Surface Analytical Study of Synroc Subjected to Hydrothermal Attack

Specimens of the ceramic Synroc, both with (Synroc C) and without the addition of a simulated nuclear waste (Synroc B), were subjected to hydrothermal attack. The near‐surface regions, both before and after attack, were characterized using X‐ray photoelectron spectroscopy, Auger electron spectroscopy, and scanning electron microscopy. Ion‐beam erosion was used in conjunction with these surface analysis techniques to obtain information from below the original surface. It was found that hydrothermal attack led to the formation of a modified layer extending to a maximum depth of ∼200 nm after 25 days at 350°C. Within this modified layer, the abundances and chemical states of the elements were different from those in the unattacked Synroc. The changes which were observed can be explained qualitatively by postulating that selective dissolution (e.g., for Ca and Ba), hydration (e.g., for Al and Fe), recrystallization (e.g., for Ti and Zr), and reaction with Co2 dissolved in the liquid phase (e.g., to form CaCO3) are all taking place.