添加CaCO3后碳热还原钒钛磁铁矿精矿过程中钛酸钙的形成

The formation of calcium titanate in the carbothermic reduction of vanadium titanomagnetite concentrate (VTC) by adding CaCO₃ was investigated. Thermodynamic analysis was employed to show the feasibility of calcium titanate formation by the reaction of ilmenite and CaCO₃ in a reductive atmosphere, where ilmenite is more easily reduced by CO or carbon in the presence of CaCO₃. The effects of CaCO₃ dosage and reduction temperature on the phase transformation and metallization degree were also investigated in an actual roasting test. Appropriate increase of CaCO₃ dosages and reduction temperatures were found to be conducive to the formation of calcium titanate, and the optimum conditions were a CaCO₃ dosage of 18wt% and a reduction temperature of 1400°C. Additionally, scanning electron microscopy–energy dispersive spectrometry (SEM–EDS) analysis shows that calcium titanate produced via the carbothermic reduction of VTC by CaCO₃ addition was of higher purity with particle size approximately 50 μm. Hence, the separation of calcium titanate and metallic iron will be the focus in the future study.     

Microwave absorption properties of SiC@SiO2@Fe3O4 hybrids in the 2-18 GHz range

To enhance the microwave absorption performance of silicon carbide nanowires (SiCNWs), SiO₂ nanoshells with a thickness of approximately 2 nm and Fe₃O₄ nanoparticles were grown on the surface of SiCNWs to form SiC@SiO₂@Fe₃O₄ hybrids. The microwave absorption performance of the SiC@SiO₂@Fe₃O₄ hybrids with different thicknesses was investigated in the frequency range from 2 to 18 GHz using a free-space antenna-based system. The results indicate that SiC@SiO₂@Fe₃O₄ hybrids exhibit improved microwave absorption. In particular, in the case of an SiC@SiO₂ to iron(Ⅲ) acetylacetonate mass ratio of 1:3, the microwave absorption with an absorber of 2-mm thickness exhibited a minimum reflection loss of -39.58 dB at 12.24 GHz. With respect to the enhanced microwave absorption mechanism, the Fe₃O₄ nanoparticles coated on SiC@SiO₂ nanowires are proposed to balance the permeability and permittivity of the materials, contributing to the microwave attenuation.     

Comparative study on the corrosion behavior of X52, 3Cr,and 13Cr steel in an O2-H2O-CO2 system:products,reaction kinetics,and pitting sensitivity

The corrosion behaviors of X52, 3Cr low-alloy steel, and 13Cr stainless steel were investigated in an O₂-H₂O-CO₂ environment at various temperatures and O₂-CO₂ partial-pressure ratios. The results showed that the corrosion rates of X52, 3Cr, and 13Cr steels increased with increasing temperature. The corrosion rates slowly increased at temperatures less than 100℃ and increased sharply when the temperature exceeded 100℃. In the absence of O₂, X52, 3Cr, and 13Cr exhibited uniform corrosion morphology and FeCO₃ was the main corrosion product. When O₂ was introduced into the system, various forms of Fe₂O₃ appeared on the surface of the samples. The Cr content strongly influenced the corrosion resistance. The 3Cr steel with a low Cr content was more sensitive to pitting than the X52 or 13Cr steel. Thus, pitting occurred on the surface of 3Cr when 1.25 MPa of O₂ was added; this phenomenon is related to the non-uniform distribution of Cr in 3Cr.     

微波预处理对复杂铜矿磨矿及浮选动力学的影响

The effect of CaCO₃, Na₂CO₃, and CaF₂ on the reduction roasting and magnetic separation of high-phosphorus iron ore containing phosphorus in the form of Fe₃PO₇ and apatite was investigated. The results revealed that Na₂CO₃ had the most significant effect on iron recovery and dephosphorization, followed by CaCO₃, the effect of CaF₂ was negligible. The mechanisms of CaCO₃, Na₂CO₃, and CaF₂ were investigated using X-ray diffraction (XRD), scanning electron microscopy and energy dispersive spectrometry (SEM–EDS). Without additives, Fe₃PO₇ was reduced to elemental phosphorus and formed an iron–phosphorus alloy with metallic iron. The addition of CaCO₃ reacted with Fe₃PO₇ to generate an enormous amount of Ca₃(PO₄)₂ and promoted the reduction of iron oxides. However, the growth of iron particles was inhibited. With the addition of Na₂CO₃, the phosphorus in Fe₃PO₇ migrated to nepheline and Na₂CO₃ improved the reduction of iron oxides and growth of iron particles. Therefore, the recovery of iron and the separation of iron and phosphorus were the best. In contrast, CaF₂ reacted with Fe₃PO₇ to form fine Ca₃(PO₄)₂ particles scattered around the iron particles, making the separation of iron and phosphorus difficult.     

