International Journal of Minerals, Metallurgy, and Materials最新文献

Metal-to-insulator transitions (MITs), which are achieved in 3d-band correlated transitional metal oxides, trigger abrupt variations in electrical, optical, and/or magnetic properties beyond those of conventional semiconductors. Among such material families, iron (Fe: 3d⁶4s²)-containing oxides pique interest owing to their widely tunable MIT properties, which are associated with the various valence states of Fe. Their potential electronic applications also show promise, given the large abundance of Fe on Earth. Representative MIT properties triggered by critical temperature (T_MIT) were reported for ReFe₂O₄ (Fe^2.5+), ReBaFe₂O₅ (Fe^2.5+), Fe₃O₄ (Fe^2.67+), Re_1/3Sr_2/3FeO₃ (Fe^3.67+), ReCu₃Fe₄O₁₂ (Fe^3.75+), and Ca_1−xSr_xFeO₃ (Fe⁴⁺) (where Re represents rare-earth elements). The common feature of MITs of these Fe-containing oxides is that they are usually accompanied by charge ordering transitions or disproportionation associated with the valence states of Fe. Herein, we review the material family of Fe-containing MIT oxides, their MIT functionalities, and their respective mechanisms. From the perspective of potentially correlated electronic applications, the tunability of the T_MIT and its resultant resistive change in Fe-containing oxides are summarized and further compared with those of other materials exhibiting MIT functionality. In particular, we highlight the abrupt MIT and wide tunability of T_MIT of Fe-containing quadruple perovskites, such as ReCu₃Fe₄O₁₂. However, their effective material synthesis still needs to be further explored to cater to potential applications.

The mechanism involved in the phase transformation process of pyrolusite (MnO₂) during roasting in a reducing atmosphere was systematically elucidated in this study, with the aim of effectively using low-grade complex manganese ore resources. According to single-factor experiment results, the roasted product with a divalent manganese (Mn²⁺) distribution rate of 95.30% was obtained at a roasting time of 25 min, a roasting temperature of 700°C, a CO concentration of 20at%, and a total gas volume of 500 mL·min⁻¹, in which the manganese was mainly in the form of manganosite (MnO). Scanning electron microscopy and Brunauer–Emmett–Teller theory demonstrated the microstructural evolution of the roasted product and the gradual reduction in the pyrolusite ore from the surface to the core. Thermodynamic calculations, X-ray photoelectron spectroscopy, and X-ray diffractometry analyses determined that the phase transformation of pyrolusite followed the order of MnO₂→Mn₂O₃→Mn₃O₄→MnO phase by phase, and the reduction of manganese oxides in each valence state proceeded simultaneously.

A Ni-P alloy gradient coating consisting of multiple electroless Ni-P layers with various phosphorus contents was prepared on the aviation aluminum alloy. Several characterization and electrochemical techniques were used to characterize the different Ni-P coatings’ morphologies, phase structures, elemental compositions, and corrosion protection. The gradient coating showed good adhesion and high corrosion and wear resistance, enabling the application of aluminum alloy in harsh environments. The results showed that the double zinc immersion was vital in obtaining excellent adhesion (81.2 N). The optimal coating was not peeled and shredded even after bending tests with angles higher than 90° and was not corroded visually after 500 h of neutral salt spray test at 35°C. The high corrosion resistance was attributed to the misaligning of these micro defects in the three different nickel alloy layers and the amorphous structure of the high P content in the outer layer. These findings guide the exploration of functional gradient coatings that meet the high application requirement of aluminum alloy parts in complicated and harsh aviation environments.

