Poly(maleic acid) – A novel dispersant for aqueous alumina slurry

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ARTICLE IN PRESSG ModelASCER 27 1–7

Journal of Asian Ceramic Societies xxx (2013) xxx–xxx

Journal of Asian Ceramic Societies

Journal of Asian Ceramic Societies

jo ur nal ho me page: www.elsev ier .com/ locate / jascer

oly(maleic acid) – A novel dispersant for aqueous alumina slurry

aralasrita Mohanty, Bodhisatwa Das, Santanu Dhara ∗

iomaterials and Tissue Engineering Laboratory, School of Medical Science and Technology, Indian Institute of Technology Kharagpur, Kharagpur 721302, India

r t i c l e i n f o

rticle history:eceived 13 April 2013eceived in revised form 13 May 2013ccepted 16 May 2013vailable online xxx

eywords:luminaispersant

a b s t r a c t

Poly(maleic acid) (PMA) was investigated as an anionic long chain dispersant for the preparation of highlyloaded aqueous alumina slurry. Suspensions with 1 wt% alumina powder were prepared through varia-tion of PMA concentrations at pH 9 to assess its dispersion efficacy in aqueous medium. Addition of PMAincreased the stability of 1 wt% alumina suspensions as evidenced by higher zeta potential and RSH (rel-ative suspension height). 55 vol% alumina slurries were prepared with different PMA concentrations atpH 9. Based on the rheological studies, 3.8 mg of PMA per gram of alumina was obtained as the optimizeddispersant amount at pH 9. All the slurries had shear thinning behavior and the slurry with optimumdispersant amount had insignificant thixotropy. Further, adsorption of dispersant was evident by Fourier

eta-potentialhixotropyiscosityicrostructure

transform infrared spectroscopy (FTIR) analysis Q3and thermogravimetric analysis (TGA). The slurry at pH9 with optimum dispersant amount had lowest viscosity and easy flowability. Microstructure of bisquefired and sintered body by SEM microscopy revealed homogeneous particle distribution and uniformgrain growth with sintered density of 3.94 g/cm3. The mechanical property evaluation revealed that thesamples prepared with optimum dispersant amount had the flexural strength of 483 ± 22 MPa.

© 2013 The Ceramic Society of Japan and the Korean Ceramic Society. Production and hosting by

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. Introduction

Colloidal processing techniques have been widely used in nearet shape forming of ceramics for diverse applications due to dif-culty in controlling the microstructure by melt processing [1–3].igh powder loading is important for slurry based colloidal pro-essing to obtain high packing density of the green body facilitatinginimum drying and sintering shrinkage which eventually reduces

he warpage of the final components [4]. However, high powderoading is difficult to achieve for fine powders due to high tendencyf agglomeration. During slurry based colloidal processing, disper-ant has important role in the preparation of ceramic green bodyith uniform green density and homogeneous particle distribution

5–9]. A stable and well-dispersed colloidal suspension facilitatesigh packing density in the green body. Uniform green density

Please cite this article in press as: S. Mohanty, et al., Poly(maleic acid)Soc. (2013), http://dx.doi.org/10.1016/j.jascer.2013.05.005

∗ Corresponding author. Tel.: +91 9434701616.E-mail addresses: [email protected], [email protected]

S. Dhara).eer review under responsibility of The Ceramic Society of Japan and the Koreaneramic Society.

187-0764 © 2013 The Ceramic Society of Japan and the Korean Ceramic Society.roduction and hosting by Elsevier B.V. All rights reserved.ttp://dx.doi.org/10.1016/j.jascer.2013.05.005

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Elsevier B.V. All rights reserved.

acilitates homogeneous microstructure of the ceramic componenturing sintering and thus improves the mechanical properties [10].

In aqueous colloidal processing of ceramics, the nature andmount of dispersant are important in order to obtain stable andniform dispersed system [11–13]. Well dispersed slurry with easyowability is achieved by optimum concentration of the dispersant.ptimum amount of dispersant provides highest surface charge

esulting in a homogeneous and well-stabilized suspension. It waseported that ceramic suspensions containing insufficient or excessmounts of dispersant than those with optimum show a rela-ively higher viscosity [14]. The increase in viscosity with less thanptimum dispersant concentration is due to insufficient surfaceoverage of the particles which facilitates formation of agglom-rates in the suspension through bridging flocculation. While inase of dispersant amount above the optimum concentration, thexcess non-adsorbed dispersant molecules facilitate zeta poten-ial reduction of the suspended particles through compression ofouble layers by excess counter ions present in the solution.

