TABLE OF CONTENTS Ceramics are solids held together by both covalent and ionic bonds, and composed of metallic or semi-metallic elements.1 These elements are usually combined with oxygen, but may possibly be combined instead with nitrogen, silicon or carbon. Such materials are typically formed by heat treatment, hence their name, which is derived from the Greek keramos (=burnt stuff). The resulting solids have characteristic properties of hardness, durability and chemical resistance. Many ceramics are based on silicates or aluminosilicates, but the class of material also includes carbides, nitrides and silicides of metals such as tungsten.
Because of their composition and structure, ceramics generally display good resistance to chemical attack; they are also resistant to the effects of elevated temperature. This is because at the atomic level they are densely packed, with small cations fitting into spaces between anions. In order to disrupt such a structure, large amounts of thermal energy are needed. Consequently, the melting temperature is high.
Many ceramics contain oxygen, and their metallic elements tend to be in a fully oxidised state. Since much deterioration of materials in their service environments is due to oxidation, the fact that ceramics are already highly oxidised means that they have significant resistance to further oxidative degradation.1
The chemical resistance of ceramics is not total in the environment of the body. The chemistry of the body is such that it provides a hostile environment for foreign materials2 and this is equally true for ceramics. Some ceramics are designed to interact significantly with...
