Investigation Of A Two Step Ion Exchange In Mixed Alkali Glasses

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Investigation Of A Two Step Ion Exchange In Mixed Alkali Glasses

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Author : David Gauss
language : en
Publisher:
Release Date : 2016

Investigation Of A Two Step Ion Exchange In Mixed Alkali Glasses written by David Gauss and has been published by this book supported file pdf, txt, epub, kindle and other format this book has been release on 2016 with categories.

Ion Exchange Of Mixed Alkali Glasses

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Author : Louis Mattos (Jr)
language : en
Publisher:
Release Date : 1999

Ion Exchange Of Mixed Alkali Glasses written by Louis Mattos (Jr) and has been published by this book supported file pdf, txt, epub, kindle and other format this book has been release on 1999 with categories.

Ion Exchange Processes And Mechanisms In Glasses

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Author :
language : en
Publisher:
Release Date : 2001

Ion Exchange Processes And Mechanisms In Glasses written by and has been published by this book supported file pdf, txt, epub, kindle and other format this book has been release on 2001 with categories.

Leaching of alkalis from glass is widely recognized as an important mechanism in the initial stages of glass-water interactions. Pioneering experimental studies [1-3] nearly thirty-five years ago established that alkali (designated as M) are lost to solution more rapidly than network-forming cations. The overall chemical reaction describing the process can be written as: {triple_bond}Si-O-M + H --> {triple_bond}Si-OH + M+ (1) or {triple_bond}Si-O-M + H3O+ --> {triple_bond}Si-OH + M+ + H2O. (2) Doremus and coworkers [4-7] fashioned a quantitative model where M+ ions in the glass are exchanged for counter-diffusing H3O+ or H+. Subsequent investigations [8], which have relied heavily on reaction layer analysis, recognized the role of H2O molecules in the alkali-exchange process, without minimizing the importance of charged hydrogen species. Beginning in the 1980s, however, interest in M+-H+ exchange reactions in silicate glasses diminished considerably because important experimental observations showed that network hydrolysis and dissolution rates were principally controlled by the chemical potential difference between the glass and solution (chemical affinity) [9]. For nuclear waste glasses, formation of alteration products or secondary phases that remove important elements from solution, particularly Si, was found to have very large impacts on glass dissolution rates [10,11]. Consequently, recent work on glass/water interactions has focused on understanding this process and incorporating it into models [12]. The ion-exchange process has been largely ignored because it has been thought to be a short duration, secondary or tertiary process that had little or no bearing on long-term corrosion or radionuclide release rates from glasses [13]. The only significant effect identified in the literature that is attributed to alkali ion exchange is an increase in solution pH in static laboratory tests conducted at high surface area-to-volume ratios [14,15]. Renewed interest in alkali ion exchange reactions has come about because of interest in development of durable Na-rich silicate glasses for immobilization of low-activity waste (LAW) at Hanford, Washington [16] and high-level wastes in China [17]. In reactive transport simulations of a LAW glass disposed in a shallow subsurface facility, Chen, McGrail, and Engel [18] showed that ion-exchange reactions increased the radionuclide release rate by over two orders of magnitude when compared with simulations where ion exchange was excluded. Sheng, Luo, and Tang [17] conducted static tests in a simulated groundwater and showed that alkali ion exchange was the dominant release mechanism over a large temperature range. Although the significance of alkali ion exchange reactions in long-term disposal system performance has now been recognized, the fundamental processes and mechanisms controlling the exchange reactions are still remarkably poorly understood, especially with regard to how glass structure affects alkali ion exchange kinetics. Experimental studies of Na release from various simple silicate glasses are numerous [19-23]. However, in all previous studies of which we are aware, no attempt was made to distinguish between M+ release through alkali exchange versus matrix dissolution. The release rate of alkali in all of the early work was convoluted by contributions from matrix dissolution, which dominates in dilute solutions. Also, none of the previous studies attempted to define the relationship, if any, between glass structure (composition) and the kinetics of the ion exchange reaction. The motivation behind this Environmental Management Science Project (EMSP) is to develop a better understanding of how glass structure impacts sodium ion exchange so that improved glasses can be developed. Development of low ion-exchange rate glasses may also permit engineers to use higher loadings in nuclear waste glasses, which would result in substantial savings in production and disposal costs. This report summarizes the experimental data, and the interpretation and analysis of this data that was collected over the duration of the project from 1997 to 2001. Three silicate glass systems were investigated: (1) Na2O-Al2O3-SiO2 system, (2) Na2O-B2O3-SiO2 system, and the (3) Na2O-Al2O3-B2O3-HfO2-SiO2 system.

