Showing papers in "Russian Journal of Non-ferrous Metals in 2018"

Conceptual Protection Model for Especially Heat-Proof Materials in Hypersonic Oxidizing Gas Flows

Abstract: This article is a continuation of the publication cycle of the authors on the subject matter “Multifunctional Protective Coatings for Especially Heat-Loaded Constructional Elements of Hypersonic Systems.” A conceptual physicochemical operation model of the protective coating in a high-speed high-enthalpy oxidizing gas flow taking into account and leveling main surface fracture sources by the gas flow is proposed. The model is successfully implemented when developing a whole series of alloys of the Si–TiSi2–MoSi2–B–Y system intended to form thin-layer coatings from them by any method of the stratified deposition providing the reproduction of the structure, phase composition, and morphological features of the deposited material in the coating. During the deposition, the formation of a microcomposition layer is provided. This layer is a refractory silicide framework with the cells filled by a low-melting (relative to the melting point of framework-forming phases) eutectic structural component. This layer transforms into a multilayer system with a series of functional layers (anticatalytic, reradiative, antierosion, heat-proof, and barrier-compensation layers) of micron and submicron thicknesses during high-temperature interaction with oxygen-containing media (the synergetic effect). The protection ability is provided by the formation of self-restoring oxide vitreous film based on alloyed silica. The self-restoring effect consists of rapid filling of random defects with a viscoplastic eutectic component and protective film formation accelerated when compared with known coatings. The high resistance to the erosion carryover is provided by the presence of a branched dendritic-cellular refractory framework. Coatings MAI D5 and MAI D5U, designed in the scope of the proposed concept, are successfully approved in high-speed high-enthalpy oxygen-containing gas flows affecting the samples and constructional elements made of especially heat-proof material of various classes (niobium alloys, carbon–carbon and carbon–ceramic composite materials, and graphitized carbon materials). The protective ability of coatings of 80–100 μm in thickness in flows with the Mach number of 5–7 and enthalpy of 30–40 MJ/kg is no shorter than 600 s at Tw = 1800°C, 200 s at 1900°C, and 60 s at 2000°C, including the constructive elements with sharp edges.

Fabrication of Cerium Oxide Nanoparticles by Solution Combustion Synthesis and Their Cytotoxicity Evaluation

Abstract: The diverse abilities such as the antioxidant effect of cerium oxide nanoparticles (CeO2-NPs) have encouraged researchers to pursue CeO2-NPs as a therapeutic agent to treat a number of diseases, including cancer and diabetes. The synthesis method of CeO2-NPs affected on its abilities. In this study, nanosize ceria powders were synthesized by combustion of aqueous containing corresponding cerium nitrate, ammonium nitrate, and glycine redox mixtures. Solution combustion synthesis is a fast and cost-efficient process with high purity product. The crystallite structures were characterized by various methods, including X-ray diffraction technique, high-resolution scanning electron microscopy, transmission electron microscopy, and UV–vis spectroscopy technique. The combustion was flaming and yields voluminous oxides with nano size (20–30 nm). In addition, no diffraction patterns that are characteristic of impurities were observed, indicating the purity of the CeO2-NPs. In vitro cytotoxicity studies on L929 cells, a non-toxic effect in all concentration (up to 1000 μg/mL) was indicated and it can be believed that this nanoparticle will have viable applications in different medical fields.

Forecasting Tribological Properties of Wrought AZ91D Magnesium Alloy Using Soft Computing Model

Abstract: The wear characteristics of wrought magnesium alloy AZ91D is assessed by varying the wear test parameters namely sliding velocity, sliding distance and normal load in the pin-on-disc tribometer. The experimental results are used to develop a statistical model, and soft computing models based on artificial neural network and Sugeno–Fuzzy logic to predict the wear rate of AZ91D alloy. Sugeno–Fuzzy model had the highest accuracy in prediction and hence used to study the effect of wear test parameters on the wear rate of AZ91D alloy. It is observed that the wear rate increases with decrease in load, increase in sliding velocity, and increase in sliding distance.

Fabrication of the Nb–16Si Alloy Powder for Additive Technologies by Mechanical Alloying and Spheroidization in Electric-Arc Discharge Thermal Plasma

Abstract: The development of new, more refractory heat-resistant materials for gas-turbine engines is one of most important problems of modern materials science. This is associated with the fact that nickel superalloys currently used for this purpose have a lower melting point of ~1400°C, which limits their own maximal working temperature by a range of 1100–1150°C. The Ni alloys can be replaced by natural composites, in which refractory metals are a matrix, while their silicides are intermetallic hardeners. Only three “refractory metal–silicon” binary systems manifest stability to the Me5Si3 silicide, notably, Nb5Si3, Re5Si3, and W5Si3. From the viewpoint of a combination of a high melting point and a low density, the Nb5Si3 compound is optimal among other silicides. The use of alloys of the Nb–Si system in additive manufacturing machines is of considerable interest. This work presents the results of experimental investigations into the treatment of the Nb–16 at % Si powder fabricated using mechanical alloying of elemental Nb and Si powders in the thermal plasma flux. The Nb–16Si alloy powder is fabricated by the mechanical alloying of powders of pure elements in a Fritsch Pulverisette 4 planetary mill. The powder spheroidization is performed in a plasma installation based on a discharge vortex-stabilized electric-arc thermal plasma generator. Based on the results of experimental investigations, the principal possibility to perform the plasma spheroidization of particles of the Nb–16Si alloy prepared by mechanical alloying is shown. It is shown that the surface of spheroidized particles is rough and reflects the cast material structure. Three phase components Nb5Si3, Nb3Si, and Nbss having different optical contrast are revealed in microslices, which is confirmed by X-ray phase analysis.