In the context of slurry processing [15], Yasuda et al. [16]eported that the quantity of polymer dispersant has majornfluence on microstructure and mechanical properties of bulkydroxyapatite during colloidal processing. Actually, high viscos-

ty of the slurry will render difficulty in removal of air bubblesntrapped during milling which eventually introduces defects inhe sample [17,18]. Takao et al. [19] studied influence of process-

– A novel dispersant for aqueous alumina slurry, J. Asian Ceram.

ng defects on mechanical properties of slip cast alumina. Thus,ptimization of dispersant amount is important in controlling sta-ility of aqueous alumina slurries with minimum viscosity in ordero achieve defect-free components.

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dx.doi.org/10.1016/j.jascer.2013.05.005


http://www.elsevier.com/locate/jascer

mailto:[email protected]

mailto:[email protected]


ARTICLE IN PRESSG ModelJASCER 27 1–7

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S. Mohanty et al. / Journal of Asia

Among various dispersant types, anionic electrosteric disper-ant such as poly(acrylic acid) [20], poly(methacrylic acid) [21],yrophosphate [22], citric acid [23], etc. are mostly studied forreparation of highly loaded ceramics (alumina, zirconia, silica, sil-

con carbide, etc.) based colloidal suspensions. The performance ofhe polyelectrolyte [24] dispersants is mainly influenced by sev-ral factors including charge density, type of monomers, functionalroups, molecular weight, pKa values, etc. In this context, polyelec-rolytes containing carboxylic group are found to be an effectiveispersant for stabilization of highly loaded aqueous alumina slur-ies. Chain length and number of carboxylic groups per unit lengthf poly anionic dispersant have influence on dispersion efficacyuring slurry preparation. The carboxylic acid groups attached tohe polymer chain are deprotonated at pH above pKa value, result-ng in an increase of surface charge of alumina in the suspensionue to adsorption of the negatively charged dispersant. At optimumispersant concentration, these molecules adsorb on suspendedowder surface forming monolayer and part of the long moietyemains in the solution facilitating eletrosteric stabilization [25].urther, the extended chain in the solution hinders formation ofny powder agglomerates and thereby stabilized the ceramics sus-ension.

It is reported by Hanaor et al. [26] that small quantity of car-oxylic acid reagent imparted high negative zeta potential valuesnd stabilized ZrO2 suspension electrosterically over a wide pHange. Hidber et al. [27] successfully used citric acid as dispersantor the deflocculation of concentrated alumina slurries. The interac-ion of citric acid with alumina powder particles leads to adsorptionf citrate ions on the hydroxylated alumina powder surface result-ng in development of negative charge. The three carboxylic groupsttached to each citrate ion impart sufficient magnitude of negativeharge on the powder surfaces. The adsorbed citrate ions also formteric barrier which offer repulsive force between individual parti-les. Davies and Binner [28] have reported a novel method for thereparation of high solid loading ceramic slurries using ammoniumolyacrylate as electrosteric dispersant at alkaline pH. Cesaranond Aksay [29] described the dispersion of sufficiently highly con-entrated (>50 vol%) �-alumina powder (particle size 0.2–1.0 �m)lurries using sodium poly(methacrylic acid) and poly(acrylic acid)t different pH for the fabrication of dense ceramic components.oly(acrylic acid) is widely used dispersant in ceramic processingue to its eletrosteric stabilization.