New insights into the effects of silicon content on the oxidation process in silicon-containing steels

Simultaneous thermal analysis (STA) was used to investigate the effects of silicon content on the oxidation kinetics of silicon- containing steels under an atmosphere and heating procedures similar to those used in industrial reheating furnaces for the production of hot-rolled strips. Our results show that when the heating temperature was greater than the melting point of Fe₂SiO₄, the oxidation rates of steels with different silicon contents were the same; the total mass gain decreased with increasing silicon content, whereas it increased with increasing oxygen content. The oxidation rates for steels with different silicon contents were constant with respect to time under isothermal conditions. In addition, the starting oxidation temperature, the intense oxidation temperature, and the finishing oxidation temperature increased with increasing silicon content; the intense oxidation temperature had no correlation with the melting of Fe₂SiO₄. Moreover, the silicon distributed in two forms: as Fe₂SiO₄ at the interface between the innermost layer of oxide scale and the iron matrix, and as particles containing silicon in grains and grain boundaries in the iron matrix.     

Incubation and development of corrosion in microstructures of low alloy steels under a thin liquid film of NaCl aqueous solution

Electrochemical measurement, optical microscopy, and scanning electron microscopy were employed to investigate the corrosion behavior of some low alloy steels. The steels were held under a thin liquid film of 0.5wt% NaCl aqueous solution. It is found that the steels with the same chemical composition but different microstructures exhibit obviously different corrosion behaviors. However, the corrosion behavior of the steels with different compositions but the same microstructures may be similar in the present investigation. The corrosion rate of bainite is slower than that of ferrite and pearlite. The corrosion products of bainite are uniform and fine. The size of carbon-rich phases produces a great impact on the corrosion of the steels, whether in the initial stage or in the long term. It is easy to induce large pitting for carbon-rich phases with large size, which damages the compactness of the rust layer.     

Fabrication of Fe–TiC–Al2O3 composites on the surface of steel using a TiO2–Al–C–Fe combustion reaction induced by gas tungsten arc cladding

The aim of the present study was to fabricate Fe–TiC–Al₂O₃ composites on the surface of medium carbon steel. For this purpose, TiO₂–3C and 3TiO₂–4Al–3C–xFe (0 ≤ x ≤ 4.6 by mole) mixtures were pre-placed on the surface of a medium carbon steel plate. The mixtures and substrate were then melted using a gas tungsten arc cladding process. The results show that the martensite forms in the layer produced by the TiO₂–3C mixture. However, ferrite–Fe₃C–TiC phases are the main phases in the microstructure of the clad layer produced by the 3TiO₂–4Al–3C mixture. The addition of Fe to the TiO₂–4Al–3C reactants with the content from 0 to 20wt% increases the volume fraction of particles, and a composite containing approximately 9vol% TiC and Al₂O₃ particles forms. This composite substantially improves the substrate hardness. The mechanism by which Fe particles enhance the TiC + Al₂O₃ volume fraction in the composite is determined.     

Influence of oxide scales on the corrosion behaviors of B510L hot-rolled steel strips

The influence of oxide scales on the corrosion behaviors of B510L hot-rolled steel strips was investigated in this study. Focused ion beams and scanning electron microscopy were used to observe the morphologies of oxide scales on the surface and cross sections of the hot-rolled steel. Raman spectroscopy and X-ray diffraction were used for the phase analysis of the oxide scales and corrosion products. The corrosion potential and impedance were measured by anodic polarization and electrochemical impedance spectroscopy. According to the results, oxide scales on the hot-rolled strips mainly comprise iron and iron oxides. The correlation between mass gain and test time follows a power exponential rule in the damp-heat test. The corrosion products are found to be mainly composed of γ-FeOOH, Fe₃O₄, α-FeOOH, and γ-Fe₂O₃. The contents of the corrosion products are different on the surfaces of the steels with and without oxide scales. The steel with oxide scales is found to show a higher corrosion resistance and lower corrosion rate.     

