Effects of zirconium silicate and chromite addition on the microstructure and bulk density of magnesia–magnesium aluminate spinel-based refractory materials

Six synthesized magnesium aluminate spinel-based refractory compositions used in steel and cement applications, were prepared using a two stage sintering process at 1760 °C, starting with approximately 1:1 wt% ratio of pure magnesia and alumina with additions of zirconium silicate (0.5, 1.0 and 2.0 wt%) and chromite (2.0, 3.0 and 5.0 wt%). These compositions were investigated for effects on densification, chemical and mineralogical phases formed. The results show that free periclase, along with the magnesium aluminate spinel, is present in all samples. In samples with zirconium silicate additives, the high melting phase CaZrO3 was formed, promoting densification and refractoriness; but also controlling the occurrence of calcium aluminate and calcium silicate phases. Zirconium silicate also caused the bulk density to increase in all samples. In samples with chromite additive, Cr3+ (and Fe3+) enters the spinel lattice, substituting for Al3+ ions, and accelerated the spinel formation as well as increased the density of the crystals and their direct bonding. The bulk density of samples with chromite additives increased with the amount of additive.