015

[12] G Schramm A Practical Approach to Rheology andRheometry Gebrueder HAAKE GmbH Karlsruhe Germany2nd edition 2000

[13] A R Studart V C Pandolfelli E Tervoot and L J GaucklerldquoGelling of alumina suspensions using alginic acid salt andhydroxyaluminum diacetaterdquo Journal of the American Ce-ramic Society vol 85 no 11 pp 2711ndash2718 2002

[14] F T Ramal R Salomatildeo and V C Pandolfelli ldquoWater contentand its effect on the drying behavior of refractory castablesrdquoRefractories Applications and News vol 10 no 3 pp 10ndash17 2005

[15] F S Ortega R H R Castro D Gouvea and V C Pandolfellildquo+e rheological behavior and surface charging of gelcastingalumina suspensionsrdquo Ceramics International vol 34 no 1pp 237ndash241 2008

[16] D M Roy B C Schutz and M R Silsbee ldquoProcessing andoptimized cements and concretes via particle packingrdquo Mate-rials Research Society Bulletin vol 18 no 3 pp 45ndash49 1993

[17] J E Funk and D R Dinger Predictive Process Control ofCrowded Particle Suspensions Applied to CeramicsManufacturing Kluwer Academic Publishers England 1994

[18] J E Funk and D R Dinger ldquoParticle size control for high-solids castables refractoriesrdquo American Ceramic SocietyBulletin vol 73 no 10 pp 66ndash69 1994

[19] M R Ismael R Salomatildeo and V C Pandolfelli ldquoOptimi-zation of the particle size distribution of colloidal silicacontaining refractory castablesrdquo Interceram vol 4 pp 34ndash392007

[20] R Salomatildeo and V C Pandolfelli ldquo+e PSD effect on thedrying efficiency of polymeric fibers containing castablesrdquoCeramics International vol 34 no 1 pp 173ndash180 2008

[21] J P Ollivier J C Maso and B Bourdette ldquoInterfacialtransition zone in concreterdquo Advanced Cement Based Ma-terials vol 2 no 1 pp 30ndash38 1995

[22] W Ma and P W Brown ldquoMechanisms of reaction ofhydratable aluminasrdquo Journal of the American Ceramic So-ciety vol 82 no 2 pp 453ndash456 1999

[23] F A Cardoso M D M Innocentini M F MirandaF A O Valenzuela and V C Pandolfelli ldquoDrying behavior ofhydratable alumina-bonded refractory castablesrdquo Journal of theEuropean Ceramic Society vol 24 no 5 pp 797ndash802 2004

[24] I R Oliveira and V C Pandolfelli ldquoCastable matrix additivesand their role on hydraulic binder hydrationrdquo Ceramics In-ternational vol 35 no 4 pp 1453ndash1460 2009

[25] R Salomatildeo and V C Pandolfelli ldquo+e role of hydraulicbinders on magnesia containing refractory castables calciumaluminate cement and hydratable aluminardquo Ceramics In-ternational vol 35 no 8 pp 3117ndash3124 2009

Advances in Materials Science and Engineering 9

[26] A D V Souza and R Salomatildeo ldquoEvaluation of the porogenicbehavior of aluminum hydroxide particles of different sizedistribution in castable high-alumina structuresrdquo Journal ofthe European Ceramic Society vol 36 no 3 pp 885ndash8972016

[27] R Salomatildeo A D V Souza and P H L Cardoso ldquoAcomparison of Al(OH)3 andMg(OH)2 as inorganic porogenicagents for aluminardquo InterceramndashRefractories Manual vol 4pp 193ndash199 2015

[28] R Salomatildeo V L Ferreira I R Oliveira A D V Souza andW R Correr ldquoMechanism of pore generation in calciumhexaluminate (CA6) ceramics formed in situ from calcinedalumina and calcium carbonate aggregatesrdquo Journal of theEuropean Ceramic Society vol 36 no 16 pp 4225ndash42352016

[29] R Salomatildeo M A Kawamura A D V Souza andJ Sakihama ldquoHydratable alumina-bonded suspensionsevolution of microstructure and physical properties duringfirst heatingrdquo InterceramndashRefractories Manual vol 1pp 28ndash23 2017

[30] H Ledbetter S Kim D Balzar S Crudele and W KrivenldquoElastic properties of mulliterdquo Journal of the American Ce-ramic Society vol 81 no 4 pp 1025ndash1028 1998

[31] A R Studart U T Gonzenbach E Tervoot andL J Gauckler ldquoProcessing routes to macroporous ceramicsa reviewrdquo Journal of the American Ceramic Society vol 89no 6 pp 1771ndash1789 2006

10 Advances in Materials Science and Engineering

CorrosionInternational Journal of

Hindawiwwwhindawicom Volume 2018

Advances in

Materials Science and EngineeringHindawiwwwhindawicom Volume 2018

Hindawiwwwhindawicom Volume 2018

Journal of

Chemistry

Analytical ChemistryInternational Journal of

Hindawiwwwhindawicom Volume 2018

ScienticaHindawiwwwhindawicom Volume 2018

Polymer ScienceInternational Journal of

Hindawiwwwhindawicom Volume 2018

Hindawiwwwhindawicom Volume 2018

Advances in Condensed Matter Physics

Hindawiwwwhindawicom Volume 2018

International Journal of

BiomaterialsHindawiwwwhindawicom

Journal ofEngineeringVolume 2018

Applied ChemistryJournal of

Hindawiwwwhindawicom Volume 2018

NanotechnologyHindawiwwwhindawicom Volume 2018

Journal of

Hindawiwwwhindawicom Volume 2018

High Energy PhysicsAdvances in

Hindawi Publishing Corporation httpwwwhindawicom Volume 2013Hindawiwwwhindawicom

The Scientific World Journal

Volume 2018

TribologyAdvances in

Hindawiwwwhindawicom Volume 2018

Hindawiwwwhindawicom Volume 2018

ChemistryAdvances in

Hindawiwwwhindawicom Volume 2018

Advances inPhysical Chemistry

Hindawiwwwhindawicom Volume 2018

BioMed Research InternationalMaterials

Journal of

Hindawiwwwhindawicom Volume 2018

Na

nom

ate

ria

ls

Hindawiwwwhindawicom Volume 2018

Journal ofNanomaterials

Submit your manuscripts atwwwhindawicom

during the curing step (Figure 5(c)) +erefore as theparticles were practically free to move around during thedrying step the water withdrawal shrank the samplesreducing their total porosity Other processing methods(such as slip-casting) use this mechanism to improveparticle packing and to produce dense structures In directcasting on the other hand the poor dimension controland the generation of cracks are significant drawbacks thatmust be avoided

+e effects of water content and consequently poregeneration upon samplesrsquo flexural elastic modulus are shownin Figure 3 As observed for TP E presented an interval oflinear dependency on the water amount (40ndash60 vol) and

different behaviors for lower and higher contents +e linearrange can be understood using a simple model known asRule of the Mixtures [30] For a composite consisting of ndifferent components an estimate of its elastic modulus(EComposite) can be calculated by the sum of each individualmodulus value (Ei) multiplied by the correspondent volu-metric fraction

EComposite 1113944n

1Ei timesemptyi( 1113857 (3)

For a porous structure the elastic modulus of the voidsequals zero and (3) can be rewritten as a function of theelastic modulus and volumetric fraction of the dense part(EDense and emptyDense resp)

EPorous EDense timesemptyDense( 1113857 (4)

Unlike more sophisticated models Rule of Mixtures isa simplification of the real case because it does not considermicromechanic effects such as the effectiveness of theconnections amongst particles and average pore sizes andshapes Nevertheless it explains the influence of TP on Elevels quite well in the linear range For water contents lowerthan 40 vol and greater than 60 vol the E values dropand rise respectively following the TP level the less porousthe structure the more rigid it becomes and vice-versa [5]

32 Samples Cured under Rotation and under IsostaticPressing +e procedure of curing under rotation preventedparticle sedimentation (Figure 7(d)) and reduced dryingshrinkage (Figure 8(a)) significantly in all the water contentranges tested (45ndash80 vol) +ese effects indicate that thestructure formed during curing comprised by particleshighly spaced amongst each other was preserved by thebinding effect of hydratable alumina +ey also explain whyTP levels became linearly similar to the initial volumetricwater amount in these compositions after drying (Figure 8(b))

