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

Both numerical and experimental studies of the stability and electronic properties of barium–sodium metaborate Ba₂Na₃(B₃O₆)₂F (P6₃/m) at pressures up to 10 GPa have been carried out. Electronic-structure calculations with HSE06 hybrid functional showed that Ba₂Na₃(B₃O₆)₂F has an indirect band gap of 6.289 eV. A numerical study revealed the decomposition of Ba₂Na₃(B₃O₆)₂F into the BaB₂O₄, NaBO₂, and NaF phases above 3.4 GPa at 300 K. Subsequent high-pressure high-temperature experiments performed using ‘Discoverer-1500’ DIA-type apparatus at pressures of 3 and 6 GPa and temperature of 1173 K confirmed the stability of Ba₂Na₃(B₃O₆)₂F at 3 GPa and its decomposition into BaB₂O₄, NaBO₂, and NaF at 6 GPa, which was verified by energy-dispersive X-ray analysis and Raman spectroscopy. The observed Raman bands of the Ba₂Na₃(B₃O₆)₂F phase were assigned by comparing the experimental and calculated spectra. The experimental Raman spectra of decomposition reaction products obtained at 6 GPa suggest the origin of a new high-pressure modification of barium metaborate BaB₂O₄.

Nanotubes, such as boron nitride nanotubes (BNNTs) and carbon nanotubes (CNTs), exhibit excellent mechanical properties. In this work, high-quality BNNTs were synthesized by ball milling and annealing. Subsequently, well-dispersed 3vol% BNNTs/Cu and 3vol% CNTs/Cu composites were successfully prepared using ball milling, spark plasma sintering, and followed by hot-rolling. Moreover, the mechanical properties and strengthening mechanisms of BNNTs/Cu and CNTs/Cu composites were compared and discussed in details. At 293 K, both BNNTs/Cu and CNTs/Cu composites exhibited similar ultimate tensile strength (UTS) of ∼404 MPa, which is approximately 170% higher than pure Cu. However, at 873 K, the UTS and yield strength of BNNTs/Cu are 27% and 29% higher than those of CNTs/Cu, respectively. This difference can be attributed to the stronger inter-walls shear resistance, higher thermomechanical stability of BNNTs, and stronger bonding at the BNNTs/Cu interface as compared to the CNTs/Cu interface. These findings provide valuable insights into the potential of BNNTs as an excellent reinforcement for metal matrix composites, particularly at high temperature.

Face-centered cubic (f.c.c.) high entropy alloys (HEAs) are attracting more and more attention owing to their excellent strength and ductility synergy, irradiation resistance, etc. However, the yield strength of f.c.c. HEAs is generally low, significantly limiting their practical applications. Recently, the alloying of W has been evidenced to be able to remarkably improve the mechanical properties of f.c.c. HEAs and is becoming a hot topic in the community of HEAs. To date, when W is introduced, multiple strengthening mechanisms, including solid-solution strengthening, precipitation strengthening (μ phase, σ phase, and b.c.c. phase), and grain-refinement strengthening, have been discovered to be activated or enhanced. Apart from mechanical properties, the addition of W improves corrosion resistance as W helps to form a dense WO₃ film on the alloy surface. Until now, despite the extensive studies in the literature, there is no available review paper focusing on the W doping of the f.c.c. HEAs. In that context, the effects of W doping on f.c.c. HEAs were reviewed in this work from three aspects, i.e., microstructure, mechanical property, and corrosion resistance. We expect this work can advance the application of the W alloying strategy in the f.c.c. HEAs.

Fe–S compounds with hexagonal crystal structure are potential hydrogen permeation barrier during H₂S corrosion. Hexagonal system Fe–S films were prepared on carbon steel through corrosion and CVD deposition, and the barrier effect of different Fe–S films on hydrogen permeation was tested using electrochemical hydrogen permeation method. After that, the electrical properties of Fe–S compound during phase transformation were measured using thermoelectric measurement system. Results show that the mackinawite has no obvious barrier effect on hydrogen penetration, as a p-type semiconductor, and pyrrhotite (including troilite) has obvious barrier effect on hydrogen penetration, as an n-type semiconductor. Hydrogen permeation tests showed peak permeation performance when the surface was deposited with a continuous film of pyrrhotite (Fe_1−xS) and troilite. The FeS compounds suppressed hydrogen permeation by the promotion of the hydrogen evolution reaction, semiconducting inversion from p- to n-type, and the migration of ions at the interface.

The iron and steel industry (ISI) involves high energy consumption and high pollution. ISI in China, a leading country in the ISI, consumed 15% of the country’s total energy and produced more than 50% of the global ISI’s carbon emissions. Therefore, in the context of global low-carbon economy and emission reduction requirements, low-carbon smelting technology in the ISI has attracted increasingly more attention in China. This review summarizes the current status of carbon emissions and energy consumption in China’s ISI and discusses the development status and prospects of low-carbon ironmaking technology. The main route to effectively reducing carbon emissions is to develop a gas-based direct reduction process and replace sintering with pelletizing, both of which focus on developing pelletizing technology. However, the challenge of pelletizing process development is to obtain high-quality iron concentrates. Consequently, the present paper also summarizes the development status of China’s mineral processing technology, including fine-grained mineral processing technology, magnetization roasting technology, and flotation collector application. This paper aims to provide a theoretical basis for the low-carbon development of China’s ISI in terms of a dressing–smelting combination.

