Search Results (874)

The precipitation characteristics and grain-boundary structure of Al–Cu–Mg alloys strongly affect their corrosion behavior, whereas the roles of Si and Ag microalloying in low Cu/Mg ratio systems are not yet fully understood. In this work, the effects of Si and Ag additions on age-hardening response, precipitation characteristics, and corrosion performance were systematically investigated by combining transmission electron microscopy with electrochemical and corrosion measurements. Si addition significantly accelerated the age-hardening kinetics, enabling the alloy to reach a hardness of 147 HV after only 6 h of aging, whereas the base alloy required 24 h to reach a similar level. This accelerated response was accompanied by refined S-phase precipitation and a markedly narrowed precipitation-free zone along grain boundaries. Further Ag addition introduced coherent Ω precipitates and a more complex multi-phase precipitation structure, which increased microstructural heterogeneity. As a result, the Al–Cu–Mg–Si alloy exhibited the lowest corrosion current density and the shallowest corrosion depth, whereas the Al–Cu–Mg–Si–Ag alloy showed deteriorated corrosion resistance. These results indicate that Si microalloying alone can simultaneously accelerate aging and improve corrosion resistance, while further Ag addition enhances precipitation complexity and strengthening potential but increases susceptibility to localized corrosion. Full article

The colloidal particles present in natural soil and groundwater systems possess distinctive properties that enable them to migrate across solid surfaces, thereby exerting a significant influence on the distribution of pollutants. While the attachment of colloidal particles to solid surfaces has been extensively investigated, the mechanisms governing their detachment under varying hydrochemical conditions remain largely unexplored. The common interaction between montmorillonite colloids and solid medium (Al₂O₃) in soil affects the fate of pollutants such as heavy metals. In our study, Al₂O₃ was used as solid medium to observe the adsorption and desorption behavior of montmorillonite colloids. It was found that the adsorption capacity of Al₂O₃ to montmorillonite colloids could reach 4.71 mg g⁻¹ (pH 5.0 and 10 mM NaCl concentration). X-ray photoelectron spectroscopy analysis shows that montmorillonite colloids react with the Al₂O₃ surface mainly through chemical groups with –O–Si bonds. Desorption experiments show that SDS drives desorption by neutralizing and reversing the surface charge of Al₂O₃, while CTAB directly modifies montmorillonite colloids and introduces steric hindrance to achieve desorption. These research data contribute to a comprehensive understanding of the migration behavior of montmorillonite colloids on solid phases. Full article

Titanium-extracted tailing is a by-product generated during titanium-bearing blast furnace slag treatment process. The crystallization behavior of the titanium-extracted tailing during the cooling process is significant to its utilization for glass ceramics preparation. In this work, the CaO-SiO₂-Al₂O₃-MgO-TiO₂-FeO slag was used to explore the effect of CaO/SiO₂ ratios on titanium-extracted tailing crystallization. FactSage 8.2 calculation and mineralogical characterizations were conducted to investigate the phase and microstructure evolution during the slag cooling process. Single hot thermocouple technique (SHTT) was employed for in situ observation of the crystallization process of the slag during the cooling process. The obtained results indicated that the perovskite, melilite, spinel, diopside and anorthite phases would be crystallized during the cooling process when the CaO/SiO₂ ratios of the slag were 0.7–1.1. Increasing the CaO/SiO₂ ratio to 1.3 and 1.5 promoted the crystallization of olivine and merwinite phases, however, inhibited the crystallization of diopside and anorthite phases. The initial crystallization temperature and the liquid phase disappeared temperature of the slag enhanced with improving CaO/SiO₂ ratios. The initial crystallization temperature was controlled by perovskite phase precipitation when the CaO/SiO₂ ratios of slag reached 0.7–1.3. Whereas the initial crystallization temperature was controlled by the crystallization of spinel phase when the CaO/SiO₂ ratio of slag was 1.5. The incubation time for crystal nucleation reduced with increasing CaO/SiO₂ ratios that promoted slag crystallization. Moreover, increasing the CaO/SiO₂ ratio from 0.7 to 1.5 enhanced the critical cooling rate from 4 °C s⁻¹ to 11 °C s⁻¹. Full article