In this context, poly(maleic acid) (PMA), being a poly car-oxylic anionic macromolecules, is adsorbed on metallic oxideslike Goethites), carbonates (calcites) and forms a Langmuir mono-ayer as reported by Wang et al. [30] and Euvrard et al. [31]. It haslso been utilized for boiler treatment as it stabilizes gypsum par-icles in aqueous solution and inhibits crystal growth by adheringo the surface [32]. There are few preliminary reports on improve-

ent of rheology and zeta potential in chalcocite slurries even atery high powder loading by addition of PMA [33]. Interestingly,MA has similar structure to poly(acrylic acid) and this polymer hasouble charge density than that of poly(acrylic acid) per unit chain

ength owing to presence of one carboxylic acid group in each car-on atom in the main back bone of the polymer chain. Maleic acidas pKa values within 1.8–6 (pK1 = 1.83; pK2 = 6.07) [34,35] and itsacromolecule (PMA) highly ionizes above pH 7 (pKa between 5

nd 7) in aqueous medium [36]. This polymer has the potential toisperse oxide ceramics for the preparation of colloidal suspension

n aqueous medium [37].In the present study, PMA is explored as an anionic dispersant


or the stabilization of highly loaded alumina slurry. Dispersionbility of the PMA was primarily evaluated by RSH (relative sus-ension height), zeta potential measurement. Optimization ofispersant dose was carried out through rheological studies of

pFas

mic Societies xxx (2013) xxx–xxx

ighly loaded slurries. Fourier transform infrared spectroscopyFTIR) analysis and thermogravimetric analysis (TGA) were per-

ormed to validate adsorption of the PMA on alumina powderurface. Density, microstructure and mechanical properties of theintered alumina prepared using 55 vol% slurry were evaluated forptimized dispersant amount at pH 9.

. Experimental procedures

.1. Materials

Alumina powder (RG 4000, Almatis Alumina Private Limited,alta, India; d50 ∼ 0.7 �m; surface area, 7 m2/g) based aqueous slur-ies were prepared using PMA (PM-200, Aquapharm Chemicalsvt. Ltd., Pune, India) for dispersion and tetramethyl ammoniumydroxide (25% solution, Merck, Mumbai, India) was used for pHdjustment.

.2. Stability of suspension with different concentrations of PMA

Different amount of PMA (average molecular weight 500–1000)as added to distilled water for the preparation of 1 wt% alumina

uspension at pH 9. The suspensions with different dispersant con-entrations (Table 1) were ultrasonicated for 10 min to breakdownhe agglomerates. The suspensions were poured into graduatedylinder and were placed vertically for over a period of one monthollowed by measurement of turbidity and sediment height at dif-erent time intervals. Further, zeta potentials of all the suspensionsith different dispersant amounts were measured by Zetasizer

Malvern instrument, Malvern, UK) at pH 9.

.3. Slurry preparation

For optimization of dispersant amount with highly loaded aque-us alumina slurries, PMA was added initially to a poly(propylene)ottle containing predetermined amount of distilled water and alu-ina powders were added in steps. In the present study, 55 vol%

lumina slurries were prepared by addition of alumina in threeteps in presence of varied amount of PMA and slurries weredjusted at pH 9. The slurries were milled by roll mill with additionf 1:1 ratio of powder to ZrO2 milling media (3 mm diameter) at0 rpm. Finally, the slurries were filtered using sieve to separate theilling media. For deairing of slurries, 100 �l of n-octanol per 100 g

lurry was added followed by rolling at 20 rpm for 30 min using therocedure discussed by Dhara et al. [18]. The deaired slurries wereeady for rheological measurement and casting.

The effect of slurry pH on suspension stability was evaluated for constant dispersant concentration. Based on optimization study,5 vol% alumina slurries with 3.8 mg PMA per gram of aluminaowder were prepared at three different pH levels (viz., 6, 9 and2, respectively). Flow behavior test of these slurries was carried

ut to evaluate influence of slurry pH on viscosity at constant shearate. Further, slurries were diluted to 1 wt% by adding deionizedater and final suspension pH was maintained at their native pHsing TMAH and HCl. The zeta potentials of these suspensions werelso measured to evaluate surface charge of alumina with constantispersant concentration at the above mentioned pH.

