Al2O3 Composites Research Articles

Electrical and Dielectrical Properties of Composites Based on Alumina and Cyclic Olefin Copolymers.

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.

Ultrahigh Capacitive Energy Storage in a Heterogeneous Nanolayered Composite

AbstractFerroelectric polymers with robust electrical polarization have been extensively investigated for capacitive energy storage. However, their inherent ferroelectric hysteresis loss limits the discharged energy density and compromises energy efficiency. Here, a heterogeneous nanolayered composite of ferroelectric polymer poly(vinylidene fluoride‐trifluoroethylene) (P(VDF‐TrFE)) and Al2O3 is presented, which effectively mitigates ferroelectric hysteresis loss while maintaining high polarization and enhanced breakdown strength. Phase‐field simulations indicate that the polarization behaviors of the heterogeneous layered structure are jointly influenced by the thickness and dielectric constant of each component, which balances the electrical energy and Landau energy within the heterogeneous system. Guided by the theoretical simulations, optimized polarization behaviors are achieved with a significant reduction in remnant polarization and ferroelectric loss in the P(VDF‐TrFE)/Al2O3 composites through careful control of P(VDF‐TrFE) thickness at nanometer scale. Moreover, the presence of multiple interfaces in the layered composites leads to a remarkable enhancement in polarization and breakdown strength. Consequently, an ultrahigh energy density of about 108 J cm−3 is achieved with a high charge–discharge efficiency of exceeding 80%. This work not only presents a straightforward approach to modify the polarization behaviors of ferroelectric polymers but also demonstrates a promising strategy for developing high‐energy‐density polymer nanocomposites.

Enhanced mechanical behavior and texture development of Al/Al2O3 composites produced by spark plasma sintering (SPS) and vacuum hot pressing (VHP) followed by simple shear extrusion (SSE)

Green compacts of Al-3vol% Al2O3 composites were produced by powder metallurgy (PM) and subsequently processed by spark plasma sintering (SPS) and vacuum hot pressing (VHP). The manufactured samples were then processed by the simple shear extrusion (SSE) process. Three SSE dies with the distortion angles (α) of 8°, 10° and 22.5° were used in this study. The SPS-ed/SSE-ed specimens for α = 10° were successfully deformed up to sixteen passes, while the VHP-ed/SSE-ed samples failed after six passes. In addition, the SPS-ed sample for α = 22.5° only underwent one pass of SSE. The SPS-ed/SSE-ed composites resulted in the highest shear punch test (SPT) load, modified porosity amount and the best reinforcement redistribution, as compared to the vacuum sintering and stir-casting manufacturing methods, which was confirmed by microstructure evaluation and porosity measurements. The crystallographic texture of the SPS-ed/SSE-ed composites for α = 10° was investigated in the sixteenth pass using the X-ray method. The results of texture development showed the very low intensity of shear and cube texture with {100} <011> and {001} <100> components, subsequently.

Enhanced water purification performance of composite PVA–ZnO–Al2O3 hollow fiber membrane: A breakthrough approach for high-temperature stability, low-pressure water separation

This work describes the development of a composite Al2O3 hollow fiber combined with multiple-layer ZnO nanoparticles and PVA polymer as the active side for low-pressure saltwater purification. The composite membrane was evaluated with an active layer-facing salt solution, and slight suction condition was applied to the permeate inside the membrane lumen. Results show that varying nanoparticle layers to tune the porosity of the composite membrane influenced its morphology, porosity, and hydrophilicity. The effect of porosity tuning on the membrane characteristics and desalination performance was investigated. A salt rejection rate of >90 % was recorded for all 5 % PVA–ZnO–Al2O3 hollow fiber membranes with the highest salt rejection of 96.34 % and the water flux of 15.49 kg·m−2·h−1. The membrane was further tested with untreated natural seawater to demonstrate its ability to withstand continuous operation. The membrane has acceptable chemical stability when exposed to untreated natural seawater. The optimal PVA–ZnO–Al2O3 hollow fiber membrane exhibited efficient water phase change transfer and high salt rejection, making it a promising candidate for seawater purification.

