Search Results (3,140)

Ordinary Portland Cement (OPC) production is a major source of global CO₂ emissions, driving growing interest in sustainable binder alternatives. This systematic review examines biomass-integrated geopolymer and alkali-activated binder (AAB) systems as low-carbon construction materials, drawing on peer-reviewed literature and expert validation interviews. This study, conducted in accordance with the PRISMA 2020 guidelines and expert validation interviews, examines biomass-integrated geopolymer and alkali-activated binder (AAB) systems as low-carbon construction materials through the systematic screening and analysis of peer-reviewed literature (37 eligible studies identified from an initial pool of 195 records) and expert validation interviews. The review focused on well-studied biomass residues such as rice husk ash (RHA), sugarcane bagasse ash (SCBA), and biochar, which can contribute reactive silica and alumina and thereby influence geopolymerisation and pozzolanic reactions. The reviewed studies indicate that optimal biomass incorporation, typically at replacement levels of 20 to 30%, can achieve compressive strengths comparable to or higher than conventional systems while also improving durability through pore refinement, reduced permeability, and denser reaction products, including C-S-H and N-A-S-H gels. The reviewed studies collectively indicate carbon footprint reductions of 40 to 60% relative to OPC under efficient processing and localised supply conditions, synthesised across multiple life-cycle assessment studies in the dataset, primarily through reduced reliance on clinker and the valorisation of agricultural waste, with additional relevance to circular economy and waste-to-value strategies. Synthesised economic findings from the reviewed literature further suggest material cost reductions of 15 to 35% under localised production models. However, widespread implementation remains constrained by feedstock variability, processing energy demand, supply chain reliability, and limited regulatory standardisation. The 37-study systematic review indicates that biomass-integrated AAB systems offer compressive strengths comparable to conventional materials, with substantial carbon footprint and cost reductions. Expert interviews corroborated these findings while highlighting feedstock inconsistency, regulatory gaps, and supply chain limitations as key barriers. Both evidence streams conclude that standardisation and scale-up research remain essential for broader adoption. Full article

A novel alumina-filled ceramic-reinforced polymer (CRP) crown (Hassawat-01; HS) was developed. This study evaluated the effect of luting cement on the marginal and internal adaptation of HS and compared its performance with a commercial DLP-printed CRP (VarseoSmile Crown Plus^®; VS) and a milled resin nanoceramic (Cerasmart^® 270; CE). Ninety-nine crowns (n = 33/material) were fabricated with a 50 µm cement space and luted using Maxcem Elite^®, RelyX Unicem^®, or Ketac Cem^® (n = 11/subgroup). Adaptation was assessed without and with cementation using micro-computed tomography at 160 measurement points per crown. Without cementation, HS demonstrated the most favorable internal adaptation, whereas VS showed the best marginal adaptation. Following cementation, gap dimensions increased in all groups. Despite its superior non-cementation fit, HS exhibited the greatest increase in marginal and internal discrepancies, suggesting increased hydraulic resistance during seating. Among the evaluated cement–crown combinations, VS luted with RelyX Unicem^® showed the most favorable post-cementation adaptation. Post-cementation analysis was limited to HS and VS because the radiopacity of CE prevented reliable cement interface segmentation. These findings indicate that adaptation is influenced by both crown geometry and cement properties, and that highly adapted intaglio surfaces may require careful cement selection to optimize clinical fit. Full article

Acidic wastewater generated during sulfuric acid leaching of reduced tionite within the EUROTITAN process was treated using three low-cost adsorbents: fly ash, bentonite, and red mud slag. Tionite is a solid residue originating from the sulfate route of TiO₂ production, whereas the investigated wastewater is a secondary acidic stream produced during hydrometallurgical treatment of reduced tionite. The initial wastewater was characterized by low pH and elevated concentrations of Fe, Al, Ti, B, Cu, Mn, Pb, Cr, and Li. Batch adsorption experiments were carried out by varying contact time from 4 to 24 h and adsorbent dosage from 5 to 15 g/L. The results showed distinct selectivity depending on adsorbent type and solution chemistry. Bentonite exhibited the most stable performance, achieving nearly complete removal of Pb, Cu, B, and Li, while Fe and Al were only partially removed and Ti removal remained limited. Fly ash showed high affinity toward Pb and Cu, but its performance was strongly affected by dosage and contact time. Red mud slag demonstrated excellent Pb removal, high Cu removal, and time- and dosage-dependent Ti removal, although partial dissolution of Fe- and Al-bearing phases occurred under strongly acidic conditions. Overall, the results confirm that industrial by-products and natural clay materials can contribute to partial purification of acidic metallurgical wastewater, while additional neutralization or polishing steps are required for complete treatment. Full article

