Search Results (1,351)

A synergistic and magnetically recoverable NiFe₂O₄–MWCNT–CA nanocomposite was developed for efficient UV-driven photodegradation of hazardous organic pollutants. Biogenic NiFe₂O₄ nanoparticles synthesized using Costus speciosus extract exhibited a crystallite size of 32.5 nm, which increased to 83.6 nm upon incorporation into the MWCNT–cellulose acetate matrix. XRD confirmed the preservation of the cubic spinel structure, while VSM analysis showed maintained ferrimagnetic behavior with a saturation magnetization of 9.64 emu/g, enabling rapid magnetic separation. Although BET analysis revealed a reduction in surface area from 112.46 to 30.99 m²/g due to hybridization, the conductive MWCNT network significantly enhanced charge separation and interfacial electron transport. The composite displayed a widened optical bandgap of 5.3 eV, necessitating UV excitation for photocatalytic activity. Under UV irradiation, it achieved rapid degradation of methylene blue (97%) and Congo red (91%) at 20 mg/L, with corresponding rate constants of 0.119 and 0.076 min⁻¹. Scavenger experiments confirmed hydroxyl radicals (•OH) as the dominant reactive species, followed by photogenerated holes (h⁺). These results demonstrate a robust and synergistically engineered photocatalyst with high efficiency in removing organic pollutants under UV illumination. Full article

Ultramafic minerals from the Goat Hill serpentine barrens, Chester County, Pennsylvania, were examined using scanning electron and transmission electron microscopy in conjunction with energy dispersive spectroscopy, selected area electron diffraction, and electron energy loss spectroscopy. Magnesium-rich lizardite and clinochlore, antigorite, chrysotile, gahnite, Fe- and Fe-Cr spinels, and vernadite were the primary minerals with amorphous phases interspersed with the minerals. The Mn-oxide vernadite had a mixed Mn⁴⁺/Mn³⁺ oxidation state, with Mn⁴⁺ > Mn³⁺ and Ni > Fe. Full article

Acidic mine drainage (AMD) poses a severe global environmental threat due to its high acidity and elevated levels of toxic hexavalent chromium (Cr(VI)), for which biogenic iron sulfide (FeS) nanoparticles have emerged as a promising remediation agent; however, their practical application is hindered by aggregation and oxidative deactivation. This research synthesized biogenic FeS nanoparticles via sulfate-reducing bacteria (SRB) and employed humic acid (HA) as a stabilizing agent to enhance Cr(VI) removal performance in simulated AMD conditions. Single-factor experiments combined with response surface methodology identified the optimal biosynthetic conditions for FeS: yeast extract powder dosage of 2.2 g/L, Fe/S molar ratio of 0.8, and NH₄Cl dosage of 3.1 g/L. Under these conditions, the material achieved 84.25% Cr(VI) removal, with the Fe/S molar ratio identified as the most influential parameter governing synthesis and performance. Introducing HA at an optimal dosage of 2 mg/L drove marked improvements in both nanoparticle yield and reactivity: FeS yield increased to 1096.26 mg/L, Cr(VI) removal efficiency reached 99.62%, and residual Cr(VI) dropped from 15.75 mg/L to just 0.38 mg/L. Kinetic and isotherm analyses, paired with SEM/TEM imaging and zeta potential measurements, revealed that HA stabilization improved particle dispersion and reduced lamellar stacking, resulting in a surface-controlled Cr(VI) removal process. FTIR and 2D-COS analyses demonstrated that HA-derived oxygen-containing functional groups, including O–H/N–H, C=O, and C–O moieties, played a central role in interfacial interactions during Cr(VI) sequestration. XRD results confirmed that Cr(VI) was reduced to Cr(III) and primarily immobilized as low-solubility CrOOH and Cr₂S₃, while the formation of Fe–Cr spinel-like phases remains tentative without X-ray Photoelectron Spectroscopy (XPS) validation. Further investigation via surface-sensitive spectroscopy and dynamic leaching tests is needed to fully assess the long-term stability of the reaction products. Full article