Reaction Pathways of Nanocomposite Synthesized in-situ from Mechanical Activated Al–C–TiO2 Powder Mixture

Abstract: In-situ Al matrix composite was synthesized from Al–TiO2–C powder mixtures using mechanical alloying and heat treatment, subsequently. The effect of ball milling on reaction processes of the resulting nanocomposite was investigated. The evaluation of powder mixture without mechanical activation showed that at 900°C aluminum reduced TiO2, forming Al3Ti and Al2O3. After 20 h mechanical activation of powder mixture, Al3Ti and Al2O3 were fabricated. After that, by increasing milling time up to 30 h, no new phases formed. The DTA analysis of 30 h milled powder indicated two peaks after aluminum melting at 730 and 900°C. The XRD results confirmed that at 730°C, molten Al reacted with TiO2 and C, forming Al3Ti, Al2O3 and Al4C3. After that, at 900°C, Al3Ti reacted with Al4C3, causing TiC formation. This results proposed that the TiC formation is associated by a series of reactions between intermediate products, Al3Ti and Al4C3 and the resultant nanocomposite was successfully synthesized after 30 h milling and heated by DTA analysis up to 1200°C.

Use of Calcium in Alloys: From Modifying to Alloying

Abstract: Calcium is one of the most widespread and, consequently, low-cost metals on Earth. It has been applied for a long time in modifying and alloying alloys of heavy metals, in particular, lead and copper. It is used as a modifier in cast irons and steels. Calcium began being applied for alloying light alloys based on aluminum and magnesium comparatively recently. In this review, the application fields of metallic calcium and its influence on the structure and properties of various alloys are considered. Alloys based on aluminum–calcium eutectic have been systematically investigated over last few years, and it has been established that they possess casting properties no worse than these of silumins, and they can be hot-rolled and cold-rolled with a high degree of deformation. Ternary and more complex phase diagrams of systems including calcium are constructed and multicomponent alloys based on them are investigated. All these circumstances make it possible to outline several groups of new promising Ca-containing aluminum alloys: (i) alloys hardening without quenching due to the isolation of nanodimensional particles of Al3Zr, Al3Sc, and Al3(Zr,Sc) phases; (ii) high-strength alloys alloyed with traditional hardening elements of the aluminum solid solution, such as zinc and magnesium; and (iii) composite alloys having more than 20% eutectic intermetallic compounds in the structure. All these materials have reduced density, an improved set of operational properties, increased corrosion resistance, and high manufacturability when producing cast and deformed half-finished products.

Characterization of Ni–Ti Alloy Powders for Use in Additive Manufacturing

Abstract: Additive manufacturing (AM) offers a fully integrated fabrication solution within many engineering applications. Particularly, it provides attractive processing alternatives for nickel-titanium (Ni–Ti) alloys to overcome traditional manufacturing challenges through layer by layer approach. Among powder-based additive manufacturing processes, the laser beam melting (LBM) and the electron beam melting (EBM) are two promising manufacturing methods for Ni–Ti shape memory alloys. In these methods, the physical characteristics of the powder used as raw material in the process have a significant effect on the powder transformation, deposition, and powder-beam interaction. Thus, the final manufactured material properties are highly affected by the properties of the powder particles. In this study, the Ni−Ti powder characteristics are investigated in terms of particle size, density, distribution and chemical properties using EDS, OM, and SEM analyses in order to determine their compatibility in the EBM process. The solidification microstructure, and after built microstructure are also examined for the gas atomized Ni–Ti powders.

Physical Methods and Flotation Practice in the Beneficiation of a Low Grade Tungsten-Bearing Scheelite Ore

Abstract: In this paper, beneficiation studies were carried out on a low-grade tungsten-bearing scheelite from Nezam Abad ore with total WO3 grade of 0.11%. Mineralogical studies showed that scheelite is mainly distributed in the ore and gangue minerals include Quartz and Tourmaline. Liberation degree (d80) of tungsten- bearing scheelite is achieved around particles size 150 μm. Gravity concentration, magnetic and flotation methods were conducted by using experimental designs including fractional factorial and response surface methodology. Gravity concentration results indicated that jig separator could not be able to improve tungsten grade in size fraction +600–1750 μm; however, shaking table increased feed grade up to 27.05% with total recovery more than 50% by using four stages concentration in the size range of +125–600 μm. Multi Gravity Separator (MGS) applied on the intermediate products, improved efficiently the total tungsten recovery of the circuit. The results of flotation practice on the pre-concentrated product demonstrated that WO3 grade could be increased up to 9.2% with total recovery of 27.04% by using one stage rougher and four stages of cleaning. Different methods including MGS, wet and dry magnetic separation were considered for upgrading fines from grinding stages; however, only MGS result was satisfactory. The MGS produced a product with WO3 grade 0.64% and total recovery 93%.

