The experiment explored the Fe₂O₃ reduction process with H₂/CO mixed gas and confirmed a promoting effect from CO when its volume proportion in mixed gas is 20% at 850°C. The ReaxFF molecular dynamics (MD) simulation method was used to observe the reduction process and provide an atomic-level explanation. The accuracy of the parameters used in the simulation was verified by the density functional theory (DFT) calculation. The simulation shows that the initial reduction rate of H₂ is much faster than that of CO (from 800 to 950°C). As the reduction proceeds, cementite, obtained after CO participates in the reduction at 850°C, will appear on the iron surface. Due to the active properties of C atoms in cementite, they are easy to further react with the O atoms in Fe₂O₃. The generation of internal CO may destroy the dense structure of the surface layer, thereby affecting the overall reduction swelling of Fe₂O₃. However, excess CO is detrimental to the reaction rate, mainly because of the poor thermodynamic conditions of CO in the temperature range and the molecular diffusion capacity is not as good as that of H₂. Furthermore, the surface structures obtained after H₂ and CO reduction have been compared, and it was found that the structure obtained by CO reduction has a larger surface area, thus promoting the subsequent reaction of H₂.

Through thermodynamic calculations and microstructural characterization, the effect of niobium (Nb) content on the solidification characteristics of Alloy 625 Plus was systematically investigated. Subsequently, the effect of Nb content on hot deformation behavior was examined through hot compression experiments. The results indicated that increasing the Nb content lowers the liquidus temperature of the alloy by 51°C, producing a denser solidification microstructure. The secondary dendrite arm spacing (SDAS) of the alloy decreases from 39.09 to 22.61 µm. Increasing the Nb content alleviates element segregation but increases interdendritic precipitates, increasing their area fraction from 0.15% to 5.82%. These precipitates are primarily composed of large Laves, δ, η, and γ″ phases, and trace amounts of NbC. The shapes of these precipitates change from small chunks to large elongated forms. No significant change in the type or amount of inclusions within the alloy is detected. The inclusions are predominantly individual Al₂O₃ and TiN, as well as Al₂O₃/TiN composite inclusions. Samples with varying Nb contents underwent hot compression deformation at a true strain of 0.69, a strain rate of 0.5 s⁻¹, and a deformation temperature of 1150°C. Increasing the Nb content also elevates the peak stress observed in the flow curves. However, alloys with higher Nb content exhibit more pronounced recrystallization softening effects. The Laves phase precipitates do not completely redissolve during hot deformation and are stretched to elongated shapes. The high-strain energy storage increases the recrystallization fraction from 32.4% to 95.5%, significantly enhancing the degree of recrystallization and producing a more uniform deformation microstructure. This effect is primarily attributed to the addition of Nb, which refines the initial grains of the alloy, enhances the solid solution strengthening of the matrix, and improves the induction of particle-stimulated nucleation.

Flotation is the most common method to recover valuable minerals by selective adsorption of collectors on target mineral surfaces. However, in subsequent hydrometallurgy of mineral flotation concentrates, the adsorbed collectors must be desorbed since it can adversely affect the efficiency of metallurgical process and produce wastewater. ZL, as a fatty acid mixture, is a typical industrially used collector for scheelite flotation in China. Sodium oleate (NaOL) has similar fatty acid group as ZL. In this study, the desorption behavior of NaOL/ZL from scheelite surface by a physical method of stirring at a low temperature was investigated. NaOL desorption tests of single mineral showed that a desorption rate of 77.75% for NaOL from scheelite surface into pulp was achieved in a stirring speed of 2500 r/min at 5°C in a neutral environment. Under the above desorption condition, in the pulp containing desorbed collector by adding extra 30% normal NaOL dosage, the scheelite recovery reached about 95% in the single mineral flotation test. Desorption and reuse of ZL collector for the flotation of real scheelite ore showed only a 75% normal dosage of ZL could produce a qualified rough concentrate. The atomic force microscope (AFM) tests showed that after desorption treatment of low temperature and strong stirring, the dense strip-like structure of NaOL on the scheelite surface was destroyed to be speck-like. Molecular dynamics simulations (MDS) demonstrated that the adsorption energy between NaOL and scheelite surface was more negative at 25°C (−13.39 kcal/mol) than at 5°C (−11.50 kcal/mol) in a neutral pH, indicating that a low temperature was beneficial for the desorption of collector from mineral surface. Due to its simplicity and economy, the method we proposed of desorption of collector from mineral surface and its reuse for flotation has a great potential for industrial application.