Effect of Phase Composition Variation of Oxy–Nitride Composite Ceramics on Heat Resistance and Preservation of Strength Parameters

The aim of this study is to determine the effect of changes in the phase composition of Al2O3–Si3N4 ceramics that were obtained using the method of mechanochemical solid-phase grinding on their resistance to the process of long-term thermal exposure, accompanied by the processes of oxidation and softening. The relevance of this research consists of determining the influence of the phase composition of ceramics on the change in their strength and thermophysical parameters, on the basis of which, we can draw a conclusion about the optimal composition of composite ceramics that have great prospects in the field of fire-resistant, heat-resistant, or radiation-resistant structural materials. During this study, the dynamics of the changes in the phase transformations of the xAl2O3–(1−x)Si3N4 ceramics, with variations in the ratio of the components, initiated by the thermal annealing of the samples, was established. According to the assessment of the phase transformations with variations in the ratio of the components, it was found that thermal annealing in an air environment at an Al2O3 concentration in the order of 0.3–0.5 M leads to the formation of an orthorhombic Al2(SiO4)O phase and an elevation in its contribution at concentrations above 0.5 M, which causes a rise in the thermophysical parameters and resistance to high-temperature degradation. During the heat resistance tests, it was found that the formation of the composite ceramics with the Si3N4(SiO2)/Al2(SiO4)O/Al2O3 phase composition results in an increase in the stability of their strength properties when exposed to thermally induced oxidation, which has a negative impact on their resistance to softening and a decrease in hardness. Moreover, the presence of the Al2(SiO4)O phase in the composition of the ceramics causes a slowdown in the processes of thermal oxidation of the Si3N4 phase under prolonged temperature exposure, alongside an increase in the degradation resistance of strength properties by more than 4–7 times, in comparison with the softening data established for single-component ceramics.

Role of scandium addition to microstructure, corrosion resistance, and mechanical properties of AA7085/ZrB2+Al2O3 composites

The effect of varying amounts of scandium (Sc) on the mechanical performance and corrosion resistance of aluminum alloy (AA7085) composites reinforced with Zirconium diboride (ZrB2) and Aluminum oxide (Al2O3) nanoparticles was investigated. The specimens were made using an in-situ process with varying amounts of Sc up to 0.5 wt%, and their microstructural behavior, corrosion, and mechanical properties were explored in detail. Phase structural analysis revealed the successful incorporation of ZrB2 and Al2O3 into the matrix through in-situ synthesis, ranging from 30 to 61.7 nm. In addition, HRTEM and XRD analysis displays the Al3Zr prominence observed with 0.1 wt% Sc content, transforming to Al3(Sc, Zr) in the 0.3 wt% Sc composite, and finally becoming Al3Sc with 0.5 wt% Sc. Corrosion analysis revealed that the 0.3 wt% Sc composite exhibited fine Al3(Sc, Zr) precipitate phases that enhanced corrosion properties. The Sc addition leads to a significant improvement in the mechanical properties of AA7085/ZrB2+Al2O3 composites. The ultimate tensile strength of 678 ± 5 MPa for 0.5 wt% Sc under the hot rolled and T6 aged condition was achieved. The optimum content of Sc in AA7085/ZrB2+Al2O3 composites has identified both corrosion and mechanical properties enhancement at 0.3 wt% and 0.5 wt%, respectively.