Removal of Hexavalent Chromium from Mine Effluents by Ion Exchange Resins-Comparative Study of Amberlite IRA 400 and IRA 900

Abstract: Strongly basic anion exchange resins, Amberlite IRA 400 and IRA 900, have been tested to remediate Cr(VI) from a model as well as from the untreated chromite mine effluent samples. For an initial concentration of 50 ppm Cr(VI), IRA 400 was found to adsorb Cr(VI) completely in less than 6 min of contact time and was efficient in a larger range of pH (1–6); however IRA 900 was able to remediate 97% Cr(VI) in the pH range 4.5–5 in less than 10 min. A cumulative loading of 112.9 and 115.2 mg/g of Cr(VI) was obtained with Amberlite IRA 400 and IRA 900, respectively from a feed of 200 ppm Cr(VI). A close adherence to the Freundlich isotherm during the adsorption reflected the strong chemical interaction of Cr6+ ions with the quaternary functional group on the resins. The adsorption process followed the pseudo second-order kinetics. The experiments were further carried out in glass columns with 10 L chromite mine effluent samples. Almost complete sorption of Cr(VI) from the effluent was achieved using 0.5% (w/v) IRA 400 and 2% (w/v) IRA 900, at a resin bed height of 7 cm and flow rate of 10 mL/min. Desorption studies in column show that 200–500 mL solutions of 15–30% (w/v) NaOH eluted the Cr(VI) completely from the metal laden Amberlite IRA 400 and IRA 900 resins.

Certain Tendencies in the Rare-Earth-Element World Market and Prospects of Russia

Abstract: The analysis of certain trends in the development of the rare-earth-element (REE) world market is presented allowing for changes in the commerce and industrial policy of China and REE-consumption tendencies. The main characteristics of modern REE markets are considered and the volume of the world production, world trade, and prices are evaluated. The market dynamics for 2000–2020 is described and main indices and prices are forecasted to 2020. The review of modern world REE reserves, production, and trade over main countries is given. The prices and main REE buyers, as well as the consumption forecast, are presented. Prospects of the domestic REE market allowing for the fulfillment of the subprogram “Development of the Industry of Rare and Rare-Earth Metals” of the State Program of the Russian Federation “Development of Industry and an Increase in Its Competitiveness” are evaluated. The purpose of the subprogram was the development of the competitive rare-earth industry of a complete fabrication cycle to satisfy the needs of the domestic defense-industry complex, civil branches of industry, and output to foreign markets. The necessity of fulfilling this subprogram, making it possible to change the market conditions and the development of production of REEs in the territory of the Russian Federation, is noted, including by normative, nontariff, and technical regulations. Loparite and apatite remain the main sources of the REE raw materials in Russia for industrial processing for the nearest period, and the REE production from apatite will increase. It is emphasized that the prospects of REE development in the Russian Federation consist mainly of the development of new enterprises consuming REE production rather than in an increase in production of primary products.

Microstructural Evolution, Powder Characteristics, Compaction Behavior and Sinterability of Al 6061–B4C Composites as a Function of Reinforcement Content and Milling Times

Abstract: Al 6061100–x–x wt % B4C (x = 0, 5, 10, 20, 30 and 40) composites, prepared by mechanical alloying and compacted at room temperature, have been used for the present investigation. The effects of B4C content and milling time on the powder morphology, powder particle size, and other powder characteristics such as the apparent density, tap density, flow rate, cohesiveness, and hausner ratio are systematically investigated. The steady state of milling process is determined by observing the correlation between apparent densities and milling time explained by the morphological evolution of the powder particles during the milling process. The Hausner ratio (HR), estimated to evaluate friction between the particles, decreases with an increase in milling duration and B4C content due to the changes in morphology and hardness of the powders. The compressibility behavior of post-compacts as a function of compaction pressure and the B4C content was analyzed by using several linear and non-linear powder compaction equations. The linear Panelli and Ambrozio Filho, and non-linear Van Der Zwan and Siskens equations give the highest regression coefficients. The results are explained in terms of the plastic deformation capacity and plastic deformation coefficient of the powders, which are influenced by the hardness and the morphology of the powder. After compaction, the supersolidus liquid phase sintering was performed at various temperatures (585, 610 and 630°C) under high purity nitrogen atmosphere. The results revealed that the sinterability was degraded by increasing the reinforcement content, particularly above 10 wt % B4C. Neutron radiography measurements conducted on the rolled composite sheet have revealed the uniform distribution of B4C particles in the composite.

Protective Coatings La–Mn–Cu–O for Stainless-Steel Interconnector 08Х17Т for SOFC, Obtained by the Electrocrystallization Method from Non-Aqueous Solutions

Abstract: A novel method for the formation of the protective layer on stainless steel interconnectors for solid oxide fuel cells was developed. The method was based on the electrocrystallization of metals from non-aqueous solutions on the stainless-steel interconnector with consecutive thermal treatments. Suggested method was applied for the stainless-steel 08X17T. Chemical composition of the electrolyte for the electrocrystallization was made in order to obtain the oxide protective layer of the stainless-steel interconnector of the following composition: LaMn0.9Cu0.1O3. As a result, a uniform oxide layer was formed on the stainless-steel interconnector surface, protected the stainless-steel from the high-temperature oxidation leading to degradation of the functional properties of the interconnector. Forming coatings were characterized by means of grazing incidence X-rays diffraction, X-rays photoelectron spectroscopy and scanning electron microscopy. Elemental analysis and phase composition have shown that the main components of the protective coatings are found to be compounds with perovskite and spinel structures. The protective coating in the contact with cathode material based on lanthanum-strontium manganite shows significant decrease of chromium propagation from the stainless steel as a result of the diffusive firing in comparison with the sample of the stainless steel without the protective coating. Electrical resistance of the interconnector with the protective coating does not show noticeable degradation during at least 500 h at the temperature 850°C in ambient air.