The exploration of new materials with stable molten calcium–magnesium–aluminum-silicate (CMAS) resistance at elevated temperatures is of great significance to the development of advanced aero-engines. In the present study, Al₂O_3−xGd₂O₃ (x = 5, 10, 20, 30 mol.%) ceramic samples were prepared by the high-temperature solid-state synthesis method. The thermochemical reaction behavior, reaction products, and growth kinetics of the reaction layer for the ceramics with molten CMAS at 1300 °C were investigated. The results reveal that the primary reaction products between Al₂O_3−xGd₂O₃ ceramics and molten CMAS are anorthite (CaAl₂Si₂O₈), gehlenite (Ca₂Al(AlSi)O₇), spinel (MgAl₂O₄), and Gd-apatite (Ca₂Gd₈(SiO₄)₆O₂). In the initial reaction stage, a dense double-layer reaction layer composed of anorthite and spinel is formed at the ceramic/CMAS interface, while its growth rate decreases with increasing reaction time. Increasing the Gd₂O₃ doping content inhibits the growth of the reaction layer and enhances the CMAS penetration resistance of Al₂O_3−xGd₂O₃ ceramics. The mechanism is discussed systematically. Full article

The incorporation of recycled metallurgical slags into refractory materials constitutes a promising approach to enhancing sustainability in the refractory industry. This study investigates the effect of vanadium-bearing slag aggregates as partial replacements for tabular alumina in castables and compares their behaviour with high-alumina and bauxite-based castables. Two vanadium-bearing slags with different mineralogical compositions were introduced in the 1–3 mm aggregate fraction with substitution up to 25 wt.%. Their effects on microstructure, thermo-mechanical performance, and corrosion resistance were evaluated. The introduction of vanadium-bearing slag significantly alters the microstructure of the castables, affecting their performance. Both slags displayed grains with higher porosity, microcracking, and heterogeneity compared with tabular alumina, but showed similarities to bauxite grains. Slag 1, enriched in calcium aluminate phases, provides limited mechanical strength but improved corrosion resistance due to improved bonding with the matrix. Slag 2, containing a higher spinel content, enhances mechanical strength, showing behaviour comparable with bauxite-based castables, particularly at 10 wt.% replacement. Vanadium is mainly present in metallic form and as Mg(Al,V)₂O₄ spinels in both slags. Upon firing, vanadium migrates toward the grain boundaries and reacts with the surrounding calcium aluminate phases to be incorporated in Ca(Al,V)₂O₄ and Ca(Al,V)₄O₇, while the spinel phase remains stable. Full article

Peridotites exposed in the southern Mariana Trench provide a rare opportunity to investigate mantle processes operating at the interface between arc and back-arc tectonic domains. This study presents petrographic observations and major element mineral chemistry of 41 depleted mantle harzburgites collected from three sites (Sites A–C) in the southern Mariana Trench. Site A is located on the east-facing slope of the West Santa Rosa Bank Fault, whereas Sites B and C are situated on the southern slope of the South Mariana Forearc Ridge along the eastern side of the Challenger Deep. The harzburgites exhibit variable microstructures ranging from coarse-grained (>1 mm) to medium-grained (<1 mm) to small-grained (>0.1 mm) textures, with or without porphyroclasts, and commonly contain amphibole associated with orthopyroxene and spinel. Olivine Mg# (Mg/[Mg + Fe]) (0.902–0.925) and spinel Cr# (Cr/[Cr + Al]) (0.304–0.720) indicate a wide range of mantle depletion across the three sites. Based on the integrated chemical characteristics of olivine, spinel, and amphibole, the harzburgites are classified into three distinct compositional trends (Trends 1–3). Trend 1 is characterized by high olivine Mg# (~0.925), high spinel Cr# (>0.6), low TiO₂ contents (<0.1 wt%), and K₂O-enriched but TiO₂-poor amphibole (TiO₂/K₂O < ~0.5), consistent with strongly depleted forearc mantle modified by slab-derived hydrous melts or fluids. In contrast, Trend 2 is defined by relatively high olivine Mg# (>~0.91), lower spinel Cr# (<0.6), slightly higher TiO₂ contents (up to ~0.2 wt%), and amphibole moderately enriched in both K₂O and TiO₂ (TiO₂/K₂O = 1–4), recording an intermediate geochemical signature that cannot be uniquely attributed to a purely forearc origin. Trend 3 is characterized by lower olivine Mg# (~0.90), lower spinel Cr# (<0.6), distinctly higher TiO₂ contents (up to ~0.8 wt%), and TiO₂-rich but K₂O-poor amphibole (TiO₂/K₂O > 4), indicating a back-arc mantle origin related to decompression melting. Trends 1 and 2 occur in harzburgites from Sites B and C of the South Mariana Forearc Ridge, whereas Trend 3 is exclusively identified in harzburgites from Site A of the West Santa Rosa Bank Fault, highlighting the juxtaposition of forearc-type, transitional, and back-arc-type mantle domains within a single forearc region. Full article

