Search Results (240)

Oolitic hematite ore represents a significant iron resource, but its utilization is challenging due to the complex multi-layered circular structure of hematite ore, which makes it difficult to be reduced. This study systematically investigated the phase transformation principle and magnetite grain growth law during the magnetization sintering of oolitic hematite ore, aiming to establish optimal conditions for efficient hematite ore to magnetite conversion. The results demonstrated that both elevated temperature and prolonged reduction duration significantly enhanced the reduction efficiency of hematite (Fe₂O₃) to magnetite. The optimal sintering conditions were determined to be 700 °C for 45 min, under which the magnetite content and Fe/O atomic ratio in the roasted products peaked at approximately 68% and 0.8%, respectively. However, temperatures exceeding 800 °C proved detrimental to magnetite formation, as further reduction to Fe_XO phases occurred. Notably, appropriate temperature elevation promoted substantial magnetite grain growth. When the sintering temperature increased from 600 °C to 700 °C, both the absolute and relative thickness of the magnetite layer exhibited remarkable enhancement, expanding from 9.52 μm to 76.76 μm and from 5.99% to 50.33%, respectively. Furthermore, comparative analysis revealed that a high sintering temperature for a short time was more effective for magnetite particle growth than a low temperature for a long time in the magnetization process of oolitic hematite ore. Full article

In this study, we report the development of a novel magnetized coal fly ash-supported nano-silver composite (AgNPs/MCFA) for dual-functional applications in wastewater treatment: the efficient degradation of methyl orange (MO) dye and broad-spectrum antibacterial activity. The composite was synthesized via a facile impregnation–reduction–sintering route, utilizing sodium citrate as both a reducing and stabilizing agent. The AgNPs/MCFA composite was systematically characterized through multiple analytical techniques, including Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), and vibrating sample magnetometry (VSM). The results confirmed the uniform dispersion of AgNPs (average size: 13.97 nm) on the MCFA matrix, where the formation of chemical bonds (Ag-O-Si) contributed to the enhanced stability of the material. Under optimized conditions (0.5 g·L⁻¹ AgNO₃, 250 °C sintering temperature, and 2 h sintering time), AgNPs/MCFA exhibited an exceptional catalytic performance, achieving 99.89% MO degradation within 15 min (pseudo-first-order rate constant k_a = 0.3133 min⁻¹) in the presence of NaBH₄. The composite also demonstrated potent antibacterial efficacy against Escherichia coli (MIC = 0.5 mg·mL⁻¹) and Staphylococcus aureus (MIC = 2 mg·mL⁻¹), attributed to membrane disruption, intracellular content leakage, and reactive oxygen species generation. Remarkably, AgNPs/MCFA retained >90% catalytic and antibacterial efficiency after five reuse cycles, enabled by its magnetic recoverability. By repurposing industrial waste (coal fly ash) as a low-cost carrier, this work provides a sustainable strategy to mitigate nanoparticle aggregation and environmental risks while enhancing multifunctional performance in water remediation. Full article

The report of the first room-temperature, ambient-pressure superconductivity in copper-doped lead apatite Pb_10−xCu_x(PO₄)₆O has attracted lots of attention. However, subsequent studies revealed the presence of numerous impurity phases in the polycrystalline sample, and the sharp superconducting-like transition is not due to a superconducting transition but most likely due to a reduction in resistivity caused by the first-order structural phase transition of Cu₂S at around 385 K from the β phase at high temperature to the γ phase at low temperature. Before now, only bulk measurements have been performed on a Pb_10−xCu_x(PO₄)₆O powder sample, which could be affected by the impurity phases, masking the intrinsic properties of Pb_10−xCu_x(PO₄)₆O. In this study, ³¹P and ^63/65Cu nuclear magnetic resonance (NMR) measurements have been performed on a Pb_10−xCu_x(PO₄)₆O powder sample to investigate its physical properties from a microscopic point of view. Our NMR data evidence the non-magnetic insulating nature of Pb_10−xCu_x(PO₄)₆O without any trace of electron correlation effects. Furthermore, the ^63/65Cu NMR results suggest that no copper or very little copper is substituted for Pb in Pb₁₀(PO₄)₆O prepared by sintering Pb₂SO₅ and Cu₃P. Full article