0

1350

2700

4050

5400

0 10 20 30 40 50 60 70 80 90 1000

3

6

9

12

Water content (W vol)

App

aren

t visc

osity

(η m

Pamiddots

at 5

0 sndash1

)

Line

ar sh

rinka

ge aft

er d

ryin

g (L

S

)

40ndash60 vol goodworkability and low

shrinkage after drying

65ndash80 vol sedimentationand significant shrinkage

after drying

5ndash35 vol poor or no workability(required external pressure) and

entrapment of air bubbles

Nonmeasurablebelow 30 vol

Linear fitting for η(40 le W le 80) R2 = 099η(W) = ndash1295W + 10452

Figure 6 Effects of water content (W vol) on compositionsrsquo apparent viscosity (η mPamiddotsminus1 measured at 50 sminus1 and 25degC) and linearshrinkage after drying (LS after 24 h at 120degC for samples cured in the conventional static way)

a)

b)

c)

d)

70 mm

70 mm

16 mm

16 mm

16 mm

5 mm

Supernatant

Precipitated particles

e)

70 mm

16 mm

Figure 7 Samples mixed and cured in the conventional static waycontaining (a) 25 vol (b) 50 vol and (c) 80 vol of water (tubecontaining sedimented suspension) (d) sample containing 80 volof water after curing under rotation (e) sample containing 25 vol ofwater cast under isostatic pressing

6 Advances in Materials Science and Engineering

0

3

6

9

12

0 10 20 30 40 50 60 70 80 90 100Water content (W vol)

Line

ar sh

rinka

ge a

er d

ryin

g (L

S

)

Curing under rotationStatic curing

Curing under pressure(nondetectable LS)

(a)

0

25

50

75

100

0 10 20 30 40 50 60 70 80 90 100Water content (W vol)

Tota

l por

osity

(TP

)

Linear fitting for TPRotation(45 le W le 80)R2 = 099 TPRotation(W) = 093W + 367

Water-free reference sample(0 2401)Curing under pressure Static curing

Curing underrotation

(b)

Figure 8 Continued

Advances in Materials Science and Engineering 7

and the increase in the average pore size (Figure 4)+e elasticmodulus values on the other hand were drastically re-duced as would be expected (the four smallest levels wereranged between 050 and 045 GPa) (Figure 8(c)) due to thelarge fraction of pores in the structures and the poor in-terconnections amongst the particles (Figure 5(c))

Such very low levels of E for samples of TP greater than50 are certainly a problem for materials that depend ex-clusively on the strengthening effect of the hydraulic bindersConcrete and mortar used in civil construction would re-quire strategies to improve mechanical properties such asfibers or steel bar reinforcement [5] On the other hand forsystems that are thermally treated after curing and drying(such as high-temperature thermal insulators eg) a sig-nificant gain of strength is expected after sintering and thehigh total porosity levels would be a technological advantage[26ndash28 31]

Compared to samples prepared by conventional staticcuring those cured under pressure presented no detectableshrinkage after drying (Figures 7(e) and 8(a)) significantlylower TP values (Figure 8(b)) and average pore size (Fig-ure 4) +ese effects relate to the high efficiency of particlepacking this shaping method produces (Figure 5(c)) and tothe extremely low volume of water added to the composi-tions In the water content range of 25ndash40 vol the TPreduction generated a huge gain of rigidity (Figure 8(c)) atwhich the greatest E value is two times higher than the bestresult achieved for conventional processing and almost threetimes than those cured under rotation +ese results suggestthat for applications where the initial green strength ismandatory curing under isostatic pressure could be a suit-able alternative to adding larger amounts of binders

For water contents below 25 vol samplesrsquo TP valuesstabilize around 25 and E levels are significantly reduced

To understand these effects it is important to observe thebehavior of the water-free reference sample Because nowater was added to this composition the TP value attainedafter compacting relates to the pores generated by packingflaws amongst the particles (248) +is residual porositycould be reduced by means of changing the particle sizedistribution of the calcined alumina matrix [16 17] butthese points are beyond the scopus of the present study Onthe other hand the rigidity of these samples is a combinationof the binding action of hydratable alumina and particlepacking [6 10 16 18] +e fact that the rigidity of the lowwater content samples is similar to the water-free one showsthe low effectiveness of the hydraulic binder in such com-positions A possible explanation for that is that there was noenough water in the system to promote full hydroxylation ofhydratable alumina [23ndash25]

4 Conclusions

Water can be a powerful porogenic agent for high-aluminastructures consolidated by direct casting In these materialschanging the volumetric amount of water in the composi-tion directly affected the physical properties of the structureattained When a conventional paddler mixer was used forhomogenization there was an intermediate water contentrange (40ndash60 vol) at which the suspensions producedpresented good workability (low apparent viscosity and nosignificant sedimentation) and low drying shrinkage In thisrange the total porosity average pore size and flexuralelastic modulus measured after drying presented a stronglinear dependency on the original water content When thewater contents were excessively increased or reducedprocessing drawbacks occurred In the diluted suspensions(65ndash80 vol of water) particle sedimentation occurred and

0

6

12

18

24

0 10 20 30 40 50 60 70 80 90 100Water content (W vol)

Elas

tic m

odul

us (E

GPa

)

Static castingCuring under rotationCuring under pressure

(c)

Figure 8 Effects of water content (W vol) on samples (a) linear shrinkage after drying (LS ) (b) total porosity (TP ) and (c) flexuralelastic modulus (E GPa) after conventional static curing curing under rotation and curing under isostatic pressure (drying performed at120degC for 24 h)

8 Advances in Materials Science and Engineering

structures of low homogeneity and high drying shrinkagewere generated For the more concentrated ones (5ndash35 volof water) on the contrary the poor workability promotedexcessive entrapment or air bubbles increasing total porosityand reducing elastic modulus +e rotating device used toprevent particle sedimentation allowed the casting andcuring of compositions containing up to 80 vol of waterwithout segregation For these samples total porosity valueswere close to the original volumetric amount of water in theformulation and their drying shrinkage was significantlyreduced compared to conventional processing Samplescured under isostatic compression and containing wateramounts between 25 and 40 vol were the strongestamongst all the compositions tested because of their lowtotal porosity and effective binding action of hydratablealumina Additional water content reductions (0ndash20 vol) onthe contrary did not further decrease the pore content +isbehavior can be explained by the interparticle packing flawsintrinsically present in this system that became the mainpore generator Besides this it is possible that the smallquantity of water present in these samples was not enough tofully hydroxilate the hydratable alumina reducing itsbinding effect

Conflicts of Interest

+e authors declare that they have no conflicts of interest

Acknowledgments

Brazilian Research Foundations FAPESP (2010-19274-5)and CNPq (4558612014-5) for supporting this study andAlmatis (Brazil USA and Germany) for kindly supplyingsamples of calcined and hydratable aluminas

References

[1] G V Givan L D Hart and G McZura ldquoCuring and firinghigh purity calcium aluminate-bonded tabular aluminacastablesrdquo American Ceramic Society Bulletin vol 54 no 8pp 710ndash713 1975

[2] A Nishikawa ldquoManufacture and properties of monolith re-fractoriesrdquo in Technology of Monolithic Refractories PlibricoCo Ltd Tokyo Japan 1984

[3] W E Lee and R E Moore ldquoEvolution of in situ refractories inthe 20th centuryrdquo Journal of the American Ceramic Societyvol 81 no 6 pp 1385ndash1410 1998

[4] F A Cardoso M D M Innocentini M M Akiyoshi andV C Pandolfelli ldquoEffect of curing time on the properties ofCAC bonded refractory castablesrdquo Journal of the EuropeanCeramic Society vol 24 no 7 pp 2073ndash2078 2004

[5] P K Mehta and P J M Monteiro Concrete MicrostructureProperties and Materials McGraw-Hill New York NY USA3rd edition 2006

[6] R Salomatildeo M R Ismael and V C Pandolfelli ldquoHydraulicbinders for refractory castables mixing curing and dryingrdquoCeramic Forum International vol 84 pp E103ndashE108 2007

[7] M R Ismael R Salomatildeo and V C Pandolfelli ldquoRefractorycastables based on colloidal silica and hydratable aluminardquoAmerican Ceramic Society Bulletin vol 86 no 9 pp 58ndash612007

