No abstract available

[en] Thermodynamic calculations were made and the process of calcium-thermic reduction of titanium and zirconium tetrafluorides and their mixtures was experimentally studied. Compound TiF₄ and its mixture with ZrF₄ in amount no more than 34.3 % are reduced producing a well-formed ingot. When ZrF₄ content is exceeded in the mixture to be reduced as well as during reduction of pure ZrF₄ and the mixture of unseparated rare earth metal fluorides, metal and alloys are produced as embedded particles in solidified slag. Additional heat should be brought to produce qualitative ingot during the reducing process. Qualitative ingots of metal in weight up to 10 kg were produced during calcium-thermic reduction of zirconium and rare earth fluorides with application of high-frequency induction heating

[en] Reactive surface-exposed anatase TiO₂ (a-TiO₂) is highly desirable for applications requiring superior photocatalytic activity. In order to obtain a favorable surface, morphology control of the a-TiO₂ using capping agents has been widely investigated. Herein, we systematically study the effects of different F sources (HF, TiF₄, and NH₄F) as the capping agent on the morphology control and photocatalytic activities of a-TiO₂ in a hydrothermal process. When either HF or TiF₄ was added, large truncated bipyramids formed with the photocatalytically active {001} facet, whereas the NH₄F was not effective for facet control, yielding nanospheres similar to the pure a-TiO₂. The morphology changes were related to the decomposition behaviors of the F sources in the solvent material: HF and TiF₄ decomposed and supplied F⁻ ions before a-TiO₂ nucleation, which changed the nucleation rate and growth direction, leading to the resultant a-TiO₂ morphology. On the other hand, NH₄F supplied F⁻ ions after a-TiO₂ nucleation and could not change the growth behavior. In terms of the photocatalytic effect, the HF- and TiF₄-treated a-TiO₂ effectively decomposed ∼90% and ∼80% of methylene blue, respectively, in 1 h, while ∼60% was decomposed for the NH₄F-treated a-TiO₂. Note that pure a-TiO₂ photocatalytically decomposed only ∼10% of methylene blue over the same time. These results pave the way to precise control of the facet of TiO₂ through using different capping agents. (paper)

[en] The growth of copper crystals on copper, by thermal decomposition of CuF₂, has been studied previously. It has been observed that, at a given temperature, the deposition rate reaches a maximum value which seems to be controlled only by the desorption of fluorine from a complete monolayer.Recent results concerning the thermal decomposition of TiF₄ and Ti and FeF₂ on Fe confirm this mechanism and give a measure of the heat of desorption of fluorine. The deposition rate can be generally improved if one uses the thermal decomposition of subfluorides. A method was developed based on sub-fluoride preparation in situ near the substrate. According to this new method, the formation of the sub-fluoride and its thermal decomposition occur simultaneously. This process is very suitable for the deposition of refractory metals at relatively low temperatures. Some examples are given, concerning mainly the decomposition of WF₅. Generally, in comparison with other halides, it seems that the thermal decomposition of fluorides is preferable for obtaining very high quality deposits, provided the technology necessary for fluorine chemistry is available

[en] Currently, the situation of titanium exploitation and processing in Vietnam is facing difficulties. Titanium mining and processing activities only stop in the field of beneficiation, which doesn't have technology for deep processing of Ilmenite concentrate. There have been many studies on the preparation of TiO₂ from ilmenite concentrate by different methods such as sulfate method, alkali resolution method, ammonium fluoride resolution method ... which have been done in Vietnam. However, most of these solutions have the disadvantages of generating large amounts of wastewater, incurring an additional iron recovery process, and high ammonium fluoride recirculation costs due to additional concentration steps. To reduce costs and expand the line of titanium oxide products of satisfactory quality for pigments and titanium metal production materials, titanium fluoride sublimation technology - the dry method should be researched to reduced wastewater volume and reduced ammonium fluoride recirculating concentration cost. Therefore, the implementation of a scientific and technological research project and processing of ilmenite concentrate using fluoride technology to separate titanium fluoride to produce white TiO₂ powder in Vietnam is urgent and completely suitable for the real situation domestic economy.

[en] Highlights: • The decomposition proceeded through several distinct steps. • The mixed materials show a dramatically low initial hydrogen release temperature. • The additives react with the Mg–B–H compounds rather than acting as catalysts. • The reaction process was studied using an in situ TEM. - Abstract: The thermal decomposition behaviors of Magnesium borohydride [Mg(BH₄)₂] and metal fluoride doped mixtures were studied by temperature programmed desorption measurement/mass spectrometry (TPD/MS), differential scanning calorimetry (DSC) and in situ transmission electron microscope (TEM) observations. The decomposition and release of hydrogen proceeded through several distinct steps, including two polymorphic transitions, ionic Mg(BH₄)₂ melting with solid Mg–B–H amorphous phase formation and Mg–B–H decomposition. The addition of additives such as CaF₂, ZnF₂ and TiF₃ resulted in a decrease in the hydrogen release temperature. ZnF₂ and TiF₃ reduced the initial hydrogen release temperature to ca. 50 °C. However, hydrogen release during the transformation from γ-Mg(BH₄)₂ to the amorphous Mg–B–H compounds at ca. 300 °C was only 4.5 wt.% in contrast to 9.8 wt.% for the direct decomposition of pure Mg(BH₄)₂. TEM observations confirmed that ZnF₂ and TiF₃ reacted with amorphous Mg–B–H compounds rather than acting as catalysts

[en] Electrochemical behaviour of Ti(IV) species in the ionic liquid (IL) 1-butyl-2,3-dimethylimidazolium tetrafluoroborate (BMMImBF₄) was studied by means of chronopotentiometry (CP) and cyclic voltammetry (CV) in melts with different concentrations of TiF₄ (2-35 mol%) within a temperature range of 65-180 deg. C. The electrochemical reduction of Ti(IV) was suggested to proceed via the sequence of one-electron steps with the formation of poorly soluble low valence intermediates (LVI). LVIs undergo further solid-state electrochemical reduction to Ti metal. Thin Ti coatings on a Pt substrate were thus obtained and characterized by ESEM method. FTIR spectroscopy was used for identification of the electrochemical active species of Ti(IV). The reaction 2BF₄^- + TiF₄ ↔ TiF₆^2- + 2BF₃↑ takes place in the concentrated solutions of TiF₄ at elevated temperatures.

[en] Hydrogen evolution reaction (HER) plays an important role in water splitting to produce hydrogen. The high price of precious platinum-based catalysts that are the best HER electrocatalysts by now hampers the commercial application. Low-cost, earth-abundant and highly-efficient HER electrocatalysts are thus long-desired. On the basis of first-principles calculations, we investigated the HER electrocatalytic performance of the non-precious TiF₃ and its analogs. Our calculations showed that TiF₃ and WO₃ can serve as efficient HER electrocatalysts with the overpotentials comparable to those of the platinum-based catalysts. To uncover the origins of electrocatalytic performance, we established a relationship between the surface adsorption ability of a material and its electronic structure. The low HER overpotentials, unique porous structure and high abundance in earth make these materials promising candidates for high-performance HER electrocatalysts.

No abstract available

[en] Using visual-polythermal and thermographical methods the ternary system K₂NbF₇-K₂TiE₆-KCl has been studied. Crystallization fields of initial components and the field of solid solutions of double compounds K₃NbClF₇ and K₃TiClF₆ are outlined. Ternary eutectics at 654 deg C, having the composition K₂NbF₆-41, K₂TiP₆-41, KCl-18 mol.%, is determined. Potassium fluoroniobate and fluorotitanate form continuous solid solutions unstable in the presence of the third component, potassium chloride