refractories WORLDFORUM 2 (2010) [2] 87

• metal bath infiltration in cracksPotential for stress relaxation/“Elasticity”• elastic deformation of the steel shell

caused by charging of liquid steel • deformation of the ladle during transport• heat shock when charging the ladle• thermal shock when cold stirring gas pas-

ses the purging plugThermodynamic stability• stability of refractory oxides against reduc-

tion by alloying or desoxidation com-pounds.

Depending on the steel ladle zone the pre-dominant wear mechanisms vary. Tab. 1gives an overview of the wear mechanismsper ladle zone and their importance for theselection of the best suited refractory prod-uct. The sidewall for example has usually lessmechanical stress due to erosion (exceptwhen there is heavy stirring) whereas thebottom, especially the impact area and thearea around the purging plug, suffer strongerosion due to the steel movement. Volume-and thermal stability are the main require-ments for the bottom to avoid cracking andaccelerated wear due to spalling whereas acontrolled volume expansion of the sidewalllining is favourable because it will brace thelining and thus reduce the opening of cracks.For the formulation of a refractory castablesome of the requirements described are hardto achieve in one product. As a consequence,several optimized refractory materials are inuse today that responds to the different wearpattern. High alumina castables with spineland/or magnesia addition are the most com-mon monolithic lining today and their differ-

fully in use. The purpose of this paper is todiscuss castables designed with pre-reactedspinel and those with alumina-magnesiaand to link their individual property profile tothe requirements for refractories in a steelladle.

2 Requirements on refractoriesfor steel ladle inings

The impact of secondary metallurgy on re-fractory linings and the different wear mech-anisms of a monolithic ladle lining are de-scribed by Buhr [6] and Alasaarela/Eitel [7].The requirements on refractory materialsused for ladle linings can be summarized asfollows: High thermal stability• increased tapping temperature into ladle• exothermic reactions by thermal heating

and alloying • hot spots from electrodes in ladle furnace

operation• oxygen cleaning of well blocks and purg-

ing plugsHigh thermo-mechanical stability• increased steel residence time in the ladle • ladle movements like tilting and hard pla-

cing down• elastic deformation of the steel shell dur-

ing ladle transport High erosion resistance• intense stirring in the ladle • vacuum (tank) degassing• tapping conditions (height/temperature)High corrosion and penetration resistance• various aggressive slag compositions• vacuum degassing

Spinel: In situ versus Preformed – Clearing the Myth

M. Schnabel, A. Buhr, R. Exenberger, C. Rampitsch

The paper discusses the differ-ence in the formulation conceptsof alumina-spinel (spinel contain-ing) and alumina-magnesia(spinel forming) castables andthe influence on their physicalproperties. The individual prop-erty profile will be discussed withregard to the requirements on re-fractory lining materials for thedifferent zones of a steel ladle.

1 Introduction

Since beginning of the 1990s alumina-spinelcastables are widely used as steel ladle liningbelow the slag line and as pre-cast shapeslike purging plugs and well blocks. A greatdeal of studies has been conducted on theeffect of spinel-types, spinel grain size andamount of spinel on the chemical and me-chanical resistance of alumina-spinel cast-ables [1–5]. In the past ten years the cast-ables used for the ladle side wall have pro-gressively changed from alumina-spinelcastables to alumina-magnesia types. Onedriver for this change was the considerationthat a finer spinel, like the in situ formedspinel in alumina-magnesia castables wouldbring better corrosion and penetration resist-ance than a pre-reacted spinel. Cost pressureand the idea to use cheaper raw materialslike alumina and magnesia that form spinelduring use instead of pre-reacted spinel wasanother reason in favour of spinel formingcastables. Today, both concepts are success-

Marion Schnabel, Andreas Buhr;

Almatis GmbH, Frankfurt, Germany

Reinhard Exenberger, Christian Rampitsch

voestalpine Stahl GmbH, Linz, Austria

Corresponding author:

marion.schnabel@almatis.com; www.almatis.com

Keywords: spinel, castables, steel ladle

Tab. 1 Requirements on refractories in different zones of a steel ladle

Ladle side wall

Ladlebottom

Impact area(pad)

Purging plug/well block

Thermal stability ++ ++ ++ +++Thermo-mechanicalstability + +++ +++ +++Erosion resistance + ++ +++ +++

Corrosion resistance ++ ++ +++ ++Potential for stress re-laxation (thermalshock resistance) +++ +++ +++ +++

88 refractories WORLDFORUM 2 (2010) [2]

ent properties with regard to the require-ments described before will be discussed inthe following.

