Vol 58, No 6 (2017)

Separation in ferromagnetic liquid (FML) is recommended for separating gold from concentration products of placers. Magnetic liquid separation is based on the appearance in FML of a ponderomotive force of a nonuniform magnetic liquid additional to the gravity buoyancy force. A horizontal component of this force in the separation medium bulk participates in the body motion along the equipotential surface across the working zone—to separation cuvette walls and towards the central plane of the pole gap, while the longitudinal component is directed along it. In order to increase process characteristics, it is recommended to limit transverse motions of bodies by vertical partitions established in the separation medium along the separator pole gap. It follows from the results of a theoretical investigation into the particle motion in a separator working zone that the influence of walls manifests itself in the appearance of the counterflow to the particle motion, which causes the rise of the hydrodynamic drag force and deceleration of the particle motion. It is shown that, in the presence of vertical walls, shortening the residence time of a light concentrate fraction in a separator working zone promotes the rise of process productivity in regards to the initial feed and productivity in regards to a heavy fraction (recovery of gold into the heavy fraction). Research tests of competitive separation methods for artificial mixtures of minerals and heavy gold-bearing concentrates are performed using methods of mathematical experiment design. It is proven that, when passing from separation in the FML volume to separation using the developed method, the apparatus productivity increases by 9%, while the recovery of gold into the heavy fraction increases from 84.34 to 91.77% due to a decrease in losses with a light fraction from 15.46 to 7.96%. The material containing gold in amounts more than 800 kg/t is acquired with a decrease in the yield of a heavy fraction by 11 rel. %.

A thermodynamic analysis of phase equilibria in the Cu–Al–Cr–O system is carried out. Thermodynamic modeling of the liquidus surface of the Cu₂O–Al₂O₃–Cr₂O₃ oxide phase diagram is performed. To describe activities of an oxide melt, the approximation of the theory of subregular ionic solutions, the energy parameters of which were determined during modeling, is used. Melting characteristics of the CuCrO₂ compound are also evaluated in the course of the calculation. Coordinates of invariant equilibria points implemented in the Cu₂O–Al₂O₃–Cr₂O₃ ternary oxide system are established by the results of the calculation. Thermodynamic modeling of interaction processes in the Cu–Al–Cr–O system in occurrence conditions of a copper-based metal melt is also performed. The temperature dependence of the equilibrium constant of the reaction that characterizes the formation of the CuCrO₂ solid compound from components of the metal melt of the Cu–Al–Cr–O system is determined. The temperature dependence for the first-order interaction parameter (by Wagner) of chromium and oxygen dissolved in liquid copper is found. The results of thermodynamic modeling for the Cu–Al–Cr–O system are presented in the form of the solubility surface of components in metal, which makes it possible to attribute the quantitative variations in the metal melt concentration with qualitative variations in the composition of forming interaction products. It is determined by the results of modeling that particles of the |Al₂O₃, Cr₂O₃|_sol.sln solid solution are formed at valuable aluminum and chromium concentrations in the copper melt of the Cu–Al–Cr–O system as the main interaction product. The results of the investigation can be interesting for improving the technology process of smelting of chromium bronzes.

In this study, a response surface methodology (RSM) model was used to analyze and optimize the factors affecting copper leaching efficiency in a copper oxide ammonia-ammonium (AA) system based on the parameters of AA concentration (ammonium hydroxide and ammonium bicarbonate matched with 1: 1), leaching time, grinding fineness, liquid-solid ratio, and temperature. The RSM analysis showed that five individual variables had a significant influence and that the interaction between AA concentration and leaching time had the most significant influence on leaching efficiency. In order to improve the estimation accuracy of the copper leaching efficiency, a model consisting of a genetic algorithm and a back propagation neural network (GA-BPNN) was used to optimize the operation index. A back propagation feed forward neural network with 3 layers (5–10–1) was applied to predict copper leaching efficiency. The genetic algorithm was applied to analyze the optimal leaching conditions. The results revealed that the GA-BPNN model outperformed the RSM model for predicting and optimizing copper oxide AA leaching. The optimization results of the GA-BPNN resulted in an R² of 0.99827 and the highest predicted copper leaching efficiency of 79.49% was obtained under the conditions of an AA concentration of 4.78 mol/L, a leaching time of 157 min, a grinding fineness of 86.86% (–74 μm content account), a liquid-solid ratio of 2.87: 1, and a temperature of 313.17 K. A prediction and optimization method combining RSM and GA-BPNN, as used in this paper, can be further employed as a reliable and accurate method for ore leaching.