Investigation into the Formation of Texture, Microstructure, and Anisotropy of Properties during Rolling Sheets of the Aluminum–Lithium 1420 Alloy

Abstract: Results of investigations into the formation of the crystallographic orientation of the structure and anisotropy of properties during rolling sheets of the aluminum–lithium 1420 alloy of the Al–Mg–Li system are given. Hot-rolled billets of the 1420 alloy were cold-rolled with intermediate quenching according to the following schedule: 7.3 mm → 4.8 mm → 3.0 mm → 1.8 mm. The samples were selected after each passage to perform mechanical testing and analyze the structure using optical microscopy and diffractometry. A deformed fibrous structure and considerable anisotropy of mechanical properties is characteristic of sheets of all considered states. Herewith, the maximal plasticity is observed at an angle of 45° to the rolling direction. The character of anisotropy of properties formed at the hot-rolling stage is not varied during cold rolling. Sheets of the 1420 alloy have a sharp deformation texture at all rolling stages due to the conservation of the unrecrystallized structure. For example, when analyzing pole figures and preferential orientations, an increase in volume fractions of rolling texture is revealed (the slow one of the brass type and more rapid of the S type) with the rise of summary deformations of cold rolling. The recrystallization texture (of the R type) is present in small amounts only after hot rolling. The volume fraction of the texture-free component decreases with an increase in summary deformations. It is concluded based on these results that, in order to decrease the fraction of the deformation texture and lower anisotropy of properties in sheets of the 1420 alloy, it is first and foremost necessary to provide the running of recrystallization at the hot-rolling stage in order to fabricate the recrystallized hot-rolled billet for subsequent cold rolling.

Structure, Mechanical Properties, and Oxidation Resistance of MoSi2, MoSiB, and MoSiB/SiBC Coatings

Abstract: Single-layer MoSi2, MoSiB, and multilayer MoSiB/SiBC coatings are fabricated by magnetron sputtering. Coating structures are investigated using X-ray diffraction, a scanning electron microscopy, and glow-discharge optical emission spectroscopy. Mechanical properties of coatings are determined by nanoindentation. The thermal stability of coatings is studied in a temperature range of 600–1200°C and oxidation resistance is studied upon heating to 1500°C. It is established that single-layer MoSiB coatings possess a hardness of 27 GPa, elasticity modulus of 390 GPa, and elastic recovery of 48%. They can also resist oxidation up to 1500°C inclusively, which is caused by the formation of the SiO2-based protective film on their surface. The MoSi2 coatings can have hardness comparable to the hardness of MoSiB coatings, but they are somewhat worse than them in regards to oxidation resistance. Multilayer MoSiB/SiBC coatings have hardness 23–27 GPa and oxidation resistance restricted by 1500°C, but they herewith have higher elastoplastic properties when compared with MoSiB.

Foundations of the Fabrication Technology of Wear-Resistant Coatings Made of Mixtures of Chromium Carbide Powders with a Metallic Binder by Explosive Pressing

Abstract: Experimental data on the explosive compaction of powder mixtures of chromium carbide (Cr3C2) with metals (Ti, Ni, Cu) are presented, their theoretical explanations are given, and scientifically substantiated principles of the composition selection and development of the explosive fabrication of wear-resistant antifriction chromium carbide hard alloys and coatings are formed on this basis. The explosive pressing of powder mixtures was performed according to the scheme with the use of a plane normally incident detonation wave in a broad range of loading parameters (the powder heating temperature in shock waves was varied in experiments from 200 to 1000°C, while the maximal pressure of the shock-wave compression varied from 4 to 16 GPa). To analyze the phase transformations, the numerical thermodynamic simulation of the phase equilibrium was performed applying the Thermo-Calc software complex. The microstructure and the chemical and phase compositions were investigated using an Axiovert 40 MAT optical microscope (Carl Zeiss, Germany), Versa 3d and Quanta 3D FEG scanning electron microscopes (FEI, United States), BS 540 (Tesla, Czech Republic) and Titan 80–300 and Techai G2 20F (FEI, United States) transmission electron microscopes, and a Solver Pro atomic force microscope (OOO NT-MDT, Zelenograd). The temperature stability and oxidation resistance at elevated temperatures of materials formed by the explosion were investigated by thermogravimetric analysis using an STA 449 F3 Jupiter device (NETZSCH, Germany) in synthetic air upon heating to 1500°C. Tribotechnical tests were performed using an MI-1M friction machine (MEZIMiV, Moscow) according to the pin–ring scheme with digging in distilled water. Mechanisms of compaction and formation of strong boundaries between the particles of powder materials during the explosive pressing are described. It is shown that chromium carbide hard alloys with a titanium binder formed by explosion retain their phase composition invariable, do not oxidize to 600°C, and have considerably better antifriction properties and wear resistance when compared with SGP-0.5 and KKhN-20 materials lubricated with water, which have been applied in friction pairs until now.