3 Why spinel?

The general formula of the spinel group isAB2O4, where A represents a divalent metalion such as magnesium, iron, nickel, man-ganese and/or zinc, and B represents tri-valent metal ions such as aluminium, iron,chromium or manganese. The most commonspinel and the only compound in the binarysystem MgO–Al2O3 is Magnesium-aluminatespinel (MgAl2O4) with a stoichiometric ratioof 71,8 % Al2O3/28,2 % MgO. Magnesium-aluminate spinel is a highly refractory mater-ial, with a melting point of 2135 °C. A strongfeature of all spinels is the tendency to sub-stitutional solid-solutioning, where largepercentages of one or both of the spinelcomponents may be substituted by others of

the group. For the Magnesium-aluminatespinel both magnesium and aluminium cat-ions can be replaced by others with similarsize. Additionally, the MgAl2O4-structureshows an increasing phase region with in-creasing temperature, especially towardshigher alumina contents. The electrochem-ical balance is achieved by vacancies at metal cation and oxygen-anion sites in thestructure. This allows the production of alu-mina-rich spinels like AR 78 and AR 90.When produced at high production temper-atures up to 1900 °C the alumina-rich spinelphase can be maintained by rapid cooling.Due to these vacancies in the crystal struc-ture, pre-reacted, alumina-rich spinel has thecapability to absorb FeO and consequentlyretard the infiltration of slag. This is an im-portant feature and a major factor in the ad-vantage of spinel containing mixes for resist-ance to steelmaking slag [8].

Tab. 2 shows a comparison of properties ofspinel and its compounds, MgO and Al2O3.The decrease in density, respectively the vol-ume increase of 7,9 % as result of the spinelformation from the compounds is a charac-teristic that needs consideration when for-mulating castables with in-situ spinel forma-tion.

4 In-situ versus preformed spinel

The formulation of castables containing pre-reacted spinel and that of spinel forming,alumina-magnesia castables require in gen-eral different approaches whereby the for-mulation of alumina-magnesia-castables isin general more challenging. The use of mag-nesia, as one of the reactants for the spinel-formation in castables, often causes difficul-ties like poor flow or quick setting because ofthe hydration of the magnesia. Furthermorethe volume expansion due to the hydrationmay lead to cracking during the drying of thecastable which is especially critical when pro-ducing pre-cast shapes. The in situ formationof spinel is also linked with a strong volumeexpansion that needs to be controlled. A toohigh expansion would lead to mechanicalstresses and thus spalling of the lining. Ex-tensive work was done in the frame of theFIRE project [10–14] to develop methods to

Tab. 3 Spinel containing and spinel forming test castables and mixtures thereof

SP SF SP-SF SP-SF-NC

Spinel Spinel forming Spinel + spinel forming Spinel + spinel forming

Mix LCC ULCC ULCC NCC

Components [%]

Coarse 0,5 - 6 mm

Tabular Alumina T60/T64 50 60 50 55Matrix <0,5 mm

Tabular Alumina T60/T64 – 15 – –

Spinel AR 78 25 – 20 10

Alumina 20 16,5 25 30

Dead burnt magnesia <90 µm – 5 1,95 2,5

Microsilica Elkem 971 U – 0,5 0,5 0,5

Cement CA-14 M 5 3 2,5 –

Alphabond 300 – – – 3

MgO content total 5,5 5,0 6,3 4,5H2O 5,0 5,5 5,0 5,3

Open Porosity [vol.-%]

