Study on prestressed coating reinforced magnesia porcelain

Abstract

The current study aimed at the preparation of high strength magnesia porcelain. In this study, a coating basic formula of natural ceramic materials of Longyan kaolin (41.94 wt%), burnt talc (52.68 wt%) and Al₂O₃ (5.38 wt%) were used. In addition, right amount of potassium feldspar and ZnO were added to adjust the coating properties. High strength magnesia porcelain was obtained by the difference of thermal expansion coefficient between coating and substrate. The study focused on the changes in the cross-sectional area ratio and thermal expansion coefficient between the coating and matrix, as well as the effect of adding potassium feldspar and ZnO on the flexural strength of ceramics. Following the addition of 4 wt% ZnO and 13 wt% potassium feldspar, the results indicated a thermal expansion coefficient difference of 3.25 × 10⁻⁶/°C and a cross-sectional area ratio of approximately 54.40. The resulting composite ceramics sintered at 1220 °C for 60 min had their flexural strength reached 237.09 ± 26.70 MPa, which was 56.53 % higher than the matrix's flexural strength of 151.70 ± 5.32 MPa. Additionally, a study of the composite ceramics' resistance to thermal shock showed an increase in the critical temperature of decrease in flexural strength from 200 °C to 220 °C.