Vol 2018, No 8 (2018)

Abstract—The thermal dehydration of GdCl₃ ⋅ 6H₂O crystalline hydrate is studied by synchronous thermal analysis and mass spectrometry using certified samples. The mechanism and the caloric effects of the chemical reactions are determined. The thermal decomposition of GdCl₃ ⋅ 6H₂O crystalline hydrate is accompanied by hydrolysis, leading to the formation of oxychloride GdOCl.

The results of high-temperature electrochemical synthesis of holmium–iron triad metal intermetallics in chloride melts are presented. The influence of the current density, the composition of an electrolysis bath, and the synthesis time on the electrolysis processes and the composition of the end product is studied. The electrolysis of the molten KCl–NaCl mixture containing 0.5–2.5 mol % holmium trichloride and 0.1–2.5 mol % nickel (cobalt) dichloride at a current density of 0.5–2.0 A/cm², a temperature of 973–1073 K, and an electrolysis time of 30–90 min is shown to cause the formation of a cathode deposit in the form of a “metal–salt pear” on a tungsten electrode. This pear consists of a mixture of metallic nickel (cobalt) and HoNi, HoNi₅, and HoNi₃ (HoCo₂, HoCo₃, HoCo₅, Ho₂Co₁₇) intermetallics. The intermetallic compound content in the cathode deposit is found to increase at a constant current density (1.2 A/cm²) and when the holmium chloride content in a melt or the ratio of the holmium chloride concentration to the nickel (cobalt) chloride concentration increases. Only a mixture of holmium–nickel (cobalt) intermetallics can exist in the cathode deposit if the electrolysis bath composition and the electrolysis parameters are controlled. The electrochemical synthesis of holmium–iron intermetallics was performed under galvanostatic conditions in molten KCl–NaCl–HoCl₃. Iron ions are introduced in a melt via the anodic dissolution of metallic iron. The results of X-ray diffraction analysis of the electrolysis products demonstrate the fundamental possibility of synthesizing holmium–iron intermetallics. The optimum conditions of electrosynthesis of holmium–iron triad metal intermetallics are determined.

The equilibrium compositions and the thermodynamic characteristics of binary Ga–Sb, Al–Sb, and In–Sb melts are studied by a thermodynamic simulation using the TERRA software package over wide temperature and composition ranges. The temperature dependences of the partial pressures of the components of the gas phase forming above the III–V (III = Ga, In; V = Sb) semiconductor melts are investigated. The concentration dependences of the component activities and the partial and integral characteristics of melt mixing are obtained. All melts under study are shown to exhibit large negative deviations from Raoult’s law, which is caused by the presence of associates and indicates a strong interaction between the melt components. The temperature dependences of the logarithms and the partial pressures of the gas phase components are obtained. These dependences are shown to be linear for the components of the gas phase forming over the Ga–Sb, Al–Sb, and In–Sb melts.

The laws of formation of a continuous deposit layer at a given direct current are considered. Equations are analyzed to calculate the time dependences of overpotential for instantaneous nucleation with kinetic or diffusion control of new-phase growth. The calculated dependences are compared with the experimental ones obtained for silicon electrodeposition from a fluoride–chloride melt.

Cyclic voltammetry is used to study the electrolytic reduction of holmium ions on a nickel electrode in a holmium chloride-containing equimolar molten mixture of sodium and potassium chlorides in a temperature range of 1073–1173 K. The potentials of formation of nickel–holmium intermetallic compounds (IMCs) are determined. Nickel–holmium intermetallic compounds are synthesized by controlled potential electrolysis. Under the selected electrolysis conditions, the prepared coating is shown to be single-phase and its composition corresponds to the HoNi₂ stoichiometry. The coefficients of reaction diffusion of holmium in nickel are calculated and the activation energy of alloy-formation process is determined.

The structure of the weld metal after welding using a flux-cored wire with the addition of 0.3% zirconia flaky nanoparticles is studied. The weld consists of an acicular ferrite. This finding can indicate that the dissociation of zirconia in an electric arc is not an obstacle to a modifying effect, which manifests itself in both the interaction of zirconium with oxygen and the surface activity of zirconium in an iron-based solidifying melt. Thus, zirconia is a modifier of both the first and second kinds for the solidifying weld metal. Excess oxygen is likely to form individual pores less than 1 μm in diameter in the weld metal; however, they only wealy affect the mechanical properties of the welded joint. These results will be used to develop electrode materials for welding pipe steels.