Formation Mechanism of In Situ Intergranular CaZrO3 Phases in Sintered Magnesia Refractories

Sintered magnesia refractories combined by in situ intergranular CaZrO 3 phases were synthesized using natural MgO-containing natural minerals with CaO and SiO 2 impurities and nano-sized ZrO 2 additive. A homogenous distribution of intergranular CaZrO 3 , independent from the intergranular CaO-MgO-SiO 2 phases, was formed in situ within the sintered magnesia aggregates by introducing 0.75 wt pct nano-sized ZrO 2 into the magnesite. The formation mechanism of the in situ intergranular CaZrO 3 phases was determined. The nano-sized ZrO 2 was introduced and uniformly distributed at grain boundaries of the magnesia due to the micron-nano-sized particles composite system and wetting grinding process. Then the CaO in impurities were prior to SiO 2 to react with the ZrO 2 for generating CaZrO 3 at the grain boundaries by increasing sintering temperature. Nevertheless, the nano-sized ZrO 2 particles were encapsulated in the MgO crystallites with similar particle size decomposed from brucite and prevented from reacting with CaO impurities in magnesite. The mixing homogeneity of magnesite particles and ZrO 2 particles and the direct contact between ZrO 2 and CaO impurities in magnesite has a crucial effect on the formation of intergranular CaZrO 3 phases. Furthermore, the intergranular CaZrO 3 phases could enhance the bonding of magnesia grains and have great potential for improving the service performance of magnesia.