Characterization of silica nanocomposites obtained by sol-gel process using positron annihilation spectroscopy

SiO2 matrix was prepared by a sol-gel method using tetraethoxysilane, TEOS, ethanol and water in a 1/3/10 mole ratio, with HCl and HF as catalysts. Th is silica gel was doped with copper with different precursors and different contents of dopant. The samples were prepared into monolithic shape, dried at 110 degrees C for 24 h and thermally treated for 2 h at 500, 900 and 11 00 degrees C. The structural evolution was studied by positron annihilation lifetime spectroscopy (PALS) which has bean shown to be a useful tool for pore size analysis in several materials, X-ray diffraction (XRD) and nitrog en gas adsorption. All the samples have shown, according to the positron sp ectroscope results, a stable pore structure up to 900 degrees C and a stron g densification process at 1100 degrees C. (C) 1998 Elsevier Science Ltd. A ll rights reserved.