Fabrication and properties of in situ intergranular CaZrO3 modified microporous magnesia aggregates

Lightweight microporous magnesia aggregates with closed porosity of 6.2%, apparent porosity of 2.1% and median pore size of 2.36 mu m were fabricated by introducing nano-sized ZrO2 combined with magnesite decomposition and sintered at 1780 degrees C. The sintering properties and microstructure revealed that nano-sized ZrO2 promoted the sintering and formation of closed intragranular pores by increasing abundant crystal defects and producing cation vacancies (V'(Mg)) raising the migration rate of grain boundaries, which induced a change in porosity type from large open pores to small closed pores. The nano-sized ZrO2 changed the bonding of magnesia grains from single CaO-SiO2-MgO phases bonding to composited CaO-SiO2-MgO phases-CaZrO3 phases bonding, significantly enhancing the slag penetration resistance. The closed porosity played a more important role in reducing the thermal conductivity compared with total porosities. The microporous magnesia aggregates and thermal conductivity of 8.994 W (m K)(-1) at 800 degrees C exhibit potential for application in wear lining refractories.