Russian Journal of Non-Ferrous Metals最新文献

In this study, A356 powder was alloyed with elemental Nickel (Ni) powder in different ratios using a mechanochemical alloying method. Alloyed A356/XNi powders were cold pressed along one axis under a load of 350 MPa and sintered at 600°C. To determine the effect of intermetallic phases formed on the microstructure in proportion to the amount of Ni, the A356/XNi alloys were characterized by X-ray diffraction (XRD) analysis, density, and microhardness values. As a result, after mechanical alloying, the spherical microstructure of the A356 alloy turned into a spongy form due to the sponge-like Ni elemental powders. After sintering, it was determined by optical microscopy and scanning electron microscopy (SEM) examinations that the grain size of A356/XNi alloys increased with an increasing amount of Ni. In addition, it was determined that the relative density and amount of porosity increased with an increasing amount of Ni. According to the XRD analysis results, it was determined that AlNi, Al₃Ni₂, Al₃Ni and AlFeNi intermetallic phases formed in the microstructure due to the mechanochemical and sintering process.

The positron emission tomography detection device uses scintillator crystals to provide high image quality. Cerium-activated lutetium orthosilicates are promising crystals for PET detectors. The optical properties of the resulting scintillator crystals directly depend on the impurity composition of the starting materials; therefore, rather stringent requirements are set for them: the content of the basic substance Lu₂O₃ is 99.999 wt % and CeO₂ is 99.99 wt %. As a starting material for obtaining lutetium oxide of the required purity, we used its concentrate with a basic substance content of 99.1 wt %, to obtain cerium oxide, REM carbonates containing up to 54% cerium in the composition. The paper presents the schemes of the technological process for obtaining high-purity Lu₂O₃ and CeO₂ based on a combination of methods of extraction and ion exchange. Extraction purification of lutetium and cerium from accompanying rare-earth impurities was carried out using Aliquat 336 and tri-n-butyl phosphate, respectively. In the work, the main modes of operation of the extraction cascades were calculated; the total number of stages for purifying lutetium was 17; for purifying cerium, it was 20. The technology for the purification of lutetium oxide and cerium oxide consists of a combination of purification methods and varying cycles depending on the content of impurities; in this regard, it is necessary to control the quality of the resulting substances practically after each stage. Analytical control of the chemical purity of technological products was carried out by mass spectrometry with inductively coupled and spark sources of sample excitation.

In this study, the microstructure and mechanical properties of ZK60 extruded alloy were investigated after adding 3 wt % of Ce and Y and T5 operation. The microstructure of the base alloy consists of α‑Mg and Mg₇Zn₃. In addition to these phases, MgZn₂Ce and Mg₃Y₂Zn₃ phases are formed by adding Ce and Y, respectively. The addition of rare earth elements reduces the grain size of the base alloy from 6.1 μm to less than 3 μm. The volume fraction of precipitates also increases because of the additions. After T5 operation for different times, it was observed that the hardness peak (88 HV) for the base alloy is achieved after 18 hours. However, the peak hardness of alloys containing rare earth elements occurred in 24 hours. Increasing the aging time results in an increase in the grain size of the base alloy, while it led to a slight increase in the grain size of alloys containing rare earth elements. The higher hardness at the peak age of all studied alloys is explained based on the increase in the volume fraction of precipitates during this operation. The delay in the peak age in alloys containing rare earth elements is due to the delay in the formation of (beta _{2}^{'}) precipitates. The shear punch test results of extruded alloys show that in alloys containing Ce and Y the shear strength is 156 and 160 MPa, respectively. While this value is about 148 MPa for the base alloy. At the peak age, this strength for ZK60-Ce and ZK60-Y alloys increases by 11% and 13%, respectively. Higher strength and hardness in Y‑containing alloys are due to the simultaneous strengthening of solid solution and precipitates along with the formation of precipitates with high thermal stability.