H2O2溶液对钛种植体表面的处理

The surface treatment is important for titanium and its alloys as promising candidates for dental implantation due to their bioinert surface. Titanium surface samples were modified using H₂O₂ solution at different times up to 72 h to boost their bioactivity. According to the results of the field emission scanning electron microscopy test, some nanostructures are formed on the surface of treated titanium samples and increased in size by increasing the time of treatment up to 24 h. After 24 h of application, the sharpness of nanostructures decreased and the micro-cracks and discontinuity in the coating surface increased. The results of the X-ray diffraction study and Raman spectroscopy revealed that anatase (TiO₂) was formed on the surface of treated titanium samples. The peak intensity of Raman spectroscopy increased with an improvement in treatment time of up to 24 h and then decreased due to the discontinuity of the coating. Full wettability and ability to form apatite were reached at 6 h of treatment. It is clear that the treatment time has a significant effect on the surface treatment of titanium using the H₂O₂ solution.     

Fabrication of a TiO2-P25/(TiO2-P25+TiO2 nanotubes) junction for dye sensitized solar cells

The dye sensitized solar cell（DSSC）, which converts solar light into electric energy, is expected to be a promising renewable energy source for today’s world. In this work, dye sensitized solar cells, one containing a single layer and one containing a double layer, were fabricated. In the double layer DSSC structure, the under-layer was TiO₂-P25 film, and the top layer consisted of a mixture of TiO₂-P25 and TiO₂ nanotubes. The results indicated that the efficiency of the DSSC with the double layer structure was a significant improvement in comparison to the DSSC consisting of only a single film layer. The addition of TiO₂-P25 in the top layer caused an improvement in the adsorption of dye molecules on the film rather than on the TiO₂ nanotubes only. The presence of the TiO₂ nanotubes together with TiO₂-P25 in the top layer revealed the enhancement in harvesting the incident light and an improvement of electron transport through the film.     

Cathodic reaction mechanisms in CO2 corrosion of low-Cr steels

The cathodic reaction mechanisms in CO₂ corrosion of low-Cr steels were investigated by potentiodynamic polarization and galvanostatic measurements. Distinct but different dominant cathodic reactions were observed at different pH levels. At the higher pH level (pH >~5), H₂CO₃ reduction was the dominant cathodic reaction. The reaction was under activation control. At the lower pH level (pH <~3.5), H+ reduction became the dominant one and the reaction was under diffusion control. In the intermediate area, there was a transition region leading from one cathodic reaction to another. The measured electrochemical impedance spectrum corresponded to the proposed cathodic reaction mechanisms.     

Effects of SiO2 on the preparation and metallurgical properties of acid oxidized pellets

The effects of SiO₂ content on the preparation process and metallurgical properties of acid oxidized pellets, including compressive strength, reduction, and softening–melting behaviors, were systematically investigated.Mineralogical structures, elemental distribution, and pore size distribution were varied to analyze the mechanism of the effects.The results show that with an increase in SiO₂ content from 3.51 wt%to 7.18 wt%, compressive strength decreases from 3150 N/pellet to 2100 N/pellet and reducibility decreases from 76.5% to 71.4%.The microstructure showed that pellets with high SiO₂ content contained more magnetite in the mineralogical structures.Additionally, some liquid phases appeared, which hindered the continuous crystallization of hematite.Also, the softening–melting properties of the pellets clearly deteriorated as the SiO₂ content increased.With increasing SiO₂ content, the temperature range of the softening–melting zone decreased, and the maximum differential pressure and the comprehensive permeability index increased significantly.When acid oxidized pellets are used as the raw materials for blast furnace smelting, it should be combined with high basicity sinters to improve the softening–melting behaviors of the comprehensive charge.     

Electrical conductivity optimization of the Na3AlF6-Al2O3-Sm2O3 molten salts system for Al-Sm intermediate binary alloy production

Metal Sm has been widely used in making Al-Sm magnet alloy materials. Conventional distillation technology to produce Sm has the disadvantages of low productivity, high costs, and pollution generation. The objective of this study was to develop a molten salt electrolyte system to produce Al-Sm alloy directly, with focus on the electrical conductivity and optimal operating conditions to minimize the energy consumption. The continuously varying cell constant (CVCC) technique was used to measure the conductivity for the Na₃AlF₆-AlF₃-LiF-MgF₂-Al₂O₃-Sm₂O₃ electrolysis medium in the temperature range from 905 to 1055℃. The temperature (t) and the addition of Al₂O₃ (W(Al₂O₃)), Sm₂O₃ (W(Sm₂O₃)), and a combination of Al₂O₃ and Sm₂O₃ into the basic fluoride system were examined with respect to their effects on the conductivity (κ) and activation energy. The experimental results showed that the molten electrolyte conductivity increases with increasing temperature (t) and decreases with the addition of Al₂O₃ or Sm₂O₃ or both. We concluded that the optimal operation conditions for Al-Sm intermediate alloy production in the Na₃AlF₆-AlF₃-LiF-MgF₂-Al₂O₃-Sm₂O₃ system are W(Al₂O₃) + W(Sm₂O₃)=3wt%, W(Al₂O₃):W(Sm₂O₃)=7:3, and a temperature of 965 to 995℃, which results in satisfactory conductivity, low fluoride evaporation losses, and low energy consumption.     

