Increasing the crystal size of calcite in magnesia can increase the reaction activity of magnesia, carbon and slag, which is beneficial to improve the slag resistance and service life of refractories.

In recent years, large crystalline magnesia has been paid more and more attention. Figure 1 shows the relationship between the crystal size of magnesite and the corrosion rate when the resin-bonded and asphalt-bonded MgO-C bricks consumed with sintered magnesia are used to distinguish the trunnion parts and the upper cone of the basic oxygen converter. It clearly indicates that the corrosion rate of MgO-C brick can be reduced by one third by using large crystalline magnesia.

The crystal size of magnesite in sintered magnesia consumed before is only 4060μm, so for magnesia used in MgO-C brick, the crystal size of magnesite is required to be great and greater than 80μm. Due to technological progress, large crystalline magnesia of 100160μm can be consumed, and the average crystal size is 200μm. Therefore, large crystalline magnesia should refer to magnesia with crystalline size greater than 100120μm. In the consumption of sintered magnesite, controlling the chemical composition, adding the forming pressure of billet ball, increasing the sintering temperature and extending the holding time can increase the crystal size of small magnesite.

Large crystalline magnesia with crystal size of 130200μm can be obtained by using oxygen enriched blast quenched up to 2200℃ in shaft kiln, while the crystal size of traditional magnesite is less than 100μm. The effect of high temperature calcination is clear, but more fuel is needed. A large amount of Zr2O can also increase the size of calcite clearly from 5080μm to more than 100μm. A large number of SiO2 and TiO2 also have the effect of increasing the crystallization size of small magnesite.