Ion-exchange-induced Phase Separation and Preparation of Porous Glass

Utilizing the difference in the size of the immiscibility regions with alkali ions, phase separation was induced at the surface of 70SiO 2 · 15B 2 O 3 · 15Na 2 O (mol %) glass by ion exchange in which Na + ions were replaced by Li + ions in molten LiNO 3 salt at 400 °C. The heat treatment after the ion exchange made the phase separation proceed and formed phases which can be dissolved by acid treatment. Through the ionexchange-induced phase separation, we prepared monolithic glasses, in which only the surface region is porous and the rest is homogeneous and transparent.