Cordierite-based ceramics (Mg₂Al₄Si₅O₁₈) were successfully synthesized and comprehensively characterized to evaluate their structural and dielectric behavior for high-temperature electronic applications. Morphological, microstructural and vibrational analyses confirm the high phase purity and structural integrity of the synthesized material. Dielectric measurements reveal high real permittivity (ε′) values at low frequencies and elevated temperatures, mainly attributed to interfacial polarization arising from Schottky-type barriers at grain–grain and surface–volume interfaces, underscoring the crucial influence of heterogeneous interfaces on the dielectric response. The electrical conductivity follows a thermally activated hopping mechanism involving both intra-grain and grain-boundary charge transport. Analysis of the electric modulus formalism provides further insight into relaxation dynamics: the real (M′) and imaginary (M″) components highlight pronounced space-charge effects, with M″ exhibiting a distinct relaxation peak (M″) associated with grain contributions. The systematic shift of this peak toward higher frequencies with increasing temperature indicates enhanced charge-carrier mobility and a strongly thermally activated relaxation process. The frequency-dependent conductivity displays two regimes: a low-frequency plateau corresponding to dc conductivity and a high-frequency dispersive region following a power-law behavior characteristic of hopping conduction, with power-law exponents (α₁ and α₂) markedly lower than unity, confirming the non-Debye character of the relaxation processes. The hopping frequency (ω) increases with temperature, further supporting the thermally activated nature of charge transport. Activation energies extracted from Arrhenius plots of dc conductivity are 0.88 eV for grain boundaries and 0.83 eV for grains, demonstrating that both microstructural regions significantly contribute to the overall conduction process. Full article

To develop a high-performance inorganic fireproof coating suitable for steel structures, this study utilized magnesium phosphate cement (MPC) as the matrix and introduced expanded perlite (EP) as a lightweight aggregate. The effects of EP content (40–55%) and magnesium-to-phosphorus ratio (M/P = 4:1–7:1) on the dry density, compressive strength, bond strength, and fire resistance of the coating were systematically investigated. X-ray diffraction (XRD), scanning electron microscopy (SEM), and thermogravimetric analysis (TGA) were employed to reveal the phase evolution and microstructure evolution mechanisms at high temperatures. The results indicate that increasing EP content significantly reduces the dry density and thermal conductivity of the coating, enhancing thermal insulation performance. However, excessive incorporation leads to the deterioration of mechanical properties, with an optimal EP content of 45%. The M/P ratio influences the interfacial bond strength and high-temperature structural stability by regulating the proportion of the hydration product K-struvite (KMgPO₄·6H₂O) and residual MgO. Compressive strength peaked at M/P = 6:1 (0.80 MPa), while bond strength was optimal at M/P = 5:1 (0.097 MPa), corresponding to the best fire resistance (back-side temperature of 180.4 °C). At high temperatures, K-struvite dehydrates and transforms into anhydrous KMgPO₄, which, together with residual MgO and crystallized SiO₂ from EP, forms a dense ceramic skeleton, ensuring the structural integrity of the coating. Comprehensive performance evaluation determined the optimal mix ratio as M/P = 5:1 and EP content = 45%. The coating with this ratio exhibits a dry density of approximately 560 kg/m³, a 14-day compressive strength of 0.53 MPa, a bond strength of 0.097 MPa, and a back-side temperature of 180.4 °C under flame exposure, demonstrating a favorable balance of lightweight character, mechanical integrity, and thermal insulation performance suitable for steel structure fire protection applications. Full article

Si₃N₄@MgSiN₂ composite powder with a core–shell structure was successfully synthesized via the in situ reaction between Mg and α-Si₃N₄ using a NaCl–KCl mixed molten salt in this study. The effects of process parameters, including the molten salt system, reaction temperature, and Mg/Si₃N₄ mass ratio, on the morphology, phase composition, and microstructure of the coating layer were investigated. The results indicate that the reaction follows a “template growth” mechanism. Mg-containing species dissolve in the molten salt, diffuse to the surface of Si₃N₄ particles, and react with α-Si₃N₄, resulting in a relatively uniform MgSiN₂ layer at 1300 °C. The yield of MgSiN₂ layer exhibits a linear positive correlation with the Mg/Si₃N₄ mass ratio, enabling controllable microstructural regulation through adjustment of the starting materials composition. The core–shell powder forms a liquid phase at a relatively low temperature (approximately 1350 °C), demonstrating excellent sintering activity. This work provides a new material foundation for the fabrication of silicon nitride ceramics with high thermal conductivity. Full article

