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The atomic-level structure of interfaces between Pt and a transition form of Al2O3 were studied using a combination of electron microscopy and first principles calculations. A model system of Pt nanoprecipitates in Al2O3 were formed in sapphire wafers via high-energy ion implantation of Pt followed by thermal annealing at 1000 °C in air. The Pt nanoparticles took the form of tetrahedra and truncated tetrahedra primarily bound by {111}Pt facets. The high prevalence of these facets motivated the development of density functional theory (DFT) based models of (111)Pt interfaces with six different chemical terminations of (2¯01) θ-alumina. The atomic-level structure of the Pt/Al2O3 interfaces was characterized with aberration-corrected scanning transmission electron microscopy (STEM) and the experimental images were compared to STEM image simulations of the DFT models. The model interface with Pt bonded to oxygen-terminated θ-Al2O3, with the Pt located on top of the O and with an underlying layer of octahedral Al, provided the best match to the experimental images. This interfacial termination is also the most stable for the thermal annealing conditions used based on thermodynamic calculations of the interfacial energy as a function of temperature and oxygen partial pressure. This experimentally verified model provides a basis for improving models of Pt/γ-alumina interfaces.

The barium titanate derivative Ba 0.85 Ca 0.15 Zr 0.1 Ti 0.9 O 3 (BCZT) offers high dielectric and piezoelectric performance but has poor mechanical properties. Ceramic composite materials combining BCZT with tougher Al 2 O 3 or ZrO 2 could be the solution to the inherent brittleness of electroceramics. This work focuses on BCZT with 1–5 vol% addition of reinforcing phase dispersed in the microstructure. While hardness was improved in all composites, especially in ZrO 2 -reinforced BCZT, toughness was positively affected only by Al 2 O 3. The chemical reactivity of BCZT during sintering resulted in the formation of new barium aluminate phases at the grain boundaries and possibly also within the grains, which affected the electrical properties of the composites. The addition of zirconia resulted in the formation of BaZrO 3 or Ba(Zr,Ti)O 3 , which is a natural part of the BCZT solid solution and shifts the phase composition towards relaxor behaviour. ZrO 2 -reinforced composites exhibited higher permittivity but lower ferroelectric properties, accompanied by a substantial Curie temperature decrease. [ABSTRACT FROM AUTHOR]

Al2O3/Castor oil, Al2O3/polyurethane (PU) prepolymer suspensions, and Al2O3/PU thermally conductive adhesives with different loadings (w(Al2O3)) and particle sizes of Al2O3 were prepared. The dynamic rheological behavior of the suspensions was characterized, and the linear viscoelastic data were fitted and quantitatively analyzed by using a twophase model. At the same time, the effects of the loading and particle size of Al2O3 on the lap shear strength and thermal conductivity of the thermally conductive adhesives were investigated. The correlation among rheological property, structure and property was explored. Results show that when w(Al2O3) is more than 80%, the second plateau region appears in the storage modulus (G') versus frequency (ω) curve, which corresponds to the formation of the percolation network. The strain amplification factor and the viscoelastic contribution factor increase, while the gel point moves towards the low-frequency region with the increase of volume fraction of Al2O3 (φ). With a fixed loading of 80%, the viscoelastic contribution to the suspension increases as the Al2O3 particle size decrease With a particle size of 70 μm and 80% loading of Al2O3, the lap shear strength of Al2O3/PU thermally conductive adhesives on aluminum alloy and stainless steel reaches 21.38 MPa and 25.85 MPa, respectively, and the thermal conductivity is the highest at 1.38 W/(m·K), which is related to the decreased Al2O3- PU phase interface and the formation of thermally conductive percolation network. [ABSTRACT FROM AUTHOR]

γ -alumina is highly employed as support for hydrotreatment catalysts prepared by impregnation and as adsorbent in water treatment. These applications consist of contacting γ -alumina with aqueous solutions, leading to the transport of ions inside the alumina pores and their adsorption on the pore surface. These physicochemical phenomena are governed by the γ -alumina pore surface and the solution characteristics. Predicting the physicochemical phenomena at the liquid/solid interface is crucial to optimize the design of catalysts and of water treatment adsorption processes. However, this is very challenging using conventional analytical techniques. In this work, the diffusion of protons and their counter-ions inside γ -alumina pores and the adsorption of protons on the pore surface are modeled at unsteady state during contact with acid solutions at different initial pH levels. Diffusion inside pores is represented using a combination of the zero current method and the Poisson-Boltzmann equation, while the proton adsorption is described by the Langmuir adsorption isotherm. Simulations agree well with the results of proton adsorption experiments in a batch system. The model accurately predicts the distribution of species inside the electrostatic double layer at the liquid/solid interface. It also computes the surface charge and the maximal adsorption capacities of different types of hydroxyl sites present on the alumina pore surface; both are very difficult to determine experimentally. This model can serve as a guide for the comprehension of the liquid/solid interface inside γ -alumina structures and their interaction with aqueous solutions during the initial stages of impregnation. [ABSTRACT FROM AUTHOR]

It is demonstrated by means of ultra high vacuum (UHV) surface‐sensitive techniques and periodic density functional theory (DFT) calculations that the electronic and NO− adsorption properties of nanosized Ni clusters deposited onto the α‐Al2O3 (0001) surface significantly depend upon the size of the cluster. The properties of the Ni cluster of the size of 2 nm and lower are predominantly determined by the formation of the Ni/Al2O3 interface bond notably polarized towards the oxide. As a result, the metal cluster acquires a net positive charge manifested by the bond strengthening of adsorbed NO compared to the bulk Ni substrate. With the increasing size of the cluster, the Ni/Al2O3 interfacial bond depolarizes due to the growing of lateral Ni–Ni interaction. With a mean coverage of Ni on the alumina surface exceeding 0.25 equivalent monolayers, their properties in terms of adsorption behavior of NO resemble those that are characteristic for the bulk Ni substrate. Such a size dependence offers an opportunity to tune the properties of metal clusters and the metal/oxide system as a whole, for example, to achieve the required electronic and adsorption‐reaction properties. [ABSTRACT FROM AUTHOR]