FeAl_xO_y powders, fabricated by solution combustion synthesis (SCS), are promising catalysts for microwave-assisted pyrolysis of methane. However, the effects of SCS parameters on the pyrolysis are not well understood. In the present work, two fuels (citric acid and glycine), two Fe:Al molar ratios, and two heating modes (a hotplate and a muffle furnace) are tested. All catalysts exhibit CH₄ conversion of around 70% and H₂ composition of about 93%. The process is one to two orders of magnitude more efficient than conventional pyrolysis. Increasing the Fe:Al ratio from 1:1 to 2:1 and using a hotplate improve H₂ generation efficiency. Use of glycine decreases the CO₂:H₂ ratio, but citric acid yields more readily reducible products due to differences in phase evolution, detected by X-ray diffraction analysis. Scanning electron microscopy and energy-dispersive X-ray spectroscopy reveal carbon nanotubes and exsolution of Fe. FeAl_xO_y catalysts, prepared via incipient wetness impregnation, are ineffective. Full article

Rapid-repair mortars require high early-age strength, dimensional stability, and reliable substrate bond simultaneously, yet conventional alkali-activated materials (AAMs) have only partially met these requirements, and AAM feedstock base itself is contracting as blast furnace slag and fly ash availability declines under steel and power sector decarbonization. Thus, in this study, the systematic production of a one-part, rapid hardening repair mortar based on calcined clay (CC) and basic oxygen furnace slag (BOFS) is presented for the first time. Concurrently, a direct comparison of three distinct modifier families is conducted within this underutilized binding system. These modifiers consist of a soluble anion-active accelerator (sodium fluoride, NF), an Fe- and Na-bearing mineral residue (red mud, RM), and a reactive oxide (calcined alumina, CAL). Finally, the mechanistic connections between the modifier-induced phases and the macroscale mortar properties are analyzed and evaluated according to ASTM C928, ASTM C1600, and EN 1504-3 standards. The precursors were activated using solid sodium metasilicate, and the setting behavior, compressive strength development, drying shrinkage, substrate bond strength, and microstructural properties were determined for each mortar system. The results indicate that all formulations satisfied the R2 strength class for rapid hardening repair mortars as per ASTM C928 and the incorporation of NF markedly promoted the early-age reactions, reducing the setting time by up to 73% and increasing the 3 h compressive strength by up to 81% (12.8 MPa at 3 h) compared to the control mortar. Furthermore, RM, CAL, and NF effectively mitigated the drying shrinkage of the control mortar from approximately 4252 µƐ down to 162 µƐ. The bond strength of the repair mortars substantially improved through the addition of CAL and NF, fulfilling the R3 and R4 structural repair mortar requirements specified in EN 1504-3. Full article

This study presents the design, development, and experimental validation of an automated flat blade grinding machine for the wood processing and plastic recycling industries in Ecuador. The machine was engineered following the VDI 2221/2222/2225 design methodology, integrating SolidWorks-based 3D modeling and ANSYS finite element analysis (FEA) to validate critical structural components. The selected configuration includes a Type 6 alumina grinding wheel (38A-60-K-VS), a mechanical clamping system, cutting fluid cooling, and a hardwired electromechanical control system that does not require a programmable logic controller (PLC). FEA results confirmed adequate safety factors (ηs > 16; ηf > 14) for the ACME 3/4–8 power screw under operational loads. Experimental testing on blade specimens (thickness: 3 mm; length: 70 mm; steel up to 60 HRC) demonstrated that four grinding passes at a 45° inclination angle reduced mean surface roughness (Ra) from 5.39 ± 1.83 µm (used blades) to 0.162 ± 0.092 µm, achieving values comparable to new blades (Ra = 0.601 ± 0.153 µm): a point-estimate reduction of 97% in mean Ra relative to the used-blade condition. The automated process reduced average grinding time by approximately 30% compared to manual methods, while maintaining noise levels within the 85 dB occupational exposure limit. Operator satisfaction surveys rated the system above 4.5/5.0 across all ergonomic and usability criteria. These results validate the proposed machine as a cost-effective, locally manufacturable solution to standardize blade maintenance in small and medium enterprises (SMEs) across Latin America. Full article