The preparation process of sodium molybdate has the disadvantages of high energy consumption, low thermal efficiency, and high raw material requirement of molybdenum trioxide, in order to realize the green and efficient development of molybdenum concentrate resources, this paper proposes a new process for efficient recovery of molybdenum from molybdenum concentrate and preparation of sodium molybdate by microwave-enhanced roasting and alkali leaching. Thermodynamic analysis indicated the feasibility of oxidation roasting of molybdenum concentrate. The effects of roasting temperature, holding time, and power-to-mass ratio on the oxidation product and leaching product sodium molybdate (Na₂MoO₄·2H₂O) were investigated. Under the optimal process conditions: roasting temperature of 700°C, holding time of 110 min, and power-to-mass ratio of 110 W/g, the molybdenum state of existence was converted from MoS₂ to MoO₃. The process of preparing sodium molybdate by alkali leaching of molybdenum calcine was investigated, the optimal leaching conditions include a solution concentration of 2.5 mol/L, a liquid-to-solid ratio of 2 mL/g, a leaching temperature of 60°C, and leaching solution termination at pH 8. The optimum conditions result in a leaching rate of sodium molybdate of 96.24%. Meanwhile, the content of sodium molybdate reaches 94.08wt% after leaching and removing impurities. Iron and aluminum impurities can be effectively separated by adjusting the pH of the leaching solution with sodium carbonate solution. This research avoids the shortcomings of the traditional process and utilizes the advantages of microwave metallurgy to prepare high-quality sodium molybdate, which provides a new idea for the high-value utilization of molybdenum concentrate.

Mg−Al alloys have excellent strength and ductility but relatively low thermal conductivity due to Al addition. The accurate prediction of thermal conductivity is a prerequisite for designing Mg−Al alloys with high thermal conductivity. Thus, databases for predicting temperature- and composition-dependent thermal conductivities must be established. In this study, Mg−Al−La alloys with different contents of Al₂La, Al₃La, and Al₁₁La₃ phases and solid solubility of Al in the α-Mg phase were designed. The influence of the second phase(s) and Al solid solubility on thermal conductivity was investigated. Experimental results revealed a second phase transformation from Al₂La to Al₃La and further to Al₁₁La₃ with the increasing Al content at a constant La amount. The degree of the negative effect of the second phase(s) on thermal diffusivity followed the sequence of Al₂La > Al₃La > Al₁₁La₃. Compared with the second phase, an increase in the solid solubility of Al in α-Mg remarkably reduced the thermal conductivity. On the basis of the experimental data, a database of the reciprocal thermal diffusivity of the Mg−Al−La system was established by calculation of the phase diagram (CALPHAD) method. With a standard error of ±1.2 W/(m·K), the predicted results were in good agreement with the experimental data. The established database can be used to design Mg−Al alloys with high thermal conductivity and provide valuable guidance for expanding their application prospects.

Exclusive responsiveness to ultraviolet light (∼3.2 eV) and high photogenerated charge recombination rate are the two primary drawbacks of pure TiO₂. We combined N-doped graphene quantum dots (N-GQDs), morphology regulation, and heterojunction construction strategies to synthesize N-GQD/N-doped TiO₂/P-doped porous hollow g-C₃N₄ nanotube (PCN) composite photocatalysts (denoted as G-TPCN). The optimal sample (G-TPCN doped with 0.1wt% N-GQD, denoted as 0.1%G-TPCN) exhibits significantly enhanced photoabsorption, which is attributed to the change in bandgap caused by elemental doping (P and N), the improved light-harvesting resulting from the tube structure, and the upconversion effect of N-GQDs. In addition, the internal charge separation and transfer capability of 0.1%G-TPCN are dramatically boosted, and its carrier concentration is 3.7, 2.3, and 1.9 times that of N-TiO₂, PCN, and N-TiO₂/PCN (TPCN-1), respectively. This phenomenon is attributed to the formation of Z-scheme heterojunction between N-TiO₂ and PCNs, the excellent electron conduction ability of N-GQDs, and the short transfer distance caused by the porous nanotube structure. Compared with those of N-TiO₂, PCNs, and TPCN-1, the H₂ production activity of 0.1%G-TPCN under visible light is enhanced by 12.4, 2.3, and 1.4 times, respectively, and its ciprofloxacin (CIP) degradation rate is increased by 7.9, 5.7, and 2.9 times, respectively. The optimized performance benefits from excellent photoresponsiveness and improved carrier separation and migration efficiencies. Finally, the photocatalytic mechanism of 0.1%G-TPCN and five possible degradation pathways of CIP are proposed. This study clarifies the mechanism of multiple modification strategies to synergistically improve the photocatalytic performance of 0.1%G-TPCN and provides a potential strategy for rationally designing novel photocatalysts for environmental remediation and solar energy conversion.