Variation in Strength, Hardness, and Fracture Toughness in Transition from Medium-Grained to Ultrafine Hard Alloy

Abstract: The microstructure and mechanical characteristics of the samples of medium-grained (WC‒8Co), submicron (WC–8Co–1Cr3C2), and ultrafine (WC–8Co–0.4VC–0.4Cr3C2) hard alloys formed by liquid-phase sintering of powders of corresponding dispersity are investigated. It is shown that the alloy hardness increases from 1356 to 1941 HV with a decrease in the average grain size from 1.65 to 0.37 μm. The comparison with the published data shows that alloys considered in this study are no worse than analogs formed by sintering under a pressure, hot pressing, and induction and spark plasma sintering by hardness and fracture toughness. Herewith, the flexural strength of alloys prepared by liquid-phase sintering is lower by a factor of 1.5–2.5 than that of alloys formed by sintering under a pressure or pressing because of the presence of pores, the maximal diameter of which is evaluated as 40 μm. An analysis of the results and published data for the correspondence of theoretical regularities is performed. It is shown that the dependences of hardness, fracture toughness, and strength on the average grain size of formed alloys and their analogs in general correspond to traditional regularities based on the Hall–Petch and Orowan–Griffiths laws, despite the presence of theoretical prerequisites for the deviation from them.

Direct Calcification–Carbonation Method for Processing of Bayer Process Red Mud

Abstract: The highly-alkaline red mud, which is the Bayer process residue generated from the alumina industry, is a severe environmental problem. In this study, a new calcification–carbonation process was proposed for red mud disposal. Red mud was processed by lime to convert the aqueous silicon phase into hydrogarnet, which was then decomposed by CO2 to recover alumina. In the direct carbonation process, the NaOH-containing solution after calcification was directly carbonated without prior liquid–solid separation. The discrete and direct carbonation processes had alumina recovery rates of 34.9 and 35.5%, respectively, with 0.15 and 0.21 wt % Na2O in the final red muds, respectively. The optimum NaOH concentration in the calcification liquor was 30 g/L. Under these conditions, alumina recovery was increased to 44.5% and the Na2O concentration in the processed red mud was reduced to <1 wt %. The final red mud can be used as a construction material.

Influence of a Silicon Additive on Resistivity and Hardness of the Al–1% Fe–0.3% Zr Alloy

Abstract: Isothermal sections of the diagram of the Al–Fe–Si–Zr alloy at temperatures of 450 and 600°C, as well as polythermal sections at concentrations of silicon up to 2 wt % and zirconium up to 1 wt %, are analyzed using computational methods with the help of Thermo-Calc software. It is shown that the favorable phase composition consisting of the aluminum solid solution (Al), the Al8Fe2Si phase, and Zr (which completely enters the composition of the solid solution (Al) during the formation of the cast billet) can be attained in equilibrium conditions at silicon concentrations of 0.27–0.47 wt %. To implement the above-listed structural components in nonequilibrium conditions and ensure that Zr enters the (Al) composition, experimental ingots were fabricated at an elevated cooling rate (higher than 10 K/s). A metallographic analysis of the cast structure of experimental samples revealed the desired structure with contents of 0.25 wt % Si and 0.3 wt % Zr in the alloy. The microstructure of the Al–1% Fe–0.3% Zr–0.5% Si alloy also contains the eutectic (Al) + Al8Fe2Si; however, the Al8Fe2Si phase partially transforms into Al3Fe. The structure of the alloy with 0.25 wt % Si in the annealing state at 600°C contains fragmented particles of the degenerate eutectic (Al) + Al8Fe2Si along the boundaries of dendritic cells. It is established that the Si: Fe = 1: 2 ratio in the alloy positively affects its mechanical properties, especially hardness, without substantially lowering the specific conductivity during annealing, which is explained by the formation of the particles of the Al8Fe2Si phase of the compact morphology in the structure. Moreover, silicon accelerates the decay of the solid solution by zirconium, which is evidenced by the experimental plots of the dependence of hardness and resistivity on the annealing step. The best complex of properties was shown by the Al–1% Fe–0.3% Zr–0.25% Si alloy in the annealing stage at 450°C with the help of the optimization function at specified values of hardness and resistivity.

Synthesis, Corrosion and Bioactivity Evaluation of Gelatin/Silicon and Magnesium Co-Doped Fluorapatite Nanocomposite Coating Applied on AZ31 Mg Alloy

Abstract: In this study, a nano-composite composed of gelatin as the matrix and Si-Mg-FA nano-particles as an additive was deposited on the AZ31 Mg alloy via dip coating method. In addition, a coating composed of MgO, MgSiO3 and Mg2SiO4 phases was applied on the AZ31 Mg alloy by anodizing process. It was found that the Nano-composite coating with a uniform distribution of nano-particles within the gelatin matrix with the thickness of about 9 µm was dense, crack-free and uniform whereas the surface of anodized layer was relatively coarse due to the presence of flaws and micro-cracks. The surface morphology, EDS analysis and FTIR results revealed the ability of nano-composite coated specimen to form the bone-like apatite. Due to the presence of aforementioned phases and special surface features, the anodized specimen possessed higher and lower corrosion resistance than uncoated and nano-composite coated specimens, respectively. The passive coating resistances (RCT) of nano-composite, anodized specimen and uncoated samples were 2164, 1449 and 1024 Ω cm2, respectively.

