7 December 1992 Properties of gel-silica optical matrices with 4.5-nm and 9.0-nm pores
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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, large 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 degree(s)C and 4.4 nm after 1000 degree(s)C. Pore volumes are 0.9 cm3/g at 900 degree(s)C and 0.7 cm3/g at 1000 degree(s)C. The ammonia aging process yields 9.0 nm radius pores at 900 degree(s)C and 8.7 nm pores at 1000 degree(s)C. Pore volumes are 1.0 cm3/g at 1000 degree(s)C. Optical properties (including UV cut-off, UV-vis-NIR transmission, IR absorption, index of refraction), bulk and structural densities of the matrices made by both methods (900 degree(s)C and 1000 degree(s)C stabilization) are compared with the 1.4 nm pore radius matrices.
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Larry L. Hench, G. P. LaTorre, S. Donovan, J. Marotta, and E. Valliere "Properties of gel-silica optical matrices with 4.5-nm and 9.0-nm pores", Proc. SPIE 1758, Sol-Gel Optics II, (7 December 1992); doi: 10.1117/12.132004; https://doi.org/10.1117/12.132004

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