AVS 47th International Symposium
    Surface Science Tuesday Sessions
       Session SS3-TuA

Paper SS3-TuA10
Surface and Near Surface Reactions in Aqueous Solution Exposed Na@sub 2@O-Al@sub 2@O@sub3@-SiO@sub 2@ Glasses

Tuesday, October 3, 2000, 5:00 pm, Room 210

Session: Water/Surface Interactions
Presenter: V. Shutthanandan, Pacific Northwest National Laboratory
Authors: V. Shutthanandan, Pacific Northwest National Laboratory
S. Thevuthasan, Pacific Northwest National Laboratory
D.R. Baer, Pacific Northwest National Laboratory
J.P. Icenhower, Pacific Northwest National Laboratory
M.H. Engelhard, Pacific Northwest National Laboratory
B.P. McGrail, Pacific Northwest National Laboratory
Correspondent: Click to Email
Glass and ceramic waste forms are proposed for the stabilization and immobilization of nuclear wastes. Recent findings show that Na ion exchange reaction control the release of radionuclides from the glass matrix. As part of understanding the processes leading to sodium release and ion exchange, the surface and near surface reaction regions on several specimens of Na@sub 2@O-Al@sub 2@O@sub 3@-SiO@sub 2@ glasses with fixed Na@sub 2@O and variable Al@sub 2@O@sub 3@ (10 mole % and 15 mole %) concentrations have been examined after exposures to isotopicaly labeled aqueous D@sub 2@@super 18@O solutions. The sodium removal and the deuterium and oxygen uptake in the glass samples were measured using Rutherford backscattering spectrometry (RBS), X-ray photoelectron spectroscopy (XPS) and nuclear reaction analysis (NRA). The results show that the Na exchange rate is much higher than the matrix dissolution rate. Although the sodium concentration is decreased in the near surface region, it is not totally removed from the outer surface. In this same region, there is also a significant amount of @super 18@O incorporated demonstrating considerable interaction between the water and the glass. On the basis of the depth distributions of Na, D and @super 18@O, different regions including reaction, transition and diffusion zones were identified in both samples. The glass samples with higher amounts of Al content have a significantly narrower reaction zone than the low Al materials.