Zirconia/alumina composites are a family of structural ceramics with excellent mechanical properties. In order to improve the engineering reliability of this kind of composites, the uniform spatial distribution of the two phases is necessary. One of the effective methods to achieve this goal is to synthesize uniform zirconia–alumina composite nano powders. Here, we report mechanochemical synthesis of zirconia–alumina composite nano powders, in which dehydration and crystallization of Zr–Y–Al hydroxide can be achieved under milling conditions, leading to the formation of the tetragonal zirconia phase with supersaturated Al3+. The mechanochemically synthesized powders have the uniform element distribution and a fine primary crystallite size of around 11 nm. After sintering at 1400°C, t‐ZrO2/α‐Al2O3 composite with the uniform phase distribution and grain size distribution could be obtained. To uncover the full benefits of these supersaturated composite powders in ceramic processing, future work could be done to break up the deagglomerations and improve the sinterability of the mechanochemically synthesized zirconia/alumina powders. [ABSTRACT FROM AUTHOR]

Copyright of Nonferrous Metals (Extractive Metallurgy) is the property of Beijing Research Institute of Mining & Metallurgy Technology Group and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

It is demonstrated by means of ultra high vacuum (UHV) surface‐sensitive techniques and periodic density functional theory (DFT) calculations that the electronic and NO− adsorption properties of nanosized Ni clusters deposited onto the α‐Al2O3 (0001) surface significantly depend upon the size of the cluster. The properties of the Ni cluster of the size of 2 nm and lower are predominantly determined by the formation of the Ni/Al2O3 interface bond notably polarized towards the oxide. As a result, the metal cluster acquires a net positive charge manifested by the bond strengthening of adsorbed NO compared to the bulk Ni substrate. With the increasing size of the cluster, the Ni/Al2O3 interfacial bond depolarizes due to the growing of lateral Ni–Ni interaction. With a mean coverage of Ni on the alumina surface exceeding 0.25 equivalent monolayers, their properties in terms of adsorption behavior of NO resemble those that are characteristic for the bulk Ni substrate. Such a size dependence offers an opportunity to tune the properties of metal clusters and the metal/oxide system as a whole, for example, to achieve the required electronic and adsorption‐reaction properties. [ABSTRACT FROM AUTHOR]

Transition to the Net‐Zero economy requires new sources of energy. Hydrogen is one of the promising candidates to replace carbohydrates. Emission‐free technologies for hydrogen production are pivotal for this transition. However, the existing technologies to produce hydrogen are either polluting or energy‐intensive. In recent years, a reaction of aluminum with water generating hydrogen has attracted a lot of attention. Most of the research is done with solid aluminum and analyzed mostly from the chemical and energy points of view. In this overview paper, rarely mentioned metallurgical aspects of this reaction are considered, as well as potential integration of the related technology into a green aluminum production cycle. The advantages of using liquid aluminum as well as related safety aspects are highlighted. [ABSTRACT FROM AUTHOR]

In the past decade, it has been observed that polymer nanocomposite industrialisation is increasing due to several advantages. So, this area is becoming vital for researchers for making new material as per technical applications. Polymer nanocomposite can be made from different types of polymers and involves one or more nanofillers coupled with it. A major application of such polymer is in the aerospace and automotive industries. In this review, several metal oxide nanofillers and their hybrid state are chosen for understanding benefits in tribology throughout recent decades. Observation of friction and wear enhancement with several other technical circumstances are taken into account from various articles of metal oxide nanofiller in polymer nanocomposite. Alumina, zinc oxide, and titanium oxide are found to be most used among other metallic nanofillers for most polymer nanocomposite fabrication in the tribology area. [ABSTRACT FROM AUTHOR]

High temperature and ultrafast heating rate, the characteristics of ultrafast high‐temperature sintering (UHS) process, make it difficult to capture the evolution of sintering behavior and explore sintering mechanism of alumina ceramics. In this study, molecular dynamic simulations are adopted to describe the sintering behaviors of equal‐sized and unequal‐sized alumina nanoparticles, particularly about shrinkage behaviors, microstructure evolution and atomic migration. Results show that high temperature and ultrafast heating rate can yield two different abnormal shrinkage behaviors, accelerating the polymerization of the nanoparticles. The main mechanism for this phenomenon is that high temperature causes the amorphization of crystal structure of nanoparticles, and ultrafast heating rates retain larger sintering driving forces at high temperatures, leading to the reduction of diffusion activation entropy and migration barriers. In particular, the appearance of viscous flow further enhances the shrinkage of the nanoparticles. In addition, surface diffusion is found to dominate the growth of sintering neck during this period. These findings are expected to deepen the understanding of ultrafast high‐temperature sintering mechanism. [ABSTRACT FROM AUTHOR]

Highlights In recent years, 3D printing technologies or additive manufacturing have gained significant attention in research and other industries. Among the various 3D printing techniques, fused deposition modeling has been the most widely adopted. This study focused on developing composite filaments by incorporating acrylonitrile butadiene styrene (ABS) with different volume percentages of aluminum oxide (alumina). The mechanical and physical properties of parts printed with these composite filaments were thoroughly evaluated. Tensile testing revealed that increasing the alumina content led to a reduction in tensile strength. At 20 vol%, tensile strength dropped by 72%. A heat deflection temperature (HDT) test indicated an 11% reduction in HDT, likely due to the defective composite structure. Thermogravimetric analysis test demonstrated improved thermal stability as alumina content increased. Linear shrinkage was measured in three directions, revealing anisotropic shrinkage patterns. Hardness tests were conducted, and a decrease was observed when the polymer was filled with alumina. Finally, the warpage was reduced by 91% as alumina content increased to 20%. Alumina/ABS composite filaments were manufactured and 3D‐printed very well. The void content in composite samples increases with alumina powders. The mechanical properties of 3D‐printed composite parts were decreased The alumina powder improves the warpage issues in 3D‐printed parts. [ABSTRACT FROM AUTHOR]

AbstractEvaluate the remnants of blasted alumina particles after cleaning by different protocols on intact, or resin coated dentine substrates, before or after aging. Seventy-eight mid-coronal dentine specimens were prepared. Six of them were kept intact as negative control (NC) group. At the same time, the other seventy-two were divided into three groups. They received three different dentine treatments: (1) sandblasted (S), (2) resin coated and blasted (RS), (3) resin coated, aged one week, and sand blasted (RAS). Subsequently, each group was cleaned via four sub-group protocols: (1) not cleaned, (2) air/water spray (A/W), (3) etched & A/W, and (4) water jet. Finally, five FE-SEM micrographs were taken from each tooth, and the number of remaining Al2O3 particles was counted on each picture. The numerical data were compared with each other using Two Way ANOVA and LSD post hoc tests (α = 0.05). Most Al2O3 particles were detected on uncleaned specimens, while all the other sub-groups displayed very few or no Al2O3 particles. Statistical analyses revealed that the dentine treatment and cleaning protocol significantly affected the remaining Al2O3 particles (p = 0.000 and 0.000, respectively). Moreover, the interaction of dentine treatment and cleaning protocol was statistically significant (p = 0.000). Cleaning protocols (A/W, etching, and water jet) could effectively remove the remnant of Al2O3 particles from the blasted dentine surface, either resin coated or not. [ABSTRACT FROM AUTHOR]

