Standard Gibbs free energy of formation of ThTi2O6 from oxides

Phase relations in the TiO-TiO2-ThO2 system at 1000 C were determined by the equilibration-and-quench technique. ThTi2O6 is found to exist in a wide range of oxygen potentials coexisting with Ti oxides from TiO2 up to Ti3O5. The two most reduced oxides, namely TiO and Ti2O3, coexist with ThO2. To determine the thermodynamic stability of ThTi2O6, the equilibrium 2/3Ti3O5+1/3O2+ThO2=ThTi2O6 was studied by means of solid state emf measurements. From the data obtained in the temperature range 950-1250 C the following relationship was calculated for the Gibbs energy: ThO2+2TiO2=ThTi2O6, ΔGof=-6039-5.60T (calmol-1). The solid solubility limits of ThO2 in Ti4O7 and Ti3O5 as obtained from the solidified melt by the SIMS technique are found to be 700 and 600 ppm, respectively. (orig.)