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The adsorption of ethanol and ammonia changes the basic properties of alumina, and new basic sites are created. Ethanol reacts with surface Al-OH groups, forming ethoxy group Al-O-C2H5. The substitution of Al-OH by Al-O-C2H5 increases the negative charge of neighbouring oxygen atoms, and they became sufficiently basic to react with adsorbed CO2 forming carbonate species CO32−. These carbonates were found to be monodentate and bidentate species. Preadsorption of ammonia also increases the basicity of alumina, but the mechanism is different than for ethanol adsorption. Adsorbed ammonia interacts with surface Lewis acid sites being three-coordinated aluminium atoms. This interaction is accompanied by an electron transfer from ammonia molecules to surface sites, and increases the basicity of the neighbouring oxygens, which can react with the absorbed CO2. The carbonate species formed are polydentate ones. [ABSTRACT FROM AUTHOR]

Iron oxide-modified 1Pd0.5Fe and 1Pd10Fe catalysts with a target content of 1 wt % Pd and 0.5 or 10 wt % Fe have been synthesized by the wet impregnation of Al2O3 with iron and palladium nitrates. The catalysts have been compared with each other and with a monometallic 1Pd catalyst in diclofenac (DCF) hydrodechlorination (HDC) in dilute aqueous solutions at 30°C in batch and flow reactors after high-temperature (320°C) and mild reduction (30°C), the latter being run in a batch or flow reactor. X-ray photoelectron spectroscopy (XPS) has revealed that, after reduction at 320°C, the catalysts contain mostly Pd0, Fe2+, and Fe3+. The Fe2+/Fe3+ ratio on the surface increases with a decrease in the iron content. The reduction of Pd2+ to Pd0 can occur even at 30°C; however, on the 1Pd0.5Fe surface, it is significantly less effective than that on 1Pd10Fe. According to XPS, temperature-programmed reduction, and diffuse reflectance infrared Fourier transform spectroscopy of adsorbed CO, modification with iron oxides leads to an increase in the palladium content on the surface compared with that on 1Pd, contributes to the formation of new Pd–O–Fe sites, and affects the reducibility of palladium. These effects enhance with an increase in the iron content. The iron-modified catalysts reduced at 320°C exhibit similar activity and stability in DCF conversion in flow and batch systems. The 1Pd10Fe catalyst, unlike 1Pd0.5Fe, is highly efficient and stable even after mild reduction at 30°C. Under flow conditions, it provides a DCF conversion comparable to that provided by 1Pd and a selectivity in the DCF HDC reaction that is higher than that provided by 1Pd, which is also active in hydrogenation. [ABSTRACT FROM AUTHOR]

Locally found Egyptian dolomite, commercial zirconia, and alumina were used to fabricate calcium zirconate-based refractory with improved thermal shock damage resistance. CaZrO3/MgO (CZM) and CaZrO3/MgAl2O4 (CZS) green compacts were obtained by mixing dolomite, commercial zirconia, and alumina with molar ratios of 1:1.23:0 and 1:1.23:0.59, respectively, and then ball milled for 1 h and uniaxially pressed at 150 MPa. The obtained green compacts were sintered at 1200, 1300, 1500, and 1650 °C for 2 h with a heating rate of 5 °C/min. The phase composition, microstructure, densification parameters, and thermal shock damage resistance of the prepared refractory were investigated. The results showed that CaZrO3 was present as the predominant phase and c-ZrO2 as a secondary phase due to the solubility of calcium and magnesium ions in the zirconia lattice structure. CZM1500 and CZS1500 showed a bulk density of 4.05 and 3.8 g/cm3 respectively. Thermal shock damage resistance of CZM samples was greatly improved with the in situ spinel synthesis where CZS1500 was able to withstand 16 cycles before fracturing compared to 10 cycles recorded for CZM1500. [ABSTRACT FROM AUTHOR]

Bauxite is the basic raw material of aluminium used to extract alumina in Bayer's process. With the huge demand and the rapid development of the global alumina industry, bauxite consumption is rising and has reached more than 160 million tonnes per year. With such a high demand for aluminium, it is becoming more difficult to meet the consumption due to the gradual global decline of high-grade bauxite resources. In the current market scenario, treating bauxites containing more than 5% reactive silica (SiO2) is generally considered uneconomic due to excessive soda consumption in Bayer's process. The present study is conducted to examine the influence of the wet beneficiation process in the pre-treatment of low-grade and high-grade bauxite ores and a comparative analysis of the results obtained regarding alumina recovery and silica reduction. For this study, High-Grade (HG) and Low-Grade (LG) bauxite ore samples were collected from different bauxite mines of the East Coast region and subjected to wet beneficiation. Comparative chemical analysis of the before and after beneficiation samples revealed the wet beneficiation process to be significantly effective in the pre-treatment of LG bauxite samples with an average increment of 10.84% in the alumina content and 18.38% average reduction in silica after wet beneficiation. [ABSTRACT FROM AUTHOR]

This contribution discusses the impact of sintering temperatures on dielectric properties of 3D-printed alumina (Al2O3) in the W-band, by evaluating high quality factor (-Q) resonators integrated in a 2D photonic crystal structure. By varying the sintering temperature of the lithography-based ceramic manufactured (LCM) samples, the microstructure of the material can be defined, which has a direct impact on the dielectric permittivity and material losses. Using a highly accurate photonic crystal structure, with a dimensional variation below 2% from print to print, an accurate extraction and evaluation of the dielectric material properties could be achieved. The relative permittivity of the alumina was tuned from 4.4 at 1250°C to 9.2 at 1650°C, whereas the observed change in dielectric losseswas moderate. Themaximum in observed dielectric loss for samples sintered at the lowest evaluated temperature, only yields an average value of 30 x 10-4. This demonstrates the versatility of the LCMtechnology for mm- and sub-mm-wave applications and its possibilities for material tuneability. [ABSTRACT FROM AUTHOR]