Methane partial oxidation (POM) offers a promising pathway for syngas production, but achieving optimal catalyst performance requires precise control of promoter loading. We systematically investigated cerium (Ce) promotion on nickel-based catalysts supported on aluminum oxide (Ni/Al₂O₃) catalysts across 1–3 wt.% loadings and identified a critical discovery: catalyst performance exhibits a pronounced non-monotonic response to Ce concentration. The 1 wt.% Ce-promoted catalyst (Ni+1Ce/Al) achieved the superior performance with 65% methane conversion and 60% hydrogen yield at 650 °C, maintaining stable output over 275 min time-on-stream. This smaller Ce amount tunes NiO reducibility, oxygen mobility, and metal–support interactions, resulting in improved activity performance of Ni+1Ce/Al. Notably, Ce promotion shifts the H₂/CO ratio from 2.5 to 2.9, with the increased hydrogen yield arising from enhanced water–gas shift chemistry and indirect oxidation pathways. Excess cerium (2–3 wt.%) causes performance deterioration, Ni particle agglomeration, and thus loss of Ni active sites, demonstrating that Ce operates as a structural promoter with a well-defined appropriate concentration window. Moreover, the best performing catalyst (Ni+1Ce/Al) remained stable during 20-h long-term POM. An artificial neural network model achieved exceptional predictive accuracy (R = 0.9758 overall), validating the experimental findings. These results indicate that the best Ce loading for industrial application is 1 wt.% and the traditional alumina supports can be competitive in performance with the advantage of thermal stability and cost-effectiveness when doped with rare-earth elements. Full article

Passive daytime radiative cooling (PDRC) materials require high solar reflectance and high atmospheric window emissivity. However, high solar reflectance achieved by scattering strategies often relies on porous structures, which can compromise the material’s mechanical reliability. To address this trade-off, we develop a layered alumina nanofiber membrane (LANM) by dual-nozzle electrospinning with programmed alternating deposition, in which alternating deposition and subsequent removal of alumina precursor layers and sacrificial polyvinyl alcohol (PVA) interlayers generate a continuously layered architecture with periodic interfaces and interlayer air gaps. This interfacial geometric design enables simultaneous regulation of solar-band scattering and bending load transfer within a single alumina system. Because photon flux attenuates with depth, shallow interfaces contribute more strongly than deeper ones; therefore, the micro-layered architecture enhances scattering while maintaining high emissivity in the atmospheric window. In outdoor testing, LANM achieved a maximum sub-ambient temperature reduction of ~5.8 °C, representing a further improvement of about 2.4 °C compared to Monolithic alumina nanofiber (ANM). Moreover, interlayer interfaces induce a multiple-neutral-axis mechanism and segmented stress transfer, thereby improving bending deformability rather than load-bearing strength. Full article

The high silica content of coal fly ash (CFA) poses a significant challenge for alumina extraction, resulting in high material and energy consumption. To reduce the silica content and improve alumina extraction efficiency, a novel process combining pre-desilication, vacuum reduction, and alkali dissolving is proposed. In the pre-desilication stage, amorphous silica in CFA is effectively removed by NaOH solution, increasing the Al₂O₃/SiO₂ mass ratio from 0.78 to 1.27. The desilicated coal fly ash (D-CFA) is then subjected to vacuum carbothermal reduction with the addition of Fe₂O₃ and CaO to produce Fe-Si alloys and CaO·xAl₂O₃. The resulting CaO·xAl₂O₃ can be dissolved via alkali dissolving to extract alumina, achieving an alumina dissolving rate of over 90%. The Fe-Si alloys remaining in the dissolved residue are subsequently recovered by magnetic separation. Compared with the process without pre-desilication, the current process reduces material input by 30.25% and energy consumption by 35.18%, demonstrating that this approach offers a low-cost, energy-efficient, and environmentally friendly route for high-value-added utilization of CFA. Full article