Antimony (Sb) contamination in water poses significant environmental and health risks due to its high toxicity, persistence and complex redox behavior. Magnetic spinel ferrites (MFe₂O₄) have shown promise for Sb removal; however, the intrinsic influence of divalent metal species (M²⁺) in regulating Sb(III)/Sb(V) adsorption performance and interfacial mechanisms remains poorly understood. In this study, MnFe₂O₄, ZnFe₂O₄ and NiFe₂O₄ nanoparticles were synthesized and systematically evaluated to elucidate how M²⁺ governs Sb immobilization behavior. Batch adsorption experiments revealed pronounced M–dependent selectivity. MnFe₂O₄ exhibited the highest Sb(III) adsorption capacity (229.89 mg·g⁻¹), whereas NiFe₂O₄ showed superior affinity toward Sb(V) (up to 257.07 mg·g⁻¹). Adsorption kinetics for both Sb species followed pseudo-second-order models, indicating chemically controlled processes. Isotherm analyses indicated predominantly monolayer complexation for Sb(III), while Sb(V) adsorption displayed mixed adsorption characteristics, reflecting surface heterogeneity. Mechanistic investigations based on FTIR and XPS analyses suggest that Sb(III) immobilization is dominated by inner-sphere complexation with surface Fe–O/Fe–OH groups, whereas Sb(V) adsorption involves synergistic coordination with both Fe–O and M–O (Mn–O/Ni–O) functional groups. XPS analysis of Sb-loaded ZnFe₂O₄ revealed the coexistence of Sb(III) and Sb(V) species after Sb(III) adsorption, indicating surface-confined partial oxidation; the extent of solution-phase conversion was not independently quantified. Therefore, the redox process is interpreted as an interfacial phenomenon rather than bulk oxidation in solution. These results clarify that M²⁺ species influence Sb removal behavior by modulating the reactivity of surface functional groups and interfacial redox characteristics, rather than merely altering adsorption capacity. This work provides spectroscopic insight into M-dependent structure–activity relationships in spinel ferrites and offers a theoretical basis for the rational design of magnetic adsorbents for selective and efficient Sb remediation. Full article

This study investigated how increased Cr and Ni contents affect the corrosion behavior and rust layer evolution of HRB500 rebar in chloride-containing environments. Corrosion of the Cr- and Ni-alloyed rebars was characterized by distinct stages: in the initial stage, before a stable rust layer formed, the corrosion rate increased; with continued immersion, corrosion products progressively covered the surface and became more compact, and the overall corrosion rate decreased. Higher Cr and Ni contents were found to mitigate overall corrosion damage, markedly suppress localized corrosion, and shift the corrosion morphology toward a more uniform attack. Electrochemical measurements showed a noble shift in corrosion potential, a reduction in corrosion current density, and significant increases in low-frequency impedance and charge transfer resistance, indicating enhanced barrier properties against charge transfer and ionic migration. With corrosion progression, rust layer phases evolved from an Fe₃O₄-dominated assemblage to enrichment in stable iron oxyhydroxides; the fraction of α-FeOOH increased, raising the α/γ* index and suggesting improved rust layer stability and protectiveness. Mechanistically, Cr and Ni enrichment was found to facilitate the conversion of metastable products to α-FeOOH and to promote the formation of compact spinel oxides FeCr₂O₄ and NiFe₂O₄, thereby hindering chloride ion ingress and interfacial corrosion reactions and markedly improving corrosion resistance. Overall, this work elucidated the Cr–Ni co-alloying mechanism for rust layer stabilization and pitting suppression. At 504 h, the high Cr–Ni rebar reduced the maximum pit depth by approximately 61.8% and lowered i_corr to approximately 43% of that of the low Cr–Ni rebar, thereby providing quantitative guidance for marine-grade rebar design. Full article

This review article provides a systematic analysis of synthesis methods, structural characteristics, and functional properties of spinel-structured ferrite nanoparticles (MFe₂O₄). The physicochemical principles, advantages, and limitations of various synthesis techniques—including co-precipitation, combustion, sol–gel, thermal decomposition, hydrothermal, solvothermal, microwave-assisted, sonochemical, electrochemical, and solid-state reaction methods—are comparatively discussed. The influence of synthesis parameters on crystal structure, morphology, and cation distribution between tetrahedral and octahedral sites, as well as on magnetic, dielectric, and optical properties, is critically analyzed. Furthermore, the capabilities of characterization techniques such as X-ray diffraction (XRD), scanning electron microscopy with energy-dispersive spectroscopy (SEM/EDS), Fourier-transform infrared spectroscopy (FTIR), FT-Raman spectroscopy, dielectric measurements, and magnetic measurements for investigating spinel ferrites are comprehensively summarized. Finally, the high potential of spinel ferrite nanoparticles for applications in electronics, microwave devices, water treatment, catalysis, sensors, and biomedical fields is highlighted. Full article