[8] R Salomatildeo M O C Villas-Boas and V C PandolfellildquoPorous alumina-spinel ceramics for high temperature ap-plicationsrdquo Ceramics International vol 37 no 4 pp 1393ndash1399 2011

[9] A D V Souza C C Arruda L Fernandes M L P AntunesP K Kiyohara and R Salomatildeo ldquoCharacterization of alu-minum hydroxide (Al(OH)3) for its use as a porogenic agentin castable ceramicsrdquo Journal of the European Ceramic Societyvol 35 no 2 pp 803ndash812 2015

[10] A D V Souza L L Sousa L Fernandes P H L Cardosoand R Salomatildeo ldquoAl2O3-Al(OH)3-based castable porousstructuresrdquo Journal of the European Ceramic Society vol 35no 6 pp 1943ndash1954 2015

[11] L L Sousa A D V Souza L Fernandez V L Arantes andR Salomatildeo ldquoDevelopment of densification-resistant castableporous structures from in situ mulliterdquo Ceramics In-ternational vol 41 no 8 pp 9943ndash9545 2015

[12] G Schramm A Practical Approach to Rheology andRheometry Gebrueder HAAKE GmbH Karlsruhe Germany2nd edition 2000

[13] A R Studart V C Pandolfelli E Tervoot and L J GaucklerldquoGelling of alumina suspensions using alginic acid salt andhydroxyaluminum diacetaterdquo Journal of the American Ce-ramic Society vol 85 no 11 pp 2711ndash2718 2002

[14] F T Ramal R Salomatildeo and V C Pandolfelli ldquoWater contentand its effect on the drying behavior of refractory castablesrdquoRefractories Applications and News vol 10 no 3 pp 10ndash17 2005

[15] F S Ortega R H R Castro D Gouvea and V C Pandolfellildquo+e rheological behavior and surface charging of gelcastingalumina suspensionsrdquo Ceramics International vol 34 no 1pp 237ndash241 2008

[16] D M Roy B C Schutz and M R Silsbee ldquoProcessing andoptimized cements and concretes via particle packingrdquo Mate-rials Research Society Bulletin vol 18 no 3 pp 45ndash49 1993

[17] J E Funk and D R Dinger Predictive Process Control ofCrowded Particle Suspensions Applied to CeramicsManufacturing Kluwer Academic Publishers England 1994

[18] J E Funk and D R Dinger ldquoParticle size control for high-solids castables refractoriesrdquo American Ceramic SocietyBulletin vol 73 no 10 pp 66ndash69 1994

[19] M R Ismael R Salomatildeo and V C Pandolfelli ldquoOptimi-zation of the particle size distribution of colloidal silicacontaining refractory castablesrdquo Interceram vol 4 pp 34ndash392007

[20] R Salomatildeo and V C Pandolfelli ldquo+e PSD effect on thedrying efficiency of polymeric fibers containing castablesrdquoCeramics International vol 34 no 1 pp 173ndash180 2008

[21] J P Ollivier J C Maso and B Bourdette ldquoInterfacialtransition zone in concreterdquo Advanced Cement Based Ma-terials vol 2 no 1 pp 30ndash38 1995

[22] W Ma and P W Brown ldquoMechanisms of reaction ofhydratable aluminasrdquo Journal of the American Ceramic So-ciety vol 82 no 2 pp 453ndash456 1999

[23] F A Cardoso M D M Innocentini M F MirandaF A O Valenzuela and V C Pandolfelli ldquoDrying behavior ofhydratable alumina-bonded refractory castablesrdquo Journal of theEuropean Ceramic Society vol 24 no 5 pp 797ndash802 2004

[24] I R Oliveira and V C Pandolfelli ldquoCastable matrix additivesand their role on hydraulic binder hydrationrdquo Ceramics In-ternational vol 35 no 4 pp 1453ndash1460 2009

[25] R Salomatildeo and V C Pandolfelli ldquo+e role of hydraulicbinders on magnesia containing refractory castables calciumaluminate cement and hydratable aluminardquo Ceramics In-ternational vol 35 no 8 pp 3117ndash3124 2009

Advances in Materials Science and Engineering 9

[26] A D V Souza and R Salomatildeo ldquoEvaluation of the porogenicbehavior of aluminum hydroxide particles of different sizedistribution in castable high-alumina structuresrdquo Journal ofthe European Ceramic Society vol 36 no 3 pp 885ndash8972016

[27] R Salomatildeo A D V Souza and P H L Cardoso ldquoAcomparison of Al(OH)3 andMg(OH)2 as inorganic porogenicagents for aluminardquo InterceramndashRefractories Manual vol 4pp 193ndash199 2015

[28] R Salomatildeo V L Ferreira I R Oliveira A D V Souza andW R Correr ldquoMechanism of pore generation in calciumhexaluminate (CA6) ceramics formed in situ from calcinedalumina and calcium carbonate aggregatesrdquo Journal of theEuropean Ceramic Society vol 36 no 16 pp 4225ndash42352016

[29] R Salomatildeo M A Kawamura A D V Souza andJ Sakihama ldquoHydratable alumina-bonded suspensionsevolution of microstructure and physical properties duringfirst heatingrdquo InterceramndashRefractories Manual vol 1pp 28ndash23 2017

[30] H Ledbetter S Kim D Balzar S Crudele and W KrivenldquoElastic properties of mulliterdquo Journal of the American Ce-ramic Society vol 81 no 4 pp 1025ndash1028 1998

[31] A R Studart U T Gonzenbach E Tervoot andL J Gauckler ldquoProcessing routes to macroporous ceramicsa reviewrdquo Journal of the American Ceramic Society vol 89no 6 pp 1771ndash1789 2006

10 Advances in Materials Science and Engineering

CorrosionInternational Journal of

Hindawiwwwhindawicom Volume 2018

Advances in

Materials Science and EngineeringHindawiwwwhindawicom Volume 2018

Hindawiwwwhindawicom Volume 2018

Journal of

Chemistry

Analytical ChemistryInternational Journal of

Hindawiwwwhindawicom Volume 2018

ScienticaHindawiwwwhindawicom Volume 2018

Polymer ScienceInternational Journal of

Hindawiwwwhindawicom Volume 2018

Hindawiwwwhindawicom Volume 2018

Advances in Condensed Matter Physics

Hindawiwwwhindawicom Volume 2018

International Journal of

BiomaterialsHindawiwwwhindawicom

Journal ofEngineeringVolume 2018

Applied ChemistryJournal of

Hindawiwwwhindawicom Volume 2018

NanotechnologyHindawiwwwhindawicom Volume 2018

Journal of

Hindawiwwwhindawicom Volume 2018

High Energy PhysicsAdvances in

Hindawi Publishing Corporation httpwwwhindawicom Volume 2013Hindawiwwwhindawicom

The Scientific World Journal

Volume 2018

TribologyAdvances in

Hindawiwwwhindawicom Volume 2018

Hindawiwwwhindawicom Volume 2018

ChemistryAdvances in

Hindawiwwwhindawicom Volume 2018

Advances inPhysical Chemistry

Hindawiwwwhindawicom Volume 2018

BioMed Research InternationalMaterials

Journal of

Hindawiwwwhindawicom Volume 2018

Na

nom

ate

ria

ls

Hindawiwwwhindawicom Volume 2018

Journal ofNanomaterials

Submit your manuscripts atwwwhindawicom

0

3

6

9

12

0 10 20 30 40 50 60 70 80 90 100Water content (W vol)

Line

ar sh

rinka

ge a

er d

ryin

g (L

S

)

Curing under rotationStatic curing

Curing under pressure(nondetectable LS)

(a)

0

25

50

75

100

0 10 20 30 40 50 60 70 80 90 100Water content (W vol)

Tota

l por

osity

(TP

)

Linear fitting for TPRotation(45 le W le 80)R2 = 099 TPRotation(W) = 093W + 367

Water-free reference sample(0 2401)Curing under pressure Static curing

Curing underrotation

(b)

Figure 8 Continued

Advances in Materials Science and Engineering 7

and the increase in the average pore size (Figure 4)+e elasticmodulus values on the other hand were drastically re-duced as would be expected (the four smallest levels wereranged between 050 and 045 GPa) (Figure 8(c)) due to thelarge fraction of pores in the structures and the poor in-terconnections amongst the particles (Figure 5(c))