To advance the precise regulation and high-value utilization of halloysite nanotubes (HNTs), this work systematically investigated five treatment strategies, including calcination, acid treatment, alkali treatment, acid treatment of calcined HNTs, and alkali treatment of calcined HNTs, to modulate their structural and application properties. The structural characteristics, surface properties, and methylene blue (MB) adsorption capacity of HNTs under multiple treatments were systematically analyzed. Calcination at varying temperatures modified the crystal structure, morphology, and surface properties of HNTs, with higher calcination temperatures reducing their reactivity towards MB. Moderate acid treatment expanded the lumen and decreased the surface potential of HNTs, significantly enhancing MB adsorption capacity. In contrast, alkali treatment dispersed the multilayered walls of HNTs and raised surface potential, reducing MB affinity. Acid treatment of calcined HNTs effectively increased their specific surface areas by leaching most of Al while maintaining the tubular structure, thereby maximizing MB adsorption. Alkali treatment of calcined HNTs destroyed the tubular structure and resulted in poor MB adsorption. HNTs pre-calcined at 600°C for 3 h and acid-treated at 60°C for 8 h exhibited an optimal specific surface area of 443 m²·g⁻¹ and an MB adsorption capacity of 190 mg·g⁻¹. Kinetic and Arrhenius equation fittings indicated that chemical reactions control interactions of acids and alkalis with HNTs. This study provides a comprehensive comparison and analysis of five treatment methods, offering insights into regulating the structures and surface properties of HNTs by controlling the treatment condition, thereby laying a foundation for their efficient utilization in practical applications.

Hydrogen-based mineral phase transformation (HMPT) technology has demonstrated its effectiveness in separating iron and enriching rare earths from Bayan Obo refractory ores. However, further research is needed to clarify the phase composition and floatability of rare earths obtained after HMPT owing to the associated phase transformations. This study explored the mineralogical characteristics and separation behavior of rare earths in HMPT-treated iron tailings. Process mineralogy studies conducted via BGRIMM process mineralogy analysis and X-ray diffraction revealed that the main valuable minerals in the tailings included rare-earth oxides (9.15wt%), monazite (5.31wt%), and fluorite (23.52wt%). The study also examined the impact of mineral liberation and gangue mineral intergrowth on flotation performance. Flotation tests achieved a rare-earth oxide (REO) grade of 74.12wt% with a recovery of 34.17% in open-circuit flotation, whereas closed-circuit flotation resulted in a REO grade of 60.27wt% with a recovery of 73%. Transmission electron microscopy and scanning electron microscopy coupled with energy-dispersive spectroscopy revealed that monazite remained stable during the HMPT process, while bastnaesite was transformed into Ce₇O₁₂ and CeF₃, leading to increased collector consumption. Nonetheless, the HMPT process did not significantly affect the flotation performance of rare earths. The enrichment of fluorite in the tailings highlighted its further recovery potential. The integration of HMPT with magnetic separation and flotation presents an efficient strategy for recovering rare earths, iron, and fluorite from Bayan Obo ores.

The corrosion degradation of organic coatings in tropical marine atmospheric environments results in substantial economic losses across various industries. The complexity of a dynamic environment, combined with high costs, extended experimental periods, and limited data, places a limit on the comprehension of this process. This study addresses this challenge by investigating the corrosion degradation of damaged organic coatings in a tropical marine environment using an atmospheric corrosion monitoring sensor and a random forest (RF) model. For damage simulation, a polyurethane coating applied to a Fe/graphite corrosion sensor was intentionally scratched and exposed to the marine atmosphere for over one year. Pearson correlation analysis was performed for the collection and filtering of environmental and corrosion current data. According to the RF model, the following specific conditions contributed to accelerated degradation: relative humidity (RH) above 80% and temperatures below 22.5°C, with the risk increasing significantly when RH exceeded 90%. High RH and temperature exhibited a cumulative effect on coating degradation. A high risk of corrosion occurred in the nighttime. The RF model was also used to predict the coating degradation process using environmental data as input parameters, with the accuracy showing improvement when the duration of influential environmental ranges was considered.

