Russian Journal of Non-Ferrous Metals最新文献

Self-dissolving medical implants, such as screws for bone fracture fixation or vascular stents, represent a promising application of magnesium alloys. Magnesium-based bioresorbable materials are currently not only the subject of research by scientific groups worldwide but also the raw material for producing commercial products—medical metallic implants that are actively used in patient treatment. Nevertheless, many technological issues remain unresolved. Chloride-containing fluxes are widely used in casting magnesium alloys. It is unclear whether the presence of flux particles in materials for bioresorbable implants poses a risk of corrosion damage to the surface of the product. This study investigates the processes of initiation and development of filiform corrosion caused by the presence of a chloride-containing particle on the metal surface. Energy-dispersive spectroscopy was used to determine the composition of corrosion products, and Kelvin probe atomic force microscopy was employed to measure their electrode potential relative to the magnesium matrix. It was shown that, under ambient temperature of 25°C and 30% humidity, filiform corrosion is initiated near the chloride-containing particle. Despite the shallow depth of damage (2–3 µm), corrosion spreads over a large area and is characterized by a high propagation rate (tens of microns per day). Analysis of the chemical composition of the corrosion products revealed that the process involves reactions leading to formation of hydroxide and its breakdown under the influence of chloride and CO₂. The corrosion products exhibit a positive potential relative to the metal, enabling the activation of anodic dissolution of the matrix. Placing the material in a vacuum completely halts progression of corrosion, which resumes upon exposure to air. This demonstrates the necessity of avoiding the use of chloride-containing fluxes in the production of bioresorbable alloys and storing finished products in a moisture-free environment whenever possible.

In this study, sulphuric acid was used to leach indium from zinc oxide dust, D2EHPA was applied to extract indium from the leaching solution, and hydrochloric acid was administered to strip indium from the indium-loaded organic phase. The effects of sulfuric acid concentration, temperature, leaching time and liquid-solid ratio on the leaching rate of indium were studied. The optimum leaching conditions for indium were as follows: sulfuric acid concentration of 200 g/L, leaching temperature of 80°C, leaching time of 120 min, and liquid-solid ratio of 8 : 1. Under these conditions, the leaching rates of indium, zinc, iron, and aluminum were 95.67, 97.97, 2.06, and 8.51%, respectively. On the contrary, lead was enriched in the leaching residue. Response surface analysis was carried out to further optimize the experimental conditions. The kinetic effects of temperature and sulphuric acid concentration on the indium leaching process were investigated using a shrinking-core model, and the activation energy of indium leaching was calculated to be 30.9 kJ/mol, with the kinetic model as: 1 – (1 – x)^1/3 = exp(5.11 – 3714/RT)t; 1 – 2x/3 – (1 – x)^2/3 = exp(8.84 + 3.599 ln[H₂SO₄])t. The results showed that the indium leaching process was controlled by a mixture of chemical reaction and diffusion, and the reaction stage of sulphuric acid was 3.599. Meanwhile, the McCabe-Thiel diagram for D2EHPA/HCl extraction/stripping of indium was constructed, and theoretically D2EHPA/HCl extraction/stripping of indium requires 2 stages to complete.

Silver extraction by percolation leaching on a pelletized sample of stale tailings with the organic binding agent Alcotac^® CB6 is studied. A column 0.5 m high and 56 mm in internal diameter was used for laboratory tests on percolation leaching. Pelletization was carried out in a drum-type granulator with the Alcotac^® CB6 reagent (BASF, Germany) consumption of 800 g/t; the moisture content of the granules was 8–10% with a size of 8–10 mm. The composition of the samples was determined based on the data of optical and electron microscopy, X-ray diffraction, local X-ray spectral, X-ray fluorescence, and mass spectrometry with inductively coupled plasma. Stale tailings of the Zhezkazgan enrichment plant (Ulytau region, Republic of Kazakhstan) were examined, in which the main part of copper is represented by oxidized minerals (78.47%); content of sulfide minerals is 21.53%. The results of physicochemical studies with the determination of the material composition of the sample and observations on the percolation leaching of copper and silver from the stale tailings of Zhezkazgan are presented. The copper leaching was studied in two stages using a sulfuric acid solution as a solvent. The next stage was the transfer of silver into the solution by cyanidation. Copper extraction into the solution was 88.55% with a sulfuric acid consumption of 80.0 kg/t of tailings, and that of silver was 75.31% with a sodium cyanide consumption of 0.55 kg/t. The studies of two-stage leaching showed the effectiveness of preliminary pelletizing of stale tailings with the Alcotac^® CB6 reagent. In the process of leaching, the pelletized material features sufficient porosity and permeability and provides access of cyanide solutions to the surface of precious metals.