Alumina is one of the crucial and extensively utilized refractory components. As the refractory wear due to dissolution at elevated temperatures during operation is a major threat to refractory lifespan, quantifying dissolution is important for developing cost-effective and resource-efficient refractories. This study investigated the dissolution of alumina particles in two silicate and one calcium aluminate slags at 1 450, 1 500, and 1 550 °C using high-temperature confocal laser scanning microscopy (HT-CLSM). Dissolution was quantified in terms of diffusivity, with all influencing factors, including Stefan flow and bath movement, incorporated into the determination process. The trends observed in total dissolution time and diffusivity in three slags at three experimental temperatures could not be explained solely on the basis of slag basicity. Two parameters, considering the influencing factors, were introduced to explain these trends. Furthermore, the linear trend observed in Arrhenius plots of diffusivities supports the diffusivity results. Additionally, good agreement between the diffusivities of alumina in one silicate slag obtained via CLSM and rotating finger test investigations verified the reliability of the results. [ABSTRACT FROM AUTHOR]

SiO2-Al2O3 composite aerogel (SAA) has shown a wide range of application in aerospace, chemical metallurgy, furnace insulation and other fields due to the characteristics of low bulk density, high specific surface area, low thermal conductivity and high temperature resistance. Ambient pressure drying has the advantages of low preparation cost, easy industrial mass production and so on, so it has a good practical application prospect. In this work, the preparation methods of SAA were introduced, with emphasis on the research status of precursors, surface modifiers and fiber reinforcements in the preparation of SAA by ambient pressure drying. Finally, the development direction of SAA prepared by ambient pressure drying was prospected. [ABSTRACT FROM AUTHOR]

Ceramic‐based polymer composites are commonly utilized as thermal management materials due to their high thermal conductivity and electrical insulation properties. One efficient method to enhance the thermal conductivity of these composites is by constructing a three‐dimensional thermal conductive network within the polymer matrix. In this study, alumina was coated onto the surface of polyurethane (PU) foam, followed by high‐temperature removal of the PU foam and sintering of the alumina sheets to obtain a continuous alumina framework. Epoxy resin was then infiltrated into this alumina framework to fabricate highly thermally conductive EP/f‐Al2O3 composites. The EP/f‐Al2O3 composite achieved a thermal conductivity of 2.44 W m−1 K−1 when the filler content of 26.8 vol%, representing a 400% improvement compared to EP/Al2O3 composite with randomly dispersed fillers, and a remarkable 1180% enhancement compared to epoxy resin. Infrared thermal imaging also confirmed the excellent heat dissipation capability of the EP/f‐Al2O3 composites. Overall, this research presents an effective method for producing highly thermally conductive and electrically insulating composites that can be used in electronic thermal management applications. Highlights: Fabrication of porous Al2O3 frameworks/epoxy composites.Porous Al2O3 frameworks were fabricated by polyurethane foam template.The obtained EP/f‐Al2O3 composite exhibited excellent thermal conductivity. [ABSTRACT FROM AUTHOR]

The encapsulation of phase change materials (PCMs) into additive manufactured porous supports is attracting great interest for developing thermal energy storage (TES) materials with improved energy performance. Here, highly porous (86 %) self-supported 3D activated carbon/alumina supports are fabricated by direct ink writing (DIW) and, then, infiltrated with solar salt, a highly corrosive PCM with a melting temperature around 220 °C commonly employed in concentrated solar power plants. This novel, robust, chemically compatible, and lightweight infiltrated 3DTES exhibits good thermal energy storage efficiency (70 %) and thermal stability, high energy storage density (381 J g−1), and avoids the liquid leakage of the molten salt. Besides, the 3D activated carbon/alumina support promotes a better ability to absorb solar energy (79 %) and enhances the thermal conductivity of the solar salt (up to 64 %). These results validate the use of DIW for manufacturing innovative TES with an enhanced energy storage behaviour.

This in vitro study examines the electrochemical responses and surface degradation of alumina and feldspar dental ceramic materials in acidic environments using cyclic polarization and electrochemical impedance spectroscopy (EIS). Alumina and feldspar demonstrate balanced responses in both Fusayama Artificial Saliva and acidic solutions, indicating effective passivation. SEM/EDX analyses after 168-h immersion reveal significant elemental variations, suggesting complex surface phenomena and chemical reactions leading to oxide layer formation. Alumina exhibits increased Si, O, Al, Na, K, and C counts, while feldspar shows increased Si, O, Al, Na with reduced C and Ca levels, indicating complex reactions. Immersion induces notable elemental composition modifications, with alumina showing remarkable corrosion resistance and feldspar undergoing selective dissolution. This study provides insights into the electrochemical and surface degradation of these materials, emphasizing long-term stability and the need for continuous monitoring of protective layer dynamics in future research on corrosion-resistant dental biomaterials.

Coolant-facing alloys in a tokamak will face harsh environments due to the synergistic effect of flowing coolant, dynamic mechanical loading, ionising radiation, and tritium embrittlement. Reduced activation ferritic/martensitic (RAF/M) EUROFER-97 is the primary candidate as the structural alloy for the breeder blanket to be used in DEMO reactor. Under fusion-like conditions, coatings are required to improve both its corrosion properties and act as a tritium permeation barrier (TPB) layer. In this study, Al-base self-passivating coatings have been investigated as possible solution to provide protection against corrosion and act as TPB layer. The aim of this study was to assess the adhesion properties between different self-passivating Al-base coatings as electroplated and chemical vapour deposited (CVD) coatings on a RAF/M EUROFER-97 under strain. These studies showed the high ductility of pure electroplated Al-coatings, whereas both CVD coatings cracked under the applied strain.

