Mechanical properties and thermal shock resistance of anorthite ceramics obtained by slip casting

Anorthite ceramics (CaAl2Si2O8) was obtained by slip casting of water suspension of kaolin (Al2O3·2SiO2·2H2O) and CaCO3 as a source of CaO. A relative density of 87 % of the theoretical density was achieved after a 3-h-long sintering of green samples at 1200 °C. It was found that slip casting allows the fabrication of anorthite with relatively small pores (<8 μm) which was beneficial for achieving a high fracture strength of 129 MPa and good thermal shock resistance. For a quantitative measurement of thermal shock resistance, a critical temperature interval (ΔTc) was determined by a reduction in the mean fracture strength of at least 30 %. The experimentally determined ΔTc of 300 °C was higher than the value calculated by the equation assuming that the thermal stress created during quenching causes the fracture. It was found that the discrepancy between experimental and calculated values of ΔTc could be explained by an introduction of cracks of various sizes by indentation method and careful observation of crack growth initiation after quenching from various temperatures. It is believed that the reason for the discrepancy lies in the different nature of stress that was used in the theoretical calculation and the stress that acts during sample quenching.