The phase equilibria in the total range of component concentrations in the V2O5-Cr2O3 system up to 1000 °C were studied by means of phase powder diffraction and DTA. Two compounds exist in the system: CrVO4, melting incongruently at 860±5 °C, and Cr2V4O13, which decomposes in the solid state at 640±5 °C to CrVO4(s) and V2O5(s). At 645±5 °C, CrVO4 and V2O5 form a eutectic mixture with the CrVO4 content not exceeding 2% mol.
Differential thermal and phase X-ray analyses have shown that MoO3 and Fe2V4O13 form a solid substitution solution, in which Mo6+ ions are incorporate into the crystal lattice of Fe2V4O13 in place of V5+ ions. The solubility limit of MoO3 in Fe2V4O13 at ambient temperature is 18 mole % of MoO3. The phase equilibria in the system Fe2V4O13-FeVMoO7, were also studied. Results are presented in the form of a phase diagram.
The course of the reaction between copper(I) sulphide and copper(II) sulphate in SO2 at 710–785 K was studied by the TG method under isothermal and non-isothermal conditions, as well as by the DTA method, X-ray analysis and scanning electron microscopy. It was established that the reaction is essentially dependent upon the initial composition of the substrate mixture, Cu2SO2 and Cu2SO2 being the chief intermediates in the reaction. Copper(I) oxide appears as the permanent final product of the reaction of interest. The reaction network, with the intermediate stages depending on the initial compositions in the temperature range studied, has been demonstrated.
The reaction between copper(I) sulphide and excess copper(II) sulphate in the temperature range 600–750 K was investigated by methods of thermal analysis as well as by measuring the phase composition as a function of the fractional conversions. The reaction proceeds in four stages. The transient products are Cu2S, a Cu2SO2 phase and CU2SO4, and the final product is CU2O with the non-defect structure. The initial composition of the substrate mixture strongly influence the reaction kinetics.
The reaction process between CuSO4 and excess Cu2S in the temperature range 650–750 K was investigated by methods of thermal analysis and by studying the phase contentss of the products as a function of the fractional conversion. The reaction proceeds in three steps, with Cu2S and a new phase described by the formula Cu2SO2 as intermediates. This new phase is liquid under the conditions of the reaction. The final product of the reaction is a defective crystalline Cu2O.
The behaviour of V2O5 against FeVMoO7 up to 1000 °C in the whole range of component concentrations was investigated using DTA and X-ray powder diffraction methods. The experimental results are presented in the form of a phase diagram.
Phase equilibria have been established in the solid state in the V9Mo6O40-Cr2O3 system. The results obtained have permitted to state that the system of interest, in the subsolidus area, is not a real two-component system in the whole component concentration range.