Vol 58, No 4 (2017)

Antimony oxide ore beneficiation has become one of the world’s largest mineral processing conundrums. In recent years, many experimental studies dealing with antimony oxide ore have been carried out, resulting in new technical achievements. Much attention has been paid to improving the mineral processing technology of antimony oxide based on such experiments. This work presents the latest research on antimony oxide ore beneficiation, outlining recent progress and developments in antimony oxide ore beneficiation around the world.

To increase the accuracy of results, two methods for investigating wetting and spreading processes on a solid substrate are studied. In the first method, liquid drops are used; in the second method, bubbles are used. The shapes of drops and bubbles vary upon spreading, and this fact can be evaluated quantitatively only by means of the Laplace equation, but the equation is applied only in the case of bubbles (the second method). In the case of the first method, this circumstance excludes the purity control of the spreading drop surface. The influence of microcontaminations on the results is considered based on precision calculations performed for both methods. Spreading curves of nanobubbles with initial diameters of 20 and 10 nm on the substrates with various wettabilities are calculated, and wettability is evaluated not by the numerical value of the wetting angle but by the corresponding easily implemented examples of such substrate Γ, Φ, and H_x, where x is the surface fraction under a bubble coated by ionogenic collector molecules: 0.8, 0.6, 0.4, and 0.2. Spreading curves clearly illustrate the range of possible nanobubble spreading from the limiting one on the Γ substrate to the almost zero one on the Φ substrate, as well as the sources of energy provision of spreading and their depletion causes. The informativity of spreading curves is caused by the fact that more than ten bubble and substrate parameters are applied in their calculation. When using the reagents, the flotation activation can spread to larger bubbles.

Results of an analysis of thermodynamic characteristic and the investigation into kinetic regularities of leaching a new type of sulfated copper–zinc middlings formed with the removal of sulfide materials that cannot be effectively selected by flotation are presented. When analyzing the kinetic curves, it is established that the reaction rate abruptly differs between the initial time period (30 min) and the subsequent period at any acid concentration in a range of 0–20 g/dm³. In the initial instant, the rate is controlled only by the external diffusion, while after 30 min of the process, the kinetic obstacles start to manifest themselves. Reaction orders of cinder leaching are determined to be as follows: 1.0 ± 0.1 for copper, 0.87 ± 0.1 for zinc, and 0.56 ± 0.1 for iron. A calculation of the apparent rate constant of the leaching reaction showed its weak temperature dependence, which correlates well with the thermodynamic analysis data.

A new method was proposed for extracting selenium from copper anode slimes with a low concentration of nitric acid in a sealed sulfuric acid leaching system. It is performed under an atmosphere of oxygen which allowed for a cyclic utilization of nitric acid. The effects of main parameters on selenium leaching were studied. The mineralogical characterizations of the typical samples were investigated by XRD and SEM. The results showed that the optimal conditions of the process are considered to be total gas pressure of 0.1 MPa, leaching temperature of 388 K, solid-liquid ratio of 0.20 g mL^–1, H₂SO₄ concentration of 2 mol L^–1, HNO₃ concentration of 0.07 mol L^–1 and leaching time of 2 h. The high selenium leaching efficiency of 99.23% was obtained under these conditions. According to the results of XRD and SEM-EDS, Cu–Ag selenide in the raw anode slimes is difficult to be leached with sulfuric acid alone; copper can be leached more easily from Cu-Ag selenide than silver; selenide is oxidized into the solution, undergoing the intermediate product of elemental selenium.

Lost foam casting (LFC) is currently one of the most efficient and promising methods of fabricating high-quality thin-wall castings possessing specified dimensional accuracy, required surface roughness, and other properties. This technology is widely used in the production of aluminum alloy products. To minimize costs in the fabrication of wares and to fabricate high-quality castings, it is reasonable to use an increased amount of secondary materials in the charge, herewith paying attention to the melt overheating temperature and holding time. The results of studying the temperature modes of smelting pouring aluminum alloys in the LFC are presented. The most efficient modes in manufacturing conditions under consideration which provide the best quality characteristics of leak-tight castings by dimensional accuracy and surface roughness were as follows: the melt overheating temperature is 880–890°C and the melt pouring temperature into the casting mold is 820–830°C. The influence of various variants of temperature parameters of smelting and pouring the melt of the AK7 composition during the LFC on the content of nonmetallic inclusions in the cast state is investigated. It is revealed that the minimal γ-Al₂O₃ content in the final alloy is provided by a melt overheating temperature of up to 880–890 or 940–950°C and a melt pouring temperature into the casting mold of 820–830°C.

Pressing methods of prismatic and screw metallic profiles are considered. An example of cold pressing of a billet from copper M4 with the formation of a solid square-cross-section profile is presented. Conventional pressing (extrusion) and extrusion followed by torsion pressing (extrusion and screw pressing (ESP)) are compared by mechanical characteristics, energy intensity, and the destruction character of copper samples. Herewith, the ESP of the billet was performed in one facility during the united production process. Pressing prismatic and screw profiles for one pass at room temperature was performed for copper billets Ø11.7 × 60 mm. The billet was loaded with a puncheon with the help of a hydraulic press. After the deformation treatment, solid prismatic and screw copper profiles with a square cross section of 8 × 8 mm were formed. The results on mechanical properties, deformation regularities, and destruction mechanism during the uniaxial tension of the samples made of technical copper M4 in the delivery state and after hardening are presented. Mechanical tests for uniaxial tension of the samples with a working size of Ø3 × 15 mm were performed using an UTS-20k testing machine at a constant loading speed of 3.33 × 10^–5 m s^–1. A certain increase in the strength of copper subjected to extrusion for one pass at room temperature is established. Screw pressing after extrusion provides higher plasticity compared with the initial state and extrusion. A fractographic research of sample ruptures is performed using a Hitachi TM 3030 scanning electron microscope in the secondary electron mode. It is shown that the destruction mechanism of copper samples in the delivery state, as well as after extrusion and ESP, is qualitatively identical. The destruction of the samples of copper M4 both in the initial state and after the deformation treatment according to the specified modes occurred according to the viscous fracture mechanism. It is revealed that ESP-subjected copper possesses larger energy intensity in connection with an increase in plasticity. The rupture in a fibrous zone for the ESP-subjected sample differs by the tier arrangement of pit blocks. Large pits and micropits in all states of copper are present both in the fibrous zone and in the peripheral cut zone.

