Spectroscopic ellipsometry study of thickness and porosity of the alteration layer formed on international simple glass surface in aqueous corrosion conditions

Dien Ngo,Raymond Lopez-Hallman,Hongshen Liu,Marie Collin,Stéphane Gin,Nisha Sheth,Seong H Kim,Nikolas J Podraza

doi:10.1038/s41529-018-0040-7

Abstract

The porosity and pore-size distribution in the glass play an important role in glass corrosion; however, such information is difficult to be obtained non-destructively. Here we report the use of spectroscopic ellipsometry (SE) under controlled humidity environments to determine those structural parameters in the alteration layers formed on international simple glass (ISG), a model nuclear waste glass, in aqueous corrosion conditions. The SE results show that the ISG sample corroded for nearly 4.5 years develops pores larger than 2 nm in diameter, while the alteration layers formed initially in less than 1 month do not have such large pores. The development of larger pores over a long period of corrosion time, while the overall thickness remains relatively constant, implies structural rearrangements of the silicate network occurring within the alteration layer, which could eventually affect the transport of reactants and products as well as the structural stability.

Highlights

The spectroscopic ellipsometry (SE) measurements of corroded samples were performed after holding the samples at 0% RH inside the environment-controlled sample cell for about 10 h
In situ, for further dehydration was not used in this experiment, since it results in collapse and delamination of the alteration layer
Interference fringes are observed in the ellipsometric spectra for the corroded samples (Fig. 1c–f), indicating a thick alteration layer with optical response differing from that of the underlying uncorroded glass substrate

Summary

Introduction

Understanding glass corrosion behaviors in aqueous media is important to develop the degradation mechanism of glass materials and predict their environmental stability.[1,2,3,4,5,6,7,8,9] Due to ion exchange, hydrolysis-condensation and/or dissolution-reprecipitation, and reconstruction of the glass network during the corrosion process, the composition and structure of the surface region of glass are changed, forming a so-called alteration layer whose structure is different from the bulk.[4,10,11,12] The alteration layer is usually rich in silica content and contains hydrous species (Si-OH and H2O) like a hydrated porous gel; this surface layer could work as a molecular sieve to protect the glass from further corrosion.[4].

Results

Conclusion