Geological Applications of High Temperature Reaction Calorimetry

Abstract

Accurate thermodynamic data for minerals can be obtained by several methods; from analysis of phase relations, by measurement of oxidation-reduction equilibria using either gas mixtures or electrochemical cells with solid-electrolytes, and by calorimetry. The last technique can be subdivided into two major categories: the determination of heat capacities, both at cryogenic temperatures and at above room temperature, and the measurement of enthalpies of chemical reactions. Because silicate minerals are generally quite unreactive at room temperature, their equilibria must be studied at temperatures above 300°C, and, quite often, in the range 1000–l600°C. Solution calorimetry of silicates using aqueous hydrofluoric acid as a solvent has been carried out at temperatures of 50–80°C (Torgeson and Sahama, 1948; Neuvonen, 1952; King, 1952; Hovis, 1971). In this paper I will describe high temperature solution and reaction calorimetry of minerals and related substances. This technique, has been applied to minerals only since the mid 1960’s (Yokokawa and Kleppa, 1964b; Navrotsky and Kleppa, 1968; Holm and Kleppa, 1966) but has proved itself to be both versatile and widely applicable to problems of geological interest.