Vol 60, No 2 (2019)

To investigate the effect of kaolin particles on the flotation performance and froth stability of different particle sizes of bastnaesite, batch flotation tests and froth stability experiments were performed. The results demonstrated that poor froth stability of the coarse particle size bastnaesite led to poor flotation recovery. The medium particle size led to appropriate froth stability and also improved the recovery of bastnaesite. The fine particle size yielded an excessively stable froth, yet did not increase the adherence of bastnaesite particles to the bubbles, but it may have increased the entrainment of kaolin. A longer flotation time may have contributed to improving the recovery of the fine size fraction bastnaesite due to its greater flotation rate. Yet, it had little impact on the recovery of the coarse-grained bastnaesite. In addition, a low proportion (20%) of kaolin improved the recovery and flotation rate of the coarse size fraction bastnaesite. In general, however, the presence of kaolin was detrimental to the flotation performance of bastnaesite. Moreover, the presence of kaolin increased the froth stability of the bastnaesite and resulted in more hydrophilic kaolin particles being entrained into the concentrate products.

The results of studying the utilization of waste effluents of a metallurgical enterprise using centrifugation and vacuum-sublimation methods are presented. The objects of study are industrial effluents of titanium–magnesium production. The influence of the centrifuge rotation speed, duration, temperature, and solid content on the separation of industrial effluents into liquid (centrate) and solid (sediment) phases is studied. A complex of studies based on using the multifactorial experimental design procedure is performed to evaluate the influence of each factor. It is established that the optimal centrifugation parameters are a rotor speed of 3000 rpm and a duration of 30 min. The centrate contains suspended substances in an amount of 195 mg/dm³, chlorides in an amount of 26 500 mg/dm³, and dry residue in an amount of 39 750 mg/dm³—evidencing its high mineralization and need for the further purification. The reasonability of using the thermal method of centrate demineralization using a rotary vacuum evaporator is shown in laboratory conditions. Optimal process parameters are t = 70°C, P_res < 50 mbar, and τ = 30 min. The residue yield after the vacuum sublimation is 6% of the centrate weight. No suspended substances are found in the condensate, and the chloride content was 50 mg/dm³. The proposed utilization technology of industrial effluents of the titanium–magnesium production will promote the development of a closed water-supply cycle at the enterprise. The residue after the vacuum sublimation of the centrate, which contains mainly alkali metal and alkali-earth metal chlorides, can be recommended as an additive for the preparation of anti-ice materials as well as drilling fluids for well mud solutions.

It is known that technical aluminum with an elevated content of iron, silicon, and other impurities cannot find application in industry because of its low performance characteristics. Therefore, the development of new alloy compositions based on such a metal is very urgent. Eutectic (α-Al + Al₃Fe) in the Al–Fe diagram and hypereutectic alloys are promising because, having a minimal crystallization range, they correspond to an iron content of 2–5 wt %. The alloy of the composition Al + 4.5% Fe (AZh4.5) is accepted in this study as a model alloy and is subjected to modification with tin. The temperature dependence of heat capacity of the tin-doped AZh4.5 alloy is determined and the variation in its thermodynamic functions is calculated. Investigations are performed in the cooling mode using a computer and the Sigma Pilot program. The polynomials of the temperature dependence of heat capacity and varying the thermodynamic functions (enthalpy, entropy, and Gibbs energy) of the tin-doped AZh4.5 alloy and reference sample (Cu) are established with correlation coefficient R_corr = 0.999. It is established that the heat capacity of the initial alloy decreases with an increase in the tin content and increases with an increase in temperature. Enthalpy and entropy of the AZh4.5 alloy increase with an increase in the tin content and temperature, while the Gibbs energy decreases.

The deformation schematics of rolling, equal channel angular pressing, and nonequal channel angular pressing are evaluated. It is noted that the transformation of a circular-section billet into a rectangular-section one with a small thickness is hampered during rolling. This problem also cannot be solved by the application of equal channel angular pressing. In connection with this fact, it is proposed to apply the schematic of nonequal channel angular pressing to workup the cast structure of magnesium. An experimental procedure based on the cold extrusion of cylinders 42 mm in diameter and 40 mm in height is described. The strip at the outlet was 40 mm wide and 1 mm in thickness. The relative reduction of the billet material determined through the area ratio is 96% at an elongation ratio of 17. Specific pressures at the puncheon in the beginning of extrusion is 1200–1300 MPa, while the extrusion force is 1670–1800 kN. A sheet billet is cut into trial lengths, which were rolled at room temperature into foils 50 and 10 μm in thickness without intermediate annealing. Rolling is performed using a Duo mill with a relative reduction of 12–20% at an average speed of 0.1 m/s. To fabricate the foil 50 μm in thickness, 20 passages are performed with a summary relative reduction of 95%. The results of computer simulation by the finite element method show that a constant degree of deformation is attained at a rather sufficient distance from the front end, which is evaluated at the 50-fold strip thickness. The configuration of the deformation region is determined by the calculation of the strain rate field. Power inputs are evaluated. This complex of computational and experimental works allows one to establish that it is possible to fabricate a thin sheet billet with a plasticity level sufficient for subsequent sheet rolling from cylindrical cast magnesium billet for one operation at room temperature. A sheet billet formed in the proposed process has a high workup level by plastic deformation, which is caused by the forming schematic in the presence of a high level of elongation and shear strains. Despite the high-pressure level that should be applied to form the schematic of the uniform compression, allowing for the absence of necessity of billet heating, power inputs turn out no higher than in conventional treatment processes.