The effect of severe plastic deformation during milling and conventional and Spark Plasma Sintering (SPS) on the wt. % microstructural, structural, thermal, magnetic, and mechanical properties of the Al–16 wt. % Mn–7 wt. % Cu alloy was studied. A milling process for up to 24 h (A24) leads to microstructure refinement and the presence of Al, Mn, and Cu solid solutions. The energy dispersive spectroscopy (EDS) analysis reveals the existence of Cu–Al, Mn–Al, and Al–Mn enriched particles. The powders exhibit weak ferromagnetism and an exchange bias (EB) behaviour that decreases with increasing milling time. The Ms values fitted using the law of approach to saturation (LAS) are comparable to the experimental values. The exothermic and endothermic peaks that appear in the differential scanning calorimetry (DSC) scans in the 500–900 °C range on heating/cooling are related to different phase transformations. The crystal structure of the A24 powders heated up to 900 °C (A24_900 °C) consists of a dual-phase microstructure of Al₂₀Cu₂Mn₃ nanoprecipitates (~28%) and Al matrix (~72%). The sintering of the A24 powders at 500 °C for one hour (A24S) leads to the precipitation of Al₆Mn, Al₂Cu, and the Al₂₀Cu₂Mn₃ T-phase into the Al-enriched matrix. In contrast, the consolidation by SPS (A24SPS) leads to a mixture of an Al solid solution, Al₆Mn, T-phase, and α-Mn with an increased weight fraction of the T-phase and Al₆Mn. The sintered samples exhibit the coexistence of a significant PM/AFM contribution to the M-H curves, with increasing Hc and decreasing EB. A higher microhardness value of about 581 HV is achieved for the A24SPS sample compared to those of the A24 (68 HV) and A24S (80 HV) samples. Full article

We present an alternative process for production of binary Nb_1−βSn_β superconducting phases using pre- and post-treatment of arc-melted Nb + Sn ingots. This process combines sequential sintering, arc melting, and annealing procedures that provide dense, bulk samples of Nb_1−βSn_β with varying stoichiometry between 0.18 < β < 0.25 depending on annealing time and temperature. We show, through magnetization measurements of these Nb_1−βSn_β bulks, that annealing of arc-melted samples at 900 °C for 3 h significantly enhances J_c values compared with arc-melted Nb_1−βSn_β samples without annealing. Microstructural analyses show that optimum grain size and orientation are achieved by sintering and annealing at lower temperatures (i.e., 720 °C and 900 °C, respectively) with short annealing times (i.e., <10 h). Processing at higher temperatures and for longer times enhances grain growth and results in fewer pinning centres. The optimum process creates effective pinning centres that deliver a J_c = 6.16 × 10⁴ A/cm² at 10 K (and ~0.2 T), compared with J_c = 3.4 × 10⁴ A/cm² for Nb_1−βSn_β subjected to a longer annealing time at a higher temperature and J_c = 775 A/cm² for an arc-melted sample without post-annealing. We suggest that further work addressing post-treatment annealing times between 3 h < t_post < 60 h at temperatures between 900 °C and 1000 °C will provide the opportunity to control stoichiometric and microstructural imperfections in bulk Nb_1−βSn_β materials. Full article

Nd–Fe–B permanent magnets are vital for numerous key technologies in strategic sectors such as renewable energy production, e-mobility, defense, and aerospace. Accordingly, the demand for rare earth elements (REEs) enormously increases in parallel to a significant uncertainty in their supply. Thus, research and innovative studies are focus on the investigation of sustainable solutions to the problem and a closed-loop value chain. The present study is based on two benign-by-design approaches aimed at decreasing the recycling loop span by preparing standardized batches of EoL Nd–Fe–B materials to be treated separately depending on their properties, as well as using mechanochemical method for waste processing. The previously reported benefits of both direct recycling and mechanochemistry include significant improvements in processing metrics, such as energy use, ecological impact, technology simplification, and cost reduction. Waste-sintered Nd–Fe–B magnets from motorbikes were collected, precisely sorted, selected, and pre-treated. The study presents a protocol of resource-efficient recycling through mechanochemical processing of non-oxidized sintered EoL magnets, involving the extraction of Nd₂Fe₁₄B magnetic grains and refining the material’s microstructure and particle size after 120 min of high-energy ball milling in a zirconia reactor. The recycled material preserves the main Nd₂Fe₁₄B magnetic phase, while an anisotropic particle shape and formation of a thin Nd/REE-rich layer on the grain surface were achieved. Full article

This work reports on the effect of the heavy rare earth element Er on Nd–Fe–B magnets by using a simple Er₆₉Fe₃₁ alloy additive, which is much less expensive than Dy and Tb elements. It was found that the corrosion resistance was improved with a minimal reduction in magnetic properties by rationally controlling the Er₆₉Fe₃₁ addition content. The main reason is that Er element partially replaces the Nd element at the edge of the main phase grain to form an (Er,Nd)₂Fe₁₄B shell with low H_A, which leads to a decrease in coercivity. However, the improvement in the corrosion resistance is mainly due to the Er₆₉Fe₃₁ alloy addition, which slows down the corrosion rate. Simultaneously, an investigation was conducted into the different advantages that target magnets when subjected to diverse heat treatment methodologies. The above findings may lead to the development of applications for other rare earth elements, thereby accelerating the development of low-cost permanent magnets comparable to commercially available sintered Nd-Fe-B magnets. Full article

