Search Results (2,987)

How would it be possible to functionalize ceramic aggregates for use in refractories? In this work, we demonstrate how paste extrusion can be used to fabricate layered and porous Nb-Al₂O₃-based composite refractories for adjusting thermal and electrical conductivity. Additive manufacturing is used to generate a specific sequence of alumina and composite layers. After drying, the samples were sintered at 1600 °C, crushed, and sieved into particle sizes up to 3150 µm. The rheology of the paste revealed the intended shear-thinning behavior with microcrack formation between the yield and flow strain. The sintered material showed promising thermal-shock characteristics reaching plateau values after the third cycle without signs of further structural damage up to the fifth thermal shock. The layered microstructure was retained after crushing the composites, establishing functionalization of the refractory granules for all particle sizes. Full article

High regeneration energy demand remains a critical barrier to the large-scale deployment of ethanolamine-based (MEA-based) CO₂ capture. This study adopts an Al₂O₃ ceramic-membrane heat exchanger (CMHE) to recover both sensible and latent heat from the stripped gas. Experiments confirm that heat and mass transfer within the CMHE follow a coupled mechanism in which capillary condensation governs trans-membrane water transport, while heat conduction through the ceramic membrane dominates heat transfer, which accounts for more than 80%. Guided by this mechanism, systematic structural optimization was conducted. Alumina was identified as the optimal heat exchanger material due to its combined porosity, thermal conductivity, and corrosion resistance. Among the tested pore sizes, CMHE-4 produces the strongest capillary-condensation enhancement, yielding a heat recovery flux (q value) of up to 38.8 MJ/(m² h), which is 4.3% and 304% higher than those of the stainless steel heat exchanger and plastic heat exchanger, respectively. In addition, Length-dependent analyses reveal an inherent trade-off: shorter modules achieved higher q (e.g., 14–42% greater for 200-mm vs. 300-mm CMHE-4), whereas longer modules provide greater total recovered heat (Q). Scale-up experiments demonstrated pronounced non-linear performance amplification, with a 4 times area increase boosting q by only 1.26 times under constant pressure. The techno-economic assessment indicates a simple payback period of ~2.5 months and a significant reduction in net capture cost. Overall, this work establishes key design parameters, validates the governing transport mechanism, and provides a practical, economically grounded framework for implementing high-efficiency CMHEs in MEA-based CO₂ capture. 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

A composite based on θ-Al₂O₃ microspheres coated with graphene oxide (GO) and reduced graphene oxide (RGO) was prepared and evaluated as a sorbent for the removal of synthetic dyes from aqueous solutions. GO was synthesized by a modified Hummers’ method and deposited onto alumina microspheres via ultrasound-assisted treatment under various conditions, followed by supercritical reduction to obtain the Al₂O₃_RGO composite. The structure, morphology, and composition of the materials were characterized by Raman spectroscopy, SEM, TGA/DSC, FTIR, and XRD, revealing the formation of mono- and few-layer GO/RGO coatings on the substrate surface. Adsorption tests for cationic methylene blue (MB) dye and anionic methyl orange (MO) dye demonstrated that the alumina substrate was inactive, whereas GO- and RGO-coated microspheres exhibited high adsorption efficiency for MB and partial uptake of MO from water solutions. In mixed-dye solutions, both Al₂O₃_GO and Al₂O₃_RGO composites showed selectivity toward MB, and the RGO-based composite demonstrated enhanced MB adsorption at low concentrations. The results highlight GO/RGO-coated θ-Al₂O₃ microspheres as convenient and selective composite sorbents for water purification processes. Full article

Road dust resuspension is widely recognized as a major contributor to traffic-related particulate matter (PM) in urban environments. Nevertheless, reported emission factors exhibit substantial variability. These discrepancies stem not only from the intrinsic complexity of the resuspension process but also from limitations in measurement techniques, which often fail to adequately control or characterize the influencing parameters. As a result, the contribution of each parameter remains difficult to isolate, leading to inconsistencies across studies. This study presents an experimental protocol developed to quantify PM10 and PM2.5 emission factors associated with vehicle-induced road dust resuspension. Experiments were conducted on a dedicated test track seeded with alumina particles of controlled mass and size distribution to simulate road dust. A network of microsensors was strategically deployed at multiple upwind and downwind locations to continuously monitor particle concentration variations during vehicle passages. Emission factors were derived through time integration of the mass flow rate of resuspended dust measured by the sensor network. The estimated PM10 emission factor showed excellent agreement, within 2.5%, with predictions from a literature-based formulation, thereby validating the accuracy and external relevance of the proposed protocol. In contrast, comparisons with U.S. EPA formulas and other empirical equations revealed substantially larger discrepancies, particularly for PM2.5, highlighting the persistent limitations of current modeling approaches. Full article