The results of fabricating dense Fe–Ag and Fe–Cu nanocomposites from mixtures of powders consolidated by high-pressure cold sintering and from nanosized powders of silver (Ag), iron (Fe), and copper (Cu) are reported. The results of mechanical tests of Fe–Ag and Fe–Cu nanocomposites are presented. Nanocomposite powders were prepared by milling the micron powder of carbonyl iron (Fe) and nanosized silver oxide (Ag₂O) powder, as well as iron and cuprous oxide (Cu₂O) nanopowders in a high-energy attritor. The microstructure was investigated using a high-resolution scanning electron microscope. Compacts with a density of about 70% of the theoretical density were annealed in hydrogen to reduce silver oxide and cuprous oxide to metals and remove oxide films from the surface of iron powder particles. Then cold sintering followed—high-pressure consolidation at room temperature. The data on the pressure dependence of density of samples are found in a range of 0.25–3.0 GPa. Densities higher than 95% of the theoretical density are attained for all nanocomposites at a pressure of 3.0 GPa, while a density of about 100% is attained for Ag and Cu powders. High mechanical properties are found for all compositions in experiments for the three-point bending and for compression. It is established that mechanical properties of nanocomposites are noticeably higher than for composites formed from micron-sized powders. The higher plasticity was observed for Fe‒Ag and Fe–Cu nanocomposites when compared with the samples formed from nanostructured Fe.

Experimental data on the fabrication of composites based on the ZrB₂–CrB system by SHS compaction are presented. Adiabatic combustion temperatures of the Zr–Cr–B system and compositions of equilibrium synthesis products are calculated using the thermodynamic data, and optimal fabrication conditions for SHS composite production are determined. It is shown that the equilibrium synthesis products are ZrB₂ and CrB refractory compounds. They provide the high thermodynamic stability of SHS composites, which are applied as a dispersed phase (ZrB₂) and ceramic binder (CrB). The adiabatic combustion temperature decreases from 3320 to 2350 K with an increase in the binder content from 25 to 64 wt %. A hard dispersed phase (ZrB₂) and molten binder (CrB) are formed under these conditions. It is revealed that the formation of a molten binder provides the formation of SHS composites with residual porosity lower than 1%. The influence of the composition of the reaction mixture on the phase composition, microstructure, and physicomechanical characteristics of SHS composites are investigated. It is established that the residual porosity at the CrB content in the limits of 30–50 wt % is <1%. Herewith, the Vickers hardness varies in a range of 31.3–42.6 GPa, while the ultimate bending strength varies in a range of 480–610 MPa. It is shown that physicomechanical characteristics depend on the residual porosity of SHS composites. Cutting plates are fabricated from the ZrB₂–30CrB SHS composite and testing is performed with the treatment of high-hardness chilled steels. The results evidence that ceramic cutters made of the ZrB₂–30CrB composite possess high wear resistance when treating ShKh15 bearing steel with hardness of 61–65 HRC.

The in situ synthesis of the Ti₂AlNb-based intermetallic alloy was studied using selective laser melting of powder materials. The object of research was the Ti–22Al–25Nb (at %) alloy, the main phase of which is the Ti₂AlNb intermetallic compound with an ordered orthorhombic lattice (O phase). The Ti–22Al–25Nb alloy has high mechanical properties both at room temperature and at elevated temperatures, as well as a low specific weight, and is considered a promising material for use in the aerospace industry. To perform the experiments, a mechanical mixture of pure powders of titanium, aluminum, and niobium in a ratio necessary to synthesize the Ti–22Al–25Nb alloy was used. Selective laser melting relating to additive technologies is most promising to fabricate parts by the layer-by-layer addition of materials. The use of this technology makes it possible to fabricate complexly shaped parts based on the CAD model data. Compact samples for the investigation are performed by selective laser melting. The microstructure, density, phase composition, and microhardness of these samples are investigated. The influence of the thermal treatment in the form of homogenization at 1250°C for 2.5 h and subsequent aging at 900°C for 24 h on the microstructure, phase composition, and chemical homogeneity of the samples is also investigated. It is shown that the compact material formed by selective laser melting contains unmolten niobium particles. Homogenizing annealing makes it possible to attain the complete dissolution these particles in the material; due to this, the material microstructure consists of B2 phase grains of various sizes and needlelike precipitates of the orthorhombic phase.

Nanosized titanium dioxide allows solving complex engineering problems. One such a problem is the development of materials and coatings that reduce the probability of nosocomial infections of the surface of orthopedic structures, including implant systems. This article presents the results of studying anatase ceramic coatings deposited according to the sol–gel technology on a sintered material based on nanosized titanium dioxide powder (rutile modification) by the Raman spectroscopy, X-ray diffraction analysis, and scanning electron microscopy. The resulting coating has a complex layered structure, which almost completely consists of titanium dioxide in the anatase phase according to the Raman spectroscopy data. The simultaneous occurrence of both phases is fixed in a coating. The identification of rutile in X-ray diffraction patterns is apparently associated with the fact that rutile with a varied peak intensity is preferentially formed at the first deposition stages of the coating on the polycrystalline rutile surface. The fact that nonstoichiometric phases are also present in X-ray diffraction patterns makes it possible to assume that the phase composition of the coating over the thickness is nonidentical and presented by a gradual layerwise transition from rutile to anatase. The coating thickness is 60 ± 15 μm. It is presented by lamellar blocks of various sizes. The thickness of a separate plate is in the limits of 60–80 nm. This procedure allows the deposition of an anatase coating not only on the ceramic samples based on titanium dioxide, but also on the surface of titanium implants when preliminarily forming the titanium dioxide layer in the form of rutile on the metal surface. The experiments on the investigation into the antibacterial properties and morphological characteristics of bone tissue contacting with the implant are performed at the Department of the Prosthetic Dentistry at the Perm State Medical University.