This CoorsTek® AD-998 High-Alumina crucible cover is for use with crucible numbers 65543. It is made of 99.8%-pure Aluminum Oxide. It is highly resistant to chemical attack. This alumina-ceramic ware is especially useful to chemists, metallurgists, and others involved in high-temperature work demanding contamination-free results. AD-998 ware is highly refractory, meant for use in reducing and oxidizing atmospheres. It is inert in hydrogen and carbonaceous atmospheres and offers high resistance to alkalies and other fluxes. It is suitable for glass melting, including borosilicate glass. Recommended for use with refractory metals such as molybdenum, platinum, rhodium, tungsten, tantalum and iridium. High-Alumina Labware temperature change rate should not exceed 150º C/hour. CoorsTek® AD-998 High-Alumina properties include a maximum use temperature (without load) of 1750°C. The specific gravity is 3.9 (typical). Hardness is 79 on Rockwell 45N scale and 9 on Mohs scale. Permeability: Gas-tight. Water Absorption: None. NOTE: Due to unavoidable variations in manufacturing processes, cover may not fit precisely on crucibles. Material: High-Alumina. CoorsTek® #: 65615.