In this work, hot-pressing of alumina in contact with hexagonal boron nitride or doped with boron carbide was conducted at 1500 °C for 30 min. After hot-pressing, abnormal grain growth induced by boron diffusion from these substances into alumina was detected, as clearly demonstrated with SEM, EDS, EBSD, and Raman spectroscopy. Grain boundary complexion transformations, solute drag, or another mechanism relating to interface-controlled grain boundary mobility are presumed to be the fundamental mechanism responsible for abnormal grain growth observed in this work.

Aluminium industry stands out as a significant source of CO2 emissions, due partially to the high energy demand of the alumina extraction stage. Accordingly, this study explores the implementation of direct resistive heating of mid-temperature processes in alumina production as an alternative to decrease CO2 emissions. Additionally, two different strategies are evaluated to decarbonize alumina industry: the generation of renewable electricity through solar photovoltaic panels and the integration of a CO2 capture plant based on calcium looping technology. This work comprehends the modelling and sizing of these plants and the assessment of their economic performance through the calculation of their Net Present Value and their respective payback periods. The integration of both strategies into an alumina refinery model reveals that electrification of low and mid-temperature processes yields a 15 % reduction in CO2 direct emissions, whereas calcium looping demonstrates the potential to capture 97 % of emissions with a 7 % energy penalty. Also, economic assessments indicate substantial potential for improvement through in-site electricity generation via solar photovoltaic panels, exhibiting a payback time of 4.5 years. Conversely, the feasibility of a calcium-looping plant is hindered by high capital expenses, necessitating a longer payback period of 19–24 years. Sensitivity analyses underscore the suitability of in-site renewable electricity generation, whereas carbon emission taxes emerge as crucial in incentivizing carbon-neutral processes, with thresholds around 95–125 €/tonne of CO2. Despite potential deviations from real industrial settings, this study provides evidence for environmentally friendly strategies in alumina production that demonstrate limited adverse effects on economic performance.

Dimethylaluminum isopropoxide (DMAI) is attracting attention as an alternative precursor for atomic layer deposition (ALD) of aluminum oxide (Al2O3). However, the surface chemical reaction mechanisms of DMAI during ALD regarding its dimeric structure under vacuum deposition process conditions has yet to be clear. In this work, the adsorption mechanism of dimeric and monomeric DMAI on a fully hydroxylated Al2O3 surface is studied using machine-learning potential (MLP) calculations. The initial adsorption of DMAI appears facile and would result in the coexistence of both methyl and isopropoxy ligands on the surface. The reactivity of DMAI is smaller than that of TMA, owing to the propensity of DMAI to adopt a dimeric form. Especially when the substrate is partially covered by other adsorbate species, the large molecular size and low reactivity of dimeric DMAI considerably hinder its reactivity toward surface adsorption. Current results are in good correspondence with the previous experimental results, where lower growth per cycle (GPC) and higher selectivity in area-selective ALD (AS-ALD) could be observed by using DMAI than compared to those of TMA processes.

Abstract In this study, we produced, through hot pressing (HP) and spark plasma sintering (SPS) techniques, Al2O3-NbC composites for applications in machining processes. We report an experimental investigation of sintered composites’ structural, thermal, morphological, physical, and mechanical properties. The results confirm that the Al2O3-NbC composite sintered by both techniques presents a heterogeneous microstructure with distinct grain sizes and irregular geometries. Another stimulating factor is the increase of 25.86% in Vickers hardness, 14.89% in Young’s modulus, and 16.52% in mechanical strength of the composite sintered by SPS about the composite sintered by HP. Thus, our results can be used to address material properties targeting the needs of specific technological applications.

More efficient electronic systems need more temperature-stable substrate materials and more flexible production possibilities. Ceramics such as alumina can be used for 2D and 3D base bodies, since they provide better thermal properties than their polymeric counterparts and can be additively manufactured utilizing e.g. Fused Filament Fabrication. Proper functionalization can be achieved by applying methods of printed electronics. Here, adhesion of the functional ink to a substrate is a crucial issue and especially challenging on ceramic substrates. This contribution reached a noteworthy increase in this matter, using a modified silver-based ink with piezojet-printing, while preserving very low electrical resistance after convection sintering. Adhesion is determined by pull-off testing, based on ISO 4624. By the approach shown in this work, printed ceramics could become a more viable choice for use in functional electronic systems.

The atomic-level structure of platinum/γ-alumina interfaces is characterized in a model system of dense γ-alumina embedded with faceted Pt NPs produced by implantation of platinum ions into sapphire followed by thermal annealing in air at 800 °C. Aberration-corrected scanning transmission electron microscopy (STEM) was used to collect atomic-resolution images, which are compared to STEM image simulations of two experimentally-based bulk models of γ-alumina by Smrčok et al. and Zhou and Snyder. A density functional theory (DFT) based model of (111) interfaces with different chemical terminations (O, Al1, Al2) of the γ-alumina developed by Oware Sarfo et al. is also compared to experimental STEM data from Pt/γ-alumina interfaces. The Smrčok γ-alumina model provides a better fit than the Zhou structure to the bulk of the γ-alumina. The oxygen-terminated Oware Sarfo model best fits the experimental data and is a very good model close to the interface. However, the fit of the interface model to the experimental data is poorer beyond the third atomic layer in the γ-alumina. This is attributed to compromises required in the design of the model to limit the cell size and computational time for DFT calculations. Understanding the accuracy and limits of the structural models of γ-alumina and Pt/γ-alumina interfaces is important to further the understanding of the structure/property relationships in this system.