Alumina-spinel refractory bricks, composed of 82 wt.% alumina and 18 wt.% MgAl₂O₄ spinel phases, are used in steel ladles due to their ability to resist chemical attack and thermal shock. Thermal shock resistance is determined, in part, by the thermal conductivity of the material. Thermal conductivity measurements for alumina-spinel refractory, three model alumina ceramics, and single crystal sapphire were made with the laser-flash technique from 20 °C to 1000 °C. At room temperature, these gave 6.5 W m⁻¹ K⁻¹ for the refractory, 5.8 to 22 W m⁻¹ K⁻¹ for the alumina ceramics, and 36 W m⁻¹ K⁻¹ for sapphire, despite all materials containing >81 vol.% of alumina. The differences are explained by the roles of porosity, grain boundary thermal resistance, and the spinel phase (refractory). In order to estimate the thermal conductivity of alumina grains in each material, these microstructural effects are modelled with Landauer’s relation for porosity and thermal resistors in series for grains combined with grain boundaries. For two alumina ceramics, the grains yielded similar behaviour to the single crystal. By taking the spinel phase into account with a two-phase mixture relation, the alumina grains in the refractory were estimated with a value of 31 ± 2 W m⁻¹ K⁻¹, close to sapphire. Full article

Lithium-rich manganese-based cathode materials (LRMs, Li_1.2Mn_0.54Ni_0.13Co_0.13O₂) are promising prospects for subsequent-generation lithium-ion batteries owing to their elevated operating voltage, large specific capacity, and affordability. Nonetheless, their actual implementation is significantly impeded by irreversible lattice-oxygen redox reactions, surface structural disorder, and interfacial phase collapse, leading to low initial Coulombic efficiency (ICE), inadequate rate capability, and sluggish Li⁺ transport. Herein, we report a simple and mild glycolic acid-assisted surface-engineering strategy to enhance the electrochemical performance of LRM. Glycolic acid treatment induces controlled H⁺/Li⁺ ion exchange at the particle surface and anchors surface transition metals through the formation of transition metals (TM)–OH and TM–O–C=O bonds. Subsequent calcination constructs an in situ carbon layer-spinel-layered heterostructure, accompanied by the generation of coupled anionic and cationic vacancies. This reconstructed surface provides fast Li⁺ diffusion pathways and stabilized ion-transport channels, while the dual-vacancy configuration enhances lattice-oxygen reversibility and suppresses structural disorder. Consequently, the modified LRM delivers a high initial discharge capacity of 285.3 mAh⋅g⁻¹ with an ICE of 89.9%, while maintaining 81% capacity retention after 100 cycles. Notably, it exhibits a significantly suppressed voltage decay of only 1.7 mV/cycle at 3C, markedly outperforming the pristine LRM. Density Functional Theory (DFT) calculations reveal that the surface-modified sample possesses enhanced electronic conductivity, as evidenced by the improved Density of States (DOS), and achieves superior structural stability through increased binding energies. This environmentally benign surface-engineering strategy offers a practical and efficient route toward the industrial application of LRM. Full article

This study investigates the evolution and influencing factors of non-metallic inclusions in industrial pipeline steel during the vacuum degassing (VD) process. Steel and slag samples were systematically collected at multiple intervals throughout the vacuum treatment using an automated robotic sampler, which integrated temperature measurement and sampling functions. The results indicate that the molten steel temperature and the concentrations of nitrogen, oxygen, and sulfur exhibited an overall decreasing trend, with removal kinetics characterized by a rapid initial reduction followed by a gradual stabilization. The dominant inclusion phases were identified as Mg-Al spinel and calcium aluminates. Specifically, the top slag composition was distributed within the C₃A phase field, trending toward the liquid C₁₂A₇ region, while the endogenous inclusions transitioned from CA₂ toward CA. With prolonged vacuum treatment, the relative fraction of calcium aluminates progressively increased at the expense of Mg-Al spinel due to continuous slag-metal reactions. Furthermore, quantitative analysis reveals that the population density of small equivalent circular diameter (ECD) inclusions continuously decreased, while the average inclusion size increased, indicating that the VD process promotes the collision and coalescence of inclusions. Full article

