Effect of zinc substitution on the structure of calcium Fluoro-Alumino-Silicate glasses and glass-ceramics

Zhang, Siqi (2011). Effect of zinc substitution on the structure of calcium Fluoro-Alumino-Silicate glasses and glass-ceramics. University of Birmingham. M.Phil.

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Abstract

Ionomer glasses are certain glass compositions that have been used as the glass component in glass ionomer cements. The term “ionomer” was traditionally related with the use of polyacrylic acid as the polymeric component of glass ionomer cements that incorrectly was characterized as an ionomer polymer. The name has been retained and therefore the glass compositions used in these materials are called ionomer glasses. A typical ionomer glass molar composition is 4.5SiO\(_2\)-3Al\(_2\)O\(_3\)-1.5P\(_2\)O\(_5\)-3CaO-2CaF\(_2\). The glass can be made by a melt-quench route at 1450°C. This glass composition has been extensively studied. Substitution of other divalent cations for calcium can offer a range of different properties in the glass including radiopacity. Sr, Ba and Mg substitutions lead to the conclusion that the cation size plays a very important role on the microstructure of the amorphous glass and the glass ceramic. This work focuses on zinc substitution for calcium. Zinc compared to calcium is a smaller cation with an atomic radius of 1.34 Å against 1.97 Å for calcium. Zinc has been proven to be bactericidal and has shown ability to stimulate osteogenesis. A series of zinc substituted glasses were produced by replacing Zn for Ca in 25mol% (LG26 25%Zn), 60mol% (LG26 60%Zn), 75mol% (LG26 75%Zn) and 100mol% (LG26 100%Zn). The new glasses were characterized by Helium Pycnometer, DSC, TGA, FTIR, Raman, ESEM and EDX. The density of the resulting glass ceramics was measured also by Helium pycnometer and X-ray diffraction was conducted to identify the crystal phases formed. The density of zinc substituted glasses and glass-ceramics increased with increasing the zinc content. However, the oxygen density did not change significantly indicating a rather stable network that was not affected by zinc substitution. The glass transition temperature decreased with zinc substitution whereas the crystallization temperature was affected by the particle size of the glasses and although when coarse particles 5 were studied crystallization was not recorded, when fine particles were studied the crystallization temperature generally increased with substitution and above 60% of substitution only one crystallization temperature was recorded. Isothermal studies for the coarse glass particles were conducted in order to study the crystallization process that was believed to be very slow. The crystallization temperatures recorded had an increasing tendency with zinc substitution. An endothermic transition appeared at a relatively low temperature (ca 1200oC) was interpreted as a crystal dissolution temperature that decreased with zinc substitution. FTIR and Raman spectroscopy showed an increase in bridging oxygens with zinc substitution. The crystallized materials exhibited sharper and more distinct peaks that corresponded to new bond formation due to different crystal phases formed. While the calcium base glass composition crystallized to Fluorapatite and mullite, zinc substitution led to the formation to a gahnite (ZnAl\(_2\)O\(_4\)) and calcium zinc phosphate (CaZn\(_2\)(PO\(_4\))\(_2\)) phases. ESEM and EDX analysis showed changes in the morphology of glass ceramics with zinc substitution.

Type of Work:

Thesis (Masters by Research > M.Phil.)

Award Type:

Masters by Research > M.Phil.

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