Search Results (180)

Model experiments were performed on the interaction of swift heavy 220 MeV Xe ions with MgAl₂O₄ spinel crystal with (100), (110), and (111) planes. A computational analysis of the energy parameters of Xe ions in MgAl₂O₄ single crystal was performed, and an estimate of the ion range in the near-surface layer (14 μm) was provided. Optical absorption spectrum was analyzed using polarized light and EPR spectroscopy of initial and irradiated crystals. It has been established that at a fluence of 10¹³ cm⁻² in a sample with an orientation plane (110), 35% more optically active F-type centers are formed. It has been shown that optically active centers V|_Al–O⁻ are observed in an unusual, polarized beam. Full article

This work employs moiré interferometry to investigate the influence of sintering temperature and sandblasting on the optical and mechanical properties of magnesium aluminate spinel (MgAl₂O₄). S25CRX14 Spinel pellets were fabricated via Spark Plasma Sintering (SPS) at 1300 °C, 1350 °C, and 1400 °C. The sintered samples were subsequently analyzed before and after sandblasting. Moiré interferometry, a non-destructive and contactless technique based on the superposition of tow linear transmission gratings, has proven particularly suitable for detecting micro-defects in transparent materials. The analysis of moiré fringes provided essential insights into the presence and size of defects, enabling accurate quality assessment without altering the samples. Its high spatial resolution, allowed the detection of even low-contrast defects. The results confirmed that the sintering temperature and sandblasting significantly influenced the mechanical and optical properties of the S25CRX14 spinel samples. The specimens sintered at 1350 °C exhibited the highest light transmission and the superior hardness. In contrast, the samples sintered at 1400 °C showed a notable degradation in their optical and mechanical properties. In conclusion, the pellets sintered at 1350 °C demonstrated the most favorable overall performance. This study confirms that moiré interferometry is a straightforward, accurate, and highly effective method for evaluating transparent ceramics, with very low implementation costs. Full article

Magnesia-dolomite refractories have emerged as sustainable alternatives to traditional carbon- or chromium-containing linings in steelmaking and cement industries. Their outstanding thermochemical stability, high refractoriness, and strong basic slag compatibility make them suitable for converters, electric arc furnaces (EAF), and argon–oxygen decarburization (AOD) units. However, their practical application has long been constrained by hydration and thermal shock sensitivity associated with free CaO and open porosity. Recent advances, including optimized raw material purity, fused co-clinker synthesis, nano-additive incorporation (TiO₂, MgAl₂O₄ spinel, FeAl₂O₄), and improved sintering strategies, have significantly enhanced density, mechanical strength, and hydration resistance. Emerging technologies such as co-sintered magnesia–dolomite composites and additive-assisted microstructural tailoring have enabled superior corrosion resistance and extended service life. This review provides a comprehensive analysis of physicochemical mechanisms, processing routes, and industrial performance of magnesia–dolomite refractories, with special emphasis on their contribution to technological innovation, decarbonization, and circular economy strategies in high-temperature industries. Full article

ZrO₂-MgO-Al₂O₃ ceramics, despite a long history of research, still attract the attention of researchers due to the high potential of their applications as refractories and matrices for metal ceramics. A unique composition combining high strength and temperature stability is particularly in demand. In this paper, a comprehensive study of ceramics of the composition (90−x)·ZrO₂-10·MgO-x·Al₂O₃ (x = 10–80 wt.%) obtained by solid-phase sintering with preliminary annealing is carried out. Preliminary annealing was used for the possible formation of metastable phases with outstanding mechanical properties. Using the X-ray diffraction method, it was found that most of the samples consist of monoclinic zirconium oxide, magnesium–aluminum spinel, and corundum phases. The exception is the sample with x = 10 wt.%, in which the main phase was a cubic modification of zirconium oxide. By formation this type of ZrO₂ polymorph in the composition hardness and flexural strength significantly increased from 400 to 1380 and 50 to 210 MPa, respectively. The total porosity of ceramics under study lies in the range 6–28%. Using the scanning electron microscopy method, it was found that the phase composition significantly affects the morphology of the microstructure of the sintered bodies. Thus, for sintered ceramics with a high corundum content, the microstructure is characterized by high porosity and a large grain size. For the first time, by applying preliminary annealing, a new type of ternary ceramic ZrO₂-MgO-Al₂O₃ was sintered with potentially outstanding mechanical properties. The presence of a stabilized zirconium oxide phase, stresses in the crystal lattice of the matrix phase, and the formation of cracks in the microstructure are the main factors influencing shrinkage, porosity, microhardness, and biaxial flexural strength. Full article

