Deagglomeration of High Purity Fine Alumina Powder via pH Control

Andanastuti Muchtar; Norazmira Wati; Nor Azri Jaafar

Andanastuti Muchtar Department of Mechanical and Material Engineering, Universiti Kebangsaan Malaysia
Norazmira Wati Department of Mechanical and Material Engineering, Universiti Kebangsaan Malaysia
Nor Azri Jaafar Department of Mechanical and Material Engineering, Universiti Kebangsaan Malaysia

Keywords: colloidal processing, fine alumina powders, pH control, rheology, sintering characteristics, microstructure

Abstract

This paper presents results from a study on the effect of the pH of suspensions on the deagglomeration of a high-purity (99.99%), fine-grained alumina powder. The pH of the suspension was varied between pH 2 and 3. It is the aim of the study to determine the best pH for a successful dispersion of the alumina powders in the suspension. A series of rheological studies and analytical work under Scanning Electron Microscopy were conducted. It was found that the best pH was pH 2. Data obtained from rheological studies using a viscometer showed that the alumina suspension prepared at pH 2 was least viscous, which may be taken as a negative indicator of the presence of agglomerates. This hypothesis is validated by visual inspection using SEM. For the pH 2 samples, a successful removal of the agglomerates in the green compact has encouraged the sinterability of the samples and thus, resulted in an earlier sintering process at a low-firing temperature. In addition, the sintering characteristics and microstructures of the samples prepared with a pH 2 suspension are also presented.

References

Inada, S., T. Kimura and T. Yamaguchi, 1990, "EffectofGreen Compact Structure on the Sintering of Alumina", Ceramics International, 16, pp. 369 - 373.
Lange, F.F.,1989, "Powder Processing Science and TechnologyforIncreased Reliability", J. Am. Ceram. Soc., 72, [1], pp. 3 - 15.
Lim,L.C., P.M.Wongand J. Ma, 1997, "Colloidal Processing of Sub-Micron Alumina Powder Compacts", J. Materials ProcessingTechnology,67, pp. 137 -142.
Misirli,Z., A. Uguz and T. Baykara, 1994, "Effect of Additives on the Microstructure and Mechanical Properties of Commercial Alumina Ceramics", Materials Characterization,33, pp. 329 - 341.
Miyahara,N., Y Mutoh, K.Yamaishi,K. Uematsu and M.Inoue, 1992, "The Effectsof Grain Size on Strength, FractureToughness,and Static FatigueCrack Growth in Alumina", In JFCC Workshop series: Materials Processing and Design: Grain Boundary ControlledPropertiesof Fine Ceramics,K. Ishizaki,K. Niihara, M. Isotani and R.G. Ford (eels),ElsevierScience Publishers.
Muchtar,A., 1999, "SinteringCharacteristicsand Microstructures of Colloidally Processed Alumina" , Jumal Kejuruteraan, 11, [2], pp. 3-12.
Muchtar,A. and L.C. Lim, 1998, "Indentation Fracture Toughness of High Purity SubmicronAlumina",ActaMaterialia,46, [5], pp. 1683- 1690.
Nunes,F.,A.G. Lamas, M. Almeida and H.M.M. Dizi 1992, "Influence of Deflocculantson the Characteristics of Alumina Bodies Obtained by Slip Casting",J. Mater.Sci., 27, pp. 6662 - 6666.
Suzuki,T.S.,Y.Sakka, K.Nakano and K.Hiraga, 1998, "Effect of Ultrasonification on Colloidal Processing of Al203 and Zr02 Powders in Ph Controlled Suspension", MaterialsTransaction,JIM, 39 (6): 689- 692. .
Tari, G., J.M.F. Ferreira, A.T. Fonseca and O. Lyckfeldt,1998, "InfluenceofParticleSize Distribution on Colloidal Processing of Alumina", Journal of the European Ceramic Society, 18, pp. 249 - 253.
Yeh, T-S. and M.D. Sacks, 1988, "Low- temperature Sintering of Aluminium Oxide",J. Am. Ceram. Soc., 71, [10], pp. 841-844.