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Beyond Speciation: A Study of Modifier Cation Clustering in Silicate Glasses by 29Si Magic Angle Flipping NMR

Sanders, Kevin Joseph
http://rave.ohiolink.edu/etdc/view?acc_num=osu1374182721

Abstract Details

2013, Master of Science, Ohio State University, Chemistry.
To elucidate trends in the chemical shift anisotropy and quantify the abundances of Q(n)-species in silicate glasses, glasses modified with the alkali and alkaline earth cations, Na+, K+, Rb+, and Cs+, Mg2+, Ca2+, Sr2+, and Ba2+, were studied using Magic Angle Flipping on the 29Si at natural abundance 29Si. Each sample was doped with CuO to aid in relaxation, and we found that Cu2+ is an effective paramagnetic dopant, which can decrease the total experiment time by a factor of about 80. The Mg2+ ion was found to be most effective at depolymerizing the glass network, leading to the most random distribution of species, whereas large alkali cations (K+, Rb+, and Cs+) were found to most closely follow the binary distribution model. We observed a general decreasing linear trend in the magnitude of the chemical shift anisotropy of Q(3), ζ(3), with increasing cation potential (Z/r). Interestingly, among glasses with the same modifier but at different molar compositions, there is a general increasing trend in ζ(3) with decreasing modifier content. This behavior suggests that the Si-NBO bond length becomes shorter as modifier content decreases, suggestive of changing cation cluster sizes or packing patters. In glasses containing Rb+ or Cs+, two unique Q(3) environments were observed, suggestive of two unique clustering patters. Eleven different cesium silicate glasses were studied to probe this behavior; a general increasing trend in ζ(3) as cesium content decreases is observed, possibly due to a change in cation coordination number. This trend may also be indicative of Q(3) sites existing in three-membered rings. The constrained and unfavorable geometry of these structures may also give rise to two unique CSA patterns; however, we determined that CSA alone cannot be used to probe the existence of three-membered rings in cesium silicate glasses. There was no clear trend in the abundances of each unique Q(3) site as a function of modifier content in cesium silicates. Nonetheless, we show that chemical shift anisotropy can be used as a reliable probe of the Si-NBO bond length in Q(3) sites, and that this length varies linearly with cation potential.
Philip Grandinetti, PhD (Advisor)
Anne Co, PhD (Committee Member)
125 p.
Analytical Chemistry; Chemistry; Environmental Geology; Materials Science; Physical Chemistry
Chemistry; Nuclear Magnetic Resonance; NMR; glass; silicate glass; glass structure; magic angle flipping; chemical shift anisotropy; 29-Si; natural abundance

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Citations

  • Sanders, K. J. (2013). Beyond Speciation: A Study of Modifier Cation Clustering in Silicate Glasses by 29Si Magic Angle Flipping NMR [Master's thesis, Ohio State University]. OhioLINK Electronic Theses and Dissertations Center. http://rave.ohiolink.edu/etdc/view?acc_num=osu1374182721

    APA Style (7th edition)

  • Sanders, Kevin. Beyond Speciation: A Study of Modifier Cation Clustering in Silicate Glasses by 29Si Magic Angle Flipping NMR. 2013. Ohio State University, Master's thesis. OhioLINK Electronic Theses and Dissertations Center, http://rave.ohiolink.edu/etdc/view?acc_num=osu1374182721.

    MLA Style (8th edition)

  • Sanders, Kevin. "Beyond Speciation: A Study of Modifier Cation Clustering in Silicate Glasses by 29Si Magic Angle Flipping NMR." Master's thesis, Ohio State University, 2013. http://rave.ohiolink.edu/etdc/view?acc_num=osu1374182721

    Chicago Manual of Style (17th edition)

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This open access ETD is published by The Ohio State University and OhioLINK.