This paper presents an analysis of the physicochemical and biological properties of the developed composite zinc phosphate cement modified with bismuth oxide and phosphorus slag additives. The powder phase was synthesized by sintering a frit with an optimal composition (ZnO, MgO, SiO₂, Bi₂O₃) using phosphorus slag as the active component. The study included an assessment of the microstructure, chemical resistance in aggressive environments (5% NaCl solution, 10% lactic acid, carbonated water), solubility in artificial saliva, and cytotoxicity in human fibroblasts. The addition of phosphorus slag was found to promote the formation of low-melting eutectics, which reduces the sintering temperature by 100 °C and increases the material’s whiteness to 97.8%. X-ray diffraction analysis confirmed the presence of zincite, quartz, and periclase phases, forming a dense microstructure without pronounced pores or cracks. The experimental cement demonstrated high acid resistance: the maximum weight loss in lactic acid was 8%, while the leaching of toxic elements (Pb, As, Cr, etc.) remained extremely low (10–67 ppm), confirming the material’s environmental safety. Testing of the composite zinc phosphate cement in artificial saliva revealed minimal weight loss compared to similar products. Biological testing showed that the cement’s cytotoxicity is dose-dependent; at a 0.3 g dose and a 1:4 dilution, the material loses its toxic properties and becomes safe for living tissue. The developed zinc phosphate composite cement composition offers improved aesthetic and mechanical properties, high chemical stability, and biocompatibility at working concentrations, making it promising for use in clinical dentistry. Full article

High-speed laser cladding (HLC) technology can provide high cooling rates and low dilution rates for the preparation of metastable Fe-based amorphous phases. In this work, the effects of Ta content on the microstructure, mechanical properties, and soft magnetic performance of Fe-based amorphous alloys were systematically investigated. The results indicated that Ta remained uniformly dispersed within the FeSiB amorphous powder, and no new phases were formed after mechanical ball milling. The higher mixing enthalpy of Ta and its atomic radius difference from other elements (such as Fe, Si, B) were beneficial in improving glass-forming ability (GFA), and with an increase in Ta element content from 0% to 2%, 4% and 6%, the amorphous phase content was 48.6%, 51.5%, 60.4% and 54.8%, respectively. The average microhardness of the coating with a Ta content of 4% was 1310 HV_0.2, which was 50HV_0.2 higher than before; in addition, the wear rate reduced from 2.21 × 10⁻⁴ mg·N⁻¹·m⁻¹ to 2.06 × 10⁻⁴ mg·N⁻¹·m⁻¹. Also, corrosion tests showed that the coating with a Ta content of 4% displayed superior corrosion resistance compared to that before the Ta addition. However, because the element Ta could alter the local electronic environment and enhance the local magnetic anisotropy of FeSiB, the saturation magnetic flux density (Ms) decreased from 1.64 T to 1.56 T, and the coercivity (Hc) increased from 0.9 A/m to 1.3 A/m, which caused degradation of the soft magnetic properties. Full article

This study characterizes the hydrochemistry and geochemical signature of the Upper Cretaceous geothermal aquifer in the Zharkunak zone (Eastern Ili Depression, SE Kazakhstan) using certified analytical datasets from five deep wells (5539, 1-RT, 3-T, 1-TP, and 2-TP). The waters are hyperthermal (89–103 °C), alkaline (pH 8.1–9.0), and weakly mineralized (TDS 0.3–1.0 g/L), with sodium-dominated facies ranging from Na–HCO₃–SO₄ to Na–SO₄–Cl. Hydrochemical analysis indicates that water–rock interaction and cation exchange are the primary controls on fluid evolution, with limited influence from evaporation or external salinity sources. Elevated fluoride (up to ~10 mg/L) and dissolved silica (H₂SiO₃, often >50 mg/L) reflect prolonged high-temperature interaction with silicate-rich lithologies under low Ca²⁺ conditions. Trace elements and radon activity (up to 0.32 nCi/L) further support deep, fault-controlled circulation pathways. PHREEQC modeling indicates near-equilibrium to slight supersaturation with respect to silica phases, suggesting a potential risk of silica scaling during cooling, while carbonate scaling remains limited. Although the dataset is based on discharge conditions from a limited number of wells, the results demonstrate that the Zharkunak system has strong geothermal utilization potential, with management considerations related to fluoride, radon, and silica scaling. Future work should focus on integrating isotopic analyses and reactive transport modeling to better constrain subsurface processes and long-term system behavior. Full article