This article investigates the development and potential applications of low-melting point lead-free glasses. Their importance is due to strong market demands to comply with the strict international regulations against the use of lead. In this work, a preliminary study of the existing interactions of a low-melting-temperature glass belonging to the P2O5–CaO–Na2O system when it is deposited on different ceramic substrates, both traditional (porcelain stoneware) and technical (alumina and zirconia), has been carried out. The ionic diffusion through the studied interfaces, the phases present, the composition of the glassy phase and the surface morphology of the coating have been studied by Field Emission Scanning Electron Microscopy (FESEM), with coupled EDX microanalysis. The chemical resistance of the different glassy coatings obtained is also evaluated. The results showed that these new lead-free low-melting-temperature glassy coatings are chemically and mechanically compatible, and promising candidates for applications and markets in a broad range of fields. Resumen: Este artículo investiga el desarrollo y aplicaciones potenciales de los vidrios sin plomo de bajo punto de fusión. La importancia de estos materiales se debe a las fuertes demandas del mercado por las estrictas normativas internacionales contrarias a la utilización del plomo. En este trabajo se ha realizado un estudio preliminar de las interacciones existentes de un vidrio de baja temperatura de fusión, perteneciente al sistema P2O5-CaO-Na2O, cuando se deposita sobre diferentes sustratos cerámicos tanto tradicionales (gres porcelánico) como técnicos (alúmina y circona). Mediante un estudio por microscopía electrónica de barrido con emisión de campo (FESEM) con microanálisis EDX acoplado, se han evaluado la difusión iónica a través de las interfases estudiadas, las fases presentes, la composición de la fase vítrea y la morfología superficial del recubrimiento. Además, se ha evaluado la resistencia química de los recubrimientos vítreos obtenidos. Los resultados muestran que son química y mecánicamente compatibles con las cerámicas tradicionales y técnicas. Estos resultados convierten a estos vidrios sin plomo y de baja temperatura de fusión en prometedores candidatos para un amplio rango de aplicaciones y mercados.

Starch consolidation casting (SCC) technique was successfully employed to produce both porous alumina and graded porous alumina ceramics. The solid content in the alumina suspension was maintained at 40 vol.%, with potato starch varying from 5 to 15%. Structures of the porous alumina (monolithic) samples obtained by SCC and uniaxial pressing were compared. In addition, the influence of the SCC consolidation temperature and the starch content were evaluated in the monolithic samples, while the consolidation temperature and the number of layers numbers were evaluated in the graded samples. The lower SCC consolidation temperature resulted in lower linear shrinkage and a slight increase in total porosity due to the increased pore size. The compressive strength values for the monolithic samples ranged from 60 to 200MPa, which can be considered high when compared to previous works. The graded samples exhibited porosity variations across layers and interfaces were free of cracks and imperfections. Linear shrinkage was the same for the adopted consolidation temperature and the porosity was slightly higher for the 3-layer samples. They achieved strength of 60MPa with fracture mode parallel to the applied load.

To increase the impulse mechanical strength of alumina, the pore structure of alumina was modified by surface coating. It was found that the impulse mechanical strength of alumina samples coated with aluminum chloride increases from 35 MPa to 51 MPa and the mechanical strength of alumina samples coated with aluminum-based complex increases from 21 MPa to 46 MPa at the calcination temperature range of 100 ℃ to 1100 ℃ by the DL-3 typed impulse mechanical strength test device, while the mechanical strength of uncoated alumina samples increases from 17 MPa to 39 MPa. According to scanning electron microscopy and X-ray diffraction, the surface coating of aluminum chloride has little influence on the crystal type of alumina materials after high temperature calcination. At the same time, it can effectively fill the matrix pore of alumina materials, increase the density of the support, and improve the mechanical strength of alumina materials. In addition, compared with the alumina sample coated with aluminum complex, the alumina material coated with aluminum chloride possesses larger surface area and smaller pore size after high temperature calcination. More importantly, the surface of the alumina sample coated with aluminum chloride formed a rough shape after high temperature calcination, which was beneficial to the loading and dispersion of the active metals.

Plasma actuators have demonstrated great potential for active flow control applications, including boundary layer control, flow separation delay, turbulence control, and aircraft noise reduction. In particular, the material used as a dielectric barrier is crucial for the proper operation of the device. Currently, the variety of dielectrics reported in the literature is still quite restricted to polymers including Kapton, Teflon, poly(methyl methacrylate) (PMMA), Cirlex, polyisobutylene (PIB) rubber, or polystyrene. Nevertheless, several studies have highlighted the fragilities of polymeric dielectric layers when actuators operate at significantly high-voltage and -frequency levels or for long periods. In the current study, we propose the use of alumina-based ceramic composites as alternative materials for plasma actuator dielectric layers. The alumina composite samples were fabricated and characterized in terms of microstructure, electrical parameters, and plasma-induced flow velocity and compared with a conventional Kapton-based actuator. It was concluded that alumina-based dielectrics are suitable materials for plasma actuator applications, being able to generate plasma-induced flow velocities of approximately 4.5 m/s. In addition, it was verified that alumina-based ceramic actuators can provide similar fluid mechanical efficiencies to Kapton actuators. Furthermore, the ceramic dielectrics present additional characteristics, such as high-temperature resistance, which are not encompassed by conventional Kapton actuators, which makes them suitable for high-temperature applications such as turbine blade film cooling enhancement and plasma-assisted combustion. The high porosity of the ceramic results in lower plasma-induced flow velocity and lower fluid mechanical efficiency, but by minimizing the porosity, the fluid mechanical efficiency is increased.

