Effects of cement and magnesia fines on in situ spinel formation in alumina–magnesia castable

The present study was carried out to determine the effects of cement content along with varying additions of medium and fine particles in added magnesia on in situ spinel formation in an alumina–magnesia castable. The effects of cement and magnesia on spinel and hibonite formation in the castable, alumina content of spinel, and associated physical changes after exposure to high temperature were studied. The presence of a larger quantity of fines in added magnesia was found to help increase spinel formation, with greater permanent linear change (PLC), provided cement content was not too high. Considering spinel formation and PLC, it appears that optimum levels are 3% cement for 50% of fines in magnesia or 4% cement for 34% of fines in magnesia, for a total addition of 6% magnesia. No clear combined effect of cement content and fines content in added magnesia on alumina content of spinel could be found. It is observed in general only that alumina content of spinel increases with increasing firing temperature. From these findings it is evident that increase in liquid phase to a certain level helps in increasing spinel formation and expansion characteristics. However for increasing alumina content of the spinel formed, it is found that temperature is more effective than increase in the liquid phase content.