Goethitic bauxite is a widely used raw material in the alumina industry. It is an essential prerequisite to clarify the effect of Ti- and Si-containing minerals on goethite transformation in the Bayer digestion process, which could efficiently utilize the Fe- and Al-containing minerals present in goethitic bauxite. In this work, the interactions between anatase or kaolinite with goethite during various Bayer digestion processes were investigated using X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), transmission electron microscopy (TEM), and scanning electron microscopy (SEM). The results showed that anatase and kaolinite hindered the transformation of goethite. Anatase exerted more significant effects than kaolinite due to the dense sodium titanate layer on the goethite surface after reacting with the sodium aluminate solution. Adding the reductant hydrazine hydrate could eliminate the retarding effect by inducing the transformation of goethite into magnetite. In this process, titanium was embedded into the magnetite lattice to form Ti-containing magnetite. Furthermore, the weakening of the interaction between magnetite and sodium aluminosilicate hydrate reduced the influence of kaolinite. As a validation of the above results, the reductive Bayer method resulted in the transformation of goethite into goethitic bauxite with 98.87% relative alumina digestion rate. The obtained red mud with 72.99wt% Fe₂O₃ could be further utilized in the steel industry. This work provides a clear understanding of the transformative effects of Ti- and Si-containing minerals on iron mineral transformation and aids the comprehensive use of iron and aluminum in goethitic bauxite subjected to the reductive Bayer method.

How to increase strength without sacrificing ductility has been developed as a key goal in the manufacture of high-performance metals or alloys. Herein, the double-nanophase intragranular yttrium oxide dispersion strengthened iron alloy with high strength and appreciable ductility was fabricated by solution combustion route and subsequent spark plasma sintering, and the influences of yttrium oxide content and sintering temperature on microstructures and mechanical properties were investigated. The results show at the same sintering temperature, with the increase of yttrium oxide content, the relative density of the sintered alloy decreases and the strength increases. For Fe–2wt%Y₂O₃ alloy, as the sintering temperature increases gradually, the compressive strength decreases, while the strain-to-failure increases. The Fe–2wt%Y₂O₃ alloy with 15.5 nm Y₂O₃ particles uniformly distributed into the 147.5 nm iron grain interior sintered at 650°C presents a high ultimate compressive strength of 1.86 GPa and large strain-to-failure of 29%. The grain boundary strengthening and intragranular second-phase particle dispersion strengthening are the main dominant mechanisms to enhance the mechanical properties of the alloy.

Although Bi₂MoO₆ (BMO) has recently received extensive attention, its visible-light photocatalytic activity remains poor due to its limited photoresponse range and low charge separation efficiency. In this work, a series of visible-light-driven Y³⁺-doped BMO (Y-BMO) photocatalysts were synthesized via a hydrothermal method. Degradation experiments on Rhodamine B and Congo red organic pollutants revealed that the optimal degradation rates of Y-BMO were 4.3 and 5.3 times those of pure BMO, respectively. The degradation efficiency of Y-BMO did not significantly decrease after four cycle experiments. As a result of Y³⁺ doping, the crystal structure of BMO changed from a thick layer structure to a thin flower-like structure with an increased specific surface area. X-ray photoelectron spectroscopy showed the presence of high-intensity peaks for the O 1s orbital at 531.01 and 530.06 eV, confirming the formation of oxygen vacancies in Y-BMO. Photoluminescence (PL) and electrochemical impedance spectroscopy measurements revealed that the PL intensity and interface resistances of composites decreased significantly, indicating reduced electron–hole pair recombination. This work provides an effective way to prepare high-efficiency Bi-based photocatalysts by doping rare earth metal ions for improved photocatalytic performance.

The role of α precipitates formed during aging in the fracture toughness and fracture behavior of β-type bio-titanium alloy Ti–29Nb–13Ta–4.6Zr (TNTZ) was studied. Results showed that the fracture toughness of the TNTZ alloy aged at 723 K decreases to the minimum of 72.07–73.19 kJ·m⁻² when the aging time is extended to 4–8 h and then gradually increases and reaches 144.89 kJ·m⁻² after 72 h. The decrease in fracture toughness within the aging time of 4–8 h is caused by the large stress concentration at the tip of acicular a precipitates with a high aspect ratio and the preferential crack propagation along the inhomogeneous acicular a precipitates distributed in “V-shape” and “nearly perpendicular shape”. When the aging time is extended to 8–72 h, the precrack tip is uniformly blunted, and the crack is effectively deflected by a precipitates with multi long axis directions, more high homogeneity, low aspect ratio, and large number density. Analysis of the effect of a precipitates on the fracture behavior suggested that the number of long axis directions of a precipitates is the key controlling factor for the fracture behavior and fracture toughness of the TNTZ alloy aged for different times.

Platinum-based nanocomposites have been considered as one of the most promising catalysts for methanol oxidation reactions (MORs), which yet still suffer from low electrochemical activity and electron-transfer properties. Apart from van-der-Waals heterostructures, herein, we report a novel nanocomposite with the structure of Pt–Ru bimetallic nanoparticles covalently-bonded onto multi-walled carbon nanotubes (MWCNTs) (Pt–Ru@MWCNT), which have been successfully fabricated via a facile and green synthesis method. It is demonstrated that the Pt–Ru@MWCNT nanocomposite possesses much enhanced electrocatalytic activity with the electrochemical active surface area (ECSA) of 110.4 m²·g⁻¹ for Pt towards MOR, which is 2.67 and 4.0 times higher than those of 20wt% commercial Pt@C and Pt-based nanocomposite prepared by other method, due to the improved electron-transfer properties originated from M–O–C covalent bonds. This work provides us a new strategy for the structural design of highly-efficient electrocatalysts in boosting MOR performance.