In this study, we investigate the phase transition process during high-alumina, low-lithium glass-ceramics (ZnO-MgO-Li₂O-SiO₂-Al₂O₃) crystallization. The differential scanning calorimetry and high-temperature X-ray diffraction results show that approximately 10 wt.% of (Zn, Mg)Al₂O₄ crystals precipitated when the heat treatment temperature reached 850 °C, indicating that a large number of nuclei had already formed during the earlier stages of heat treatment. Field emission transmission electron microscopy used to observe the microstructure of glass-ceramics after staged heat treatment revealed that cation migration occurred during the nucleation process. Zn and Mg aggregated around Al to form (Zn, Mg)Al₂O₄ nuclei, which provided sites for crystal growth. Moreover, high-valence Zr aggregated outside the glass network, leading to the formation of nanocrystals. Raman spectroscopy analysis of samples at different stages of crystallization revealed that during spinel precipitation, the Q³ and Q⁴ structural units in the glass network increased significantly, along with an increase in the number of bridging oxygens. Highly coordinated Al originally present in the network mainly participated in spinel nucleation, effectively suppressing the subsequent formation of Li_xAl_xSi_1−xO₂, which eventually resulted in the successful preparation of glass-ceramics with (Zn, Mg)Al₂O₄ and ZrO₂ as the main crystalline phases. The grains in this glass-ceramic are all nanocrystals. Its Vickers hardness and flexural strength can reach up to 875 Hv and 350 MPa, respectively, while the visible light transmittance of the glass-ceramic reaches 81.5%. This material shows potential for applications in touchscreen protection, aircraft and high-speed train windshields, and related fields. Full article

This study explores the catalytic performance of V³⁺-modified Mg/Al hydrotalcite-derived materials in the oxidative dehydrogenation (ODH) of n-butane, compared with catalysts derived from pyrovanadate and decavanadate precursors. Different methods for preparing hydrotalcite-like materials were applied to obtain vanadium-containing Mg-Al mixed oxide catalysts for n-butane ODH. The hydrotalcite-like precursors were doped with vanadates (V⁵⁺) via ion exchange or co-precipitation or with V³⁺ cations incorporated into brucite-like layers. During calcination in air or argon flow, different vanadium-containing phases were obtained. Our findings demonstrate that V³⁺-doped hydrotalcites exhibit superior activity and selectivity toward the total C₄H₈ products, with enhanced selectivity for 1,3-butadiene. The highest n-butane conversion was observed for catalysts with an MgO structure and vanadium dispersed in the oxide matrix. A similar conversion level (~44%) was obtained for a spinel-like Mg₂VO₄ catalyst, but only a 15% level was found for the highly crystalline α-Mg₂V₂O₇ catalyst. In contrast, the highest selectivities toward dehydrogenated products were observed for V³⁺-containing and α-Mg₂V₂O₇ catalysts. NH₃- and CO₂-temperature programmed desorption (TPD) analyses showed that high basicity combined with low acidity favors the formation of butene isomers and 1,3-butadiene. This work highlights the strategic potential of tailoring vanadium speciation and hydrotalcite-based catalyst design for low-carbon chemical manufacturing, supporting the transition toward a circular economy. Full article

