ADVANCED STRUCTURAL CERAMICS

ceramic materials that demonstrate enhanced mechanical properties under demanding conditions. Because they serve as structural members, often being subjected to mechanical loading, they are given the name structural ceramics. Ordinarily, for structural applications ceramics tend to be expensive replacements for other materials, such as metals, polymers, and composites. For especially erosive, corrosive, or high-temperature environments, however, they may be the material of choice. This is because the strong chemical bonding in ceramics-described in the article ceramic composition and properties: Chemical bonds-makes them exceptionally robust in demanding situations. For example, some advanced ceramics display superior wear resistance, making them ideal for tribological (wear) applications such as mineral processing equipment. Others are chemically inert and therefore are used as bone replacements in the highly corrosive environment of the human body. High bond strengths also make ceramics thermochemically inert; this property shows promising areas of application in engines for automobiles, aerospace vehicles, and power generators. A number of technological barriers have to be surmounted in order to make advanced structural ceramics an everyday reality. The most significant challenges are the inherent flaw sensitivity, or brittleness, of ceramics and the variability of their mechanical properties. In this article toughening methods are described and prospects for toughened ceramics assessed. The survey ends with links to articles on various established and prospective applications for advanced structural ceramics. Additional reading The section titled "Structural Applications for Technical, Engineering, and Advanced Ceramics," in Theodore J. Reinhart (ed.), Engineered Materials Handbook, vol. 4, Ceramics and Glasses, ed. by Samuel J. Schneider (1991), pp. 959-1014, presents an overview of advanced structural ceramics. A good introduction to ceramics in general is provided by David W. Richerson, Modern Ceramic Engineering: Properties, Processing, and Use in Design, 2nd ed., rev. and expanded (1992). The processing of advanced ceramics is described in James S. Reed, Introduction to the Principles of Ceramic Processing (1988); I.J. McColm and N.J. Clark, Forming, Shaping, and Working of High Performance Ceramics (1988); George Y. Onoda, Jr., and Larry L. Hench, Ceramic Processing Before Firing (1978); and four sections of the Reinhart work cited above: "Ceramic Powders and Processing," pp. 41-122; "Forming and Predensification, and Nontraditional Densification Processes," pp. 123-241; "Firing/Sintering: Densification," pp. 242-312; and "Final Shaping and Surface Finishing," pp. 313-376. Thomas O. Mason