Such very low levels of E for samples of TP greater than50 are certainly a problem for materials that depend ex-clusively on the strengthening effect of the hydraulic bindersConcrete and mortar used in civil construction would re-quire strategies to improve mechanical properties such asfibers or steel bar reinforcement [5] On the other hand forsystems that are thermally treated after curing and drying(such as high-temperature thermal insulators eg) a sig-nificant gain of strength is expected after sintering and thehigh total porosity levels would be a technological advantage[26ndash28 31]

Compared to samples prepared by conventional staticcuring those cured under pressure presented no detectableshrinkage after drying (Figures 7(e) and 8(a)) significantlylower TP values (Figure 8(b)) and average pore size (Fig-ure 4) +ese effects relate to the high efficiency of particlepacking this shaping method produces (Figure 5(c)) and tothe extremely low volume of water added to the composi-tions In the water content range of 25ndash40 vol the TPreduction generated a huge gain of rigidity (Figure 8(c)) atwhich the greatest E value is two times higher than the bestresult achieved for conventional processing and almost threetimes than those cured under rotation +ese results suggestthat for applications where the initial green strength ismandatory curing under isostatic pressure could be a suit-able alternative to adding larger amounts of binders

For water contents below 25 vol samplesrsquo TP valuesstabilize around 25 and E levels are significantly reduced

To understand these effects it is important to observe thebehavior of the water-free reference sample Because nowater was added to this composition the TP value attainedafter compacting relates to the pores generated by packingflaws amongst the particles (248) +is residual porositycould be reduced by means of changing the particle sizedistribution of the calcined alumina matrix [16 17] butthese points are beyond the scopus of the present study Onthe other hand the rigidity of these samples is a combinationof the binding action of hydratable alumina and particlepacking [6 10 16 18] +e fact that the rigidity of the lowwater content samples is similar to the water-free one showsthe low effectiveness of the hydraulic binder in such com-positions A possible explanation for that is that there was noenough water in the system to promote full hydroxylation ofhydratable alumina [23ndash25]

4 Conclusions

Water can be a powerful porogenic agent for high-aluminastructures consolidated by direct casting In these materialschanging the volumetric amount of water in the composi-tion directly affected the physical properties of the structureattained When a conventional paddler mixer was used forhomogenization there was an intermediate water contentrange (40ndash60 vol) at which the suspensions producedpresented good workability (low apparent viscosity and nosignificant sedimentation) and low drying shrinkage In thisrange the total porosity average pore size and flexuralelastic modulus measured after drying presented a stronglinear dependency on the original water content When thewater contents were excessively increased or reducedprocessing drawbacks occurred In the diluted suspensions(65ndash80 vol of water) particle sedimentation occurred and

0

6

12

18

24

0 10 20 30 40 50 60 70 80 90 100Water content (W vol)

Elas

tic m

odul

us (E

GPa

)

Static castingCuring under rotationCuring under pressure

(c)

Figure 8 Effects of water content (W vol) on samples (a) linear shrinkage after drying (LS ) (b) total porosity (TP ) and (c) flexuralelastic modulus (E GPa) after conventional static curing curing under rotation and curing under isostatic pressure (drying performed at120degC for 24 h)

8 Advances in Materials Science and Engineering

structures of low homogeneity and high drying shrinkagewere generated For the more concentrated ones (5ndash35 volof water) on the contrary the poor workability promotedexcessive entrapment or air bubbles increasing total porosityand reducing elastic modulus +e rotating device used toprevent particle sedimentation allowed the casting andcuring of compositions containing up to 80 vol of waterwithout segregation For these samples total porosity valueswere close to the original volumetric amount of water in theformulation and their drying shrinkage was significantlyreduced compared to conventional processing Samplescured under isostatic compression and containing wateramounts between 25 and 40 vol were the strongestamongst all the compositions tested because of their lowtotal porosity and effective binding action of hydratablealumina Additional water content reductions (0ndash20 vol) onthe contrary did not further decrease the pore content +isbehavior can be explained by the interparticle packing flawsintrinsically present in this system that became the mainpore generator Besides this it is possible that the smallquantity of water present in these samples was not enough tofully hydroxilate the hydratable alumina reducing itsbinding effect

Conflicts of Interest

+e authors declare that they have no conflicts of interest

Acknowledgments

Brazilian Research Foundations FAPESP (2010-19274-5)and CNPq (4558612014-5) for supporting this study andAlmatis (Brazil USA and Germany) for kindly supplyingsamples of calcined and hydratable aluminas

References

[1] G V Givan L D Hart and G McZura ldquoCuring and firinghigh purity calcium aluminate-bonded tabular aluminacastablesrdquo American Ceramic Society Bulletin vol 54 no 8pp 710ndash713 1975

[2] A Nishikawa ldquoManufacture and properties of monolith re-fractoriesrdquo in Technology of Monolithic Refractories PlibricoCo Ltd Tokyo Japan 1984

[3] W E Lee and R E Moore ldquoEvolution of in situ refractories inthe 20th centuryrdquo Journal of the American Ceramic Societyvol 81 no 6 pp 1385ndash1410 1998

[4] F A Cardoso M D M Innocentini M M Akiyoshi andV C Pandolfelli ldquoEffect of curing time on the properties ofCAC bonded refractory castablesrdquo Journal of the EuropeanCeramic Society vol 24 no 7 pp 2073ndash2078 2004

[5] P K Mehta and P J M Monteiro Concrete MicrostructureProperties and Materials McGraw-Hill New York NY USA3rd edition 2006

[6] R Salomatildeo M R Ismael and V C Pandolfelli ldquoHydraulicbinders for refractory castables mixing curing and dryingrdquoCeramic Forum International vol 84 pp E103ndashE108 2007

[7] M R Ismael R Salomatildeo and V C Pandolfelli ldquoRefractorycastables based on colloidal silica and hydratable aluminardquoAmerican Ceramic Society Bulletin vol 86 no 9 pp 58ndash612007

[8] R Salomatildeo M O C Villas-Boas and V C PandolfellildquoPorous alumina-spinel ceramics for high temperature ap-plicationsrdquo Ceramics International vol 37 no 4 pp 1393ndash1399 2011

[9] A D V Souza C C Arruda L Fernandes M L P AntunesP K Kiyohara and R Salomatildeo ldquoCharacterization of alu-minum hydroxide (Al(OH)3) for its use as a porogenic agentin castable ceramicsrdquo Journal of the European Ceramic Societyvol 35 no 2 pp 803ndash812 2015

[10] A D V Souza L L Sousa L Fernandes P H L Cardosoand R Salomatildeo ldquoAl2O3-Al(OH)3-based castable porousstructuresrdquo Journal of the European Ceramic Society vol 35no 6 pp 1943ndash1954 2015

[11] L L Sousa A D V Souza L Fernandez V L Arantes andR Salomatildeo ldquoDevelopment of densification-resistant castableporous structures from in situ mulliterdquo Ceramics In-ternational vol 41 no 8 pp 9943ndash9545 2015

[12] G Schramm A Practical Approach to Rheology andRheometry Gebrueder HAAKE GmbH Karlsruhe Germany2nd edition 2000

[13] A R Studart V C Pandolfelli E Tervoot and L J GaucklerldquoGelling of alumina suspensions using alginic acid salt andhydroxyaluminum diacetaterdquo Journal of the American Ce-ramic Society vol 85 no 11 pp 2711ndash2718 2002

[14] F T Ramal R Salomatildeo and V C Pandolfelli ldquoWater contentand its effect on the drying behavior of refractory castablesrdquoRefractories Applications and News vol 10 no 3 pp 10ndash17 2005

[15] F S Ortega R H R Castro D Gouvea and V C Pandolfellildquo+e rheological behavior and surface charging of gelcastingalumina suspensionsrdquo Ceramics International vol 34 no 1pp 237ndash241 2008

[16] D M Roy B C Schutz and M R Silsbee ldquoProcessing andoptimized cements and concretes via particle packingrdquo Mate-rials Research Society Bulletin vol 18 no 3 pp 45ndash49 1993

[17] J E Funk and D R Dinger Predictive Process Control ofCrowded Particle Suspensions Applied to CeramicsManufacturing Kluwer Academic Publishers England 1994

[18] J E Funk and D R Dinger ldquoParticle size control for high-solids castables refractoriesrdquo American Ceramic SocietyBulletin vol 73 no 10 pp 66ndash69 1994

