Search Results (142)

This study proposes a process combining alkali-activated potassium feldspar, acid leaching, and sol–gel coupling with supercritical drying to prepare high-performance silica–alumina composite aerogel. The optimal parameters for potassium feldspar alkali-melt activation are a calcination temperature of 350 °C, mass ratio of potassium feldspar to sodium hydroxide of 1:1.2, and calcination time of 120 min, achieving an acid-leaching efficiency of 97.3% for the activated potassium feldspar. The acid leachate, using propylene oxide as a gelling promoter, was processed through aging, solvent exchange, and supercritical drying to yield SiO₂-Al₂O₃ aerogel with typical three-dimensional nanoporous network structure. EDS spectroscopy revealed that the spatial distributions of aluminum and silicon elements were highly coincident and uniformly dispersed. XPS and FTIR further confirmed the formation of Si-O-Al bonds, indicating that aluminum atoms were successfully incorporated into the silico-aluminate tetrahedral network, constructing silicon–aluminum composite framework. The SiO₂-Al₂O₃ aerogel exhibits specific surface area of 660.841 m²/g and a pore volume of 1.321 cm³/g. Its mass loss within the 0–1000 °C range is only 9.55%, far lower than the 28% mass loss of pure aluminum oxide aerogel, indicating that the silicon–aluminum composite structure effectively suppresses high-temperature phase transitions and framework collapse. 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

Methods for the preparation of aluminum hydroxides and alumina-supported catalysts through the interaction of activated Al–In–Ga alloys with water were developed. Bayerite was obtained from an alloy containing 99.0% Al + 0.5% In + 0.5% Ga at 303 K, while pseudoboehmite was synthesized from 90% Al + 5% In + 5% Ga at 363 K. The maximum specific surface area of aluminum oxide reached 700 m²/g. Dehydration of aluminum hydroxides proceeds via a sigmoidal mechanism with induction, acceleration, and deceleration stages. The dehydration rate increases with calcination temperature. Kinetic analysis revealed both kinetic and diffusion-controlled transformation regions for pseudoboehmite and bayerite. Transformation of pseudoboehmite into γ-Al₂O₃ at 523–673 K preserves a high specific surface area of 630–640 m²/g. Two platinum deposition methods were proposed: synthesis in the presence of soluble platinum salts and incorporation of Pt into the Al–Ga–In alloy followed by reaction with water. Alongside metallic Pt, Ptδ⁺, Pt²⁺, and Pt⁴⁺ species were detected and reduced to Pt⁰ at 900 K. Alumina–platinum catalysts showed high activity in cyclohexane dehydrogenation. A Zn–Al catalyst for methanol decomposition was developed, providing up to 70% H₂ in gaseous fuel and complete methanol conversion at 573 K. Full article

The cement industry is a major contributor to global carbon emissions. Therefore, reducing emissions while utilizing industrial wastes is critical for its sustainable development. Red mud, a solid waste byproduct of alumina smelting with main components like SiO₂, Al₂O₃, and CaO, can partially replace limestone as a raw material in cement production. TG-DSC thermal analysis clarified red mud’s three-stage weight loss characteristic during calcination (total weight loss rate of 22.11%), and orthogonal experiments identified calcination temperature as the core factor for its CaO content, with the optimal calcination pretreatment process confirmed (0.075–0.09 mm particle size, 1373 K, 1 h residence time, CaO content up to 21.1%). Based on the results, this study uses ANSYS Fluent 2021 R1 to simulate a TTF-type precalciner, establishing a validated multi-physical field model (all relative errors < 5%) to explore red mud blending ratios of 0%, 2.5%, 5%, 7.5% and 10%. Unlike previous experimental studies, this work uses a CFD model to quantify how red mud blending ratios affect the coupled thermo-chemical environment in a TTF precalciner, revealing a mechanism-driven trade-off among decomposition rate, CO₂, and NO_x that experiments alone cannot capture. Results show red mud slightly alters the internal temperature field and reduces the raw meal decomposition rate. The decomposition rate remains within the industrial acceptable range of 85–95% when the red mud blending ratio is no more than 5%, while further increasing the blending ratio to 7.5% and 10% causes the decomposition rate to drop below 85%. Therefore, a blending ratio of 5% is recommended, which balances waste utilization, decomposition rate, and emission reduction, providing solid technical support for red mud’s large-scale use in cement production. Full article

