Preparation of Powders for Ceramic Processing

Preparation of Powders for Ceramic Processing 17.2.2.3. Solution Preparation... 

On the other hand, improvements in ceramic powder processing technology, the routine preparation of high-purity ceramics of nanometre scale, and the new techniques for the processing of these powders such as HIP, SPS, microwave furnace, etc., will be the driving forces for a very active study on nanoceramics in the near future, probably opening up new phenomena and new applications. 

In this chapter, we have described the colloid chemistiy of ceramic powders in suspension. Colloid stability is manipulated by electrostatic and steric means. The ramifications on processing have been discussed with emphasis on single-phase ceramic suspensions with a distribution of particle sizes and composites and their problems of component segregation due to density and particle size and shape. The next chapter will discuss the rheology of Uie ceramic suspensions and the mechanical behavior of dry ceramic powders to prepare the ground for ceramic green body formation. The rheology of ceramic suspensions depends on their colloidal properties. 

Advantages and drawbacks are inherent to the process itself. The requested characteristics of fine ceramic powders used for electrode fabrication of anode and cathode are less strict than those of electrolyte. The hydrothermal method and glycine-nitrate combustion process (GNP) are essentially employed to prepare the nano-scale ceramic powders at INER . The solid state reaction method may be used for preparation of the mixed ceramic powders without the restrict limitations of the characteristics of particle size and surface area. 

Unlike silicate ceramics, raw materials used for the preparation of non-silicate ceramics are generally synthetic powders and not mixtures of crashed rocks. But these synthetic powders can result from natural products, which the English terminology makes easy to understand by distinguishing between starting materials (for example, alumina powders) and raw materials (bauxite rocks, in this case, whose treatment by the Bayer process yields the alumina powders) [CAS 90],... 

Achievement of appropriate suspensions for the specific technology is fundamental and preparation of well dispersed ceramic slurries is one of the most important issues. Obviously the process is much more complicated in the case of eomposite ceramics, where the stabilization of different ceramic powders, and thus possibly with different characteristics (density, particle size, surface properties, etc.) must be accomplished. For slurry preparation, attrition milling can be useful to get ceramic... 

Powder Preparation. The goal in powder preparation is to achieve a ceramic powder which yields a product satisfying specified performance standards. Examples of the most important powder preparation methods for electronic ceramics include mixing/calcination, coprecipitation from solvents, hydrothermal processing, and metal organic decomposition. The trend in powder synthesis is toward powders having particle sizes less than 1 p.m and Httie or no hard agglomerates for enhanced reactivity and uniformity. Examples of the four basic methods are presented in Table 2 for the preparation of BaTiO powder. Reviews of these synthesis techniques can be found in the Hterature (2,5). 

The preparation of ceramic powders by CVD is a promising and growing field. These powders are used as precursors for the processing of advanced ceramics, or directly as powder for such applications as abrasives. 

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