After drying at 110 °C 13,0 14,5 14,5 14,8

After firing at 1000 °C 13,6 15,9 16,1 17,9

After firing at 1500 °C 17,7 17,5 15,3 16,2

SpinelMgAl2O4

PericlaseMgO

CorundumAl2O3

Density [g/cm3] 3,58 3,58 3,99

Thermal conductivity [W/m·K] 5,9 7,1 6,3

Thermal expansioncoefficient [Δl/l · K·10-6] 7,6 13,5 8,8

Tab. 2 Properties of spinel, periclase and corundum [9]

refractories WORLDFORUM 2 (2010) [2] 89

control the expansion behaviour of alumina-magnesia castables. Beside the right finenessfor the reactive components alumina andmagnesia, the addition of fumed silica in arange of 0,5-1 % is commonly applied tocounterbalance the expansion and toachieve good workability of the castables.Most of the commercially available spinel-forming products follow this route. Castablescontaining pre-reacted spinel do neitherhave this expanding behaviour nor any un-wanted hydration and can thus be formu-lated without fumed silica addition.The influence of these different formulationconcepts on the properties of the castablesare described based on four different kindsof spinel castables (Tab. 3). The castableschosen for comparison test are:• spinel containing low cement castable

(SP),• spinel forming ultra low cement castable

(SF),• spinel containing plus spinel forming ultra

low cement castable (SP-SF),• spinel containing plus spinel forming no

cement castable (SP-SF NCC).Castable SP (Spinel containing) was formu-lated with an addition of 25 % pre-reactedspinel type AR 78 in the matrix (<0,5 mm).The spinel forming castable contains 5 %dead burnt magnesia ≤90 µm thus leadingto a theoretical spinel formation of 22 %. Inpractical applications, a combination ofspinel formation with pre-reacted spinel isalso widely used. The two remaining cast-ables belong to this group of products, onewith an ultra low cement bond (SP-SF) andthe other with Alphabond as binder (SP-SF-NC). A MgO-content of 4,5–6,3 % respect-ively spinel content in the range of 16–25 %provides the best balance between corrosionand penetration resistance according to lit-erature [1]. Practical experiences over thepast 20 years have also proved this. An add-ition of 0,5 % of fumed silica was made forthe castables with in situ spinel formation(SF, SP-SF, SP-SF-NC) to control the expan-sion whereas the castable with only pre-reacted spinel (SP) was formulated withoutfumed silica. The water addition was kept inthe same range for all castables to achieve acomparable porosity level. The castableswere fired at 1000 °C and 1500 °C to meas-ure their permanent linear change (PLC),open porosity and cold mechanical strength(CCS, MOR). The samples for the measure-

explained by a not completely developed (ce-ment) matrix. The sample prefired at 1000 °Chas not sufficient time during heat-up in theRUL test (heating rate 5 K/min) to form astrong CA2-structure. The same test withsamples prefired at higher temperature doesnot show this slight deformation in the tem-perature range from 1250 to 1400 °C.The expansion at temperatures >1400 °C iscaused by the CA6-formation and can be in-fluenced by the cement amount in the mix.The spinel forming, spinel containingcastable (SP-SF) reaches its dmax at 1250 °Cwhereas the spinel forming castable (SP)shows the lowest dmax at 1150 °C. This is inline with the theory. The CaO-MgO-Al2O3-SiO2 phase diagram shows that the tempera-ture of onset of melting for the castable com-positions concerned would decrease fromabove 1820 °C for SiO2-free formulations tobelow 1400 °C for SiO2-containing formu-lations [16]. The degree of softening dependson the composition of the matrix fines, theirreactivity and the position in the phase dia-gram. The softening of the cement free mix

ment of refractoriness under load (RUL) andhot modulus of rupture (HMOR) and for thecorrosion test were prefired at 1000 °C except for the castable with Alphabond-bonding which required prefiring at 1200 °Cto achieve sufficient strength for samplepreparation.