Parameters of technique to prepare of V₂O₅ by microwave intensification from ammonium metavanadate were optimized using central composite design of response surface methodology. A quadratic equation model for decomposition rate was built and effects of main factors and their corresponding relationships were obtained. The microwave heating behavior indicated that ammonium metavanadate had weak capability to absorb microwave radiation, while V₂O₅ had good capability to absorb microwave radiation. The results of the statistical analysis showed that the decomposition rate of ammonium metavanadate was significantly affected by calcination temperature and calcination time in the range studied. The optimized conditions were as follows: calcination temperature 645.35 K, calcination time 9.66 min and 4.3 g, respectively. The decomposition rates of ammonium metavanadate were 99.13%, which coincided well with experiments values 99.33% under these conditions. These suggest that regressive equation fits the decomposition rates perfectly. XRD reveals that it is feasible to prepare the V₂O₅ by microwave intensification from ammonium metavanadate, which mixed with small amounts of V₂O₅.

In the present study, yttrium(III) ion imprinted polymers (Y(III)-IIPs) and non-imprinted polymers (and non-Y(III)-IIPs) materials were synthesized. The materials were characterized by FTIR spectroscopy, scanning electron microscopy (SEM)-EDS studies. Characterization by FTIR showed that the IIPs have been successfully synthesized as indicated by the absence of a peak for the alkene functional group at 3000–3300 cm^–1. From the FTIR data and SEM-EDS images showed that Y(III) ions have been successfully released from the polymer. The retention properties by batch procedure showed that the adsorption capacity of Y(III)-IIPs was 10.26 mg/g at pH 7 with a contact time of 10 min. Y(III) ions adsorption onto Y(III)-IIPs follows the Langmuir adsorption isotherm with a correlation coefficient of 0.9671, which showed a maximum adsorption capacity value of 14.68 mg/g and follows the Lagergren pseudo-second order kinetics model. The IIPs materials selectivity against other rare earth metals showed a better selectivity than NIPs.

The relevance of this research is connected to the increasing requirements for accuracy in stamped parts produced from aged aluminum alloys, and can also be applied for making layered composites. Indexed requirements can be provided by controlling the structure of sheet blanks, particularly by the phase composition and distribution behavior. Results of experimental research into the effect of aging modes on composition, dispersion behavior, and stamping number of sheet samples of the D16 aluminum alloy (AA2014) are presented. Heat treatment includes quenching from a temperature of 500°С into water of room temperature and further aging: natural aging for 7 days and artificial aging at temperatures of 50, 100, 150, and 200°С with a duration at each temperature of 15, 30, 60, 120, and 240 min. A method of estimating the quantity of the characteristics of dispersion phases is proposed for the microstructural picture. Stamp ability is evaluated using the stamping number, which is the ration between yield stress and tensile strength. It is found that increasing aging temperature and durance leads to the growth of the stamping number, which shows a low ability for sheet-stamping operations of alloy. Aging at 50°С did not lead to the sedimentation of dispersion phases for either optical metallography or scan electron microscopy. The inhomogeneity of phase dispersion inside the grain grows at the initial stages of aging, when durance is less than 1 h and temperature is 100, 150 and 200°С. Further increasing durance to 4 h leads to inhomogeneity decreasing. There is no correlation between the uniformity of phase dispersion and the stamping number. The chemical composition of phases plays the main role in stamping number, outside of phase-dispersion uniformity. The phase-composition changes depend on the mode of heat treatment: at an annealed and naturally aged state, the θ and S phase is sediment. After aging at a temperature lower 150°С after a short durance of less than 1 h, the θ, S and T phases are revealed; the θ phase appears after aging at temperatures higher than 150°C and long durance reaching 4 h.