Manganese oxides (manganites) are among the most studied materials in condensed matter physics due to the famous colossal magnetoresistance and very rich phase diagrams characterized by strong competition between ferromagnetic (FM) metallic and antiferromagnetic (AFM) insulating phases. One of the key questions that remains open even after more than thirty years of intensive research is the exact conductivity mechanism in insulating as well as in metallic phases and its relation to the corresponding magnetic structure. In order to shed more light on this problem, here, we report magnetotransport measurements on sintered nanocrystalline samples of the very poorly explored manganites ${\mathrm{Ca}}_{1-x}{\mathrm{Gd}}_x{\mathrm{MnO}}_3$ with $x=0.05$ and $x=0.10$, in the temperature range 2–300 K, and in magnetic fields up to 16 T. Our results indicate that both compounds at low temperatures exhibit metallic behavior with a peculiar resistivity upturn and a large negative magnetoresistance. We argue that such behavior is consistent with a Kondo-like scattering on Gd impurities coupled with the percolation of FM metallic regions within insulating AFM matrix. Full article

Objectives: Radio frequency (RF) induction sintering has demonstrated superior performance compared to conventional sintering methods in previous studies. Furthermore, the annealing process is expected to further enhance the mechanical properties of sintered zirconia. This study aimed to investigate the effects of annealing on RF-sintered zirconia and provide empirical evidence supporting its role in optimizing sintering outcomes. Methods: A custom-built RF induction sintering furnace was utilized to process zirconia specimens under various annealing conditions (temperature range, annealing time). The sintered specimens underwent three-point flexural strength testing, followed by microstructural analysis using scanning electron microscopy (SEM). Statistical analysis was performed using one-way ANOVA and Tukey’s post hoc tests to assess the significance of differences between groups. Results: The optimal sintering temperature for RF induction sintering was determined to be 1350 °C, with a minimum annealing duration of 20 min at 1220 °C. Notably, even in the absence of annealing, RF sintering at 1350 °C for 20 min produced specimens with higher flexural strength than those obtained through conventional sintering methods. However, due to variability in mechanical properties, the incorporation of annealing is recommended for clinical applications to ensure consistency and reliability. Conclusions: RF induction sintering significantly reduced both energy consumption and processing time compared to conventional sintering techniques, particularly when combined with annealing. While full densification could be achieved within 20 min without annealing, a total processing time of 30 min, including annealing, was found to enhance process stability and ensure reliable mechanical properties. These findings suggest that both sintering and annealing are critical for achieving optimal densification in zirconia, with annealing playing a key role in improving consistency and reproducibility. Full article

This article demonstrates the concept proof to manufacture parts of MgB₂ by Laser Powder Bed Fusion (L-PBF) coupled to Spark Plasma Sintering (SPS) by an optimization of the L-PBF and SPS conditions to limit the phase degradation and complete the sintering. Optimal L-PBF parameters were identified in order to obtain the material preforms with a minimal degradation of the MgB₂ phase, and then these preforms were sintered by SPS using an inert powder as matrix with a purpose to receive a mechanically more reliable product. Sintered samples show superconductivity state inherent for the raw material and demonstrate superconducting transition around 38 K according to the magnetic moment measurements. Full article

Soft magnetic materials are crucial in motors, generators, transformers, and many electronic devices. We synthesized the FeSi soft magnetic composites (SMCs) with different doping contents of Fe₂O₃ nanopowders as fillers via the hot-press sintering technique. This work explores the incorporation of high-resistivity magnetic fillers through a novel compaction technique and investigates the influence of Fe₂O₃ nanopowder on the structure and magnetic properties of Fe₂O₃ nanopowder-filled composites. The finding reveals that Fe₂O₃ nanopowders effectively fill the air gaps between FeSi powders, increasing SMC density. Moreover, all samples exhibit excellent effective permeability frequency stability, ranging from 15 kHz to 100 kHz. Notably, the effective permeability µ_e improves from 22.32 to 30.45, a 36.42% increase, when the Fe₂O₃ doping concentration increases from 0 to 2 wt%. Adding Fe₂O₃ nanopowders also enhances electrical resistivity, leading to a 37.21% reduction in eddy current loss in samples for 5 wt% Fe₂O₃ addition, compared to undoped samples. Furthermore, as Fe₂O₃ content increases from 0 to 5 wt%, the power loss P_cv of the Fe₂O₃-doped Fe-6.5Si SMCs decreases from 25.63 kW/m³ to 16.13 kW/m³, a 37% reduction. These results suggest that Fe₂O₃-doped FeSi SMCs, with their superior soft magnetic properties, hold significant potential for use in high-power and high-frequency electronic applications. Full article