The interactions of dendrimers having a phosphorus atom at each branching point, of type poly(phosphorhydrazone) (PPH), with different types of materials based on silicon and aluminum are reviewed. These dendrimers can be used for the functionalization of solid surfaces at the nanoscale, either by covalent immobilization, or by electrostatic interactions, especially for constructing perfectly controlled multi‐layers by layer‐by‐layer (LbL) deposit. The properties of such hybrid materials as chemical sensors, as very sensitive biological sensors, as well as substrates for the growing of cells are described. The PPH dendrimers can also be embedded inside materials. The resulting hybrid materials have been used for the capture of pollutants, in particular CO2 in air and chromate and methylene blue in waste water. [ABSTRACT FROM AUTHOR]

The SiO 2 -Al 2 O 3 refractories and corresponding inks for 3D printing were prepared from silica glass binder suspensions and fused alumina with grain sizes of 75 and 240 μm. Phase analysis (XRD) and morphological studies (SEM) were conducted to investigate the influence of sintering temperature and Al 2 O 3 content on the strength, porosity, and density of the refractories. Rheological studies (rotational viscometry) were carried out determine the effect of polyethylene glycol (PEG) and hydroxypropyl methylcellulose (HPMC) content on the flow behavior of the inks. It was established that firing refractories based on fused silica and fused alumina at 1500 and 1600 °C led to the formation of mullite and aluminosilicate melt on the surface of Al 2 O 3 grains, enhancing the strength of the synthesized materials. Addition of PEG and HPMC to the ink composition was found to improve their rheological properties by increasing yield strength and promoting plastic flow. The ink demonstrated high printability and they are suitable for producing refractories using the Direct Ink Writing method. [ABSTRACT FROM AUTHOR]

Geopolymers represent a distinct class of materials characterised by their X-ray amorphous nature and nanoporous, nanoparticulate structure. Geopolymers can be conveniently mixed, poured, and cured under ambient conditions. This makes this class of materials an interesting alternative to ordinary Portland cement for structural processes. Additionally, the addition of alumina can improve mechanical properties, while the addition of glass can form an impermeable glaze which could be useful for molten salt containment. Therefore, in this investigation, potassium metakaolin-based geopolymer composites with varying proportions of glass particles and alumina platelets were fabricated, cured, heat-treated, and analyzed to study the effects of composition on material properties. Various attributes including rheological properties, densities, mass loss, shrinkage, and porosities were compared. It was observed that certain compositions exhibited high viscosities, making high shear mixing challenging, while also displaying significant permeability that would hinder their ability to contain liquids without leakage. Additionally, certain samples showed reduced densities, suggesting potentially weaker mechanical properties; however, the investigation did not include a direct assessment of mechanical properties. The most promising candidates for containing liquids at high temperature contained 50 wt% KGP, 25 or 35 wt% glass powder, and 25 or 15 wt% alumina platelets, respectively. ASH-G slurries required a minimum of 65 vol% KGP to produce a homogenous material compatible with additive manufacturing. The minimum amount of glass phase to form surface glazes was 16 vol%. Only samples containing more glass phase than alumina phase produced glazed composites. [ABSTRACT FROM AUTHOR]

This work addresses the challenges in brazing thermohydraulic sealings involving dissimilar materials, specifically 316Ti stainless steel and alumina, which have significantly different coefficients of thermal expansion (CTEs) and elastic constants. Traditional brazing methods require complex interlayers or extensive metallization steps, leading to issues such as dimensional changes, braze voids, and inadequate corrosion resistance due to prolonged high‐temperature exposure. A novel laser‐based brazing technique utilizing a diode laser is introduced to create high‐quality, localized joints while preserving the integrity of the parent materials. The study systematically optimizes laser process parameters using finite‐element modeling and the Taguchi method to achieve the desired bead geometry and thermal stress distribution with minimal heat input. Comparative analysis between laser active brazing (LAB) and conventional furnace brazing was conducted through metallography, shear testing, and autoclave testing. Results indicate that LAB parameters significantly affect bead thickness and shear strength, with laser‐brazed joints demonstrating superior quality and stability post‐autoclave testing compared with furnace‐brazed joints. The thermodynamic and kinetic aspects of the brazing process were also analyzed. In conclusion, the LAB method for brazing 316Ti to alumina proves to be a successful and efficient alternative, with joint properties meeting or exceeding those of traditional furnace brazing. [ABSTRACT FROM AUTHOR]

Volatility of technetium poses a challenge during the vitrification of low-activity waste (LAW) feed to glass. Although this is typically resolved through recycle loops, this can lead to other problems, such as sulfate phase formation. Thus, ensuring high single-pass retention of Tc (or Re, its non-radioactive surrogate) is required for enabling high waste-loading formulations. In our previous study, we observed significantly higher Re retention in final waste glass produced from a LAW melter feed containing gibbsite as the alumina source compared to a compositionally similar feed containing kyanite. To investigate this effect, we prepared representative LAW melter feeds with kyanite and gibbsite as alumina sources and measured the Re retention in the produced glasses. We found that the Re retention is consistently higher in glasses produced with gibbsite, by up to 20 %. We attribute this result to the formation of nanocrystalline alumina in melter feeds containing gibbsite. Possessing a high surface area, nanocrystalline alumina can adsorb the perrhenate-containing molten salt, increasing the rate at which Re is incorporated into the alkali-alumino-boro-silicate glass-forming melt. In addition, we demonstrate that replacing kyanite with gibbsite in LAW melter feeds has no adverse effects on their processing during vitrification. [ABSTRACT FROM AUTHOR]

To enhance the bio-based synthesis of acrolein from glycerol, a hybrid approach combining in situ nonthermal plasma (NTP) with thermo-catalytic dehydration was employed. This study investigated the impact of the reaction temperature and NTP discharge field strength on glycerol conversion, acrolein selectivity, byproduct formation, and coke deposition using two catalysts of silicotungstic acid supported on mesoporous alumina and silica. The results revealed that, while the reaction temperature and NTP field strength exhibited complex interactions, the in situ application of NTP markedly improved both glycerol conversion and acrolein selectivity when optimized for specific temperature–NTP field strength combinations. Additionally, the reaction mechanisms of glycerol dehydration with the two catalysts, in the presence and absence of NTP, were systematically analyzed and discussed based on the experimental data. [ABSTRACT FROM AUTHOR]