Under conditions of depletion of natural resources and increasing volumes of techno-genic waste from metallurgical and alumina production, the development of technologies for the integrated processing of sludges with the extraction of valuable components becomes highly relevant. This study proposes a method for the combined processing of red mud and dump sludge to obtain pig iron, a rare earth element concentrate, and titanium dioxide. The reduction smelting of a briquetted charge composed of sludge mixtures was carried out in a muffle furnace at 1350–1400 °C with the addition of a reducing agent. Magnetic separation of cast iron slag made it possible to reduce the iron content in the non-magnetic fraction and increase the concentration of REEs. As a result of nitric acid leaching of the non-magnetic slag fraction, followed by neutralization and calcination of the titanium-containing precipitate, a rare earth element concentrate and titanium dioxide containing 96.5% TiO₂ were obtained. The developed method ensures the utilization of technogenic raw materials and contributes to the creation of an additional resource base for the production of strategically important materials. Full article

Epoxy resins are widely used thermosetting polymers, but their limited toughness and flexural resilience restrict broader applications. In this study, diglycidyl ether of bisphenol A (DGEBA) epoxy was reinforced with 5 wt.% ceramic fillers of different origins: sol–gel alumina calcined at 550 °C (γ-Al₂O₃) and 1000 °C (α-Al₂O₃), silica derived from rice husk, silica from diatomaceous earth, and a hybrid alumina–silica mixture prepared by sol–gel and calcined at 1000 °C. Fillers were structurally characterized by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), and field-emission scanning electron microscopy (FESEM). Mechanical properties were evaluated through tensile (ASTM D638) and flexural (ASTM D790) testing. All reinforcements enhanced the performance of neat epoxy. γ-Al₂O₃ provided superior tensile reinforcement compared to α-Al₂O₃, underscoring the importance of particle morphology and surface reactivity. The hybrid alumina–silica filler achieved the highest flexural strength of 50.6 MPa, compared to 9.91 MPa for the neat epoxy. Bio-derived silica showed improved flexural properties, although its tensile reinforcement was less pronounced compared to the sol–gel derived fillers. These results establish clear structure–property relationships and confirm that filler phase, morphology, and calcination temperature critically govern the mechanical performance of epoxy composites. Full article

Ce-Ni@WSA (WSA = water-resistant silica–alumina gel) ozone catalyst was prepared with an impregnation–calcination method using WSA as the support and characterized by SEM, XRD, BET, XRF, and XPS analyses. The operating conditions and reaction mechanism of the Ce-Ni@WSA catalytic ozonation of norfloxacin (Nor)-simulated wastewater were systematically studied. A data-envelopment analysis model (DEA-B²C) was then established to evaluate the catalytic ozonation process. Under the optimal conditions of initial pH 7.42 (raw water), ozone dosage = 0.4 g/L/h, catalyst-filling ratio = 5%, humic acid dosage = 0 mg/L, the removal rates of chemical oxygen demand (COD) and Nor reached 84.95% and 93.52%, respectively. Ce-Ni@WSA retained its high catalytic performance and mechanical strength after 50 cycles of repeated use. Mechanistic studies showed that •OH oxidation was dominant in the catalytic-ozonation system, and Nor can be degraded into small molecules through three different pathways and eventually mineralized. The DEA-B²C model analysis showed that the treatment cost was low and the catalytic efficiency was high under the optimal operating conditions. Full article

The synthesis of a manganese-doped α-alumina pink pigment via the spray drying technique was explored. Three samples were prepared: pure α-alumina and two doped variants, where 3 and 6% of aluminum were substituted with manganese. The materials were analyzed using differential thermal and thermogravimetric analysis, X-ray diffraction, scanning electron microscopy, energy-dispersive X-ray spectroscopy, and UV-Vis reflectance spectroscopy. Calcination at 1000 °C resulted in α-alumina with minor traces of hausmannite. The incorporation of manganese into the α-alumina crystal lattice was confirmed through lattice constant calculations and EDS. Higher-temperature treatments eliminated hausmannite but led to the formation of manganese aluminate. Washing the samples with hot concentrated hydrochloric acid removed hausmannite, unveiling the desired pink coloration. Full article

