Differential thermal analysis (DTA) and X-ray powder diffraction (XRD) were used to study phase equilibria, established in
air in the V2O5-Sb2O4 system up to 1000C. It has been found that there is a new phase =SbVO5. The =SbVO5 has been prepared by two methods: by heating equimolar mixtures of V2O5 and α-Sb2O4 in air and by oxidation of the known phase of rutile type obtained in pure argon at temperatures between 550 and 650C. Thermal
decomposition of =SbVO5 in the solid state starts at 710C giving off oxygen. The results provide a basis for constructing only a part of the phase
diagram of the investigated system (up to 50.00 mol% Sb2O4).
The use of XRD and DTA methods has allowed studies on the interaction of the SbVO5 and MoO3, taking place in the solid state and in the medium of ambient air. The experimental results of XRD and DTA for all the samples
showed the presence of a novel phase, i.e. Sb3V2Mo3O21 apart from various amounts of MoO3 and V9Mo6O40 or SbVO5 and V2O5(s.s.). The SbVO5–MoO3 system is not a real two-component system over the entire range of component concentrations up to the solidus line.
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.
It has been shown by the methods of X-ray powder diffraction (XRD), differential thermal analysis (DTA) and infrared spectroscopy
(IR) that solid solutions of a formula Cr1−xAlxVMoO7, where x& (0−0.65), are formed in the system CrVMoO7-AlVMoO7. The obtained research results have proven that the ions Al3+ are incorporated into the crystal lattice of CrVMoO7 instead of Cr3+, which causes a contraction of the lattice and a shift of IR absorption bands towards higher values of wavenumbers. The phases
Cr1−xAlxVMoO7 melt incongruently in the temperature range from 710C (for x=0.65) to ∼820C in the case of x close to zero
DTA and XRD studies of the Fe2V4O13–Cr2V4 O13 system have shown that continuous solid solutions of a Fe2–xCrxV4O13 type, bearing a Fe2 V4 O13 structure, are formed in the system. With the increasing degree of the Cr3+ ion incorporation into the Fe2 V4 O13 structure, a contraction of the solid solution crystal lattice develops. Solid solutions of a Fe2–x Crx V4 O13 type melt incongruently, their melting temperature increasing from 953 to 1003 K with increase in the degree of the Cr3+ ion incorporation. The solid product of melting Fe2–x Crx V4 O13 solid solutions for 0.2<x >1.2 is the Fe1–x Crx VO4 solution phase, and for x ≤0.2 and x ≥1.4 – the Fe1–x Crx VO4 phase as well as FeVO4 or CrVO4 , respectively.
X-ray phase analysis (XRD), differential thermal analysis (DTA) and IR spectroscopy have shown that continuous substitution
solid solutionsin are formed in the FeVMoO7–CrVMoO7 system. With increasing the degree of Cr3+ ion incorporation into the FeVMoO7 structure, a crystal lattice contraction of the Fe1–xCrxVMoO7 solid solution arise. Elevation of temperature of its incongruent melting and gradual shifting of the corresponding IR absorption
bands towards higher wavenumbers have been noticed, as well. The solid product of incongruent melting for x≤0.5 is the Fe4–yCryV2 Mo3 O20 solid solutions phase, whereas for x>0.5 Fe2–zCrz(MoO4)3 and Fe2–u Cru O3 solid solutions.
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.
The interactions between MoO3 and Sb2O3 or α-Sb2O4 taking place in the solid state in air during high-temperature as well as mechanochemical treatments have been investigated.
The high-energy ball milling of MoO3 with Sb2O3 converts α-Sb2O3 to β-Sb2O3 and leads to formation of Sb2MoO6 and Sb4Mo10O31 phases. They are the final products of thermal synthesis in an inert atmosphere but not in air. The solid solution of MoO3 in β-Sb2O4 was obtained in high-temperature reaction of MoO3 with Sb2O3 or α-Sb2O4 as well as by milling of mixture MoO3/α-Sb2O4 for 14 h. The milling resulted in higher than 3 mol% solubility of MoO3 in β-Sb2O4. The constructed phase diagram of MoO3–α-Sb2O4 system is presented.