Microsilica role in the CA6 formation in cement-bonded spinel refractory castables

Assisted sintering tests, permanent linear change and microstructural evaluation were carried out in alumina–magnesia and alumina–spinel castables to analyze the microsilica effects on the CA6 development in each system. Unlike the alumina–magnesia ones, alumina–spinel castables did not present linear changes due to the CaO·2Al2O3 (CA2) formation. The morphology of the calcium hexaluminate (CaO·6Al2O3CA6) grains throughout the castable microstructure was shown to be quite similar for both systems. The CA6 distribution showed to be dependent not only on the ion diffusion mechanism but also on the in situ spinel formation in the Al2O3–MgO castables matrix, which also indicated that by a correct raw material selection, it is possible for the alumina–spinel castables to attain the spinel and CA6 benefits with very low overall expansion.