In the present study, the effects of back pressure on the filling fraction of die and the effective strain distribution throughout severely deformed material during pure shear extrusion, a novel severe plastic deformation process, are investigated by finite element analysis. A pure shear extrusion process found in the literature is employed and the predicted forming load is compared with experiments. A good agreement is observed between the results of the simulation with Coulomb friction of 0.12 and experiments. Various back pressures are applied to plunger at the exit channel of the die, and their influence on the filling fraction of the die and the effective strain in severely deformed billets are studied, indicating that the homogeneity of the effective strain on the cross-section of the deformed billet is decreased slightly. It is also found that the filling fraction of the die exit channel as well as average strain on the cross-section of the billet are increased.

Microstructural features of new master alloys of the Al–Hf–Sc system with metastable aluminides with a cubic lattice identical to the lattice of a matrix of aluminum alloys are investigated using optical microscopy, scanning electron microscopy, and electron probe microanalysis. Binary and ternary alloys are smelted in a coal resistance furnace in graphite crucibles in argon. Alloys Al–0.96 at % Hf (5.98 wt % Hf) and Al–0.59 at % Hf (3.77 wt % Hf) are prepared with overheating above the liquidus temperature of about 200 and 400 K, respectively. Alloys are poured into a bronze mold, the crystallization rate in which is ~10³ K/s. Metastable Al₃Hf aluminides with a cubic lattice are formed only in the alloy overheated above the liquidus temperature by 400 K. Overheating of ternary alloys, in which metastable aluminides Al_n(Hf_1–xSc_x) formed, is 240, 270, and 370 K. Depending on the Hf-to-Sc ratio in the alloy, the fraction of hafnium in aluminides Al_n(Hf_1–xSc_x) varies from 0.46 to 0.71. Master alloys (at %) Al–0.26Hf–0.29Sc and Al–0.11Hf–0.25Sc (wt %: Al–1.70Hf–0.47Sc and Al–0.75Hf–0.42Sc) have a fine grain structure and metastable aluminides of compositions Al_n(Hf_0.58Sc_0.42) and Al_n(Hf_0.46Sc_0.54), respectively. Sizes of aluminides do not exceed 12 and 7 μm. Their lattice mismatch with a matrix of aluminum alloys is smaller than that for Al₃Sc. This makes it possible to assume that experimental Al–Hf–Sc master alloys manifest a high modifying effect with their further use. In addition, the substitution of high-cost scandium with hafnium in master alloys can considerably reduce the consumption of the latter.