.4. Rheological measurement

To measure slurry viscosity, 11.5 mL of alumina slurry was


oured into cylindrical cup of the rotational viscometer (Visco Elite,ungilab, UK) along the wall and a spindle was placed carefully tovoid entrapment of air bubbles. To prevent water loss during mea-urement, 5 drops of n-octanol were added on top the slurries. Prior

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S. Mohanty et al. / Journal of Asian Ceramic Societies xxx (2013) xxx–xxx 3

Table 1Effect of PMA concentrations on RSH, zeta potential and viscosity of alumina powders in aqueous medium at pH 9.

PMA concentrations (mg/g of alumina powder) 1 wt% suspension 55 vol% slurry

RSH (%) after one month Zeta potential (mV) Viscosity (Pa s) at (5.6 s−1)

2.3 29.8 ± 0.5 −28.7 ± 0.5 5.13.0 36.3 ± 0.2 −42.3 ± 1.4 2.2

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3.8 59.0 ± 0.1

4.6 52.6 ± 0.4

5.3 48.2 ± 0.3

o measurement, the slurries were subjected to stirring by rotat-ng the spindle at 100 rpm to maintain similar condition prior to

easurement. Viscosity of the slurries was measured at differenthear rates ranging from 0.14 and 16.8 s−1 at 25 ◦C from upwardo downward sweep cycle. Thixotropic behavior of the slurriesas also measured to examine influence of dispersant amount on

ime dependent aging behavior at corresponding shear rate duringpward and downward sweep viscosity measurement. Thixotropyf alumina slurry was expressed in terms of difference in viscosityῃdw

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ῃuw

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) viscosity against shear rate measurement.

.5. Green body preparation

The deaired slurry with optimized dispersant amount at pH 9as used for the preparation of green body. Prior to the slurry cast-

ng, all the molds were coated with white petroleum jelly. Siliconubber molds were used to prepare rectangular bars for flexuraltrength measurement under 3-point bending mode. The samplesere dried under controlled humidity and vacuum dried samplesere removed from the mold carefully. The polished samples were

eady for sintering. The density of the vacuum dried green andintered samples was measured via Archimedes principle.

.6. FTIR study of alumina powders for adsorption of PMA

FTIR analysis of different samples was carried out usingpectrophotometer (NEXUS-870, Thermo Nicolet Corporation,adison, WI, USA) controlled by Spectrum software. To prepare

amples for FTIR analysis, slurries were diluted with deionizedater to 1 wt% and centrifuged to collect the alumina precipitate.

he vacuum dried precipitates were made into pellets after mixingith KBr (1:10) and used for FTIR analysis. Also, the freeze dried

MA was crushed into powder and made into palate by mixingith KBr (1:10) for analysis. To validate adsorption of PMA on alu-ina powder surface during preparation of aqueous slurries, the

acuum dried as received alumina powder was analyzed by FTIRpectroscopy using KBr palate (1:10) and compared.

.7. Thermogravimetric analysis

TGA was carried out for analyzing quantitative adsorption ofMA on alumina surface by Thermo-gravimetric analyzer (Perkinlmer Pyris Diamond Model, MA) using alumina crucible under airtmosphere in the temperature range of 50–650 ◦C with a heat-ng rate of 10 ◦C/min. Different slurries were diluted to 1 wt% using


eionized water and centrifuged to collect the precipitate. The alu-ina precipitates after centrifugation and the as received alumina

owders were vacuum dried at 40 ◦C for a period of 24 h in a vacuumven. Thermal degradation behavior of all the samples was carried

osoc

−55.1 ± 2.5 1.5−50.8 ± 1.8 1.9−44.0 ± 1.4 2.6

ut and amount of PMA dispersant adsorbed on the surface of alu-ina powder for suspensions with different PMA concentrationsas calculated by the percentage weight loss during decomposition

f organics by heat treatment.

.8. Microstructure analysis

The samples were placed in furnace for bisque firing and sinter-ng. The samples were bisque fired at 1000 ◦C in air by holding for

h in a chamber furnace (N. R. Enterprise, Kolkata, India). Fractureurface of bisque fired samples was gold coated and analyzed viaEM (SEM; EVO ZEISS, Carl Zeiss SMT AG, Germany) at an accelerat-ng voltage of 10–20 kV for particles distribution in the green body.urther, the green samples were also sintered at 1550 ◦C for 2 h inir by a chamber furnace (Bysakh, Kolkata, India) for microstructurend mechanical properties analysis.