Ionic Diffusion In Oxide Glasses

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Author : Günther Heinz Frischat
language : en
Publisher:
Release Date : 1975

Ionic Diffusion In Oxide Glasses written by Günther Heinz Frischat and has been published by this book supported file pdf, txt, epub, kindle and other format this book has been release on 1975 with Science categories.

Investigation Of Mixed Alkali Glasses

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Author : S. C. Waterton
language : en
Publisher:
Release Date : 1932

Investigation Of Mixed Alkali Glasses written by S. C. Waterton and has been published by this book supported file pdf, txt, epub, kindle and other format this book has been release on 1932 with categories.

An Investigation Of The Mixed Alkali Effect In Disilicate Glasses By Spectroscopic Methods

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Author : Angeline Tiong-Whei Yap
language : en
Publisher:
Release Date : 1996

An Investigation Of The Mixed Alkali Effect In Disilicate Glasses By Spectroscopic Methods written by Angeline Tiong-Whei Yap and has been published by this book supported file pdf, txt, epub, kindle and other format this book has been release on 1996 with categories.

The Mechanical Strength Of Alkali Aluminosilicata Glasses After Ion Exchange

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Author : Anthonie Jan Burggraaf
language : en
Publisher:
Release Date : 1966

The Mechanical Strength Of Alkali Aluminosilicata Glasses After Ion Exchange written by Anthonie Jan Burggraaf and has been published by this book supported file pdf, txt, epub, kindle and other format this book has been release on 1966 with categories.

The Mechanical Strength Of Alkali Aluminosilicate Glasses After Ion Exchange

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Author : A. J. Burggraaf
language : en
Publisher:
Release Date : 1966

The Mechanical Strength Of Alkali Aluminosilicate Glasses After Ion Exchange written by A. J. Burggraaf and has been published by this book supported file pdf, txt, epub, kindle and other format this book has been release on 1966 with Glass categories.

Strengthening Glass By A Two Step Ion Exchange Process

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Author : Nathan Sonneville
language : en
Publisher:
Release Date : 2003

Strengthening Glass By A Two Step Ion Exchange Process written by Nathan Sonneville and has been published by this book supported file pdf, txt, epub, kindle and other format this book has been release on 2003 with categories.

Internal Friction Of Ion Exchanged Li2o Al2o3 2sio2 Glasses

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Author : A. Ismail A. Abdel-Latif
language : en
Publisher:
Release Date : 1971

Internal Friction Of Ion Exchanged Li2o Al2o3 2sio2 Glasses written by A. Ismail A. Abdel-Latif and has been published by this book supported file pdf, txt, epub, kindle and other format this book has been release on 1971 with Ceramic materials categories.

"Li2O·Al2O3·2SiO2 glass fibers were ion-exchanged from 1 to 300 minutes in a sodium nitrate bath at 366°C. The internal friction was measured along with the lithium and sodium concentration profiles. As sodium progressively replaced lithium, the alkali internal friction peak became smaller while a new peak (mixed alkali peak) appeared and increased in magnitude. These changes in the internal friction are similar to those that occur upon the addition of a second alkali to glasses prepared by conventional melting. The magnitude of both internal friction peaks in ion exchanged glasses was dependent on the overall glass composition. The magnitude of the alkali peak depended upon the unexchanged glass core, whereas that of the mixed alkali peak depended upon the exchanged layer on the glass surface. Dissolving the exchanged surface layer led to the restoration of the original alkali peak and the disappearance of the mixed alkali peak. Changing the alkali distribution did not affect much the mixed alkali peak, but caused the alkali peak to shift to higher temperatures and become smaller. The activation energy for both peaks remained essentially constant during ion exchange of the chilled fibers and this is attributed to the rigid network structure at 366°C. The height of the alkali peak can be used to determine the maximum depth of penetration of the second alkali"--Abstract, pages iv-v.