Effect of Cr 2 O 3 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 1550°C 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 1550°C owing to its solid solution in mullite and spinel.