Search Results (335)

We report a scalable route to hybrid aluminum matrix composites (AMCs) based on Al6060 (as-fabricated condition) reinforced with 2 wt.% TiB₂ and 1 wt.% microsilica, fabricated by ultrasonically assisted stir casting (UASC) followed by radial-shear rolling (RSR). Premixing and preheating of powders combined with acoustic cavitation/streaming during UASC ensured uniform, non-sedimentary particle dispersion and low-defect cast billets. X-ray diffraction of the as-cast composite shows fcc-Al with weak TiB₂ reflections and no reaction products; microsilica remains amorphous. Electron microscopy and EBSD after RSR reveal full erasure of cast dendrites, fine equiaxed grains, weakened texture, and a high fraction of high-angle boundaries due to the concurrent action of particle-stimulated nucleation (micron-scale TiB₂) and Zener pinning/Orowan strengthening (50–350 nm microsilica). Mechanical testing shows that, in the cast state—comparing cast monolithic Al6060 to the cast hybrid-reinforced composite—yield strength (YS) increases from 61.7 to 77.2 MPa and ultimate tensile strength (UTS) from 103.4 to 130.7 MPa, without loss of ductility. After RSR to Ø16 mm (cumulated true strain ≈ 0.893), the hybrid attains YS 101.2 MPa, UTS 150.6 MPa, and elongation ≈ 22.0%, i.e., comparable strength to rolled Al6060 (UTS 145.1 MPa) while restoring/raising ductility by ~9.7 percentage points. Microhardness follows the same trend, increasing from 50.2 HV0.2 to 73.1 HV0.2 when comparing the base cast condition with the rolled hybrid. The route from UASC to RSR thus achieves a favorable mechanical strength–ductility balance using an economical, eco-friendly oxide/boride hybrid reinforcement, making it attractive for formable AMC bar and rod products. Full article

To address the issues of insufficient capacity and difficult regeneration of adsorbents for phosphate removal from wastewater, in this study, FeOOH/Al₂O₃ adsorbents were successfully developed by in situ growing amorphous iron oxyhydroxide (FeOOH) within the pores of alumina (Al₂O₃) using a simple method. The physicochemical properties of FeOOH/Al₂O₃ adsorbents were characterized using X-ray Diffraction (XRD), N₂ adsorption/desorption analysis, and scanning electron microscopy (SEM). Additionally, their phosphate adsorption properties were comparatively investigated. The results revealed that FO-A-3, one of the FeOOH/Al₂O₃ samples prepared with Fe/Al molar ratio of 0.47, exhibited excellent adsorption capacity and a relatively fast adsorption rate, surpassing those of Al₂O₃ and amorphous FeOOH alone. The adsorption process of phosphate using FO-A-3 conformed to the pseudo-second-order kinetic model and the Langmuir isotherm model, with a maximum adsorption capacity of 131.00 mg/g. To tackle the problem of poor regeneration performance, this study innovatively proposed a repeatable and simple regeneration strategy. Experiments demonstrated that FO-A-3 maintained a relatively high adsorption capacity after four cycles of regeneration. Full article

This paper presents the growth and in situ optical characterization of silicon nanowires (Si NWs) on Al₂O₃(0001) substrates that are thermally faceted using the atomic low angle shadowing technique (ATLAS) method. Annealing Al₂O₃ substrates in air before surface faceting was used for the first time, as identified by atomic force microscopy (AFM). Planar Si NW arrays were subsequently deposited and characterized in real-time by reflectance anisotropy spectroscopy (RAS). RAS measurements detected irreversible spectral changes during growth, e.g., red-shift in peak energy for marking amorphous Si NW formation. Blue-shifts in RAS spectra following annealing post-growth at varied temperatures were found to be associated with structural nanowire development. AFM analysis following annealing detected dramatic changes in morphology, e.g., quantifiable differences in NW height and thickness and complete disappearance of nanowire structures at high temperatures. These results confirm the validity of in situ RAS as a monitoring tool for nanowire growth and illustrate Si NW morphology’s sensitivity to thermal processing. Full article

