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 H2O/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 H2O/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.
BT - Journal of Non-Crystalline Solids DA - 10/1994 DO - 10.1016/0022-3093(94)90206-2 IS - 1 LA - eng N1 -0022-3093doi: DOI: 10.1016/0022-3093(94)90206-2
N2 -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 H2O/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 H2O/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.
PY - 1994 SP - 18 EP - 25 T2 - Journal of Non-Crystalline Solids TI - Improving the visible transparency of silica aerogels VL - 176 ER -