No 2 (2023)

The nickel refining company "Norilsk Nickel Harjavalta Oy" (NNH) produces three main types of nickel products: cathode nickel, nickel powders (briquettes), nickel salts. The decisive role in achieving high performance and guaranteed quality the nature of the impurities distribution and  their behavior control, in particular selenium, plays a role in nickel products. Selenium has a sharply negative effect on the process of obtaining a cathode nickel base. At elevated concentrations in nickel-cobalt solution, this impurity makes it impossible to stable obtain commercial nickel cathodes. The study of the selenium behavior patterns in the processing circuit of metallurgical intermediates, such as feinstein and stein of electric slag-cleaning furnace (ESCF), made it possible to make the necessary changes to the technological scheme of the NNH leaching shop and to clarify the operating parameters of the main operations. A hypothesis is proposed about the possible mechanism of the effect of metallized fraction (alloy) contained in the feedstock on the process of reducing Se6+ to Se4+. The experiments performed confirmed the direct dependence of the selenium deposition degree from the solution to the solid precipitate from the alloy content in the feedstock.  It has been established that by combining the applied ESCF matte with feinstein and/or nickel concentrate (NC) from feinstein separation, it is possible to effectively control the distribution of selenium in NNH technology, preventing its critical concentrations in nickel catholyte. Based on the research results, a two-flow scheme for processing processed products has been implemented, in which it is envisaged to use a combination of NC and products with a high content of metallized fraction. This method allowed to minimize the concentration of selenium in nickel catholyte.

The study results of the structure and mechanical properties of magnesium alloys obtained by rotary forging, similar in composition to the IMB7-1 alloy of the Mg-Y-Gd-Zr system, are presented. Mechanical properties were determined after rotary forging and after rotary forging with subsequent aging at 200 °C for up to 64 hours. The alloys were aged both immediately after rotary forging and after homogenization at 515 °C of the deformed alloys obtained. It is established that rotary forging contributes to the hardening of the studied alloys as a result of grain grinding and intensive twinning. Aging carried out after rotary forging leads to additional hardening of alloys as a result of the decomposition of supersaturated magnesium solid solution. Annealing after rotary forging increases the grain size in the studied alloys due to collective recrystallization and thereby reduces the strength properties of the alloys.

Rhodium borides of the compositions Dy0,8Er0,2Rh3,8Ru0,2B4 and Dy0,6Er0,4Rh3,8Ru0,2B4 were synthesized on the basis of the compound DyRh3,8Ru0,2B4 by partial substitution of dysprosium (Dy) with erbium (Er) with a LuRu4B4 type structure. The dependences of χ-1(T), M(B) and Bc2(T) were studied for these compounds. It is established that the compounds Dy0,8Er0,2Rh3,8Ru0,2B4 and Dy0,6Er0,4Rh3,8Ru0,2B4 are magnetic superconductors with a critical temperature Tc ≈ 5.1 and 5.8 K, respectively; at T ≈ 3 K the magnetic subsystem of these compounds goes into the antiferromagnetic state. Based on measurements of the magnetic moment from the field (M(B)) for samples of compounds Dy0,8Er0,2Rh3,8Ru0,2B4 and Dy0,6Er0,4Rh3,8Ru0,2B4, using the Bean model, dependences on the field of the critical current density jc(B) and the reduced pinning force fp(h) are obtained. The value of jc   in the studied samples did not exceed 400 A/cm2 at T ≈ 2 K. It is established that in the case of magnetic superconductors with antiferromagnetic ordering (Dy0,8Er0,2Rh3,8Ru0,2B4 and Dy0,6Er0,4Rh3,8Ru0,2B4) at h > 0.4 there is a significant deviation from the law of similarity.

As part of the research on the development of a new standard for welded and seamless stainless steel pipes, the microstructure, phase composition and mechanical properties in the temperature range of 20-650 °C of pipe samples from austenitic chromium-nickel steels of the Fe-18Cr-10Ni family were evaluated. Significant spread of mechanical characteristics is shown, a quantitative assessment of the contribution of various hardening factors is carried out. It is noted that grain size and solid-solution hardening with carbon, nitrogen or titanium have the most significant effect on mechanical properties, providing up to 45% of the yield strength of steel. It is established that the temperature dependence of the tensile strength is determined by the resistance to the formation of deformation martensite and the intensity of the action of dynamic deformation aging.

Estimates of the nitrogen solubility in model steels of various compositions based on Fe-13%Cr with additional alloying (a small amount from hundredths of a percent to 1.5%) with elements (Mn, Mo, V, Nb) that increase the solubility of nitrogen in iron-based solid solutions are calculated. 60 variants of compositions were studied. Based on previously obtained own experimental data for nitrogen-containing steels with a content of 16%Cr-5%Ni-Nb for martensitic steel, a preliminary assessment of the composition stability coefficient of nitrogen used in the calculations of its (nitrogen) solubility was carried out. The resulting value of the composition stability coefficient  is lower than for austenitic steels. For steels of all composition variants with calculated nitrogen content and different content of additional alloying elements (Mn, Mo, V, Nb), the phase composition was estimated using a modified Scheffler—Delong diagram and a nonequilibrium Potak—Sagalevich diagram for steel, which processed on solid solution.  It is shown, among other things, that all compositions of Fe-13%Cr-Mn, Mo, V, Nb with a low carbon content (0.03—0.05%) with the maximum calculated solubility of nitrogen in the metal are in the martensitic-ferritic region. By calculation, the temperature of the martensitic transformation beginning was obtained using the empirical Finkler—Schirra formula and a correlation was established between the temperature of the martensitic transformation beginning and the Niequivalent/Crequivalent ratio (chromium and nickel equivalents calculated using formulas for the modified Scheffler—Delong diagram).

The influence of the sorption conversion conditions for the eudialyte concentrate in low-concentration nitric and hydrochloric acid solutions (concentration and consumption of acid, temperature and duration of the process, sorbent consumption) on the valuable metals extraction efficiency (zirconium, hafnium, niobium, rare earth elements, titanium, manganese) into sulphocationite was studied. Optimal conditions for the process have been determined. It has been shown that sorption conversion in nitric acid solutions is more effective for separating valuable components from the silica component of eudialyte concentrate compared to both the traditional method decomposition by nitric acid and the method of sorption conversion in sulfuric and hydrochloric acid environments. The reasons for the loss of valuable metals and the behavior of natural radionuclides are discussed.