Papers by Keyword: Al Powder

Abstract: Al₂O₃-MgO-Al composites were prepared by sintering in carbon tube furnace at 1700°C under nitrogen atmosphere with tabular alumina, sintered magnesia and aluminum powder as raw materials. Effect of Al powder content on the porosity, microstructure and phase constitution of Al-Al₂O₃-MgO composites were investigated. The results show that the main phase was non-stoichiometric spinel solid solution, and a little AlN, AlON and MgAlON were detected by XRD. With Al power content increasing, the amount of the porosity and AlN, AlON and MgAlON around the porosity detected by SEM increased. These new phases enhance the combination of the large particles and the matrix.

Abstract: Porous Al is a lightweight material with excellent heat insulation and sound absorption properties and is expected to be used in a wide range of applications. A method based on mechanochemical reactions has been developed as an environmentally friendly approach to porous Al production. Pure Al powder reacts with pure water to form a coating layer of Al (OH)₃ on the surface of the powder particles. Adjacent particles then bind together by adhesion of their coating layers. Since a large number of voids remain between the individual particles, the compact is classified as porous Al. In the present study, a mixture of pure Al powder and pure water was subjected to uniaxial compressive stresses ranging from 0 to 100 MPa to form porous Al. The mechanical properties of the resulting compact were evaluated in terms of the amount of H₂ produced, the density, the Al (OH)₃ texture, the amount of Al (OH)₃ formed, and the results of subsequent compression tests. The density of the porous Al was found to increase with increasing compressive stress during formation. The largest amounts of H₂ (800 ml) were produced under a compressive stress of 10 MPa. As the compressive stress was increased, the total amount of generated Al (OH)₃ increased, was approximately constant from 30 to 50 MPa, and then decreased. The initial maximum stress, the plateau stress, and the absorbed energy increased with increasing compressive stress and were 100 MPa, 17.5 MPa, and 10.1 MJ/m³, respectively, for a compressive stress of 100 MPa.

Abstract: High performance Al-Cr₂O₃-Al₂O₃ sliding gate are made from tabular corundum, white fused corundum, aluminum powder, and chromium oxide powder. Phenolic resin is used as binder. The properties of the Al-Cr₂O₃-Al₂O₃ sliding gates with the different content of chromium oxide(mass percent 3%,6%,9%,12%,15%) which are made from different processes (dried at 200°C in air, fired at 1300°Cin N₂ and fired at 1450°C in CO), are researched respectively. The results show that in different processes, the samples which contain 6% chromium oxide powder have higher cold crushing strength and hot modulus of rupture. After fired in N2, the new phases Al₈Cr₅ (1327°C), AlN are formed, and after fired in CO, Al₈Cr₅, Al₂OC and Cr₃C₂ are formed. These materials are contributed to improve the mechanical properties of samples. The samples fired in N₂ have the best performance.

Abstract: Unburned Al₂O₃ - C slide plate specimens were prepared at different temperatures, using tabular corundum, graphite, Al, Si powder as starting materials and silicone resin as binder. The results reveal that heat treatment temperatures have a significant impact on the performance of unburned Al₂O₃ - C slide plate. Between 200°C and 600 °C, the internal structure of the specimens is loose, and the apparent porosity increases significantly, meanwhile the cold crushing strength is very low. Between 800 oC and 1000 °C, the bulk density increases significantly, the apparent porosity have a sharp decline, and the cold crushing strength value increases. Over 1000 °C, there are many holes in the specimens, specimen mass and thermal expansion significantly increases, the bulk density decreases, and the apparent porosity increases, in the same time, the cold crushing strength has a downward trend.

Abstract: Porous mullite was prepared from a reactive mixture of Al metal powder and the fly ash produced by power plant. The sintering ceramics was characterized for the pore structure and phase identification studies. It was found that the sintered specimen expands at first (1300-1400°C) and then shrinks which was correspondence to the changing of open porosity. The expansion was attributed to the fact that the alumina produced from the oxidation reaction of Al powder made the volume larger than the starting mixtures. At 1550°C, it was inferred that the alkaline element in the fly ash made the mullite decomposed then destroyed the mullite structure. The SEM photographs suggested us that the pore diameter of the sintered ceramics might be adjusted by adding Al powder with different grain sizes. Moreover, because of the rod-like mullite produced in the pores, Mg metal addition could develop the further modification of the pore structure with similar porosity (47% at 1400°C/4h) compared with that (53%) with 0wt % Mg metal powders.