Study On Microwave Sintered Al₂O₃/SiC Composites

Microwave heating technology was used for the preparation of alumina powder and Al2O3/SiC composite material. The high dispersed α-Al2O3powder was firstly obtained by microwave pyrolysis precursor method to get the optimum parameters of the preparation of alumina powder. Then using the powder as raw material, Al2O3/SiC composite ceramic was prepared by adding SiC powder and the surface modification of the SiC particles.During the microwave pyrolysis process of α-Al2O3powder, an insulation structure based on hybrid heating mode was well designed with the sample compartment of Al2O3crucible and the aided heaters of SiC. The results show that about0.3μm size of alumina powders with uniform particle size, excellent dispersion and no-reunion were obtained using Ammonium aluminum sulphate and aluminium hydroxide as the precursor and microwave heating to1100℃for5min. As the microwave sintering temperature increased to1200℃, the particles of alumina began to grow. But the extension of the preservation time did not have the influence on the morphology and size of the particles. Compared with the Resistance heating method, the0.3μm of alumina powder can also be obtained when the temperature was increased to1200℃for30min. But the powder appeared to reunite seriously.Alumina powder can not absorb microwave and so the experiment get the optimal parameters of the preparation of the alumina composite ceramic by microwave pyrolysis via varying the concentration of the addition of SiC (5vol.%,10vol.%,15vol.%,20vol.%) and the sintering temperature (1300℃,1350℃,1400℃,1450℃,1500℃). In the microwave sintering process of Al2O3/SiC composite ceramic, the insulation material was added around the sintered samples on the base of before-mentioned hybrid heating insulation structure, to reduce the temperature gradient between sintered samples and surrounding environment. Meanwhile, the power was controlled to achieve stable heating and cooling. The results indicate that with the increasing of sintering temperature, the density of composite ceramic is generally rising while the porosity is decreasing. When the powder was fired at1450℃for30min, the density is the highest. In addition, as the content of SiC increases, mullite petrochemical of Al2O3/SiC composite ceramic was enhanced. When the additive amount of SiC is20vol.%, the composite ceramic is completely mullitized. In order to decrease the sintering temperature of composite ceramic and the mullitization, Sol gel method and high temperature oxidation method are both used to modified the surface of SiC to obtain SiO2/SiC core-shell structure. The green body was fired to form SiC-Mullite-Al2O3composite structure. In the sol-gel method, when the quantity of packages reaches to40vol.%, the oxidation of SiC powder can be well prevented. The Al2O3/(SiO2)SiC samples prepared via microwave sintering sol gel method, owing to "Hot cluster" effect of microwave, appeared more melting zones and inside of the melting zone, a great many of tiny alumina grain were generating.