The urgent need to decarbonize the global cement industry is compounded by the declining availability of conventional supplementary cementitious materials (SCMs). Limestone-calcined clay cement (LC3) emerges as a highly sustainable alternative, enabling up to 50 percent clinker replacement and an approximate 40 percent reduction in carbon dioxide emissions. Unlike existing reviews that focus on basic material properties, this paper critically bridges the gap between fundamental hydration thermodynamics and next-generation sustainable engineering applications. Through a structured bibliographic analysis of 135 contemporary sources published between 2000 and 2026, it traces the evolution of LC3 from a laboratory innovation to a highly promising solution for large-scale industrial implementation and circular economy integration. The discussion highlights the synergistic alumina carbonate reaction. This reaction forms carboaluminate phases. These phases significantly densify the microstructure and enhance long term durability. Key engineering properties are examined, contrasting rheological challenges from high water demand and carbonation susceptibility against its exceptional chloride resistance in aggressive environments. The transition to field application is thoroughly assessed, emphasizing technological advances in flash calcination, environmental footprint reduction through life cycle assessment (LCA), and production scalability. Finally, rather than restating known challenges, this review exposes the limitations of current empirical mitigation strategies. It proposes a targeted research agenda focused on molecular-level green admixture design and field calibrated durability models to support the integration of LC3 into emerging sustainable technologies such as 3D concrete printing. Full article

Refractories are advanced ceramics essential for high-temperature operations in the steel, glass, cement, and power sectors. In response to growing sustainability requirements, life cycle assessment (LCA) is increasingly applied to quantify and mitigate their environmental impacts. However, current refractory-related LCA research remains limited by the scarcity of comprehensive inventories and the lack of systematic evaluation of uncertainties affecting results and ecodesign strategies. This study addresses these gaps by presenting the first published LCAs of tabular alumina, white fused alumina, and fused cast high-alumina block production, thereby expanding the environmental knowledge base across alumina products. The analysis shows that uncertainties in characterization models can significantly influence impact-category prioritization, underscoring the need for robust interpretation frameworks. Differences in category criticality across methodological levels and LCIA methods are examined, highlighting the suitability of the Product Environmental Footprint (PEF) approach for refractory applications due to its explicit consideration of model uncertainty and comprehensive coverage of impact categories. Results indicate that alumina products significantly contribute to climate change, fossil resource depletion, particulate matter formation, acidification, freshwater eutrophication, and non-cancer human toxicity. Energy supply constitutes the main environmental hotspot, both through its direct consumption and its indirect contribution during raw material preparation. Red mud disposal is also a major contributor to impacts associated with calcined alumina production. Based on these insights, improvement strategies are proposed, demonstrating the value of LCA as an ecodesign tool. Scenario analysis for fused cast high-alumina block further quantifies the potential for impact reduction under varying operational conditions. Full article

The use of monolithic alumina is limited by its intrinsic brittleness, which is commonly addressed through second-phase reinforcement. Silicon carbide (SiC) is an attractive reinforcement due to its high-temperature stability; however, its oxidation behavior strongly influences composite processing and properties. In this study, alumina/SiC composites containing 1, 5, and 10 wt.% SiC were prepared by conventional powder mixing, calcined at 800 °C for 1 h, and pressureless sintered at 1400 °C in air. Phase evolution, microstructure, densification, and mechanical properties were investigated using XRD, SEM/EDS, density–porosity measurements, and flexural testing. Air sintering led to SiC oxidation and the formation of silica-rich glassy phase and mullite, which significantly affected densification. The composite containing 1 wt.% SiC exhibited the best performance, with a flexural strength of 248.7 MPa, a Weibull modulus of 5.7, an average grain size of 1.86 µm, and a porosity of 11.08%. Higher SiC contents resulted in excessive porosity and severe degradation of mechanical properties. Full article

Metakaolin (MK) obtained from calcined kaolinitic clay is a highly reactive pozzolanic ingredient for use as an emerging supplementary cementitious material (SCM) in modern sustainable binder productions. It provides elevated alumina to promote formations of Alumina Ferrite Monosulfate (AFm) and Calcium-Aluminium-Silicate-Hydrate (C-A-S-H) phases, enhancing the chloride binding capacity. However, due to inherent material uncertainty and lack of approach in quantifying hydration kinetics and chloride binding capacity across varied mixes, robustly assessing the chloride resistance of metakaolin-blended concrete remains challenging. In light of this, a machine learning-aided framework that encompasses physics-based material characterisation and ageing modelling is developed to bridge the knowledge gap. Through applying to laboratory experiments, the impacts of uncertainty on the phase assemblage of hydrated system and chloride penetration are quantified. Moreover, the novel Extended Support Vector Regression (XSVR) method is incorporated and verified against a crude Monte Carlo Simulation (MCS) to demonstrate the capability of achieving effective and efficient uncertainty-aware chloride resistance analyses. With the surrogate model established using XSVR, quality control of metakaolin towards durable design optimisation against chloride-laden environments is discussed. It is found that the fineness and purity of adopted metakaolin play important roles. Full article

