Application of chromium-containing silica for synthesising functional glasslike materials by the sol-gel method

A new variant of the sol–gel method for synthesising silica glasses and optical composites containing nanoparticles of chromium oxide has been designed. Monolithic gels are produced by mixing preformed silica modified with chromium oxide (Cr2O3/SiO2), with a sol–gel solution containing Si(OC2H5)4, and gelation catalyst ((CH2)6N4 or NH3). Highly dispersed Cr2O3/SiO2 samples were synthesised through a step-by-step controlled adsorption of vapours of CrO2Cl2 and C6H14 on the surface of fumed silica (A-300) and a subsequent thermal decomposition. With increasing chromium concentration in samples from 0.9 to 5.1 wt.%, the size of chromium oxide nanoparticles increases from 10 to 46 nm. XRD, DTA, TG, IR-spectroscopy and measurements of specific surface area have been used to investigate structural and physico-chemical properties of Cr2O3/SiO2 and xerogels during the course of their thermal transformations up to formation of glasses. A study has also been carried out of optical properties of transparent samples (distribution of refractive index values through cross section of a preform). The glasses synthesised with the aid of Cr2O3/SiO2 have a more uniform distribution of doping constituents and exhibit a larger refractive index in comparison to glasses synthesised through impregnation of silica matrices with a solution of (NH4)2Cr2O7.