Gravity casting and semi-solid extrusion were employed to prepare Mg₂Si-Al composites. X-ray diffraction (XRD), optical microscopy (OM), scanning electron microscopy (SEM), EDS analysis, Vickers hardness testing, and tensile testing were used to compare the microstructures and mechanical properties of the two composites, aiming to clarify the effects of the fabrication processes and aging times on their microstructures and mechanical performance. The findings show that semi-solid extrusion converts dendritic α-Al into spherical or ellipsoidal grains (60 ± 25 μm) and induces the spheroidization of Mg₂Si reinforcing phases (29 ± 12 μm). Vickers hardness data show that both composites exhibit a rise-and-fall hardness trend with an increasing aging time, reaching a maximum at 8 h. At this aging stage, the semi-solid extruded composite has a Vickers hardness of 214 ± 32.71 HV, 22.99% higher than that of the gravity-cast composite under the same treatment. Tensile tests demonstrate that the semi-solid extruded composite attains its best tensile strength (254 MPa) and elongation (3.26%) at 8 h of aging. Compared with the semi-solid extruded composites aged for 4 h and 16 h, the 8 h-aged sample exhibits 32.30%/49.41% higher tensile strength and 52.34%/38.72% higher elongation, respectively. After 8 h of aging, the semi-solid extruded composite shows a 59.75% increase in tensile strength and an 88.44% increase in elongation compared with the gravity-cast composite. Full article

Silicon carbide (SiC) ceramics are among the most attractive materials for lightweight armor because they combine low density (3.0–3.2 g/cm³), high hardness, and high thermal and chemical stability; however, their densification remains challenging because of strong covalent bonding and low self-diffusion. This review analyzes the main sintering routes used for armor-grade SiC ceramics, including solid-state sintering, liquid-phase sintering, hot pressing, gas-pressure sintering, hot-isostatic pressing, ultra-high-pressure sintering, two-step sintering, and spark plasma sintering, together with additive systems based on B, C, Al₂O₃, Y₂O₃, MgO, CaO, and rare-earth oxides. Reported data show that solid-state sintering typically requires 2100–2300 °C and yields 90–95% relative density, whereas hot pressing and liquid-phase sintering achieve 96–99% density at lower temperatures, generally with a flexural strength of 350–800 MPa, fracture toughness of 3.5–7.0 MPa·m^1/2, and hardness of 20–30 GPa. Among the reviewed methods, spark plasma sintering provides near-theoretical density (≥99%) together with the most favorable combination of strength (up to 850 MPa) and hardness (up to 35 GPa). Overall, liquid-phase sintering and spark plasma sintering offer the most favorable balance between densification, microstructural control, and armor-relevant mechanical performance. Full article

Aluminum–silicon (Al-Si) alloys are widely used in aerospace, automotive manufacturing, power electronics, marine engineering and other fields due to their excellent physical properties. However, their corrosion resistance is insufficient in harsh service environments. In this study, a variety of characterization methods were adopted, including scanning electron microscopy (SEM), X-ray diffraction (XRD), electrochemical measurements (electrochemical impedance spectroscopy (EIS) and potentiodynamic polarization), immersion corrosion tests, and scanning vibrating electrode technique (SVET). The results show that the appropriate heat treatment regime can significantly enhance the corrosion resistance of the alloy, while improper aging parameters will aggravate the corrosion tendency. The optimal heat treatment regime is solution treatment at 500 °C for 4 h followed by aging at 200 °C for 48 h. Under this condition, the corrosion current density (i_corr) is as low as 79.30 μA/cm², and the low-frequency impedance modulus and phase angle in EIS tests are optimal. The as-extruded alloy exhibits severe localized corrosion, while the heat-treated alloy transforms into mild and uniform corrosion. The underlying mechanism is that heat treatment induces the formation of uniformly distributed nanoscale Mg₂Si and Al₃(Sc,Zr) precipitates, which synergistically improve the corrosion resistance of the alloy by weakening micro-galvanic coupling and facilitating the formation of a stable passive film. Full article