Realization of Atomically Uniform ALD-Al2O3 and TiO2 on SiO2 and GeO2 by UV-Ozone Treatment

Recently, Interface Dipole Modulation (IDM) has been observed in amorphous HfO2/1-Monolayer (ML) TiOx/SiO2 stack structures [1]. To fabricate IDM devices, the thickness of the modulation layer, which is at the atomic layer level, must be precisely controlled to produce a uniform film with high-quality. Therefore, Atomic Layer Deposition (ALD) is one of the promising methods. However, it is difficult to form very thin oxide films on thermally oxidized SiO2/Si or GeO2/Ge by ALD because the oxide film surface is chemically inert. In fact, deposition delays, which is called incubation cycles, and island growth have been observed in the 0-20 cycle range for Al2O3 with Trimethylaluminum (TMA) and H2O as precursors [2, 3]. This is thought to depend on the time it takes for -OH bonds to form on the surface, so surface modification with low damage is necessary. Several surface modification methods exist, especially UV-Ozone (UVO) treatment [4], which has been reported to modify the surface of oxide films such as SiO2 and Al2O3 and has the advantage of being environmentally harmless and compatible with CMOS processes. In this study, the effect of surface modification of insulating films by the UVO method on ALD deposition was investigated for the purpose of controlling atomic layer thickness and producing a uniform oxide film.The samples for the measurement were prepared by the following procedure. First, the chemically cleaned Si or Ge substrate was thermally oxidized to form a ~10 nm thick oxide film. Next, after 15 min of UVO treatment in air at room temperature, the oxide films of Al2O3 or TiO2 were deposited using ALD method on two kinds of substrate. The precursor used for Al2O3 deposition and for TiO2 deposition were TMA and Tetrakis(dimethylamido)titanium (TDMAT), respectively. The oxidant is H2O. The samples were evaluated by Atomic Force Microscopy (AFM), Spectroscopic Ellipsometry (SE) and X-ray Photoelectron Spectroscopy (XPS).Al 2p photoelectron spectra from Al2O3 films deposited after UVO treatment were measured by XPS to confirm the composition of Al2O3. As shown in Fig. 1(a), fitting is possible with two peaks of Al 2p 3/2 and 2p 1/2, which can be said to be stoichiometric Al2O3. Next, Fig. 1(b) shows the photoelectron spectrum of the TiO2 film used as the modulation layer in the IDM device. The Ti 2p spectra, as same as the Al 2p spectra, can be fitted with two peaks, and the photoelectron intensity increases almost in proportion to the number of cycles. The thickness of the ALD film was then calculated from the photoelectron intensity ratio from the Al2O3, TiO2 and the lower oxide film. As shown in Fig. 1(c), there is a delay of one-cycle for the deposition of Al2O3 on SiO2, but it can be seen that the film thickness increases in proportion to the increase in the number of cycles. This is thought to have occurred by the following mechanism. First, UVO treatment breaks the Si-O or Ge-O bonds on SiO2 or GeO2 surface. This dangling bond is the starting point for precursor formation during initial layer formation. Therefore, the H2O during the ALD process is thought to have formed a Si-OH or Ge-OH bond and improved reactivity with methyl groups. The growth per cycle (GPC) can be calculated to be about 0.10 nm/cycle, which is in close agreement with the literature value [5]. Furthermore, SE measurements of Al2O3 films deposited on SiO2 at 50 and 200 cycles yielded thicknesses of 4.83 and 19.97 nm, respectively, which were in close agreement with the GPC calculated using XPS. The TiO2 film deposited on SiO2 also experienced a one-cycle delay similar to that of the Al2O3 film, and the GPC could be calculated to be 0.046 nm/cycle. Furthermore, as shown in Fig. 1(d), UVO treatment increased the average film thickness and reduced the surface roughness from the AFM images. These results indicate that UVO treatment is effective for surface modification of SiO2 and GeO2, and it can be concluded that the ALD method can deposit uniform oxide films without delay.This work was partly supported by TOKYO CITY UNIVERSITY Interdisciplinary Research Center for Nano Science and Technology for instrumental analysis.[1] N. Miyata, Sci. Rep., 8, pp. 8486, 2018.[2] H. Fukumizu et al., Jpn. J. Appl. Phys. 59 016504, 2020.[3] E. Shigesawa et al., Semicond. Sci. Technol. 33 124020, 2018.[4] D. Guo et al., Chem. Phys. Lett., 429, 124–128, 2006.[5] A.W. Ott et al., Thin Solid Films, 292, pp. 135-144, 1997. Figure 1