.9. Mechanical properties

The flexural strength (3-point bending configuration) of sin-ered rectangular bars, each of dimensions 40 mm × 5 mm × 4 mm,ere measured by UTM (Model HEK25, Hounsfield, UK) with a span

f 25 mm at a cross-head speed of 0.5 mm/min using 5000 N loadell. All the failures occurred on the tensile side of the bar sampleshile performing the bending test. Ten specimens were tested forexural strength measurements of the sintered alumina.

. Results and discussion

The pH of 1 wt% alumina suspensions was adjusted above theKa value of PMA (at pH 9) for high degree of ionization of polymerolecules. Stability of the aqueous alumina suspensions at pH 9as increased significantly with addition of PMA as evidenced bySH measurement. The RSH data in Table 1 clearly depicted thattability of the suspensions increased with increasing PMA con-entrations. Alumina powders in suspension took more than thirtyays to settle down in presence of PMA, whereas the suspensionithout PMA (at pH 9) sedimented within an hour. This suspen-

ion stability is also reflected by the zeta potential values (Table 1).ll the suspensions had zeta potential values higher than that of25 mV at pH 9 with addition of different concentrations of PMA

anging between 2.3 and 5.3 mg/g of alumina powder.Based on the above results, 55 vol% aqueous alumina slurries

ere prepared using different concentrations of PMA at pH 9 andheir flow behavior was studied by viscosity measurement at dif-erent shear rates. The shear rate sweep measurement of all thelurries indicated non-Newtonian flow behavior (shear thinning)wing to their high powder loading (Fig. 1a). It was also found thatiscosities of the slurries were strongly influenced by the amountf PMA. As viscosity is function of shear rate, while viscosity values


f all slurries were plotted against different PMA amounts at con-tant shear rate, all the curves passed through a minima at 3.8 mgf polymer/g of alumina (Fig. 1b). At this PMA concentration, vis-osity of the slurry was 1.6 Pa s at 5.6 s−1 shear rate. Further, above

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Fig. 1. Flow behavior and change in viscosity of 55 vol% alumina slurrie

his dose, viscosity of the slurries increased gradually with increasen polymer concentrations.

The pseudoplastic behavior of highly loaded slurries was due toormation of inter-particle network at relatively lower shear rate.

ith gradual increase in shear rate, this inter-particle network wasransformed into small flowable clusters and resulted in reductionf slurry viscosity. For different PMA concentrations, viscosity of thelurries reduced gradually with increase in polymer concentrationsp to 3.8 mg/g of alumina mainly due to increase in zeta potentialalue associated with higher surface coverage. At lower concen-ration of PMA, there is actually incomplete coverage of polymer

olecules leading to strong network formation via inter-particledsorption of long chain molecules. At 3.8 mg of PMA/g of alu-ina, the suspended powder surface had the highest surface charge

−55 mV) owing to monolayer coverage of polymers. Beyond thismount, the excess un-adsorbed polymer molecules remained inhe aqueous solution and their counter ions minimized the sur-ace charge by compression of the double layers which resultedn reduction of zeta potential value. From this fact, it can be con-luded that 3.8 mg of PMA/g of alumina is the optimum amount ofispersant for preparation of highly loaded slurry. These data are


lso supported by RSH and zeta potential values.Further, 55 vol% slurries with 3.8 mg/g of alumina were also

repared at different pH (6, 9 and 12) to evaluate effect of pHn flowability (Fig. 2b). All the slurries prepared at different pH

ctto

Fig. 2. Influence of pH on (a) zeta potential and (b) viscosity of 55 vol% alumina slur

H 9) (a) at different shear rates; (b) with different PMA concentrations.