Revisiting the Possibility of Formation of Hard Alloys from Powder Mixtures of Carbides with Metals by Explosive Compacting without Sintering

Abstract: The results of experimental investigations into the possibility of formation of consolidated power hard alloys by the explosive compacting method without subsequent sintering are presented. Carbides of tungsten (WC), chromium (Cr3C2), and silicon (SiC) are used as main carbide components, and titanium, nickel, and copper serve as a metallic binder. The compression pressure of the powder mixture in shockwaves during the explosive compacting is varied in a range from 5 to 16 GPa, and the heating temperature is varied from 250 to 950°C. The structure, chemical composition, and phase composition are investigated using optical (Axiovert 40MAT, Carl Zeiss), scanning electron (FEI Versa 3D), and transmission electron (FEI Titan 80-300, Tecnai G2 20F) microscopes. It is shown that powder compositions with the titanium binder are densified substantially better than mixtures with copper or nickel. The hardness of materials after the explosive compacting reaches 1200 HV. The range of temperatures corresponding to (0.35–0.4)tm (where tm is the absolute melting point of the main alloy carbide), the cleavage character of the samples changes from intercrystallite to transcrystallite when passing through it. It is revealed that this is associated with the formation of strong boundaries between carbide particles and metallic matrix, which represent interlayers with a thickness of the order of 80–100 nm with its proper crystalline structure differing from the structure of main alloy components.

Experimental and Kinetic Study of Magnesium Extraction and Leaching from Laterite Nickel Ore by Roasting with Ammonium Sulfate

Abstract: Laterite-nickel ore was roasted with ammonium sulfate to extract magnesium by a single-factor experiment, and an orthogonal test was employed to optimize the conditions. The optimum roasting conditions were: calcination temperature, 450°C; calcination time, 120 min; molar ratio of reactants, 2 : 1; granularity <80 µm. The kinetics of the roasting process were also studied. The experimental results showed that the extraction rate of magnesium increased as the calcination temperature increased. The reaction rate of magnesium is in accordance with the shrinking non-reacted nuclear model for the solid product formation reaction. The roasting reaction is controlled by internal diffusion. The apparent activation energy is E = 18.96 kJ mol–1. The kinetic equation is $${\text{1}} + {\text{2}}\left( {{\text{1}} - {\alpha\text{}}} \right) - {\text{3}}{{\left( {{\text{1}} - {\alpha\text{}}} \right)}^{{{{\text{2}} \mathord{\left/ {\vphantom {{\text{2}} {\text{3}}}} \right. \kern-0em} {\text{3}}}}}} = {\text{0}}{\text{.05061exp}}\left[ { - {{{\text{18}}{\text{963}}} \mathord{\left/ {\vphantom {{{\text{18}}{\text{963}}} {\left( {RT} \right)}}} \right. \kern-0em} {\left( {RT} \right)}}} \right]t.$$ A single factor experiment and orthogonal test were carried out to optimize the magnesium leaching process reaction conditions. The optimum conditions of the leaching process were: leaching temperature, 60°C; leaching time, 60 min; liquid to solid ratio, 2.5 : 1; stirring intensity, 400 r min–1. The kinetic equation is 1 – (1 – α)2/3 = 0.3991exp(–8632/RT)t. The apparent activation energy is E = 8.63 kJ mol–1. The reaction rate of the leaching process was controlled by external diffusion.

Solvent Extraction of Copper Using TBP, D2EHPA and MIBK

Abstract: In this research, a synergetic system of solvent extraction process was developed to recover copper from aqueous solutions with tri-n-butyl phosphate (TBP), di-2-ethyl hexyl phosphoric acid (D2EHPA) and methyl iso-butyl ketone (MIBK). The effect of significant parameters such as pH, organic phase composition, aqueous to organic phase ratio (A : O), sodium acetate (CH3COONa) concentration and presence of HCl were studied. The optimum mixing ratio of TBP: MIBK was found to to 7 : 3 for the copper extraction. In addition, the usage of HCl caused a reduction in the extraction percentage due to the instability of the TBP complex with copper in the presence of HCl. The A : O ratio of 1 : 1 resulted in a higher percentage of copper extraction. Finally, MIBK-TBP-D2EHPA-acetate system could extract more than 99% of copper under the optimum condition.

A Beneficiation Study on a Low Grade Iron Ore by Gravity and Magnetic Separation

Abstract: In this paper, a sample from Tange-zagh iron mine was characterized by gravity and magnetic separation methods. The mineralogical studies showed that hematite and goethite are the main iron-bearing minerals with insignificant amounts of FeO. The results indicated that spiral separation yields higher separation efficiency than others. The combination of spiral and multi gravity methods showed that the grade and recovery could be obtained 58.7 and 55.6%, respectively. Scrubbing and de-sliming stages increased the recovery in the wet high intensity magnetic process. With a four-stage process of separation, the WHIMS by scrubbing and de-sliming was applied to achieve a final concentrate with grade of 62.6% Fe and recovery of 57.1% Fe.

