Influence of ZrO2 on the phase composition and mechano-physical properties of MgO-ZrO2 refractories prepared by cold isostatic pressing

MgO-ZrO2 refractories were produced by combining MgO refractories (with a CaO/SiO2 ratio of 2.1) with monoclinic ZrO2 powder using wet-bag cold isostatic pressing. The phase composition and mechano-physical properties of the MgO-ZrO2 materials were influenced by the interaction between ZrO2 and MgO refractories. ZrO2 enhanced the cold modulus of fracture of MgO refractories but decreased the hot modulus of fracture due to changes in bonding phases. The addition of 1 wt% ZrO2 transformed Ca2SiO4 into CaMgSiO4 and CaZrO3. CaMgSiO4 with a low melting point deteriorated the hot modulus of fracture of MgO-ZrO2 refractories from 13.3 to 2.97 MPa. With an increase in ZrO2 to 3-5 wt.%, CaMgSiO4 remained while CaZrO3 gradually transformed into the solid-solution Ca0.2Zr0.8O1.8. This transformation occurred because ZrO2 seized CaO from CaZrO3 to stabilize itself. Based on thermodynamic equilibrium ZrO2 preferentially reacts with CaO-containing phases in the MgO matrix in the following order: Ca3SiO5 > Ca2SiO4 > CaZrO3 > CaMgSiO4. The thermal shock resistance of MgO-ZrO2 refractories with less than 5 wt% ZrO2 was not significantly improved by assessing their strength loss and coefficient of thermal expansion. In conclusion, it is recommended to incorporate ZrO2 into MgO refractories with low SiO2 or CaO to develop high-performance MgO-ZrO2 refractories.