The conversion of bioethanol to ethylene in gas phase and atmospheric pressure was investigated over γ‐Al2O3 supported copper and nickel catalysts. These catalysts were prepared by co‐precipitation and pre‐treated with hydrogen at 450 °C. Six catalysts were studied at 450 °C under a nitrogen atmosphere. It was found that the monometallic Cu/γ‐Al2O3 catalyst exhibited the highest ethylene concentration, with a selectivity of around 90 %. The bioethanol conversion obtained was between 57 %‐86 %. Another catalyst that exhibited high concentration values was the NiCu1 : 7 bimetallic catalyst. The catalysts were characterised using XRD, SEM, EDS, TEM, TGA, FTIR, Raman, and N2‐physisoption techniques. Furthermore, the Cu/γ‐Al2O3 catalyst was studied under different reduction temperatures and gas flow conditions. It was found that the catalysts reduced at 350 °C and 35 ml/min N2 flow presented ethylene concentrations between (0.18–0.21) g/L. Moreover, the catalyst deactivation was identified to be first order and the equation of the Cu/γ‐Al2O3 catalyst deactivation model was determined. Carbonaceous deposits over the used sample were not detected by Raman and FTIR. It was determined that the Cu/γ‐Al2O3 catalyst deactivation could be mainly attributed to the blocking of the catalytic sites by strongly adsorbed compounds and hydroxylation of the catalyst surface. [ABSTRACT FROM AUTHOR]

Understanding the performance of polymer dielectrics at different temperatures is becoming increasingly important due to the rapid development of electric cars, electromagnetic devices, and new energy production solutions. Cyclic olefin copolymers (COCs) are an attractive material due to their low water absorption, good electrical insulation, long-term stability of surface treatments, and resistance to a wide range of acids and solvents. This work focused on the dielectric and electrical properties of cyclic olefin copolymer (COC)/Al2O3 composites over a wide range of temperature and frequency domains, from room temperature to cryogenic temperatures (around 125 K). Permittivity, electrical conductivity, and electrical modulus are given consideration. A composite of up to 50% Al2O3 mixed with COC was prepared via a conventional melt-blending method. The final samples were formed in sheets and processed using injection and extrusion moldings. It was found that formulations with Al2O3 concentrations ranging from 10 to 50% resulted in higher electrical conductivity while maintaining the viscosity of the composite at a level acceptable for polymer-processing machinery. Our data show that COC/alumina composites present substantial potential as materials for high-frequency applications, even at the regime of cryogenic temperatures. [ABSTRACT FROM AUTHOR]

Shell‐derived materials are promising heterogeneous catalysts for biodiesel production due to their nontoxic and renewable nature, but they have the disadvantage of being highly leachable. To overcome this issue, Ca(OCH3)2 formed through the reaction of CaO with methanol, and supported in turn on Al2O3 is proposed as a catalytic system for the transesterification of fresh soybean oil and waste cooking oil (WCO). First, catalysts with several Al/Ca molar ratios (0.2, 0.5, and 0.8‐AC), as well as their precursors (CaO and Al2O3) alone, were tested at 60 °C, catalyst loading 6% wt, methanol‐to‐oil molar ratio (MOR) 10, for 1 h for fresh oil, and 3 h for WCO. The 0.2‐AC catalyst generated the highest biodiesel yield for both oils. The optimum operating conditions for WCO transesterification, determined by using a univariable approach, were 60 °C, 9 wt% catalyst loading, MOR of 12.5, and a reaction time of 3 h. These improved conditions led to yields higher than 90% for pure CaO and the 0.2, 0.5, and 0.8‐AC catalysts. The density, kinematic viscosity, and refractive index of the biodiesel obtained were measured. [ABSTRACT FROM AUTHOR]

Cracks induced by internal stresses compromise the structural integrity of ceramic laminates. Such stresses can be classified into thermal stress derived from thermal expansion mismatch and shrinkage stress derived from shrinkage mismatch. Analytical models have been proposed for the former, whereas only numerical predictions have been explored for the latter. In this study, an equation is constructed to predict the shrinkage stress by modifying an elastic solution proposed in previous studies. We fabricated laminates with three‐layer sandwiched structures using only alumina specimens with high and low densities to control the shrinkage and avoid thermal mismatch. Surface cracks were initiated when the shrinkage stress exceeded the flexural strength of the surface layer. Although the original strength of the surface layer was 308.8 MPa, the laminates' flexural strength was lower than that because of shrinkage constraint. Our results demonstrate that the shrinkage stress was successfully estimated analytically using a few material properties measured in an ordinary environment. This study will ensure the structural integrity of ceramic laminates in laminate designs. [ABSTRACT FROM AUTHOR]

Freeze casting is an effective way to fabricate the porous ceramics with anisotropic and interconnected porous structures and can be used in various applications, such as filtration, adsorption, and insulation. However, the ceramic‐based scaffolds fabricated by freeze casting have the upper limit of porosity since excessively low solid content in the slurry will lead to structural instability and cracks formation in scaffolds. This study aims at combining the freeze casting and sol–gel method and developing a hybrid process to overcome the limitation of freeze casting. Besides, the effects of solid content and cooling rates on the microstructure of ultralightweight alumina scaffolds (ULASs) and their mechanical and thermal properties were investigated. Aluminum isopropoxide was selected as the precursor to conduct the hydrolysis reaction in acid environment and condensation process by heat treatment. The successfully synthesized alumina scaffolds have ultrahigh porosity (>90%), low bulk density (0.1240–0.2429 g/cm3), and low relative density (0.0314–0.0615). The anisotropic porous lamellar structure was evaluated by scanning electron microscope, µ‐CT, and mercury porosimeter. A lot of nanoscale pores are observed on the lamellae surfaces, forming the dual‐scale porous structure inside the scaffolds and contributing to higher specific surface area. The unique anisotropic structure, high porosity, and stable mechanical properties enable ULASs to deliver a low thermal conductivity of 0.2 W/m/K and large anisotropy in thermal properties, possessing great potential for thermal insulative materials. This sol–gel/freeze‐casting hybrid approach is believed to be extended to different material systems and provide promising potentials in fabricating the porous materials with various functionalities. [ABSTRACT FROM AUTHOR]