The electrochemical and corrosion behavior of four alloys (wt %) is investigated: Al–6Ca (further Al6Ca), Al–6Ca–1Fe (further Al6Ca1Fe), Al–1Fe (further Al1Fe), and Ak12M2. An increased iron content (up to 1%) in alloys is necessary for the high productivity of casting under pressure. Electrochemical studies are performed in a 3% aqueous NaCl solution at 26 ± 0.5°C using an IPC-Pro 3A digital potentiostat (IPC-2000). Anodic polarization is performed in a potentiodynamic mode with a potential scan rate of 1 mV/s. The initial polarization potential is–800 mV with respect to the standard hydrogen electrode. The direction of the potential scan was changed to inverse upon the “critical” current density i_cr = 10 mA/cm² performing polarization with the same rate. The tendency of the alloy to form pits was judged by the ratio of amounts of electricity that passed through the electrode before pitting formation and their repassivation (Q_for/Q_inv) and values of pitting resistance bases: the difference in the pitting formation potential and stationary potential and the difference in the repassivation potential and stationary potential. Corrosion tests of casting aluminum alloys were performed holding the samples in a salt fog chamber and in a 3% aqueous NaCl solution for 700 h. After these holdings, the surface morphology of the samples was investigated using an Olympus GX51 optical microscope. It is established that Al6Ca1Fe and Al6Ca experimental alloys, in contrast to the AK12M2 industrial alloy and Al1Fe alloy, are not subjected to pitting corrosion in a 3% aqueous NaCl solution. It is assumed that the increased corrosion resistance of Al6Ca1Fe alloy is caused by the fact that iron enters the Al₁₀CaFe₂ intermetallic compound, which is not an efficient cathode because of the considerable negative potentials of Al and Ca. Due to the high casting and mechanical properties of the Al6Ca1Fe alloy, which are no worse than the properties of eutectic silumin and surpass them by the corrosion resistance, the Al6Ca1Fe alloy is promising for use in an industrial scale.

The structure formation and properties during infiltration, free sintering, and spark-plasma sintering in Cu–(12.5–37.5 vol %) powder materials Ti₃SiC₂ are investigated by electron microscopy, X-ray phase analysis, and energy-dispersion analysis. The independence of the phase composition of composite materials (CMs) on the sintering method and temperature in a range of 900–1200°C is established. The peculiarities of formation of the CM structure during sintering are the intercalation of silicon from titanium carbosilicide and the formation of a carbon solid solution based on Ti₅Si₃(C) titanium disilicide, small amounts of titanium carbide, silicon carbide, and TiSi₂ silicide. An increase in Ti₃SiC₂ in the CM certainly lowers electrical conductivity, but considerably increases the hardness, strength, and electroerosion wear resistance of CM electrodes for electroerosion broaching.

Highly porous permeable materials have been fabricated from zirconia nanopowders stabilized with 2, 3, and 7 mol % yttria by duplicating the polymer matrix. It is shown that the samples are characterized by a complex surface relief formed by sintered powder agglomerates resulted from the agglomeration treatment. It is established by Raman spectroscopy that the phase composition of the material surface is identical to the composition of initial nanopowders and is presented only by the tetragonal modification in all studied cases. It is shown that the deposition of nickel (an active catalytic component) from nickel nitrate solutions or the deposition of metallic nickel on surfaces of ZrO₂ stabilized with 3 mol % Y₂O₃ causes the formation of a monoclinic modification. Only a tetragonal modification is identified on the surface of highly porous ZrO₂ samples stabilized with 2 and 7 mol % Y₂O₃. When using the peak splitting procedure, the shift of the integral peak intensity toward lines characteristic of the monoclinic modification is fixed.

The thermal stability of multilayered nanostructured coatings is evaluated by analyzing the diffusion mobility of layer components. The possibility of increasing the thermal stability of multilayered coatings based on mutually soluble Ti–Al–N and Cr–N layers due to the introduction of an additional barrier layer based on Zr–N into a multilayered nanostructure is investigated in detail. Calculated diffusivities of basic metallic elements of the coating into corresponding nitride layers upon heating in a temperature range of 800–1000°C evidence the absence of noticeable diffusion spread of layer boundaries in the presence of the Zr–N-based barrier layer. For example, their values lower upon its introduction (it is found at t = 1000°C, cm²/s: D_Cr/TiN = 5 × 10^–17, D_cr/ZrN = 2 × 10¹⁸, \({D_{Ti/C{r_2}N}}\) = 9 × 10^–18, and D_Ti/ZrN = 3 × 10^–18). The physicomechanical properties of coatings do not vary upon their vacuum annealing at t < 900°C; however, they noticeably lower with a further increase in temperature due to the degradation of a multilayered coating structure during annealing.