Background: Adhesive indirect restorations have become increasingly common in daily clinical routine in most dental practices. Before etching and adhesive application, a sandblasting procedure is essential to clean and increase the microporosity of the surface. Air abrasion with aluminum oxide particles significantly improves the bond strength. However, this procedure may have some limitations, such as the presence of powder particles. Recently, the Er:YAG laser in QSP mode has been proposed for conditioning build-ups prior to adhesive cementation. The aim of this study was a retrospective analysis of adhesive indirect restoration in which build-up was conditioned or using a traditional sandblaster with alumina powder or using the Er:YAG laser in QSP mode. Methods: 187 posterior indirect adhesive restorations were cemented using two different conditioning techniques: in 96 cases (51.34%) build-up conditioning was performed using an intraoral sandblaster with alumina oxide (Microetcher CD, Kavo, Biberach, Germany); in 91 cases (48.66%) build-up conditioning was performed using the Er:YAG laser (Fotona LighWalker^®, Ljubljana, Slovenia) in QSP modality (1 W, 10 Hz, 100 mJ). The clinical efficacy of the two techniques was evaluated and compared, assessing the occurrence of complications such as debonding, fracture, secondary leakage, and hypersensitivity over time. Results: The frequency of secondary complications was very low in both groups. Only one case of debonding and one case of restoration cracking was observed in the sandblasting group, with none in the laser group (p = 0.329). Secondary caries occurred in both groups. A difference was observed in postoperative hypersensitivity: 6% in the sandblasting group and 1% in the laser group (p = 0.064). The Kaplan–Meier curves of the two conditioning techniques showed comparable survival over time (Log-rank test χ² = 2.4864/p = 0.1148). The mean follow-up was 30 months. Conclusions: The success rates of these restorations are very high if adhesive cementation steps are properly followed. Conditioning the build-up before etching is essential. Among these, the Er:YAG laser in QSP mode seems to provide excellent results in the absence of dust and smear layer. Recurrence rates of complications such as decementation, leakage, and cracking resulted in less than 1%. Furthermore, it is interesting to note that using the laser to condition the build-up appears to reduce the recurrence of post-cementation hypersensitivity. These data require confirmation through prospective clinical trials. Full article

To achieve the resource utilization of solid waste generated from the papermaking process, this study proposes a method for preparing sintered bricks by partially replacing shale with paper-mill sludge. The brick samples were prepared through a process of mixing in proportion, extrusion molding, drying and roasting. An orthogonal experimental design was employed to investigate the effects of sintering temperature, raw material proportion, and holding time on the physical and mechanical properties of the bricks. The results indicate that the optimal technological parameters are determined as follows: a raw material proportion (paper-mill sludge:shale) of 30:70, a sintering temperature of 1050 °C, a holding time of 8 h, and a heating rate of 1 °C/min. Under these conditions, the produced paper-mill sludge–shale bricks exhibited a compressive strength of 14.91 MPa, a flexural strength of 8.26 MPa, a water absorption of 12.7%, and a bulk density of 1712 kg/m³. These performance indicators meet the requirements for Grade MU10 specified in the national standard Sintered Common Bricks (GB/T 5101-2017). Regarding microscopic analysis, the SEM results reveal significant liquid-phase sintering within the brick body at 1050 °C, while XRD analysis confirmed the presence of stable quartz, alumina, and hematite phases, which contribute to enhancing the mechanical properties and densification of the bricks. Full article

Silicalite nanosheet (SN) laminated membranes are promising for pervaporation (PV) desalination of concentrated brines for water purification and critical material concentration and recovery. However, scaling up the SN-based membranes is limited by inefficient synthesis of monodispersed open-pore SN single crystals (SNS). Here, we report a scalable approach to fabricate multilayered silicalite nanosheet plate (SNP) laminated membranes on porous alumina and PVDF substrates and demonstrate their excellent PV desalination performance for simulated brines containing lithium and high total dissolved salts (TDS). At 73 ± 3 °C, the SNP laminated membrane on alumina support achieved a remarkable water flux ($J_w$) of nearly 20 L/m²·h, significantly outperforming the alumina-supported SNS laminated membrane ($J_w$ = 9.56 L/m²·h), while both provided near-complete salt rejection ($r_i$ ~99.9%) when operating with vacuum pressure on the permeate side. The PVDF-supported SNS and SNP laminated membranes exhibited excellent $J_w$ (14.0 L/m²·h) and near-complete $r_i$ (>99.9%), surpassing the alumina-support SNP laminated membranes when operating by air sweep on the permeate side. However, the $r_i$ of the PVDF-supported membranes was found to decline when operating with vacuum pressure on the permeate side that was apparently caused by minimal liquid permeation through the inter-SNP spaces driven by the transmembrane pressure. With scalable SNP production, SNP-A membranes show potential for PV desalination of high-TDS solutions, especially in harsh environments unsuitable for polymer membranes. Full article