Copyright of DYNA - Ingeniería e Industria is the property of Publicaciones Dyna SL and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Air pollution, climate changes, and global warming are strongly correlated with burning huge amounts of petroleum fuels. Biodiesel has emerged as a promising alternative to alleviate these problems. Nonetheless, high density and viscosity, low energy content, and poor atomization of biodiesel restrict its widespread usage in diesel engines. The addition of nanoparticles (NPs) in biodiesel-based fuels has recently received considerable attention to modify the physicochemical properties of fuel as well as to improve the performance and emission characteristics of diesel engines. Among the various NP additives, alumina (Al2O3) NPs are of high interest owing to their excellent chemical and thermal stability, nontoxicity, high catalytic activity, etc. Hence, the present paper attempts to review the available literature concerning biodiesel fuels containing Al2O3 NPs. In this regard, the preparation techniques and physiochemical properties of these fuels including density, kinematic viscosity, cetane number, flash point, and calorific value are first discussed. Furthermore, the impact of Al2O3 NPs on the spray atomization and evaporation features of as-used fuels is investigated. Finally, the performance, combustion, and emission characteristics of diesel-fueled engines with Al2O3 NP-added biodiesel fuels are assessed. In conclusion, it was found that the use of Al2O3 NPs in biodiesel fuels can lead to enhanced engine performance by increasing the brake thermal efficiency, decreasing brake-specific fuel consumption, and lowering the emission of various harmful pollutants. The performance of Al2O3 nanoadditives for biodiesel-fueled diesel engines [ABSTRACT FROM AUTHOR]

The irregular and deep cracks induced by thermal shock in Al2O3 ceramics were repaired by applying Cu powder layer on their surface and heating at 1200 °C under an atmosphere of air. The Al-Cu-O liquid phase formed at 1200 °C by the reaction of molten Cu, oxygen, and Al2O3 phases penetrate deep into the narrow cracks, and the precipitation phases of Cu2O and CuAlO2 densely fill the crack interior. Our observation and analysis of the filled cracks and the surrounding areas of the repaired cracks, as well as the microstructural analysis results obtained through SEM-EDS and TEM observation, suggested the aforementioned crack repair mechanism. The bending strength of the coated surface after repairing the cracks is 301.8 MPa (ΔT = 300 °C), which is twice as strong as the specimen after thermal shock and 10% higher than the original strength of the base material. [ABSTRACT FROM AUTHOR]

Copyright of Bulletin of the Chinese Ceramic Society is the property of Bulletin of the Chinese Ceramic Society Editorial Office and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

This research aimed to achieve three main objectives: studying the effect of milling time on graphite exfoliation, reducing fabrication heating time to prevent aluminum carbide formation, and investigating the impact of (alumina/graphene)/silver on aluminum properties. Four aluminum nanocomposites were produced using cold and hot pressing at 560 °C for 50 min under 1000 MPa. Raman analysis confirmed graphite exfoliation with alumina to graphene after 40 h of milling. The hot-pressed aluminum-5(alumina/graphene)/10 silver exhibited the smallest crystallite size at 79.926 nm and the highest hardness at 61 HV. It also demonstrated the lowest wear rate under different applied loads (45 and 90 N). The coefficient of friction was measured under 90 N, revealing the lowest mean coefficient of friction of 0.5 for aluminum-5(alumina/graphene)/10 silver, attributed to the presence of graphene and silver as solid lubricants. Aluminum/(alumina/graphene) showed superior corrosion resistance in the absence of silver, reducing the corrosion rate from 0.01 mm/year for pure aluminum to 0.0073 mm/year with the addition of 5 (alumina/graphene). The aluminum-5(alumina/graphene)/10 silver recorded a corrosion rate of 0.0114 mm/year. [ABSTRACT FROM AUTHOR]

The demand for pellets in blast furnaces has recently increased because of their uniform shape and size, controlled chemistry, iron-enriched feed, high strength, and quality consistency. To meet this demand, low- and medium-grade iron ore fines with alumina (> 3.5 wt%) must be used for pelletization because of the limited availability of high-grade ore. The alumina present in the ore has an adverse effect on the pellet properties because of its refractory nature. Therefore, a study was conducted to optimize the firing temperature and chemistry of the feed blend to produce pellets with good pellet properties. Firing temperature (1280 °C, 1300 °C, and 1320 °C), carbon (1 and 1.2%) in the form of coke fines, and MgO (0.60 and 0.80%) in the form of dolomite were used to optimize the pellet-making process for high-alumina iron ore fines. The best result was obtained for feed blend with 1.2% carbon and 0.80% MgO fired at 1300 °C to produce pellets of cold compressive strength more than 300 kg/pellet, reduction degradation index (− 6.33 mm) near 7%, and porosity near 20%. [ABSTRACT FROM AUTHOR]

The performance of multi‐layer ceramic/composite ballistic armor consisting of Alumina, Carbon fiber, and Ultra High Molecular Weight Polyethylene (UHMWPE) under the impact of 7.62 × 51 M61 caliber armor‐piercing (AP) bullets was examined by experimental and finite element methods. The alumina ceramic thickness used in the experiments is 12 mm. The composite structure thickness used in all samples is 10 mm. Explicit dynamic analyses were also conducted using the Ls‐Dyna to verify the experimental studies. The analysis results were compared with experimental studies and evaluated by considering the damage status of the bullet and armor. According to ballistic test results, partial penetration was observed in all armor produced. The front ceramic layer caused corrosion of the bullet, and a mushrooming effect occurred on it. The carbon fiber layer has dramatically helped as an alternative or support to UHMWPE. Since the results obtained with the carbon fiber ratios used remain within the standards, it will not pose a problem regarding usage. On the contrary, using carbon fiber, which is relatively easier to produce and supply than UHMWPE and more economically suitable, will provide more significant benefits. Experimental and numerical studies have revealed consistent results for all armors. Highlights: The effect of a 7.62 × 51 armor‐piercing bullet on ceramic/composite armor was examined.Carbon fiber and UHMWPE hybrid structure was created in different thicknesses.The carbon fiber layer has dramatically helped as an alternative or support to UHMWPE.Using carbon fiber, which is relatively easier to produce and supply than UHMWPE and is more economically suitable.Experimental and numerical studies have revealed consistent results for all armors. [ABSTRACT FROM AUTHOR]

Spark plasma sintering (SPS) is one of the most promising technologies for producing polycrystalline transparent ceramics. However, it has limitations regarding the complexity of the geometries that can be produced. This study addresses these limitations by combining additive manufacturing techniques with spark plasma sintering. Additionally, a Multiphysics sintering model based on the continuum theory of sintering is employed to predict the outcomes of the SPS process, particularly the microstructure of the densified parts. As a result, the geometrically complex Al 2 O 3 transparent parts manufactured in this study exhibit a uniform microstructure, high density (∼99 %), and a linear transmittance of 16 % at 490 μm. [ABSTRACT FROM AUTHOR]