Upgrading and dephosphorization of Western Australian iron ore using reduction roasting by adding sodium carbonate

The technology of direct reduction by adding sodium carbonate (Na₂CO₃) and magnetic separation was developed to treat Western Australian high phosphorus iron ore. The iron ore and reduced product were investigated by optical microscopy and scanning electron microscopy. It is found that phosphorus exists within limonite in the form of solid solution, which cannot be removed through traditional ways. During reduction roasting, Na₂CO₃ reacts with gangue minerals (SiO₂ and Al₂O₃), forming aluminum silicate-containing phosphorus and damaging the ore structure, which promotes the separation between iron and phosphorus during magnetic separation. Meanwhile, Na₂CO₃ also improves the growth of iron grains, increasing the iron grade and iron recovery. The iron concentrate, assaying 94.12wt% Fe and 0.07wt% P at the iron recovery of 96.83% and the dephosphorization rate of 74.08%, is obtained under the optimum conditions. The final product (metal iron powder) after briquetting can be used as the burden for steelmaking by an electric arc furnace to replace scrap steel.     

Relationship between the specific surface area of rust and the electrochemical behavior of rusted steel in a wet-dry acid corrosion environment

The relationship between the specific surface area (SSA) of rust and the electrochemical behavior of rusted steel under wet-dry acid corrosion conditions was investigated. The results showed that the corrosion current density first increased and then decreased with increasing SSA of the rust during the corrosion process. The structure of the rust changed from single-layer to double-layer, and the γ-FeOOH content decreased in the inner layer of the rust with increasing corrosion time; by contrast, the γ-FeOOH content in the outer layer was constant. When the SSA of the rust was lower than the critical SSA corresponding to the relative humidity during the drying period, condensed water in the micropores of the rust could evaporate, which prompted the diffusion of O₂ into the rust and the following formation process of γ-FeOOH, leading to an increase of corrosion current density with increasing corrosion time. However, when the SSA of the rust reached or exceeded the critical SSA, condensate water in the micro-pores of the inner layer of the rust could not evaporate which inhibited the diffusion of O₂ and decreased the γ-FeOOH content in the inner rust, leading to a decrease of corrosion current density with increasing corrosion time.     

硫酸溶液中IrO2–ZrO2二元氧化物涂层的电化学行为及耐蚀性

In this study, we prepared Ti/IrO₂–ZrO₂ electrodes with different ZrO₂ contents using zirconium-n-butoxide (C₁₆H₃₆O₄Zr) and chloroiridic acid (H₂IrCl₆) via a sol–gel route. To explore the effect of ZrO₂ content on the surface properties and electrochemical behavior of electrodes, we performed physical characterizations and electrochemical measurements. The obtained results revealed that the binary oxide coating was composed of rutile IrO₂, amorphous ZrO₂, and an IrO₂–ZrO₂ solid solution. The IrO₂–ZrO₂ binary oxide coatings exhibited cracked structures with flat regions. A slight incorporation of ZrO₂ promoted the crystallization of the active component IrO₂. However, the crystallization of IrO₂ was hindered when the added ZrO₂ content was greater than 30at%. The appropriate incorporation of ZrO₂ enhanced the electrocatalytic performance of the pure IrO₂ coating. The Ti/70at%IrO₂–30at%ZrO₂ electrode, with its large active surface area, improved electrocatalytic activity, long service lifetime, and especially, lower cost, is the most effective for promoting oxygen evolution in sulfuric acid solution.     