Hot compression tests were conducted on an ultrahigh-alloyed Al–Zn–Mg–Cu alloy within a temperature range of 250 to 450°C and a strain rate range of 0.001 to 1 s^–1. The effects of strain rate and temperature on the flow curves were analyzed, along with the relationship between flow stress and microstructural evolution. The results indicate that, except for a strain rate of 1 s^–1 across all temperatures, the flow curves following the peak stress do not exhibit monotonic work hardening or dynamic softening. In contrast, continuous work hardening is observed at this strain rate. The diverse shapes of the flow curves are attributed to the various precipitates formed due to the high alloying element content. Dynamic recovery (DRV) is identified as the main flow softening mechanism for the ultrahigh-alloyed Al–Zn–Mg–Cu alloy. While dynamic recrystallization (DRX) contributes to flow softening at a strain rate of 0.001 s^–1, the deformed microstructure becomes the predominant softening mechanism at lower temperatures and higher strain rates. Additionally, the low intensity of isotropic texture at higher temperatures and strain rates facilitates DRX, resulting in a decrease in peak stress.

The aim is to conduct research in the field of hydrometallurgical refining of metallurgical silicon. The object of research was metallurgical silicon after oxidative refining from AO Kremnii, part of the United Company RUSAL (Shelekhov, Irkutsk oblast, Russia). The chemical composition of the obtained samples was studied by X-ray fluorescence analysis and X-ray spectral microanalysis. According to elemental analysis, metallurgical silicon contains (wt %) 0.53Al, 0.6094Fe, 0.0491Ti, 0.0628Ca, 0.0066V, 0.002Cr, 0.014Mn, 0.003Cu, 0.010P, 0.007Ba, 0.007Ni, 0.002Zn. It is shown that intermetallic compounds of the following composition were recorded in the studied samples: AlFeSi₂ (with an admixture of Ca), FeSi₂ (with an admixture of Al), FeSi₂Ti (with an admixture of Zr). To reduce the content of impurities in silicon, we selected the following acids as solvents: 10% H₂SO₄, HCl, and HNO₃, as well as 4% HF in various ratios. To study the possibility of reactions of interaction of intermetallic compounds with selected solvents, the values of the Gibbs energy change, which had negative values, were calculated. Experimental leaching of impurities was conducted on silicon samples with particle sizes of –200 μm under constant stirring using a magnetic stirrer. The process parameters included a temperature of 60°C, a liquid-to-solid ratio of 5 : 1, and a purification duration of 60 min. It was found that using a solvent mixture of sulfuric and hydrofluoric acids in a 1 : 1 ratio achieved the highest degree of silicon purification, with an impurity removal rate of 86.85%. It is shown that when using a mixture of sulfuric and hydrochloric acids in a ratio of 1 : 3, the degree of purification of metallurgical silicon was 41.48%. In this way, solvents that enable maximum purification of silicon from impurity elements were identified.

