Study On Corundum - Mullite Refractory For Microwave Metallurgy In Situ Synthesis Of Mullite Whisker

Considering the characteristics of fast heating rate and selectivity to heat the materials of microwave-heating in the microwave-metallurgy process, the refractory meet unique demands, such as:good thermal shock resistance, good heat impact resistance, high microwave-penetration ability and good bearing ability to physical, chemical and mechanical attacks at high temperature. These complex demands make the candidate range of microwave-metallurgy refractory very narrow. In this paper, the refractory, respectively suitable to high temperature, intermediate temperature and low temperature during microwave-metallurgy process, are explored.The thermal shock resistance of corundum-mullite refractory, used in microwave-metallurgy reaction unit at high temperature, becomes worse as the ratio of corundum in this composite increases. As a consequence, the service life becomes shorter. In this paper, the corundum-mullite refractory is roughed by in-situ synthesized mullite whisker. Firstly, chemical pure Al(OH)3 and SiO2 are used as raw materials, while AIF3 and V2O5 as catalytic agent and assistant materials. At the same time, the effects of sintering temperature, holding time, molding pressure and content of catalytic agent on corundum-mullite properties are investigated. Then, the influences of upper factors on the ratio of length to diameter of mullite whiskers are optimized. Mullite whiskers with an aspect ratio of 15.0 could be obtained under the optimized conditions (forming pressure of 25 MPa, V2O5 addition amount of 4%, sintering temperature of 1 320℃and holding time of 2 h).On the basis of these optimum parameters, the composite refractory with corundum-mullite theory ratio of 1:2,1:1 and 2:1 are roughed and discuss the factors on the bending strength and fracture toughness of influence of performance. The results show that optimum performance of the composite refractory could be obtained under the optimized conditions (corundum-mullite theory ratio of 1:1, AlF3 addition amount of 2-6%,V2O5 and addition amount of 3-7%, sintering temperature of 1300-1500℃). On the basis of these optimum parameters, the optimization of some parameters (such as sintering temperature, addition amount of V2O5 and addition amount of AIF3) for bending strength and fracture toughness in the preparation process was carried out by means of a response surface method. The bending strength and fracture toughness with 60.09MPa and 9.15 MPa.m-1/2 could be obtained under the optimized conditions (sintering temperature of 1400℃, V2O5 addition amount of 5.5%, AlF3 addition amount of 4.5%). Compared with no add mullite whiskers corundum-mullite refractories, bending strength and fracture toughness increased more than 5 times and 3 times.