Research Article Effect of Anodic Current Density...

Hindawi Publishing CorporationJournal of CeramicsVolume 2013 Article ID 350931 14 pageshttpdxdoiorg1011552013350931

Research ArticleEffect of Anodic Current Density on Characteristics andLow Temperature IR Emissivity of Ceramic Coating onAluminium 6061 Alloy Prepared by Microarc Oxidation

Mohannad M S Al Bosta1 Keng-Jeng Ma2 and Hsi-Hsin Chien2

1 PhD Program in Engineering Science College of Engineering Chung Hua University Hsinchu 30012 Taiwan2 College of Engineering Chung Hua University Hsinchu 30012 Taiwan

Correspondence should be addressed to Mohannad M S Al Bosta mmbosta2005yahoocom

Received 8 June 2013 Revised 7 November 2013 Accepted 10 November 2013

Academic Editor Baolin Wang

Copyright copy 2013 Mohannad M S Al Bosta et al This is an open access article distributed under the Creative CommonsAttribution License which permits unrestricted use distribution and reproduction in any medium provided the original work isproperly cited

High emitter MAO ceramic coatings were fabricated on the Al 6061 alloy using different bipolar anodic current densities in analkali silicate electrolyte We found that as the current density increased from 1094Adm2 to 4375Adm2 the layer thickness wasincreased from 109 120583m to 185120583m the surface roughness was increased from 079120583m to 127 120583m the area ratio of volcano-likemicrostructure was increased from 556 to 596 the volcano-like density was decreased from 2620mmminus2 to 1420mmminus2 and the120574-alumina phase was decreased from 666wt to 262 wt while the 120572-alumina phase was increased from 39wt to 276 wtThe sillimanite and cristobalite phases were around 20wt and 9wt respectively for 1094Adm2 and approximately constantaround 40wt and less than 5wt respectively for the anodic current densities 1458 2188 and 4375 Adm2The ceramic surfaceroughness and thickness slightly enhanced the IR emissivity in the semitransparent region (40ndash78120583m) while the existing phasescontributed together to raise the emissivity in the opaque region (86ndash160 120583m) to higher but approximately the same emissivities

1 Introduction

The growing demand of limited energy sources requiresadoption of effective methods to save energy consumptionand to prevent unwanted energy loss The high emitter sur-faces enhance the thermal performance of heating and cool-ing systems and consequently reduce the needed energy [12] Several methods are applied to the material surfaces toenhance their emissivities such as coating by thin tape filmspaint and lacquer roughening and surface anodizing

One of the promising coating methods is the microarcoxidationMAOTheMAOceramic coating has perfect prop-erties such as wear resistance corrosion resistance hardnessstrong adhesion and thermal shock resistance and can be fab-ricated on the surfaces of aluminium magnesium and tita-nium alloys [3ndash62]The properties of theMAO ceramic coat-ing are affected by the electrolyte compositions [63ndash71] treat-ment time [14 28 70ndash75] electrolyte temperature [70 76]voltage [72 77ndash80] current density [6 47 55 70 81ndash83]current mode [84 85] and electrode geometry [86]

The applied current modes in the MAO process are DCAC unipolar and pulsed bipolar The pulsed bipolar modewas found to enhance the surface properties of treatedmetalsimprove the thickness and homogeneity of oxide layers andlimit the growth of the porous layer [6ndash8 54]

Coating aluminiumwith a high thermal radiator ofMAOceramic will find its applications in low profile devices heatsinks electronic parts LED lasers refrigeration air condi-tioning transport industries liquefaction plants powerplants petroleum refineries and others Previous studiesrarely demonstrated the IR emissivity of the MAO coatingsFor example Wang et al [87] studied the IR emissivity at500∘C of MAO ceramic coating on 2024 aluminium sub-strates and illustrated that 120574-Al

2O3 silicon oxides and phos-

phate oxides contributed to high emissivity at wavelengths8ndash20120583m while the surface roughness was responsible forincreasing emissivity at wavelength range 3ndash5120583m Tang et al[39] studied the emissivity of MAO ceramic prepared onTi6Al4V substrate and reported that more Co contents

2 Journal of Ceramics

enhanced the emissivity of the ceramic surface at 700∘C andat wavelengths 3ndash20 120583m A relatively high emissivity wasfound by Wang et al [88] when they studied the emissivity(8ndash14 120583m 700∘C) of the surface of ceramic coating onTi6Al2Zr1Mo1V alloy and they pointed out that the TiO

2

phases were contributed to enhance the emissivityThe geometry of the MAO-treated samples plays a main

role in the industrial applications as a finishing process Thefirst effect comes to mind (by keeping the current outputof main power supply constant and changing the sampledimensions) is the variation of current density Previousworks kept the sample dimensions constant and changed theinput current density Khan et al [6] fabricatedMAOaluminaceramic coatings on Al 6082 alloy using a DC current modeof densities ranged from 5Adm2 to 20Adm2 in variousconcentrations of KOH electrolytes at temperatures rangedbetween 20∘C and 25∘C for 30 minutes They reported thatthe denser current formed thicker coatings with minimalstress level dense morphology and a relatively high contentof 120572-Al

2O3phase Raj and Mubarak Ali [70] used different

direct current densities (5ndash20Adm2) for MAO treating ofaluminium in the alkaline silicate electrolyte at 10∘C for 45minutes and obtained thicker coatings higher growth rateand coating ratio at 15 Adm2 of current density but the20Adm2 of current density decreased these properties dueto the dominant of electrolyte dissolution over the coatingbuilding The effects of bipolar current density on MAOceramic coating formed on titanium alloy were studied bySun et al [83] in an electrolyte of sodium aluminate andhypophosphate at 35∘C for 70 minutes The cathodic (119895

119888) and

anodic (119895119886) current densities ranged between 6 and 12Adm2

They pointed out that the lowest ratio of 119895119886119895119888formed a denser

and thinner layerwithmore uniformmicrostructures and didnot contain 120572-alumina phase while the highest 119895

119886119895119888ratio

formed a thicker ceramic coating comprised of entirely 120572-alumina phase with poor adhesion to the substrate

Themain aim of the present work is to change the sampledimensions and find out the effect of the anodic current den-sity on the microstructural and compositional properties ofthe MAO ceramic coating and the resultant low-temperatureIR emissivity

2 Experimental

Rectangular pieces (4 times 4 times 02 cm3) of aluminium alloy 6061(Mg 1 Si 065 Fe 07 Cu 03 Cr 02 Mn 015 Ti015 and Al balance) were used as substrates in this studyThe exposed surfacewas ground to a 1200 grit SiC finish usingthe water as a lubricant followed by rinsing in the doublydistilled water and drying in the air while the other side wastotally insulated using a Teflon tape

Four different assemblies were applied by mounting adifferent number of pieces into a 6061-Al alloy clamp to get16 32 48 and 64 cm2 of exposed working area to the elec-trolyte and consequently different applied current densitiesThe preparation of samples was conducted for 10 minutesin a fresh electrolyte which consisted of 0046M sodium

silicate and 0042M sodium hydroxide and the PH was 128in a cooling and stirring bath which kept the electrolytetemperature below 17∘C We used the pulse controller SPIK2000A (Shen Chang Electric Co Ltd Taiwan) to generatean asymmetric bipolar pulsing mode with parameters of 200200 360 and 200120583s for 119905+on 119905

+

off 119905minus

on and 119905minus

off respectively Twoelectrical power supplies (PR Series 650V 77 A Matsusada)were connected to the pulse controller with 100V 35 A forDC1 and 500V 70 A for DC2 as shown in Figure 1 Thesamples were connected to the output E2 while another243 cm2 aluminium 6061 plate was connected to E1 OnlyAl 6061 alloy touched the electrolysis solution to avoidany contamination due to diffusion of wires electrodes orscrews According to Figure 1 both electrodes (E1 and E2)were alternating between the cathodic and anodic biasingaccording to the output bipolar pulse the DC2 supplied thesample in the anodic period and the DC1 supplied it in thecathodic period The resultant peak anodic biasing currentdensities 119869

119886 were 1094 1458 2188 and 4375Adm2

Unlike the sample no microarc oxidation was occurredon the aluminium plate due to the relatively low voltageduring its anodic period To avoid the effect of chemicalreaction with the plate surface we renewed the plate for eachMAO experiment despite being in a good situation Aftercompleting every treatment the samples were immediatelyimmersed and cleanedwith distilledwater and then dried andstored in a sealed container Before any use or test sampleswere cleaned using an ultrasonic bath of doubly distilledwater propanol acetone and again doubly distilled water 10minutes for each followed by air drying in the fume hood

Different 27 randomly selected places were captured foreach sample by the SEM (S4160 Hitachi) We performedthe image analysis using Image Pro Plus 70 software (MediaCybernetics Inc) to estimate the volcano-likemicrostructurearea ratioThe density of volcano-like was estimated by divid-ing its total number over the total area of SEM frames for thesame sample

The elemental composition analysis of ceramic coatinglayers was carried out using Hitachi EDX S4800 Low-angleX-ray diffraction (CuK120572 XRD XrsquoPert PRO MPD PANalyti-cal The Netherlands) was used to obtain the XRD patternsof as-deposited ceramic coatings We performed the semi-quantitative analysis of the XRD spectra using the so-calledreference intensity ratio method (RiR method de Woolf andVisser [89]) by MATCH software (V111f Crystal ImpactGbR) and selected the best fit phases and compositions inaddition to estimating their weight percentage

For each sample at least 16 different locations were stud-ied to determine the average of surface roughness using asurface roughness tester (Mitutoyo SJ310) and layer thick-ness using an eddy-current coating-thickness tester (ExtechCG204)

We used a modified Fourier transform infrared spec-troscopy (FTLA2000 Series Spectrometer ABB) to analyzethe IR emissivity of the samples at 70∘C by comparing witha reference blackbody radiation in the wavelength rangingbetween 4120583m and 16 120583m

Journal of Ceramics 3

100V 35A

+ minus

+ minus

DC1

DC1

DC2

500V 70A

E1 Al plate

E2 the sample

Alternatingelectric

field

Vout

100

360 200 200 200

V

500V

DC2DC2

tonminus ton

+ toff+toff

minus

(120583s)

+

++

minus

minus

minus

Discharging DischargingSputtering

SPIK 2000A

Figure 1 A scheme of the arrangement of power supplies and the pulse generator SPIK 2000A in addition to the polarity of alternatingelectrodes according to the bipolar output pulse

3 Possible Chemical ElectrochemicalReactions and Phase Transformation

Our MAO treatment was conducted in an electrolyte con-tained sodium hydroxide and sodium silicate The sampleswere alternating between the cathodic and anodic polariza-tions as a result of the asymmetrical bipolar pulse modeFigure 1The forming of compositions and phases can be clas-sified into four periods according to the bipolar pulse mode

(a) 119905+off a neutral period where there is no applied voltagethe chemical reactions will etch the aluminium and releasethe aluminate ions AlO

2

minus and Al(OH)4

minus into the electrolyte[90 91]