Nanoferrites of the CoMn_xFe(_2−x)O₄ series (x = 0.00, 0.05, 0.10, 0.15, 0.20) were synthesized in this study using the sol–gel auto-combustion approach. The lattice constants were computed within the range of 8.312–8.406 Å, while crystallite sizes were estimated to range between 55.20 and 31.40 nm using the Scherrer method. The different functional groups were found to correlate with various absorption bands using Fourier transform infrared (FTIR) spectroscopy. Five active modes were identified by Raman spectroscopy, revealing vibration modes of O²⁻ ions at tetrahedral and octahedral locations. The ferromagnetic hysteresis loop was observed in all the synthesized samples, which can be explained by Neel’s model. The results showed that AC conductivity decreased with increasing Mn²⁺ content at the Fe²⁺ site, while the dielectric constant and dielectric loss increased with increasing frequency. Furthermore, the saturation magnetization (M_s), remnant magnetization (M_r), and coercivity (H_c) all showed declining trends with the increase in Mn²⁺ doping. Finally, the CoMn_0.20Fe_1.8O₄ samples showed M_s and M_r values ranging from 73.12 to 66.84 emu/g and from 37.77 to 51.89 emu/g, respectively, while H_c values ranged from 1939 to 1312 Oe, after which coercivity increased. Thus, the CoMn_0.20Fe_1.8O₄ sample can be considered a promising candidate for magnetic applications.

FeCoCrMnNiN_x high entropy nitride ceramics thin films were prepared using the magnetron sputtering method, and the effects of nitrogen content on the thin films’ properties were later examined. The addition of N₂ affected the microstructures of the thin films and their mechanical and corrosion properties. Compared with the FeCoCrMnNi thin films with 1-sccm N₂, the addition of 2 and 3 sccm of N₂ by as much as 5.45at% and 6.34at% changed the solid solution’s crystalline structure into an amorphous structure. The addition of nitrogen caused drastic changes to the surface morphology, creating a smoother and more uniform surface without cauliflower units. The atomic force microscopy image analysis indicated that the addition of nitrogen reduced the surface roughness from 5.58 to 1.82 nm. Adding N₂ to the CoCrFeMnNi thin film helped increase its mechanical properties, such as hardness and strength, while the Young’s modulus decreased. The hardness of (8.75 ± 0.5) GPa and the reduced Young’s modulus of (257.37 ± 11.4) GPa of the FeCoCrMnNi thin film reached (12.67 ± 1.2) and (194.39 ± 12.4) GPa, respectively, with 1 sccm N₂. The applied coating of the CoCrFeMnNi thin film on 304SUS increased the corrosion resistance, whereas the addition of nitrogen to the CoCrFeMnNi thin film also improved its corrosion resistance compared with that of the CoCrFeMnNi thin film without nitrogen.

Electrochemical metallurgy at low temperature (<473 K) shows promise for the extraction and refinement of metals and alloys in a green and sustainable manner. However, the kinetics of the electrodeposition process is generally slow at low temperature, resulting in large overpotential and low current efficiency. Thus, the application of external physical fields has emerged as an effective strategy for improving the mass and charge transfer processes during electrochemical reactions. This review highlights the challenges associated with low-temperature electrochemical processes and briefly discusses recent achievements in optimizing electrodeposition processes through the use of external physical fields. The regulating effects on the optimization of the electrodeposition process and the strategies for selecting various external physical fields, including magnetic, supergravity, and ultrasonic fields are summarized from the perspectives of equipment and mechanisms. Finally, advanced methods for in-situ characterization of external physical field-assisted electrodeposition processes are reviewed to gain a deeper understanding of metallic electrodeposition. An in-depth exploration of the mechanism by which external physical fields affect the electrode process is essential for enhancing the efficiency of metal extraction at low temperatures.