4.1 Thermo-mechanical behaviour

Cement bonded alumina-magnesia-cast-ables show three expansive reactions relatedto new mineral formations (Tab. 4). The expansion of the spinel reaction is coun-terbalanced by a liquid phase formation dueto the addition of fumed silica. But even asmall amount of fumed silica has a consider-able impact on the refractoriness under load(RUL). As shown in Fig. 1 all castables withsilica addition show a beginning of softeningat a temperature of around 1200 °C. The sil-ica-free formulation with pre-reacted spinelin contrary has no softening effect. The slightdrop in the RUL-curve in the temperaturerange from 1250 to 1400 °C is not a soften-ing due to liquid phase formation but can be

Tab. 4 Expansion reactions of cement bonded, spinel forming castables [10, 15, 16]

Fig. 1 Refractoriness under load (RUL) of spinel containing and spinel forming castablesand mixtures thereof. Samples prefired at 1000 °C/5 h respectively 1200 °C/5 h for SP-SF-NC

Temperature[°C]

Reaction Permanent Dimensional changeafter 5 h hold [%]

Volume Linear

1100–1400 MgO + Al2O3 → MgAl2O4 +7,9 +1,99

1100–1300 CaO·Al2O3 + Al2O3 → CaO·2Al2O3 +13,6 +4,76

1400–1650 CaO·2Al2O3 + 4Al2O3→ CaO ·6Al2O3 +3,01 +1,01

90 refractories WORLDFORUM 2 (2010) [2]

with Alphabond (SP-SF-NC) starts at slightlyhigher temperatures and the drop is less dra-matic corresponding to a higher maximumapplication temperature for this castable.It is important to mention that there will bea softening effect even so no fumed silica isadded when impure aggregates like brownfused alumina or bauxite are used togetherwith pre-reacted high-alumina spinel. The

same effect can be seen using Bauxite basedspinels due to their high impurity level (SiO2,TiO2, Fe2O3, alkalis). This type of formulationscan not be compared with mixes using highpurity spinels and Tabular alumina.

4.2 Erosion resistance

The hot modulus of rupture (HMOR) gives anindication about the behaviour of the mater-

ials when used in erosive conditions. A lowHMOR is an indication for the presence ofliquid phase in the matrix. Under erosiveconditions the matrix can not withstand andthe grains get washed out. For cement bonded mixes the development of the hotstrength is mainly associated with the for-mation of CA6. In mixes with pre-reactedspinel and high purity alumina the CA6 isformed by a solid state reaction creating astrong bridging effect between the particles.When silica fume is present like in alumina-magnesia castables the formation is a liquidphase reaction leading to small CA6-crystalsin the matrix, embedded in a glassy phase[11]. This effect can be clearly seen in Fig. 2.The spinel containing mix (SP) reaches aHMOR of 23 MPa whereas none of the silicacontaining mixes shows a significant hotstrength.

4.3 Corrosion- and penetration resistance

The slag resistance of alumina-rich spinels isone of their most important properties, andthe primary reason for the use of spinel insteel-making refractories. Alumina richspinels can incorporate low-melting, low-vis-cosity components such as MnO and FeO ofthe infiltrated slag into the spinel crystalstructure. This leads to an increase of theslag viscosity and reduces further penetra-tion. A reduced penetration is important fortwo reasons. It hampers the progress of thecorrosion front and reduces the risk ofspalling. Under thermal cycling the penetrat-ed layers of a refractory lining tend to spalloff due to the stresses caused by differentdensities and expansion coefficients of penetrated layer and original lining material.Such spalling is leading to predominantwear.In situ formed spinel in a steel ladle castablewill show a stoichiometric composition butno alumina rich solid solution. The tempera-tures of about 1600 °C are too low. Stoi-chiometric spinel can incorporate FeO orMnO only in substitution for MgO. The corrosion and penetration behaviour ofthe selected castables was tested in an in-duction furnace test at the German Refrac-tory Institute (DIFK)/Bonn. The samples weresimultaneously subjected to 15 kg of steelST 52 and calcium aluminate rich slag underoxidizing atmosphere (air).The slag compos-itions is typical for aluminium-killed steel.