The development of cost-effective non-noble metal catalysts for the partial oxidation of methane (POM) remains a key strategy for producing hydrogen-rich syngas while mitigating greenhouse gas emissions. In this study, cobalt-supported alumina (Co/Al₂O₃) catalysts were prepared using 5 wt.% of Co and calcined at 600, 700, and 800 °C. Subsequently, Co/Al₂O₃ catalysts were promoted with 10 wt.% Mg, Si, Ti, and Zr at the optimized calcination temperature. The catalysts were systematically characterized by FT-IR, XRD, N₂ physisorption, H₂-TPR, and XPS analyses. Catalytic activity tests for POM of CH₄ were conducted at 600 °C (CH₄/O₂ = 2 and GHSV = 14,400 mL g⁻¹ h⁻¹). Catalysts calcined at 700 °C (5Co/Al_700) exhibited the highest activity among unpromoted samples, with CH₄ conversion of 43.9% and H₂ yield of 41.8%. The superior performance was attributed to its high surface area and the abundance of reducible Co³⁺ species, generating a greater number of Co⁰ active sites. XPS results confirmed the structural stability of γ-Al₂O₃ and preserved Co–Al interactions across calcination temperatures, while promoters mainly modulated Co dispersion and redox accessibility. Among the promoted catalysts, the activity order followed: 5Co/10ZrAl > 5Co/10MgAl> unpromoted-5Co/Al_700 > 5Co/10SiAl > 5Co/10TiAl. Si and Ti promoted catalysts acquired less concentration of active sites and less activity as well. The concentration of reducible species as well as initial activity towards POM are comparable over Zr and Mg-promoted catalysts. However, earlier one has a higher edge of reducibility and sustained constant activity over time in a stream study. The Zr-promoted catalyst exhibited superior reducibility and remarkable stability, achieving 47.3% CH₄ conversion and 44.4% H₂ yield sustained over 300 min time-on-stream. TEM analysis of spent 5Co/10ZrAl indicated that Zr promotion suppressed graphitic carbon formation. Full article

Coal gangue, a major industrial solid waste from coal mining and processing, requires efficient alumina and silica separation for high-value utilization. This study focused on mineral reaction mechanisms and characteristics of coal gangue during calcination and alkaline leaching. Results showed calcination at 900–1200 °C altered its phase composition, affecting silica separation efficiency, with the optimal calcination range being 960–1120 °C. Poorly crystallized mullite and Al₂O₃ in calcined gangue were insoluble under low-alkaline and low-temperature conditions. On the contrary, amorphous silica is soluble and forms a sodium silicate solution in the proper alkaline conditions. This characteristic facilitates the efficient separation of alumina and silica. It was determined that the suitable conditions for silica removal from coal gangue are as follows: 1080 °C calcination for 90 min, leaching at 75 °C with 200 g/L NaOH (solid–liquid ratio of 1:4) for 4 h. Under these selected conditions, the silica leaching efficiency was 77.31%, the alumina leaching efficiency was 12.21%, the Na₂O content in the leached residue was 1.94%, and the mass ratio of alumina to silica (A/S) in the leached residue increased from 0.88 to 3.42. A potential desilication mechanism was also analyzed. Full article

Alumina nanoparticles have broad applications in catalysis, electronics, and the construction sector, and are widely incorporated as additives in coating formulations to enhance mechanical durability and functional performance. This work focuses on the green synthesis of aluminum oxide (Al₂O₃) nanoparticles using lemongrass (Cymbopogon citratus) extract. Aluminum nitrate [Al(NO₃)₃] and aluminum chloride (AlCl₃) were used with extract. The reaction was carried out at 70 °C for 1 h at 250 rpm and then thermal treatments at 700 °C and 900 °C were applied. The results showed that nanoparticles synthesized from the AlCl₃ and calcined at 700 °C exhibited a smaller particle size (36 ± 14 nm) as compared with those synthesized from the [Al(NO₃)₃] and calcined at 700 °C (49 ± 25 nm). Despite both precursors yielding nanoparticles, the peaks related to the γ-Al₂O₃ crystal phase were observed in the AlCl₃ at 700 °C calcination. Conversely, the nanoparticles synthesized from the [Al(NO₃)₃] required a high temperature treatment at 900 °C to display this stable crystal phase. This study reports an easy and cost-effective green chemistry route to obtain γ-Al₂O₃ nanoparticles, highlighting the importance of the selection of precursors as a critical step to achieve a sustainable and low-energy process, suggesting the potential applications in paints with multifunctional properties. Full article