The solubility of Zr-bearing minerals in peralkaline, H2O-saturated alkali aluminosilicate melts with or without added F reaches a maximum of about 4 and 3.5 wt.% ZrO2 respectively at approximately 57 wt.% SiO2. The saturating phase for melts with SiO2 content above this threshold is zircon. In the halogen-free experiments, the saturating phase for melts with lower silica content is wadeite (K2ZrSi 3O9), while ZrO2 crystallizes from melts with 1 wt.% added F. Experiments with Cl-bearing melts indicate no maximum solubility of Zr minerals; the solubility remains at 2 to 2.2 wt.% ZrO2 across a wide compositional range. The saturating phases in the Cl-bearing melts are the same as those of the F-bearing melts and the transition from ZrO 2 to zircon occurs at the same composition. The positive slope of the wadeite saturation curve on XZrO2-XSiO2 plots for the halogen-free melts suggests that increasing SiO2 activity increases the solubility of wadeite. / Peralkaline Ti,Zr-bearing sodium aluminosilicate glasses have been analyzed by Raman spectroscopy to determine the effect of Cl on glass structure. The spectra of the Ti-bearing glasses show a significant difference between the Cl-free and the Cl-bearing composition. The Cl-free glass spectrum contains a strong, asymmetric peak at 900 cm--1 which is associated with Ti in five-fold coordination. This peak is shifted to higher frequency and becomes more symmetric with the addition of 0.3 wt.% Cl. Deconvolution of the high-frequency waveband suggests that differences between spectra result from the contribution of a peak at 945 cm--1. This peak is believed to be the result of Ti-O vibrations in fully-polymerized titanate tetrahedra. It is proposed that the addition of Cl destabilizes [5] Ti in favour of tetrahedral coordination as a result of competition between Cl and titanate groups for alkalis. / 23Na NMR MAS analyses of a suite of Na-aluminosilicate glasses with Na/Al = 2 and varying SiO2 content has revealed a trend toward more negative chemical shift (greater shielding of the nucleus) as the glass structure becomes more polymerized, i.e. the average number of non-bridging oxygen atoms per tetrahedron (NBO/T) decreases. This trend is observed only for glasses with NBO/T ≤ 0.3. For more polymerized glasses no change in chemical shift is measured. (Abstract shortened by UMI.)
| Identifer | oai:union.ndltd.org:LACETR/oai:collectionscanada.gc.ca:QMM.35011 |
| Date | January 1998 |
| Creators | Marr, Robert A. (Robert Allen), 1965- |
| Contributors | Baker, Don R. (advisor), Williams-Jones, A. E. (advisor) |
| Publisher | McGill University |
| Source Sets | Library and Archives Canada ETDs Repository / Centre d'archives des thèses électroniques de Bibliothèque et Archives Canada |
| Language | English |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
| Format | application/pdf |
| Coverage | Doctor of Philosophy (Department of Earth and Planetary Sciences.) |
| Rights | All items in eScholarship@McGill are protected by copyright with all rights reserved unless otherwise indicated. |
| Relation | alephsysno: 001641782, proquestno: NQ44511, Theses scanned by UMI/ProQuest. |
Page generated in 0.0019 seconds