Fig. 2 Hot Modulus of Rupture (HMOR) at 1500 °C of spinel containing and spinel form-ing castables and mixtures thereof. Samples prefired at 1000 °C/5 h respectively 1200 °C/5 h for SP-SF-NCa

°

Fig. 3 Test bars of spinel containing and spinel forming castables and mixtures thereofafter induction furnace corrosion test 1650 °C/2h; C/A ratio 1,08

Test conditionsTemperature [°C] Duration [h] Steel [kg] Slag [kg]

1650 2 15/St 52 0,75Slag composition [mass %]

CaO Al2O3 SiO2 MgO FeO MnO CaF2 C/A ratio

40 37 5 5 3 4 6 1,08

Tab. 5 Test conditions for induction furnace test at DIFK, Bonn, Germany

refractories WORLDFORUM 2 (2010) [2] 91

Calcium fluoride (CaF2) was added to theslag to give more severe test conditions. Thedetailed test conditions are given in Tab. 5.The test specimens were cut in longitudinaldirection and the wear profile was measuredat the slag level. Furthermore the dis-colouration of the sample, slag penetrationand the formation of cracks were investi-gated. Fig. 3 illustrates the result of the cor-rosion test on the cut samples and Fig. 4gives detailed data on penetration depthand wear rate.Although visually the samples show no ma-jor difference, the penetration depth variesin the range of 5,9–11,4 mm and is thehighest for the alumina-magnesia castable(SF). The cement bonded castables contain-ing pre-reacted spinel show a slightly lowerpenetration but still higher than the Alphabond bonded castable. Since the openporosity of the castables is in the samerange (Tab. 3) the different penetration be-haviour can either be caused by a differentpore size or the distribution of spinel in thematrix. As described by Buhr et al. [18] theaddition of fumed silica to a calcium alu-minate matrix leads to a significant growthof the pore size in the temperature rangeabove 1000 °C. Fig. 5 shows the evolutionof the pore size distribution for the silica-freecastable SP (5a) and the spinel formingcastable SF with addition of 0,5 % fumedsilica (5b). The presence of the liquid phasein the silica containing mixes leads to a sig-nificant pore size growth reaching an aver-age pore size of 2–3 µm after firing at1500 °C. In comparison the silica freecastable containing pre-reacted spinel hasan average pore size of about 0,8 µm whenfired at 1500° C. The Alphabond bondedcastable with the smallest average pore sizediameter of ~0,3 µm at 1000 °C conse-quently shows the lowest penetration depth.Some literature describes that the volumeexpansion caused by the spinel formationleads to a densification of the microstructureof the castable. This would reduce the openporosity and have a beneficial effect on thepenetration resistance of castables with insitu spinel formation. However, Soudier et al.[17] could not find a direct proof for this.They found no correlation between the per-manent linear change (PLC) and the densifi-cation of the structure when firing the casta-bles under constrained conditions. This wasalso confirmed by the corrosion test done

penetration resistance. Although the lowerpenetration rate is achieved with mixes con-

with the selected castables, where the spinelforming castables did not show a higher

0

2

4

6

8

10

12

14

16

18

20

SP SF SP-SF SP-SF-NC

Pe

ne

ntr

atio

n [

mm

]

0

1

2

3

4

5

6

7

8

9

10

we

ar

rate

[m

m/h

]

Penetration

wear rate

Fig. 4 Penetration depth and wear rate of spinel containing and spinel forming cast-ables and mixtures thereof after induction furnace test 1650 °C/2 h; C/A ratio 1,08

Fig. 5 Pore size distribution of a) spinel containing (SP) and b) spinel forming (SF)castables after pre-firing at 1000 °C/5 h and 1500 °C/5 h

