Drying-induced forming of alumina ceramics using high solid-loaded slurries with addition of glycerol
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A new drying-induced forming (DIF) of ceramics has been developed using high solid-loaded alumina slurries with addition of glycerol, in which the slurry was simply dried in an open mold at the ambient condition. The drying-induced forming approach is facilitated by the high stability of concentrated slurries during drying where glycerol was added to maximize the critical solid loading and play simultaneously as a drying control agent. The drying and rheological behaviors of slurries were examined with respect to the glycerol addition. A slurry of 60 vol% solid loading with 20 wt% glycerol addition was chosen for the drying induced forming test. The green samples exhibited no bending or cracks, and a small degree of shrinkage anisotropy during sintering. The sintered samples showed a high relative density of 99.2% and an average strength of 420 MPa. We demonstrate here a possibility of producing near-net-shaped and bulk ceramic components in a simple scheme by using the drying-induced approach.
I. INTRODUCTION
Ceramic colloidal processing has been studied intensively in recent years because it provides the promise to achieve homogeneous green structure and near-net shaping of ceramic products.1,2 In ceramic colloidal processing, the controls of forming and drying processes are of great importance in addition to the achievement of a good dispersion state of the colloids. They play key roles in determining the particle packing in green structure prior to sintering. A successful forming method should be one that can transfer the original homogeneity of colloid as much as possible to the formed body, and introduces no new heterogeneities. Until now, various forming methods have been developed in colloidal processing. They can be categorized into two methods: shaping by concentrating slurry through evaporation or outflow of fluid (e.g., tape casting and slip casting), and in-situ shaping by polymerization or particle coagulation (e.g., gel casting, temperature induced forming, freeze casting, and direct coagulation casting).3,4 In the former methods, structural orientation is developed due to particle rearrangement if anisometric particles were used.5 The compacts made by in situ forming methods have very uniform structure of “frozen” suspension, but are
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Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/JMR.2007.0026 244
http://journals.cambridge.org
J. Mater. Res., Vol. 22, No. 1, Jan 2007 Downloaded: 16 Mar 2015
more prone to cracking due to the significant shrinkage during subsequent drying. In this study, a novel and simple ceramic forming method of drying-induced forming (DIF) is developed using glycerol addition. The DIF concept was previously proposed by G. Tarì et al., in whose work highly solidloaded alumina slurries (68–72 vol%) were achieved by using powders having a bimodal particle size distribution, and the slurries were poured into non-porous silicon rubber molds to dry in air at different temperatures to get thin and crack-free green bodies, but the sin
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