Vol 52, No 7 (2016)

We have carried out thermodynamic modeling of the GaI₃–S and ZnI₂–S systems by the method of equilibrium constants and calculated the chemical compositions of the condensed and vapor phases in the temperature range 200–500°C. Our experimental data demonstrate the feasibility of preparing zinc thiogallate by reacting gallium(III) iodide and zinc(II) iodide with sulfur. Synthesis was carried out at a temperature of 450°C over a period 2 h, followed by calcination of the product at 650°C in order to remove the residual iodine. The practical ZnGa₂S₄ yield was 92–94%.

Thermodynamic modeling of the Hf–C–F system has been carried out in wide temperature and pressure ranges. Analysis of the calculated molecular composition of the vapor phase in equilibrium with Hf + HfC and the vapor phase in equilibrium with C + HfC has shown that the chemical vapor transport of hafnium under isothermal conditions is mediated by lower hafnium fluorides. The content of the lower hafnium fluorides increases with increasing temperature and decreasing total pressure in the system. Reactive hafnium carbide deposition on a carbon material, with CF₄ as a transport agent, has been studied experimentally. The coating obtained in this way is sufficiently dense and consists of hafnium carbide nanocrystals ranging in size from 100 to 200 nm.

We have studied the mechanical properties and corrosion resistance of an amorphous Fe_76.5P_13.6Si_4.8Mn_2.4V_0.2C_2.5 alloy and their response to nanocrystallization as a result of brief lamp processing and heat treatment. The results demonstrate that the lamp processing time needed to obtain a given phase composition through partial crystallization of the amorphous alloy is two orders of magnitude shorter than the corresponding heat treatment time. We have found lamp processing conditions that ensure the formation of an amorphous–nanocrystalline composite with a twofold increase in hardness, without loss of plasticity. It has been shown that, with increasing loading rate during nanoindentation, the hardness of the alloy decreases because of the increase in plasticity, which shows up as the formation of a larger number of shear bands. Under uniaxial tension, the material exhibits microplasticity, which may be due to intercluster sliding, with the amorphous structure retained. The corrosion resistance of the as-prepared amorphous alloy in a medium contaminated with sulfur dioxide exceeds that of the partially crystallized alloys.

We have identified the main general trends of variations in the spectral and kinetic properties of the Nd³⁺ and Yb³⁺ IR luminescence bands in (Y_0.99–xNd_0.01Yb_x)₂O₂S solid solutions under excitation at wavelengths of 0.810 and 0.940 µm. Using these results, we have developed the first multispectral IR phosphors with various relative intensities of the IR luminescence bands in the ranges 0.88–0.94, 0.94–1.06, 1.06–1.12, and 1.35–1.42 µm under excitation with 0.810-µm light and bright IR luminescence in the range 0.94–1.06 µm under excitation with 0.940-µm light.

The influence of small additions (1, 3, 5 mol %) of transition metal (Co, Cu, Mn, Zn) oxides on the properties of solid electrolyte Ce_0.9Gd_0.1O_2–δ (GDC) have been investigated. It has been shown that the addition of dopants results in intensification of GDC sintering and reduction of the shrinkage end temperature by 300–400°C, which decreases in the sequence Zn–Mn–Co–Cu. The ultimate dopant concentration above which the further activation of GDC sintering does not occur is about 3 mol % for Co, Cu, and Mn and about 1 mol % for Zn. It has been shown that Co and Cu increase the total conductivity of GDC, while Mn and Zn decrease it.

We describe barothermal processing (hot isostatic pressing) of an Al–10 at % Si binary alloy for 3 h at a temperature of 560°C and pressure of 100 MPa. The results demonstrate that this processing ensures a high degree of homogenization of the as-prepared alloy, which is chemically and structurally inhomogeneous. The morphology of the silicon microparticles in the material suggests that heat treatment of the Al–10 at % Si alloy at 560°C and a pressure of 100 MPa leads to a thermodynamically driven, essentially complete silicon dissolution in the aluminum matrix and the formation of a metastable, supersaturated solid solution, which subsequently decomposes during cooling. We analyze the associated porosity elimination process, which makes it possible to obtain a material with 100% relative density. Barothermal processing of the Al–10 at % Si alloy is shown to produce a bimodal size distribution of the silicon phase constituent: microparticles 1.6 µm in average size and nanoparticles 43 nm in average size. Barothermal processing is shown to reduce the thermal expansion coefficient of the alloy, and the microhardness of the two-phase alloy is determined. Based on the present results, we conclude that barothermal processing is an effective tool for eliminating microporosity from the Al–10 at % Si alloy, reaching a high degree of homogenization, and producing a near-optimal microstructure, which surpasses results of conventional heat treatment of the material at atmospheric and reduced pressures.

Ti–Al–Mo–N coatings have been grown by arc PVD at different bias voltages, V_b, applied to the substrate and partial pressures of nitrogen reaction gas, p(N₂), in the working chamber. The coatings have a nanocrystalline structure, with an average grain size on the order of 30–40 nm and a layered architecture made up of alternating layers based on a (Ti,Al)N nitride and Mo-containing phases of thickness comparable to the grain size. It has been shown that the phase composition of the coatings depends on V_b and p(N₂): raising the energy of deposited ions by increasing V_b from–120 to–140 V, as well as raising p(N₂) from 0.3 to 0.5 Pa, leads to a more complete molybdenum nitride formation during coating growth, which causes a transition from (Ti,Al)N–Mo–Mo₂N compositions to (Ti,Al)N–Mo₂N. Measurements of the binding energy of Mo 3d photoelectrons in metallic Mo and the Mo₂N nitride by X-ray photoelectron spectroscopy have shown that the transition from the former phase to the latter is accompanied by a negligible energy shift.