Refractive Index and Pore Structure of Acid-Leached Surface Layer of Glass

Abstract

It is known that acids leach out metal ions from the outermost layer of glass, leaving a skeleton film. We found that the refractive index of such a film n_f changes with the relative humidity p⁄p₀, and studied n_f vs. p⁄p₀ relations for some dense flint and dense crown glasses. The following conclusions are derived from the analysis of n_f vs. p⁄p₀ curves: (1) The refractive index of the skeleton n_s (>n_f) is always greater than that of fused silica, indicating that metal ions are still contained in the skeleton. (2) The porosity of the film ranges from 0.05 to 0.21, and the mean pore radius from 6Å to 23Å, depending on the composition of glass as well as the leaching conditions.