[19] M R Ismael R Salomatildeo and V C Pandolfelli ldquoOptimi-zation of the particle size distribution of colloidal silicacontaining refractory castablesrdquo Interceram vol 4 pp 34ndash392007

[20] R Salomatildeo and V C Pandolfelli ldquo+e PSD effect on thedrying efficiency of polymeric fibers containing castablesrdquoCeramics International vol 34 no 1 pp 173ndash180 2008

[21] J P Ollivier J C Maso and B Bourdette ldquoInterfacialtransition zone in concreterdquo Advanced Cement Based Ma-terials vol 2 no 1 pp 30ndash38 1995

[22] W Ma and P W Brown ldquoMechanisms of reaction ofhydratable aluminasrdquo Journal of the American Ceramic So-ciety vol 82 no 2 pp 453ndash456 1999

[23] F A Cardoso M D M Innocentini M F MirandaF A O Valenzuela and V C Pandolfelli ldquoDrying behavior ofhydratable alumina-bonded refractory castablesrdquo Journal of theEuropean Ceramic Society vol 24 no 5 pp 797ndash802 2004

[24] I R Oliveira and V C Pandolfelli ldquoCastable matrix additivesand their role on hydraulic binder hydrationrdquo Ceramics In-ternational vol 35 no 4 pp 1453ndash1460 2009

[25] R Salomatildeo and V C Pandolfelli ldquo+e role of hydraulicbinders on magnesia containing refractory castables calciumaluminate cement and hydratable aluminardquo Ceramics In-ternational vol 35 no 8 pp 3117ndash3124 2009

Advances in Materials Science and Engineering 9

[26] A D V Souza and R Salomatildeo ldquoEvaluation of the porogenicbehavior of aluminum hydroxide particles of different sizedistribution in castable high-alumina structuresrdquo Journal ofthe European Ceramic Society vol 36 no 3 pp 885ndash8972016

[27] R Salomatildeo A D V Souza and P H L Cardoso ldquoAcomparison of Al(OH)3 andMg(OH)2 as inorganic porogenicagents for aluminardquo InterceramndashRefractories Manual vol 4pp 193ndash199 2015

[28] R Salomatildeo V L Ferreira I R Oliveira A D V Souza andW R Correr ldquoMechanism of pore generation in calciumhexaluminate (CA6) ceramics formed in situ from calcinedalumina and calcium carbonate aggregatesrdquo Journal of theEuropean Ceramic Society vol 36 no 16 pp 4225ndash42352016

[29] R Salomatildeo M A Kawamura A D V Souza andJ Sakihama ldquoHydratable alumina-bonded suspensionsevolution of microstructure and physical properties duringfirst heatingrdquo InterceramndashRefractories Manual vol 1pp 28ndash23 2017

[30] H Ledbetter S Kim D Balzar S Crudele and W KrivenldquoElastic properties of mulliterdquo Journal of the American Ce-ramic Society vol 81 no 4 pp 1025ndash1028 1998

[31] A R Studart U T Gonzenbach E Tervoot andL J Gauckler ldquoProcessing routes to macroporous ceramicsa reviewrdquo Journal of the American Ceramic Society vol 89no 6 pp 1771ndash1789 2006

10 Advances in Materials Science and Engineering

CorrosionInternational Journal of

Hindawiwwwhindawicom Volume 2018

Advances in

Materials Science and EngineeringHindawiwwwhindawicom Volume 2018

Hindawiwwwhindawicom Volume 2018

Journal of

Chemistry

Analytical ChemistryInternational Journal of

Hindawiwwwhindawicom Volume 2018

ScienticaHindawiwwwhindawicom Volume 2018

Polymer ScienceInternational Journal of

Hindawiwwwhindawicom Volume 2018

Hindawiwwwhindawicom Volume 2018

Advances in Condensed Matter Physics

Hindawiwwwhindawicom Volume 2018

International Journal of

BiomaterialsHindawiwwwhindawicom

Journal ofEngineeringVolume 2018

Applied ChemistryJournal of

Hindawiwwwhindawicom Volume 2018

NanotechnologyHindawiwwwhindawicom Volume 2018

Journal of

Hindawiwwwhindawicom Volume 2018

High Energy PhysicsAdvances in

Hindawi Publishing Corporation httpwwwhindawicom Volume 2013Hindawiwwwhindawicom

The Scientific World Journal

Volume 2018

TribologyAdvances in

Hindawiwwwhindawicom Volume 2018

Hindawiwwwhindawicom Volume 2018

ChemistryAdvances in

Hindawiwwwhindawicom Volume 2018

Advances inPhysical Chemistry

Hindawiwwwhindawicom Volume 2018

BioMed Research InternationalMaterials

Journal of

Hindawiwwwhindawicom Volume 2018

Na

nom

ate

ria

ls

Hindawiwwwhindawicom Volume 2018

Journal ofNanomaterials

Submit your manuscripts atwwwhindawicom

and the increase in the average pore size (Figure 4)+e elasticmodulus values on the other hand were drastically re-duced as would be expected (the four smallest levels wereranged between 050 and 045 GPa) (Figure 8(c)) due to thelarge fraction of pores in the structures and the poor in-terconnections amongst the particles (Figure 5(c))

Such very low levels of E for samples of TP greater than50 are certainly a problem for materials that depend ex-clusively on the strengthening effect of the hydraulic bindersConcrete and mortar used in civil construction would re-quire strategies to improve mechanical properties such asfibers or steel bar reinforcement [5] On the other hand forsystems that are thermally treated after curing and drying(such as high-temperature thermal insulators eg) a sig-nificant gain of strength is expected after sintering and thehigh total porosity levels would be a technological advantage[26ndash28 31]

Compared to samples prepared by conventional staticcuring those cured under pressure presented no detectableshrinkage after drying (Figures 7(e) and 8(a)) significantlylower TP values (Figure 8(b)) and average pore size (Fig-ure 4) +ese effects relate to the high efficiency of particlepacking this shaping method produces (Figure 5(c)) and tothe extremely low volume of water added to the composi-tions In the water content range of 25ndash40 vol the TPreduction generated a huge gain of rigidity (Figure 8(c)) atwhich the greatest E value is two times higher than the bestresult achieved for conventional processing and almost threetimes than those cured under rotation +ese results suggestthat for applications where the initial green strength ismandatory curing under isostatic pressure could be a suit-able alternative to adding larger amounts of binders

For water contents below 25 vol samplesrsquo TP valuesstabilize around 25 and E levels are significantly reduced

To understand these effects it is important to observe thebehavior of the water-free reference sample Because nowater was added to this composition the TP value attainedafter compacting relates to the pores generated by packingflaws amongst the particles (248) +is residual porositycould be reduced by means of changing the particle sizedistribution of the calcined alumina matrix [16 17] butthese points are beyond the scopus of the present study Onthe other hand the rigidity of these samples is a combinationof the binding action of hydratable alumina and particlepacking [6 10 16 18] +e fact that the rigidity of the lowwater content samples is similar to the water-free one showsthe low effectiveness of the hydraulic binder in such com-positions A possible explanation for that is that there was noenough water in the system to promote full hydroxylation ofhydratable alumina [23ndash25]

4 Conclusions

Water can be a powerful porogenic agent for high-aluminastructures consolidated by direct casting In these materialschanging the volumetric amount of water in the composi-tion directly affected the physical properties of the structureattained When a conventional paddler mixer was used forhomogenization there was an intermediate water contentrange (40ndash60 vol) at which the suspensions producedpresented good workability (low apparent viscosity and nosignificant sedimentation) and low drying shrinkage In thisrange the total porosity average pore size and flexuralelastic modulus measured after drying presented a stronglinear dependency on the original water content When thewater contents were excessively increased or reducedprocessing drawbacks occurred In the diluted suspensions(65ndash80 vol of water) particle sedimentation occurred and

0

6

12

18

24

0 10 20 30 40 50 60 70 80 90 100Water content (W vol)

Elas

tic m

odul

us (E

GPa

)

Static castingCuring under rotationCuring under pressure

(c)

Figure 8 Effects of water content (W vol) on samples (a) linear shrinkage after drying (LS ) (b) total porosity (TP ) and (c) flexuralelastic modulus (E GPa) after conventional static curing curing under rotation and curing under isostatic pressure (drying performed at120degC for 24 h)