7039 Al alloys are widely used in armor vehicles, given the material’s high specific strength and fracture toughness. However, laminar tearing in the thickness plane of the base metal (BM), specifically in the normal direction (ND) and rolling direction (RD) plane, was occasionally observed after the welding of thick plates, resulting in premature material failure. A vertically metal-inert gas (MIG)-welded laminar tearing component of a 30 mm thick plate was analyzed to determine the factors associated with this phenomenon. The texture, residual stress, microhardness, and tensile properties were also investigated. The results indicated that the crack extended along the RD as a transcrystalline fracture and terminated at the BM. The grains near the crack grew preferentially in the (001) crystal direction. Furthermore, the tensile strength (83 MPa) and elongation (6.8%) in the RD were relatively higher than those in the ND. In particular, the primary factors for crack initiation include stronger texture, higher dislocation density, increased Al₇Cu₂Fe phases, lower proportion of small-angle grain boundaries, and varying grain sizes in different regions, leading to the fragile microstructure. The higher residual stress of the BM promotes the formation and extension of cracks. The restraining force due to fixation and welding shrinkage force transformed the crack into laminar tearing. Preventive measures of laminar tearing were also proposed.

To address the limitations associated with conventional Fenton processes, which often exhibit a restricted pH range and present challenges in terms of catalyst recovery and second pollutant, magnetic heterogeneous halloysite (HNT)/MnFe₂O₄ catalysts were optimally synthesized, which could achieve 90% removal efficiency for 50 mg/L methylene blue (MB) at pH 4–10 and have high hydrogen peroxide (H₂O₂) utilization efficiencies. In addition, the catalysts could be easily separated from a solution through magnetic separation. The degradation efficiency of MB exhibited remarkable resilience against common aqueous interferents with anions (NO₃⁻, Cl⁻, SO₄²⁻) and humic acid, demonstrating negligible inhibitory effects. Notably, carbonate species (CO₃²⁻ and HCO₃⁻) even elicited a promotional effect on the catalytic process. Furthermore, the removal efficiency of MB only decreased by less than 10% in the fifth cycle compared with that of a fresh catalyst. Furthermore, the HNT/MnFe₂O₄ catalyst effectively degraded various organic pollutants, such as benzohydroxamic acid, xanthate, and eosin Y. The excellent catalytic performance of the catalysts was attributed to the synergistic effects between HNT and MnFe₂O₄. The electron paramagnetic resonance spectra and quenching experiments indicated that the main reactive oxygen species that participated in the degradation process were ·OH and ·O₂⁻. ·OH directly attacked MB molecules, and ·O₂⁻ accelerated the reduction of metal ions. Therefore, the catalysts showed considerable potential for organic pollutant degradation. This study provides valuable insights into the synthesis of novel catalysts and their practical applications in organic wastewater purification.

Hemimorphite exhibits poor floatability during sulfidization flotation. Cu²⁺ and Pb²⁺ addition enhances the reactivity of the hemimorphite surface and subsequently improves its flotation behavior. In this study, the mechanisms of Cu²⁺ + Pb²⁺ adsorption onto a hemimorphite surface were investigated. We examined the interaction mechanism of xanthate with the hemimorphite surface and observed the changes in the mineral surface hydrophobicity after the synergistic activation with Cu²⁺ + Pb²⁺. Microflotation tests indicated that individual activation with Cu²⁺ or Pb²⁺ increased the flotation recovery of hemimorphite, with Pb²⁺ showing greater effectiveness than Cu²⁺. Meanwhile, synergistic activation with Cu²⁺ + Pb²⁺ considerably boosted the flotation recovery of hemimorphite. Cu²⁺ and Pb²⁺ were both adsorbed onto the hemimorphite surface, forming an adsorption layer containing Cu or Pb. Following the synergistic activation with Cu²⁺ + Pb²⁺, the activated layer on the hemimorphite surface consisted of Cu and Pb and a larger amount of the active product compared with the surface activated by Cu²⁺ or Pb²⁺ alone. In addition, xanthate adsorption on the hemimorphite surface increased noticeably after synergistic activation with Cu²⁺ + Pb²⁺, suggesting a vigorous reaction between xanthate and the activated minerals. Therefore, synergistic activation with Cu²⁺ + Pb²⁺ effectively increased the content of active products on the hemimorphite surface, thereby enhancing mineral surface reactivity, promoting collector adsorption, and improving surface hydrophobicity.