2Al + 2H2O + 2OHminus = 2AlO

2

minus(aq) + 3H

2(1)

Al + 4OHminus 997888rarr Al(OH)4

minus(gel) (2)

The chemical dissolution for the alumina ceramic reduces itsthickness as given by the following reactions [91]

Al2O3+ 2OHminus + 3H

2O 997888rarr 2Al(OH)

4

minus(gel)

997888rarr 2Al(OH)3darr + 2OHminus

(3)

The boehmite AlO2H also may be produced by the following

reaction [92]

Al(OH)4

minus+H2O 997888rarr AlO

2H darr +2H

2O +OHminus (4)

The OHminus combines the aluminium hydroxide [8]

Al(OH)3+OHminus 997888rarr Al(OH)

4

minus (5)

The aluminium oxidation [8] is

2Al + 3H2O = Al

2O3+ 3H2uarr (6)

Based on the above the alumina ceramic surface is chemicallydissolved by the attack of OHminus [8] and this dissolution is

more aggressive with the increment of liberated heat into theelectrolyte from the treated surface

(b) 119905+on the cathodic period in this period the negativelycharged sample attracts the electrolyte cations the anionsincluding the products of the neutral period will be repelledaway into the electrolyte and the possible reactions are asfollows

The inward deposition of cations into the ceramic surfaceequations is following

Na+ + eminus 997888rarr Na (7)

Al3+ + 3eminus 997888rarr Al (8)

The sodium is a highly reactive metal and it will immediatelyreact and dissolve into the electrolyte (9) except that whichpenetrates into the inner layers of the ceramic

Na +H2O = Na+ +OHminus +H

2uarr (9)

The water cathodic electrolysis is

2H2O + 2eminus 997888rarr H

2uarr + 2OHminus (10)

(c) 119905minusoff a neutral period it has the same chemical reac-tions for the neutral period 119905+off (1)ndash(6)

(d) 119905minuson the anodic period this period is characterized bythe MAO discharging due to the effect of high electric fieldand the production of alumina ceramic by the reaction bet-ween the inward immigrant O2minus [93] and the outward immi-grant Al3+ according to

2Al3+ + 3O2minus 997888rarr Al2O3

(11)


(a) (b)

Figure 2 Two SEMmicrographs for the same sample after MAO treatment by (a) a month and (b) six months

Someof the immigrantAl3+ will be ejected into the electrolyteand combine with the hydroxide or silicate

Al3+ (ejected) + 3OHminus 997888rarr Al(OH)3darr (12)

2Al3+ (ejected) + 3SiO3

2minus997888rarr Al

2(SiO3)3

(13)

A part of silica will attach (without reaction) to the moltenalumina and transfer into one of the silica phases whileanother silica quantity combines with the ejected molten alu-mina and produces an aluminosilicate phase according to thetransfer temperature and pressure

Al2O3(molten) + SiO

2

Δ

997888rarr Al2O5Si (14)

The ejected molten alumina will contact the surroundingelectrolyte rapidly quenched and solidified to form the 120574-alumina phase [94]

Al2O3

rapid cooling997888997888997888997888997888997888997888997888997888997888rarr 120574-Al

2O3

(15)

While the slower cooling rate in the inner layers of the spark-ing channels is favored to form the 120572-alumina phase [45 94]

Al2O3

slow cooling997888997888997888997888997888997888997888997888997888rarr 120572-Al

2O3

(16)

Heating the attached aluminium hydroxide and boehmiteto an elevated temperature will transfer it into one of thealumina phases [95]

Al(OH)3

450ndash750∘C997888997888997888997888997888997888997888rarr 120574-Al

2O3

(17)

Al(OH)3

gt1100∘C

997888997888997888997888997888997888rarr 120572-Al2O3

(18)

AlO2H 450ndash750

∘C997888997888997888997888997888997888997888rarr 120574-Al

2O3

(19)

AlO2H gt1100

∘C997888997888997888997888997888997888rarr 120572-Al

2O3

(20)

The anions will be attracted toward the surface during theanodic polarization and produce alumina and other compo-sitions [10 70]


minus(gel) (21)

2Al + 6OHminus 997888rarr Al2O3+ 3H2O + 6eminus (22)

4OHminus 997888rarr O2+ 2H2O + 4eminus (23)

The silica is produced (24) by the combination betweenattracted silicate anions and H+ which is produced by thewater electrolysis on the anode (25)

SiO3

2minus+ 2H+ 997888rarr SiO

2+H2O (24)

2H2O 997888rarr O

2+ 4H+ + 4eminus (25)

Generally the chemical dissolution occurs during the anodicand neutral periods the MAO only occurs during the anodicperiod and the cathodic period does not contribute to theceramic building or dissolution

As a result of the previous reactions the most likelycompositions and phases on the surface of MAO-treated alu-minium in the alkaline sodium silicate electrolyte are aluminaphases silica phases and aluminosilicate phases whileother compositionsmostly will be released or dissolved in theelectrolyte or in water during the cleaning process

4 Results

After the preparation by amonth and sixmonths the sampleswere studied by the SEM and XRD A disappearance of somesmall particles was notified in the accumulated particlesregion as shown in Figure 2 By comparing theXRDpatternsa strong peak for cristobalite (an SiO

2phase) and other

small peaks were almost vanished Figure 3 which suggestedthat these released particles mostly consist of the cristobalitephase The small size cristobalite particles provide more sur-face area or surface energy which are prone to be dissolvedin water or other solvents during cleaning process whichtends to enhance the detachment of cristobalite particles [96]Due to this phenomenon all presented measurements andresults in this study belong to the samples after six monthsof treatment

A linear correlation occurred for the layer thicknessand surface roughness with the current densities 119869

119886le

2188Adm2 followed by a deflection from the linearity forthe highest current density as shown in Figures 4(a) and 4(b)The thinnest coating 109120583mwas formed at the lowest currentdensity 1094Adm2 while the thickest coating 185 120583m wasformed at the highest current density 4375Adm2 The sur-face roughness ranged between 079 120583m and 127120583m for cur-rent densities 1094Adm2 and 4375Adm2 respectivelySimilar response of thickness-current density was found


20 40 60 80

Inte

nsity

(au

)In

tens

ity (a

u)

2120579

(a)

(b)

Figure 3 XRD patterns of a sample after the MAO treatment by (a)a month and (b) six months The arrows are pointing to the peakswhich were decreased significantly after six months of storage

using DC current by Raj and Mubarak Ali [70] A linearcorrelation between theMAOalumina ceramic thickness androughness is illustrated in Figure 5 which is consistent withsome previously published works [87 97 98]

Figure 6 illustrates the apparent microstructures in theSEM micrographs which can be classified into accumulatedparticles microcracks and volcano-like microstructures Avolcano-like microstructure includes a solidified pool and acentered openblind craterThe volcano-like microstructuresare formed by the discrete localized microdischarge eventsThe rapid solidification of the molten alumina forms themicrocracks and accumulated particles on and around thedischarge channels [99] Wei et al [45] reported that more120572-alumina can be formed in the inner layers due to the lowcooling rate while the high cooling rate on the outer layersurface was favorable to form more 120574-alumina during thesolidification

The increment of anodic current density significantlyaffected the size of volcano-like as presented in Figures7(a)ndash7(d) Smallest volcano-like microstructures with morepopulation occurred for the lowest 119869

119886(1094Adm2) while

the largest volcano-like microstructures associated with thehighest 119869

119886(4375Adm2) To get more comprehensive results

an average of 27 different randomly selected positions werecaptured by the SEM for each sample and digitally analyzed

by the Image-Pro Plus software to estimate the ratio of theoccupied area by the volcano-like microstructures to themicrograph frame and the results are presented in Figure 8A slight increment in the area ratio from 556 to 596occurred for the occupied area ratio of the volcano-likemicrostructures due to the increment of the 119869

119886from

1094Adm2 to 4375Adm2 On the contrary a significantdecrement from 2620mmminus2 to 1420mmminus2 was accomplishedin the volcano-like density due to the increment of anodiccurrent density as shown in Figure 9

Figure 10 shows the elemental compositions of severalEDX study points over samples prepared at various anodiccurrent densities For all samples the aluminium was domi-nant near to the craters while its concentrationwas decreasedas the study point moved away from the craters More siliconwas found in the accumulated particles Figures 10(a)ndash10(d)Few sodium amounts were found in the accumulated parti-cles of the MAO ceramic surface prepared at 4375Adm2

Figure 11 shows the XRD patterns of MAO aluminaceramics prepared at various anodic biasing current densitiesThe most apparent peaks belong to aluminium due to the X-ray penetration into the substrate through the ceramic layerTo identify the compositions and phases related to othershorter peaks we applied the RiR method by MATCH soft-ware The other major phases were 120572-alumina 120574-aluminacristobalite (an SiO

2phase) and sillimanite (an Al

2SiO5

phase) while there were few amounts of Si and Na which arelocalized in the inner ceramic layerTheweight percentages ofthe major phases are presented in Figure 12 after subtractingthe weight percentages of Al Si and Na The 120574-aluminaphase was the dominant in the ceramic coating at low anodiccurrent density As the anodic current density increasedthe 120574-alumina decreased from 666wt to 262 wt whilethe 120572-alumina phase increased from 39wt to 276 wtThe sillimanite was around 20wt for the lowest anodiccurrent density of 1094Adm2 and approximately constantaround 40wt for anodic current densities of 1458 2188and 4375Adm2 The cristobalite was 9wt for anodiccurrent density of 1094Adm2 and less than 5wt for 119869

119886ge

1458Adm2Figure 13 shows the infrared spectra ofMAOceramic sur-

faces prepared at different anodic current densities in addi-tion to an untreated saw cut aluminium surface The mea-surements were conducted at 70∘C the shaded rectanglesbelong to the absorption bands of CO

2(centered at 43 and

149 120583m) and H2O (centered at 61 120583m) in the ambient air

[100ndash104]TheMAO ceramic surfaces have higher emissivityvalues compared to the untreated saw cut aluminium surface

The emissivity spectrum has three distinguishable wave-length regions The emissivity increased with the wavelengthincrement in the first region between 40 120583mand 78120583mThesecond region is characterized by a rapid ascending that startsfrom 78120583m and ends at 86120583m The third region for wave-lengths longer than 86 120583m is characterized by a relativelyhigh emissivitywith three apparent peaks centered at 102120583m128 120583m and 155 120583m The high intensity values of the peakat 102 120583m ranged between 966 and 974 for 1094Adm2and 4375Adm2 respectively


10 20 30 40 50

10

12

14

16

18

20

Anodic biasing current density (Adm2)

Cer

amic

laye

r thi

ckne

ss (120583

m)

(a)

07

08

09

1

11

12

13

10 20 30 40 50Anodic biasing current density (Adm2)

Ra

(120583m

)

(b)

Figure 4 The effect of anodic biasing current density on the (a) layer thickness and (b) surface roughness of the MAO ceramic coating

201816141210

08

12

14

1Ra

(120583m

)