Development of Fabrication Modes of Deformed Semifinished Products from the Experimental Scandium-Containing Aluminum Alloy and Investigation into Their Mechanical Properties

Abstract: The urgency of works directed at the fabrication of new alloys of the Al–Mg system alloyed with scandium, which are characterized by a profitable combination of operational and mechanical properties such as weldability, corrosion resistance, and sufficient strength, is shown. Flat ingots of the experimental scandium-containing alloy 560 × 1360 × 4520 mm in size are fabricated in industrial conditions. Modes of thermal treatment and sheet rolling are developed and approved for billets with a maximal thickness of 40 mm cut from them. A DUO 330 mill with flat rolls with an initial diameter of 330 mm and barrel width of 540 mm is used as the rolling equipment. Experimental investigations, which include the preparation of billets to rolling (homogenizing annealing and face milling), hot rolling at 450°C, cold rolling to a thickness of 3 mm, and annealing of cold-deformed semifinished products, result in the fabrication of deformed semifinished products fabricated according to various schemes of reduction during rolling and passed heat treatment. The maximal degree of summary deformation while rolling the billets to a thickness of 3 mm is 92.5%, while drawing for the passage varies from 1.04 to 1.2. Mechanical properties of deformed and annealed semifinished products of various thicknesses made of the experimental alloy are determined using an LFM400 universal test machine with an effort of 400 kN according to GOST (State Standard) 1497–84 and regularities of their variation, depending on the summary degree of deformation during rolling, are revealed. It is established that, when rolling strips made of the experimental scandium-containing aluminum alloy, the temporary tensile strength and yield strength of the material increase, while the relative elongation decreases, which corresponds to general ideas of the theory of metal forming. An analysis of the mechanical properties of the semifinished products shows that the level of strength and plastic properties is rather high, wherein the temporary tensile strength for cold-deformed samples reaches 453–481 MPa, the yield strength of metal reaches 429–457 MPa, and the relative elongation reaches 3.8–5.0%. The application of annealing made it possible to increase the relative elongation to 14–16% at sufficiently high values of the yield strength (up to 277 MPa). The results of our investigations allow us to develop the modes of casting, rolling, and annealing for the preparation of semifinished products made of the alloy of the Al–Mg system economically alloyed with scandium in limits of 0.10–0.14%, which will be used when approving the machining technologies in industrial conditions.

Influence of the Magnetic Field on the Crystallization of Aluminum Melts

Abstract: In order to control the crystallization of metals consciously with the purpose of forming the specified ingot microstructure, various physical fields are used. They vary the internal state of the melt and, consequently, the crystallization kinetics when affecting the melt. In this article, the thermodynamic and kinetics of the crystallization of aluminum under melt processing with the magnetic field is described. A rather simple experimental setup which makes it possible to investigate the magnetic-field effect on the melts of aluminum or other metals and alloys is designed. It consists of several main units: (1) the electrical furnace, (2) the water-cooled copper crystallizer combined with an electromagnetic coil, (3) mechanical facility for the rapid motion of a crucible with the aluminum melt, (4) the monitoring and control system of the melt temperature, and (5) the electronic part for recording and processing information. It is established experimentally that the magnetic field varies the temperature of the melt–crystal phase equilibrium, latent heat of the phase transition, and supercooling temperature of the melt during crystallization. It is shown that the variation in these parameters leads to a decrease in the radius of critical nuclei and an increase in their nucleation rate. The temperature–temporal dependences of crystallization are found. It is established experimentally that the crystallization time shortens under the aluminum melt treatment with the magnetic field. The analysis of aluminum samples formed under the magnetic-field effect showed that their structure is finer grained when compared with the samples not subjected to such treatment.

Roasting Pre-Treatment of High-Sulfur Bauxite for Sulfide Removal and Digestion Performance of Roasted Ore

Abstract: Alumina refineries in China continue to face challenges in achieving clean and efficient utilization of high-sulfur bauxite. Disulfide ions, $${\text{S}}_{2}^{{2 - }},$$ in FeS2 can be considered as active components in the Bayer process for alumina production, but they lead to corrosion of the equipment used in the processing of bauxite. Our research investigates the transformation rules of $${\text{S}}_{2}^{{2 - }}$$ in bauxite during roasting, and the impact of digestion conditions on the digestion efficiency of the roasted ore and $${\text{S}}_{2}^{{2 - }}$$ distribution. The results revealed that the onset temperature of kaolinite dehydration was approximately 700°C. The standard Gibbs free energy of all other reactions, including pyrite oxidation at 500–750°C, was negative. Dehydration began at 433.0°C, attained its maximum rate at 508.5°C, and ended at 593.0°C. Roasting pre-treatment removed approximately 95% of the sulfide, promoted digestion of alumina in bauxite, and reduced the active sulfur content by ~27%.

