Corrosion modeling of simple glasses from the systems SiO2-Na2O-CaO and SiO2-Na2O-MgO

Abstract

Static corrosion tests were conducted on two model glasses with the following composition (in mol%): 75 SiO2, 15 Na2O, 10 CaO and 75 SiO2, 15 Na2O, 10 MgO. The tests were performed in deionized water at 80 °C. Glass grains were combined with a monolithic sample in one reacdon vessel to achieve sufficient elemental release and to provide a monolithic sample for analysis. Vapor hydration tests (VHT) were performed on monolithic samples at 200 °C. Solution composition was analyzed with atomic absorption spectrometry (AAS), depth profiles of all elements in the surface layers of monolithic samples were analyzed with secondary neutral mass spectrometry (SNMS), and both monolithic and crushed samples were analyzed with scanning electron microscopy with energy dispersive spectrometry (SEM/EDS). Solution compositions and saturation indexes of secondary minerals were modeled with the geochemical code PHREEQC version 2.41 using LLNL database. The results showed that the sodium diffusion profiles in the surface layers of the glasses were established during the first few hours of the test. Both glasses showed that the dissolution rate depends on the chemical affinity for dissolution between the surface gel layer and the corrosion solution. Α glass alteration model based on transition state theory taking into account solution chemistry and precipitation of secondary alteration products is presented.