The recycling of interconnects from solid oxide electrolyzer (SOEL) stacks is essential for closing material loops in green hydrogen systems. Since it is mostly made of high-quality stainless steel, remelting is the most practical recovery route, but it inevitably generates slag, where strategic elements like chromium (Cr) are retained. This study investigates the mineralogical and grain characteristics of slag from SOEL interconnect remelting, with an emphasis on Cr distribution and its recovery potential. A correlative approach was applied using X-ray diffraction (XRD), scanning electron microscopy-based mineral liberation Analysis (MLA), and X-ray computed tomography (XCT). Cr was primarily found in magnesiochromite Mg(Al,Cr)₂O₄ (~54 wt.% Cr), constituting only ~5 wt.% of the slag, while lower concentrations were also detected in monticellite and åkermanite. XCT revealed the macroscopic heterogeneity of the slag system, with metallic inclusions and pores concentrated near the metal–slag interface, indicating density-driven settling. Cr-rich spinels were fine-grained (x_50,2 ≈ 55 µm), irregular in shape, and partially intergrown, presenting challenges for mechanical liberation and physical recovery. These features, combined with their compositional selectivity, suggest that Cr-rich spinels are promising candidates for future Engineered Artificial Mineral (EnAM) strategies aimed at enhancing selective recovery from slag. Full article

This study explores the development of aluminum-doped MgV₂O₄ spinel cathodes for aqueous zinc-ion batteries (AZIBs), addressing the challenges of poor Zn²⁺ ion diffusion and structural instability. Al³⁺ ions were pre-inserted into the spinel structure using a sol-gel method, which enhanced the material’s structural stability and electrical conductivity. The doping of Al³⁺ mitigates the electrostatic interactions between Zn²⁺ ions and the cathode, thereby improving ion diffusion and facilitating efficient charge/discharge processes. While pseudocapacitive behavior plays a dominant role in fast charge storage, the diffusion of Zn²⁺ within the bulk material remains crucial for long-term performance and stability. Our findings demonstrate that Al-MgV₂O₄ exhibits enhanced Zn²⁺ diffusion kinetics and robust structural integrity under high-rate cycling conditions, contributing to its high electrochemical performance. The Al-MgVO cathode retains a capacity of 254.3 mAh g⁻¹ at a high current density of 10 A g⁻¹ after 1000 cycles (93.6% retention), and 186.8 mAh g⁻¹ at 20 A g⁻¹ after 2000 cycles (90.2% retention). These improvements, driven by enhanced bulk diffusion and the stabilization of the crystal framework through Al³⁺ doping, make it a promising candidate for high-rate energy storage applications. Full article

The Paleoproterozoic Kovdozero complex, one of largest in the Fennoscandian Shield, was emplaced in a peripheral region of the SB–TB–LBB (Serpentinite Belt–Tulppio Belt–Lapland–Belomorian Belt) megastructure. Coronitic rocks of ultrabasic–basic compositions, investigated along a cross-section in the Gabrish area, are members of a cryptically layered series. They crystallized from the northern margin inward, as indicated by variations in mineral compositions and geochemical trends. Unsteady conditions of crystallization arose because of uneven cooling of the shallowly emplaced complex. Rapid drops in temperature likely caused the forced deposition of different generations of variously textured pyroxenes and chromian spinel or resulted in the unique development of narrow recurrent rims of orthopyroxene hosted by olivine. The unstable conditions of crystallization are expressed by (1) textural diversity, (2) broad variations in values of Mg#, and (3) virtual presence of double trends of Mg# as a function of distance. The coronitic textures are intimately associated with interstitial grains of plagioclase (An_≤65), also present as relics in a rim of calcic amphibole. The coronas are results of (1) rapid cooling leading to unsteady conditions of crystallization, which caused the sudden cessation of olivine crystallization and the development of an orthopyroxene rim on olivine and (2) an intrinsic enrichment in H₂O (and essential Cl in scapolite) coupled with a progressive accumulation of Al and alkalis, giving rise to fluid-rich environments in the intercumulus melt at advances stages of crystallization. These processes were followed by deuteric composite rims of calcic amphibole and reaction of fluid with early rims or grains of pyroxenes and late plagioclase. The coronitic sequences Ol → Opx → Cpx → calcic Amp → Pl (plus Qz + Mca) observed at a microscopic scale reproduce, in miniature, the normal order of crystallization in an ultrabasic–basic complex. A composite orthopyroxene + calcic amphibole corona resembles some rocks in complexes of the Serpentinite Belt. The prominence of such coronas may well be characteristic of the crystallization of komatiite-derived melts. Full article

