Stoichiometric (Ni,Mg)-Cordierite Glass-Ceramics

摘要

Both the properties and crystallization behavior of xNiO·(2-x)MgO·2Al_2O_3·5SiO_2 glasses for x = 0.0, 0.25, 0.5, 0.75, and 1.0 are studied. The glass transition temperature and dilatometric softening temperature decrease as increasing amounts of nickel are substituted for magnesium. The coefficient of thermal expansion (CTE) of the glasses is largely independent of the glass composition-the CTE for all nickel containing glasses is ca. 4.0 ppm/K, which is slightly higher than the CTE for the nickel-free glass (ca. 3.8 ppm/K). The crystallization behavior of the glasses is studied using differential thermal analysis data and high-temperature X-ray diffraction data. All glasses crystallize to form a β-quartz solid solution at the surface; this phase transforms to cordierite at higher temperatures and/or longer annealing times. The crystallization temperature of the β-quartz is related to the occurrence of phase separation. The temperature at which β-quartz transforms to hexagonal cordierite increases with increasing amounts of nickel. Glasses where x ≥ 0.50 crystallize to form a spinel phase in the bulk of the glass. The spinel crystallization temperature decreases with increasing amounts of nickel substituted for magnesium. The spinel composition is dependent on the initial glass composition and crystallization temperature. Competing transformation processes (spinel in the bulk and cordierite at the surface) in glasses where x ≥ 0.75 result in a compound activation energy value.