The Structure of Na2O-Al2O3-SiO2 Glass: Impact on Sodium Ion Exchange in H2O and D2O

Journal Article · Sun Oct 28 04:00:00 EST 2001 · Journal of Non-crystalline Solids, 296(10-26

DOI:https://doi.org/10.1016/S0022-3093(01)00890-0· OSTI ID:882387

McGrail, B PETER; Icenhower, Jonathan P; Shuh, D K; Liu, P; Darab, John G; Baer, Donald R; Thevuthasan, Suntharampillai; Shutthanandan, V; Engelhard, Mark H; Booth, C H; Nachimuthu, P

The kinetics of matrix dissolution and alkali-exchange for a series of sodium aluminosilicate glass compositions was determined at constant temperature and solution pH(D) under conditions of silica-saturation. Steady state release rate for sodium was 10 to 50 times faster than the rate of matrix dissolution, demonstrating that alkali exchange is an important long-term reaction mechanism that must be considered when modeling systems near saturation with respect to dissolved glass components. Sodium release rates were 30% slower in D2O compared to rates in H2O; but matrix dissolution rates were unaffected. These results are consistent with rupture of the O-H bond as the rate-limiting reaction in Na+-H+ exchange whereas matrix dissolution is controlled by OH- or H2O catalyzed hydrolysis of Si-O-Si and Si-O-Al bonds. Changes in Na exchange rate with increasing Al2O3 content could not be reconciled with changes in the number of non-bridging oxygen (NBO) sites in the glass alone. A simple model was used to estimate a structural energy barrier for alkali ion exchange using Na-O bond length and coordination as measured by Na K-edge XANES spectroscopy, and binding energy shifts for Si-O-Na sites measured by XPS. The energy barrier was calculated to increase from 34 kJ/mol for Na2O?2SiO2 glass to 50 kJ/mol for a glass containing 15 mol% Al2O3, consistent with stronger bonding of Na on NBO sites and increasing mechanical stiffness of the glass network with increasing Al content. The calculated ion-exchange enthalpies were then used to calculate Na ion exchange rates as a function of glass composition. Agreement between the calculated and measured Na ion exchange rates was excellent.

• Research Organization: Pacific Northwest National Laboratory (PNNL), Richland, WA (US)
• Sponsoring Organization: USDOE
• DOE Contract Number: AC05-76RL01830
• OSTI ID: 882387
• Report Number(s): PNNL-SA-33877; KC0303020
• Journal Information: Journal of Non-crystalline Solids, 296(10-26, Journal Name: Journal of Non-crystalline Solids, 296(10-26
• Country of Publication: United States
• Language: English

Related Subjects

alkali
glass
ion exchange
oxygen
saturation
sodium