ABSTRACT
Ceramic powders are the basic starting materials for the majority of fabrication processes for producing components and samples of both monolithic and composite ceramics. Thus, sintering processes, whether with or without pressure, are the most used processes for fabrication of monolithic and composite ceramics. These processes not only start with powders, but generally depend critically on the nature of the powder for both component shape fabrication and subsequent sintering to be successful in their goals. Meeting these two goals of forming and densifying components generally imposes conflicting demands on powder character, for example, particle size, thus requiring adequate control of the powder preparation to provide powders of suitable compromise character. Very fine particle sizes are desirable for easier, more complete sintering, but can present problems of anion contamination, as well as green body fabrication limitations (see Sec. 2.2 and 8.2.1). Fabrication of many ceramic composites requires some similar and some different requirements on the particle character used as the dispersed phase in particulate composites. More severe densification challenges are found with composites with dispersed whiskers, platelets, or fibers. Fabrication of such composites shifts the emphasis in fabrication from pressureless to pressure sintering and some other processes as one goes progressively from mono-lithic ceramics to ceramic particulate composites, While some preparation of whiskers and platelets is briefly noted in this chapter, such preparation is typically dependent on additives (see Chap. 3), and preparation of fibers is via specially modified or designed processes (see Sec. 7.2).
