Onset of alkali adsorption on the vitreous silica surface

The molecular dynamics computer simulation technique has been used to study the atomic level structure at the vitreous silica surface and the effect that this surface structure has on the early stages of adsorption of K and Li ions. K ions preferentially adsorb at nonbridging oxygen (NBO), often diffusing over the surface prior to finding such sites. After saturation of these NBO's, the K ions attack siloxane bonds. The K ions do not diffuse into the silica substrate, even though there are channels available for such diffusion. Li ions initially adsorb at both the NBO as well as the bridging oxygen at strained siloxane bonds. Also the Li ions readily diffuse into the subsurface regions of the glass.