CHROMIUM, COBALT, NICKEL AND COPPER AS PIGMENTS OF SOL-GEL GLASSES

Studies referring to the application of the sol-gel method to obtain c oloured coatings on flat glass are reviewed. The authors present their own investigations on the production of coloured gel glasses (bulk an d films) of the systems R(n)O(m)-SiO2, where R is Cr, Co, Ni or Cu. Ba sed on transmission spectra measurements the valency and the coordinat ion states of transition metals in the starting solutions, gels, bulk glasses and films were determined. The mechanism of colouring of gel g lasses containing up to 15 mol of R(n)O(m) oxides has an ionic charact er. The most intense colouring is demonstrated by coatings of the Cr2O 3-SiO2 system. At higher transition metal concentrations segregation o f the respective oxides and selective scattering of light occur. It ha s been demonstrated that the soda-calcium-silicate glass covered with gel films of R(n)O(m)-SiO2 systems are characterized by microhardness which is 30-60 times higher than that of the basic glass.