Cobalt-based oxides are promising candidates for supercapacitor electrodes, but their practical application is often hindered by poor electrical conductivity, limited ion diffusion, and insufficient cycling stability. Herein, we present a novel strategy to improve the electrochemical performance of Co₃O₄ by growing grape-like Co₃O₄ clusters on a nitrogen-doped carbon framework consisting of nitrogen-doped graphene oxide (NGO) and nitrogen-doped carbon nanotubes (NCNTs) through a controlled hydrothermal process. The nitrogen functionalities in the carbon matrix not only facilitate strong interactions between the NGO and NCNTs but also provide abundant nucleation sites for the growth of Co₃O₄ spinel nanoparticles (30–50 nm). This unique structure promotes an efficient electron conduction and ion transport network, which significantly improves the electrochemical performance of the Co₃O₄ electrode. The Co₃O₄@NGO/NCNT ternary nanocomposite, containing 39% Co₃O₄ and featuring a high specific surface area of 162 m² g⁻¹, delivers a specific capacitance of 269 F g⁻¹ at 1 A g⁻¹ and maintains 82% of its capacitance when the current density increases to 10 A g⁻¹. Notably, the nanocomposite demonstrates outstanding cycling stability, with negligible capacitance decay after 2000 charge–discharge cycles at a current density of 5 A g⁻¹, underscoring its excellent electrochemical robustness. This Co₃O₄@NGO/NCNT nanocomposite represents a promising and efficient material for high-performance supercapacitor electrodes. Full article

Interfacial coupling between CoFe₂O₄ (CFO) nanoparticles and oxidatively functionalized multi-walled carbon nanotubes (MWCNTs) enables controlled modulation of structural, optical, and spin dynamic properties in CFO–MWCNT nanocomposites. The solvothermal synthesis promotes nucleation of CFO on –COOH/–OH functional groups, ensuring uniform anchoring along the nanotube surface. X-ray diffraction confirms a cubic spinel phase with lattice expansion from 8.385 Å to 8.410 Å and crystallite growth from 18 nm to 25 nm, reflecting strain transfer and partial nanoparticle coalescence at the carbon interface. The observed bandgap narrowing from 2.72 eV to 2.50 eV, confirmed via Tauc plot analysis, is attributed to localized defect states induced by charge delocalization and orbital hybridization at the interface of the CFO–MWCNT boundary. DC magnetometry reveals a reduction in saturation magnetization from 46 emu/g to 35 emu/g due to diamagnetic dilution and interfacial spin canting, while coercivity decreases from 852 Oe to 841 Oe, indicating modified pinning and domain-wall dynamics associated with exchange-coupled interfaces. Ferromagnetic resonance measurements show a resonance field shift from 3495 G to 3500 G and an increase in the Landé g-factor from 1.97 to 2.00, signifying altered spin–orbit coupling and enhanced local magnetic perturbations. The spin–lattice relaxation time increases from 1.41 ns to 1.59 ns, demonstrating suppressed phonon-mediated relaxation and improved spin coherence across the hybrid network. Spin density rises from 3.72 × 10²² to 4.58 × 10²² spins/g, confirming an increase in unpaired electrons generated by orbital asymmetry at the interface. The anisotropy field and effective magnetocrystalline anisotropy constant exhibit pronounced modulation, evidencing strengthened exchange stiffness and altered Co²⁺/Fe³⁺ superexchange pathways. These results establish CFO-MWCNT nanocomposites as tuneable platforms for spintronic logic elements, high-frequency microwave attenuation, and magneto-optical device architectures. Full article

Two cobalt alloys and one nickel alloy, containing Ta and C in similar atomic contents and either 5 or 10 wt.% Al, were cast. Their microstructures and their oxidation behaviors in air at 1200 °C over 50 h were investigated. All contained eutectic script-like TaC carbides and a dendritic matrix which was either single-phased (FCC) or double-phased (FCC + Co₃Al). The cobalt sample with 5 wt.% oxidized catastrophically, became thinner, lost all its TaC, and was covered by a thick oxide shell (outer CoO and inner mixture of CoO, CoAl₂O₄ and Ta-rich oxides). The two other alloys, Ni-based with 5 wt.% Al and Co-based with 10 wt.% Al, oxidized more slowly, with a mass gain kinetic slightly lower than that for chromia-forming alloys at 1200 °C and a continuous duplex oxide scale made of an outer MAl₂O₄ spinel and inner Al₂O₃ scales. This evidences the existence of two Al content thresholds, depending on the base element, that must be exceeded to obtain acceptable oxidation behavior. Full article