Ion-Exchange Method for Fabricating High-Silica Glasses

Porous glasses produced by phase separation and leaching are used as substrates for the exchange of metal cations from a basic solution for the protons of silicon-bonded hydroxyl ions on the pore surfaces and on residual silica gel present in the pores. This method yields extremely homogeneous, fully dense high-silica glasses with low to moderate concentrations of metal dopants after sintering to collapse the pores. The quantity and rate of ion exchange are studied as a function of time, solution pH, and solution ion concentration for various dopant salts. In addition, a double ion-exchange method is described whereby, during the second exchange, ions which have a relatively low solubility in basic solutions can be exchanged from a neutral or acidic solution onto the glass surface.