Journal of the American Ceramic Society, Vol.103, No.12, 7041-7055, 2020
Investigations into the thermal stability of sol-gel-derived glasses as models for thermally grown oxides
The thermal stability of sol-gel-derived silica and borosilicate glasses exposed to dry O(2)at 800 and 1200 degrees C for 100 hours was characterized by weight change, thermal transitions, morphology, structure, and composition to investigate suitability as models for thermally grown oxides. Rapid weight loss was observed in the first few hours of isothermal exposure for borosilicate glasses, followed by constant weight loss at a low rate for the balance of the exposure. Weight loss resulted from loss of residual hydroxyl species retained from the sol-gel synthesis, and from oxidation of carbon retained from thermal decomposition of the organic precursors by pyrolysis. Characterization of the sol-gel-derived glasses showed structural similarities to silica and binary borosilicate glasses synthesized by melt or vapor deposition methods, and to thermally grown oxides. Oxygen transport mechanisms through the sol-gel-derived glasses is not thought to be affected by the retained carbon. However, a silica-enriched glass surface resulting from boria volatility, observed from a borosilicate glass exposed dry O(2)at 1200 degrees C, will slow O(2)transport rates. The results show that sol-gel-derived silica and borosilicate glasses can be used as models for thermally grown oxides.