Fabrication of Cu/Al–Al2O3 laminar composites using squeeze casting and roll bonding techniques: Evaluation of microstructure, mechanical properties and wear characteristics

The influence of Al2O3 whiskers addition on the microstructure, tensile, hardness, and wear characteristics of Cu/Al–Al2O3 composites were examined. The squeeze casting was used to fabricate Al–Al2O3 composites with different volume fractions of whiskers. Then, they were bonded to Cu layers. The microstructural and morphological examination were carried out by using SEM, XRD, and EBSD analyses. For the as-cast composites, the agglomeration of whiskers was observed which was then decreased by the following roll bonding process. For the roll bonded composites, the tensile strengths of composites were 210 MPa, 233 MPa, and 250 MPa For Cu/Al-(5 % vol) Al2O3, Cu/Al-(15 % vol) Al2O3, and Cu/Al-(25 % vol) Al2O3, respectively. The wear rate decreased versus volume fraction of whiskers which is correlated with the enhanced hardness of layers in composites. Less material loss and less debris were observed in composites with a higher volume fraction of whiskers.

Vat Photopolymerization of Sepiolite Fiber and 316L Stainless Steel-Reinforced Alumina with Functionally Graded Structures.

Alumina (Al2O3) ceramics are widely used in electronics, machinery, healthcare, and other fields due to their excellent hardness and high temperature stability. However, their high brittleness limits further applications, such as artificial ceramic implants and highly flexible protective gear. To address the limitations of single-phase toughening in Al2O3 ceramics, some researchers have introduced a second phase to enhance these ceramics. However, introducing a single phase still limits the range of performance improvement. Therefore, this study explores the printing of Al2O3 ceramics by adding two different phases. Additionally, a new gradient printing technique is proposed to overcome the limitations of single material homogeneity, such as uniform performance and the presence of large residual stresses. Unlike traditional vat photopolymerization printing technology, this study stands out by generating green bodies with varying second-phase particle ratios across different layers. This study investigated the effects of different contents of sepiolite fiber (SF) and 316L stainless steel (SS) on various aspects of microstructure, phase composition, physical properties, and mechanical properties of gradient-printed Al2O3. The experimental results demonstrate that compared to Al2O3 parts without added SF and 316L SS, the inclusion of these materials can significantly reduce porosity and water absorption, resulting in a denser structure. In addition, the substantial improvements, with an increase of 394.4% in flexural strength and an increase of 316.7% in toughness, of the Al2O3 components enhanced by incorporating SF and 316L SS have been obtained.

Diffusion Bonding of Al2O3 Dispersion-Strengthened 316L Composite by Gleeble 3800.

The aim of this work is to investigate the bonding properties of the ceramic dispersion-strengthened 316L (CDS-316L) composites with the reference 316L stainless steel (REF-316L) using a Gleeble 3800 physical simulator. In previous works, two different composites, REF-316L and 316L, with 1 wt% Al2O3 composite (CDS-316L) have been prepared by spark plasma sintering (SPS). In the present work, these specimens were diffusion-bonded using the following parameters: a temperature range of 950-1000 °C and a uniaxial pressure of 20-30 MPa. It was observed that the deformation of the CDS-316L during the uniaxial bonding process was higher compared to the 316L steel rods. The addition of alumina particles increased the micro-hardness of the 316L steel. The samples were broken in the CDS-316L zones, not at the diffusion-bonded interfaces. No diffusion zones have been observed within the investigated magnification for all composites, where the interfaces between the different specimens were well defined.