howed shear thinning behavior against shear rate sweep mea-urement at room temperature. Viscosities of all the slurries weretrongly influenced by pH with same dispersant concentration.mong all the slurries, minimum viscosity was evident for slurryrepared at pH 9. The slurry with pH 6 showed highest viscos-

ty, whereas moderate viscosity was obtained for slurry with pH2. The viscosity values of the slurries at pH 6, 9, and 12 were.18 Pa s, 1.34 Pa s, and 2.46 Pa s, respectively, at constant shear ratef 5.6 s−1. This result was also supported by lower zeta potentialalue of suspension prepared at pH 9 (Fig. 2a). Thixotropic behaviorf highly loaded alumina slurries (55 vol%) was strongly depen-ent on PMA concentrations (Fig. 3). In this study, three differentMA concentrations, such as 2.3 mg (below optimum), 3.8 mg (opti-um) and 5.3 mg (above optimum) per gram of alumina, were

hosen to investigate their effect on thixotropic behavior. From thelot in Fig. 3, it is evident that the slurry with optimum amount ofispersant showed minimum thixotropy in comparison to belownd above the optimum amount of dispersant. However, the slurryith less than optimum amount of dispersant had pronounced

hixotropy in comparison to more than optimum amount, evenith same magnitude of deviation from the optimum dispersant


oncentration. Actually, tendency of inter-particle network forma-ion is more with less than optimum amount of dispersant owingo their less surface coverage with respect to optimum and aboveptimum dispersant concentrations. However, slurry with more

ries prepared using optimum amount of dispersant (3.8 mg PMA/g alumina).

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S. Mohanty et al. / Journal of Asian Ceramic Societies xxx (2013) xxx–xxx 5

Fig. 3. Thixotropy of 55 vol% alumina slurries expressed as difference in viscosity

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uring downward ( ) and upward ((ῃdw) ) shear rate sweep for slurries withifferent amounts of PMA dispersant.

han optimum amount of dispersant had lowering of zeta potentialhich facilitated relatively higher inter-particle interaction due to

ompression of double layer.FTIR spectra of dried PMA, as received alumina and alumina

ith different PMA concentrations were plotted under transmit-ance mode as shown in Fig. 4. Being a polycarboxylic acid, PMA has

−1


ajor characteristic peak at 1723 cm for C O stretching vibra-ion of free molecules [38]. Additionally for COO− group, peaks at633 cm−1 and 1557 cm−1 were assigned for asymmetric stretch-

ng vibration and peaks at 1487 cm−1 and 1400 cm−1 appeared due

ig. 4. FTIR spectra of (a) freeze dried PMA; (b) vacuum dried alumina powder;acuum dried powder residues from alumina slurries with (c) below optimum, (d)ptimum and (e) above optimum amount of PMA (at pH 9), respectively.

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ersed alumina slurries with different concentrations of PMA, viz. below optimum,ptimum and above optimum.

o symmetric stretching vibration. For alumina powder, the peak at636 cm−1 is mainly associated with physisorbed water on the sur-ace, and the peaks at 1401 cm−1 and 1384 cm−1 are due to surfaceydroxide [39]. For FTIR spectra of alumina with different amountf PMA, the peak at ∼1636 cm−1 and additional peak at ∼1573 cm−1

re associated with asymmetric stretching vibration of carboxylateons [23] of the adsorbed PMA. There were also two more peakst 1401 cm−1 and 1384 cm−1 associated with symmetric stretch-ng vibration of carboxylate ion [23]. However, carbonyl stretchingibration peak at 1723 cm−1 for dried PMA was absent in case oflumina containing adsorbed PMA. It is noteworthy that the peaksssociated to carboxylate symmetric and asymmetric vibrationsere broadened for optimum and above optimum (3.8 mg/g and

bove) dispersant concentrations due to the presence of adsorbednd unadsorbed carboxylate groups of the long chain polymers.

Fig. 5 shows weight loss profile of vacuum dried alumina withifferent PMA concentrations of slurries and as received aluminauring thermogravimetric analysis in air. From the TGA curve of aseceived alumina powder, 0.1% weight loss was evident mainly dueo evaporation of adsorbed water and surface hydroxide. Appear-nce of two endothermic peaks at ∼100 ◦C and ∼400 ◦C was mainlyue to evaporation of adsorbed water and removal of surfaceydroxide, respectively [40]. In case of alumina with different con-entrations of PMA, percent weight loss was relatively higher inomparison to as received alumina due to presence of adsorbedispersant. Specifically, percent weight loss of 0.68, 0.98 and 1.0as evidenced for below optimum, optimum and above optimum

mount of dispersant, respectively. These data clearly evidencedhat there was a significant increase in %weight loss with increasen dispersant amount from below optimum to optimum level,

hereas the increase in %weight loss was insignificant with beyondhe optimum level. Actually, with addition of more than optimummount of dispersant, surface coverage did not increase signifi-antly and unadsorbed PMA remained in the aqueous medium.urther, presence of exothermic peak in DTA curve was also evidentor different dispersant concentrations within 239–400 ◦C mainlyue to thermal decomposition of adsorbed PMA.