Achieving a balanced combination of mechanical performance and corrosion resistance remains a critical challenge restricting the broader application of Al–Zn–Mg–Cu alloys in aerospace, marine, and transportation industries. In this investigation, the addition of Si significantly enhances the mechanical properties of the alloy. Among them, the alloy containing 0.35Si has the best corrosion resistance, which is closely related to the transformation of precipitates. A non-monotonic relationship between Si content and corrosion resistance was observed. At low Si levels, the simultaneous precipitation of η, T, and GPB-II phases leads to a large electrochemical potential difference among these phases, which promotes micro-galvanic corrosion. With increasing Si content, the microstructure evolves toward the dominance of GPB-II precipitates, thereby reducing the internal potential difference and improving corrosion resistance. However, excessive addition of Si will lower the equilibrium solid phase temperature, resulting in overburning during the solid solution treatment process and a significant decrease in corrosion resistance. In addition, lowering the solution treatment temperature effectively improves corrosion resistance by suppressing the formation of remelted spheres and low-melting-point brittle phases along grain boundaries. These phases can form strong micro-galvanic couples with the matrix, accelerating anodic dissolution. Therefore, by adding an appropriate amount of Si and optimizing the solid solution temperature, a corrosion-resistant high-strength Al-Zn-Mg-Cu-Si alloy can be obtained. This strategy also provides a broader compositional and heat-treatment design window, which could be further expanded through the incorporation of rare-earth (RE) elements. Full article

The study investigates the influence of Ca addition (0, 0.5, 0.7, and 1 wt.%) on the microstructure and mechanical properties of friction stir-processed (FSPed) Mg-2.5Si-4Zn-xCa alloys. The microstructures of the processed alloys were characterized using OM, SEM, EBSD, and TEM. The results indicated that Ca addition combined with FSP can synergistically refine and homogenize the Mg₂Si phase, and with increasing Ca content, the size of both primary and eutectic Mg₂Si phases first decreases and then increases, reaching an optimum refinement at 0.7 wt.% Ca. In this composition, the Mg₂Si phases were uniformly dispersed, and the stir zone exhibited significantly refined recrystallized grains compared to its Ca-free counterpart. Under identical FSP conditions, the Mg₂Si phases in the Ca-containing alloys underwent a higher degree of fragmentation. The addition of Ca promoted the formation of the CaMgSi phase by enriching Ca atoms at or near the Mg₂Si phases during FSP, which further assisted in fragmenting the Mg₂Si phases. Consequently, the alloy with 0.7 wt.% Ca demonstrated the best mechanical properties at both room and elevated temperatures, exhibiting tensile strength and elongation of 276.57 MPa and 11.60% at room temperature, 190.13 MPa and 12.17% at 150 °C, and 133.43 MPa and 15.96% at 200 °C, respectively. Full article

The reconstruction of detrital flux, paleoclimate, paleosalinity, paleo-primary productivity, paleohydrodynamic conditions, and paleo-water depth enhances understanding of sedimentary processes and their drivers during deep-time greenhouse-icehouse transitions, such as the Eocene–Oligocene transition. This study uses detailed geochemical analyses of major oxides and trace elements in sediment samples collected from the Beni Suef Formation (Bartonian–Priabonian) and the Maadi Formation (Priabonian) in the southern Tethys shelf (Egypt, northeastern Desert). Detrital proxies, including Si/Al, Ti/Al, and Zr/Al, indicate an enhanced influx of terrigenous sediments in the middle portion of the Qurn Member of the Beni Suef Formation, as further supported by noticeable facies variations, particularly the transition from shale to coarser silt- and sand-sized fractions. Paleoclimate indicators (Sr/Ba, Rb/Sr, K₂O/Al₂O₃, and Sr/Cu) point to a climatic shift from humid to arid conditions, consistent with the regional Late Eocene aridification across the Tethyan realm. Paleosalinity proxies (Sr/Ba, Ca/Al, and Mg/Al×100) suggest episodic intensification of open-marine influence and a reduction in freshwater input, with an upsection increase in Sr/Ba ratios, reflecting phases of enhanced marine water settings or decreased terrestrial runoff. Primary productivity was evaluated using multiple geochemical proxies, including P, Ni/Al, Cu/Al, P/Al, P/Ti, and Babio ratios. These collectively indicate generally low primary productivity interrupted by intervals of enhanced paleoproductivity or increased organic matter export to the sediments. This interpretation is further supported by the low total organic carbon (TOC) values. These results highlight the sensitivity of the southern Tethys shelf to Middle–Late Eocene climatic variability and the key role of prevailing paleoenvironmental conditions in controlling sediment supply, water chemistry, and biological productivity. Full article