Influence of silica and magnesia on in situ spinel formation in alumina-magnesia castable

The present study was carried out on the matrix composition of spinel forming high alumina castable to determine the effects of silica, magnesia particle size and temperature on spinel formation, the alumina content of the spinel formed, and associated physical characteristics at high temperature. It was found that an increase in silica content and use of finer magnesia helps to increase spinel formation. However to increase the alumina content of the spinel, increased temperature and magnesia particle size were more effective than an increased amount of silica. Furthermore the permanent linear change and porosity of the matrix are adversely affected when the amount of silica is increased or when magnesia is added in the form of fines. These findings suggest that medium and fine magnesia particles and an optimum amount of silica in the matrix composition of a spinel forming castable are necessary to obtain a matrix with increased alumina rich spinel content with controlled permanent linear change and porosity when exposed to high temperature during service.