The selection of abrasive material and parameters of the Air-Abrasion device for a particular application is a crucial detail. However, there are no standard recommendations or manuals for choosing these details; the operator must depend on his experience and knowledge of the procedure to select the best possible material and set of parameters. This short review attempts to identify some of the effects that the selection of material and parameters could have on the performance of the Air-Abrasion procedure for a particular application. The material and parameter data are collected from various studies and categorized according to the most popular materials in use right now. These studies are then analyzed to arrive at some inferences on the performance of Air-Abrasion materials and parameters. This review arrives at a few conclusions on the effectiveness of a material and parameter set, and that there is potential for developments in the area of standardizing parameter selection; also, there is scope for further studies on Bio-Active Glass as an alternative to the materials currently used in Air-Abrasion.

Abstract We created AA2024–AA1050 and AA2024–AA1050/0.005 vol.% Al2O3 nanocomposites by six accumulative roll bonding (ARB) process cycles. We used AA2024 and AA1050 sheets with a thickness of 0.7 mm and plate-shaped alumina nanoparticles to create a composite. The two AA1050 and one AA2024 sheets (among the two AA1050 sheets) were ARB-ed up to six cycles with and without adding alumina nanoparticles. Also, a sample of the AA1050 without composite making was ARB-ed up to six cycles. We aged some composites after the ARB process in the furnace at 110, 150, and 190 °C. This project performed SEM, TEM, and EDS-MAP analyses, tensile strength, microhardness, and Pin-on-Disc tests to study the ARB-ed sheets. The results of the tensile tests showed that the tensile strength of AA2024–AA1050 created by the six cycles ARB process was two times more than primary AA1050. Also, the wear resistance of this composite was 74% more than six cycles ARB-ed the AA1050. Using 0.005 vol.% alumina nanoparticles in AA2024–AA1050 composite improved its wear resistance by 30%. In the following, the aging process caused an improvement in tensile strength and total elongation of AA2024–AA1050/Al2O3 nanocomposites.

Alumina is widely used in the automotive, electrical component and aircraft industries due to its low thermal conductivity and high hardness. However, alumina is notoriously difficult to machine due to its extreme hardness. According to some researchers, laser machining offers a cost-effective machining technique for alumina. Even though many works on laser machining of alumina have been published, most have focused on thin alumina plates. This study determined the effect of a CO2 laser machining method on hole quality in terms of the heat-affected zone (HAZ) and taper angle for 3 mm alumina thickness. Design of Experiment (DOE) was performed to identify the effect of laser power and frequency on the output findings. The HAZ and the taper angle were measured using a Scanning Electron Microscopy image. Based on the ANOVA analysis, HAZ and taper angles were influenced by the laser power input. The HAZ thickness increased as laser power and frequency decreased, but the taper angle decreased as frequency decreased. Low laser power (50 W) resulted in a small inlet diameter (0.236 mm), while high laser power (150 W) resulted in a larger inlet diameter (0.272 mm). Multi-response optimization analysis for both HAZ and taper angle showed that 149 W and 2956 Hz frequency were the optimum process parameters which yielded the best output conditions.

Military equipment development, especially means of transportation, currently revolves around material selection, which includes hybrid laminate composite as a prominent material choice due to its strength-to-weight ratio. The hybrid laminate composite was fabricated by involving aluminum alloy 7075-T6 sheets and Kevlar fabrics that were introduced to shear thickening fluid (STF). STF was made by mixing PEG-400, alumina nanoparticles, and ethanol in a certain ratio. The composites were fabricated using variations of Kevlar layers of 8, 16, and 24 layers. Ballistic impact resistance of the hybrid laminate composite was observed through a ballistic test that was performed according to the National Institute of Justice (NIJ) 1080.01 level II standard. The energy absorption of the composites was evaluated by analyzing the diameter of the perforation. Additionally, the failure mode of the Al7075 matrix and Kevlar fabric are discussed. The findings from ballistic testing indicated that the addition of alumina nanoparticles into three variations of Kevlar layers in hybrid laminate composite yielded the improvement of ballistic performance and impact energy of the composites.

High-quality porous ceramics are extremely attractive in terms of energy conservation and consumption reduction, and thus are one of the research hotspots pursued in recent years. For this purpose, porous MgO-based ceramics with outstanding thermal shock resistance and thermal insulation performance were designed and prepared by using the direct firing method and introducing alumina with different paticle sizes as additives. The results reveal that the in-situ formed MgAl2O4 phase by alumina additives simultaneously improves the apparent porosity, thermal insulation, and thermal shock resistance of the prepared MgO-based ceramics. Specifically, the increase in the apparent porosity can be attributed to the volume expansion effect of MgAl2O4 phase, so the industrial alumina with larger particle size is more effective (20 wt% addition: the apparent porosity from 43.5 % to 55.4 %, the thermal conductivity from 0.977 to 0.389 W m−1 K−1 at 800 °C); moreover, the enhancement in thermal shock resistance can be ascribed to the residual stress effect caused by the MgAl2O4 particles, so the micron alumina with smaller particle size is more efficient (10 wt% addition: the residual strength ratio from 93.48 % to 65.13 %–113.92 % and 94.47 % after one and five air-quenching). Therefore, this work demonstrates a novel synthetic strategy for porous ceramics with great potential in the field of high-temperature thermal insulation.

