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[en] Measurement of redox potential in fluoride media is a major problem due to the difficulty to design a reference electrode with high stability, high mechanical resistance and high accuracy. In the frame of molten salt reactor studies, a dynamic reference electrode (DRE) is developed to measure redox potential in fluoride molten salt at high temperature. DRE is based on the in-situ generation of a transient redox system. The choice of the redox couple corresponds to the cathodic limit of the molten salt considered. As a preliminary step, the demonstration of feasibility of generating a DRE was done in LiF-NaF-KF (46.5–11.5–42 mol%) media at 500 °C. In this salt, the reference redox system generated by coulometry at applied current is KF/K, metallic potassium being electrodeposited on a tungsten wire electrode. The validation of the DRE response and the experimental optimization parameters for DRE generation were realized by following the NiF2/Ni redox potential evolution as a function of NiF2 concentration in the fused salt. The current value applied for DRE generation was optimized. It depends on the amount of metallic cations contained in the fused salt and which can be electrochemically reduced simultaneously during the DRE generation. The current corresponding to the DRE generation has to be 4 times greater than the current corresponding to the reduction of the other elements.
[en] This article considers obtaining and thermodynamic characteristics of cobalt (II) and nickel (II) fluorides. Therefore, tetrahydrate of cobalt (II) and nickel (II) fluorides have been obtained by interaction of corresponding metal of hydroxo carbonate with hydrofluoric acid solutions of different concentrations. The enthalpy value of this and adverse reactions has been determined by means of calorimetry method. According to thermochemical cycle, the values of enthalpy of formation of tetrahydrate fluorides and hydroxo carbonates of cobalt (II) and nickel (II) have been defined. (author)
[en] The lowest order spin wave theory for CsNiF3 is presented and compared with neutron scattering experiments and the predictions based on the dilute soliton gas model. We conclude that further experiments and theoretical development are necessary to distinguish the soliton contribution to the central peak intensity from the scattering by pairs of spin waves
[en] Results of neutron scattering studies on CsNiF3 in an external field are presented. These results give direct experimental evidence for the existence of nonlinear (soliton-) excitations in this 1D-ferromagnetic chain system. These solitons can be regarded as a gas of noninteracting relativistic quasiparticles. (orig.)
[en] The magnons in the canted rutile-structure antiferromagnet NiF2 have been studied by Raman scattering. Results are presented for the polarization dependences of the one-magnon spectum over a wide range of temperatures below T N and the two-magnon spectrums at low temperatures. A theoretical analysis of the data, including the important role of the spin canting for the one-magnon properties, is shown to provide good agreement with the measurements
[en] The results of studying zirconium tetrafluoride purification from hafnium by the process of multiple sublimation of ZrF4 from HfF4 in its structure in the presence of a sorbent are given. The best sorbents are found to be difluorides of metals from the iron subgroup. They ought to be added as 3-5 wt. % to grinded complex zirconium and hafnium tetrafluoride to be separated. Sublimation distillation of ZrF4 out of this mixture is shown to be carried out at temperature of 750-850 deg C and residual pressure of 3-5 Pa in the sublimators with the sublimation degree of 60 %. Zirconium tetrafluoride in which the hafnium content is 0.05 wt. % was produced after eight sublimation cycles in the presence of a sorbent (nickel difluoride). The method can be realized in the production of zirconium of reactor purity according to the anhydrous fluoride technique
[ru]Приведены результаты исследований по очистке тетрафторида циркония от гафния способом многократной сублимации ZrF4 от внедренного в его структуру HfF4 в присутствии сорбента. Установлено, что наилучшим для этой цели сорбентами являются дифториды металлов подгруппы железа. Их следует добавлять к измельченному разделяемому комплексному тетрафториду циркония и гафния в количестве 3-5 % (по массе). Показано, что сублимационную отгонку ZrF4 из этой смеси следует проводить при температуре 750-850 град С, остаточном давлении в сублиматоре 3-5 Па и степени сублимации 60 %. При 8 циклах сублимации в присутствии сорбента (дифторида никеля) получен тетрафторид циркония, содержание гафния в котором 0.05 % (по массе). Способ может быть реализован в производстве циркония реакторной чистоты по безводной фторидной технологии
[en] Highlights: • The addition of NiO reduced the crystallite size of Cr2O3. • NiF2 formed during the pre-fluorination provided new surface acid sites. • NiO/Cr2O3 catalysts showed higher activities and better stability than the Cr2O3. • Much lower Ea on 15NiO/Cr2O3 than that on Cr2O3 implied different reaction pathways. • Acidic Ni2+ and basic F− ions were respectively responsible for cleavage of CF and CH bonds. Catalytic dehydrofluorination of 1,1,1,3,3-pentafluoropropane to 1,3,3,3-tetrafluoropropene was performed on a series of fluorinated NiO/Cr2O3 catalysts. The NiO/Cr2O3 catalysts were more active than the Cr2O3 because the new acid sites provided by NiF2 had higher turnover frequencies (9.43 × 10−3 − 12.08 × 10−3 s−1) than those on the Cr2O3 (4.55 × 10−3 s−1). Also, the NiO/Cr2O3 was more stable than the Cr2O3 due to its lower density of surface acid sites, which alleviated the coke deposition on the catalyst as evidenced by the Raman spectroscopic results. The kinetic results revealed that the15NiO/Cr2O3 had much lower activation energy (63.6 ± 4.5 kJ mol−1) than the Cr2O3 (127.6 ± 3.8 kJ mol−1). Accordingly, different reaction pathways on the two catalysts were proposed, which involved the cleavage of the CF and CH bonds on the surface acid and base sites, respectively.
[en] The interaction of nickel carbonate with hydrofluoric acid has been studied in the present article. The reactions of hydroxo carbonate nickel with hydrofluoric acid in the dissolution calorimetry have been studied in order to determine the reaction enthalpy of formation of nickel fluoride tetrahydrate. The thermal stability of nickel fluoride tetrahydrate by means of static method has been studied. The enthalpy values of formation of nickel fluoride tetrahydrate and nickel fluoride monohydrate have been obtained for the first time.