Papers by Keyword: Al₂O₃

Abstract: Al2O3 matrix composites reinforced with Ba-b-Al2O3 phase were synthesized through reactive sintering using Al2O3 and BaCO3 as starting powders. Dense Al2O3/Ba-b-Al2O3 composites can be obtained by spark plasma sintering from Al2O3/BaO•Al2O3 powder, which was prepared by calcining Al2O3/BaCO3 powder mixture. The Ba-b-Al2O3 reinforcing phase exhibited an elongated morphology due to preferred diffusion of Ba cations. The existence of Ba-b-Al2O3 phase as well as low sintering temperature and short holding time during reactive sintering inhibit grain growth and thus result in small grain sizes of the Al2O3 matrix.

Abstract: The influence of Nb2O5 and La2O3 on the phase and microstructure evaluation and mechanical properties of composite ceramics sintered with 2.45 GHz microwave energy was investigated. The results showed that Nb2O5 could densify the pure alumina with a lower sintering temperature and a short sintering time. Nb2O5 reacted with Al2O3 to form AlNbO4 completely and the amount of AlNbO4 increased with the increasing content of Nb2O5, distributing at the Al2O3 grain boundaries. The specimen doped with 10 Vol.% Nb2O5 sintered at 1500 °C exhibited plenty of columnar grains with draw ratio about 1:3. La2O3 reacted with Al2O3 to form LaAl11O18 completely, the specimen doped with 10 Vol.% and 15 Vol.% La2O3 sintered at 1500 °C exhibited plenty of columnar grains with draw ratio about 1:4. The existence of columnar grains enhanced the microhardness and fracture toughness of composite ceramics.

Abstract: Graphene nanosheet (GNS)/ Al₂O₃ composite powder with homogeneously distributed GNSs has been fabricated from wet ball milled expanded graphite and Al₂O₃, and then followed by the rotary evaporator at relatively low temperature to dry the mixture and the residual solvent was removed in atmosphere-vacuum pipe-type furnace accessing mixed gases of Argon and Hydrogen at 600 for 6h. During the process, homogeneously dispersed and mixed GNS/ Al₂O₃ composite powders with quite few damage of GNSs structure and properties have been obtained. The microstructures and grain sizes of GNS/ Al₂O₃ composite powders have been investigated. The results showed that the addition of GNSs had diminished the size of Al₂O₃ particles and also the as-prepared GNSs/ Al₂O₃ composite powders can be dispersed and mixed more homogeneously remarkably with the presence of GNSs.

Abstract: Alumina ceramic, with high mechanical strength, good electric insulation, high hardness and good corrosion resistance performance, has been widely used in machinery, electronic and electrical, chemical, medicine, construction and other high-tech areas. In this study, both silicon sol and zirconia particles are incorporated into the system and dense alumina composite ceramics were prepared by cold isostatic processing and pressureless sintering at 1550 . The influence of additives on phase composition, microstructure and mechanical properties were investigated. The XRD results show that mullite phase was generated in the composite ceramic. The composite ceramic has excellent comprehensive performance. For example, the sample with 3wt.% SiO₂ and 5wt.% ZrO₂ has density of 3.87g·cm^-3, Vickers hardness of 17.6GPa, flexural strength of 369.0MPa, youngs modulus of 374.2GPa and fracture toughness of 3.57MPa·m^1/2.

Abstract: Martensitic high-carbon high-strength SAE 52100 bearing steel has been widely used as the main alloys for rolling contact applications, and also at the components under bending and tension-compression. In order to enhance the material’s strength, refining the prior austenite grain size through repeated heating has been investigated. In this work, the microstructure of repeatedly quenched-tempered Ti, N-rich SAE 52100 steel was investigated. The material was melted by an electric furnace and formed by continuous casting and forging, and the crack origin on the fracture surface was investigated. It was found that repeated furnace quenching and tempering effectively refined the martenstic structure.