The electrification of high-temperature industrial processes requires refractory materials that combine thermal stability with tailored electrical functionality. In this study, Ta/Nb-Al₂O₃ composites were prepared by spark plasma sintering (SPS) to investigate densification, metal-phase deformation, electrical conductivity and percolation behavior. Coarse, fine and superfine alumina powders were combined with tantalum or niobium and sintered at 1300–1600 °C for 5 min with 50 MPa uniaxial pressure. The results show that the alumina particle size and morphology strongly influence the formation of conductive metal networks. Coarse alumina promotes deformation and elongation of the metallic phase, thereby improving metal-phase connectivity and lowering the operational percolation threshold. Fine and superfine alumina enhance densification but can delay percolation by embedding metal particles in a dense ceramic matrix. Combining these fractions, both effects can be balanced, enabling improved densification while maintaining effective conductive pathways. An operational percolation threshold of 7.5 vol.-% was obtained for Ta/coarse alumina, indicating highly effective metal-phase connectivity after SPS. Microstructural analysis supports the interpretation that matrix-controlled metal-particle deformation and spatial distribution govern the electrical response. Tailored alumina matrix design can reduce the refractory metal content required for conductive ceramic–metal composites. Full article

Multi-sulfonated anionic azo dyes are difficult to remove from water because their high solubility and ionized sulfonate groups reduce their affinity toward many oxide adsorbents. In this study, magnesium oxide-modified alumina composites were prepared by loading magnesium oxide onto mesoporous alumina to increase the density of surface hydroxyl groups. Sunset Yellow and Amaranth were selected as model dyes containing two and three sulfonate groups, respectively. Compared with pristine alumina, the modified adsorbents exhibited higher isoelectric points, stronger hydroxyl-related infrared signals, and significantly enhanced adsorption capacities. At pH 4.0, the maximum adsorption capacities reached 787 mg/g for Sunset Yellow and 709 mg/g for Amaranth. Notably, MgA-2 exhibited the highest utilization efficiency of MgO active sites. Adsorption kinetics were well described by the pseudo-second-order model, while equilibrium data followed the Langmuir model. Mechanistic analysis indicated that adsorption process mainly proceeded through ion exchange between surface hydroxyl groups and dye sulfonate groups. The higher adsorption capacity of Sunset Yellow was attributed to its lower number of sulfonate groups and lower demand for hydroxyl binding sites. These results demonstrate that magnesium oxide modification is an effective strategy for enhancing alumina-based adsorbents for the removal of multi-sulfonated anionic dyes from water. Full article

Hydrolysis of cellulose to produce ethanol has become an effective way to utilize biological resources, but its large-scale industrial application has been limited. In this study, a one-pot catalytic conversion process for transforming cellulose into ethanol was developed. Meanwhile, multifunctional Mo/Pt/WO_x/Al₂O₃ catalysts were prepared by loading nano-alumina (Nano-Al₂O₃) via a stepwise impregnation method. The influence of catalysts with varying metal ratios on the types of products generated during the cellulose hydrolysis process to ethanol was examined. The catalyst with 0.1% Mo, 2% Pt, and 7.5% W loadings showed the best selectivity. With an ethanol yield of 45.3% after heating at 5 MPa H₂ and 518 K for 2 h. Nano-Al₂O₃ can provide suitable active sites. The addition of W⁵⁺ and Mo⁰ increased the surface oxygen vacancy density and enhanced the hydrodeoxidation and metal anchoring capacity of the catalyst. The solid solution structure facilitates electron transfer from W and Mo atoms to Pt atoms, forming electron-rich Pt^δ- species, promoting the hydrolysis of cellulose and the formation of ethanol. Full article

