Kinetics of sub-liquidus phase separation in silicate and borate glasses. A review

Abstract

Many silicate and borate glass systems exhibit sub-liquidus immiscibility. The fine-scale microstructure of phase separated systems has been studied mainly by electron microscopy and small angle X-ray scattering. The classical theories of homogeneous nucleation, spinodal decomposition and coarsening, and more recent statistical theories of segregation are outlined. These theories are compared with experimental data for the kinetics of amorphous phase separation. In the early stages of separation, for compositions and temperatures in the region between the binodal and spinodal and in particular close to the binodal, the results are consistent with a homogeneous nucleation process. The classical theory of spinodal decomposition only agrees qualitatively with experimental data for the central region of the miscibility gap. The kinetics of coarsening are in general agreement with theory. Recent predictions from computer simulation studies on model alloys appear to be valid for glass systems. Experimental studies of the influence of amorphous phase separation on crystallization of glasses are also reviewed. In certain circumstances there is clear evidence that amorphous phase separation enhances the rates of crystal nucleation and growth.