Abstract: In the present study, applying Al₂O₃ capping layer as suppressing layer of oxygen diffusion to SiC-MOS structures, we investigated the effect of Al₂O₃ layer as suppression of reoxidation at SiO₂/SiC interface and decrease of Dit. We evaluated MOS capacitors which have SiO₂/SiC and Al₂O₃/SiO₂/SiC structure on 4H-SiC (0001) Si-face epitaxial wafers after post-oxidation anneal process (N₂O:N₂=1:9 [slm]) at temperatures ranging from 1000 °C to 1300 °C for 30min. The Al₂O₃/SiO₂/SiC structure of reoxidation thickness, surface roughness and Dit are smaller than those of SiO₂/SiC structure. These results show that the suppression of reoxidation during POA is important to improve the SiO₂/SiC interfacial qualities.

Abstract: In this paper, the electrical and physical analysis is carried out to investigate the effect of Al2O3 capping layer on ZnO film using atomic layer deposition. ZnO TFTs shows the metallic conduction behavior as Al2O3 capping layer thickness increases. From SIMS analysis, it is found out that the diffusion of Al into ZnO film is enhanced according to Al2O3 capping layer thickness. Moreover, the defects related to oxygen such as oxygen vacancy increase from XPS analysis and ZnO films reveal less compressive stress by substitution of Zn with Al form XRD analysis. That is, the metallic conduction behavior of ZnO TFTs with Al2O3 capping layer can be explained due to increase in the carrier concentration in ZnO channel layer from oxygen vacancy and substitution of Zn with Al.

Abstract: LiOH is known to be one of the most efficient CO₂ adsorbent because it reacts with CO₂ to form Li₂CO₃. However, LiOH still suffers from lack of enough hardness for practical use. In this study, various substrates, were modified with LiOH. Their X-ray diffraction patterns were investigated, and LiOH peak was observed from all prepared samples. CO₂ adsorption capacity of each prepared sample was measured by monitoring CO₂ concentration change during the adsorption process under constant CO₂ gas inflow condition. LiOH-modified Al₂O₃ and zeolite 5A showed good CO₂ adsorption performance, while LiOH-modified AC and SiO₂ showed relatively poor CO₂ adsorption. Al₂O₃ and zeolite 5A contains many basic functional groups of Al3+, which promote the neutralization reaction with acidic CO₂. The effect of carrier gas, carrier gas flow rate, initial CO₂ concentration, and amount of LiOH-modified Al₂O₃ loading was investigated. CO2 adsorption performance was better when the carrier gas was N₂, because O₂ competes with CO₂ on LiOH. CO₂ adsorption performance was better with lower carrier gas flow rate, lower initial CO₂ concentration, and less loading of adsorbent due to the increase of contact time and contact points.

Abstract: Asymmetric porous aluminium-oxide ceramic hollow fibre membranes have been prepared by the phase inversion / sintering technique. The effect of non-solvent such as ethanol, isopropanol and ethylene glycol monomethylether(2-methoxyethanol) on the geometry and performance of hollow fibres was investigated. Morphologies of Al2O3 ceramic hollow fibre membranes were characterized using a scanning electron microscope (SEM). The effective porosity and the mechanical strength were determined by Archimedes method, and three point method, respectively. The prepared Al2O3 hollow fibre membranes show the asymmetric structure with a finger-like layer and a sponge-like layer. The effective porosity of the prepared hollow fibre membranes exceeds 47%, and the bending strength of the hollow membranes exceeds 63 MPa. The Al2O3 hollow fibre membranes with moderate permeation characteristics for gas and pure water are prepared by the introduction of nonsolvent in membrane casting solution. The separation factors of H2 to N2 or CO2 of the hollow fibers with nonsolvent are over 2.0.

Abstract: The effects of Al₂O₃ and Al(OH)₃ on expansion due to alkali-silica reaction (ASR) were tested by using Accelerated Mortar Bar Test and through prolonging the curing age, and the ffect was compared with silicon fume and fly ash. The results show that ASR can be inhibited effectively by proper content of silicious admixtures within 14 days, but can not in long term, while it can be inhibited by proper content of Al₂O₃ and Al(OH)₃ not only within 14 days but also in long term. The composite of silicious admixtures and aluminous admixtures has synergetic effect on inhibiting ASR, and there exists a value of Al₂O₃/SiO₂ with which ASR is suppressed best. For the composite, ASR is suppressed mainly by silicious admixtures in early age and mainly by aluminous admixtures in long term.