Photoemission studies of adsorbed oxygen and oxide layers

The standard Gibbs free energies of formation of CuAlO2 and CuAl2O4 were determined in the range 700° to 1100°C, using emf measurements on the galvanic cells (1) Pt,CuO +] Cu2O/CaO-ZrO2/O2,Pt; (2) Pt,Cu +] CuAlO2+] Al2O3/CaO-ZrO2/ Cu +] Cu2O,Pt; and (3) Pt,CuAl2O4+] CuAlO2+]Al2O3/CaO-ZrO2/O2,Pt. The results are compared with published information on the stability of these compounds. The entropy of transformation of CuO from tenorite to the rock-salt structure is evaluated from the present results and from earlier studies on the entropy of formation of spinels from oxides of the rock-salt and corundum structures. The temperatures corresponding to 3-phase equilibria in the system Cu2O-CuO-Al2O3 at specified O2 pressures calculated from the present results are discussed in reference to available phase diagrams.

Thermodynamics of CuAlO2 and CuAl2O4 and Phase Equilibria in the System Cu2O-CuO-Al2O3

Transposed temperature drop calorimetry and hightemperature drop solution calorimetry in molten 2PbO·B2O3 at 977 K were used to study the energetics of some manganese oxides, namely pyrolusite (MnO2), bixbyite (Mn2O3), hausmannite (Mn3O4), and manganosite (MnO). The enthalpies of oxidation at 298 K in the manganeseoxygen system, which were determined by appropriate thermodynamic cycles, were (in kJ/mol of oxygen): –441.4 ± 5.8 for the reaction 6MnO + O2→ 2Mn3O4, –201.8 ± 8.7 for the reaction 4Mn3O4+ O2→ 6Mn2O3, and –162.1 + 7.2 for the reaction 2Mn2O3+ O2→ 4MnO2. These values agreed very well with previous data that were obtained using equilibrium measurements that were reported in the literature. Thus, direct calorimetric measurements were well suited to obtain reliable enthalpy of formation data for oxides that contain manganese in the 2+, 3+, and 4+ states. Using these new values of enthalpies and reliable standard entropies, the phase-stability diagram of the manganeseoxygen system was constructed.

Thermodynamic Properties of Manganese Oxides

Experimental data on the thermodynamics and the phase diagram of the Mn-O system were reviewed, and by application of the CALPHAD method, a consistent set of thermodynamic model parameters was optimized. The phases pyrolusite (MnO2), bixbyite (Mn2O3), and hausmannite (Mn3O4) were described as stoichiometric compounds. Manganosite (Mn1−xO) was described using the compound-energy model and the liquid described using the two-sublattice model for ionic liquids.

Assessment of the La-Mn-O System

The chemical potential of oxygen Vto2)defined by the reactions 1.5Fe + O2 '" 0.5Fe304) 2Fe + O2 '" 2"FeO," 6"FeO" + O2 '" 2Fe304, 4Fe304 + O2 '" 6Fe203, 4Cu + O2 '" 2Cu20, and 2Cu20 + O2 '" 4CuO has been determined using an electrochemical method with calcia-stabilized zirconia solid electrolytes. The Fe + Fe304, Fe + "FeO," and Cu + Cu20 equilibria were measured using air as the reference, and these results are thus absolute determinations of /J-02. Cu + Cu20 and Fe + "FeO" were then used as reference electrodes for other measurements reported both here and elsewhere. The results for the /J-02 values are [in J. mol-I, T in kelvins, with a reference pressure for O2of I bar (lOs Pa)]

/pdf/systems-fe-o-and-cu-o-thermodynamic-data-for-the-equilibria-wcyij2oxfv.pdf

Systems Fe-O and Cu-O; thermodynamic data for the equilibria Fe-“FeO,” Fe-Fe3O4, “FeO”-Fe3O4, Fe3O4-Fe2O3, Cu-Cu2O, and Cu2O-CuO from emf measurements

A "closed system" solid electrolyte electrochemical cell has been designed to investigate the thermodynamic properties of metal oxides. The measurements with this cell are free of mixed potentials arising from nonequilibrium oxygen pressure conditions in the electrode compartments. The oxide systems investigated include , , , , , , , , and .

https://iopscience.iop.org/article/10.1149/1.2411434/pdf

G. G. Charette

Papers

Thermodynamic Properties of the Oxides of Fe, Ni, Pb, Cu, and Mn, by EMF Measurements