Thermo-mechanical behaviours investigation of Nano-Sized Al2O3, TiO2, and Graphene Nanoplatelet Reinforced Epoxy Composites

Composite materials find extensive applications in various industries, thanks to their remarkable properties. These sectors include energy, maritime, motor sports, aviation, space and defense. The materials commonly used in these sectors are fiber reinforced plastic (FRP) composite materials. Epoxy materials are commonly used as matrix in the production of FRP materials. This study delves into the enhancement of epoxy-based nanocomposites by using graphene nanoplatelets (GNP-5nm), TiO2 (13nm), and Al2O3 (8nm) nanoparticles. These nanoparticles were added at varying mass ratios into a commercial epoxy to investigate their effects on some chemical, thermal and mechanical properties. Meticulous mixing methodologies were used to reduce clumping effects and ensure even distribution during the process. The curing process was carried out in a PLC (Programmable Logic Controller) controlled hot air oven under isothermal conditions under the influence of 100 °C for 30 minutes. Tensile strength, elongation at break, toughness, resilience modulus, elasticity modulus, hardness, FTIR analysis and thermal conductivity properties were characterized to assess the nanoparticle influence on the epoxy matrix. The results showed that there were remarkable improvements in mechanical properties with nanoparticle reinforcement. Especially, 1.25% Al2O3 inclusion exhibited a substantial increase of 140.32% in tensile strength and a 7% rise in shore D hardness compared to pure epoxy. This enhancement was attributed to enhanced O-H bonding between 'O' atoms in Al2O3 nanoparticles and epoxy polymer chains, enhancing matrix-filler interactions. Additionally, the effect of 1.0% TiO2 led to plasticity, displaying a 32% rise in elongation at break, signifying improved deformation energy absorption compared to neat epoxy. In thermal conductivity measurements, the highest thermal conductivity was observed in the sample with 1.25% GNP added and it increased by 123.5% compared to neat epoxy. In TiO2 and Al2O3 added samples, an increase of 69% and 47%, respectively, was observed at 1.25% additive rates compared to neat epoxy. According to the results, thanks to the nanoparticle reinforcement added into the epoxy matrix, composite structures can be given new and superior properties specific to the applications.

Development of a low-temperature novel porous Si3N4–Al2O3 composite with excellent specific mechanical properties

Porous composites of Si3N4 and Al2O3 have potential applications for various engineering applications. Fabrication of porous ceramic composites is generally expensive due to the requirement of high sintering temperatures and expensive raw materials. A relatively simple, cost-effective, versatile, and novel processing technique with phosphoric acid performing the dual roles of binder and pore-former has been proposed in this work. Porous Si3N4–Al2O3 composites with up to 20 vol% Al2O3 content and porosities in the range of 37–54 vol% were fabricated at only 1200 °C. Young's modulus, flexural strength, and compressive strength of the porous composites were found to be in the range of 21–54 GPa, 31–110 MPa, and 39–103 MPa, respectively. The best combination of mechanical properties was achieved at 10 vol% Al2O3 content, which corresponded to 39 % total porosity. The combination of low density and good mechanical properties yielded outstanding specific properties, which are significantly higher than monolithic porous Si3N4. The excellent combination of a low processing cost, tunable porosity and pore morphology, outstanding mechanical properties, as well as the inherent chemical and thermal stability of these porous composites render them potentially very attractive as chemical filters, porous membranes, as well as porous preforms for interpenetrating metal/ceramic composites.

Strain rate-dependent behavior of cold-sprayed additively manufactured Al–Al[formula omitted]O[formula omitted] composites: Micromechanical modeling and experimentation

Metal matrix composites (MMCs) fabricated by cold spray additive manufacturing (CSAM) are increasingly gaining attention as structural materials due to their rapid production and scalability. Herein, the failure behavior of CSAM Al–Al2O3 composites under quasi-static and dynamic compression was studied by an experimentally informed/validated 3D microstructure-based finite element (FE) model. The debonding mechanism was found to grow at a higher rate consequently dampening the particle cracking mechanism when the strain rate rises to dynamic regimes. The stress-bearing capacity of the particles plays a key role in enhancing the flow stress and elongation at failure of the CSAM composite under high strain rates due to the lower propensity of particle cracking. Eventually, the model was exercised to study the microscale failure progression in the material under elevated temperatures. For the first time in the literature, this study informs on the correlation between the microscale failure mechanisms and the mechanical performance of CSAM MMCs at the macro scale across strain rates and temperatures whose outcomes are applicable to the design of next-generation materials with a tailored performance.