The performance of cement adhesive in large-tonnage insulators is crucial for determining their structural stability and service life when subjected to long-term electromechanical loading and complex environmental interactions. This work addresses the issue of late-stage strength reduction in alumina cement by employing a rapid steam curing process. The influence of curing temperature on the phase composition and microstructure of the hydration products is investigated, along with the evolution over time of the mechanical properties, dry shrinkage rate and elastic modulus. These findings are further validated through thermal–mechanical performance testing of bonded insulators. The results demonstrate that: (1) The hydration products of the adhesive are significantly influenced by steam curing temperature: the metastable phase CAH₁₀ forms at 20 °C; it transforms into the metastable phase C₂AH₈ at 50–60 °C; it changes to the stable phase C₃AH₆ at 70 °C; and microcracks appear and porosity increases at 80–90 °C, although the stable phase C₃AH₆ remains the dominant phase. (2) Alumina cement adhesive prepared via 2 h steam curing at 70 °C exhibited superior properties, with flexural and compressive strengths reaching 14.2 MPa and 112.7 MPa, respectively. After 360 days, flexural strength remained above 12 MPa and compressive strength exceeded 110 MPa. Dry shrinkage was below 0.04%, with an elastic modulus of approximately 49.6 GPa. (3) Microstructural analysis revealed that the hydration products of the cured adhesive were predominantly C₃AH₆ and AH₃, exhibiting stable structures. After 90 days, porosity decreased to 3.56%, with the C₃AH₆ and AH₃ gels tightly enveloping the aggregates and forming a dense, three-dimensional network structure. (4) All bonded insulators successfully passed thermomechanical performance tests. Therefore, this work can provide a good way to prepare a high-performance cement adhesive for insulators. Full article

The use of e-fuels, such as methanol (MeOH), is considered an alternative for the reduction of carbon emissions. MeOH can be produced from captured CO₂ and green H₂, with the exothermic (equilibrium-limited) reaction favoured at low temperatures and high pressures. However, CO₂ is a very stable molecule and requires high temperature (>200 °C) to overcome the slow activation kinetics. In this study, MeOH was synthesized from CO₂ and H₂ in a packed-bed membrane reactor (PBMR) using a commercial Cu/ZnO/Al₂O₃ catalyst and a tubular-supported, water-selective composite alumina–carbon molecular sieve membrane (Al-CMSM) immersed in the catalytic bed. A mixture of H₂/CO₂ (3/1) was fed into both sides of the membrane to increase the driving force of the gases produced by the reaction. The effect of the temperature of reaction (200, 220, and 240 °C), pressure difference (0 and 3 bar), and the sweep gas/reacting gas ratio (SW = 1, 3, 5) in the CO₂ conversion and products yield was studied. For comparison, the reactions were also carried out in a packed-bed reactor (PBR) configuration where the tubular membrane was replaced by a metallic tube of the same size. CO₂ conversion and MeOH yield are much higher in PBMR than in PBR configuration, showing the benefit of using the water-selective membrane. In PBMR, MeOH yield increases with SW and slightly decreases with the temperature, overcoming the limitation imposed by the thermodynamics. Full article

Photo-Fenton advanced oxidation processes are promising and sustainable approaches for water treatment, particularly under visible-light irradiation. In this study, Cu-Fe bimetallic catalysts supported on silica and γ-alumina were developed for visible-light-driven photo-Fenton reactions, with emphasis on the influence of metal ratios and support-metal interactions on charge–carrier dynamics and hydroxyl radical formation. Comprehensive characterization (XRD, TEM, UV-Vis DRS, PL, TCSPC, and EPR) revealed stronger metal–support interactions and higher metal dispersion on γ-alumina, while silica-supported catalysts showed CuO aggregation at higher Cu loadings. Catalytic performance was evaluated using coumarin oxidation as both a model reaction and a quantitative probe for ^•OH radical generation. Alumina-supported catalysts exhibited superior activity, and ^•OH production increased with increasing Cu content on both supports. Importantly, iron was found to play a dual role: low Fe loading enhances photo-Fenton activity, whereas higher Fe content promotes charge–carrier recombination, leading to reduced activity under visible-light irradiation. These results highlight how the interplay between Fe/Cu ratio and support material governs charge dynamics and provides clear guidelines for the rational design of efficient heterogeneous photo-Fenton catalysts. Full article

