High-temperature materials chemistry and thermodynamics

Many of the uses of materials at high temperature require their persistence, with minimal change in chemical composition and microstructure, over long periods of time (hours to years). Chemical reactions at high temperature often occur fast and thus the thermodynamic equilibrium state, rather than persistence of metastable states, often governs the suitability of a given material or set of materials for a proposed application. The term “high temperature” cannot be defined uniquely; perhaps the most useful practical definition is one that says that for a given material, high temperature is the temperature above which the material is strongly chemically reactive in use. From the point of view of solid state chemistry and thermodynamics, there is vast empirical knowledge about such reactivity and moderately adequate thermodynamic data bases for common alloys and ceramics (Sundman et al., 1985; Schenck and Dennis, 1989; Pankratz, 1982; Ondik and Messina, 1989; Liu et al., 2003; Levin and McMurdie, 1975; Kubaschewski and Alcock, 1979; Gisby et al., 2002; Eriksson and Hack, 1984; Davies et al., 2002; Chase et al., 1985a,b; Chart, 1978; Barry et al., 1979). Nevertheless, an inexperienced or only moderately knowledgeable scientist or engineer may have a hard time selecting materials for high temperature use and avoiding pitfalls of unanticipated reactivity and degradation. The purpose of this article is to organize such chemical knowledge into a short and useful guide on materials use and compatibility, taking advantage of general trends governed by the regularity of chemical bonding and thermodynamics among groups of elements in the periodic table.