Ceramic layer thickness (120583m)

Figure 5 The linear correlation between the MAO ceramic thick-ness and surface roughness

5 Discussions

At the first beginning of the MAO process the relativelyhigh anodic voltage activates the inward oxidation of the alu-minium substrate by the reaction between the inward immi-grant O2minus and the outward immigrant Al3+ according to (11)[93]The growth of aluminium oxide layer increases the elec-trical resistance and at a specific thickness the currentbegins to flow through weak points on the oxide layer and

b

d

c

a

30120583m

Figure 6 The main microstructures in the SEM micrographs are(a) resolidified pools (b) craters (c) accumulated particles and (d)microcracks

strengthens the electrical field which in turn significantlyincreases the reionization of the surrounding electrolyteand the aluminium substrate and consequently triggers theplasma microdischarges The elevated temperature of local-ized plasma (which ranges between 2 kK [105] and 11 kK[106]) melts the alumina and vaporizes the electrolyte inthe discharging circumference and evacuates the region ofplasma discharging Due to the pressure reduction themolten alumina will be suctioned out of the dischargingchannel and the electrolyte flows toward the low pressureregion and will be vaporized by the molten alumina Some of


(a) (b)

(c)

30120583m

(d)

Figure 7 Surface morphologies of MAO ceramic coatings prepared at different anodic biasing current densities (a) 1094Adm2 (b)1458Adm2 (c) 2188Adm2 and (d) 4375 Adm2

055

056

057

058

059

06


Volc

ano-

like a

rea r

atio

Figure 8 The effect of anodic current density on the relativelyoccupied area by volcano-like microstructures

solid molecules such as silica and ions may be attached onthe surface of molten alumina which forms the cristobaliteand sillimanite phases which were found on the accumulatedparticles and on the solidified pools according to the EDXand

1200

1600

2000

2400

2800


Volc

ano-

like d

ensit

y (m

mminus2)

Figure 9 The inverse proportional of volcano-like density with theanodic current density

XRD results The volcano-like microstructures are createdby the solidification of the molten alumina which spreadover the surface around the discharging channels formingthe solidified pools and the craters According to the EDX


SampleStudy point Al O Si Na Sample

Study point Al O Si Na

a 523 477 a 594 406b 459 488 53 b 523 418 59c 162 550 288 c 493 461 46d 272 540 188 d 485 446 69e 392 476 132 e 268 503 229

f 99 490 411g 196 429 375



a 549 361 90 a 564 436b 542 352 106 b 620 343 37c 481 458 61 c 569 396 35d 137 489 374 d 623 272 105e 292 302 406 e 92 437 471f 230 420 350 f 260 452 288g 413 462 125 g 182 521 278 19

mdashmdashmdashmdashmdashmdash

mdashmdashmdashmdashmdashmdashmdashmdash

mdashmdashmdashmdashmdashmdashmdash


a

cd

b

(a) (b)

(c) (d)

e

acef g

bd

ba

cd

e

fg

abc

d

e

f

g

10120583m 20120583m

20120583m20120583m

Figure 10 The results of the EDX analysis at several locations on the MAO ceramic surfaces prepared at different anodic current densities(a) 1094 (b) 1458 (c) 2188 and (d) 4375 Adm2

1094Adm2

1458Adm2

2188Adm2

4375Adm2

20 40 60 80

2120579

Inte

nsity

(au

)

Al

120572-Al2O3

120574

Sillimanite Cristobalite

-Al2O3

Figure 11 XRD spectra for MAO alumina ceramic coatings pre-pared at different anodic current densitiesThemost apparent peaksare for aluminium which minimize the appeared intensities forother phases and compositions

results more silicon was found on the accumulated particlesand the edges of the solidified pools which were identifiedby the XRD results to be the cristobalite and sillimanitephases The increment of cristobalite and sillimanite phaseson the accumulated particles and edges of solidified pools was

because of the longer travelling distance during the ejectionof alumina out of the discharging channel which allowedmore silica to be attached After the solidification the surfacetension forms the microcracks and the accumulated smallparticles on the solidified pool edges which contain morecristobalite and sillimanite phases [107] Also the EDX resultsstated that the aluminium concentration increased as thestudy point approached the crater this reflects that less reac-tion happened between the center of ejected molten aluminaand the silica due to the flow of the vaporized electrolytewhich might start from the edges and consequently moresilica was attached on the edges

Figure 4 states the effect of anodic current density on thelayer thickness and surface roughness The small workingarea increased the current density which resulted in strongermicrodischarges and consequently ejected more moltenalumina out of the discharging channels which increasedthe growth of the MAO ceramic coating Figure 4(a) Asthe MAO ceramic grew the current flowed through lessweak points which strengthened the electrical plasma dis-charges and produced wider volcano-like microstructuresFigure 7(d) less volcano-like density Figure 9 and a roughersurface Figure 4(b) The stronger microdischarges liberatedmore elevated temperature and vaporized more electrolyteswhich in turn formed an envelope of gas which surroundedthe working area and slowed the cooling rate and was favor-able to form more 120572-alumina phases Figure 12(a) Thegrowth of the ceramic layer Figure 4(a) was less at thehighest current density 4375 Adm2 due to the incrementof liberated heat which increased the chemical dissolutionaround the working area [70]

The alumina ceramic is semitransparent in the range 4ndash77120583m and opaque in the 77ndash250120583m range as reported byRozenbaum et al [108] Boumaza et al found that the 120574-alu-mina has a broadband between 111 120583m and 333 120583m [109]


10 20 30 40 50

0

20

40

60

80


(wt

)

120574-Al2O3

120572-Al2O3

Total alumina phases

(a)

10 20 30 40 50

0

20

40

60

80


(wt

)Sillimanite

Cristobalite

Sillimanite + cristobalite

(b)

Figure 12 Effect of anodic current density on the MAO ceramic (a) alumina phases and (b) sillimanite and cristobalite phases

84 12 160

20

40

60

80

100

Emiss

ivity

()

4375Adm2

2188Adm2

1458Adm2

1094Adm2

Untreated saw cut aluminium surface

CO2

CO2

H2O

Wavelength (120583m)

Figure 13 IR spectral emissivity of the MAO ceramic surfacesprepared at different anodic current densities

and the 120572-alumina has IR band positions at 1550 and1645 120583m [109]The cristobalite phase has IR peaks at 96 114125 and 153 120583m measured at 300∘C which shift into longerwavelengths at lower temperatures [110] The sillimanitephase has IR peaks at 1075 1163 1316 and 1515 120583m and

a broadband ranges from 855 120583m to 980120583m[111]These factsexplain the behavior of IR emissivity spectra in Figure 13 Forthe range between 40 120583m and 78 120583m the ceramic aluminais semitransparent and its emissivity is lower than that inthe region (86ndash160 120583m) where the ceramic turns to beopaque and stronger emitter due to the existence of 120574-alumina and other phases The existing phases contributedto enhancing the emissivity in the opaque region and theapparent peaks centered at 102 120583m and 128 120583mwere formedby the cristobalite and sillimanite while the 155 120583m wasformed by the 120572-alumina and cristobalite phases

Previous studies showed that the infrared emissivityof ceramic surfaces depends on its chemical and physicalproperties such as compositions phases roughness porositygrain size pore size spatial repetition of the grains andlayer thickness and each wavelength region has its owneffective factors [88 98 108 112] According to Figure 13the intensity of emissivity has a slight variation in the semi-transparent region whereas no significant variation occurredin the opaque region Referring to the phase concentra-tions in Figure 12 the lowest current density formed 9 and20wt of cristobalite and sillimanite phases respectivelywhile their weight percentages were approximately constantsfor 119869119886ge 1458Adm2 The 120572- and 120574-alumina phases are

semitransparent for the wavelengths shorter than 77120583m Onthe other hand both of the surface roughness and layerthickness were increased with the 119869

119886 This leads to the

conclusion that the slight variation of the emissivity in thesemitransparent region was due to the surface roughness andthickness and the existing phases did not contribute to thevariations of emissivity in this region


The emissivity averages of long wavelength infrared(LWIR) region (8ndash15 120583m) were 884 886 886 and 894for the MAO alumina ceramics prepared at anodic currentdensities of 1094 1458 2188 and 4375Adm2 respec-tively The anodic current density did not change the LWIRemissivity significantly which has a good application in theindustrial field to fabricate a relatively high emitterMAO alu-mina ceramic surface which also provides a strong adhe-sion to the aluminium substrate corrosion resistance wearresistance thermal shock resistance and high hardness asfound in previously published works The high emitter MAOalumina ceramic will enhance the heat dissipation of differentcooling and heating systems which use aluminium such asLED laser electronic circuits CPU heat sink vehicle indoorradiators and others Further works are needed to study theIR emissivity of different MAO alumina ceramics fabricatedon the aluminium surfaces using different MAO treatmentconditions and electrolyte compositions

6 Conclusions

The increment of anodic current density widened the vol-cano-like microstructures and lowered its density while therelatively occupied area by the volcano-like microstructureswas approximately constant

The high anodic current density thickened and rough-ened the MAO alumina ceramic The major phases in theMAO alumina ceramic were 120572-alumina 120574-alumina silliman-ite and cristobalite The increment of current density from1094Adm2 to 4375Adm2 increased the concentration of120572-alumina from 39wt to 276 wt and decreased the con-centration of 120574-alumina from666wt to 262 wt For 119869

119886ge

1458Adm2 the sillimanite and cristobalite concentrationswere approximately constant around 40wt and less than5wt respectively

The spectral IR emissivity was slightly varied in the semi-transparent region whereas no significant variation occurredin the opaque region The slight variation of the emissivity inthe semitransparent region was due to the surface roughnessand thickness and the existing phases did not contribute tothe variations of emissivity in the semitransparent regionTheexisting phases contributed to enhancing the emissivity inthe opaque region The apparent peaks centered at 102 120583mand 128 120583m were formed by the cristobalite and sillimanitephases while another peak at 155 120583m was formed by the 120572-alumina and cristobalite phases

Using an ecofriendly alkaline silicate electrolyte a rela-tively high emissivity MAO alumina ceramic was fabricatedon the aluminium substrate The MAO alumina ceramic hasan emissivity peak of 97 at 128120583m measured at 70∘C andan average of LWIR emissivity ranged between 884 and894 More future studies are required to fabricate highemissivity ceramic surfaces using different MAO processingconditions and electrolytes

Acknowledgments

The authors wish to express their sincere gratitude to DrHong-Jen Li for his cooperation and help in using FTIR

spectroscopy The technical support of Shi-Rui Li Shu-WeiHuang Yuan-Yi Sung Chan-Hsuan Chen Shi-Chung ChenWei-Tie Wu Chien-Huang Kuo Chih-Yeh Lin Jie-MineWu and Wan-Yi Chen is gratefully acknowledged Also theauthors wish to thank Asian Vital Component CompanyTaipei for providing the aluminium pieces

