Properties of gel-silica optical matrices with 4.5-nm and 9.0-nm pores

Abstract

Sol-gel processing of tetramethyl orthosilicate with HNO3 as a catalyst has been used to make optically transparent silica matrices with interconnected porosity of 1.2 to 1.4 nm radii. However, larger pores are often needed for impregnation of the matrices with optically active organics. Larger pore volumes are also desirable for many applications of these optical composites. Two methods for producing larger pore matrices are compared: 1) Catalysis with dilute HF, and 2) aging in a basic NH4OH solution. Pore radii of matrices made by the HF method are 5.0 nm after thermal stabilization at 900°C and 4.4 nm after 1000°C. Pore volumes are 0.9 cm3/g at 900°C and 0.7 cm3/g at 1000°C. The ammonia aging process yields 9.0 nm radius pores at 900°C and 8.7 nm pores at 1000°C. Pore volumes are 1.0 cm3/g at 1000°C. Optical properties (including UV cut-off, UV-vis-NTR transmission, IR absorption, index of refraction), bulk and structural densities of the matrices made by both methods (900°C and 1000°C stabilization)are compared with the 1.4 urn pore radius matrices.