Transparent, refractory glass-ceramics based on 10nm crystals of spinel solid solution in a highly siliceous residual glass can be produced from compositions in the Si02-Al203-Zn0-Mg0-Ti02-Zr02 system. The glass-ceramics possess excellent chemical durability as well as thermal expansion coefficients of 35-40 x 10-7/deg C & strain point temperatures of over 900 deg C. Titania serves as both an extremely effective nucleating agent in these glasses & as an integral component of the spinel crystals. The materials are designed such that fluxes in the glass partition into the spinel crystals during the crystallization process, leaving a continuous residual glass very high in silica. The strain points of the resultant glass-ceramics approach those of vitreous silica & quartz mateirals which require significantly more expensive manufacturing process.
