Effect of zirconia addition amount in glaze on mechanical properties of porcelain slabs

Applying toughened glaze layer on porcelain slabs can improve the fracture toughness of slabs and greatly reduce the production cost. In this study, porcelain slabs glaze with high toughness was fabricated by the processes of impregnation glazing and single firing method, using opaque frits, kaolin clay as the main raw materials, zirconia as an additive, and the effect of the addition amount of zirconia in glaze on fracture toughness of porcelain slabs was investigated. The results showed that the type and content of crystal phase of the glaze were greatly influenced by the addition amount of zirconia. Meanwhile, compared with the base glaze, the hardness and fracture toughness of the sample with zirconia glaze were significantly improved. Porcelain slabs with 10 wt% zirconia in glaze, sintering at 1200 °C, exhibited higher quality glaze and outstanding properties, including a water absorption of 1.95%, a Vickers hardness of 6.36 GPa, and a fracture toughness of 2.71 MPa m1/2. The toughening mechanism of the glaze layer was as follows: a large number of zirconium silicate grains with high hardness were generated by the reaction of added zirconia with silica in the glass phase, which increased the content of crystal phase and then prevented the propagation of cracks; moreover during the martensitic transformation of the tetragonal zirconia grains, the volume and shear strain were generated to offset the stress field generated by the crack tip, thus toughening the material.