Ceramic powders are the basic starting materials for the majority of fabrication processes for producing components

Ceramic powders are the basic starting materials for the majority of fabrication processes for producing components and samples of both monolithic and composite 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. 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 monolithic ceramics to ceramic particulate composites. While some preparation ofwhiskers and platelets is briefly noted in this chapter, such preparation is typically dependent on additives), and preparation of fibers is via specially modified or designed processes .
It is desirable to have powders tailored to the specific ceramic fabrication process of interest, for example, pressureless sintering. However, this is often not practical, especially in development and limited production stages, since it is often more cost-effective to use available powders, possibly by modifying them (e.g., by comminution), the fabrication process, or both. There are a variety of other uses of ceramic powders that have different requirements, some often less demanding than in sintering. The latter includes the large field of raw materials for melt processing of ceramics, much of which is less demanding in terms of physical character of the powder .The broad field of abrasives for sawing, grinding, lapping, sanding, and polishing, though often using diamond, also often uses other ceramics, such as SiC and alumina, and other processes than typical preparation of sinter able powders. Another important
application of ceramic powders is as feed material for plasma and other melt spraying processes, where there have been major shifts in processing technology for feed materials in the past 20 years, .There are also needs for dispersed ceramic particles for a variety of metal as well as some polymer matrix composites that differ in character from those for ceramic composites and the particles needed; for instance, in terms of size, shape, and single crystal or polycrystalline character.
It should be noted that the earlier powder preparation for traditional ceramics
such as glasses and various porcelain bodies were primarily extraction, cleaning, and comminution of natural minerals such as clays, talc, silica sands, quartz, limestone, and feldspars. Such traditional ceramics are still important, but are not central to this book, the interested reader is referred to other sources.
The technology of interest in this book and chapter, that of fine or higher technology ceramics, entails more chemical processing in preparing of the ceramic powders, which is thus the focus of this chapter. However, physical aspects of powder processing such as comminution are still important, and are thus noted here, but are often accomplished in conjunction with other steps, such as milling for mixing of other ceramic, and organic (e.g., binder) constituents, and thus not
extensively addressed here.
There is now a diverse and expanding array of various methods of preparing ceramic powders, many focused on conventional wet chemical processing, as well as use of other physical and especially chemical methods. The latter have resulted from increased chemical input to ceramic powder preparation, which has significantly broadened technical opportunities, but has also often left issues of practicality and cost. Only key aspects and examples of the processes can be addressed here, since most of these topics are large subjects in themselves, but at least some of the practicality issues will be addressed. There are other reviews, generally not as comprehensive, but with different perspectives, and with some different examples.
Processes based on conventional wet chemical processing of various salt precursors for oxide ceramics are addressed first along with their conversion (i.e., calcining) to ceramic powders. Then, extensions of conversion of oxide salt precursors to ceramics via processes such as freeze-drying and spray pyrolysis are discussed, followed by extension to other chemical processing of precursors, via sol-gel and preceramic polymers and their conversion to ceramics. This is followed by various melt, vapor, and other reaction processing of oxide powders, especially ternary oxides; then processing of non-oxide powders, especially by various reaction processes, including extensively used carbothermal reduction, and other processes (e.g., wet chemical, melt, or vapor-phase based) are addressed. While there has only been limited use of ternary nonoxide or mixed nonoxide-oxide compounds, their preparation is briefly addressed. Then, the important emerging technologies of coating ceramic (and metal) powder particles with a ceramic (or metal) coating are addressed, along with a summary of powder Characterization