Phosphate glasses for potential applications as bioactive materials have been studied using Solid state Nuclear Magnetic Resonance (NMR), owing to the fact that their bioactivity is strongly correlated to their atomic structure. A multinuclear NMR approach has been conducted on numerous series of phosphate bioactive glasses including 31P, 23Na, along with 27Al MAS NMR on a series of Al doped glasses, and the less widely studied 71Ga and 17O MAS NMR on multiple series of Ga doped glasses. In addition, the first implementation of the recently developed 31P refocused INADEQUATE Spin-Echo (REINE) experiment on a coherent series of glasses has been shown, providing greater insight into the distribution of J couplings throughout the phosphate network. Upon incorporation of Al into the phosphate network, 27Al MAS NMR has shown a subsequent change from initially octahedral to tetrahedral Al coordination. In addition, an increase in shielding and decrease in the quadrupolar parameter CQ of the Na ions from 23Na MAS NMR, along with a decrease in the 31P J coupling indicated from the REINE data, evidences the role of Al within the glass network cross linking phosphate chains, resulting in a strengthened more condensed network. In the Ga doped glass series the 71Ga MAS NMR data shows a similar trend for the Ga coordination as found in the Al series, with the 23Na MAS NMR also indicating comparable results. The 31P REINE results however, do not provide observable trends, thus indicating that the Ga is having a slight different in uence in the glass network to that of the Al cation. 17O 3QMAS results show the presence of both non bridging and bridging oxygens as expected in these systems. Mullite materials are of interest to material scientists owing to their favourable properties, making them ideal for `advanced ceramic' applications. However, the structure of mullite is complex owing to the disorder, arising from the vacancies present in the aluminosilicate network. A comprehensive multinuclear solid state MAS NMR investigation has been carried out on the structure of both undoped 3:2 mullite, and B doped 3:2 mullite materials. 27Al single pulse MAS NMR has enabled the identification of the octahedral and tetrahedral sites present, along with the 27Al 3QMAS experiment providing conclusive evidence of the Al tri-cluster sites in the structure. 100 % 29Si labelled samples have enabled the acquisition of quantitative and high resolution 29Si MAS NMR data, along with 29Si refocused INADEQUATE and f29Sig-27Al J-HMQC correlation experiments, providing detailed information on the connectivities in the aluminosilicate network. Both the 27Al and 29Si MAS NMR data have enabled determination of the nature of the tri-cluster site. 11B MAS NMR on B doped 3:2 mullite materials have shown B to occupy a BO3 coordination within the mullite structure according to a substitution with Si, cross linking the octahedral Al chains.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:640967 |
| Date | January 2014 |
| Creators | King, Scott P. |
| Publisher | University of Warwick |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
| Source | http://wrap.warwick.ac.uk/66689/ |
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