Fabrication and Dry-Sliding Wear Characterization of Open-Cell AlSn6Cu–Al2O3 Composites with LSTM-Based Coefficient of Friction Prediction

This study investigates the fabrication, wear characterization, and coefficient of friction (COF) prediction of open-cell AlSn6Cu–Al2O3 composites obtained by a liquid-state processing technique. Focusing on wear behavior under varying loads using the pin-on-disk method, this research characterizes microstructure and phase composition via SEM, EDS, and XRD analyses. A novel aspect of this research is the application of an LSTM recurrent neural network model for the fast and accurate prediction of the COF of the composites, eliminating the need for extensive experimental work. Additionally, feature importance analysis using Random Forest regressors is conducted to ascertain the relative contribution of each input variable to the output variable, enhancing our understanding of the wear mechanisms in these materials. The results demonstrate the effectiveness of the composite’s reinforcement in improving wear resistance, highlighting the critical role of mechanical stress and the reinforcement’s hardness in the wear process. The quantitative findings related to the wear behavior include a mass-wear reduction in the open-cell AlSn6Cu–Al2O3 composite from 8.05 mg to 1.90 mg at 50 N and a decrease from 17.55 mg to 8.10 mg at 100 N, demonstrating the Al2O3 particles’ effectiveness in improving wear resistance under different loads.

Broadband near-infrared emission in barium gallo-germanate glasses co-doped with bismuth, chromium and erbium ions

This work presents barium gallo-germanate glasses co-doped with Bi+/Er3+ and Cr3+/Er3+ ions for NIR luminescence. The addition of Al2O3 content in the glass matrix made it possible to obtain luminescence corresponding to the 3P1→3P0 transition of Bi+ ions. Co-doping with the Bi+/Er3+ system resulted in a broad luminescence spectrum of 1.0-1.6 µm and Cr3+/Er3+ co-doping in selected glass matrix resulted in luminescence in 0.9-1.6 µm band. However, the luminescence of the Cr3+ ions is much lower than that of Er3+ ions. Full Text: PDF References T. Suzuki, G.S. Murugan, and Y. Ohishi, 'Optical properties of transparent Li2O-Ga2O3-SiO2 glass-ceramics embedding Ni-doped nanocrystals', Appl. Phys. Lett., 86(13), 131903 (2005). CrossRef N.V. Golubev et al., 'Pre-crystallization heat treatment and infrared luminescence enhancement in Ni2+-doped transparent glass-ceramics', J. Non-Cryst. Solids, 515, 42 (2019) CrossRef Z. Xu, W. Feng, T. Chen, X. Liu, and J. Qiu, 'Tuning optical properties in PbSe quantum dot-doped borosilicate glass fiber by modulation of network topology', Opt. Laser Technol., 158, 108910 (2023). CrossRef M.A. Hughes, T. Suzuki, and Y. Ohishi, 'Spectroscopy of bismuth-doped lead-aluminum-germanate glass and yttrium-aluminum-silicate glass', J. Non-Cryst. Solids, 356(44), 2302 (2010). CrossRef J. Song, Z. Zhou, B. Zhong, M. Zhang, J. Huang, and L. Han, 'Ultra-broadband near-infrared Cr3+-doped multi-phase glass-ceramics realized by the selective enrichment strategy for near-infrared spectroscopy applications', J. Alloys Compd., 968, 172126 (2023). CrossRef M.A.U. Martines, M.R. Davolos, M.J. Júnior, D.F. de Souza, and L.A.O. Nunes, 'Cr3+ and Cr4+ luminescence in glass ceramic silica', J. Lumin., 128(11), 1787 (2008). CrossRef S. Zhou, H. Dong, H. Zeng, J. Hao, J. Chen, and J. Qiu, 'Infrared luminescence and amplification properties of Bi-doped GeO2−Ga2O3−Al2O3 glasses', J. Appl. Phys., 103(10), 103532 (2008). CrossRef T. Suzuki and Y. Ohishi, 'Ultrabroadband near-infrared emission from Bi-doped Li2O-Al2O3-SiO2 glass', Appl. Phys. Lett., 88(19), 191912 (2006). CrossRef T. Minh Hau et al., 'Super broadband near-infrared emission and energy transfer in Bi-Er co-doped lanthanum aluminosilicate glasses', Opt. Mater., 35(3), 487 (2013). CrossRef H.K. Dan et al., 'Effects of Y3+on the enhancement NIR emission of Bi+-Er3+ co-doped in transparent silicate glass-ceramics for Erbium-doped fiber amplifier (EDFA)', J. Lumin., 219, 116942 (2020). CrossRef E.M. Dianov, 'Bismuth-doped optical fibers: a challenging active medium for near-IR lasers and optical amplifiers', Light Sci. Appl., 1(5) (2012). CrossRef L. Wang, L. Tan, Y. Yue, M. Peng, and J. Qiu, 'Efficient Enhancement of Bismuth NIR Luminescence by Aluminum and Its Mechanism in Bismuth‐Doped Germanate Laser Glass', J. Am. Ceram. Soc., 99(6), 2071 (2016). CrossRef Z. Jiang et al., 'Effects of Al2O3 composition on the near-infrared emission in Bi-doped and Yb-Bi-codoped silicate glasses for broadband optical amplification', J. Non-Cryst. Solids, 383, 196 (2014). CrossRef