References

[1] A K A Shati S G Blakey and S B M Beck ldquoThe effect ofsurface roughness and emissivity on radiator outputrdquo Energyand Buildings vol 43 no 2-3 pp 400ndash406 2011

[2] S-H Yu D Jang and K-S Lee ldquoEffect of radiation in a radialheat sink under natural convectionrdquo International Journal ofHeat and Mass Transfer vol 55 no 1-3 pp 505ndash509 2012

[3] F Mecuson T Czerwiec T Belmonte L Dujardin A Violaand G Henrion ldquoDiagnostics of an electrolytic microarc pro-cess for aluminium alloy oxidationrdquo Surface and Coatings Tech-nology vol 200 no 1-4 pp 804ndash808 2005

[4] S Stojadinovic R Vasilic I Belca et al ldquoCharacterization ofthe plasma electrolytic oxidation of aluminium in sodium tung-staterdquo Corrosion Science vol 52 no 10 pp 3258ndash3265 2010

[5] Z Wang L Wu Y Qi W Cai and Z Jiang ldquoSelf-lubricatingAl2O3PTFE composite coating formation on surface of alu-

minium alloyrdquo Surface and Coatings Technology vol 204 no20 pp 3315ndash3318 2010

[6] R H U Khan A Yerokhin X Li H Dong and A MatthewsldquoSurface characterisation of DC plasma electrolytic oxidationtreated 6082 aluminium alloy effect of current density andelectrolyte concentrationrdquo Surface andCoatings Technology vol205 no 6 pp 1679ndash1688 2010

[7] L O Snizhko A L Yerokhin A Pilkington et al ldquoAnodic pro-cesses in plasma electrolytic oxidation of aluminium in alkalinesolutionsrdquo Electrochimica Acta vol 49 no 13 pp 2085ndash20952004

[8] S-M Moon and S-I Pyun ldquoThe corrosion of pure aluminiumduring cathodic polarization in aqueous solutionsrdquo CorrosionScience vol 39 no 2 pp 399ndash408 1997

[9] L Wen Y Wang Y Zhou J-H Ouyang L Guo and D JialdquoCorrosion evaluation of microarc oxidation coatings formedon 2024 aluminium alloyrdquo Corrosion Science vol 52 no 8 pp2687ndash2696 2010

[10] J R Morlidge P Skeldon G E Thompson H Habazaki KShimizu and G C Wood ldquoGel formation and the efficiency ofanodic film growth on aluminiumrdquo Electrochimica Acta vol 44no 14 pp 2423ndash2435 1999

[11] P I Butyagin Y V Khokhryakov and A I Mamaev ldquoMicro-plasma systems for creating coatings on aluminium alloysrdquoMaterials Letters vol 57 no 11 pp 1748ndash1751 2003

[12] J Jovovic S Stojadinovic NM Sisovic andNKonjevic ldquoSpec-troscopic characterization of plasma during electrolytic oxida-tion (PEO) of aluminiumrdquo Surface andCoatings Technology vol206 pp 24ndash28 2011

[13] A L Yerokhin L O Snizhko N L Gurevina A Leyland APilkington and A Matthews ldquoSpatial characteristics of dis-charge phenomena in plasma electrolytic oxidation of alu-minium alloyrdquo Surface andCoatings Technology vol 177-178 pp779ndash783 2004

[14] T Abdulla A Yerokhin and R Goodall ldquoEffect of Plasma Elec-trolytic Oxidation coating on the specific strength of open-cell


aluminium foamsrdquoMaterials andDesign vol 32 no 7 pp 3742ndash3749 2011

[15] A L Yerokhin A A Voevodin V V Lyubimov J Zabinski andM Donley ldquoPlasma electrolytic fabrication of oxide ceramicsurface layers for tribotechnical purposes on aluminium alloysrdquoSurface and Coatings Technology vol 110 no 3 pp 140ndash1461998

[16] E Matykina R Arrabal P Skeldon G E Thompson and PBelenguer ldquoAC PEO of aluminium with porous alumina pre-cursor filmsrdquo Surface and Coatings Technology vol 205 no 6pp 1668ndash1678 2010

[17] SVGnedenkovOAKhrisanfovaAG Zavidnaya et al ldquoPro-duction of hard and heat-resistant coatings on aluminiumusinga plasma micro-dischargerdquo Surface and Coatings Technologyvol 123 no 1 pp 24ndash28 2000

[18] M Trevino N F Garza-Montes-de-Oca A Perez M A LHernandez-Rodrıguez A Juarez and R Colas ldquoWear of an alu-minium alloy coated by plasma electrolytic oxidationrdquo Surfaceand Coatings Technology vol 206 no 8-9 pp 2213ndash2219 2012

[19] T S Lim H S Ryu and S-H Hong ldquoElectrochemical corro-sion properties of CeO

2-containing coatings on AZ31 magne-

sium alloys prepared by plasma electrolytic oxidationrdquo Corro-sion Science vol 62 pp 104ndash111 2012

[20] A V Timoshenko and Y VMagurova ldquoInvestigation of plasmaelectrolytic oxidation processes of magnesium alloy MA2-1under pulse polarisation modesrdquo Surface and Coatings Technol-ogy vol 199 no 2-3 pp 135ndash140 2005

[21] J Liang P B Srinivasan C Blawert and W Dietzel ldquoCom-parison of electrochemical corrosion behaviour of MgO andZrO2coatings on AM50 magnesium alloy formed by plasma

electrolytic oxidationrdquo Corrosion Science vol 51 no 10 pp2483ndash2492 2009

[22] F Liu D Shan Y Song E-H Han and W Ke ldquoCorrosionbehavior of the composite ceramic coating containing zirco-nium oxides on AM30 magnesium alloy by plasma electrolyticoxidationrdquoCorrosion Science vol 53 no 11 pp 3845ndash3852 2011

[23] G-H Lv H Chen L Li et al ldquoInvestigation of plasma elec-trolytic oxidation process on AZ91Dmagnesium alloyrdquo CurrentApplied Physics vol 9 no 1 pp 126ndash130 2009

[24] P Bala Srinivasan R Zettler C Blawert and W Dietzel ldquoAstudy on the effect of plasma electrolytic oxidation on the stresscorrosion cracking behaviour of a wrought AZ61 magnesiumalloy and its friction stir weldmentrdquoMaterials Characterizationvol 60 no 5 pp 389ndash396 2009

[25] P Zhang X Nie HHu andY Liu ldquoTEManalysis and tribolog-ical properties of Plasma Electrolytic Oxidation (PEO) coatingson a magnesium engine AJ62 alloyrdquo Surface and CoatingsTechnology vol 205 no 5 pp 1508ndash1514 2010

[26] F Liu D Shan Y Song and E-H Han ldquoEffect of additives onthe properties of plasma electrolytic oxidation coatings formedon AM50 magnesium alloy in electrolytes containing K2ZrF6rdquoSurface and Coatings Technology vol 206 no 2-3 pp 455ndash4632011

[27] P Wang J Li Y Guo and Z Yang ldquoGrowth process and cor-rosion resistance of ceramic coatings of micro-arc oxidation onMg-Gd-Ymagnesium alloysrdquo Journal of Rare Earths vol 28 no5 pp 798ndash802 2010

[28] J Liang L Hu and J Hao ldquoCharacterization of microarc oxi-dation coatings formed on AM60B magnesium alloy in silicateand phosphate electrolytesrdquo Applied Surface Science vol 253no 10 pp 4490ndash4496 2007

[29] F Jin P K Chu G Xu J Zhao D Tang andH Tong ldquoStructureand mechanical properties of magnesium alloy treated bymicro-arc discharge oxidation using direct current and high-frequency bipolar pulsing modesrdquo Materials Science and Engi-neering A vol 435-436 pp 123ndash126 2006

[30] K R Shin Y G Ko and D H Shin ldquoEffect of electrolyte onsurface properties of pure titanium coated by plasma elec-trolytic oxidationrdquo Journal of Alloys and Compounds vol 509supplement 1 pp S478ndashS481 2011

[31] X Wang X Pan W Ye Y Wei and Y Chen ldquoPreparation andproperties of TiC

119909N1minus119909

coatings containing calcium on tita-nium surface by plasma electrolytic carbonitridingrdquo Surface andCoatings Technology vol 228 supplement 1 pp S194ndashS197 2013

[32] DWei Y Zhou YWang andD Jia ldquoCharacteristic ofmicroarcoxidized coatings on titanium alloy formed in electrolytes con-taining chelate complex and nano-HArdquoApplied Surface Sciencevol 253 no 11 pp 5045ndash5050 2007

[33] W Zhang K Du C Yan and F Wang ldquoPreparation and char-acterization of a novel Si-incorporated ceramic film on puretitanium by plasma electrolytic oxidationrdquo Applied SurfaceScience vol 254 no 16 pp 5216ndash5223 2008

[34] K R Shin Y G Ko and D H Shin ldquoSurface characteristics ofZrO2-containing oxide layer in titanium by plasma electrolytic

oxidation in K4P2O7electrolyterdquo Journal of Alloys and Com-

pounds vol 536 supplement 1 pp S226ndashS230 2012[35] Y M Wang L X Guo J H Ouyang Y Zhou and D C Jia

ldquoInterface adhesion properties of functional coatings on tita-nium alloy formed by microarc oxidation methodrdquo AppliedSurface Science vol 255 no 15 pp 6875ndash6880 2009

[36] P Huang K-W Xu and Y Han ldquoPreparation and apatite layerformation of plasma electrolytic oxidation film on titanium forbiomedical applicationrdquo Materials Letters vol 59 no 2-3 pp185ndash189 2005

[37] Y Wang T Lei L Guo and B Jiang ldquoFretting wear behaviourofmicroarc oxidation coatings formed on titanium alloy againststeel in unlubrication and oil lubricationrdquo Applied SurfaceScience vol 252 no 23 pp 8113ndash8120 2006

[38] S Stojadinovic R Vasilic M Petkovic and L Zekovic ldquoPlasmaelectrolytic oxidation of titanium in heteropolytungstate acidsrdquoSurface and Coatings Technology vol 206 pp 575ndash581 2011

[39] H Tang Q Sun T Xin C Yi Z Jiang and F Wang ldquoInfluenceof Co(CH

3COO)

2concentration on thermal emissivity of coat-

ings formed on titanium alloy by micro-arc oxidationrdquo CurrentApplied Physics vol 12 no 1 pp 284ndash290 2012

[40] S Cui J Han Y Du andW Li ldquoCorrosion resistance and wearresistance of plasma electrolytic oxidation coatings on metalmatrix compositesrdquo Surface and Coatings Technology vol 201no 9ndash11 pp 5306ndash5309 2007

[41] G Rapheal S Kumar C Blawert and N B Dahotre ldquoWearbehavior of plasma electrolytic oxidation (PEO) and hybridcoatings of PEO and laser on MRI 230D magnesium alloyrdquoWear vol 271 no 9-10 pp 1987ndash1997 2011

[42] X Nie E I Meletis J C Jiang A Leyland A L Yerokhin andA Matthews ldquoAbrasive wearcorrosion properties and TEManalysis of Al

