Vol 59, No 5 (2023)

This paper reports on titanium carbide synthesis in an atmospheric-pressure arc plasma reactor by exposing a stoichiometric starting mixture (Ti : C ~ 1 : 1.05) to a plasma jet. The phase composition of the synthesized TiC powder has been determined as a function of the time during which the starting mixture was exposed to a thermal plasma flow and the current (40–120 A) through the electric arc plasma source. The powders obtained under optimal conditions consist of the cubic titanium carbide phase and have a broad particle size distribution, with distinct agglomerates on the order of 50–100 μm in size. It is worth noting that the surface of the agglomerates has the form of a densified perforated crust (with a pore diameter no greater that 2 μm).

This paper presents potentiodynamic and thermogravimetric data on the anodic behavior and oxidation of thallium-containing alloy Zn22Al in different media. We have determined anodic, kinetic, and energetic characteristics of the alloys under isothermal conditions. The electrochemical corrosion, pitting, and repassivation potentials of the thallium-containing alloys are shifted to positive values. The addition of 0.1–1.0 wt % thallium to alloy Zn22Al leads to an increase in its anodic oxidation resistance. The oxidation and corrosion rates of the thallium-containing (0.01–0.1%) alloys are a factor of 1.5–2 lower than those of alloy Zn22Al. The oxidation products of the alloys consist of a mixture of protective ZnO, Al2O3, Tl2O3, and ZnAl2O4 oxide films.

This paper presents data on ozone detection. The purpose of this work was to find materials offering selectivity in analysis for ozone in air by examining the shape of the resistive response of some thin-film oxide semiconductor sensors operated in thermal modulation mode. For this purpose, thin Pd, Cd, Zn, and W metal layers were produced by sputter deposition on polycrystalline alumina (Al2O3) test structures with Pt electrodes for electrical resistance measurements. Next, the metallic layers were oxidized in air at a temperature of 550°C. The thickness of the resultant PdO, CdO, ZnO, and WO3 oxide films was ~30 nm. The resistive response of the thin-film PdO, CdO, ZnO, and WO3 oxide materials was measured in an ozone–air atmosphere in thermal modulation mode. The temperature of the sensors was varied sinusoidally between 50 and 300°C, and the ozone concentration in air was varied from 25 to 250 ppb. The use of thermal modulation made it possible to reveal differences in the shape of the response between the sensors at different ozone concentrations. The PdO sensor differs significantly in the shape of the resistive response from the other sensors. This characteristic feature of this material opens up the possibility of improving the selectivity of ozone detection with a PdO oxide sensor.

The Mg3(PO4)2–Mg4Na(PO4)3 system has been studied using thermal analysis, X-ray diffraction, and X-ray microanalysis. Firing the constituent phosphates at 800°C has been shown to cause no phase changes, whereas firing above 1000°C leads to the formation of a single-phase material, which is due to the incongruent melting of the magnesium sodium double orthophosphate Mg4Na(PO4)3. The homogeneity range of the compounds in the Mg3(PO4)2–Mg4Na(PO4)3 system differing in composition has been determined by X-ray microanalysis. The microstructure of Mg3–xNa2x(PO4)2-based ceramic materials prepared by sintering at a temperature of 1000°C has an average grain size under 10 μm. The synthesized bioceramic materials are potentially attractive for use as implants for bone tissue regeneration.

This paper presents additional data on carbon, hydrogen, and oxygen impurities in molecular form in extrapure selenium. Using gas chromatography/mass spectrometry analysis, selenium has been shown for the first time to contain hydrocarbons, halogenated hydrocarbons, and sulfur- and selenium-containing substances. Forty-six elemental impurities were detected in selenium by inductively coupled plasma atomic emission spectroscopy. Data on carbon-, oxygen-, and hydrogen-containing molecular impurities in commercially available extrapure selenium will be helpful in choosing and optimizing methods for its further ultrapurification.

Magnesium aluminate spinel (MgAl2O4) ceramics have been subjected to hot isostatic pressing. The process led to a 0.28% increase in the density of the ceramics compared to samples prepared by primary hot pressing. IR spectroscopy has been used to evaluate structural changes in the densified material. In the IR reflection spectrum measured from 40 to 1000 cm–1, the increase in density showed up as a decrease in the intensity of some bands due to isolated vibrational modes in the MgO4 and AlO4 tetrahedra. The effect was attributed to vibrational mode mixing in the tetrahedral structural units in the densified ceramics. This finding indicates that consolidation of the material is accompanied by an increase in the inner connectivity of crystallites. At the same time, the frequency and intensity of the stretching modes of the Al–O groups in the AlO6 octahedra remained unchanged after isostatic pressing, suggesting that the heat treatment caused no stoichiometric distortion.

WC–(1, 3, 5)% ZrO2 ceramics have been produced by spark plasma sintering (SPS). WC–ZrO2 powder mixtures have been prepared by ultrasonic homogenization and stirring of WC nanopowder and submicron t-ZrO2 powder. The WC–ZrO2 sintering rate has been shown to be limited by the grain-boundary diffusion process. Increasing the percentage of ZrO2 leads to a slight increase in optimal SPS temperature, an increase in the concentration of W2C particles, and a decrease in hardness.

We have investigated phase relations along a number of joins in the subsolidus region of the Cs2MoO4–BaMoO4–Gd2(MoO4)3 system using X-ray diffraction and differential thermal analysis and constructed its phase compatibility diagram. A ternary molybdate with the composition CsBaGd(MoO4)3 and a monoclinic scheelite-like structure (sp. gr. P21/n) has been synthesized. Codoping CsBaGd(MoO4)3 with Er3+/Yb3+ ions, we have obtained an upconversion phosphor exhibiting anti-Stokes luminescence in the range 400–700 nm under IR excitation (λex = 977 nm). The synthesized phosphor has been characterized by X-ray diffraction, differential thermal analysis, and vibrational spectroscopy, and its luminescence spectrum has been measured.