The amount of oxygen blown into the converter is one of the key parameters for the control of the converter blowing process, which directly affects the tap-to-tap time of converter. In this study, a hybrid model based on oxygen balance mechanism (OBM) and deep neural network (DNN) was established for predicting oxygen blowing time in converter. A three-step method was utilized in the hybrid model. First, the oxygen consumption volume was predicted by the OBM model and DNN model, respectively. Second, a more accurate oxygen consumption volume was obtained by integrating the OBM model and DNN model. Finally, the converter oxygen blowing time was calculated according to the oxygen consumption volume and the oxygen supply intensity of each heat. The proposed hybrid model was verified using the actual data collected from an integrated steel plant in China, and compared with multiple linear regression model, OBM model, and neural network model including extreme learning machine, back propagation neural network, and DNN. The test results indicate that the hybrid model with a network structure of 3 hidden layer layers, 32-16-8 neurons per hidden layer, and 0.1 learning rate has the best prediction accuracy and stronger generalization ability compared with other models. The predicted hit ratio of oxygen consumption volume within the error ±300 m³ is 96.67%; determination coefficient (R²) and root mean square error (RMSE) are 0.6984 and 150.03 m³, respectively. The oxygen blow time prediction hit ratio within the error ±0.6 min is 89.50%; R² and RMSE are 0.9486 and 0.3592 min, respectively. As a result, the proposed model can effectively predict the oxygen consumption volume and oxygen blowing time in the converter.

Cation additives can efficiently enhance the total electrochemical capabilities of zinc-ion hybrid capacitors (ZHCs). However, their energy storage mechanisms in zinc-based systems are still under debate. Herein, we modulate the electrolyte and achieve dual-ion storage by adding magnesium ions. And we assemble several Zn//activated carbon devices with different electrolyte concentrations and investigate their electrochemical reaction dynamic behaviors. The zinc-ion capacitor with Mg²⁺ mixed solution delivers 82 mAh·g⁻¹ capacity at 1 A·g⁻¹ and maintains 91% of the original capacitance after 10000 cycling. It is superior to the other assembled zinc-ion devices in single-component electrolytes. The finding demonstrates that the double-ion storage mechanism enables the superior rate performance and long cycle lifetime of ZHCs.

A high thrust-to-weight ratio poses challenges to the high-temperature performance of Ni-based superalloys. The oxidation behavior of GH4738 at extreme temperatures has been investigated by isothermal and non-isothermal experiments. As a result of the competitive diffusion of alloying elements, the oxide scale included an outermost porous oxide layer (OOL), an inner relatively dense oxide layer (IOL), and an internal oxide zone (IOZ), depending on the temperature and time. A high temperature led to the formation of large voids at the IOL/IOZ interface. At 1200°C, the continuity of the Cr-rich oxide layer in the IOL was destroyed, and thus, spallation occurred. Extension of oxidation time contributed to the size of Al-rich oxide particles with the increase in the IOZ. Based on this finding, the oxidation kinetics of GH4738 was discussed, and the corresponding oxidation behavior at 900–1100°C was predicted.

W-based WTaVCr refractory high entropy alloys (RHEA) may be novel and promising candidate materials for plasma facing components in the first wall and diverter in fusion reactors. This alloy has been developed by a powder metallurgy process combining mechanical alloying and spark plasma sintering (SPS). The SPSed samples contained two phases, in which the matrix is RHEA with a body-centered cubic structure, while the oxide phase was most likely Ta₂VO₆ through a combined analysis of X-ray diffraction (XRD), energy-dispersive spectroscopy (EDS), and selected area electron diffraction (SAED). The higher oxygen affinity of Ta and V may explain the preferential formation of their oxide phases based on thermodynamic calculations. Electron backscatter diffraction (EBSD) revealed an average grain size of 6.2 μm. WTaVCr RHEA showed a peak compressive strength of 2997 MPa at room temperature and much higher micro- and nano-hardness than W and other W-based RHEAs in the literature. Their high Rockwell hardness can be retained to at least 1000°C.