%0 Journal Article
%A Wanqing Cao
%A Arlon J Hunt
%B Journal of Non-Crystalline Solids
%D 1994
%G eng
%N 1
%P 18-25
%R 10.1016/0022-3093(94)90206-2
%T Improving the visible transparency of silica aerogels
%V 176
%8 10/1994
%X <p>Silica alcogels have been prepared in two steps, first in an acid and then in a base to control the relative rates of hydrolysis and condensation of TEOS. Increasing the H<sub>2</sub>O/TEOS ratio in the base-catalyzed step was the most important factor in reducing light scattering of the alcogel. The two-step gel could be practically made with H<sub>2</sub>O/TEOS = 30, achieving a scattering intensity less than 1/5 that of the best one-step gel. Lower scattering of the gel results in an aerogel with improved visible transparency and more homogeneous microstructure. TEM observation reveals that the two-step aerogel has a microstructure containing both linear polymers and colloidal particles that are cross-linked to a gel network.</p>