2O3coatings fabricated using plasma electrolysisrdquo

Surface and Coatings Technology vol 149 no 2-3 pp 245ndash2512002

[43] Y Jiang Y Zhang Y Bao and K Yang ldquoSliding wear behaviourof plasma electrolytic oxidation coating on pure aluminiumrdquoWear vol 271 no 9-10 pp 1667ndash1670 2011


[44] M Aliofkhazraei A Sabour Rouhaghdam and T ShahrabildquoAbrasive wear behaviour of Si

3N4TiO2nanocomposite coat-

ings fabricated by plasma electrolytic oxidationrdquo Surface andCoatings Technology vol 205 supplement 1 pp S41ndashS46 2010

[45] T Wei F Yan and J Tian ldquoCharacterization and wear- andcorrosion-resistance of microarc oxidation ceramic coatings onaluminum alloyrdquo Journal of Alloys and Compounds vol 389 no1-2 pp 169ndash176 2005

[46] L Wang J Zhou J Liang and J Chen ldquoMicrostructure andcorrosion behavior of plasma electrolytic oxidation coatedmag-nesium alloy pre-treated by laser surface meltingrdquo Surface andCoatings Technology vol 206 no 13 pp 3109ndash3115 2012

[47] P Su X Wu Y Guo and Z Jiang ldquoEffects of cathode currentdensity on structure and corrosion resistance of plasma elec-trolytic oxidation coatings formed on ZK60 Mg alloyrdquo Journalof Alloys and Compounds vol 475 no 1-2 pp 773ndash777 2009

[48] R O Hussein D O Northwood and X Nie ldquoThe influenceof pulse timing and current mode on the microstructure andcorrosion behaviour of a plasma electrolytic oxidation (PEO)coated AM60B magnesium alloyrdquo Journal of Alloys and Com-pounds vol 541 pp 41ndash48 2012

[49] L Rama Krishna G Poshal and G Sundararajan ldquoInfluence ofelectrolyte chemistry on morphology and corrosion resistanceof micro arc oxidation coatings deposited onmagnesiumrdquoMet-allurgical andMaterials Transactions A vol 41 no 13 pp 3499ndash3508 2010

[50] J Liang L Hu and J Hao ldquoImprovement of corrosion prop-erties of microarc oxidation coating on magnesium alloy byoptimizing current density parametersrdquoApplied Surface Sciencevol 253 no 16 pp 6939ndash6945 2007

[51] C Blawert V Heitmann W Dietzel H M Nykyforchyn andM D Klapkiv ldquoInfluence of electrolyte on corrosion propertiesof plasma electrolytic conversion coated magnesium alloysrdquoSurface and Coatings Technology vol 201 no 21 pp 8709ndash87142007

[52] D Y Hwang Y M Kim D-Y Park B Yoo and D H ShinldquoCorrosion resistance of oxide layers formed on AZ91 Mgalloy in KMnO

4electrolyte by plasma electrolytic oxidationrdquo

Electrochimica Acta vol 54 no 23 pp 5479ndash5485 2009[53] Y M Wang B L Jiang T Q Lei and L X Guo ldquoMicroarc

oxidation coatings formed on Ti6Al4V inNa2SiO3system solu-

tion microstructure mechanical and tribological propertiesrdquoSurface and Coatings Technology vol 201 no 1-2 pp 82ndash892006

[54] J Liang B Guo J Tian H Liu J Zhou and T Xu ldquoEffect ofpotassium fluoride in electrolytic solution on the structure andproperties of microarc oxidation coatings onmagnesium alloyrdquoApplied Surface Science vol 252 no 2 pp 345ndash351 2005

[55] Y Guangliang L Xianyi B Yizhen C Haifeng and J ZengsunldquoThe effects of current density on the phase compositionand microstructure properties of micro-arc oxidation coatingrdquoJournal of Alloys and Compounds vol 345 no 1-2 pp 196ndash2002002

[56] C-C Tseng J-L Lee T-H Kuo S-N Kuo and K-H TsengldquoThe influence of sodium tungstate concentration and anodiz-ing conditions on microarc oxidation (MAO) coatings foraluminum alloyrdquo Surface and Coatings Technology vol 206 no16 pp 3437ndash3443 2012

[57] H J Robinson A E Markaki C A Collier and T W ClyneldquoCell adhesion to plasma electrolytic oxidation (PEO) titaniacoatings assessed using a centrifuging techniquerdquo Journal of

the Mechanical Behavior of Biomedical Materials vol 4 no 8pp 2103ndash2112 2011

[58] S V Gnedenkov O A Khrisanfova A G Zavidnaya et alldquoComposition and adhesion of protective coatings on alu-minumrdquo Surface and Coatings Technology vol 145 no 1ndash3 pp146ndash151 2001

[59] K Ramachandran V Selvarajan P V Ananthapadmanabhanand K P Sreekumar ldquoMicrostructure adhesion microhard-ness abrasive wear resistance and electrical resistivity of theplasma sprayed alumina and alumina-titania coatingsrdquo ThinSolid Films vol 315 no 1-2 pp 144ndash152 1998

[60] Y Wang Z Jiang and Z Yao ldquoMicrostructure bondingstrength and thermal shock resistance of ceramic coatings onsteels prepared by plasma electrolytic oxidationrdquo Applied Sur-face Science vol 256 no 3 pp 650ndash656 2009

[61] Y Xu Z Yao F Jia Y Wang Z Jiang and H Bu ldquoPreparationof PEO ceramic coating on Ti alloy and its high temperatureoxidation resistancerdquo Current Applied Physics vol 10 no 2 pp698ndash702 2010

[62] Y Wang Z Jiang and Z Yao ldquoFormation of titania compositecoatings on carbon steel by plasma electrolytic oxidationrdquoApplied Surface Science vol 256 no 20 pp 5818ndash5823 2010

[63] J Ding J Liang L Hu J Hao and Q Xue ldquoEffects of sodiumtungstate on characteristics of microarc oxidation coatingsformed onmagnesium alloy in silicate-KOH electrolyterdquoTrans-actions of Nonferrous Metals Society of China vol 17 no 2 pp244ndash249 2007

[64] M Tang H LiuW Li and L Zhu ldquoEffect of zirconia sol in elec-trolyte on the characteristics of microarc oxidation coating onAZ91D magnesiumrdquo Materials Letters vol 65 no 3 pp 413ndash415 2011

[65] Q Cai L Wang B Wei and Q Liu ldquoElectrochemical perfor-mance of microarc oxidation films formed on AZ91D magne-sium alloy in silicate and phosphate electrolytesrdquo Surface andCoatings Technology vol 200 no 12-13 pp 3727ndash3733 2006

[66] C-E Barchiche E Rocca and J Hazan ldquoCorrosion behaviourof Sn-containing oxide layer on AZ91D alloy formed by plasmaelectrolytic oxidationrdquo Surface and Coatings Technology vol202 no 17 pp 4145ndash4152 2008

[67] M Tang W Li H Liu and L Zhu ldquoPreparation Al2O3ZrO2

composite coating in an alkaline phosphate electrolyte contain-ing K

2ZrF6on aluminum alloy by microarc oxidationrdquo Applied

Surface Science vol 258 no 15 pp 5869ndash5875 2012[68] M Tang W Li H Liu and L Zhu ldquoInfluence of titania sol

in the electrolyte on characteristics of the microarc oxidationcoating formed on 2A70 aluminum alloyrdquo Surface and CoatingsTechnology vol 205 no 17-18 pp 4135ndash4140 2011

[69] E Matykina R Arrabal P Skeldon and G E ThompsonldquoInvestigation of the growth processes of coatings formed byAC plasma electrolytic oxidation of aluminiumrdquo ElectrochimicaActa vol 54 no 27 pp 6767ndash6778 2009

[70] V Raj and M Mubarak Ali ldquoFormation of ceramic aluminananocomposite coatings on aluminium for enhanced corrosionresistancerdquo Journal of Materials Processing Technology vol 209no 12-13 pp 5341ndash5352 2009

[71] C S Dunleavy J A Curran and TW Clyne ldquoSelf-similar scal-ing of discharge events through PEO coatings on aluminiumrdquoSurface and Coatings Technology vol 206 no 6 pp 1051ndash10612011

[72] M Montazeri C Dehghanian M Shokouhfar and A Barada-ran ldquoInvestigation of the voltage and time effects on the forma-tion of hydroxyapatite-containing titania prepared by plasma


electrolytic oxidation on Ti-6Al-4V alloy and its corrosionbehaviorrdquo Applied Surface Science vol 257 no 16 pp 7268ndash7275 2011

[73] W Xue Q Zhu Q Jin and M Hua ldquoCharacterization ofceramic coatings fabricated on zirconium alloy by plasma elec-trolytic oxidation in silicate electrolyterdquo Materials Chemistryand Physics vol 120 no 2-3 pp 656ndash660 2010

[74] J Li H Cai X Xue and B Jiang ldquoThe outward-inward growthbehavior of microarc oxidation coatings in phosphate andsilicate solutionrdquoMaterials Letters vol 64 no 19 pp 2102ndash21042010

[75] G Sundararajan and L Rama Krishna ldquoMechanisms underly-ing the formation of thick alumina coatings through the MAOcoating technologyrdquo Surface and Coatings Technology vol 167no 2-3 pp 269ndash277 2003

[76] H Habazaki S Tsunekawa E Tsuji and T Nakayama ldquoFor-mation and characterization of wear-resistant PEO coatingsformed on 120573-titanium alloy at different electrolyte tempera-turesrdquo Applied Surface Science vol 259 pp 711ndash718 2012

[77] E V Parfenov R R Nevyantseva and S A Gorbatkov ldquoProcesscontrol for plasma electrolytic removal of TiN coatings Part 1duration controlrdquo Surface and Coatings Technology vol 199 no2-3 pp 189ndash197 2005

[78] P Huang F Wang K Xu and Y Han ldquoMechanical propertiesof titania prepared by plasma electrolytic oxidation at differentvoltagesrdquo Surface and Coatings Technology vol 201 no 9-11 pp5168ndash5171 2007

[79] D Wei Y Zhou D Jia and Y Wang ldquoEffect of applied voltageon the structure of microarc oxidized TiO

2-based bioceramic

filmsrdquoMaterials Chemistry and Physics vol 104 no 1 pp 177ndash182 2007

[80] H Wu X Lu B Long X Wang J Wang and Z Jin ldquoTheeffects of cathodic and anodic voltages on the characteristics ofporous nanocrystalline titania coatings fabricated by microarcoxidationrdquoMaterials Letters vol 59 no 2-3 pp 370ndash375 2005

[81] C B Wei X B Tian S Q Yang X B Wang R K Y Fu and PK Chu ldquoAnode current effects in plasma electrolytic oxidationrdquoSurface and Coatings Technology vol 201 no 9-11 pp 5021ndash5024 2007

