Acid–Base Reactions of Transition Metal Oxides in the Solid State

Subsolidus compatibility data exist for a number of ternary oxide systems containing a transition metal oxide. Ternary diagrams, suitable for the present purpose, are limited mainly to those that include FeO, Fe₂O₃, ZnO, or Cr₂O₃, and these are examined in the context of Lewis acid–base interaction by considering the electron densities borne by the oxygen atoms or ions. These electron densities can be expressed on the optical basicity scale, and a significant acid–base difference exists between the reactants when they differ markedly in optical basicity. For many reactions the optical basicity difference between the products is much less, suggesting that acid–base neutralization is a major driving force. This principle has been found previously for nontransition metal oxide ternary systems. However, there are notable exceptions, especially in reactions where FeO or ZnO is the end product. This exceptional behavior is examined.