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High resolution multinuclear nuclear magnetic resonance studies of oxide glasses
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Lockyer, Martin William Geoffrey (1993) High resolution multinuclear nuclear magnetic resonance studies of oxide glasses. PhD thesis, University of Warwick.
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Official URL: http://webcat.warwick.ac.uk/record=b1416221~S15
Abstract
Multinuclear Magic Angle Spinning nuclear resonance has been used as the main technique in the investigation of the structure of glasses from three different systems.
A series of K₂O. 4SiO₂ based glasses with P₂O₅ addition have been investigated via natural abundance ²⁹Si, ³¹P and ²⁷A1 (present as an impurity) MAS NMR. The ²⁹Si spectra reveal the occurrence of octahedrally coordinated silicon in addition to the normal tetrahedrally coordinated silicon for glasses with analysed P₂O₅ contents in excess of 28 mol%. Increasing the P₂O₅ concentration increases the relative proportion of the higher coordination species. IRAS also detected the presence of Siᵛⁱ but only for concentrations >10% of the total Si content. ²⁷A1 MAS NMR has shown the presence only of four coordinated aluminium for 5 mol% P₂O₅, whereas for 10 and 15 mol% small amounts of six and possibly five coordinated aluminium species occur. Higher concentrations of P₂O₅ also increase the amount of higher coordinated aluminium until 28 mol% when practically all the aluminium is octahedrally coordinated with phosphorus in the next nearest shell. The ³¹P MAS NMR spectra show the formation of metaphosphate chains for P₂O₅ concentrations greater than 10 mol%, which increase in length and become more disordered as the P₂O₅ content rises. The relative concentration of octahedral silicon has been found to be a function of fictive temperature, with the proportion of Siᵛⁱ higher for higher Tf. An estimated energy for the conversion Siⁱᵛ to Siᵛⁱ was obtained, of 9.98 kJ/mol, indicating the reaction is exothermic. The relative proportions of Siⁱᵛ and Siᵛⁱ also affect the measured density of the glasses, density increasing as the proportion of Siᵛⁱ increases. Potassium phosphosilicate and silicon phosphate xerogels were also prepared, but it did not prove possible to prepare amorphous samples free from water or organic residue. MAS NMR indicates that no Si - O - P bonding was formed below 500°C and XRD shows the presence of both SiP₂O₇ and Si₅O(PO₄)₆ as crystal phases in the heated potassium phosphosilicate xerogel and Si₃(PO₄)₄ in the silicon phosphate xerogel.
Multinuclear MAS NMR investigations of Na₂O. CaO. SiO₂ . P₂O₅ glasses has indicated a preferential association of Na⁺ ions with the Q³ species and Ca²+ with Q² units. The glasses are believed to consist of a mixture of two amorphous silicate environments similar to calcium metasilicate and sodium disilicate, which has been interpreted in terms of a possible model for the structural requirements for bioactivity. The glasses were subsequently converted into glass- ceramics via a controlled heat treatment process and the resulting structures investigated via MAS NMR and XRD. It has been established that all compositions prepared from within the bioactive region of the phase diagram contain Na₂CaSi₃O₈ as the major crystalline phase. Certain crystal phases that went undetected by XRD were observed via MAS NMR.
Glasses prepared from the PbO . P₂O₅. A1₂O₃ system have shown some interesting structural species. Compositions with >10 mol% A1₂O₃ contained Al in 4,5 and 6 coordination with a variety of next nearest neighbours. It is supposed that this multiple coordination stabilises longer metaphosphate chains than previously observed in glasses. In PbO . P₂O₅. glasses with >46.6 mol% PbO the network contains (PbO₄) tetrahedra which act in an apparent intermediate-like role in a similar manner to that observed in PbO . SiO₂ glasses.
This study has emphasised that multinuclear MAS NMR is an ideal technique for the investigation of completely or partially amorphous inorganic materials, particularly when employed in conjunction with other techniques such as thermal analysis, IRAS and XRD.
Item Type: | Thesis (PhD) | ||||
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Subjects: | Q Science > QC Physics Q Science > QD Chemistry |
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Library of Congress Subject Headings (LCSH): | Nuclear magnetic resonance, Oxides, Glass, Nuclear magnetic resonance spectroscopy, Nuclear magnetism | ||||
Official Date: | September 1993 | ||||
Dates: |
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Institution: | University of Warwick | ||||
Theses Department: | Department of Physics | ||||
Thesis Type: | PhD | ||||
Publication Status: | Unpublished | ||||
Supervisor(s)/Advisor: | Holland, Diane ; Dupree, Ray | ||||
Sponsors: | Science and Engineering Research Council (Great Britain) | ||||
Extent: | xii, 210 leaves :|billustrations | ||||
Language: | eng |
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