Tuber melanosporum, the black truffle, is a fungus of high economic and ecological value, but its underground detection remains a challenge due to the lack of reliable, non-invasive methods. This study presents the development and proof of concept of a portable optoelectronic nose that integrates nine optical sensors and one electrochemical sensor for the in vitro identification of T. melanosporum. The optical sensors use colorimetric and fluorogenic molecular indicators supported on UVM-7, alumina, and silica. Tests were performed with truffles at different depths and in the presence of soil and compost to evaluate the device’s multi-source response. Partial least squares discriminant analysis (PLS-DA) models showed robust discrimination between soil, compost, and truffles, with an accuracy of 0.91 under most conditions. Detection at 30 cm showed an accuracy of 0.94, confirming the system’s ability to differentiate between sample types. Performance improved in simplified scenarios based on the presence or absence of truffles. Furthermore, the artificial neural network models achieved optimal results in binary classification. Taken together, the results support the system’s potential as an accurate, non-invasive tool with possible application to the agronomic management of truffle orchards. Full article

Alumina ceramics, known for their hardness, thermal resistance, and chemical stability, are widely applied in engineering and industry. This study investigates the flexural strength of 95% and 99% alumina ceramics using tubes with two or four cross-sectional holes, tested by 3-point and 4-point bending methods. Macroscopic analysis was performed with a Leica DM6M microscope to determine specimen areas and ensure measurement accuracy. Results indicate that 99% alumina ceramics exhibit approximately 35% higher bending strength compared to 95% alumina ceramics, highlighting the influence of alumina content on mechanical performance. Full article

Alumina (Al₂O₃) reinforced copper matrix composites are widely used in the electronic industry, rail transit, and other fields due to their excellent electrical conductivity, ductility, and wear resistance. However, due to problems such as non-wetting and thermal expansion differences between alumina and Cu, weak interfacial bonding can easily reduce physical and thermal properties. A uniform silver layer was deposited on Al₂O₃ via chemical plating to enhance interface bonding with copper. Al₂O₃@Ag/Cu composites with 1–3 wt.% Al₂O₃ were prepared by rapid hot-press sintering. The effects of plating temperature and Al₂O₃ content on microstructure and properties were investigated. The results show that the optimum coating temperature is 25 °C, and a thin and uniform silver coating can be formed. This effectively improved Al₂O₃–Cu interface bonding while maintaining 77.8% of copper’s thermal conductivity (320.7 W/(m·K)). The composites showed improved wear resistance with increasing Al₂O₃ content. At 3 wt.% Al₂O₃@Ag, the wear rate was 3.36 × 10⁻⁵ mm³/(N·m), 84.4% lower than pure copper, with plow groove wear as the main mechanism. Full article

The solid-state synthesis of alkali–tantalum(V) oxyfluorides KTa₂O₅F and CsTa₂O₅F was revisited with the aim of streamlining their preparation as single-phase polycrystalline solids. Alkali fluorides (KF, CsF) and trifluoroacetates (KH(CF₃COO)₂, CsH(CF₃COO)₂) and tantalum oxide (Ta₂O₅) were used as precursors. Reaction temperatures were optimized by means of thermal analysis coupled with powder X-ray diffraction. Phase-pure KTa₂O₅F was obtained by heating stoichiometric mixtures of KF + Ta₂O₅ and KH(CF₃COO)₂ + Ta₂O₅ at 900–1000 °C in alumina crucibles under ambient atmosphere. Similar conditions were employed to synthesize phase-pure CsTa₂O₅F from a stoichiometric mixture of CsF + Ta₂O₅ heated to 800 °C. On the other hand, the preparation of CsTa₂O₅F from a mixture of CsH(CF₃COO)₂ + Ta₂O₅ required an excess of the trifluoroacetate precursor to obtain the targeted oxyfluoride as the sole crystalline phase. Results presented herein demonstrate that mixed-metal oxyfluorides previously thought to be synthetically challenging may be synthesized via facile solid-state reactions without the need for specialized containers and stringent conditions. In addition to streamlined synthetic routes to alkali– tantalum(V) oxyfluorides, a neutron powder diffraction study of the crystal structure of KTa₂O₅F is presented to fill a gap in crystallographic databases commonly accessed by materials and solid-state chemists. Full article