Measurement, Evaluation, and Tabulation of Thermodynamic Properties

Abstract

Adequate knowledge of the nature of the thermodynamic data reproduced in tables is a necessary first step for calculating mineralogical phase equilibria. Thermodynamic data tables, in vogue today, fall into two categories. The first of these seeks to deal with each phase individually, drawing heavily on calorimetric (and a few electrochemical cell) measurements. The compilation of thermodynamic data of minerals and related substances by Robie et al. (1979) belongs to this category. The second type of database strives to relate the thermodynamic properties 1) of the minerals to each other, to come up with what is known as an internally consistent set of thermodynamic data. Two recent examples of such databases are Holland and Powell (1985) and Berman (1988). In the Chapters 4 to 6, we shall employ the Robie et al. (1979) table to calculate a variety of phase diagrams. Though calorimetry is, and will remain, the fundamental and an indispensable source of thermodynamic data, the exercises in those three chapters will reveal to us the perils of depending exclusively on such data, and urge us to develop the internally consistent thermodynamic database, which is achieved by a simultaneous treatment of the calorimetric and phase equilibria measurements. One of the methods of deriving internally consistent data will be discussed in detail in Chap. 7. The availability of such a database is a prerequisite for generating geologically meaningful phase diagrams. But more on that later on.