Thermodynamic Insights into the Energetics of Ternary Oxides with Mineralogical Significance

3b Thermodynamic Insights into the Energetics of Ternary Oxides with Mineralogical Significance 

In the previous example, (Section 15.3a) we considered a process that can be described as phase equilibria. Mineralogical processes may also be chemical reactions, such as 

Formation of Ternary Oxides12 Many compounds of mineralogical importance are ternary compounds of oxygen with a formula ABaOi+, where A = Ca, Mg, Mn, Fe, Co, and Ni, and B = Si,W, C, and S. These compounds may be considered to be formed from the reaction of the binary oxides. That is 

Knowledge of the factors that determine the sign and magnitude of ArG° for reaction (15.33) contributes to an understanding of the range of stability of ternary oxides relative to binary oxides. In some cases, favorable enthalpy effects may tend to stabilize a material, while in other instances, a favorable entropy effect may dominate stability considerations/ 

We will focus on looking for factors that determine the energy (or enthalpy) of formation of ternary oxide compounds. Oxides can be characterized on an acid/base scale. An acidic oxide, A 0, is an oxide ion donor, while a basic oxide, B 0, is one that accepts another oxide ion. The two reactions can be represented as 

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