8 Advances in Materials Science and Engineering

structures of low homogeneity and high drying shrinkagewere generated For the more concentrated ones (5ndash35 volof water) on the contrary the poor workability promotedexcessive entrapment or air bubbles increasing total porosityand reducing elastic modulus +e rotating device used toprevent particle sedimentation allowed the casting andcuring of compositions containing up to 80 vol of waterwithout segregation For these samples total porosity valueswere close to the original volumetric amount of water in theformulation and their drying shrinkage was significantlyreduced compared to conventional processing Samplescured under isostatic compression and containing wateramounts between 25 and 40 vol were the strongestamongst all the compositions tested because of their lowtotal porosity and effective binding action of hydratablealumina Additional water content reductions (0ndash20 vol) onthe contrary did not further decrease the pore content +isbehavior can be explained by the interparticle packing flawsintrinsically present in this system that became the mainpore generator Besides this it is possible that the smallquantity of water present in these samples was not enough tofully hydroxilate the hydratable alumina reducing itsbinding effect

Conflicts of Interest

+e authors declare that they have no conflicts of interest

Acknowledgments

Brazilian Research Foundations FAPESP (2010-19274-5)and CNPq (4558612014-5) for supporting this study andAlmatis (Brazil USA and Germany) for kindly supplyingsamples of calcined and hydratable aluminas

References

[1] G V Givan L D Hart and G McZura ldquoCuring and firinghigh purity calcium aluminate-bonded tabular aluminacastablesrdquo American Ceramic Society Bulletin vol 54 no 8pp 710ndash713 1975

[2] A Nishikawa ldquoManufacture and properties of monolith re-fractoriesrdquo in Technology of Monolithic Refractories PlibricoCo Ltd Tokyo Japan 1984

[3] W E Lee and R E Moore ldquoEvolution of in situ refractories inthe 20th centuryrdquo Journal of the American Ceramic Societyvol 81 no 6 pp 1385ndash1410 1998

[4] F A Cardoso M D M Innocentini M M Akiyoshi andV C Pandolfelli ldquoEffect of curing time on the properties ofCAC bonded refractory castablesrdquo Journal of the EuropeanCeramic Society vol 24 no 7 pp 2073ndash2078 2004

[5] P K Mehta and P J M Monteiro Concrete MicrostructureProperties and Materials McGraw-Hill New York NY USA3rd edition 2006

[6] R Salomatildeo M R Ismael and V C Pandolfelli ldquoHydraulicbinders for refractory castables mixing curing and dryingrdquoCeramic Forum International vol 84 pp E103ndashE108 2007

[7] M R Ismael R Salomatildeo and V C Pandolfelli ldquoRefractorycastables based on colloidal silica and hydratable aluminardquoAmerican Ceramic Society Bulletin vol 86 no 9 pp 58ndash612007

[8] R Salomatildeo M O C Villas-Boas and V C PandolfellildquoPorous alumina-spinel ceramics for high temperature ap-plicationsrdquo Ceramics International vol 37 no 4 pp 1393ndash1399 2011

[9] A D V Souza C C Arruda L Fernandes M L P AntunesP K Kiyohara and R Salomatildeo ldquoCharacterization of alu-minum hydroxide (Al(OH)3) for its use as a porogenic agentin castable ceramicsrdquo Journal of the European Ceramic Societyvol 35 no 2 pp 803ndash812 2015

[10] A D V Souza L L Sousa L Fernandes P H L Cardosoand R Salomatildeo ldquoAl2O3-Al(OH)3-based castable porousstructuresrdquo Journal of the European Ceramic Society vol 35no 6 pp 1943ndash1954 2015

[11] L L Sousa A D V Souza L Fernandez V L Arantes andR Salomatildeo ldquoDevelopment of densification-resistant castableporous structures from in situ mulliterdquo Ceramics In-ternational vol 41 no 8 pp 9943ndash9545 2015

[12] G Schramm A Practical Approach to Rheology andRheometry Gebrueder HAAKE GmbH Karlsruhe Germany2nd edition 2000

[13] A R Studart V C Pandolfelli E Tervoot and L J GaucklerldquoGelling of alumina suspensions using alginic acid salt andhydroxyaluminum diacetaterdquo Journal of the American Ce-ramic Society vol 85 no 11 pp 2711ndash2718 2002

[14] F T Ramal R Salomatildeo and V C Pandolfelli ldquoWater contentand its effect on the drying behavior of refractory castablesrdquoRefractories Applications and News vol 10 no 3 pp 10ndash17 2005

[15] F S Ortega R H R Castro D Gouvea and V C Pandolfellildquo+e rheological behavior and surface charging of gelcastingalumina suspensionsrdquo Ceramics International vol 34 no 1pp 237ndash241 2008

[16] D M Roy B C Schutz and M R Silsbee ldquoProcessing andoptimized cements and concretes via particle packingrdquo Mate-rials Research Society Bulletin vol 18 no 3 pp 45ndash49 1993

[17] J E Funk and D R Dinger Predictive Process Control ofCrowded Particle Suspensions Applied to CeramicsManufacturing Kluwer Academic Publishers England 1994

[18] J E Funk and D R Dinger ldquoParticle size control for high-solids castables refractoriesrdquo American Ceramic SocietyBulletin vol 73 no 10 pp 66ndash69 1994

[19] M R Ismael R Salomatildeo and V C Pandolfelli ldquoOptimi-zation of the particle size distribution of colloidal silicacontaining refractory castablesrdquo Interceram vol 4 pp 34ndash392007

[20] R Salomatildeo and V C Pandolfelli ldquo+e PSD effect on thedrying efficiency of polymeric fibers containing castablesrdquoCeramics International vol 34 no 1 pp 173ndash180 2008

[21] J P Ollivier J C Maso and B Bourdette ldquoInterfacialtransition zone in concreterdquo Advanced Cement Based Ma-terials vol 2 no 1 pp 30ndash38 1995

[22] W Ma and P W Brown ldquoMechanisms of reaction ofhydratable aluminasrdquo Journal of the American Ceramic So-ciety vol 82 no 2 pp 453ndash456 1999

[23] F A Cardoso M D M Innocentini M F MirandaF A O Valenzuela and V C Pandolfelli ldquoDrying behavior ofhydratable alumina-bonded refractory castablesrdquo Journal of theEuropean Ceramic Society vol 24 no 5 pp 797ndash802 2004

[24] I R Oliveira and V C Pandolfelli ldquoCastable matrix additivesand their role on hydraulic binder hydrationrdquo Ceramics In-ternational vol 35 no 4 pp 1453ndash1460 2009

[25] R Salomatildeo and V C Pandolfelli ldquo+e role of hydraulicbinders on magnesia containing refractory castables calciumaluminate cement and hydratable aluminardquo Ceramics In-ternational vol 35 no 8 pp 3117ndash3124 2009

Advances in Materials Science and Engineering 9

[26] A D V Souza and R Salomatildeo ldquoEvaluation of the porogenicbehavior of aluminum hydroxide particles of different sizedistribution in castable high-alumina structuresrdquo Journal ofthe European Ceramic Society vol 36 no 3 pp 885ndash8972016

[27] R Salomatildeo A D V Souza and P H L Cardoso ldquoAcomparison of Al(OH)3 andMg(OH)2 as inorganic porogenicagents for aluminardquo InterceramndashRefractories Manual vol 4pp 193ndash199 2015

[28] R Salomatildeo V L Ferreira I R Oliveira A D V Souza andW R Correr ldquoMechanism of pore generation in calciumhexaluminate (CA6) ceramics formed in situ from calcinedalumina and calcium carbonate aggregatesrdquo Journal of theEuropean Ceramic Society vol 36 no 16 pp 4225ndash42352016

[29] R Salomatildeo M A Kawamura A D V Souza andJ Sakihama ldquoHydratable alumina-bonded suspensionsevolution of microstructure and physical properties duringfirst heatingrdquo InterceramndashRefractories Manual vol 1pp 28ndash23 2017

[30] H Ledbetter S Kim D Balzar S Crudele and W KrivenldquoElastic properties of mulliterdquo Journal of the American Ce-ramic Society vol 81 no 4 pp 1025ndash1028 1998

[31] A R Studart U T Gonzenbach E Tervoot andL J Gauckler ldquoProcessing routes to macroporous ceramicsa reviewrdquo Journal of the American Ceramic Society vol 89no 6 pp 1771ndash1789 2006

