Enhanced mechanical properties and thermal shock resistance of magnesia refractories via in situ formation of tetragonal zirconia

The research and development of chrome-free refractories for non-ferrous metal smelting furnace is imperious for environmental protection. In present investigation, the magnesia-zirconia composite refractories were fabricated with sintered magnesia and desilicated zirconia as raw materials. The mechanical properties, thermal shock resistance properties, phase and microstructure of samples were investigated, and the specific fracture energy of magnesia-zirconia refractories matrix was obtained by statistical grid nanoindentation. The results showed that the magnesia-zirconia refractories added 5 wt%(MZ1 sample) desilication zirconia obtained the best performance, where the apparent porosity was only 18.06 % and the CMOR was 14.9 MPa. In addition, the specific fracture energy of MZ1 sample was 248 N m−1, which was 98 % higher than MZ0 (125 N m−1). Compared with the sample without desilicated zirconia, the residual strength ratio of magnesia-zirconia refractories increased more than 50.0 %. The improvement of the thermal shock resistance and mechanical properties of magnesia refractories was greatly attributed to the formation of t-ZrO2 in the matrix, where the dissolve of Ca2+ into the ZrO2 in the matrix is more benefit to the formation of the stable t-ZrO2 phase. The propagation of cracks is prevented by t-ZrO2, which further prevent the trans-granular fracture of magnesia aggregate. Therefore, the magnesia-zirconia refractories contained t-ZrO2 was expected to be candidate materials as chromium-free refractories used in non-ferrous metal smelting furnaces.