92 refractories WORLDFORUM 2 (2010) [2]

taining pre-reacted spinel and conclusions inthe direction of higher corrosion resistance ofpre-reacted, alumina-rich spinel in compari-son to in situ formed spinel would be tempt-ing, there is not sufficient data proving thatthis is actually the case. The wear rates of the castables are very closeand in the range of 7 to 8,5 mm/h. This iscomparable to the wear rate of AMC brickswith 5–6 % MgO tested under the sameconditions [19]. The cement bonded castables with in situspinel formation (SF and SP-SF) have thehighest corrosion resistance whereas the Alphabond bonded mix (SP-SF-NC) and thespinel containing (SP) corrode at a slightlyhigher speed. According to Reisinger et al.[20] a spinel containing matrix improves thecorrosion behaviour of a castable independ-ently whether the spinel has been added assuch to the matrix, whether it developed dueto the reaction of alumina with added finemagnesia or whether it is newly formed “in

situ” together with the MgO of the infiltra-ting slag. The two important facts for an im-proved corrosion resistance are the totalamount of spinel and its distribution/finesse. The amount of spinel in the test castablesranges from 16 to 25 %. The spinel contain-ing castable has the highest amount of25 %, followed by the spinel formingcastable (SF) with ~22 % and the spinel con-taining, spinel forming castable (SP-SF) with~20 %. The spinel forming NCC mix has atotal spinel content of only 16 % which ex-plains the slightly inferior corrosion resist-ance of the castable in the test.As described by Braulio et al. [14] the spinelformation is controlled by the finesse of themagnesia. The spinel forming castables con-tain fine, dead burnt magnesia of <90 µmsize and reactive alumina as partner for thespinel formation. The in situ formed spinel isfinely distributed in the matrix whereas thepre-reacted spinel was added as coarser0–0,5 mm fraction. For the same amount byweight of spinel after firing the pre-reactedspinel is not as well dispersed as the in situformed. Consequently the spinel-containingmix was less efficient than the castables withspinel formation. Overall the spinel contain-ing, spinel forming castable (SP-SF) showsthe best results when considering both pene-tration depth and wear rate. With the add-ition of extremely fine ground spinel in thesizing of <45 µm or <20 µm and the co-ground reactive alumina E-SY 2000 in thematrix the slag resistance of the latter mixcould be further improved.

4.4 Potential for stress relaxation“Elasticity”

Thermal shock during tapping and coolingdown and the deformation of the ladle shellcreate thermo mechanical stress that cancause severe damage to the refractory lining.

Developing materials with extremely highstrength to avoid crack formation will notlead to the desired results since the occurringstress is far above the mechanical resistanceof even the best known refractory material.The maximum thermal stress under uniaxialload in an alumina ceramic exposed to athermal shock of 1000 K will be in the rangeof 3000 MPa [21]. The only way to improvethe resistance of refractory materials underthese conditions is to improve their resist-ance to crack propagation by increasing theirpotential for stress relaxation. Seven differ-ent mechanisms for stress release are de-scribed in the literature. Castables with pre-reacted spinel haveproven their good thermal shock behaviourin practical applications, for example in purg-ing plugs when cold stirring gas is blownthrough the hot ceramic. This behaviour ismainly due to differences in thermal expan-sion between alumina and spinel (Tab. 2).The different expansion leads to microcracksin the matrix that act as crack arresters(mechanism b in Fig. 6) when the material isthermally stressed. For spinel forming cast-ables the situation is different. Magnesia hasthe highest thermal expansion of all refracto-ry oxides (Tab. 2). Therefore it reduces thethermal shock resistance of spinel formingcastables unless the spinel has been formed.However, spinel forming castables show anelastic behaviour at elevated temperatures(mechanism c in Fig. 6). The liquid phase for-mation by the addition of fumed silica leadsto a softening of the castable (steep drop inRUL curve) so that thermal stresses can bereleased.

5 Material selection for steel ladle lining

The final properties that will be achievedwith spinel forming or spinel containingcastables are quite different (Tab. 6). Cast-ables formulated with high quality pre-reacted spinel exhibit high thermomechan-ical stability, high mechanical strength anderosion resistance as well as an improvedpenetration resistance. Spinel additions inthe fine fraction of the formulation show thehighest benefit. Spinel forming mixes proof agood corrosion resistance but have a low hotstrength and consequently low erosion re-sistance. The softening of the castable is adrawback when high thermo-mechanicalstability is required but is advantageous

Fig. 6 Various stress shielding processesaccording to Sakai, Bradt [22]

