PNNL

Abstract

Characterization of the alteration layers that form on glass surfaces during corrosion processes is imperative to understand both the mechanism and rate of glass alteration. In recent years, state-of-the-art materials and surface characterization techniques have been employed to study various aspects of the alteration layers that result from corrosion. In most cases, these techniques are destructive and thus can only be employed at the end of the corrosion experiment. In contrast, we show that the alteration layers can be investigated by non-destructive spectroscopic ellipsometry (SE), which provides pertinent information on alteration layer thickness, morphology, and, through correlation of the index of refraction, porosity. SE measurements of silicate glass coupons altered in aqueous solutions of pH 3, 5, 7, 9, 11, and deionized water at 90°C for 7 days are compared to cross-sectional secondary electron microscopy with electron-dispersive spectroscopy (SEM-EDS) line profiles. In most cases, quantitative agreement of the alteration layer thickness is obtained. Reasonable correlations are found between the fractional porosity calculated from the index of refraction and the porosity calculated from elemental analysis of the aqueous solutions by ICP-OES. These results open the possibility of performing non-destructive measurements as corrosion experiments progress.