Compositional Changes as Evidence for Spinodal Decomposition in Glass

The phase separation of some borosilicate glasses shows the gradual approach of 2‐phase compositions to those of equilibrium. The change in the etch (or leaching) rate is caused by the gradual change in the alkali borate‐rich phase composition and the gradual change in viscosity is caused by the gradual change of silica‐rich phase composition. The gradual change of the 2‐phase compositions rejects the classical nucleation and growth mechanism and supports the transformation mechanism developed by Hillert and Cahn. Although the latter mechanism covers both spinodal decomposition and nucleation and growth, the observed gradual change of two compositions for glasses with initial compositions falling near the center of the immiscibility dome is direct evidence of spinodal decomposition