Molecular transport membranes are promising alternatives to conventional cryogenic separation processes. Here, solvent polarity effects were investigated by varying the DMF/MeOH ratio during the solvothermal synthesis of supported ZIF-7 membranes. A DMF:MeOH ratio of 1:3 preserved the characteristic sodalite topology while suppressing dense-phase formation. Methanol incorporation modified heterogeneous crystallization behavior, intercrystalline organization, membrane morphology, and film densification on α-alumina supports while reducing DMF consumption by approximately 75%. These effects are associated with solvent-mediated precursor solvation, Zn²⁺–benzimidazole coordination equilibria, and heterogeneous nucleation at the support–solution interface. Although low BET surface areas were obtained from N₂ adsorption at 77 K, these values were interpreted cautiously considering the known limitations of nitrogen physisorption in flexible ultramicroporous frameworks. Overall, the results support solvent polarity engineering as a physicochemical strategy for regulating membrane microstructural evolution under reduced DMF conditions. Accordingly, the transport behavior discussed herein is interpreted primarily from a solvent-mediated microstructural perspective rather than as a direct quantitative descriptor of accessible porosity. Full article

Piezoelectric pressure sensors for dynamic monitoring face a trade-off between charge output and measurement range, and existing high-sensitivity designs are largely confined to narrow ranges. This study presents a composite layered piezoelectric pressure sensor in which a 316L stainless-steel diaphragm drives a centrally suspended PZT-5H wafer supported by a perforated alumina gasket, with the wafer thickness and cavity radius optimized under a 10 MPa full-scale stress constraint. Over 0–10 MPa, quasi-static calibration gave a highly repeatable quadratic pressure–charge relationship ($R^2=0.99995$) with a maximum residual below 1% FS. The sensitivity is pressure-dependent: the secant sensitivity increased monotonically from 3.16 pC/kPa at 1 MPa to 5.36 pC/kPa at 10 MPa, reflecting a stress-stiffening response rather than a measurement tolerance band. The output deviation remained within 3% from 25 °C to 150 °C. Shock-tube testing yielded a resonance of ∼50 kHz and a mutually consistent 10–90% leading-edge interval of 10.12 $\mathsf{\mu }$s. Combining high charge sensitivity over a wide 0–10 MPa range with a fast transient response and stable operation up to 150 °C, the proposed sensor is suited to dynamic pressure-pulsation monitoring in fluid-power and thermal and power-plant fluid systems. Full article

Continuous alumina (Al₂O₃) fibers are critical reinforcement materials for ceramic matrix composites (CMCs) utilized in extreme high-temperature environments. While their baseline thermal and mechanical properties are well-documented, their long-term service reliability in complex, multi-field environments—specifically coupled thermal, hygral, and atmospheric conditions—remains insufficiently quantified. This study systematically investigates the degradation mechanisms of alumina ceramic fiber ropes subjected to simulated engine exhaust atmospheres and cyclic rain exposure. By integrating macroscopic tensile testing with rigorous multi-scale microstructural characterizations (SEM, XRD, TGA, and advanced surface chemical state analyses via EDS and XPS), a comprehensive degradation model is proposed. Our findings reveal a pronounced two-stage mechanical degradation behavior: an initial catastrophic strength collapse followed by a stabilization phase. We elucidate that the initial embrittlement is governed not merely by thermal damage, but fundamentally by the hydrothermal volatilization and depletion of the surface amorphous SiO₂ binder, which annihilates the inter-fiber cooperative load-sharing capability. Concurrently, quantitative XPS and XRD analyses strongly suggest that the internal amorphous grain-boundary films undergo rapid structural rearrangement and crystallization, effectively homogenizing the microstructure and shifting the fracture mechanics from energy-dissipative crack deflection to unhindered brittle cleavage. After the preferential depletion of the amorphous silicate phase, the exposed α-Al₂O₃ core dictates a stabilized mechanical response. This research provides critical theoretical frameworks and experimental evidence for the life-cycle assessment and microstructural optimization of advanced oxide ceramic fibers in next-generation aerospace applications. Full article