Carbon nanotube/silica composites obtained by sol-gel and high-pressure techniques.

The successful incorporation of functionalized single-walled carbon nanotubes (f-SWCNTs) into a silica matrix prepared by the sol-gel method is reported herein. SWCNTs produced through catalytic chemical-vapor deposition (CCVD) have been purified and functionalized with sulfuric, nitric and hydrochloric acids to ensure a good dispersion in an aqueous solution. The nanotube composites are prepared using three concentrations of f-SWCNTs (0.025, 0.050 and 0.075 wt%.) in a silica matrix, resulting in translucent monoliths after gelation. Dense, crack-free and hard compacts are obtained by high-pressure processing at 7.7 GPa and room temperature. Compared to the pure silica compact, compacts containing 0.025 and 0.050 wt% f-SWCNTs show an increased toughness of about 54% and 69%, respectively. The influence of f-SWCNTs on some microstructural aspects of the silica matrix has been studied using nitrogen adsorption/desorption isotherms. Raman spectroscopy has been applied to analyze the effect of the silica matrix and high-pressure compaction on the f-SWCNTs incorporated into the silica matrix. These measurements showed that f-SWCNTs remained in the silica matrix under pressure, suggesting an important interaction with the matrix.