Effect of MgO and ZrO2 additions on the properties of magnesite-chrome composite refractory

Magnesite-chrome aggregates have been prepared from friable chrome ore and magnesia of different reactivity in the presence of an additive, ZrO2. Two types of batch compositions using sintered magnesia, caustic magnesia and chrome ore have been selected for preparing mag-chrome composites. The batch consisting of sintered magnesia and friable chrome ore (SMC) was vibromilled for 8 h, whereas caustic magnesia compositions were added directly to a vibromilled chrome ore (CMC) and mixed in a fluidized bed mixer. Additions of 1–5 wt.% ZrO2 were made to the batches. Firings were carried out between 1700 and 1750 °C with 2 h soaking. Aggregates were characterized by evaluating densification, hot modulus of rupture and microstructure. The reactivity of magnesia was found to play an important role in the final properties of samples. Introducing less reactive sintered magnesia improved all the properties of the aggregates. ZrO2 was found to be a good sintering aid in the magnesite-chrome composites.