Introduction: Polyetheretherketone, also known as PEEK, is a semicrystalline thermoplastic material with many advantages. Since its grey material, it has to veneering with composite resin to enhance its aesthetic appeal. Bonding PEEK and composite veneers poses challenges due to its inert surface. Aim: To assess and compare the Shear Bond Strength (SBS) between various polyetheretherketone materials and veneering composites following various surface treatments. Materials and Methods: The in-vitro study was conducted at KSR Dental College and Hospital in Tiruchengode, Tamil Nadu, India, over a period of three months from December 2022 to February 2023. A total of 108 PEEK discs were prepared for the study, divided into three groups: unfilled PEEK, 30% carbon reinforced PEEK, and 10% carbon + 10% graphite + 10% Polytetrafluoroethylene (PTFE) reinforced PEEK. The specimens underwent different surface treatments, including no treatment, sandblasting with 110 um alumina particles, and acid etching with 98% sulphuric acid. Additionally, 108 composite discs were prepared and bonded to the PEEK specimens using adhesive and resin cement. The bonded specimens were immersed in distilled water for 24 hours, and the Shear Bond Strength (SBS) was determined using a universal testing machine. Statistical analysis was performed using one-way ANOVA, and mean values were compared using posthoc tests. Results: The results indicated significant variation in SBS among the three groups without treatment (p=0.011) and after sandblasting with 110 um alumina (p=

In this work, refractory components based on alumina were produced by binder jetting using a large-scale 3D printer. The formulation contained several particle fractions up to a grain size of 3 mm, equal to the printer resolution. The binder system contained fine dead burnt magnesia, milled citric acid and reactive alumina, which were added to the aggregate mixture to create the powder bed. Deionized water was deposited from the printer's nozzles and triggered the binding reaction between the magnesia and citric acid. After 24 h, the printed samples were removed from the powder bed, dried and sintered at 1600 °C for 5 h. Reactive alumina contributed to the in situ creation of magnesium aluminate spinel at high temperature. The samples were characterized in terms of Young's modulus of elasticity, bending and compressive strength in 2 directions (parallel and perpendicular to the printing direction). The broken parts were used to investigate physical properties such as the open porosity and bulk density. The microstructure was studied by means of computed tomography. Finally, powder samples were used to determine the phase composition at different stages of production by means of XRD.

MgO and Al2O3 are two typical ceramics with high secondary electron yield (SEY) and are widely applied in electron multiplier devices as dynode coating. However, dynodes in multipliers are inevitably exposed to various environments, degenerating their SEY performance. To specify the influence of the atmospheric environment on SEY for MgO and Al2O3 ceramics, we conducted environmental stability experiments on MgO and Al2O3 nanofilms. By exposing the nanofilms fabricated by atomic layer deposition to air for certain durations, it was found that although the MgO film possessed high SEY, its SEY decreased significantly as the storage duration increased, specifically, its SEY peak value (δ m) decreased from 5.97 to 3.35 after 180 d. Whereas the SEY of the Al2O3 film changed very little with the storage duration extending, its δ m decreased from 4.01 to 3.70 after 180 d, indicating the Al2O3 film had good SEY environmental stability. To reveal the mechanism of SEY degradation, the modification analysis of surface composition was implemented. It was found that the surface of MgO film underwent degradation besides unavoidable contamination, generating Mg(OH)2 and MgCO3. Whereas, there is no chemical reaction occurred on the Al2O3 surface. Combining the advantages of high SEY of MgO and good environmental stability of Al2O3, several Al2O3/MgO double-layer nanofilms were prepared. The δ m value of 20 nm MgO nanofilms covered by 1 nm Al2O3, decreased from 4.90 to 4.56, with a reduction of only 6.94% after 180 d. The results showed that the Al2O3 film achieved effective protection of the MgO film. The SEY environmental stability of the double-layer structure was significantly improved, and the effect of thickness on SEY was theoretically interpreted. This work makes significant sense for understanding the influence of the environment on the SEY for MgO and Al2O3, which has potential applications in electron multipliers. [ABSTRACT FROM AUTHOR]

The study aimed to explore synergies resulting from the combination of dry reforming and partial oxidation of methane, using 10%Ni/Al 2 O 3 –CeO 2 catalysts with varying CeO 2 proportions (10, 30, 50, and 70 wt%). The manufacturing involved mechanochemical and impregnation methods for supports and catalysts, respectively. The inclusion of 10 wt% CeO 2 played a crucial role in enhancing nickel dispersion and reinforcing interaction with the support. Particularly noteworthy was the exceptional performance of the 10%Ni/Al 2 O 3 –10%CeO 2 catalyst, achieving an impressive 83% methane conversion at 700 °C, surpassing other prepared nickel-based catalysts. The introduction of a small quantity of O 2 during methane dry reforming, inferred from TPO and FESEM analyses, effectively mitigated carbon deposition. Demonstrating remarkable endurance, the catalyst 10%Ni/Al 2 O 3 –10%CeO 2 maintained efficacy for 440 min at 700 °C, yielding CH 4 and CO 2 conversion rates of 93% and 34%, respectively. Higher calcination temperatures led to nickel particle aggregation, causing a decline in catalytic efficiency. • Dry reforming and partial oxidation of methane were done on Ni/Al 2 O 3 –CeO 2 catalyst. • The Ni/Al 2 O 3 –10CeO 2 possessed the best efficacy among the investigated samples. • Introducing oxygen during reforming significantly reduced carbon formation. • Higher reduction temperature boosts stability and performance. • Higher T calcination reduces BET area, lowering performance via particle sintering. [ABSTRACT FROM AUTHOR]