Causes of the appearance of anisotropy of properties in products manufactured according to the technology of selective laser melting of metallic powder materials are investigated. The results of an evaluation of mechanical properties of the samples made of Ti–6Al–4V and VT6 titanium-based alloys and Inconel 718 refractory nickel alloy in various directions are presented. The dependence of their mechanical properties on the orientation of billets relative to the working platform of the installation is presented. An analysis of microslices of the Ti–6Al–4V alloy showed that the direction of the granular structure for a rectangular sample corresponds to the growth direction, while, when manufacturing thin elements of a net construction, other thermal processes flow due to their smaller cross section, which affects the crystallization conditions and microstructure being formed. Grain directions and shapes change depending on the slope angle of the element of the net structure.

The influence of the heating rate of the Mg + 2B mixture on the dynamics of the phase formation during the thermal explosion in the helium medium is investigated by the time-resolved X-ray diffraction method. It is shown that the MgB₂ phase appears without the formation of intermediate compounds. The presence of impurity oxygen is a substantial factor affecting the formation kinetics of MgB₂. The oxide film on the surface of magnesium particles has no time to form with the heating rate of the charge mixture of 150–200°C/min. A result of this circumstance is the reaction diffusion mechanism of the Mg + 2B = MgB₂ reaction immediately after the melting of magnesium. Synthesis products mainly consist of MgB₂ and MgO traces at a level of 5%. The thermal explosion temperature is 1100°C. A comparatively thick oxide film which retards melt spreading and shifts the onset of the formation reaction of MgB₂ by 8–9 s grows on the magnesium surface at a heating rate of 30–50°C/min. Synthesis products contain MgB₂ and up to 15% MgO. The thermal explosion temperature is 1020°C in this case.

Nanocrystalline Ni₅₀Al_{50 − x}Mo_x (x = 0, 0.5, 1, 2.5, and 5) intermetallic powders were synthesized by mechanical alloying (MA). Microstructural characterization and structural changes of powder particles during mechanical alloying were studied by X-ray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The results confirmed that the synthesis behavior of NiAl intermetallic depends on the Mo content and milling time. The SEM micrograph outcomes confirmed the specimen with longer milling time includes finer and more homogenous particles with attention to the ones with lesser milling time. Mo enhance has a considerable effect on the lowering of crystallite size. The TEM image showed that the Ni₅₀Al₄₅Mo₅ nano-particles were less than 10 nm.

The influence of alloying the TiC_0.5N_0.5 titanium carbonitride with zirconium on the mechanism and kinetic features of the contact interaction with the Ni–25%Mo melt (t = 1450°C, rarefaction 5 × 10^–2 Pa) is investigated for the first time by electron probe microanalysis and scanning electron microscopy. The main effects of the modifying influence of zirconium on the dissolution, phase formation, and structure formation processes which occur during the interaction of the Ti_1–nZr_nC_0.5N_0.5 carbonitride (n = 0.05 and 0.20) with the Ni–Mo melt are revealed and the factors promoting their manifestation are analyzed. The practical absence of zirconium and nitrogen in the composition of the K-phase (the Ti_{1 – n}Mo_nC_x metastable solid solution, where n ≤ 0.65 and x = 0.7 ± 0.1) is confirmed experimentally. It is shown that the zirconiumenriched Ti_0.80Zr_0.20C_0.5N_0.5 carbonitride cannot be recommended as a refractory component of cermet because of the limitations of the chemical character.

Titanium having high demand in aircraft industries because of its mechanical properties like high strength to weight ratio, high temperature performance and it’s resistant to corrosion. Therefore, Titanium and its alloys are used in airplane and engine applications. One of the major usages of alloy in the aircraft industries are Titanium alloy. By using Powder Metallurgy, the powder materials are compacted and sintered in the furnace to achieve high densities for the further process of the samples. In this paper reviews the various research investigations of Titanium and its alloy (Ti–% Al–% V–% X alloy), to optimize the microstructure and mechanical properties by various sintering methods like Conventional, Spark plasma and Microwave sintering techniques. From this the major advantages in the Spark plasma sintering tend to reduce the sintering time with high temperatures, achieving higher densities and improved microstructures tends to improve the mechanical properties of the material.

Samples of Al₂O₃–TiO₂ coatings are fabricated by the flame spraying of a flexible cord. The influence of process parameters and composition of the sprayed material on the structure, composition, and mechanical properties of coatings is investigated. It is shown that an increase in the spraying distance and feed rate of the sprayed material leads to a decrease in their density. An increase in the concentration of the low-melting TiO₂ component predetermines a decrease in the coating porosity and has no significant effect on the coating hardness. Being subjected to measuring scratching, Al₂O₃–TiO₂ flame coatings formed with minimal porosity (Π = 3.2%) are characterized by cohesion fracture behavior and no substrate opening under an indenter load of up to 90 N. The friction factor of coatings under study varies from 0.2 to 0.78 after 2800 counterbody revolutions (44 m of the friction path). This is associated with the accumulation of fatigue cracks in the coating material and its subsequent cohesive fracture by the formation of large fragments serving as an abrasive.