Phase separation in glass and glass-ceramic systems

The capabilities and limitations of the small-angle X-ray scattering technique which have been found for the establishment of the mechanisms of early stages of phase separation in glass systems are examined. This includes the evaluation of the criteria for distinguishing between the mechanisms of initial separation such as nucleation and spinodal decomposition. The application of this technique for directly following nucleation processes is given. The information obtained employing these methods concerning qualitative differences in the early stages of phase separation as functions of composition and temperature of ZrO2-containing phases in two MgO·Al2O3·3SiO2·X ZrO2 glasses are presented. The X-ray scattering results show that precipitation of a ZrO2 phase is not a necessary prelude to the crystallization of the glass.