Powder bed fusion (PBF) is an additive manufacturing (AM) technique that holds a great promise for alumina ceramic materials to be processed in a one step. To ensure an effective outcome, the powder material should be thoroughly tailored, and the process parameters should be appropriately investigated. These process parameters include laser power, scanning speed, hatching space, and scanning strategies. The alumina powder has been tailored and modified to be appropriately used for PBF using the spray-drying technique, and the process parameters have been predicted and selected using a developed numerical model. Different scanning speeds of 100, 200, 300, and 400 mm/s have been considered, and the other parameters have been numerically predicted. The results demonstrated that spray drying is an effective technique for tailoring the characteristics of alumina powder, such as particle shape, particle size distribution, flowability, and absorptivity, making it ideally suited for PBF processing. Furthermore, the developed numerical model demonstrated outstanding reliability in predicting the most effective laser power and hatching space for different scanning speeds, resulting in significant cost and time savings when compared to relying solely on experimental trials. Employing a scanning speed of 400 mm/s yielded a significant improvement in relative density and quality of the printed samples surpassing other scanning speeds. Moreover, this speed effectively addressed various challenges encountered by other scanning speeds. Following the optimization of process parameters, it was determined that a relative density of 94.5% could be achieved by utilizing a scanning speed of 400 mm/s, a laser power of 210 W, and a hatching space of 30 µm. However, the evaluation of mechanical performance revealed that while the microhardness of the printed alumina samples matched the values reported in the literature, the attained compressive strength fell significantly below the values reported in the literature. [ABSTRACT FROM AUTHOR]

Low temperature enamel (LTE) coating has advantages in material durability, hardness, corrosion resistance, and high-temperature tolerance, but shows unsatisfying abrasion resistance due to its brittle nature. Here, alumina was added to the LTE coating with contents of 0, 5, and 10 wt%. The thermal stability of alumina in the LTE matrix and the microstructure, phase composition, microhardness, impact resistance, adhesion strength, abrasion resistance, and corrosion protection properties of different LTE coatings were investigated. Results indicated that alumina had high thermal and chemical stabilities in the LTE matrix without affecting the pore structure of the coating. As an abrasion-resistant filler, alumina increased the hardness and impact resistance of LTE coatings while reducing adhesion strength. In the abrasion test, alumina showed an advantage in delaying the formation and expansion of cracks, and the alumina-enhanced LTE coating demonstrated a 70 % reduction in mass and thickness losses when compared to pure LTE coating. In particular, all LTE coatings survived 8000 cycles of abrasion without significant degradation in corrosion protection. The findings of this study confirmed the feasibility of alumina as an abrasion-resistant filler and provided a modified LTE coating for coupled corrosion and abrasion conditions. [ABSTRACT FROM AUTHOR]

Aluminum nanocrystals (AlNCs) are of increasing interest as sustainable, earth-abundant nanoparticles for visible wavelength plasmonics and as versatile nanoantennas for energy-efficient plasmonic photocatalysis. Here, we show that annealing AlNCs under various gases and thermal conditions induces substantial, systematic changes in their surface oxide, modifying crystalline phase, surface morphology, density, and defect type and concentration. Tailoring the surface oxide properties enables AlNCs to function as all-aluminum-based antenna-reactor plasmonic photocatalysts, with the modified surface oxides providing varying reactivities and selectivities for several chemical reactions. [ABSTRACT FROM AUTHOR]

A ceramic-metal composite was produced by using the sol–gel method and the electrospinning technique as a potential enhancement substrate for infrared spectroscopy. The precursor solution of tetraethyl orthosilicate, aluminum nitrate, and zirconium butoxide was mixed with polyvinylpyrrolidone and then electrospun into nonwoven fibrous membranes. The membranes were sintered, decorated with silver nanoparticles, and characterized by using scanning electron microscopy (SEM), X-ray diffraction (XRD), and attenuated total reflectance-Fourier transform infrared spectroscopy (ATR-FTIR). The ceramic membranes were composed of cylindrical fibers with an average diameter of ∼190 nm with a smooth surface and spherical particles with an average diameter of ∼9 nm embedded evenly on top. The enhancement capacity of the substrates was tested using pyridine at different concentrations with infrared spectroscopy. An enhancement factor of approximately 1 × 106 times for the signal of pyridine 1 nM was achievable, showing the material is a promising alternative to a low-cost nanostructured surface enhancement substrate for infrared spectroscopy. [ABSTRACT FROM AUTHOR]

The viscosity properties of GNP-alumina hybrid nanofluids are of significant importance in various engineering applications. This study compares the predictive performance of response surface methodology (RSM), artificial neural network (ANN), and adaptive neuro-fuzzy inference system (ANFIS) for the viscosity (µrel) and relative viscosity (µrel) of GNP-alumina hybrid nanofluid at varying mixing ratio (0–3) and temperature (15–55 °C). The ANN and ANFIS models were optimised by varying the number and type of neurons and membership functions (MFs), respectively. In contrast, the RSM model was optimised by varying the source model. The efficacy of the models was assessed using various measures of performance metrics, including residual sum of squares, root mean square error, mean absolute error, and mean absolute percentage error (MAPE). The ANN architecture with 4 neurons exhibited exceptional proficiency in forecasting the µnf, achieving an R2 value of 0.9997 and a MAPE of 0.3100. Meanwhile, the best ANN architecture for the µrel was achieved with 5 neurons, resulting in an R2 of 0.9817 and MAPE of 0.2588. Furthermore, the ANFIS model with the difference of two sigmoidal MFs and the product of two sigmoidal MFs for µnf and Generalized Bell MFs for µrel exhibited the best performance with (3 5) and (4 5) input membership functions, respectively. An R2 value of 0.9999 and 0.9872, with a corresponding MAPE value of 0.0945 and 0.1214, were reported for the optimal ANFIS architecture of µnf and µrel, respectively. The RSM model also produced its most accurate prediction with the quadratic model for both µnf and µrel, with an R2 value of 0.9986 and 0.8835, respectively. Thus, comparative analysis across various models indicated that the ANFIS model outperformed others regarding performance metrics for both µnf and µrel. This study underscores the potential of ANN and ANFIS models in accurately forecasting the viscosity properties of GNP-alumina hybrid nanofluids, thus offering reliable tools for future applications. [ABSTRACT FROM AUTHOR]

