Correlation between chemical composition and alkali attack resistance of bauxite-SiC refractories in cement rotary kiln

Alkali vapor release during alternative fuel combustion severely attacked bauxite-SiC refractories in cement rotary kiln. The present work investigated the effect of chemical compositions on microstructure, refractoriness under load and alkali attack resistance of bauxite-SiC refractories by the incorporation of different amount of micron sized α-Al2O3 and microsilica powders. Results showed that the addition of α-Al2O3 improved the refractoriness under load of specimens, whereas alkali attack products, e.g. KAlSiO4 and KAlSi2O6 phases were largely formed in the alumina-rich matrix, leading to the large volume expansion and cracks formation. By comparison, the addition of microsilica resulted in the decrease of refractoriness under load. Moreover, the volume expansion during alkali exposure can be controlled by increasing amounts of microsilica, which was attributed to the fact that less K-aluminosilicate phases mentioned above and more liquid were formed. In this case, the newly formed liquid blocked up some pores and further prevented the penetration of K vapor into the matrix. Alkali attack resistance and refractoriness under load of bauxite-SiC refractories can be balanced when the mole fraction of Al2O3 was approximately 0.6 in the matrix of refractories.