Passive daytime radiative cooling (PDRC) achieves cooling by simultaneously reflecting sunlight and radiating heat to outer space, without consuming any external energy. Traditional PDRC designs use organic materials that are prone to aging and secondary pollution under solar illumination. Here, a flexible alumina fiber membrane (FAFM) is prepared using electrospinning technology. The fiber‐membrane hierarchical structure ensures macroscopic flexibility, allowing this inorganic material to be assembled on complex surfaces just like organic materials. It can efficiently dissipate heat by emitting infrared radiation that matches the atmospheric window and scattering sunlight. Importantly, it is notable that no aging phenomenon occurs even under prolonged ultraviolet irradiation, which brings additional benefits to its green energy‐saving properties. As a result, its outstanding fire resistance and thermal insulation prevent the possibility of spontaneous combustion in extremely hot weather during the summer and may serve as a multifunctional insulation layer for buildings. This preparation method promotes surface design based on more inorganic structural materials in the future, enabling the design of more low‐cost, highly flexible inorganic PDRC materials. [ABSTRACT FROM AUTHOR]

Objectives Optimum flexural strength and viscosity are essential for longevity while efficiently handling dental luting composite. This study aims to investigate the effects of zirconia and alumina on the flexural strength (FS)and viscosity of dental cement made of silica rice husk. Materials and Methods Study groups with different percentages of weight (wt.): Group 1 (3 wt.% zirconia), Group 2 (3 wt.% alumina), and Group 3 (3 wt.% zirconia and 2 wt.% alumina), negative control specimen (0 wt.% zirconia/alumina) and Rely-X U200 (3M ESPE). A universal testing machine and a rheometer were used to test FS and viscosity, respectively. One-way ANOVA and post-hoc Bonferonni test were used for data analyses. Results and Discussion FS and viscosity for Group 3 (3 wt.% zirconia and 2 wt.% alumina) were significantly higher compared to the negative control (p<0.05). Conclusion: Adding zirconia and alumina improved flexural strength without compromising the viscosity of dental luting composite. This experimental dental luting cement using hybrid fillers could be an alternative to resin luting cement. [ABSTRACT FROM AUTHOR]

Mullite is an aluminosilicate compound that can be fabricated from various sources of raw materials. Mullite (α) was synthesized from six different mine tailings reinforced with alumina. The tailings were finely ground into powder to determine their chemical components using X‐ray fluorescence (XRF) and X‐ray diffraction (XRD) spectroscopic technologies. Silica was discovered in all the tailings in significant quantities followed by alumina (high purity α‐alumina). 50 g of the first sample which composed 68.8 w(M)/10−2 of SiO2 and 13.2 w(M)/10−2 of Al2O3 was measured, reinforced with 81.1 g of Al2O3 and subjected to a high‐energy ball mill for 30 min to enhance the reaction between SiO2 and Al2O3. The process was repeated for all six powdered tailings. Each mixture was sintered at 1100°C and 1200°C in a muffle furnace for 4 hours at a heating rate of 10°C/min. The sintered materials were characterized using SEM, EDS, XRD, and FTIR techniques. Results and analysis show a significant amount of prismatic α‐mullite formed in all six sintered samples. The formation of mullite crystals was observed to increase with an increase in temperature from 1100°C to 1200°C. The phenomenal fabrication of mullite from mine tailings is significant in ceramic technology. [ABSTRACT FROM AUTHOR]

The development of dense alumina ceramics through additive manufacturing necessitates the careful analysis of various parameters. The extrusion pressure during printing is a crucial but often overlooked factor in the literature. This study investigates the impact of extrusion pressure on the densification and mechanical properties of alumina ceramics. The primary objective is to analyze extrusion pressure to achieve superior physical and mechanical characteristics while maintaining minimal shrinkage. All other printing parameters were kept constant, and the extrusion pressure was varied from 1 to 2.85 bar during the extrusion‐based additive manufacturing of alumina green bodies. The printed and sintered samples were analyzed for linear shrinkage, density, compressive strength, and microhardness. The results indicate that an extrusion pressure in the 2.2–2.5 bar range leads to alumina ceramics with the best combination of densification and other mechanical properties. Additionally, the interparticle bonding mechanisms contributing to the improved properties of the alumina ceramics were examined. This study provides valuable insights into the role of extrusion pressure in the additive manufacturing process, underscoring its significance in achieving high‐quality alumina ceramics. [ABSTRACT FROM AUTHOR]

Massive heat generated by electronic components during continuous operation will affect the operation of the equipment, so it is of significance to face up to the heat dissipation problem of electronic packaging materials. Epoxy resin (EP) is widely applied to electronic components for its excellent electrical insulation and processability. To improve the thermal conductivity of composites, this study prepared BN-Al2O3/EP composites by adding a hybrid of modified boron nitride (mBN) and modified alumina (Al2O3) into EP. Profiting from the high thermal conductivity and low dielectric constant of BN and Al2O3, the thermal and dielectric properties of EP composites were improved. Specifically, the composite of 4 wt.% BN-3 wt.% Al2O3 not only occupied the high thermal conductivity 0.25 W/(m K) at 50°C, but also kept the relatively inferior dielectric constant (4.27) and the low dielectric loss (0.0037) at 102 Hz. The composite could be applied in electronic packaging materials as it has excellent dielectric properties and high thermal conductivity. [ABSTRACT FROM AUTHOR]

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The aim of this study is to provide tailored alumina particles suitable for reinforcing the metal matrix film. The sol–gel method was chosen to prepare particles of submicron size and to control crystal structure by calcination. In this study, copper-based metal matrix composite (MMC) films are developed on brass substrates with different electrodeposition times and alumina concentrations. Scanning electron microscopy (FE-SEM) with energy-dispersive spectroscopy (EDS), TEM, and X-ray diffraction (XRD) were used to characterize the reinforcing phase. The MMC Cu-Al2O3 films were synthesized electrochemically using the co-electrodeposition method. Microstructural and topographical analyses of pure (alumina-free) Cu films and the Cu films with incorporated Al2O3 particles were performed using FE-SEM/EDS and AFM, respectively. Hardness and adhesion resistance were investigated using the Vickers microindentation test and evaluated by applying the Chen–Gao (C-G) mathematical model. The sessile drop method was used for measuring contact angles for water. The microhardness and adhesion of the MMC Cu-Al2O3 films are improved when Al2O3 is added. The concentration of alumina particles in the electrolyte correlates with an increase in absolute film hardness in the way that 1.0 wt.% of alumina in electrolytes results in a 9.96% increase compared to the pure copper film, and the improvement is maximal in the film obtained from electrolytes containing 3.0 wt.% alumina giving the film 2.128 GPa, a 134% hardness value of that of the pure copper film. The surface roughness of the MMC film increased from 2.8 to 6.9 times compared to the Cu film without particles. The decrease in the water contact angle of Cu films with incorporated alumina particles relative to the pure Cu films was from 84.94° to 58.78°. [ABSTRACT FROM AUTHOR]

