Hydrothermal leaching of R7-T7 borosilicate glass

The results of hydrothermal leach tests are intended to be used to predict long-term low-temperature glass dissolution. It is often assumed that data can be extrapolated to other conditions using an Arrhenius-type equation. Hydrothermal leaching mechanisms and their temperature dependence in R7T7 glass were investigated in static experiments lasting from 7 days to 1 year at 1500C and 2500C. Leachates, surface layers and crystalline products were analyzed by ICP, TEM, SEM, EMP, XRD and cathodoluminescence. Unexpectedly, no actual saturation conditions in solutions were reached after one year leaching at 1500C nor at 2500C. The effect of precipitation of alteration products (a silica-enriched amorphous layer and aluminosilicates [smectite at 1500C, smectite and zeolites at 2500C]) is discussed. However, the formation of large cracks in the bulk glass results in a higher glass reacting surface and a higher dissolution rate at 2500C. Arrhenius calculations cannot be used to extrapolate our hydrothermal data to lower-temperatures