Russian Journal of Non-Ferrous Metals最新文献

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.

The paper presents the results of an experimental study into the possibility of producing ultrahigh temperature ceramics constituting solid solutions of HfC and ZrC carbides by the single-stage electrothermal explosion (ETE) method under pressure. Adiabatic flame temperature and phase composition of the equilibrium final product were calculated on the basis of thermodynamic data. It was shown that, when the ZrC content in the final product is less than 20 wt %, the adiabatic flame temperature reaches 3800–3900 K, and the combustion product contains hafnium and zirconium carbides. The effect of mechanical activation modes in an AGO-2 planetary centrifugal mill used for a reaction mixture containing Hf, Zr, and C powders on its properties, phase composition formation, and the microstructure of carbide solid solutions was studied. It was shown that high-energy mixing in hexane leads to the destruction of the crystal structure of Hf and Zr particles and the formation of amorphous composite particles. The synthesized samples of ultrahigh temperature ceramics were studied by X-ray diffraction and microstructure analyses. It was shown that exothermic synthesis leads to the formation of single-phase solid solutions of HfC and ZrC carbides with the average particle size of 1.5–0.2 µm. The residual porosity of the binary carbides obtained is 10–12%. It was found that, despite the high temperature of sample heating during ETE under pressure, the particle size of the resulting solid solutions is significantly (by an order of magnitude) smaller than the particle size of similar complex carbides (20–50 µm) obtained by other methods (SPS and hot pressing). This is associated with the rapidity of the exothermic interaction of the reagents (10–50 ms) during ETE.

Phase transformations taking place during synthesis of WC by electrothermal explosion (ETE) were investigated within the following range of process parameters: T = 293–3700 K, 49.8–50.2 at % C, P = 96 MPa, V = 10 V, I = 20 МА/m², sample diameter of 20 mm. The thermogram of the ETE process was subdivided into four stages (I–IV). Stage I, warmup, temperature range of 293–563 K, endothermic reaction (isothermic plateau), input electric energy Q = 2.96 kJ, specific input energy Е = 111.6 kJ/mol. Low-temperature stage II, 563–1190 K, ignition, Q = 5.46 kJ, Е_а = 109.2 kJ/mol. High-temperature stage III, 1190–2695 K, eutectoid decay, order–disorder transformation, Q = 14.25 kJ, Е_а = 424 kJ/mol. Stage IV, melting, 2695–3695 K, Q = 14.31 kJ, Е_а = 143.2 kJ/mol. The rate of ETE reaction is highly sensitive to applied pressure, concentration of reagents, sample shape, oxide film, etc. Variation in E affords facile control of the ETE process.

In this paper, a kind of cermet with Mo25ZrB₂ component was prepared by hot pressing sintering method, and its phase composition and mechanical properties were characterized. The characteristics show that after hot pressing sintering, Mo metal and ZrB₂ ceramic react to generate a certain amount of MoB, which makes the powder bond closely, the bending strength is close to 250 MPa, and the fracture toughness is close to the fracture toughness of the casting die H13. In addition, the static oxidation behavior of the material at different temperatures was also characterized. The experimental results show that the composite with ZrB₂ ceramic powder can overcome the problem of melting failure of Mo matrix at 800°C. The results of static oxidation at 800°C show that the oxidation of Mo matrix is not obvious. This shows that the compound of ZrB₂ effectively protects the Mo matrix and makes the Mo matrix reach a higher operating temperature. The oxidation behavior at 1000°C also showed that zirconium boride would still combine with high temperature oxygen and consume it in the first step, which played a protective role on Mo matrix. This shows that the material still has good application potential at higher temperatures.

We present the results of a study on the preparation of dense titanium carbide by SHS compaction. It was found that the use of a mechanically activated reaction mixture of titanium and carbon black powders made it possible to obtain titanium carbide samples with a maximum relative density of 95%. The specific feature of this work is that the mechanical activation of the components of the Ti + C mixtures was carried out in a ball mill for several tens of hours. The influence of the modes of activated mixing on the characteristics of the reaction mixture and combustion parameters was studied. The influence of technological parameters on combustion characteristics and structure of consolidated titanium carbide was also investigated. It was found that the rate and temperature of combustion strongly depend on the size, mass, and density of charge compacts. With an increase in the diameter (20–58 mm) and weight (10–70 g) of pressed samples from mixtures with activated reagents, the combustion rate varied from 10 to 100 cm/s, and the combustion temperature varied from 2200 to 3100°C. A strong influence of the prepressing pressure (applied at the combustion stage) on the combustion rate and temperature was shown: in the pressure range of 0–10 MPa, the combustion rate sharply decreases from 100 to 10 cm/s. In the pressure range of 0–40 MPa, the combustion temperature decreases monotonically from 3000 to 2000°C. A mechanism of high-speed combustion of the reaction mixture of titanium and soot has been proposed, in which the determining factors are the mechanical activation of the components of the mixture (titanium and soot) and the formation of radial cracks (channels) in the pressed samples, which ensure the propagation of incandescent impurity gases into the inner layers and the initiation of the carbidization reaction in the volume of charge compacts.