The application of liquid core reduction (LCR) technology in thin slab continuous casting can refine the internal microstructures of slabs and improve their production efficiency. To avoid crack risks caused by large deformation during the LCR process and to minimize the thickness of the slab in bending segments, the maximum theoretical reduction amount and the corresponding reduction scheme for the LCR process must be determined. With SPA-H weathering steel as a specific research steel grade, the distributions of temperature and deformation fields of a slab with the LCR process were analyzed using a three-dimensional thermal-mechanical finite element model. High-temperature tensile tests were designed to determine the critical strain of corner crack propagation and intermediate crack initiation with various strain rates and temperatures, and a prediction model of the critical strain for two typical cracks, combining the effects of strain rate and temperature, was proposed by incorporating the Zener–Hollomon parameter. The crack risks with different LCR schemes were calculated using the crack risk prediction model, and the maximum theoretical reduction amount for the SPA-H slab with a transverse section of 145 mm × 1600 mm was 41.8 mm, with corresponding reduction amounts for Segment 0 to Segment 4 of 15.8, 7.3, 6.5, 6.4, and 5.8 mm, respectively.

The enrichment of chromium in the magnetic iron chromite (Fe(Cr_xFe_1−x)₂O₄) phase is crucial for the recovery and recycling of chromium in stainless-steel pickling sludge. The kinetics and reaction mechanism of the solid-phase reaction between Fe₃O₄ and Cr₂O₃ were investigated using the diffusion couple method at 1473 K. Not only the diffusion behavior of Fe²⁺ ions and Cr³⁺ ions was elucidated, but also the solid solution behavior of Fe³⁺ ions was discussed clearly. The microscopic morphology of the diffusion couple and the change in the concentrations of Fe and Cr cations across the diffusion layers were analyzed using scanning electron microscopy and energy dispersive spectroscopy. The self-diffusion coefficients of cations were calculated based on the concentration profiles of Fe and Cr, with the results indicating that the self-diffusion coefficient of the Fe ions was consistently higher than that of the Cr ions. Additionally, a mixture of Fe₃O₄ and Cr₂O₃ was annealed at 1373–1473 K for 1–5 h, and the kinetic parameters were calculated by studying the phase content of the product. The phase content of Fe(Cr_xFe_1−x)₂O₄ in the product was determined by Rietveld refinement of X-ray diffraction data, revealing that an activation energy (E) of 177.20 kJ·mol⁻¹ and a pre-exponential factor (B) of 610.78 min⁻¹ of the solid-phase reaction that produced the Fe(Cr_xFe_1−x)₂O₄ spinel.

Thermal and mechanical properties of yttrium tantalate (YTaO₄), a top coat ceramic of thermal barrier coatings (TBCs) for aeroengines, are enhanced by synthesizing Y_1−xTa_1−xM_2xO₄ (M = Ti, Zr, Hf; x = 0.06, 0.12, 0.18, 0.24) medium-entropy ceramics (MECs) using a two-step sintering method. In addition, the thermal conductivity, thermal expansion coefficients (TECs), and fracture toughness of MECs were investigated. An X-ray diffraction study revealed that the Y_1−xTa_1−xM_2xO₄ MECs were monoclinic, and the Ti, Zr, and Hf doping elements replaced Y and Ta. The variations in atomic weights and ionic radii led to disturbed atomic arrangements and severe lattice distortions, resulting in improving the phonon scattering and reduced thermal conductivity, with Y_1−xTa_1−xM_2xO₄ MECs (x = 0.24) exhibiting the lowest thermal conductivity of 1.23 W·m⁻¹·K⁻¹ at 900°C. The introduction of MO₂ increased the configurational entropy and weakened the ionic bonding energy, obtaining high TECs (10.4 × 10⁻⁶ K⁻¹ at 1400°C). The reduction in the monoclinic angle β lowered the ferroelastic domain inversion energy barrier. Moreover, microcracks and crack extension toughening endowed Y_1−xTa_1−xM_2xO₄ MECs (x = 0.24) with the highest fracture toughness of (4.1 ± 0.5) MPa·m^1/2. The simultaneous improvement of the thermal and mechanical properties of the MO₂ (M = Ti, Zr, Hf) co-doped YTaO₄ MECs can be extended to other materials.