Mesoporous alumina spherical particles, synthesized via spray-drying with the self-assembly of EO n PO m EO n , have been utilized for the development of clinical-grade molybdenum-99/technetium-99 m (99Mo/99mTc) generators. When evaluated as molybdenum (Mo) adsorbents, the mesoporous alumina spherical particles are useful for effective adsorption of Mo ions rather than commercially available particulate alumina. The effects of surfactant removal methods on the Mo adsorption property are also systematically investigated using the batch method. Batch adsorption studies reveal practical adsorption capacities ranging from 45.9 to 91.2 mg Mo g−1 in a Mo solution (1000 mg Mo L−1) at pH 3. The experimental results indicate the following trend in Mo adsorption capacity: solvent extraction >calcination (400 °C and 800 °C) >commercially available alumina (Medical Al2O3 used as is). To explore the feasibility of developing a clinical-scale generator, a novel tandem column generator concept is employed. Using the spray-dried and extracted mesoporous alumina, 99mTc eluted from the generator exhibits high radionuclidic, radiochemical, and chemical purity, making it suitable for the preparation of 99mTc-labeled radiopharmaceuticals. [ABSTRACT FROM AUTHOR]

This study demonstrated that high-purity alumina can be generated from kaolin using various methods. It examined different leaching techniques, considering the size and percentage recovery of alumina by weight in selected kaolin samples, the calcination temperature, and the molar concentration of acids over time. Additionally, it analyzed the characteristics of several kaolin sources in Nigeria with the aim of extracting alumina. The research indicates that Nigerian kaolinite clay typically contains 22–40% alumina by weight. However, leaching kaolin yielded alumina with a purity of 60–97 wt%, with particle sizes ranging from 16 to 177 nm. Alumina derived from kaolin is deemed beneficial for manufacturing refractory materials, water purification, and biomedical applications.

In this study, the variant effects of alumina and graphene reinforcing nanoparticle percentages on the tensile and wear properties of the nanocomposites, produced using digital light processing (DLP), were determined by employing SEM images of fracture and worn surfaces to introduce a hybrid (alumina + graphene)/PLA nanocomposite with desirable wear and mechanical properties. With the addition of alumina up to 2 wt%, the tensile strength was initially decreased exhibiting a rapid brittle fracture over the flat fracture surface. However, with a continued increase in the amount of reinforcing particles, the tensile strength eventually increased by 16% compared to the pure resin sample at 8 wt% of alumina while changing the fracture mode with plenty of cleavages accompanied by crack deflections. The specific wear rate in the 8 wt% alumina sample decreased by almost 62% compared to the pure resin sample. Graphene caused a significant drop in tensile strength due to the generation of cavities and porosities around the graphene agglomerates, but it greatly improved the wear properties, with the specific wear rate decreasing by almost 77% at just 1 wt%. Then hybrid nanocomposites of alumina and graphene reinforcements were produced with the aim of optimal tensile and wear properties. The 0.5% graphene +3.5% alumina improved the wear resistance and provided moderate tensile properties; however, the 1% graphene +3% alumina could not increase the wear resistance due to the weakening of graphene plates sticking to the polymer substrate.

Secondary aluminum (Al) dross (SAD) is a hazardous waste discharged from Al production, processing and recycling. Over 6.7 million tons of SAD was discharged on the planet in 2023. SAD is consisted of 40–60 wt% of alumina (Al2O3), 10–30 wt% of AlN, 5–15 wt% of salts and 3–10 wt% of heavy metal oxides. Currently, recycling of SAD to make Al2O3 by hydrometallurgy is a promising method for disposal of SAD. Hydrometallurgy method is mainly divided into acid leaching and alkali leaching. In acid leaching, Al, AlN and Al2O3 react with acid to form aluminum sulfate and aluminum chloride. In alkali leaching, Al, AlN and Al2O3 react with alkali to form sodium aluminate. High-purity Al2O3 is obtained after precipitation, washing, drying and calcination from the leachate. Resource consumption and emission was calculated to evaluate the economic and environmental benefits. About 147.9 and 172.6 dollars was earned after making Al2O3 from a ton of SAD by alkali and acid leaching process, respectively. And carbon emissions of a ton of Al2O3 was risen about 596.5 and 2216.0 kg CO2, respectively, compared with the Bayer process with bauxite. We proposed a calcination pre-treatment with quicklime on SAD to reduce the carbon emission. The Al and AlN are oxidized into Al2O3 after calcination, and the Al2O3 reacts with CaO to form CaO·Al2O3. The Al in CaO·Al2O3 can be leached out easily with a low concentration of alkali. This review provides a guidance for the recycling of SAD by hydrometallurgy, and proposes a novel idea for the energy and consumption reduction in alumina (Al₂O₃) production.

Porous α-Al2O3 ceramics are a highly sought-after material with a multitude of applications; for example, they are used as filters, substrates, biomedicine materials, etc. Despite the availability of raw materials, a challenge associated with this technology is the high energy budget caused by sintering above 1500 °C. For the cold sintering processing (CSP) of ceramics, lowering the α-Al2O3 sintering temperature is one of the most urgent challenges in the background of its rapid development. This paper is the first to demonstrate a solution to this problem using the CSP of α-alumina ceramics in the presence of pure water as a transient liquid. The manufactured materials were examined using XRD analysis; the evolution of their microstructures during CSP was revealed by SEM; and the porosity was evaluated using the Archimedes method. Ceramics with an open porosity up to 36% were produced at 380–450 °C and 220 MPa in 30 min. An increase in the pressure was found to impede α-Al2O3 formation from γ-AlOOH. The development of the microstructure was discussed within the framework of the dissolution–precipitation model and homogenous nucleation. The results of the SEM study pointed to the coalescence of γ-AlOOH grains during CSP.