This study investigates the application of spinel (MgAl₂O₄) hollow fiber membranes for clarification of clove basil (Ocimum gratissimum L.) aqueous extract, a rich source of bioactive compounds. The membranes were produced using a phase-inversion and sintering method at 1350 °C, combining alumina and dolomite as raw materials. The calcination of the powder materials at 1350 °C resulted in the spinel phase formation, as indicated by the XRD analyses. The spinel hollow fiber membrane presented a hydrophilic surface (water contact angle of 74°), moderate roughness (144.31 ± 12.93 nm), and suitable mechanical strength. The ceramic membrane demonstrated a water permeability of 35.28 ± 2.46 L h⁻¹ m⁻² bar⁻¹ and a final permeate flux of 9.22 ± 1.64 L h⁻¹ m⁻² for filtration of clove basil extract at 1.0 bar. Fouling analysis identified cake formation as the dominant mechanism for flux decline. The membrane retained 44% of the total phenolic compounds and reduced turbidity by 60%, while preserving significant antioxidant capacity in the permeate. The results highlight the potential of spinel-based hollow fiber membranes as a cost-effective and efficient solution for clarifying bioactive plant extracts, offering enhanced mechanical properties and lower sintering temperatures compared to conventional alumina membranes. Full article

Using machine learning models, this study innovatively introduces multi-element compositions to optimize the performance of spinel refractories. A total of 1120 spinel samples were fabricated at 1600 °C for 2 h, and an experimental database containing 112 data points was constructed. High-throughput performance predictions and experimental verifications were conducted, identifying the sample with the highest hardness, (Al₂Fe_0.25Zn_0.25Mg_0.25Mn_0.25)O₄ (1770.6 ± 79.1 HV1, 3.35 times that of MgAl₂O₄), and the highest flexural strength, (Al₂Cr_0.5Zn_0.1Mg_0.2Mn_0.2)O₄ (161.2 ± 9.7 MPa, 1.4 times that of MgAl₂O₄). Further analysis of phase composition and microstructure shows that the mechanism of hardness enhancement is mainly the solid solution strengthening of multi-element doping, the energy dissipation of the large-grain layered structure, and the reinforcement of the zigzag grain boundary. In addition to solid solution strengthening and a compact low-pore structure, the mechanism of improving bending strength also includes second-phase strengthening and phase concentration gradient distribution. This method provides a promising way to optimize the performance of refractory materials. Full article

Magnesia-spinel multicomponent materials have been used as refractories for a long time. In addition to a few binary systems, the influence of spinel phases on the thermal expansion ($\alpha$) of MgO or the resulting compound has not been studied so far. As $\alpha$ is critical for refractories in application, this work investigates the thermal expansion of complex MgO-based spinel systems using X-ray diffraction (XRD) in combination with Rietveld refinement in the temperature range between 30 °C and 1200 °C. All studied periclase solid solutions, in contact with spinels of the systems Mg_1.01(Al_0.23Cr_1.64Fe_0.13)O₄, ${\mathrm{Fe}}_3{\mathrm{O}}_4$–${\mathrm{MgFe}}_2{\mathrm{O}}_4$, NiFe₂O₄–NiAl₂O₄, MgAl₂O₄–MgFe₂O₄, Fe₃O₄–FeAl₂O₄ and ${\mathrm{Fe}}_3{\mathrm{O}}_4·{\mathrm{NiFe}}_2{\mathrm{O}}_4·2{\mathrm{MgAl}}_2{\mathrm{O}}_4$ showed $\alpha$ trends below plain MgO, or even decreasing values above 1000 °C. Many spinels showed large negative thermal expansion coefficients. It was found that the structural change in spinels is constrained, leading to a common analytical expression to calculate the lattice parameter of spinels with temperature, which was used to study the nature of the investigated spinels in more detail. The work highlights that Cr-free MgO-spinel systems show similar or even better high-temperature behaviour than commonly used magnesia–chrome aggregates. Full article

