Study On Preparation And Thermal Stability Of Microcrystalline MgAlON And Corundum Composites

Micro/nano-crystalline composite refractory materials with very high grain boundary energy being not conducive to the emergence and expansion of crack can increase thermal shock resistance, and have most of nanoscale pores impeding the penetration of slag to increase slag resistance, so micro/nano-crystalline composite refractory materials are expected to solve the problem about how to obtain materials with slag resistance and thermal shock resistance well. But long-term use at high temperatures will gradually make the grain grow to the equilibrium microstructure, and quality and appearance of the materials gradually change, the change will lead to unstable performance.In this paper, Al2O3-MgAlON composite was fabricated by hot-pressing and spark plasma sintering (SPS) with aluminum, magnesium oxide and alumina as raw material, high purity graphite as a mold, in a nitrogen atmosphere; the best preparation temperature, molding pressure, preparation time were determined by the bending strength of samples; the preparation methods of Al2O3-MgAlON composite materials were determined by the performance of the sample by the hot-pressing and spark plasma sintering; Carbon impact on the sample preparation, as well as the mechanism of micron-sized crystal particles generated were study by XRD, EDS and SEM and other research tools in the system; the stable condition maintaining microcrystalline structure was study. The main results are as follows:The best hot pressing condition was 42MPa pressure,950℃and 8min. The main crystal phases of Al2O3-MgAlON composite prepared under best preparation conditions were corundum and MgAlON. Microstructure analysis showed that the materials structure was dense; there were micro-crystal particles about 300nm. Under the same experimental conditions, the samples sintered by hot pressing had better performance than the ones by SPS; Al2O3-MgAlON composites with good performance were obtained by hot pressing at lower temperature.The study of graphite impact on the sample during the preparation suggested that: carbon diffusion from graphite into the sample increased as the temperature, the presence of carbon in the sample was conducive to maintaining a low partial pressure of oxygen and thus helped to obtain MgAlON in the interior of sample. The mechanism studies of Al2O3-MgAlON composite materials prepared by hot pressing process had shown that the reaction includes three stages:preparation stage, liquid aluminum control stage, the crystalline stage; the presence of liquid aluminum and the pressure created the conditions for the Al2O3-MgAlON composite materials at low temperature:(a) sufficiently wetting Al2O3 and MgO particles; (b) liquid aluminum generated at high temperature bulit fast track for the ions proliferation and transport of different substances, and provided a site for the occurrence of reaction, so materials with good crystallization were prepared at low temperature.Thermal stability studies of Al2O3-MgAlON composite had shown that:When the temperature was at 1300℃and below, the heat treatment time was 12h, the microcrystalline structure of Al2O3-MgAlON composite would not change, although phase composition changed when the temperature was higher than 1300℃, the strength did not decrease.