Tab. 6 Properties of spinel castables by formulation concept

SpinelAlumina-magnesia

Alumina-magnesia + Spinel

Alumina-magnesia+ Spinel/NC

Thermal stability +++ + + ++Thermo-mechanical stability +++ + + ++

Erosion resistance +++ + + +

Corrosion resistance ++ ++ +++ ++Potential for stress relaxation (thermal shock resistance) + +++ +++ ++

refractories WORLDFORUM 2 (2010) [2] 93

when stress relaxation (elastic behaviour) isimportant. However, which concept is the best dependsupon the application. As shown in Tab. 1, insteel ladle bottoms the volumetric stabilityunder high temperature and pressure is mostimportant. High erosion resistance is also im-portant. Castables containing pre-reactedspinel are the material of choice for these ap-plications. The reduced erosion resistance ofin-situ spinel formulations would reduce thelife and increase operating cost. The requirements in steel ladle side walls aredifferent. Since every steel ladle shell showssome deformation when manipulated, theability for stress relaxation is of high impor-tance to avoid stress peaks which may leadto cracking. Therefore castables with spinelformation provide advantages in ladle sidewalls. A remaining expansion level in therange of 1–2 % permanent linear changewill be beneficial when open cracks in thelining can be closed due to spinel formation.Ladle sidewalls are less subject to erosionwhen compared to the bottom. The lower hotstrength of the in-situ castable is thereforeless of a factor. However, poor tapping prac-tices or extensive stirring can cause signifi-cant higher sidewall erosion, and spinel-forming refractories with high silica contentswill then exhibit higher erosion rates. Thecombination of spinel containing and spinelforming can be considered the best solutionhere.Pre-cast shapes like impact pads, purgingplugs and well blocks are exposed to higherosion thus demanding a material with highhot strength. Furthermore a high thermalstability is required. Spinel containing cast-ables are mainly used in this application, al-though impact pads made of spinel-formingcastables can be found. But the productionof pre-cast shapes with spinel-forming for-mulations is more difficult and requires spe-cial attention. The use of magnesia additivemay lead to short workability and the dryingcurves need to be adapted to reduce the crit-ical time in warm, humid atmosphere toavoid cracking by the hydration of magnesia.

6 Conclusion

The influence of the formulation concepts ofalumina-spinel (spinel containing) and alu-mina-magnesia (spinel forming) castableson their physical properties was shown. Al-though the achieved property profiles are

Refractory Castables. American Ceramic Socie-

ty Bulletin 86 (2007) [12] 9201–9206

[11] Braulio, M.A.L.; Bittencourt, L.R.M.; Porier J.;

Pandolfelli, V.C.: Micosilica Effects on Cement

Bonded Alumia-magnesia Refractory Casta-

bles. Journal of the Technical Association of Re-

fractories-Japan 28 (2008) [3] 180–184

[12] Braulio, M.A.L.; Castro, J.F.R.; Pagliosa, C.; Bit-

tencourt, L.R.M.; Pandolfelli, V.C.: From Macro

to Nanomagnesia: Designing the in situ Spinel

Expansion. Journal of the American Ceramic

Society 91 (2008) [9] 3090–3093

[13] Braulio, M.A.L.; Bittencourt, L.R.M.; Pandolfelli,

V.C.: Selection of Binders for in situ Spinel Re-

fractory Castables. Journal of the European Ce-

ramic Society 28 (2009) [13] 2727–2735

[14] Braulio, M.A.L.; Brant, P.O.; Bittencourt, L.R.M.;

Pandolfelli, V.C.: Microsilica or MgO Grain Size:

Which one mostly Affects the in situ Spinel Re-

fractory Castable Expansion? Ceramics Interna-

tional

[15] Kopanda, J.E. ; MacZura, G.: Production Proces-

ses, Properties and Applications for Calcium

Aluminate Cements. Alumina Chemicals Hand-

book (1990) 171–183

[16] Buhr, A.: PhD Thesis and publication: Tonerde-

reiche Feuerfestbetone für den Einsatz in der

Stahlindustrie (High alumina refractory casta-

bles for steel applications). RWTH Aachen

1996; Stahl und Eisen 116 (1996) [9] 59–66

[17] Soudier, J.; Meunier, P. ; Nozahic, V.: Character-

isation of Alumina-magnesia Castables after Fi-

ring in Expansion Controlled Environement

[18] Buhr, A.; Baier, B.; Aroni, J. M.; McConnell, R.