[82] X-M Zhang X-B Tian C-Z Gong and S-Q Yang ldquoEffectsof current density on coating kinetic and micro-structure ofmicroarc oxidation coatings fabricated on pure aluminumrdquoin Proceedings of the 3rd IEEE International NanoelectronicsConference (INEC rsquo10) pp 1482ndash1483 January 2010

[83] X Sun Z Jiang Z Yao andX Zhang ldquoThe effects of anodic andcathodic processes on the characteristics of ceramic coatingsformed on titanium alloy through the MAO coating technol-ogyrdquo Applied Surface Science vol 252 no 2 pp 441ndash447 2005

[84] P Bala Srinivasan J Liang R G Balajeee C Blawert MStormer and W Dietzel ldquoEffect of pulse frequency on themicrostructure phase composition and corrosion performanceof a phosphate-based plasma electrolytic oxidation coatedAM50 magnesium alloyrdquo Applied Surface Science vol 256 no12 pp 3928ndash3935 2010

[85] Z Yao Y Liu Y Xu Z Jiang and F Wang ldquoEffects of cathodepulse at high frequency on structure and composition ofAl2TiO5ceramic coatings on Ti alloy by plasma electrolytic

oxidationrdquoMaterials Chemistry and Physics vol 126 no 1-2 pp227ndash231 2011

[86] P Gupta G Tenhundfeld E O Daigle and D Ryabkov ldquoElec-trolytic plasma technology science and engineeringmdashan over-viewrdquo Surface and Coatings Technology vol 201 no 21 pp8746ndash8760 2007

[87] Y MWang H Tian X E Shen et al ldquoAn elevated temperatureinfrared emissivity ceramic coating formed on 2024 aluminiumalloy bymicroarc oxidationrdquoCeramics International vol 39 pp2869ndash2875 2013

[88] ZWWang YMWang Y Liu et al ldquoMicrostructure and infra-red emissivity property of coating containing TiO

2formed on

titanium alloy by microarc oxidationrdquo Current Applied Physicsvol 11 no 6 pp 1405ndash1409 2011

[89] P M de Woolf and J W Visser ldquoAbsolute Intensitiesmdashoutlineof a recommended practicerdquo Powder Diffraction vol 3 pp 202ndash204 1988

[90] E P G T van deVen andHKoelmans ldquoThe cathodic corrosionof Aluminumrdquo Journal of The Electrochemical Society vol 123pp 143ndash144 1976

[91] E V Koroleva G E Thompson G Hollrigl and M BloeckldquoSurfacemorphological changes of aluminium alloys in alkalinesolution effect of second phasematerialrdquoCorrosion Science vol41 no 8 pp 1475ndash1495 1999

[92] C Zhu P Lu Z Zheng and J Ganor ldquoCoupled alkali feldspardissolution and secondary mineral precipitation in batch sys-tems 4 Numerical modeling of kinetic reaction pathsrdquo Geo-chimica et Cosmochimica Acta vol 74 no 14 pp 3963ndash39832010

[93] Y K Pan C Z Chen D G Wang X Yu and Z Q Lin ldquoInflu-ence of additives on microstructure and property of microarcoxidizedMg-Si-O coatingsrdquo Ceramics International vol 38 pp5527ndash5533 2012

[94] R McPherson ldquoFormation of metastable phases in flame- andplasma-prepared aluminardquo Journal of Materials Science vol 8no 6 pp 851ndash858 1973

[95] P S Santos H S Santos and S P Toledo ldquoStandard transitionaluminas Electronmicroscopy studiesrdquoMaterials Research vol3 pp 104ndash114 2000

[96] R K Iler Chemistry of SilicamdashSolubility Polymerization Col-loid and Surface Properties and Biochemistry chapter 1 JohnWiley amp Sons 1979

[97] L Rama Krishna K R C Somaraju and G SundararajanldquoThe tribological performance of ultra-hard ceramic compositecoatings obtained through microarc oxidationrdquo Surface andCoatings Technology vol 163-164 pp 484ndash490 2003

[98] F-Y Jin KWang M Zhu et al ldquoInfrared reflection by aluminafilms produced on aluminum alloy by plasma electrolyticoxidationrdquo Materials Chemistry and Physics vol 114 no 1 pp398ndash401 2009

[99] K Wang B-H Koo C-G Lee Y-J Kim S-H Lee and EByon ldquoEffects of electrolytes variation on formation of oxidelayers of 6061 Al alloys by plasma electrolytic oxidationrdquoTransactions of Nonferrous Metals Society of China vol 19 no4 pp 866ndash870 2009

[100] G EWalrafen and E Pugh ldquoRaman combinations and stretch-ing overtones from water heavy water and NaCl in water atshifts to ca 7000 cm-1rdquo Journal of Solution Chemistry vol 33no 1 pp 81ndash97 2004

[101] S P Langley ldquoXXII The selective absorption of solar energyrdquoPhilosophicalMagazine Series 5 vol 15 no 93 pp 153ndash183 1883

[102] RD Aines andG R Rossman ldquoThehigh temperature behaviorof water and carbon dioxide in cordierite and berylrdquo AmericanMineralogist vol 69 no 3-4 pp 319ndash327 1984


[103] H Rubens and E Aschkinass ldquoObservations on the absorptionand emission of aqueous vapor and carbon dioxide in the infra-red spectrumrdquoThe Astrophysical Journal vol 8 p 176 1898

[104] J Ryczkowski ldquoIR spectroscopy in catalysisrdquo Catalysis Todayvol 68 no 4 pp 263ndash381 2001

[105] K M Lee B U Lee S I Yoon E S Lee B Yoo and D H ShinldquoEvaluation of plasma temperature during plasma oxidationprocessing of AZ91 Mg alloy through analysis of the meltingbehavior of incorporated particlesrdquo Electrochimica Acta vol 67pp 6ndash11 2012

[106] R O Hussein X Nie D O Northwood A Yerokhin andA Matthews ldquoSpectroscopic study of electrolytic plasma anddischarging behaviour during the plasma electrolytic oxidation(PEO) processrdquo Journal of Physics D vol 43 no 10 Article ID105203 2010

[107] Y Wang Z Jiang X Liu and Z Yao ldquoInfluence of treating fre-quency on microstructure and properties of Al

2O3coating on

304 stainless steel by cathodic plasma electrolytic depositionrdquoApplied Surface Science vol 255 no 21 pp 8836ndash8840 2009

[108] O Rozenbaum D De Sousa Meneses and P Echegut ldquoTextureand porosity effects on the thermal radiative behavior ofalumina ceramicsrdquo International Journal of Thermophysics vol30 no 2 pp 580ndash590 2009

[109] A Boumaza L Favaro J Ledion et al ldquoTransition aluminaphases induced by heat treatment of boehmite an X-ray dif-fraction and infrared spectroscopy studyrdquo Journal of Solid StateChemistry vol 182 no 5 pp 1171ndash1176 2009

[110] TMorioka S KimuraN Tsuda C Kaito Y Saito andCKoikeldquoStudy of the structure of silica film by infrared spectroscopyand electron diffraction analysesrdquoMonthly Notices of the RoyalAstronomical Society vol 299 no 1 pp 78ndash82 1998

[111] C H Ruscher ldquoThermic transformation of sillimanite singlecrystals to 32 mullite plus melt Investigations by polarized IR-reflectionmicro spectroscopyrdquo Journal of the European CeramicSociety vol 21 no 14 pp 2463ndash2469 2001

[112] K Nouneh I V Kityk R Viennois et al ldquoInfluence of anelectron-phonon subsystem on specific heat and two-photonabsorption of the semimagnetic semiconductors Pb

1minus119909Yb119909X

(X=S SeTe) near the semiconductor-isolator phase transfor-mationrdquo Physical Review B vol 73 no 3 Article ID 0353292006

Submit your manuscripts athttpwwwhindawicom

ScientificaHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

CorrosionInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Polymer ScienceInternational Journal of



CeramicsJournal of


CompositesJournal of

NanoparticlesJournal of



International Journal of

Biomaterials


NanoscienceJournal of

TextilesHindawi Publishing Corporation httpwwwhindawicom Volume 2014

Journal of

NanotechnologyHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Journal of

CrystallographyJournal of


The Scientific World JournalHindawi Publishing Corporation httpwwwhindawicom Volume 2014


CoatingsJournal of

Advances in

Materials Science and EngineeringHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Smart Materials Research



MetallurgyJournal of


BioMed Research International

MaterialsJournal of


Nano

materials


Journal ofNanomaterials


enhanced the emissivity of the ceramic surface at 700∘C andat wavelengths 3ndash20 120583m A relatively high emissivity wasfound by Wang et al [88] when they studied the emissivity(8ndash14 120583m 700∘C) of the surface of ceramic coating onTi6Al2Zr1Mo1V alloy and they pointed out that the TiO

2

phases were contributed to enhance the emissivityThe geometry of the MAO-treated samples plays a main

role in the industrial applications as a finishing process Thefirst effect comes to mind (by keeping the current outputof main power supply constant and changing the sampledimensions) is the variation of current density Previousworks kept the sample dimensions constant and changed theinput current density Khan et al [6] fabricatedMAOaluminaceramic coatings on Al 6082 alloy using a DC current modeof densities ranged from 5Adm2 to 20Adm2 in variousconcentrations of KOH electrolytes at temperatures rangedbetween 20∘C and 25∘C for 30 minutes They reported thatthe denser current formed thicker coatings with minimalstress level dense morphology and a relatively high contentof 120572-Al

2O3phase Raj and Mubarak Ali [70] used different

direct current densities (5ndash20Adm2) for MAO treating ofaluminium in the alkaline silicate electrolyte at 10∘C for 45minutes and obtained thicker coatings higher growth rateand coating ratio at 15 Adm2 of current density but the20Adm2 of current density decreased these properties dueto the dominant of electrolyte dissolution over the coatingbuilding The effects of bipolar current density on MAOceramic coating formed on titanium alloy were studied bySun et al [83] in an electrolyte of sodium aluminate andhypophosphate at 35∘C for 70 minutes The cathodic (119895

119888) and

anodic (119895119886) current densities ranged between 6 and 12Adm2

They pointed out that the lowest ratio of 119895119886119895119888formed a denser

and thinner layerwithmore uniformmicrostructures and didnot contain 120572-alumina phase while the highest 119895

119886119895119888ratio

formed a thicker ceramic coating comprised of entirely 120572-alumina phase with poor adhesion to the substrate

Themain aim of the present work is to change the sampledimensions and find out the effect of the anodic current den-sity on the microstructural and compositional properties ofthe MAO ceramic coating and the resultant low-temperatureIR emissivity

2 Experimental

Rectangular pieces (4 times 4 times 02 cm3) of aluminium alloy 6061(Mg 1 Si 065 Fe 07 Cu 03 Cr 02 Mn 015 Ti015 and Al balance) were used as substrates in this studyThe exposed surfacewas ground to a 1200 grit SiC finish usingthe water as a lubricant followed by rinsing in the doublydistilled water and drying in the air while the other side wastotally insulated using a Teflon tape

