Na-, Al-, and Si K-edge XANES study of sodium silicate and sodium aluminosilicate glasses: influence of the glass surface.

X-ray Absorption Near Edge Structure (XANES) experiments were performed at the O-, Na-, Al-, and Si K-edges in sodium silicate and aluminosilicate glasses with a NBO/T (non-bridging oxygen per tetrahedron) ratio ranging from 0 to 1. In order to better understand how the sample surface can affect the measured XANES spectra, special attention was paid to the glass surface (i.e., fresh vs. “old” surfaces but also surfaces vs. powders) and to the detection mode (fluorescence vs. electron yield). We observe that, at the Na K-edge, XANES experiments on glass compositions with high Na/Al ratios must be performed on highly “fresh” surfaces (i.e., at most a couple of hours old). In these compositions, the collected XANES may show features that are relevant to major structural reorganization near the surface (carbonate-like re-organizations). In contrast, highly polymerized glasses (such as albitic glass, Na2O–Al2O3–6SiO2) are much less sensitive to long-term exposure to atmospheric agents (namely water and CO2). A study of a 30-year-old albite glass and a natural rhyolitic glass confirms these observations, suggesting that these glasses are highly durable