Red mud (RM), a highly alkaline waste from alumina production, poses severe environmental threats due to massive stockpiling (>350 million tons in China) and groundwater contamination. This study evaluates three scalable strategies to repurpose RM: iron recovery via magnetic separation, sintered brick production using RM–fly ash–granulated blast furnace slag (6:1:3 ratio), and non-calcined cementitious binders combining RM and phosphogypsum (PG). Industrial-scale iron extraction achieved 23.85% recovery of iron concentrate (58% Fe₂O₃ grade) and consumed 3.6 million tons/year of RM, generating CNY 31 million annual profit. Sintered bricks exhibited 10–15 MPa compressive strength, meeting ASTM C62-23 standard while reducing material costs by 30%. The RM–PG binder achieved 40 MPa compressive strength at 28 days without cement or calcination, leveraging RM’s alkalinity (21.95% Na₂O) and PG’s sulfate activation. Collectively, these approaches reduced landfill reliance by 50% and CO₂ emissions by 35%–40% compared to conventional practices. The results demonstrate RM’s potential as a secondary resource, offering economically viable and environmentally sustainable pathways for the alumina industry. Full article

In order to meet the demand for high-frequency current sensors in 5G communication and new energy fields, there is an urgent need to develop high-performance nickel-zinc ferrite-based co-fired ceramic magnetic cores. In this study, a nickel-zinc ferrite core based on low temperature co-fired ceramic (LTCC) technology was developed. The regulation mechanism of BaCo_0.06Bi_0.94O₃ doping on the low-temperature sintering characteristics of NiZn ferrites was systematically investigated. The results show that the introduction of BaCo_0.06Bi_0.94O₃ reduces the sintering temperature to 900 °C and significantly improves the density and grain uniformity of ceramics. When the doping amount is 0.75 wt%, the sample exhibits the lowest coercivity of 35.61 Oe and the following optimal soft magnetic properties: initial permeability of 73.74 (at a frequency of 1 MHz) and quality factor of 19.64 (at a frequency of 1 MHz). The highest saturation magnetization reaches 66.07 emu/g at 1 wt% doping. The results show that BaCo_0.06Bi_0.94O₃ doping can regulate the grain boundary liquid phase distribution and modulate the magnetocrystalline anisotropy, which provides an experimental basis and optimization strategy for the application of LTCC technology in high-frequency current sensors. Full article

Magnetocrystalline anisotropy has many advantages over shape anisotropy regarding coercivity in permanent magnets, making it a promising approach to enhance the coercivity of AlNiCo magnets. In this work, AlNiCo magnets with NdFeB-nanocrystalline phase were prepared by spark plasma sintering (SPS), and the effect of the NdFeB phase on coercivity was uncovered. AlNiCo powder with a spinodal structure and NdFeB powder with a nanocrystalline structure, which exhibit shape anisotropy and magnetocrystalline anisotropy, respectively, were sintered by SPS. With the advantages of low-temperature densification achieved by the SPS process, the spinodal and nanocrystalline structures were mostly retained. The microstructure analysis indicated that the SPS-ed magnet primarily consisted of AlNiCo regions with a spinodal structure, NdFeB regions with a nanocrystalline structure, and a transition region approximately 1~7 µm wide between them. A significant effect of the magnetic anisotropy of the NdFeB phase on magnetization behavior was found. The hysteresis loop of the SPS-ed magnets became single-phase magnetization, in contrast with the double-phase magnetization observed in the simple mixed powder. As the magnetocrystalline anisotropy of the NdFeB phase possesses higher coercivity, the coercivity of the SPS-ed magnet increased from 1250 Oe (of the AlNiCo raw powder) to 2490 Oe. This work provides valuable information for the coercivity enhancement of AlNiCo magnets. Full article

Two NdFeB magnets with distinct compositions were fabricated via an identical process. One magnet was doped with 2.5 wt.% of Ho, whereas the other remained undoped. Subsequently, grain boundary diffusion was performed on both magnets using metallic Tb, adopting the same set of technological parameters. A comprehensive analysis was conducted on the magnetic properties, phase compositions, microstructures, and elemental distributions of these two magnets. The findings indicate that the incorporation of Ho enhances the utilization efficiency of Tb. As a result, the magnets can achieve higher coercivity across different temperatures, with only a minor reduction in remanence. During the sintering process of the Ho-doped magnet, fine precipitated particles of Ho₂Fe₁₄B are generated inside the magnet. This phenomenon causes the refinement of the main grains of the magnet. The refined main grains facilitate the effective diffusion of Tb within the magnet, eliminating the formation of the anti-shell structure. Furthermore, when Ho substitutes for Nd, it leads to a more homogeneous distribution of the Nd-rich phase. Additionally, it increases the densification degree of the sintered NdFeB magnets. These effects contribute to a further enhancement of the magnets’ coercivity. Full article