In many advanced materials production processes, the analysis must be non-invasive, rapid, and, if possible, operando. The Raman signal of the various forms of alumina, especially transition alumina, is very weak due to the highly ionic nature of the Al-O bond, which requires long exposure times that are incompatible with monitoring transitions. Here, we explore the use of the fluorescence signal of chromium, a natural impurity in alumina, and the Rayleigh wing to follow the crystallization process up to alpha alumina. To clarify the assignment of the fluorescence components, we compare the transformation of beta alumina single crystals into transition (gamma and theta) alumina and then into alpha alumina with the transformation of optically transparent alumina xerogel and glass, obtained by very slow hydrolysis-polycondensation of aluminum sec-butoxide, into alpha alumina. Vibrational modes are better resolved in thermally treated single crystals than in thermally treated xerogels. Measurements of the Rayleigh wing, the Boson peak, and the fluorescence signal are easier than those of vibrational modes for studying the evolution from amorphous to alpha alumina phases. The fluorescence spectra allow almost instantaneous (<1 s) quantitative control of the phases present. Full article

The use of molybdenum-based alloys as materials for components operating under high temperatures and significant mechanical loads is widely recognized due to their excellent mechanical properties. However, their low high-temperature resistance remains a critical limitation, which can be effectively mitigated by applying protective coatings. In this study, we investigate the influence of a two-step coating process on the properties and performance of the TZM molybdenum alloy. In the first step, pack cementation was performed. Simultaneous surface saturation with aluminum and silicon, a process known as aluminosiliconizing, was conducted at 1000 °C for 6 h. The saturating mixture comprised powders of aluminum, silicon, aluminum oxide, and ammonium chloride. The second step involved the application of a pre-ceramic coating based on polyhydrosiloxane modified with silicon and boron. This treatment effectively eliminated pores and cracks within the coating. Thermodynamic calculations were carried out to evaluate the likelihood of aluminizing and siliconizing reactions under the applied conditions. Aluminosiliconizing of the TZM alloy resulted in the formation of a protective layer 20–30 µm thick. The multiphase structure of this layer included intermetallics (Al₆₃Mo₃₇, MoAl₃), nitrides (Mo₂N, AlN, Si₃N₄), oxide (Al₂O₃), and a solid solution α-Mo(Al). Subsequent treatment with silicon- and boron-modified polyhydrosiloxane led to the development of a thicker surface layer, 130–160 µm in thickness, composed of crystalline Si, amorphous SiO₂, and likely amorphous boron. A transitional oxide layer ((Al,Si)₂O₃) 5–7 µm thick was also observed. The resulting coating demonstrated excellent structural integrity and chemical inertness in an argon atmosphere at temperatures up to 1100 °C. High-temperature stability at 800 °C was observed for both coating types: aluminosiliconizing, and aluminosiliconizing followed by the pre-ceramic coating. Moreover, additional oxide layers of SiO₂ and B₂O₃ formed on the two-step coated TZM alloy during heating at 800 °C for 24 h. These layers acted as an effective barrier, preventing the evaporation of the substrate material. Full article

The removal of nickel from industrial wastewater necessitates efficient sorbent materials. This study investigates nanostructured potassium- and sodium-substituted aluminosilicate-based nanocomposites for this application. Materials were synthesized and characterized using SEM-EDS, XPS, XRD, FTIR, low temperature N₂ adsorption–desorption and Ni²⁺ adsorption experiments. SEM and XRD confirmed an X-ray amorphous structure attributable to fine crystallite size. The sodium-substituted material Na₂Al₂Si₂O₈ exhibited the lowest specific surface area (48.3 m²/g) among the tested composites. However, it demonstrated the highest Ni(II) sorption capacity (64.6 mg/g, 1.1 mmol/g) and the most favorable sorption kinetics, as indicated by a Morris-Weber coefficient of 0.067 ± 0.008 mmol/(g·min¹/²). Potassium-substituted analogs with higher Si/Al ratios showed increased surface area but reduced capacity. Analysis by XPS and SEM-EDS established that Ni(II) uptake occurs through a complex mechanism, involving ion exchange, surface complexation, and chemisorption resulting in the formation of new nickel-containing composite surface phases. The results indicate that optimal sorption performance for Ni(II) is achieved with sodium-based aluminosilicates at a low Si/Al ratio (Si/Al = 1). The functional characteristics of Na₂Al₂Si₂O₈ compare favorably with other silicate-based sorbents, suggesting its potential utility for wastewater treatment. Further investigation is needed to elucidate the precise local coordination environment of the adsorbed nickel. Full article

