Thermal characterization of magnesium containing ionomer glasses

Kartelia, Eleni Maria (2011). Thermal characterization of magnesium containing ionomer glasses. University of Birmingham. M.Res.

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Abstract

Ionomer glasses are one of the components to produce glass ionomer cements or glass polyalkenoate cements, a popular type of white dental fillings. A typical glass composition for this application is 20-36% wt.% SiO\(_2\), 15-40% Al\(_2\)O\(_3\), 0-35% CaO, 0-10% AlPO\(_4\), 0-40% CaF\(_2\), 0-5% Na\(_3\)AlF\(_6\) and 0-6% AlF\(_3\). These glasses can be made by mixing the appropriate oxides followed by fusion of ingredients in the temperature range of 1200 ˚C to 1590 ˚C. The glass composition used in this study is 4.5SiO\(_2\)-3Al\(_2\)O\(_3\)-1.5P\(_2\)O\(_5\)-3CaO-2CaF\(_2\). A series of new glasses were produced by Mg substitutions for Ca. Magnesium replaced calcium, by 25 (LG26 25%Mg), 50 (LG26 50%Mg), 75 (LG26 75%Mg) and 100 molar % (LG26 100%Mg). The new glasses were characterised by Helium Pycnometer, FTIR, DSC and XRD. The optimum nucleation temperatures and activation energies were calculated by DSC, the crystal size was measured using the Sherrer equation from the XRD patterns and finally the chemical structure was analysed by FTIR. The glass density and the oxygen density were calculated in order to understand how magnesium substitutions can affect the glass network. In this study was showed that the density of glasses and glass ceramics decreased whereas the oxygen density increased slightly with Mg substitution. Furthermore in FTIR spectra there are four absorption regions of Mg containing aluminosilicate glasses which were associated with stretching and bending vibrations. In FTIR was also observed some shift towards higher wavenumbers with Mg substitution. On the other hand, DSC analysis showed that the glass transition temperature (Tg), Tp1 and 9 Tp2 did not undergo significant changes with Mg substitution comparing all Mg substituted glasses but a significant change was observed between the Tp1 and Tp2 values of LG26 and Mg substituted glasses. A decrease in optimum nucleation temperature (Tn) with Mg substitution in all Mg substituted glasses except of LG26(100%)Mg was also observed. The LG26(100%)Mg glass did not exhibit an optimum nucleation temperature indicating that the glass undergoes spontaneous crystallisation. Furthermore, XRD analysis showed that the substitution of Mg for Ca resulted in the formation of Wagnerite (Mg\(_2\)PO4F), Ca-FAP and Mullite (Al\(_6\)Si\(_2\)O\(_{13}\)) in the case of LG26(25%)Mg and LG26(50%)Mg containing glass ceramics and Wagnerite (Mg\(_2\)PO\(_4\)F) and Mullite (Al\(_6\)Si\(_2\)O\(_{13}\)) in the case of LG26(75%)Mg and LG26(100%)Mg glass ceramics. The crystal size and the activation energy of Ca- FAP/Wagnerite were calculated. The activation energy increased for all glass compositions with the exception of LG26(75%)Mg.

Type of Work:

Thesis (Masters by Research > M.Res.)

Award Type:

Masters by Research > M.Res.

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