Passive and active oxidation of Al in the Al–Al2O3 composite refractory at high temperatures in air

The active and passive oxidation of Al in Al–Al2O3 composites was investigated in air at high temperatures. As fresh air impinged on the surface of the Al–Al2O3 composite sample, a thin Al2O3 layer was preferentially formed via passive oxidation of Al, which consumed most of the oxygen and lowered the local Po2 inside the sample. At low Po2, active oxidation of Al occurred and predominated in the interior transition layer, which further lowered the local Po2 to extremely low values within the non-oxide stability field. The local equilibrium PAlxOy generated by the active oxidation of Al reached a micro-positive pressure state and served as a gas barrier, hindering the inward diffusion of O2. The Po2 inside the composite was lowered by Al in the outer layers via a self-gettering process. Subsequently, Al4O4C and Al2OC-AlN solid solution were formed by both the direct reaction of Al(l) and the indirect reaction of AlxOy(g). After sintering in air, the Al–Al2O3 composite exhibited a functional gradient structure with a thin oxide layer and an interior non-oxide-reinforced corundum. A reaction mechanism model was established.

Physicomechanical, water absorption and thermal properties and morphology of Paederia foetida fiber–Al2O3 powder hybrid‐reinforced epoxy composites

AbstractHybridization of natural fibers with ceramic materials for reinforcing composites allows the optimization of the properties of these materials. For this reason, the present study aims to investigate physical, mechanical, water absorption, swelling and thermal properties as well as morphological characteristics of a hybrid Paederia foetida fibers–alumina powder (PFs–Al2O3)‐reinforced epoxy composite. Epoxy resin served as the matrix, while PFs and Al2O3 were employed as reinforcement. Five types of composites were fabricated using the hot‐pressing technique. The corresponding ratios of PFs:Al2O3 volume fractions (%) considered here were 0:40 (SFA), 10:30 (SFB), 20:20 (SFC), 30:10 (SFD) and 40:0 (SFE). The results reveal that the density of the hybrid PFs–Al2O3 composites decreased for increasing volume fractions of PFs: from 2.173 g cm−3 of SFA to 1.042 g cm−3 of SFE. The highest values of tensile strength (i.e. 49.085 MPa), tensile elastic modulus (i.e. 1.431 GPa) and impact strength (24 kJ m−2) were obtained for the SFD composite material with 30% volume fraction of PFs and 10% volume fraction of Al2O3: this happened because interface bonds between PFs, Al2O3 and epoxy phases achieved their optimal configuration. Overall, mechanical properties of the hybrid PFs–Al2O3‐reinforced epoxy composites were superior to those of composites reinforced only by PF fibers or only by Al2O3. Water absorption and swellability reached their maximum values at the steady state occurring after tested samples remained immersed in water for 820 h. The SFE composite reinforced only by PFs presented the highest water absorption and swelling (i.e. 6.034% and 5.81%, respectively) while for all other hybrid composites (SFD, SFC and SFB) these two quantities remained below 5%. Density and volume fraction of voids of hybrid PFs–Al2O3‐reinforced composites were consistent with the corresponding properties of the composites reinforced only by Al2O3 or PFs. SFD was also the most thermally stable material. Scanning electron microscopy observations of fractured surfaces indicated that the microstructure of the PFs–Al2O3‐reinforced epoxy composites presents several voids, fiber pullouts and transverse fibers, which together optimize the mechanical response of the composite material. Remarkably, the SFD composite material was highly competitive with the most recently developed hybrid composites employing natural reinforcements. © 2024 Society of Industrial Chemistry.

