Leaching behavior of a polyphase glass–ceramic containment matrix

In order to understand the alteration mechanisms affecting a glass matrix comprising a secondary phase dispersed in a durable encapsulating glass, a simplified conservative model was used to estimate the expected normalized mass loss variation during a Soxhlet leach test. The model showed that once the secondary phases directly exposed to water have been fully altered, the overall behavior of the glass matrix corresponds to the behavior of the durable encapsulating glass. The additional release due to the secondary phase depends essentially on the dimensions of the dispersed phase and on its volume fraction within the matrix. The model was applied to a glass–ceramic containing several secondary phases dispersed in a durable borosilicate glass. Some of the secondary phases are rich in boron, and thus of a lower chemical resistance compared to the major encapsulating glassy phase. In order to compile the parameter data necessary for applying the model to these glass–ceramics, their microstructure was analyzed and the dimensional characteristics and composition of the secondary phases were determined by scanning electron microscopy coupled with image analysis and electron microprobe analysis. The model was then compared with the results of leach tests of the same samples in Soxhlet mode at 100 °C.