Four different assemblies were applied by mounting adifferent number of pieces into a 6061-Al alloy clamp to get16 32 48 and 64 cm2 of exposed working area to the elec-trolyte and consequently different applied current densitiesThe preparation of samples was conducted for 10 minutesin a fresh electrolyte which consisted of 0046M sodium

silicate and 0042M sodium hydroxide and the PH was 128in a cooling and stirring bath which kept the electrolytetemperature below 17∘C We used the pulse controller SPIK2000A (Shen Chang Electric Co Ltd Taiwan) to generatean asymmetric bipolar pulsing mode with parameters of 200200 360 and 200120583s for 119905+on 119905

+

off 119905minus

on and 119905minus

off respectively Twoelectrical power supplies (PR Series 650V 77 A Matsusada)were connected to the pulse controller with 100V 35 A forDC1 and 500V 70 A for DC2 as shown in Figure 1 Thesamples were connected to the output E2 while another243 cm2 aluminium 6061 plate was connected to E1 OnlyAl 6061 alloy touched the electrolysis solution to avoidany contamination due to diffusion of wires electrodes orscrews According to Figure 1 both electrodes (E1 and E2)were alternating between the cathodic and anodic biasingaccording to the output bipolar pulse the DC2 supplied thesample in the anodic period and the DC1 supplied it in thecathodic period The resultant peak anodic biasing currentdensities 119869

119886 were 1094 1458 2188 and 4375Adm2

Unlike the sample no microarc oxidation was occurredon the aluminium plate due to the relatively low voltageduring its anodic period To avoid the effect of chemicalreaction with the plate surface we renewed the plate for eachMAO experiment despite being in a good situation Aftercompleting every treatment the samples were immediatelyimmersed and cleanedwith distilledwater and then dried andstored in a sealed container Before any use or test sampleswere cleaned using an ultrasonic bath of doubly distilledwater propanol acetone and again doubly distilled water 10minutes for each followed by air drying in the fume hood

Different 27 randomly selected places were captured foreach sample by the SEM (S4160 Hitachi) We performedthe image analysis using Image Pro Plus 70 software (MediaCybernetics Inc) to estimate the volcano-likemicrostructurearea ratioThe density of volcano-like was estimated by divid-ing its total number over the total area of SEM frames for thesame sample

The elemental composition analysis of ceramic coatinglayers was carried out using Hitachi EDX S4800 Low-angleX-ray diffraction (CuK120572 XRD XrsquoPert PRO MPD PANalyti-cal The Netherlands) was used to obtain the XRD patternsof as-deposited ceramic coatings We performed the semi-quantitative analysis of the XRD spectra using the so-calledreference intensity ratio method (RiR method de Woolf andVisser [89]) by MATCH software (V111f Crystal ImpactGbR) and selected the best fit phases and compositions inaddition to estimating their weight percentage

For each sample at least 16 different locations were stud-ied to determine the average of surface roughness using asurface roughness tester (Mitutoyo SJ310) and layer thick-ness using an eddy-current coating-thickness tester (ExtechCG204)

We used a modified Fourier transform infrared spec-troscopy (FTLA2000 Series Spectrometer ABB) to analyzethe IR emissivity of the samples at 70∘C by comparing witha reference blackbody radiation in the wavelength rangingbetween 4120583m and 16 120583m


100V 35A

+ minus

+ minus

DC1

DC1

DC2

500V 70A

E1 Al plate

E2 the sample

Alternatingelectric

field

Vout

100

360 200 200 200

V

500V

DC2DC2

tonminus ton

+ toff+toff

minus

(120583s)

+

++

minus

minus

minus


SPIK 2000A





2

minus and Al(OH)4



2

minus(aq) + 3H

2(1)


minus(gel) (2)




4

minus(gel)


(3)


reaction [92]

Al(OH)4


2H darr +2H

2O +OHminus (4)



4

minus (5)


2Al + 3H2O = Al

2O3+ 3H2uarr (6)









2uarr (9)







(11)


(a) (b)





2minus997888rarr Al

2(SiO3)3

(13)


Al2O3(molten) + SiO

2

Δ

997888rarr Al2O5Si (14)


Al2O3


2O3

(15)


Al2O3


2O3

(16)


Al(OH)3

450ndash750∘C997888997888997888997888997888997888997888rarr 120574-Al

2O3

(17)

Al(OH)3

gt1100∘C

997888997888997888997888997888997888rarr 120572-Al2O3

(18)

AlO2H 450ndash750

∘C997888997888997888997888997888997888997888rarr 120574-Al

2O3

(19)

AlO2H gt1100

∘C997888997888997888997888997888997888rarr 120572-Al

2O3

(20)



minus(gel) (21)




SiO3


2+H2O (24)

2H2O 997888rarr O

2+ 4H+ + 4eminus (25)



4 Results


2phase) and other



119886le



20 40 60 80

Inte

nsity

(au

)In

tens

ity (a

u)

2120579

(a)

(b)





119886(1094Adm2) while





119886from





2SiO5


119886ge








10 20 30 40 50

10

12

14

16

18

20


Cer

amic

laye

r thi

ckne

ss (120583

m)

(a)

07

08

09

1

11

12

13


Ra

(120583m

)

(b)


201816141210

08

12

14

1Ra

(120583m

)



5 Discussions


b

d

c

a

30120583m




(a) (b)

(c)

30120583m

(d)


055

056

057

058

059

06


Volc

ano-

like a

rea r

atio



1200

1600

2000

2400

2800


Volc

ano-

like d

ensit

y (m

mminus2)






a 523 477 a 594 406b 459 488 53 b 523 418 59c 162 550 288 c 493 461 46d 272 540 188 d 485 446 69e 392 476 132 e 268 503 229

f 99 490 411g 196 429 375



a 549 361 90 a 564 436b 542 352 106 b 620 343 37c 481 458 61 c 569 396 35d 137 489 374 d 623 272 105e 292 302 406 e 92 437 471f 230 420 350 f 260 452 288g 413 462 125 g 182 521 278 19





a

cd

b

(a) (b)

(c) (d)

e

acef g

bd

ba

cd

e

fg

abc

d

e

f

g

10120583m 20120583m

20120583m20120583m


1094Adm2

1458Adm2

2188Adm2

4375Adm2

20 40 60 80

2120579

Inte

nsity

(au

)

Al

120572-Al2O3

120574


-Al2O3







10 20 30 40 50

0

20

40

60

80


(wt

)

120574-Al2O3

120572-Al2O3


(a)

10 20 30 40 50

0

20

40

60

80


(wt

)Sillimanite

Cristobalite


(b)


84 12 160

20

40

60

80

100

Emiss

ivity

()

4375Adm2

2188Adm2

1458Adm2

1094Adm2


CO2

CO2

H2O











6 Conclusions



119886ge




Acknowledgments



References






































119909N1minus119909












3COO)

























































2-based bioceramic












2formed on






















2O3coating on







1minus119909Yb119909X









CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of


Nano

materials




100V 35A

+ minus

+ minus

DC1

DC1

DC2

500V 70A

E1 Al plate

E2 the sample

Alternatingelectric

field

Vout

100

360 200 200 200

V

500V

DC2DC2

tonminus ton

+ toff+toff

minus

(120583s)

+

++

minus

minus

minus


SPIK 2000A





2

minus and Al(OH)4



2

minus(aq) + 3H

2(1)


minus(gel) (2)




4

minus(gel)


(3)


reaction [92]

Al(OH)4


2H darr +2H

2O +OHminus (4)



4

minus (5)


2Al + 3H2O = Al

2O3+ 3H2uarr (6)









2uarr (9)







(11)


(a) (b)





2minus997888rarr Al

2(SiO3)3

(13)


Al2O3(molten) + SiO

2

Δ

997888rarr Al2O5Si (14)


Al2O3


2O3

(15)


Al2O3


2O3

(16)


Al(OH)3

450ndash750∘C997888997888997888997888997888997888997888rarr 120574-Al

2O3

(17)

Al(OH)3

gt1100∘C

997888997888997888997888997888997888rarr 120572-Al2O3

(18)

AlO2H 450ndash750

∘C997888997888997888997888997888997888997888rarr 120574-Al

2O3

(19)

AlO2H gt1100

∘C997888997888997888997888997888997888rarr 120572-Al

2O3

(20)



minus(gel) (21)




SiO3


2+H2O (24)

2H2O 997888rarr O

2+ 4H+ + 4eminus (25)



4 Results


2phase) and other



119886le



20 40 60 80

Inte

nsity

(au

)In

tens

ity (a

u)

2120579

(a)

(b)





119886(1094Adm2) while





119886from





2SiO5


119886ge








10 20 30 40 50

10

12

14

16

18

20


Cer

amic

laye

r thi

ckne

ss (120583

m)

(a)

07

08

09

1

11

12

13


Ra

(120583m

)

(b)


201816141210

08

12

14

1Ra

(120583m

)



5 Discussions


b

d

c

a

30120583m




(a) (b)

(c)

30120583m

(d)


055

056

057

058

059

06


Volc

ano-

like a

rea r

atio



1200

1600

2000

2400

2800


Volc

ano-

like d

ensit

y (m

mminus2)






a 523 477 a 594 406b 459 488 53 b 523 418 59c 162 550 288 c 493 461 46d 272 540 188 d 485 446 69e 392 476 132 e 268 503 229

f 99 490 411g 196 429 375



a 549 361 90 a 564 436b 542 352 106 b 620 343 37c 481 458 61 c 569 396 35d 137 489 374 d 623 272 105e 292 302 406 e 92 437 471f 230 420 350 f 260 452 288g 413 462 125 g 182 521 278 19





a

cd

b

(a) (b)

(c) (d)

e

acef g

bd

ba

cd

e

fg

abc

d

e

f

g

10120583m 20120583m

20120583m20120583m


1094Adm2

1458Adm2

2188Adm2

4375Adm2

20 40 60 80

2120579

Inte

nsity

(au

)

Al

120572-Al2O3

120574


-Al2O3







10 20 30 40 50

0

20

40

60

80


(wt

)

120574-Al2O3

120572-Al2O3


(a)

10 20 30 40 50

0

20

40

60

80


(wt

)Sillimanite

Cristobalite


(b)


84 12 160

20

40

60

80

100

Emiss

ivity

()

4375Adm2

2188Adm2

1458Adm2

1094Adm2


CO2

CO2

H2O











6 Conclusions



119886ge




Acknowledgments



References






































119909N1minus119909












3COO)

























































2-based bioceramic












2formed on






















2O3coating on







1minus119909Yb119909X









CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of


Nano

materials




(a) (b)





2minus997888rarr Al

2(SiO3)3

(13)


Al2O3(molten) + SiO

2

Δ

997888rarr Al2O5Si (14)


Al2O3


2O3

(15)


Al2O3


2O3

(16)


Al(OH)3

450ndash750∘C997888997888997888997888997888997888997888rarr 120574-Al

2O3

(17)

Al(OH)3

gt1100∘C

997888997888997888997888997888997888rarr 120572-Al2O3

(18)

