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Multinuclear solid state NMR studies of α-tricalcium phosphate and silicon substituted α-tricalcium phosphate
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MacDonald, James F. (2012) Multinuclear solid state NMR studies of α-tricalcium phosphate and silicon substituted α-tricalcium phosphate. PhD thesis, University of Warwick.
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WRAP_THESIS_MacDonald_2012.pdf - Submitted Version Download (6Mb) | Preview |
Official URL: http://webcat.warwick.ac.uk/record=b2684231~S1
Abstract
a-tricalcium phosphate (a-TCP, Ca3(PO4)2) demonstrates both bioactive and resorbable
characteristics. Substitution of SiO4
4- for PO4
3- in a-TCP (Si-a-TCP) is
found to stabilize the structure at lower temperatures and improve mechanical (and
possibly bioactive) properties. The mechanism of electroneutrality in the Si-a-TCP
structure is not fully understood, though is thought to take place through the creation
of O2- vacancies or through excess Ca2+. This study addresses some structural properties
of a-TCP using 31P MAS NMR at intermediate B0 fields (11.7 T) and 43Ca DOR
NMR at multiple fields (20.0 T, 14.1 T, 11.7 T), and via correlation of the measured
31P and 43Ca isotropic chemical shifts (Oiso) against calculated values obtained with
GIPAW DFT methods using the CASTEP code. These results show that the structure
has high short range order and clearly support the monoclinic P21/a (12 P site/18 Ca
site) model.
In contrast, solid state 31P MAS and 43Ca DOR NMR studies of Si-a-TCP demonstrate
that significant disorder broadening is characteristic of these data, however the
corresponding 29Si MAS NMR data affords reasonably resolved resonances, a low intensity
Q2 resonance at 0iso {84.5 ppm, and multiple resonances in the range 0iso -
{70 -{75 ppm, despite this shift range normally associated with Q0 speciation, 29Si
refocused-INADEQUATE data shows that Q1 resonances can also exist in this region.
31P-29Si HETCOR data from these systems suggests that, despite the intrinsic disorder,
explicit PO43- framework species can be associated with the different Q0/Q1 Si
species, and while there is some dispersion of the silicon throughout the structure it
is predominantly associated with a small number of P sites. DFT calculations for the
Si-a-TCP system suggest that the more favourable mechanism for charge balance is
Ca2+ excess, despite this, the 29Si NMR data is in greater agreement with the DFT calculations
for the O2- mechanism, whereby two adjoining cation-anion-columns in the
structure are bridged together by a Q1 unit , 29Si NMR data also suggests the existence
of Ca2SiO4 and Ca3Si3O9 existing as solid solutions within the a-TCP structure.
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 spectroscopy, Calcium phosphate, Silicon, Nuclear magnetic resonance, Substitution reactions | ||||
Official Date: | November 2012 | ||||
Dates: |
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Institution: | University of Warwick | ||||
Theses Department: | Department of Physics | ||||
Thesis Type: | PhD | ||||
Publication Status: | Unpublished | ||||
Supervisor(s)/Advisor: | Hanna, John V. | ||||
Sponsors: | Engineering and Physical Sciences Research Council (EPSRC); Advantage West Midlands (AWM); European Regional Development Fund (EDRF) | ||||
Extent: | xxii, 167 leaves : illustrations, charts. | ||||
Language: | eng |
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