Refractory glass-ceramics based on alkaline earth aluminosilicates

摘要

Glass-ceramics that can be used at temperatures of 1200-1500 deg C are found in the alkaline earth aluminosilicate field, and are generally nucleated internally with titania. These glass-ceramics have good strength (>100MPa, abraded), can be tailored to produce high fracture toughness (2-5 MPa m~(1/2)), and have good dielectric properties. Coefficients of thermal expansion (CTEs) are low to moderate ((25-45) X 10~(-7) deg C~(-1), from 25 to 1000 deg C). The major crystalline phase in the glass-ceramics exhibiting the lowest CTEs is hexagonal cordierite (indialite), while important toughening accessory phases are enstatite and acicular magnesium dititanate. The most refractory glass-ceramics that are easily melted at 1650 deg C, yet when crystallized do not deform at 1450 deg C, are based on strontium and barium monoclinic feldspars of the celsian type. CTEs range from 35 to 45 X 10~(-7) deg C~(-1). Acicular mullite is an important accessory phase aiding fracture toughness in these materials. Mullite glass-ceramics which contain considerable siliceous residual glass are probably the most refractory of these glass-ceramics, but they require melting above 1700 deg C. Nevertheless, they can be used at temperatures near 1600 deg C. Potential applications for refractory glass-ceramics include improved radomes, engine components, substrates for semiconductors and precision metallurgical molds.