ABSTRACT
Thermodynamic concepts are used to describe certain features of thermitic reactions and thermites in this chapter. Initially, several prominent periodic trends involving the stabilities of metal oxides are presented. While it is shown that a comparison of stabilities—as indicated by the Gibbs energy changes associated with formation reactions—can be instructive, the importance of enthalpy is also stressed. This is because pyrotechnic mixtures react spontaneously and exothermically. Ellingham diagrams, which describe the relative stabilities of oxides as a function of temperature, are introduced, and a collection of such diagrams is presented. Subsequently, Gibbs energy, enthalpy, and entropy are reconciled as far as the thermodynamic characteristics of thermites are concerned. General comments are offered regarding the metallic fuels and oxidizers that should engender the most extreme pyrotechnic reaction temperatures. The major features of adiabatic temperature and gas production profiles are described, and it is shown that the adiabatic temperatures of spontaneous and exothermic chemical reactions are ultimately limited by endothermic processes. Phase transitions often limit the adiabatic equilibrium temperatures of thermitic reactions. When computational methods are used to probe energetic chemical systems, some types of database deficiencies appear to be more problematic than others.
