THE EFFECT OF LONG-TERM EXPOSURE TO HIGH TEMPERATURE ATMOSPHERE ON THE MECHANICAL PROPERTIES OF Al₂O₃-BASED CERAMIC MATERIALS

Two corundum-based ceramic materials (C799 and C795) and one type of mullite ceramics (C610) have been tested for the production of components of technological circuits working with high-temperature helium and supercritical water. The materials were exposed to an atmosphere of high-temperature helium (900 °C), air (900 °C) and supercritical water (577 °C; 24 MPa) for 1000 hours and subsequently tested for bending strength at temperatures up to 1400 °C. The highest bending strength was exhibited by the corundum ceramics C799 (more than 300 MPa at 25 °C); for a significant decrease in the strength, it was necessary to use temperatures higher than 1000 °C. This material also exhibited relatively good stability during exposure to high-temperature helium, hot air as well as supercritical water; after 1000-hour exposure, its tensile strength decreased by maximally 11 %. Therefore, the pure corundum material has been evaluated as the most suitable among the tested materials for the production of components of the mentioned technological circuits.