Insufficient corrosion resistance of magnesium alloys limits their technical and medical applications. It is known that the corrosion rate of these materials depends, among other things, on the orientation of the samples relative to the workpieces, for example, rods or sheets obtained by thermomechanical processing. There is an opinion in the literature that this is primarily due to the influence of crystallographic texture. In this work, the corrosion resistance of samples cut from extruded rods of industrial alloys ZK60 and AZ31 along and across the extrusion direction was investigated. The corrosion rate was determined by the loss of weight and volume of the samples, as well as by the volume of hydrogen released when they were dissolved in a 0.9% NaCl solution. The microstructure and surface of the samples after corrosion tests were investigated using scanning electron microscopy, energy-dispersive X-ray microanalysis, and electron backscatter diffraction. It is shown that the rod has a pronounced basal texture, and therefore the crystallographic orientation of the grains to the lateral surface of the transverse and longitudinal samples is very different. It was found that samples of both alloys cut across the rod had higher corrosion resistance than longitudinal samples. According to published data, if the anisotropy of corrosion properties were caused by crystallographic texture, then longitudinal samples, on the contrary, should have a lower corrosion rate than transverse ones. Therefore, it is concluded that, in the case of medium- and high-alloy magnesium alloys, the anisotropy of corrosion properties is associated mainly with the nature of the volume distribution of second-phase particles, and not with the crystallographic texture. It is shown that the row arrangement of particles on the surface of longitudinal samples leads to deterioration of corrosion resistance.

Aluminium closed-cell foams are valued for their low density, high stiffness, corrosion resistance, and recyclability, making them suitable for aerospace, marine, and automotive applications. The quality of these foams depends on raw materials and processing methods. Therefore, employing an efficient and cost-effective processing method and raw materials is vital for ensuring that the foam’s properties are not compromised. This work investigates the use of bio-waste chicken eggshell powder and recycled aluminium alloy as a foaming agent for closed-cell aluminium/SiC_p composite foams. The foams produced are examined for micro & macrostructure and its characteristic mechanical behavior. The influence of SiC_p concentration on foam expansion and stability are investigated. Eggshell powder enabled the aluminium alloy to expand and form foam, further adding SiC_p resulted in the homogeneous distribution of pores with negligible metal drainage.

To obtain products made of aluminum-matrix composite materials (AMCM) with the required level of mechanical properties, processing by means of intense deformation is necessary. To model the deformation behavior in nonstationary conditions of thermal deformation treatment, the identification of the AMCM model remains an urgent task. One of the approaches to the description of material fluidity is the use of the Johnson–Cook plasticity model. In the proposed work, the object of research is an AMCM made of granulated high-strength aluminum alloy V95 of the Al–Zn–Mg–Cu system, reinforced with 10 wt % SiC particles. The aim of the work is to determine the influence of nonstationary thermomechanical (pressure on the workpiece and heating temperature) deformation conditions on the true deformation and deformation rate of the composite material, as well as to identify the material model and verify its application to study the processes of shape change in the studied pressure and temperature range. An experimental study of the precipitation process under uniaxial compression of sintered cylindrical samples of AMCM in the range of initial pressures of 5.65–7.81 MPa when heated to 510, 530, and 550°C is conducted. In this range, the dependences of the degree of deformation and the average deformation rate for the process are obtained. Identification of the rheological model of the material was carried out. A mode of preliminary thermomechanical processing is proposed and a prototype is manufactured at an initial pressure of 6.7 MPa on the workpiece and heated to 550°C in 84 min. The above mode provided relatively uniform filling of the stamp cavities with composite material. To confirm the possibility of applying the results of parametric identification of the material model, simulation modeling of the technological process of manufacturing a prototype was carried out.

The concentrated sulfuric acid roasting method and caustic soda method, as the main processes for treating Bayan Obo mixed rare earth concentrate, have been operating normally for decades. However, due to their serious pollution, high cost, and waste of accompanying resources, relevant rare earth enterprises are facing severe environmental and cost pressures. The sodium carbonate roasting method is a clean method for treating rare earth minerals, but due to the phenomenon of “ring formation” in the rotary kiln during the reaction process, this process has not been widely promoted. Based on the above facts, this article proposes a decomposition method for sodium pelletizing to decompose monazite, which effectively alleviates the related technical problems caused by the “ring formation” problem. Moreover, the rare earth leaching rate is 86.87%, and the recovery rates of F, P, and Th are 98.64, 13.87, and 88.96%. It is a potential rare earth mineral cleaning production process and can provide certain technical references for relevant rare earth enterprises.