The calcification–carbonization method can effectively treat bauxite residue. In this paper, carbide slag is used as the calcium source of the calcification process to treat bauxite residue, which greatly reduces the process cost while realizing the utilization of two kinds of solid waste resources. Through the investigation of the influencing factors of the calcification process, we ascertained the optimal calcification condition is the calcium-to-silicon ratio of 2.5, calcification temperature of 160°C, the liquid-to-solid ratio of 5 : 1, and reaction duration of 60 min. Under this condition, a Na₂O recovery rate of 94.7% was achieved, and the extraction rates of Al₂O₃ reach 33.9%. The main phase composition of tailings after treatment is CaCO₃ and CaSiO₄, which are environmentally harmless and can be reused as raw materials. On the other hand, using carbide slag to treat 1t bauxite residue can save 15.69$ of production cost, and the comprehensive economic benefit can reach 26.67$ per ton. Therefore, carbide slag is promising as a calcium source in the treatment of bauxite residue.

In this work, a comparative study of the methods of boriding, carboboronizing, and borosiliconizing of VT-1.0 titanium is carried out in order to increase the wear resistance in aggressive environments at elevated temperatures. The microstructure of diffusion coatings is investigated, and their thickness and microhardness are determined. Diffusion saturation of VT-1.0 titanium specimens with dimensions of 10 × 10 × 25 mm was carried out from saturating mixtures based on boron carbide. Saturation mode: process temperature of 950°C, saturation time of 1.5 h. At the end of the high-temperature exposure, the samples were removed from the furnace and cooled in air to room temperature, the saturating coating was cleaned from the samples with wooden spatulas, and the samples were boiled in soap and soda solution for 1 h. A continuous diffusion layer 80–100 µm thick forms on the titanium surface. The borosilicized diffusion layer obtained by saturation of titanium from a mixture of 45% B₄C–5% Na₂B₄O₇–22% Si–5% NaF–3% NaCl–20% CrB₂ has a higher microhardness: 1520 HV_0.1 versus 1280 HV_0.1 for carboboronizing one and 1120 HV_0.1 for boriding. In this case, boriding and carboboronizing coatings obtained, respectively, by saturation from daubs of the composition 45% B₄C–5% Na₂B₄O₇–5% NaF–25% Al₂O₃–20% CrB₂ and 70% B₄C–5% Na₂B₄O₇–5% NaF–20% CrB₂ have a pronounced zonal structure. The upper zone of these coatings, having a high microhardness, also has high brittleness indicators, which does not allow accurately measuring the microhardness distribution indicators because of chipping and cracking in the places where the microhardness is measured. X‑ray diffraction studies of the qualitative composition of coatings on titanium were carried out on a DRON-6 X-ray diffractometer in filtered CuK_α radiation (λ = 1.5418 Å) in the angle range 2θ = 20°–80°. The diffusion coating exhibits reflections of titanium carbide, chromium and titanium borides, and a certain amount of Cr₂Ti intermetallic compound. Boride phases of chromium and titanium refer to high boron phases with a high specific boron content: TiB, CrB, Ti₂B₅, Ti₃B₄, and Cr₂B₃.

Al7075/TiO₂ and Al7075/TiO₂/SiC composite layers were produced on the surface of commercially pure aluminum substrate (CP Al) using friction surfacing. SiC and TiO₂ particles were introduced into axial holes drilled on the cross section of cylindrical Al7075 pins that used as primary consumable material for the friction surfacing process. Cross-sectional scanning electron and optical microscopy images of the specimens showed a uniform distribution of the reinforcing particles within the composite layers. Grain sizes were decreased significantly after addition of the ceramic particles. SiC had a greater effect on grain refining of the composite layers than TiO₂. Microhardness improved after addition of the reinforcing particles and adding SiC particles had increased the microhardness more than TiO₂. Wear tests showed that the wear resistance of aluminum can be increased dramatically by friction surfacing and by addition of the ceramic particles. SiC increased the wear resistance of the composite layers through its high grain refining role, while TiO₂ improved the wear resistance by production of the lubricating oxide layers. The sample containing of the both reinforcing particles showed the highest wear resistance.