The potential for creating composite cements by incorporating fly ash is demonstrated. Analysis revealed that the fly ash examined consists of 69.66 wt. % silicon oxide, 21.34 wt. % aluminum oxide, 1.57 wt. % calcium oxide and 2.78 wt. % iron oxide. Fly ash mainly consists of quartz (SiO₂), goethite (FeO(OH)) and mullite (3Al₂O₃·2SiO₂). The properties of the cement composition containing 5 to 25 wt. % fly ash were studied. Incorporating fly ash enhances system dispersion, promotes mixture uniformity, and stimulates the pozzolanic reaction. Compositions of composite cements consisting of 90% CEM I 42.5 and 10% fly ash were developed. The cement stone based on the obtained composite cement had a compacted structure with a density of 2.160 g/cm³, which is 9.4% higher than the control sample. It is shown that when composite cement containing 10% fly ash interacts with water, hydration reactions of cement minerals (C₃S, C₂S, C₃A and C₄AF) begin first. This is accompanied by the formation of hydrate neoplasms, such as calcium hydroxide (Ca(OH)₂) and calcium hydrosilicates (C-S-H). Fly ash particles containing amorphous silica progressively participate in a pozzolanic reaction with Ca(OH)₂, leading to the formation of additional calcium hydrosilicates phases. This process enhances structural densification and reduces the porosity of the cement matrix. After 28 days of curing, the compressive strength of the resulting composite cements ranged from 42.1 to 54.2 MPa, aligning with the strength classes 32.5 and 42.5 as specified by GOST 31108-2020. Full article

To reduce the proliferation of greenhouse gases in the construction industry, ternary blended concrete comprising fly ash (FA) powder, waste glass (WG) powder, and ordinary Portland cement (OPC) was developed such that the WG to total binder varied from 0 to 20% at intervals of 5% (C₈₀FA_20-xWG_x:x = WG/(WG + FA + OPC)). The developed concrete was investigated for water absorption, workability, 28-day compressive strength, binder phases, bond characteristics, microstructure, and elemental composition of the concrete. The mixture proportions of C₈₀FA₁₅WG₅ and C₈₀FA₁₀WG₁₀ exhibited better consistency and water absorption than the OPC concrete (C₁₀₀FA₀WG₀). Furthermore, the 28 d strength of C₈₀FA₁₅WG₅ marginally outperformed those of C₈₀FA₁₀WG₁₀ and C₈₀FA₂₀WG₀. The sample with equal proportions of FA and WG (C₈₀FA₁₀G₁₀) was more amorphous owing to the disappearance of the hedenbergite phase (CaFeSi₂O₆) and conversion of tobermorite (CSH) to C-A-S-H. C₈₀FA₁₀WG₁₀ also exhibited better microstructural stability than FA + OPC concrete (C₈₀FA₂₀G₀), owing to the pore-filling of the microcracks within the matrix. Finally, higher Si/Ca, Ca/Al, and Si/Al ratios were recorded in C₈₀FA₁₀WG₁₀ than in the case of FA preponderating WG in ternary blending. Finally, structural concrete can be produced through the ternary blending of glass waste, fly ash, and OPC, thereby promoting the valorization of solid waste and a sustainable environment. Full article