Purpose: To assess utility, benefits, and risks of 4th-generation alumina–zirconia ceramic pairings in elective total hip arthroplasty (THA). Methods: A comprehensive mixed-methods best-evidence synthesis using data from systematic reviews, randomized controlled trials (RCTs), prospective and retrospective cohort studies, as well as joint replacement registries, was conducted to estimate overall revision and survival rates, periprosthetic infection, bearing fractures, and noise phenomena with 4th-generation alumina–zirconia ceramic versus other tribological couplings in elective THA. The systematic review part across multiple databases was registered with PROSPERO (CRD42023418076), and individual study data were extracted for statistical re-analysis. Results: Twenty overlapping systematic reviews, 7, 17, and 8 references from RCTs, cohort studies, and joint replacement registries form the basis of this work. According to current best evidence, it is (i) 15–33 times more likely that 4th-generation alumina–zirconia pairings avoid a revision for infection than causing a revision for audible noise, (ii) 38–85 times more likely that 4th-generation alumina–zirconia pairings avoid a revision for infection than causing a revision for ceramic head fractures, and (iii) three to six times more likely that 4th-generation alumina–zirconia pairings avoid a revision for infection than cause a revision for ceramic liner fractures. Conclusion: Fourth-generation alumina–zirconia pairings in THA show a favorable benefit–risk ratio, with rare compound-specific adverse events and complications significantly outbalanced by long-term advantages, such as a markedly lower incidence of revision for infection.

Tin (Sn) doped platinum (Pt) nanoparticles supported on γ‐alumina are important materials catalyzing various reactions, such as the dehydrogenation of methylcyclohexane (MCH) into toluene, involved in liquid organic hydrogen carriers process, and naphtha catalytic reforming. The role of oxidized forms of Sn, remains misunderstood. Relying on catalysts' models made of a Pt13cluster on the (100) surface of γ‐alumina, the location and effects of Sn4+and Sn2+ interfacial atoms are investigated by density functional theory (DFT) calculations. A simulated annealing approach based on ab initio molecular dynamics enables to explore the configurations of the catalytic systems. The Pt clusters' stabilities and that of the adsorbed molecular intermediates are linked to the electronic properties of the cluster and to its ductility modulated by the adsorbed species, the alumina support and the Sn atoms. The Gibbs free energy profiles related to the reaction mechanism of the MCH dehydrogenation into toluene are quantified on the basis of transition state search. The energy span concept reveals that the dual (either detrimental or beneficial) impact of Sn oxidized forms on the intrinsic reactivity of the Pt13 cluster depends on temperature. Based on this DFT analysis, we attempt to clarify the debated role of Sn oxidized species. [ABSTRACT FROM AUTHOR]

In this paper, we demonstrate a method of measuring the flexural elastic modulus of ceramics at an intermediate (~millimeter) scale at high temperatures. We used a picosecond laser to precisely cut microbeams from the location of interest in a bulk ceramic. They had a cross-section of approximately 100 μm × 300 μm and a length of ~1 cm. They were then tested in a thermal mechanical analyzer at room temperature, 500 °C, 800 °C, and 1100 °C using the four-point flexural testing method. We compared the elastic moduli of high-purity Al2O3 and AlN measured by our method with the reported values in the literature and found that the difference was less than 5% for both materials. This paper provides a new and accurate method of characterizing the high-temperature elastic modulus of miniature samples extracted from representative/selected areas of bulk materials. [ABSTRACT FROM AUTHOR]

This study investigates the fabrication, microstructural characteristics and plasma resistance of Y–Al–Si–O (YAS) glass-ceramics coated on alumina ceramics. YAS frits were initially prepared using a melt-quenching method, then homogenously milled and coated onto alumina ceramics. The melt-coating process was conducted at 1650 °C for 1 h. The composition and microstructure of the glass frits and coatings were thoroughly characterized using X-ray diffraction, scanning electron microscopy, and energy-dispersive X-ray spectroscopy. These analyses revealed a dense microstructure with a polycrystalline structure predominantly composed of Y3Al5O12 (YAG) phase and a minor phase of Y2Si2O7. The YAS coatings on alumina revealed a dense layer with strong adhesion to the substrate. Subsequently, the coatings underwent C4F6/Ar/O2 plasma treatment for 1 h. Plasma exposure tests demonstrated that the YAS-coated alumina exhibited significantly better etching resistance compared to uncoated alumina, with minimal surface damage observed on the YAS coating, confirming its protective properties against plasma. The superior plasma resistance of YAS coatings is attributed to the predominance of its YAG phase. This research offers a more stable and cost-efficient solution for protecting ceramics in demanding plasma environments. [ABSTRACT FROM AUTHOR]

Porous alumina structures were developed by indirect Powder Bed Fusion with Laser Beam (PBF-LB), employing a novel feedstock (composite granules) based on alumina (Al 2 O 3), bio-renewable polyamide 612 (PA612), and micron-sized graphite (MG) using a commercial PBF-LB machine that operates with a low-power visible light diode laser. Regular and slightly rounded composite granules were prepared via the thermally induced phase separation (TIPS) process in dimethyl sulfoxide (DMSO) using 0.05 vol% of PA612, 40/60 vol% of Al 2 O 3 /PA612 and 6.25 wt% of MG, and then characterized via density measurements, Hausner's ratio, SEM-EDS, particle size distribution, Raman spectroscopy, DSC, and TGA. Experimental conditions to be used in the PBF-LB process were determined in order to obtain high-quality green porous structures with a controlled geometry. After the heating treatments, sintered components with good structural integrity, a high open porosity associated with interconnected pores in the struts, and a ceramic matrix with microsized-equiaxial grains were obtained. The evaluation of the mechanical properties was performed by diametral compression testing. In order to improve these properties, a vacuum infiltration process involving a low-concentration alumina-ethanol suspension was used on pre-sintered discs. As a consequence of the infiltration process, the discs showed improved mechanical properties after sintering without the porosity having been significantly affected. [ABSTRACT FROM AUTHOR]

Reticulated alumina ceramic foams manufactured by the Schwartzwalder technique are coated with a sodium aluminosilicate glass using an aqueous precursor containing alumina particles and sodium silicate. After a heat treatment, a well‐adhering glass layer with a thickness between 10 and 120 μm is obtained. Besides the strut surface, the glass phase also penetrates the hollow strut cavities as well as strut cracks. The total porosity of the glass‐coated foams is between 88% and 90%, and the open cellular structure is not negatively affected by the glass coating. The compressive strength increases by a factor of two under consideration of the decrease in total porosity; a compressive strength in the order of magnitude of 2 MPa is feasible. An ion exchange of Na+ by K+ into the glass coating layer (chemical strengthening) is successfully demonstrated, but does not result in an additional improvement of the compressive strength. [ABSTRACT FROM AUTHOR]