Thermodynamic data for Mn₃O₄, Mn₂O₃ and MnO₂

Abstract

Thermodynamic properties of Mn₃O₄, Mn₂O₃ and MnO₂ are reassessed based on new measurements and selected data from the literature. Data for these oxides are available in most thermodynamics compilations based on older calorimetric measurements on heat capacity and enthalpy of formation, and high-temperature decomposition studies. The older heat capacity measurements did not extend below 50 K. Recent measurements have extended the low temperature limit to 5 K. A reassessment of thermodynamic data was therefore undertaken, supplemented by new measurements on high temperature heat capacity of Mn₃O₄ and oxygen chemical potential for the oxidation of MnO_1-x, Mn₃O₄, and Mn₂O₃ to their respective higher oxides using an advanced version of solid-state electrochemical cell incorporating a buffer electrode. Because of the high accuracy now achievable with solid-state electrochemical cells, phase-equilibrium calorimetry involving the “third-law” analysis has emerged as a competing tool to solution and combustion calorimetry for determining the standard enthalpy of formation at 298.15 K. The refined thermodynamic data for the oxides are presented in tabular form at regular intervals of temperature.