Aluminum nitride (AlN) powder, a cornerstone material for advanced ceramics. This study examines the low-temperature formation of AlN crystals as well as their phase transformation by employing amorphous aluminum oxalate (AAO) as a novel precursor for carbothermal reduction, contrasting it with conventional aluminum hydroxide (Al(OH)₃). Through characterization using X-ray diffraction (XRD), scanning electron microscopy (SEM), High-Resolution Transmission Electron Microscope (HRTEM), ²⁷Al Magic-Angle Spinning Nuclear Magnetic Resonance (²⁷Al-MAS-NMR) energy-dispersive spectroscopy (EDS), and Fourier-transform infrared spectroscopy (FTIR), we unraveled the phase evolution pathways and the formation of AlN. Key findings reveal striking differences between the two precursors. When Al(OH)₃ was used, no AlN phase was detected at 1350 °C, and even at 1500 °C, the AlN obtained with significant residual alumina impurities. In contrast, the AAO precursor demonstrated exceptional efficiency: nano-sized α-Al₂O₃ formed at 1050 °C, followed by the emergence of AlN phases at 1200 °C, ultimately gaining the pure AlN at 1500 °C. The phase transformation sequence—Al(OH)₃ → γ-Al₂O₃ (950 °C) → (α-Al₂O₃ + δ-Al₂O₃) (1050 °C) → (AlN + α-Al₂O₃) (1200 °C~ 1350 °C) → AlN (≥1500 °C)—highlights the pivotal role of nano-sized α-Al₂O₃ in enabling low-temperature nano AlN synthesis. By leveraging the unique properties of AAO, we offer a transformative strategy for synthesizing nano-sized AlN powders, with profound implications for the ceramics industry. Full article

High-silica–alumina coal gangue is rich in kaolinite, quartz, and other mineral components. The potential for resource utilization is huge, but the silica–aluminate structure is highly stable, and it is difficult to achieve efficient dissociation and elemental enrichment using traditional extraction processes. This study selects typical high-silica–alumina coal gangue as the research object and systematically studies the rules of the physical phase transformation mechanism and ion migration behavior in the activation process of the sodium-based additives stage. In addition, a graded leaching and separation processing route is established, realizing the effective separation and extraction of silica–alumina. The key parameters were optimized using response surface methodology (RSM), obtaining the optimal activation conditions of 800 °C, 30 min, and an additives ratio of 0.8. Under these conditions, the highest dissolution rates of silica and alumina are 82.1% and 92.36%, respectively. Characterization techniques such as XRD, FTIR, and SEM reveal that the activation mechanism of coal gangue involves the decomposition of the aluminosilicate framework and the erosion of sodium ions. At the same time, the chemical bonding reorganization contributes to forming water-soluble sodium silicate (Na₂SiO₃) and insoluble nepheline (NaAlSiO₄), which significantly promotes the release of Si and Al. When the activation temperature is too high, the nepheline phase is transformed into amorphous glassy sodium aluminate and precipitated on the surface, which gradually encapsulates the sodium silicate. This encapsulation restricts dissolution pathways, thereby leading to system densification. Moreover, enhanced resistance to acid attack leads to a decrease in the dissolution rates of Si and Al. This study elucidates the mineral phase reconstruction and element migration mechanisms involved in sodium-based activation and presents a viable approach for the high-value utilization of coal gangue. Full article

Hollow coaxial double-shell submicron fibers were fabricated by combining electrospinning and atomic layer deposition (ALD). Polyvinyl alcohol (PVA) fibers were electrospun to serve as templates for the subsequent atomic layer deposition (ALD) of ZnO doped with transition metals (TM: Ni, Co, and Fe). An inner shell of amorphous Al₂O₃ was first deposited at low-temperature ALD to protect the polymer template. The PVA core was then removed through high-temperature annealing in air. Finally, a top shell of TM-doped ZnO was deposited at an elevated temperature within the ALD window for ZnO. The morphology, microstructure, elemental composition, and crystallinity of these submicron hollow double-shell fibers were thoroughly investigated using scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDX), X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS). Full article

Solketal is an important chemical product with widespread applications, and the raw materials glycerol and acetone are inexpensive, making it highly economically viable. The glycerol-acetone condensation reaction is a typical acid-catalyzed reaction. Traditional homogeneous acidic catalysts cause significant environmental pollution and are difficult to recover. Herein, PEG-800 was used as an additive, and a one-pot process was employed to prepare a series of aluminum phosphate catalysts (xP-Al-O) with different P/Al molar ratios. The physical and chemical properties of the prepared xP-Al-O catalysts were thoroughly investigated using XRD, FTIR, SEM, Py-FTIR, BET, and NH₃ (CO₂)-TPD methods. The results indicated that different P/Al molar ratios indeed affect the catalyst structure, and all prepared xP-Al-O samples exist in the form of amorphous aluminum phosphate, with weak acidic sites dominating the surface. The prepared catalysts were investigated for their catalytic behavior in the acetalization reaction of glycerol and acetone. The 1.1P-Al-O catalyst exhibited the highest acetone glycerol acetal yield and demonstrated good catalytic stability. Full article