The simultaneous analysis of optical and electronic paramagnetic resonance spectra of all 3d metals, doped into transparent α-Al₂O₃ and MgAl₂O₄ spinel, was effectuated with a view of establishing the speciation pattern of the dopants. The examination of these patterns enabled the revelation of certain regularities (rules) affecting the correlation between the physical factors controlling the process and speciation patterns. It was observed that structural dissimilarities between the lattices significantly affected the correlation. Thus, the spinel lattice was found to impose the accommodation of the dopants as 2+ cations replacing native Mg²⁺ ions located in tetrahedral sites, with the process concerning only the late 3d elements. The difference in behavior between the early and late 3d elements is mostly caused by the increase in ionization potential along the series. In alumina, the dopants are accommodated as 3+ cations in octahedral sites; 6-coordinated 2+ cation stabilization is feasible but requires extremely reductive conditions for late 3d elements. Full article

Concentrated solar power plant (CSP) technology holds significant application value in the renewable energy sector for converting solar radiation into thermal and electrical energy. As a heat storage medium for next-generation solar thermal power stations, chloride salts exhibit strong corrosive effects on structural components. To enhance corrosion resistance of the heated body in molten salt environments, Inconel 625 is modified by incorporating aluminum, which facilitates the formation of a protective oxide film. In this study, High-Aluminum Inconel 625, after cold rolling and solution treatment, was immersed in a NaCl-KCl-MgCl₂ eutectic chloride melt at 650 °C for 200 h. Post-corrosion analysis revealed the formation of an alumina layer on the surface, effectively mitigating corrosion. Increased aluminum content resulted in thicker alumina layers and the formation of oxidation products, such as Cr₂O₃, Fe₂O₃, MoO₂, and MgCr₂O₄ spinel structures, significantly enhancing the alloy’s corrosion resistance. The Inconel 625 cold-rolled plate with 5.31 wt% Al exhibited the best corrosion resistance (3510 μm/year), making it a promising candidate for use in next-generation CSP heat storage and exchange components. Full article

The influence of Mg doping in α-Al₂O₃ crystals is investigated in this article by first-principles calculations and formation energies, density of states, and computed absorption spectra. Three models related to Mg²⁺ substituting for Al³⁺ doping structures were constructed, as well as spinel structure models with varying aluminum-magnesium ratios. The formation energy calculations confirmed the rationality of the Mg_AlV_O model, which means that Mg substitutional doping incorporating oxygen vacancies is most likely to form in crystals. The combined action of magnesium and oxygen vacancies introduced new defect energy levels in the bandgap. The calculated absorption spectra of the Mg_AlV_O and Mg-rich spinel structures exhibited various color centers. The experimental absorption spectra and thermoluminescence characteristics of α-Al₂O₃:Mg and alumina-magnesium (Al-Mg) spinel crystal samples were tested. The thermoluminescence peak of the Al-Mg spinel was significantly stronger than that of the α-Al₂O₃:Mg crystal. The consistency between the model-calculated absorption spectra and the experimental results confirmed the theoretical predictions. Based on the experimental and computational results, the influence of Mg²⁺ substitutional doping in α-Al₂O₃ and the impact of the locally Mg-rich spinel on the optical and radiation performance of α-Al₂O₃:Mg crystals are elucidated. Full article