Colloidal silver formation at the surface of float glass

Abstract

The formation of colloidal silver during the heating in air of silver films on float glass has been observed. The presence of colloidal silver gives to a yellow color and an absorption band centered at 400–420 nm. The results of this study indicate that the formation of colloidal silver is strongly dependent upon the concentration of stannous tin in the glass. The optical density of the absorption band induced in the glass is much greater for samples silvered on the tin-rich face of the glass and varies with the thermal history of the sample. Removal of the outer few micrometers of the glass surface results in a radical change in the amount of colloidal silver formed. Silver colloids are formed only if the sample is heated in an atmosphere containing oxygen, suggesting that the silver must be ionized before it will diffuse into the glass. The colloid formation process has an activation energy of approximately 30 kcal/mol, which is very near that reported for silver-sodium interdiffusion in similar glasses.