10 Advances in Materials Science and Engineering

CorrosionInternational Journal of

Hindawiwwwhindawicom Volume 2018

Advances in

Materials Science and EngineeringHindawiwwwhindawicom Volume 2018

Hindawiwwwhindawicom Volume 2018

Journal of

Chemistry

Analytical ChemistryInternational Journal of

Hindawiwwwhindawicom Volume 2018

ScienticaHindawiwwwhindawicom Volume 2018

Polymer ScienceInternational Journal of

Hindawiwwwhindawicom Volume 2018

Hindawiwwwhindawicom Volume 2018

Advances in Condensed Matter Physics

Hindawiwwwhindawicom Volume 2018

International Journal of

BiomaterialsHindawiwwwhindawicom

Journal ofEngineeringVolume 2018

Applied ChemistryJournal of

Hindawiwwwhindawicom Volume 2018

NanotechnologyHindawiwwwhindawicom Volume 2018

Journal of

Hindawiwwwhindawicom Volume 2018

High Energy PhysicsAdvances in

Hindawi Publishing Corporation httpwwwhindawicom Volume 2013Hindawiwwwhindawicom

The Scientific World Journal

Volume 2018

TribologyAdvances in

Hindawiwwwhindawicom Volume 2018

Hindawiwwwhindawicom Volume 2018

ChemistryAdvances in

Hindawiwwwhindawicom Volume 2018

Advances inPhysical Chemistry

Hindawiwwwhindawicom Volume 2018

BioMed Research InternationalMaterials

Journal of

Hindawiwwwhindawicom Volume 2018

Na

nom

ate

ria

ls

Hindawiwwwhindawicom Volume 2018

Journal ofNanomaterials

Submit your manuscripts atwwwhindawicom

structures of low homogeneity and high drying shrinkagewere generated For the more concentrated ones (5ndash35 volof water) on the contrary the poor workability promotedexcessive entrapment or air bubbles increasing total porosityand reducing elastic modulus +e rotating device used toprevent particle sedimentation allowed the casting andcuring of compositions containing up to 80 vol of waterwithout segregation For these samples total porosity valueswere close to the original volumetric amount of water in theformulation and their drying shrinkage was significantlyreduced compared to conventional processing Samplescured under isostatic compression and containing wateramounts between 25 and 40 vol were the strongestamongst all the compositions tested because of their lowtotal porosity and effective binding action of hydratablealumina Additional water content reductions (0ndash20 vol) onthe contrary did not further decrease the pore content +isbehavior can be explained by the interparticle packing flawsintrinsically present in this system that became the mainpore generator Besides this it is possible that the smallquantity of water present in these samples was not enough tofully hydroxilate the hydratable alumina reducing itsbinding effect

Conflicts of Interest

+e authors declare that they have no conflicts of interest

Acknowledgments

Brazilian Research Foundations FAPESP (2010-19274-5)and CNPq (4558612014-5) for supporting this study andAlmatis (Brazil USA and Germany) for kindly supplyingsamples of calcined and hydratable aluminas

References

[1] G V Givan L D Hart and G McZura ldquoCuring and firinghigh purity calcium aluminate-bonded tabular aluminacastablesrdquo American Ceramic Society Bulletin vol 54 no 8pp 710ndash713 1975

[2] A Nishikawa ldquoManufacture and properties of monolith re-fractoriesrdquo in Technology of Monolithic Refractories PlibricoCo Ltd Tokyo Japan 1984

[3] W E Lee and R E Moore ldquoEvolution of in situ refractories inthe 20th centuryrdquo Journal of the American Ceramic Societyvol 81 no 6 pp 1385ndash1410 1998

[4] F A Cardoso M D M Innocentini M M Akiyoshi andV C Pandolfelli ldquoEffect of curing time on the properties ofCAC bonded refractory castablesrdquo Journal of the EuropeanCeramic Society vol 24 no 7 pp 2073ndash2078 2004

[5] P K Mehta and P J M Monteiro Concrete MicrostructureProperties and Materials McGraw-Hill New York NY USA3rd edition 2006

[6] R Salomatildeo M R Ismael and V C Pandolfelli ldquoHydraulicbinders for refractory castables mixing curing and dryingrdquoCeramic Forum International vol 84 pp E103ndashE108 2007

[7] M R Ismael R Salomatildeo and V C Pandolfelli ldquoRefractorycastables based on colloidal silica and hydratable aluminardquoAmerican Ceramic Society Bulletin vol 86 no 9 pp 58ndash612007

[8] R Salomatildeo M O C Villas-Boas and V C PandolfellildquoPorous alumina-spinel ceramics for high temperature ap-plicationsrdquo Ceramics International vol 37 no 4 pp 1393ndash1399 2011

[9] A D V Souza C C Arruda L Fernandes M L P AntunesP K Kiyohara and R Salomatildeo ldquoCharacterization of alu-minum hydroxide (Al(OH)3) for its use as a porogenic agentin castable ceramicsrdquo Journal of the European Ceramic Societyvol 35 no 2 pp 803ndash812 2015

[10] A D V Souza L L Sousa L Fernandes P H L Cardosoand R Salomatildeo ldquoAl2O3-Al(OH)3-based castable porousstructuresrdquo Journal of the European Ceramic Society vol 35no 6 pp 1943ndash1954 2015

[11] L L Sousa A D V Souza L Fernandez V L Arantes andR Salomatildeo ldquoDevelopment of densification-resistant castableporous structures from in situ mulliterdquo Ceramics In-ternational vol 41 no 8 pp 9943ndash9545 2015

[12] G Schramm A Practical Approach to Rheology andRheometry Gebrueder HAAKE GmbH Karlsruhe Germany2nd edition 2000

[13] A R Studart V C Pandolfelli E Tervoot and L J GaucklerldquoGelling of alumina suspensions using alginic acid salt andhydroxyaluminum diacetaterdquo Journal of the American Ce-ramic Society vol 85 no 11 pp 2711ndash2718 2002

[14] F T Ramal R Salomatildeo and V C Pandolfelli ldquoWater contentand its effect on the drying behavior of refractory castablesrdquoRefractories Applications and News vol 10 no 3 pp 10ndash17 2005

[15] F S Ortega R H R Castro D Gouvea and V C Pandolfellildquo+e rheological behavior and surface charging of gelcastingalumina suspensionsrdquo Ceramics International vol 34 no 1pp 237ndash241 2008

[16] D M Roy B C Schutz and M R Silsbee ldquoProcessing andoptimized cements and concretes via particle packingrdquo Mate-rials Research Society Bulletin vol 18 no 3 pp 45ndash49 1993

[17] J E Funk and D R Dinger Predictive Process Control ofCrowded Particle Suspensions Applied to CeramicsManufacturing Kluwer Academic Publishers England 1994

[18] J E Funk and D R Dinger ldquoParticle size control for high-solids castables refractoriesrdquo American Ceramic SocietyBulletin vol 73 no 10 pp 66ndash69 1994

[19] M R Ismael R Salomatildeo and V C Pandolfelli ldquoOptimi-zation of the particle size distribution of colloidal silicacontaining refractory castablesrdquo Interceram vol 4 pp 34ndash392007

[20] R Salomatildeo and V C Pandolfelli ldquo+e PSD effect on thedrying efficiency of polymeric fibers containing castablesrdquoCeramics International vol 34 no 1 pp 173ndash180 2008

[21] J P Ollivier J C Maso and B Bourdette ldquoInterfacialtransition zone in concreterdquo Advanced Cement Based Ma-terials vol 2 no 1 pp 30ndash38 1995

[22] W Ma and P W Brown ldquoMechanisms of reaction ofhydratable aluminasrdquo Journal of the American Ceramic So-ciety vol 82 no 2 pp 453ndash456 1999

[23] F A Cardoso M D M Innocentini M F MirandaF A O Valenzuela and V C Pandolfelli ldquoDrying behavior ofhydratable alumina-bonded refractory castablesrdquo Journal of theEuropean Ceramic Society vol 24 no 5 pp 797ndash802 2004

[24] I R Oliveira and V C Pandolfelli ldquoCastable matrix additivesand their role on hydraulic binder hydrationrdquo Ceramics In-ternational vol 35 no 4 pp 1453ndash1460 2009

[25] R Salomatildeo and V C Pandolfelli ldquo+e role of hydraulicbinders on magnesia containing refractory castables calciumaluminate cement and hydratable aluminardquo Ceramics In-ternational vol 35 no 8 pp 3117ndash3124 2009