This paper is concerned with obtaining metal-ceramic composite materials through the method of SHS compaction. The study investigates the influence of mechanical activation of metallic components in reactive mixtures based on the Ti + C + Cr + Ni system on the structure and properties of the resulting composites. Mechanical activation of the Ti, Cr, and Ni metallic powders was performed using two methods. In the first method, Cr and Ni powders were activated separately from the other components of the reactive mixtures using grinding media in a ball mill, after which they were mixed with Ti and carbon black powders. It was shown that the preliminary mechanical activation of the inert components reduces the combustion temperature and rate, which increases the average size of carbide grains. The second method involved a joint processing of Ti + Cr, Ti + Ni, and Ti + Cr + Ni powder mixtures in a ball mill, which were then mixed with carbon black. This method provided mechanical activation of titanium particles while minimizing the impact of grinding media on Cr and Ni powders. This led to an increase in the combustion rate and temperature, a decrease in the average size of carbide grains, and an improvement in the uniformity of the composite structure. A mechanism of interaction between the reagents (Ti + C) involving activated Cr and Ni particles in the combustion and structure formation zones is proposed. According to this mechanism, the mechanical activation of inert components leads to their direct participation in the reaction between titanium and carbon, which determines the reduction in combustion rate and temperature and affects the dispersion and uniformity of the structure of compact composites. The results were used to enhance the uniformity and refine the structure of the STIM-3B composite (synthetic hard tool material grade 3B).

TIG welding is the most common method for producing high-quality aluminium alloy welds. Variants of Tig welding will increase productivity. Some variants of TIG welding are hot wire TIG welding, activated TIG welding, and pulse TIG welding. Activated Tig welding has its own variants, such as FB-TIG, FZ-TIG, etc. for aluminium, TIG welding with argon inert gas is the most suitable welding technique. In activated TIG welding, various fluxes are used for welding SiO₂, TiO₂, and CaF₂, and the mixing of acetone and methanol will increase the penetration in the weldment. In this paper, we discuss the various fluxes used in aluminium welding for different variants of Tig welding and also the effect of welding parameters on aluminium alloys. also, Experiment was performed on aluminium AA7004 alloy with the convention, A-TIG and FB-TIG welding process. For the ensuring of quality of weld hardness, Microstructure, EDS, SEM and Potentiodynamic testing was performed.

In this paper, an alloy with a group of Nb5Cr was prepared by hot pressing sintering and its phase composition was characterized. After hot pressing sintering, Cr element exists in the form of solid solution outside the Nb matrix, and a certain amount of NbCr₂ phase is formed. The bending strength of the obtained alloys is not less than 250 MPa, and the fracture toughness is close to that of H11 casting die steel. In addition to the mechanical properties of the alloy, the oxidation behavior of the alloy at different temperatures was also studied. The experimental results show that the change of the alloy is not obvious at 1000°C except for the dissolution of Cr element, and at 1000–1200°C, the alloy can spontaneously form a CrNbO₄ oxide film which is weakly bound to the alloy matrix. This is very conducive to the application of separation between the mold and the casting mold during casting. This product provides the casting industry with a material that can spontaneously form a Self-oxidizing film under high temperature oxidation environment and provides a usable choice for materials used in high temperature casting environment.

The paper proposes a method for the formation of superhydrophobic electrochemical coatings based on copper with relatively high mechanical strength. The method of electrodeposition of copper composites with nanodispersed silicon carbide particles is considered as the main approach to obtaining such coatings. Electrochemical codeposition of nanoparticle agglomerates and a copper matrix makes it possible to obtain the required multimodal roughness of coatings. This coating, after treatment with stearic acid, acquires superhydrophobic properties. The paper presents data on the morphology, superhydrophobic properties and chemical composition of coatings. The optimal mode for the formation of such coatings has been determined. According to the results of mechanical tests, the superhydrophobic Cu–SiC composite is superior in resistance to dry friction to many other superhydrophobic coatings formed by electrochemical methods. The resulting coatings have a developed surface morphology, which makes it possible to achieve a wetting angle of 162°. This determines the increased corrosion resistance of copper coated with a superhydrophobic Cu–SiC composite in the salt spray chamber. The time until the first corrosion damages appears on copper in the salt spray chamber increases from several hours (without coating) to 3.5 days (with coating). In this case, the coating continues to remain generally superhydrophobic for more than a day, and after the loss of superhydrophobicity, it remains hydrophobic.

A thermodynamic assessment of the influence of alloying elements (Si, Mg, Cu, Ti) on the processes of phase formation during the production and liquid-phase processing of cast aluminum matrix composite materials with exogenous reinforcement (Al–SiC, Al–B₄C) has been carried out. It is shown that without suppression of the formation of Al–Si–C and Al₄C₃ carbides in the range of carbon concentrations from 0 to 4.5 wt %, the equilibrium phase composition of composites of the Al–SiC system in the solid state at temperatures from 423 to 575ºC lies in the three-phase region (Al) + Si + Al₄SiC₄, and below a temperature of 423ºC, the Al₄SiC₄ ternary carbide is replaced by the Al₈SiC₇ compound. In the Al–SiC–Mg system, the crystallization of composites containing more than 0.58 wt % magnesium ends in the four-phase region (Al) + Al₃Mg₂ + SiC + Mg₂Si. In the Al–SiC–Ti system, the end of crystallization is fixed in the three-phase region (Al) + Al₃Ti + SiC. In the Al–B₄C system, after suppression of the formation of the Al₄C₃ phase, with a deviation from the concentrations of elements that provide 10 vol % B₄C, aluminum borides are formed in the direction of increasing boron, and free carbon is formed in the direction of decreasing boron. Under equilibrium conditions, with a silicon content of up to 0.67 wt %, the crystallization of the Al–B₄C–Si system ends in the four-phase region (Al) + B₄C + AlB₁₂ + Al₈SiC₇, and at a higher silicon content, it ends in the region (Al) + Si + AlB₁₂ + Al₈SiC₇. In the Al–B₄C–Ti system, with a Ti content of less than 0.42 wt %, crystallization ends in the three-phase (Al) + TiB₂ + B₄C region.