Producing Metallic Antimony with Low Arsenic Content from Antimony Concentrate

Abstract: The basis of the concentrate is sodium hexahydroxoantimonate or mineral mopungite. Upon reduction of the concentrate with coke, ground antimony containing 0.34% arsenic was obtained. To reduce the arsenic content in the rough metal to 0.1% and exclude the stages of antimony refining from arsenic, reductive melting is proposed in the presence of lead compounds. Because of the smelting reduction of the antimonate concentrate in the presence of sodium plumbite or lead oxide, a rough antimony with an arsenic content of 0.07–0.1% was obtained. The process of reductive smelting of the antimonate concentrate on black antimony was carried out in an oven with silicate heaters in alundum crucibles with batches of charge of 100–150 grams. The content of impurities and the base metal in antimony was determined by chemical and atomic absorption methods. The form of arsenic in the concentrate was determined by X-ray phase analysis. The analysis was carried out on an automated diffractometer DRON-3 with CuKα radiation, s-filter. The concentration of arsenic in the slag phase in the form of lead diarsenate Pb2As2O7 is shown. Thermal gravimetric analysis of the smelting reduction process of the antimonate concentrate was studied on the Q-1000/D derivatograph of the F. Paulik, J. Paulik and L. Erdey systems of the “MOM” company. Thermogravimetric researches of process of recovery melting of the furnace charge consisting of an antimony concentrate, lead oxide and coke as a result of which it is established that process of formation of metal antimony proceeds in the range of temperatures 445–950°C are conducted.

Study on Pure Mercurous Chloride Leaching with Sodium Thiosulfate

Abstract: Mercurous chloride (Hg2Cl2), also known as Calomel, is a typical mercury-containing mineral found in nature. In this work, the leaching behaviour of pure mercurous chloride dissolved in pure water and in thiosulfate solution was investigated. The mercurous chloride hardly dissolved in sulfuric acid solution at pH of 3 and pure water at pH of 6.4, with the corresponding maximum Hg extraction percentage at 3.1 and 7.5% respectively. However, the Hg extraction percentage increased to 45.8% in sodium hydroxide solution at pH of 11.2. The mercury extraction percentage reached a high of 62.6% in thiosulfate solution, and the leaching kinetics results show that the activation energy is 6.6 kJ/mol. This study indicates that the thiosulfate solution can efficiently extract mercury from mercurous chloride.

Recovery of Silicon and Iron Oxides from Alumina-Containing Sweepings of Aluminum Production

Abstract: The method of recovery of contaminating components from sweepings of the aluminum production for their further return into the electrolyzer is proposed. To concentrate the material, the following processing flowsheet is proposed: milling–classification–reverse flotation–thickening. For the most complete removal of silicon and iron oxides during the flotation of sweepings, the Flotigam 7266 flotation reagent produced by Clariant (Germany), which is a mixture of primary fatty alkyl amines, is used. To remove carbon particles, the combination of pine oil in a mixture with kerosene is used. Flotation is performed using a FML 0.3 flotation machine. The initial material, chamber product, and tails are analyzed for the content of carbon and aluminum, iron, and silicon oxides using X-ray spectral (XSA), X-ray phase (XPA), and chemical analyses. It is established that processing the total material mass does not make it possible to acquire a product with an acceptable content of silicon and iron oxides. Based on the XPA of various fractions of the initial material, it is proposed to process the material fractions containing the minimal amount of contaminating substances (carbon and silicon and iron oxides). Two fractions are selected for processing using the flotation method by the XRS results of various material fractions:–0.071 mm and +5.0 mm. When processing the first of them, the chamber product of the acceptable quality is acquired. A product with a high content of alumina and fluorinated components at low carbon and iron oxide concentrations but a considerable amount of silicon oxide is acquired from a coarse electrolyte-containing fraction (+5.0 mm). The further use of this product is possible to fabricate aluminum–silicon alloys.

Effect of Heat Treatment on the Structure and Properties of Sheet Semifinished Products Made of a Heat-Resistant Alloy Based on Titanium and Alloyed with Rare-Earth Metal

Abstract: This study is a continuation of investigations into the influence of microalloying with rare-earth metal gadolinium on the structure formation and properties of the titanium alloy under the thermal effect. It has been established previously that the introduction of gadolinium into an experimental heat-resistant alloy promotes the structural transformation in the cast state, leads to a decrease in size of structural components, and affects the growth and nucleation rates of the particles. It is revealed that additional alloying with gadolinium exerts no significant effect on the formation of the microstructure of hot-rolled sheets made of heat-resistant experimental alloy after annealing at 950°C. The structure is presented by equiaxial particles of the primary α-phase, secondary α-phase with lamellar morphology, and a small amount of the β-phase. It is determined that ordering proceeds in primary α-phase particles and precipitation α2-phase particles is observed during isothermal holding (t = 700°C, τ = 100 h), while silicide chemical compounds form at the α/β-boundary. It is shown that the α2-phase is formed in the body of the particles of the primary α-phase, while its near-boundary regions are free of inclusions, which is caused by their depletion with aluminum due to the β → α transformation. It is established that the sizes of precipitating silicide particles decrease with an increase in the gadolinium content in the alloy. The average particle size is 0.2–0.3 μm in the alloy with 0% Gd; on the contrary, it decreases to 0.05–0.1 μm in the alloy with 0.2% Gd. It is shown that the introduction of 0.2% Gd into the heat-resistant titanium alloy leads to a decrease in the depth of the “alpha-case” layer and an increase in cyclic durability and short-term strength at 700°C by 30%.