Advances in Materials Science and Engineering 9

[26] A D V Souza and R Salomatildeo ldquoEvaluation of the porogenicbehavior of aluminum hydroxide particles of different sizedistribution in castable high-alumina structuresrdquo Journal ofthe European Ceramic Society vol 36 no 3 pp 885ndash8972016

[27] R Salomatildeo A D V Souza and P H L Cardoso ldquoAcomparison of Al(OH)3 andMg(OH)2 as inorganic porogenicagents for aluminardquo InterceramndashRefractories Manual vol 4pp 193ndash199 2015

[28] R Salomatildeo V L Ferreira I R Oliveira A D V Souza andW R Correr ldquoMechanism of pore generation in calciumhexaluminate (CA6) ceramics formed in situ from calcinedalumina and calcium carbonate aggregatesrdquo Journal of theEuropean Ceramic Society vol 36 no 16 pp 4225ndash42352016

[29] R Salomatildeo M A Kawamura A D V Souza andJ Sakihama ldquoHydratable alumina-bonded suspensionsevolution of microstructure and physical properties duringfirst heatingrdquo InterceramndashRefractories Manual vol 1pp 28ndash23 2017

[30] H Ledbetter S Kim D Balzar S Crudele and W KrivenldquoElastic properties of mulliterdquo Journal of the American Ce-ramic Society vol 81 no 4 pp 1025ndash1028 1998

[31] A R Studart U T Gonzenbach E Tervoot andL J Gauckler ldquoProcessing routes to macroporous ceramicsa reviewrdquo Journal of the American Ceramic Society vol 89no 6 pp 1771ndash1789 2006

10 Advances in Materials Science and Engineering

CorrosionInternational Journal of

Hindawiwwwhindawicom Volume 2018

Advances in

Materials Science and EngineeringHindawiwwwhindawicom Volume 2018

Hindawiwwwhindawicom Volume 2018

Journal of

Chemistry

Analytical ChemistryInternational Journal of

Hindawiwwwhindawicom Volume 2018

ScienticaHindawiwwwhindawicom Volume 2018

Polymer ScienceInternational Journal of

Hindawiwwwhindawicom Volume 2018

Hindawiwwwhindawicom Volume 2018

Advances in Condensed Matter Physics

Hindawiwwwhindawicom Volume 2018

International Journal of

BiomaterialsHindawiwwwhindawicom

Journal ofEngineeringVolume 2018

Applied ChemistryJournal of

Hindawiwwwhindawicom Volume 2018

NanotechnologyHindawiwwwhindawicom Volume 2018

Journal of

Hindawiwwwhindawicom Volume 2018

High Energy PhysicsAdvances in

Hindawi Publishing Corporation httpwwwhindawicom Volume 2013Hindawiwwwhindawicom

The Scientific World Journal

Volume 2018

TribologyAdvances in

Hindawiwwwhindawicom Volume 2018

Hindawiwwwhindawicom Volume 2018

ChemistryAdvances in

Hindawiwwwhindawicom Volume 2018

Advances inPhysical Chemistry

Hindawiwwwhindawicom Volume 2018

BioMed Research InternationalMaterials

Journal of

Hindawiwwwhindawicom Volume 2018

Na

nom

ate

ria

ls

Hindawiwwwhindawicom Volume 2018

Journal ofNanomaterials

Submit your manuscripts atwwwhindawicom

[26] A D V Souza and R Salomatildeo ldquoEvaluation of the porogenicbehavior of aluminum hydroxide particles of different sizedistribution in castable high-alumina structuresrdquo Journal ofthe European Ceramic Society vol 36 no 3 pp 885ndash8972016

[27] R Salomatildeo A D V Souza and P H L Cardoso ldquoAcomparison of Al(OH)3 andMg(OH)2 as inorganic porogenicagents for aluminardquo InterceramndashRefractories Manual vol 4pp 193ndash199 2015

[28] R Salomatildeo V L Ferreira I R Oliveira A D V Souza andW R Correr ldquoMechanism of pore generation in calciumhexaluminate (CA6) ceramics formed in situ from calcinedalumina and calcium carbonate aggregatesrdquo Journal of theEuropean Ceramic Society vol 36 no 16 pp 4225ndash42352016

[29] R Salomatildeo M A Kawamura A D V Souza andJ Sakihama ldquoHydratable alumina-bonded suspensionsevolution of microstructure and physical properties duringfirst heatingrdquo InterceramndashRefractories Manual vol 1pp 28ndash23 2017

[30] H Ledbetter S Kim D Balzar S Crudele and W KrivenldquoElastic properties of mulliterdquo Journal of the American Ce-ramic Society vol 81 no 4 pp 1025ndash1028 1998

[31] A R Studart U T Gonzenbach E Tervoot andL J Gauckler ldquoProcessing routes to macroporous ceramicsa reviewrdquo Journal of the American Ceramic Society vol 89no 6 pp 1771ndash1789 2006

10 Advances in Materials Science and Engineering

CorrosionInternational Journal of

Hindawiwwwhindawicom Volume 2018

Advances in

Materials Science and EngineeringHindawiwwwhindawicom Volume 2018

Hindawiwwwhindawicom Volume 2018

Journal of

Chemistry

Analytical ChemistryInternational Journal of

Hindawiwwwhindawicom Volume 2018

ScienticaHindawiwwwhindawicom Volume 2018

Polymer ScienceInternational Journal of

Hindawiwwwhindawicom Volume 2018

Hindawiwwwhindawicom Volume 2018

Advances in Condensed Matter Physics

Hindawiwwwhindawicom Volume 2018

International Journal of

BiomaterialsHindawiwwwhindawicom

Journal ofEngineeringVolume 2018

Applied ChemistryJournal of

Hindawiwwwhindawicom Volume 2018

NanotechnologyHindawiwwwhindawicom Volume 2018

Journal of

Hindawiwwwhindawicom Volume 2018

High Energy PhysicsAdvances in

Hindawi Publishing Corporation httpwwwhindawicom Volume 2013Hindawiwwwhindawicom

The Scientific World Journal

Volume 2018

TribologyAdvances in

Hindawiwwwhindawicom Volume 2018

Hindawiwwwhindawicom Volume 2018

ChemistryAdvances in

Hindawiwwwhindawicom Volume 2018

Advances inPhysical Chemistry

Hindawiwwwhindawicom Volume 2018

BioMed Research InternationalMaterials

Journal of

Hindawiwwwhindawicom Volume 2018

Na

nom

ate

ria

ls

Hindawiwwwhindawicom Volume 2018

Journal ofNanomaterials

Submit your manuscripts atwwwhindawicom

CorrosionInternational Journal of

Hindawiwwwhindawicom Volume 2018

Advances in

Materials Science and EngineeringHindawiwwwhindawicom Volume 2018

Hindawiwwwhindawicom Volume 2018

Journal of

Chemistry

Analytical ChemistryInternational Journal of

Hindawiwwwhindawicom Volume 2018

ScienticaHindawiwwwhindawicom Volume 2018

Polymer ScienceInternational Journal of

Hindawiwwwhindawicom Volume 2018

Hindawiwwwhindawicom Volume 2018

Advances in Condensed Matter Physics

Hindawiwwwhindawicom Volume 2018

International Journal of

BiomaterialsHindawiwwwhindawicom

Journal ofEngineeringVolume 2018

Applied ChemistryJournal of

Hindawiwwwhindawicom Volume 2018

NanotechnologyHindawiwwwhindawicom Volume 2018

Journal of

Hindawiwwwhindawicom Volume 2018

High Energy PhysicsAdvances in

Hindawi Publishing Corporation httpwwwhindawicom Volume 2013Hindawiwwwhindawicom

The Scientific World Journal

Volume 2018

TribologyAdvances in

Hindawiwwwhindawicom Volume 2018

Hindawiwwwhindawicom Volume 2018

ChemistryAdvances in

Hindawiwwwhindawicom Volume 2018

Advances inPhysical Chemistry

Hindawiwwwhindawicom Volume 2018

BioMed Research InternationalMaterials

Journal of

Hindawiwwwhindawicom Volume 2018

Na

nom

ate

ria

ls

Hindawiwwwhindawicom Volume 2018

Journal ofNanomaterials

Submit your manuscripts atwwwhindawicom