Weathered crust elution-deposited rare earth ores (WCE-REOs) are the primary global source of medium and heavy rare earth elements (M/HREEs). The recent discovery of high-altitude (1500–2500 m) WCE-REOs in southern Yunnan Province, China, presents new opportunities for the development of M/HREE resources. This study investigates the enrichment and fractionation mechanisms of rare earth elements (REEs) in these deposits through a systematic analysis of three representative weathering profiles associated with the Lincang granite batholith. The analytical results indicate that the profiles consist mainly of clay minerals (kaolinite, halloysite, illite, minor montmorillonite) and iron oxides, with high SiO₂ (64.10–74.40 wt.%) and Al₂O₃ (15.50–20.20 wt.%) and low CaO/MgO—typical of weathered REE deposits. The total REE contents (238.12–1545.53 ppm) show distinct fractionation: LREE-enriched upper layers and HREE-enriched deeper zones. Sequential extraction revealed that the REEs in the Lincang granite weathering profiles predominantly occur in ion-exchangeable, residual, and iron-manganese oxide-bound states (>95% total REEs). Ion-exchangeable REEs showed depth-dependent enrichment (peaking at 819.96 ppm), while iron-manganese oxides exhibited a strong REE affinity (up to 47% total REEs), with amorphous phases that were preferentially enriched in Ce (partitioning >80%). Fissure systems exerted critical control over the redistribution of elements, particularly REEs. Full article

To address the critical challenge of synergistically enhancing both high-temperature mechanical properties and thermal conductivity in neutron-absorbing materials for dry storage of spent nuclear fuel, this study proposes an innovative strategy. This approach involves the controlled distribution, size, and crystalline states of nano-Al₂O₃ within an aluminum matrix. By combining plastic deformation and heat treatment, we aim to achieve a structurally integrated functional design. A systematic investigation was conducted on the microstructural evolution of Al₂O₃/10 wt.% B₄C/Al composites in their forged, extruded, and heat-treated states. We also examined how these states affect high-temperature mechanical properties and thermal conductivity. The results indicate that applying hot extrusion deformation along with optimized heat treatment parameters (500 °C for 24 h) allows for a lamellar dispersion of nano-Al₂O₃ and a crystallographic transition from amorphous to γ-phase. As a result, the composite demonstrates a tensile strength of 144 MPa and an enhanced thermal conductivity of 181 W/(m·K) at 350 °C. These findings provide theoretical insights and technical support for ensuring the high density and long-term safety of spent fuel storage materials. Full article

Quarry dust (QD) landfill causes environmental issues that cannot be ignored. In this study, we systematically explore its potential application as a supplementary cementitious material (SCM) in cemented paste backfill (CPB), revealing the activated mechanism of modified QD (MQD) and exploring the hydration process and workability of CPB containing QD/MQD. The experimental results show that quartz, clinochlore and amphibole components react with CaO to form reactive dicalcium silicate (C₂S) and amorphous glass phases, promoting pozzolanic reactivity in MQD. QD promotes early aluminocarbonate (M_c) formation through CaCO₃-derived CO₃²⁻ release but shifts to hemicarboaluminate (H_c) dominance at 28 d. MQD releases active Al³⁺/Si⁴⁺ due to calcination and deconstruction, significantly increasing the amount of ettringite (AFt) in the later stage. With the synergistic effect of coarse–fine particle gradation, MQD-type fresh backfill can achieve a 161 mm flow spread at 20% replacement. Even if this replacement rate reaches 50%, a strength of 19.87 MPa can still be maintained for 28 days. The good workability and low carbon footprint of MQD-type backfill provide theoretical support for—and technical paths toward—QD recycling and the development of low-carbon building materials. Full article