The green alumina bodies were prepared through casting oflurry into silicone rubber mold with optimum PMA concentra-ion (3.8 mg/g) at pH 9. The vacuum dried samples were ready forintering and did not have any visual crack on the surface. All the

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Fig. 6. SEM micrographs of fracture surface of (a) green, (b) bisque

amples were polished and sintered at 1550 ◦C for 2 h. The sinteredlumina prepared using optimum slurry did not develop any sig-ificant warpages or cracks during sintering. All the samples had15% linear shrinkage associate with densification during sinter-

ng. The green density of the sample was ∼65% of the theoreticalensity. Sintered density of the sample was ∼99.5% for optimummount of dispersant. The green body microstructure of the frac-ure surface had no significant defects associated to agglomeratesnd entrapped air bubbles (Fig. 6a). The particle distribution ofisque fired samples prepared using optimum dispersant amountas homogeneous as shown in Fig. 6b. The sintered microstruc-

ure of alumina showed homogeneous grain growth with minimumorosity (Fig. 6c). The average grain size of the sintered alumina

s ∼2 �m. Flexural strength of alumina with optimum concentra-ion of dispersant showed 483 ± 22 MPa. Here it is to be noted thatsetsekou et al. [41] carried out optimization study of polyacryliccid dispersant (Duramax D 3005) for alumina (mean particleize 3 �m and specific surface area 4.5 m2/g). They have reportedending strength of ∼330 MPa for alumina with sintered den-ity of 3.7 g/cm3. Similarly, Volceanov et al. [42] reported bendingtrength of 470 MPa for alumina (average particle size 0.8 �m)ith sintered density 3.8 g/cm3 using polyelectrolyte dispersant

Dolapix). Thus, PMA can be used for dispersion of alumina at pH 9or the preparation of highly loaded slurry in aqueous medium.

. Conclusions

PMA was successfully used as an anionic dispersant for thereparation of aqueous alumina slurry. Stability of 1 wt% alu-ina suspensions in presence of different PMA concentrations

2.3–5.3 mg PMA per gram of alumina powder) at pH 9 wasncreased significantly as evident by RSH measurement due toncrease in zeta potential. Highly loaded alumina slurries with5 vol% powder loading were prepared using PMA as dispersant.low behavior of 55 vol% alumina slurries with different concen-rations of PMA showed shear thinning behavior. The slurry with.8 mg PMA/g of alumina had minimum viscosity (1.5 Pa s at 5.6 s−1)nd was the optimum dispersant concentration owing to high zetaotential value (−55 mV), minimum thixotropy and better flowa-ility. Adsorption of PMA on alumina powder surface was evidenty FTIR spectroscopy. Further, differential quantitative adsorptionf PMA on alumina powder surface was evident by thermogravi-etric analysis. SEM microstructure of the fracture surface of

reen body prepared using optimum level of dispersant revealed


omogeneous microstructure with negligible defects. The sinteredamples achieved ∼99.5% of the theoretical density while sinteredt 1550 ◦C for 2 h. The alumina samples with optimum dispersantmount had flexural strength of 483 ± 22 MPa.

[

[[[

nd (c) sintered alumina at pH 9 with optimum dispersant amount.

onflict of interest statement

The authors declare that there are no conflicts of interest.

cknowledgements

Funding of Department of Biotechnology (DBT), Council of Sci-ntific & Industrial Research (CSIR) and Department of Science andechnology (DST) Govt. of India is acknowledged. Financial sup-ort of Indian Institute of Technology Kharagpur is acknowledgedor Mr. Saralasrita Mohanty.

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