AlO2H 450ndash750

∘C997888997888997888997888997888997888997888rarr 120574-Al

2O3

(19)

AlO2H gt1100

∘C997888997888997888997888997888997888rarr 120572-Al

2O3

(20)



minus(gel) (21)




SiO3


2+H2O (24)

2H2O 997888rarr O

2+ 4H+ + 4eminus (25)



4 Results


2phase) and other



119886le



20 40 60 80

Inte

nsity

(au

)In

tens

ity (a

u)

2120579

(a)

(b)





119886(1094Adm2) while





119886from





2SiO5


119886ge








10 20 30 40 50

10

12

14

16

18

20


Cer

amic

laye

r thi

ckne

ss (120583

m)

(a)

07

08

09

1

11

12

13


Ra

(120583m

)

(b)


201816141210

08

12

14

1Ra

(120583m

)



5 Discussions


b

d

c

a

30120583m




(a) (b)

(c)

30120583m

(d)


055

056

057

058

059

06


Volc

ano-

like a

rea r

atio



1200

1600

2000

2400

2800


Volc

ano-

like d

ensit

y (m

mminus2)






a 523 477 a 594 406b 459 488 53 b 523 418 59c 162 550 288 c 493 461 46d 272 540 188 d 485 446 69e 392 476 132 e 268 503 229

f 99 490 411g 196 429 375



a 549 361 90 a 564 436b 542 352 106 b 620 343 37c 481 458 61 c 569 396 35d 137 489 374 d 623 272 105e 292 302 406 e 92 437 471f 230 420 350 f 260 452 288g 413 462 125 g 182 521 278 19





a

cd

b

(a) (b)

(c) (d)

e

acef g

bd

ba

cd

e

fg

abc

d

e

f

g

10120583m 20120583m

20120583m20120583m


1094Adm2

1458Adm2

2188Adm2

4375Adm2

20 40 60 80

2120579

Inte

nsity

(au

)

Al

120572-Al2O3

120574


-Al2O3







10 20 30 40 50

0

20

40

60

80


(wt

)

120574-Al2O3

120572-Al2O3


(a)

10 20 30 40 50

0

20

40

60

80


(wt

)Sillimanite

Cristobalite


(b)


84 12 160

20

40

60

80

100

Emiss

ivity

()

4375Adm2

2188Adm2

1458Adm2

1094Adm2


CO2

CO2

H2O











6 Conclusions



119886ge




Acknowledgments



References






































119909N1minus119909












3COO)

























































2-based bioceramic












2formed on






















2O3coating on







1minus119909Yb119909X









CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of


Nano

materials




20 40 60 80

Inte

nsity

(au

)In

tens

ity (a

u)

2120579

(a)

(b)





119886(1094Adm2) while





119886from





2SiO5


119886ge








10 20 30 40 50

10

12

14

16

18

20


Cer

amic

laye

r thi

ckne

ss (120583

m)

(a)

07

08

09

1

11

12

13


Ra

(120583m

)

(b)


201816141210

08

12

14

1Ra

(120583m

)



5 Discussions


b

d

c

a

30120583m




(a) (b)

(c)

30120583m

(d)


055

056

057

058

059

06


Volc

ano-

like a

rea r

atio



1200

1600

2000

2400

2800


Volc

ano-

like d

ensit

y (m

mminus2)






a 523 477 a 594 406b 459 488 53 b 523 418 59c 162 550 288 c 493 461 46d 272 540 188 d 485 446 69e 392 476 132 e 268 503 229

f 99 490 411g 196 429 375



a 549 361 90 a 564 436b 542 352 106 b 620 343 37c 481 458 61 c 569 396 35d 137 489 374 d 623 272 105e 292 302 406 e 92 437 471f 230 420 350 f 260 452 288g 413 462 125 g 182 521 278 19





a

cd

b

(a) (b)

(c) (d)

e

acef g

bd

ba

cd

e

fg

abc

d

e

f

g

10120583m 20120583m

20120583m20120583m


1094Adm2

1458Adm2

2188Adm2

4375Adm2

20 40 60 80

2120579

Inte

nsity

(au

)

Al

120572-Al2O3

120574


-Al2O3







10 20 30 40 50

0

20

40

60

80


(wt

)

120574-Al2O3

120572-Al2O3


(a)

10 20 30 40 50

0

20

40

60

80


(wt

)Sillimanite

Cristobalite


(b)


84 12 160

20

40

60

80

100

Emiss

ivity

()

4375Adm2

2188Adm2

1458Adm2

1094Adm2


CO2

CO2

H2O











6 Conclusions



119886ge




Acknowledgments



References






































119909N1minus119909












3COO)

























































2-based bioceramic












2formed on






















2O3coating on







1minus119909Yb119909X









CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of


Nano

materials




10 20 30 40 50

10

12

14

16

18

20


Cer

amic

laye

r thi

ckne

ss (120583

m)

(a)

07

08

09

1

11

12

13


Ra

(120583m

)

(b)


201816141210

08

12

14

1Ra

(120583m

)



5 Discussions


b

d

c

a

30120583m




(a) (b)

(c)

30120583m

(d)


055

056

057

058

059

06


Volc

ano-

like a

rea r

atio



1200

1600

2000

2400

2800


Volc

ano-

like d

ensit

y (m

mminus2)






a 523 477 a 594 406b 459 488 53 b 523 418 59c 162 550 288 c 493 461 46d 272 540 188 d 485 446 69e 392 476 132 e 268 503 229

f 99 490 411g 196 429 375



a 549 361 90 a 564 436b 542 352 106 b 620 343 37c 481 458 61 c 569 396 35d 137 489 374 d 623 272 105e 292 302 406 e 92 437 471f 230 420 350 f 260 452 288g 413 462 125 g 182 521 278 19





a

cd

b

(a) (b)

(c) (d)

e

acef g

bd

ba

cd

e

fg

abc

d

e

f

g

10120583m 20120583m

20120583m20120583m


1094Adm2

1458Adm2

2188Adm2

4375Adm2

20 40 60 80

2120579

Inte

nsity

(au

)

Al

120572-Al2O3

120574


-Al2O3







10 20 30 40 50

0

20

40

60

80


(wt

)

120574-Al2O3

120572-Al2O3


(a)

10 20 30 40 50

0

20

40

60

80


(wt

)Sillimanite

Cristobalite


(b)


84 12 160

20

40

60

80

100

Emiss

ivity

()

4375Adm2

2188Adm2

1458Adm2

1094Adm2


CO2

CO2

H2O











6 Conclusions



119886ge




Acknowledgments



References






































119909N1minus119909












3COO)

























































2-based bioceramic












2formed on






















2O3coating on







1minus119909Yb119909X









CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of


Nano

materials




(a) (b)

(c)

30120583m

(d)


055

056

057

058

059

06


Volc

ano-

like a

rea r

atio



1200

1600

2000

2400

2800


Volc

ano-

like d

ensit

y (m

mminus2)






a 523 477 a 594 406b 459 488 53 b 523 418 59c 162 550 288 c 493 461 46d 272 540 188 d 485 446 69e 392 476 132 e 268 503 229

f 99 490 411g 196 429 375



a 549 361 90 a 564 436b 542 352 106 b 620 343 37c 481 458 61 c 569 396 35d 137 489 374 d 623 272 105e 292 302 406 e 92 437 471f 230 420 350 f 260 452 288g 413 462 125 g 182 521 278 19





a

cd

b

(a) (b)

(c) (d)

e

acef g

bd

ba

cd

e

fg

abc

d

e

f

g

10120583m 20120583m

20120583m20120583m


1094Adm2

1458Adm2

2188Adm2

4375Adm2

20 40 60 80

2120579

Inte

nsity

(au

)

Al

120572-Al2O3

120574


-Al2O3







10 20 30 40 50

0

20

40

60

80


(wt

)

120574-Al2O3

120572-Al2O3


(a)

10 20 30 40 50

0

20

40

60

80


(wt

)Sillimanite

Cristobalite


(b)


84 12 160

20

40

60

80

100

Emiss

ivity

()

4375Adm2

2188Adm2

1458Adm2

1094Adm2


CO2

CO2

H2O











6 Conclusions



119886ge




Acknowledgments



References






































119909N1minus119909












3COO)

























































2-based bioceramic












2formed on






















2O3coating on







1minus119909Yb119909X









CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of


Nano

materials






a 523 477 a 594 406b 459 488 53 b 523 418 59c 162 550 288 c 493 461 46d 272 540 188 d 485 446 69e 392 476 132 e 268 503 229

f 99 490 411g 196 429 375



a 549 361 90 a 564 436b 542 352 106 b 620 343 37c 481 458 61 c 569 396 35d 137 489 374 d 623 272 105e 292 302 406 e 92 437 471f 230 420 350 f 260 452 288g 413 462 125 g 182 521 278 19





a

cd

b

(a) (b)

(c) (d)

e

acef g

bd

ba

cd

e

fg

abc

d

e

f

g

10120583m 20120583m

20120583m20120583m


1094Adm2

1458Adm2

2188Adm2

4375Adm2

20 40 60 80

2120579

Inte

nsity

(au

)

Al

120572-Al2O3

120574


-Al2O3







10 20 30 40 50

0

20

40

60

80


(wt

)

120574-Al2O3

120572-Al2O3


(a)

10 20 30 40 50

0

20

40

60

80


(wt

)Sillimanite

Cristobalite


(b)


84 12 160

20

40

60

80

100

Emiss

ivity

()

4375Adm2

2188Adm2

1458Adm2

1094Adm2


CO2

CO2

H2O











6 Conclusions



119886ge




Acknowledgments



References






































119909N1minus119909












3COO)

























































2-based bioceramic












2formed on






















2O3coating on







1minus119909Yb119909X









CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of


Nano

materials




10 20 30 40 50

0

20

40

60

80


(wt

)

120574-Al2O3

120572-Al2O3


(a)

10 20 30 40 50

0

20

40

60

80


(wt

)Sillimanite

Cristobalite


(b)


84 12 160

20

40

60

80

100

Emiss

ivity

()

4375Adm2

2188Adm2

1458Adm2

1094Adm2


CO2

CO2

H2O











6 Conclusions



119886ge




Acknowledgments



References






































119909N1minus119909












3COO)

























































2-based bioceramic












2formed on






















2O3coating on







1minus119909Yb119909X









CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of


Nano

materials





6 Conclusions



119886ge




Acknowledgments



References






































119909N1minus119909












3COO)

























































2-based bioceramic












2formed on






















2O3coating on







1minus119909Yb119909X









CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of


Nano

materials

























119909N1minus119909












3COO)

























































2-based bioceramic












2formed on






















2O3coating on







1minus119909Yb119909X









CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of


Nano

materials



















































2-based bioceramic












2formed on






















2O3coating on







1minus119909Yb119909X









CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of


Nano

materials









2O3coating on







1minus119909Yb119909X









CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of


Nano

materials










CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of


Nano

materials



Research Article Effect of Anodic Current Density...

Documents

Transcript of Research Article Effect of Anodic Current Density...