Manufacturing thick (>10 mm) alumina (Al2O3) parts through the ceramic additive manufacturing technique of digital light processing (DLP) is difficult due to the large amount of polymer that must be removed. Nearly 35–65 vol% of a fugitive UV‐curable polymer is used in commercial ceramic slurries in order to maintain shape through the DLP process. During the thermal debind, gases form and escape quickly due to pressure build‐up, leading to defects in the form of print layer delamination. Here, we analyze the polymer decomposition through thermogravimetric analysis in order to design a less aggressive thermal debind schedule through strategic thermal holds and decreased heating rates. The new schedule led to a 83% reduction in average delaminations per sample (from 6.9 delaminations per sample to 1.2 delaminations per sample) and up to a 100% increase in wall thickness (from nominally 10–20 mm). A complex, Al2O3 turbine rotor (with maximum wall thickness of 5 mm in the center hub section) of a JetCat P400 engine was fabricated to compare the new schedule to the manufacturer provided one. The improved thermal debind schedule produced a turbine rotor with no observable delamination defects. [ABSTRACT FROM AUTHOR]

This paper presents the development of yttria‐stabilized zirconia–alumina (YSZ–Al2O3) nanocomposite coatings deposited on Inconel 738LC superalloy substrates using the electrophoretic deposition technique. To prepare stable suspensions of YSZ and Al2O3 nanoparticles, a mixture of 75 mL acetone and 25 mL ethanol was used as a medium with.4 g/L iodine as a dispersant. The effects of Al2O3 concentration on suspension stability, electrical conductivity, and pH were studied in detail to optimize the suspension chemistry. The deposition kinetics were systematically investigated as a function of suspension concentration, deposition voltage, deposition time, and iodine concentration (CI2${C}_{{{\mathrm{I}}}_2}$) to optimize the process parameters. The as‐dried coatings deposited at Vd = 10 V for 90 s were uniform, crack‐free, and sintered at 1150°C for 4 h. The microstructure, phase composition, hardness, and adhesion strength of the coatings were analyzed using scanning electron microscopy, X‐ray diffraction, Vickers microhardness measurements, and conducting shear loading tests, respectively. The results showed that adding Al2O3 to YSZ reduces porosity, crack density, and sintering temperature while stabilizing the tetragonal phase and retarding the martensitic transformation and crack formation. Among the studied coatings, the YSZ–20 wt.% Al2O3 nanocomposite coating deposited at Vd = 10 V for 90 s exhibited the most improved microstructural features, hardness, and adhesion strength. [ABSTRACT FROM AUTHOR]

Preceramic polymers are of interest for use in many manufacturing techniques such as injection molding, ceramic fiber infiltration, and additive manufacturing. However, off‐gassing of low molecular weight oligomers occurs when these polymers cure, potentially leading to porosity in the cured part. To study how porosity and strength are affected by the size of the printed part, and the presence of a high surface area nano‐scale filler, polycarbosilane (PCS) microrods of varying diameter were fabricated via direct ink writing (DIW), an additive manufacturing technique, with two ink formulations containing either zirconium diboride (ZrB2) alone, or ZrB2 and fumed alumina (FA). Sets of microrods were printed in a range of sizes by using print nozzles of 450, 634, 979, 1 346, or 1 702 μm in diameter, which were thermally cured, pyrolyzed to form ceramic composite microrods, and tested in 3‐pt flexure. Porosity increased with increasing diameter, while failure strength decreased. For a given nozzle size, the microrods containing FA displayed lower porosity and higher strength (up to ∼500 MPa) compared to the microrods containing only ZrB2. Weibull strength analysis was performed on each group of microrods and shows that the addition of FA increased Weibull modulus from 4.63 ± 1.56 to 9.35 ± 0.601. In conjunction with optical microscopy, this analysis indicates two distinct flaw populations in the printed materials, porosity which arises during the curing step and cracking which arises during pyrolysis of the larger specimens. [ABSTRACT FROM AUTHOR]

Anisole (methoxybenzene) often serves as a potent biomass model compound in hydrodeoxygenation (HDO) reactions with the primary aim to underpin conditions and operations that facilitate conversion of bio-oil into non-oxygenated fuel. However, the majority of studies in literature has focused on its HDO in a solvent environment under excessive conditions of high hydrogen flow rate and elevated pressures. Herein, we investigate HDO of an evaporated stream anisole on a continues flow reactor over four combination of Ni/Co catalysts supported on Zeolite or Al2O3. Catalysts were characterized by various methods which span XRD, SEM-EDS and TPR. The reaction was carried out between 300–600 °C. The highest conversion at 87% was acquired using the Ni–Co/Zeolite catalyst (87%) while producing high yield of phenols and cresols. Synergistic effects brought by the incorporation of Co in the lattice of the catalyst has been discussed. Overall, we obtained a viable HDO path for this biomass model compound using combination of different supported catalysts at moderate operational conditions (relatively intermediate temperatures, ambient pressure, and low H2/Feed ratio). [ABSTRACT FROM AUTHOR]