W.: Raw Material Concepts for SiO2 free High

Strength Castables in the Temperature Range

up to 1200 °C. 43. Conference of Metallurgists

(2004) Hamilton, Ontario, Canada

[19] Buhr, A.: The Impact of Innovative Synthetic

Alumina Raw Materials on Trend in European

Steel Ladle Lining. Interceram Refractories Ma-

nual (2004) 26–27

[20] Reisinger, P.; Preßlinger, H.; Pissenberger, E.;

Posch, W.: Evaluation of the Interaction of Dif-

ferent Ladle Slags with two Different Alumina

Castable. Veitsch-Radex-Rundschau (1998) [1]

3–19

[21] Pandolfelli, V.C.: Thermal Shock Resistance of

Engineered Microstructure. Short course UNI-

TECR 2009, Salvador, Brazil

[22] Sakai, M.; Bradt, R.C.: Fracture Toughness Test-

ing of Brittle Materials. International Materials

Review 38 (1993) [2] 53–78

significantly different, both types of cast-ables have their advantages in the lining ofsteel ladles. In order to achieve a long ser-vice life it is necessary to select the right ma-terial, taking into consideration the differentrequirements on refractory lining materialsfor the different zones of a steel ladle. Butwhatever the formulation concept, the in-stallation of the castables has an importantinfluence on their final performance. Segre-gation and vibrating holes, especially in theladle bottom often lead to a predominantwear of the lining. The use of self flowingcastables reduces this risk of inhomo-geneities leading to a reduced and pre-dictable even wear of the lining.

References

[1] Mori, J.; Sakaguchi, M.; Yoshimura, S.; Oguchi,

M.; Kawakami, T.: Suppression of Slag Penetra-

tion on Spinel added Alumina Castables for

Steel ladle. Taikabutsu 10 (1988) 40

[2] Nagasoe, A.; Tsurumoto, S. I.; Kitamura, A.: Re-

fractory Characteristics of Spinels with Various

MgO Contents. Taikabutsu Overseas, 11 (1991)

[3] 20–28

[3] Yamamura, T.; Kubota,Y.; Kaneshige, T.; Nanba,

M.: Effect of Spinel Clinker Composition on

Properties of Alumina-Spinel Castable. Taikab-

utsu Overseas 13 (1992) [2] 39–45

[4] Kriechbaum, G.W.; Gnauck, V.; Routschka, G.:

The Influence of SiO2 and Spinel on the Hot

Properties of High-Alumina Low-Cement Ca-

stables. 37th International Colloquium on Re-

fractories, Aachen (1994)

[5] Ko, Y.-C.: Effect of Microsilica Addition on the

Properties of Alumina-Spinel Castables. Inter-

ceram 51 (2002) [6] 388–392

[6] Buhr, A.: Refractories for Steel Secondary

Metallurgy. CN-Refractories 6 (1999) [3]

19–30

[7] Alasaarela, E.; Eitel, W.: How Infinte is Endless

Lining of Ladles? 34th International Colloquium

on Refractories, Aachen (1991)

[8] Racher, R. P.; McConnell, R. W. ; Buhr, A.: Mag-

nesium Aluminate Spinel Raw Materials for

High Performance Refractories for Steel Ladles,

43rd Conference of Metallurgists; Hamilton, On-

tario, Canada (2004)

[9] Bartha, P.: Spinell und spinellhaltige feuerfeste

Werkstoffe. Berichtsband Feuerfesttechnik, Ver-

lag Stahleisen mbH (1984), 113–133

[10] Braulio, M.A.L.; Milanez, D.H.; Sako, E.Y.; Bit-

tencourt L.R.M.; Pandolfelli, V.C.: Expansion Be-

havior of Cement Bonded Alumina-magnesia