Sedimentological and geochemical evaluation of sandstones of the Ilaro formation, Dahomey Basin, Southwestern Nigeria : Insights into paleoenvironments, provenance, and tectonic settings

Grain size analysis, geochemistry, and petrography of sandstones of the Ilaro Formation exposed at the Ajegunle area were investigated to infer provenance, transportation history, tectonic setting, paleoenvironment, and degree of palaeoweathering of the sediments. Selected sandstones were analyzed, and the major, trace, and rare earth elements were determined using Inductively Coupled Plasma Mass Spectrometry (ICP-MS). Results from the granulometric analysis showed that sandstones were deposited in fluvial conditions. The sandstones exhibit a coarse-grained texture, displaying poor sorting and being texturally immature. The petrographic analysis indicated that quartz was predominant, whereas opaque minerals, muscovite, and ferruginous ground mass were present in smaller quantities. The sandstones can be geochemically classified as arkose and subarenite. The sandstones have an average composition of SiO2 (82.87%) and Al2O3 (9.49%), while K2O, Na2O, MgO, CaO, and P2O5 have &lt;1% each. The elevated Al2O3 content is associated with the lithic fragment composition, whereas the low concentrations of MgO (mean 0.03%), Na2O (mean 0.008%), and K2O (mean 0.04%) suggest chemical destruction in an oxidizing environment. The angularity of the grains indicated a short transportation history very close to the provenance. Bivariate and discriminant plots from major elements and trace elements suggest the sandstones were non-marine and sourced from intermediate rocks. The sandstones were deposited in an oxic-dyoxic condition under a humid climate and passive or active continental margins. The average values of the weathering indices indicate an intense degree of chemical weathering.

Wettability and Mechanical Properties of Red Mud-Al2O3 Composites.

In 2023, the global production of new red mud is expected to reach nearly 200 million tons, but less than 10% of it is currently being utilized in an environmentally friendly manner. To reduce the sintering temperature of alumina ceramics, a sintering aid method is used, as high-purity alumina ceramics require a solid-phase sintering temperature of over 1700 °C. The metal oxides present in red mud are necessary components for high-performance composite alumina ceramics. Composites were obtained by mixing and sintering red mud and Al2O3. This study focused on the mechanical properties and wettability of these composites. The results indicated that the 10% red mud-Al2O3 composite exhibited the highest hardness (20.12 GPa) and flexural strength (346 MPa). This is attributed to the formation of a mineral phase dominated by CaAl12O19, generated by the red mud during the sintering process, which filled the pores and reduced porosity. The surface energy of the red mud-Al2O3 composite was the highest at room temperature and high temperature, reaching 49.60 mJ·m-2 and 1164.7 mJ·m-2, respectively, indicating that it has better stability at both room and high temperatures. This study provides an important fundamental basis for the application of red mud-alumina composites to replace alumina-based composites in the field of construction materials, molten metal filters, ceramic cleavers, etc.

Construction of alumina framework with a sponge template toward highly thermally conductive epoxy composites

AbstractCeramic‐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.