功能梯度Ni?W/Er2O3稀土纳米颗粒复合膜的电沉积

Multi-layered functionally graded (FG) structure Ni?W/Er₂O₃ nanocomposite films were prepared by continuously changing the deposition parameters, in which the Er₂O₃ and W contents varied with thickness. The microstructure and chemical composition of the electrodeposited Ni?W/Er₂O₃ films were determined by scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDS). The anti-corrosion and wear properties of the electrodeposition films were investigated by electrochemical measurement and ball-on-disk friction test. The microhardness distribution of the cross section of nanocomposites was measured by nanoindentation. The results showed that with decreasing agitation rate or increasing average current density, the contents of Er₂O₃ nanoparticles and tungsten were distributed in a gradient along the thickness, and the contents on the surface were larger. By comparison, FG Ni?W/Er₂O₃ films had better anti-corrosion and wear properties than the uniform Ni?W/Er₂O₃ films. Atomic force microscopy (AFM) and profilometry measurements indicated that Er₂O₃ nanoparticles had an effect on the surface roughness.     

9Cr?5Si?3Al铁素体耐热钢的高温氧化行为

To improve the oxidation properties of ferritic heat-resistant steels, an Al-bearing 9Cr?5Si?3Al ferritic heat-resistant steel was designed. We then conducted cyclic oxidation tests to investigate the high-temperature oxidation behavior of 9Cr?5Si and 9Cr?5Si?3Al ferritic heat-resistant steels at 900 and 1000°C. The characteristics of the oxide layer were analyzed by X-ray diffraction, scanning electron microscopy, and energy dispersive spectroscopy. The results show that the oxidation kinetics curves of the two tested steels follow the parabolic law, with the parabolic rate constant k_p of 9Cr?5Si?3Al steel being much lower than that of 9Cr?5Si steel at both 900 and 1000°C. The oxide film on the surface of the 9Cr?5Si alloy exhibits Cr₂MnO₄ and Cr₂O₃ phases in the outer layer after oxidation at 900 and 1000°C. However, at oxidation temperatures of 900 and 1000°C, the oxide film of the 9Cr?5Si?3Al alloy consists only of Al₂O₃ and its oxide layer is thinner than that of the 9Cr?5Si alloy. These results indicate that the addition of Al to the 9Cr?5Si steel can improve its high-temperature oxidation resistance, which can be attributed to the formation of a continuous and compact Al₂O₃ film on the surface of the steel.     

Activity coefficients of NiO and CoO in CaO-Al2O3-SiO2 slag and their application to the recycling of Ni-Co-Fe-based end-of-life superalloys via remelting

To design optimal pyrometallurgical processes for nickel and cobalt recycling, and more particularly for the end-of-life process of Ni-Co-Fe-based end-of-life (EoL) superalloys, knowledge of their activity coefficients in slags is essential. In this study, the activity coefficients of NiO and CoO in CaO-Al₂O₃-SiO₂ slag, a candidate slag used for the EoL superalloy remelting process, were measured using gas/slag/metal equilibrium experiments. These activity coefficients were then used to consider the recycling efficiency of nickel and cobalt by remelting EoL superalloys using CaO-Al₂O₃-SiO₂ slag. The activity coefficients of NiO and CoO in CaO-Al₂O₃-SiO₂ slag both show a positive deviation from Raoult's law, with values that vary from 1 to 5 depending on the change in basicity. The activity coefficients of NiO and CoO peak in the slag with a composition near B=(%CaO)/(%SiO₂)=1, where B is the basicity. We observed that controlling the slag composition at approximately B=1 effectively reduces the cobalt and nickel oxidation losses and promotes the oxidation removal of iron during the remelting process of EoL superalloys.     

低氧LiF–NdF3熔盐体系阳极过程的电化学行为研究

The oxidation of oxygen ions and the generation of an anode effect at a low oxygen content of 150 mg/kg were discussed in this paper. Cyclic voltammetry and square-wave voltammetry tests were conducted to explore the anodic processes of LiF–NdF₃ melt after a lengthy period of pre-electrolysis purification at 1000°C (during which the oxygen content reduced from 413 to 150 mg/kg). The oxidation process of oxygen ions was found to have two stages: oxidation product adsorption and CO/CO₂ gas evolution. The adsorption stage was controlled by diffusion, whereas the gas evolution was controlled by the electrochemical reaction. In comparison with oxygen content of 413 mg/kg, the decrease in the amplitude of the current at low oxygen content of 150 mg/kg was much gentler during the forward scanning process when the anode effect occurred. Fluorine-ion oxidation peaks that occurred at about 4.2 V vs. Li/Li+ could be clearly observed in the reverse scanning processes, in which fluorine ions were oxidized and perfluorocarbons were produced, which resulted in an anode effect.