Calcination experiments were carried out using calcined clay and optimum calcination conditions were determined as 750°C and 60 min. The Box–Behnken design (BBD) was used to model, predict, and optimize the experimental parameters. The effective parameters and their interactions were explained with a mathematical model. The correlation coefficient (R²) of the proposed model for the relationship between the yield of alumina extraction and experimental parameters was calculated as 0.9573 and it was determined that the predicted and actual values were in good agreement. The modeling results showed that the significance order of the parameters was leaching temperature > acid concentration > leaching time > acid/clay ratio. Finally, an extra optimization study was carried out to maximize the yield of alumina extraction and the yield was found to be 88.15% under the optimum conditions determined by the model (2.56 M acid concentration, 154.46 min leaching time, 89.77°C leaching temperature, and 53.21% acid/clay ratio).

The boiling point method (isothermal version) was used to determine the partial pressure of saturated lead vapor over lead and tin solutions, the lead content of which (the rest is tin) was 96.43, 93.02, 89.55, 80.73, 64.18, and 43.80 wt % (93.93, 88.42, 83.08, 70.59, 50.65, and 30.87 at %, respectively). The partial pressures of tin were calculated by numerically integrating of the Duhem–Margules equation using the auxiliary function proposed by Darken. The tin and lead partial pressure values over their melts were approximated by temperature-concentration dependences. The total error of determination was calculated as the sum of errors of independent measurements: temperature, weighing, pressure, approximation of experimental data, equal to 7.78%. On the basis of the values of the partial pressure of the saturated lead and tin vapor, the boundaries of the fields of coexistence of liquid and vapor in the tin−lead system in a primary vacuum of 100 and 1 Pa were calculated and refined: the boiling temperature as the temperature at which the sum of the partial pressures of metals was equal to 100 and 1 Pa; the composition of vapor as the ratio of the partial pressure of vapor of metals at this temperature. It was found that the reason for the increased content of tin in lead condensate during the distillation of alloys with a lead content of less than 5 at % (8.41 wt %) and the accumulations of tin in the distillation residues are values of the partial vapor pressure of tin comparable to lead. In the distillation separation of lead and tin melts by evaporation of lead in a real process under nonequilibrium conditions, the accumulations of tin in the distillation residue should not exceed a concentration of ~50 wt %. Exceeding the specified concentration will be accompanied by the production of condensate, for which it is necessary to repeat the process of evaporation–condensation.

Semi-industrial tests of the chloride sublimation technology for extracting lithium from petalite ore with concurrent production of cement clinker have been carried out. The main technical and economic indicators of production of lithium carbonate have been determined. Chloride sublimation roasting method allows combining ore roasting and lithium sublimation with the process of obtaining (roasting) Portland cement clinker. Thus, it becomes possible to distribute energy costs for high-temperature roasting over a much larger volume of products: clinker and lithium salts. The recovered lithium in the form of lithium chloride vapor is captured by an aqueous absorbing solution, which has a much smaller volume as compared to the volumes of leaching solutions in lime, sulfuric acid, or autoclave alkaline technologies. Correspondingly, the flows of the solutions being processed are reduced, which significantly saves reagents and energy during their processing and considerably reduces the capital costs of tank equipment. Owing to the high content of aluminum and silicon oxides in lithium aluminosilicate ores, it is possible to use them in the production of cement clinker instead of the clay component of the charge.

Of late, there has been an increase in the application of Metal Matrix Composites (MMCs) as they provide significant mechanical and tribological properties. In tune with the rapid global attention to this composite, this research analysis is an attempt on employing Taguchi method in order to minimize the rate of wear and friction on co-efficiency in aluminium MMC. The study involves in investing the tribological behaviour of aluminium alloy, Al-6063, by reinforcing with silicon carbide and aluminium oxide particles. As such, the investigation was carried out by fabrication the alloy by stir casting process. In addition, wear test was performed to analyse the wear and frictional properties of the metal matrix composites with the aid of a pin-on-disc wear tester. For the purpose of the process in an effective manner, Taguchi technique was adopted to perform the experiments on a fixed plan. Further, in analysing the experimental data, A L₉ Orthogonal array was applied. More analyses such as the influencing effect of higher load applied, higher speed of sliding and distance found in sliding on wear rate, and the friction occurring out of co-efficiency during the process of wearing were carried out by employing ANOVA and regression equation. These measures were used for each response for the abovementioned analyses. The experimental results exhibit that the highest influence is observed in sliding distance, while the speed of load and sliding coming behind it. In order to prove the justification of this study, the experimental results were verified with the tests carried out for confirmation.