Effect of Cr2O3 on sinterability and properties of mullite-spinel composites

Seven mixes of mullite-spinel composites composed of 100:0, 80:20, 60:40, 50:50, 40:60, 20:80, and 0:100 wt% of presynthesised mullite and magnesium aluminate (MA) spinel were prepared and fired up to 1550degreesC for 2 h. The phase compositions of the fired mixes were investigated using X-ray diffractometry. The physical, mechanical, and refractory properties of the fired composite batches were determined according to DIN standard specifications. The two mixes containing 40 and 20 wt-% mullite with 60 and 80 wt-%, MA spinel were considered as optimum mixes, since they combined better physical, mechanical, and refractory properties than the other compositions. Additions of 2 wt-%Cr2O3 to both mixes resulted in further improvements in physical and mechanical properties after firing at 1550degreesC owing to its solid solution in mullite and spinel.