ABSTRACT
Use of additives plays a large role in ceramic technology, with two of the largest uses being to aid densification, as addressed in Chapter 5, and in modifying properties. The latter is a very large field, with various classes of properties and mechanisms of controlling properties ranging from various microstructural control, second phase, crystal structure, or lattice effects, and combinations of these. Many of these require considerable expertise in specific properties to be properly addressed and hence are not generally addressed in this book (but are illustrated some, e.g., in Sec. 3.3 and Chap. 5). However, there are other applications of additives in fabricating and processing of ceramics that are addressed here. These include processing of ceramic powders, whiskers, and platelets, (i.e., of some raw materials), and of enhancing, retarding, or eliminating formation of some crystalline phases, i.e. of structural changes that occur and are significant in some important ceramics. Such transformation control impacts some aspects of fabrication as well as some important applications, including some structural ones and especially the very important field of catalysis. Other uses of additives covered include nucleation of crystallization of glasses, solidifying melts, and of seeding and control of grain structure in and following sintering, including in situ growth of single crystals. Finally, additives also play a role in flux growth of ceramic crystals, and for various other miscellaneous uses such as surface ef-fects. All of these uses are covered in this chapter, in the order listed. Besides being of importance to the specific goal for the additive, their individual uses can have implications for other uses, including for densification.
