Characterization of the boron profile and coordination in altered glass layers by EEL spectroscopy.

Electron energy-loss spectroscopy was used to characterize the boron profile and its coordination (BIII and BIV), along the complex alteration layer of glass samples altered for 511 days at 50 °C in solution containing FeCl2, MgCl2 and/or CaCl2. To reach this goal, the impact of both TEM operating conditions and sample preparation on the determination of the boron coordination was first studied using mineralogical and pristine glasses reference samples. Then, the boron concentration profiles were characterized in the glass alteration layer. These profiles were found to be S-shaped with a thickness around forty nanometers. The proportion of BIII was found to decrease with the boron total concentration (from the pristine glass to the gel layer), which suggests a higher bonding strength for BIV bonds than that of BIII bonds under the alteration conditions. These findings are of tremendous interest to advance further in the understanding of glass alteration mechanisms.

Silicate glass alteration enhanced by iron: origin and long-term implications.

Silicate glasses are used as containment matrices for deep geological disposal of nuclear waste arising from spent fuel reprocessing. Understanding the dissolution mechanisms of glasses in contact with iron, an element present in large amounts in the immediate environment (overpack, claystone, etc.) would be a major breakthrough toward predicting radionuclide release in the geosphere after disposal. Two different reacted glass-iron interfaces-a short-term nuclear system and a long-term archeological system-were examined using a multiscale and multianalytical approach including, for the first time on samples of this type, STXM under synchrotron radiation. Comparisons revealed remarkable similarities between the two systems and shed light on Fe-Si interactions, including migration of iron within a porous gel layer and precipitation of Fe-silicates that locally increase short-term glass alteration and are sustainable over the long-term.