Secondary Phase Separation in Lead Borate Glasses

The effect of secondary phase separation on the apparent volume fraction of second phase was examined in the immiscible region of the PbO-B₂A₃ system. The volume fraction, V₂, of the PbO-rich phase agreed well with theoretical expressions relating V₂ to density and composition, except for 0.2< V₂ <0.5. The discrepancy in this region was explained in terms of the peculiar shape of the immiscible phase boundary and the resulting mutual supersaturation of the immiscible phases with respect to each other.