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Title: Advanced structural characterisation of glasses and amorphous oxides
Author: Al-Hasni, Bushra M.
Awarding Body: University of Kent
Current Institution: University of Kent
Date of Award: 2011
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Abstract:
This thesis begins with a molecular dynamics simulation of magnesium silicate glasses. Although an extensive literature addresses various techniques in studying the structure of x(MgO).(100-x)(Si02) glasses, this study has discussed in detail the environment of Mg atom and the presence of non-network oxygen atoms in these glasses. The average coordination number of magnesium by oxygen was increased from 4.5 ± 0.3 to 5.0 ± 0.3 by increasing x from 50 to 67. There are - 5% non-network oxygen for x=50 and the proportion increases up to 16% for x=67. Moreover, this study reported slight changes in Si-O and Mg-O environments; however, the changes in 0-0 correlations were noticeable in magnesium silicate glasses at pressures up to 9GPa. Most of this thesis presents studies of the structure of a range of important iron phosphate glasses. The ,effect of the, different oxidation states of Fe in xFeO.(100-x)P20s glasses and xFe203~(100-X) P20S glasses has been investigated by building several models using molecular dynamics simulation. The short range order in these glass models is realistic, with a well-defined phosphate network, and both Fe2+ and Fe3+ ions were found to have a typical c~ordination of - 4.5 in 40FeO and 40F~03 glasses. This thesis also includes modelling of multi-component phosphate glasses such as (P20S)sO(CaO)3o(Na20ho glass and sodium borophosphate glasses containing niobium. Both Ca and Na play the role of modifier in the (P20S)SO(CaO)3o(Na20)20 glass model with estimated .;.' coordination numbers of 5 and 6 respectively. Sodium borophosphate glasses containing niobium models confirmed that Nb06 octahedra prefer to be isolated at low Nb content, and connected to other Nb06 at higher Nb content. A series of techniques was used to investigate the structure of sodium iron phosphate glasses prepared by melt quenching: X-ray and neutron diffraction, X- ray absorption spectroscopy, Fourier transform infrared spectroscopy and Mossbauer spectroscopy. The environment of both Fe and Na and their effect on IV • the chemical durability in phosphate glasses have been investigated. This study proposed that Fe-O coordination number in these glasses is in the range of 4.8- 5.7 with a trend of decreasing the coordination number with increasing iron content. Whereas the Na coordination number of approx. 5 remains the same through different compositions. In depth structural studies have been carried out on amorphous FeP04 prepared by two different methods, and on amorphous LiFeP04" prepared by electrochemical insertion of Li. The local environment of Fe in these samples was investigated using Mossbauer spectroscopy and X-ray absorption spectroscopy. X-ray and neutron diffraction "and transmission electron microscopy have been applied to elucidate the first complete structural study of these materials. The Fe environment in amorphous FeP04 was found to be similar to that in quartz FeP04 where every Fe is surrounded by four oxygen' atoms. However, the Fe environment in amorphous LiFeP04 is affected by the appearance of Fe metal in this sample as a consequence of Li insertion. Small- angle scattering measurements confirmed the presence of nm-scale internal structure in the amorphous FeP04 prepared by thermal decomposition and in amorphous LiFeP04.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID: uk.bl.ethos.590072  DOI: Not available
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