Origin and consequences of silicate glass passivation by surface layers

Area of Science:

• Materials Science
• Geochemistry
• Nuclear Engineering

Background:

• Silicate glasses are considered for long-term radioactive waste confinement due to their inherent durability.
• Understanding the long-term aqueous corrosion mechanisms of these glasses is critical for ensuring safe geological disposal.
• The durability of nuclear waste glasses over hundreds of thousands of years remains a key question.

Purpose of the Study:

• To investigate the aqueous corrosion behavior of a model nuclear glass in silica-saturated conditions.
• To elucidate the mechanisms responsible for glass corrosion and the formation of protective layers.
• To assess the long-term durability of silicate glasses for radioactive waste containment.

Main Methods:

• Corrosion experiments were conducted on a model silicate glass in silica-saturated solutions.
• Analysis of glass alteration involved studying water ingress, element release, and silicate network repolymerization.
• Characterization of the passivating layer's properties, including its molecular sieve capabilities.

Main Results:

• A significant drop in corrosion rate was observed as a passivating layer formed on the glass surface.
• Water ingress led to congruent release of mobile elements (B, Na, Ca), followed by silicate network repolymerization.
• The formed passivating layer acts as a molecular sieve with a pore cutoff below 1 nm, limiting further degradation.

Conclusions:

• The formation of a stable, self-healing passivating layer dramatically enhances the durability of silicate glasses.
• This low corrosion rate meets the stringent durability requirements for nuclear waste geological disposal.
• Fundamental understanding of glass corrosion mechanisms can guide the optimization of nuclear glass design for disposal.