Stage III Glass Corrosion Behavior for Different Glass Compositions at Multiple Temperatures

The corrosion of borosilicate waste glass has been studied by groups around the world to understand and estimate the long-term performance of the waste form in the disposal environment. In static conditions, glass first briefly corrodes at the forward rate (Stage I), but the corrosion rate then progressively slows by orders of magnitude to a residual rate (Stage II) due to a combination of solution feedback effects and formation of a stable protective gel layer. However, the corrosion rate can later accelerate above the sustained Stage II corrosion rate, referred to as the resumption (or Stage III) rate. This behavior may be induced by the precipitation of a sink phase, which perturbs the leachate chemistry and stability of the protective gel layer. The sink phases commonly observed during Stage III are zeolite phases, such as analcime, P1, P2, and chabazite. These sink phases act as sources that consume major glass and gel components (alkali, alkaline earth, Al₂O₃, and SiO₂) resulting in accelerated glass corrosion rates. While Stage III behavior has been observed at 70 °C and 90 °C in long-term static testing of crushed glass (e.g., Product Consistency Test), its stochastic nature and long onset times make Stage III corrosion rate measurements extremely challenging. In this work, zeolite seeds (zeolite P1, P2, analcime, and clinoptilolite) were used to induce Stage III behavior at 22 °C, 40 °C, 70 °C, and 90 °C to measure Stage III corrosion rates of low-activity waste glasses and examine resulting alteration products. Results showed that zeolite P2 consistently triggered a Stage III response, the magnitude and persistence of which were correlated to glass composition, solution pH, and temperature. The response to zeolitic seeds varied from transitory acceleration (short events) to sustained linear acceleration to progressively faster acceleration. In many cases, additional zeolite types formed in addition to the original zeolite seeds, which was generally accompanied by a second faster acceleration than the initial response to seeds. Apparent activation energy measurements between 22 °C to 90 °C showed that lower temperature resulted in smaller differences between Stage II and Stage III corrosion rates, along with decreased persistence of Stage III behavior.