Date

2008

Author

Park, Jongee

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The glass-ceramics containing apatite [Ca10(PO4)6(O,F2)] and wollastonite [CaOSiO2] crystals as the predominant crystalline phases, (A-W glass-ceramics) were produced through controlled crystallization of the glasses in the MgO-CaO-SiO2-P2O5-F system. Phases formed in the crystallized counterpart of the glasses were identified by powder X-ray diffraction (XRD) analysis. The crystal morphology of the resultant glass-ceramics was examined using a scanning electron microscope (SEM). The crystallization kinetic parameters consisting of the activation energy for crystallization, (E), the Avrami parameter, (n), and frequency factor of the glass were determined with regard to small amount of TiO2 additions using non-isothermal differential thermal analysis (DTA). The values for E and n for apatite and wollastonite were 460 kJ/mol and 433 kJ/mol, and 3.1±0.1 and 1.5±0.1, respectively. When 4 wt% TiO2 was incorporated into the base glass, the values for E decreased to 408 and 320 kJ/mol for apatite and wollastonite, respectively; but the values for n increased from 3.1±0.1 to 3.3±0.1, and from 1.5±0.1 to 1.9±0.1 for apatite and wollastonite, respectively. TiO2 is an effective nucleating agent in this glass system for promoting the precipitation of both apatite and wollastonite crystals. Structure oriented changes in the indentation microhardness and tribological properties of the A-W glass-ceramics were evidenced. The microhardness at the free surface was 650±12 HV, but decreased with increasing depth distance from the free surface and attained 520±8 HV at a distance 0.5 mm below the free surface. The wear rate at the free surface was 0.7±0.05 ×10-4 mm3/Nm, but increased as the distance from the free surface increased and became 2.9±0.15 ×10-4 mm3/Nm at a distance 0.5 mm below the free surface. Tribological properties of the A-W glass-ceramics were compared with those of commercially available dental ceramics including IPS Empress 2®, Cergo Pressable Ceramic®, Cerco Ceram®, Super porcelain EX-3®, and bovine enamel. The wear rate, friction coefficient, and wear mechanisms of the A-W glass-ceramics were similar to currently used artificial dental materials.

Subject Keywords

Mechanics of materials., Metallurgy.

URI

http://etd.lib.metu.edu.tr/upload/12609331/index.pdf
https://hdl.handle.net/11511/17603

Collections

Graduate School of Natural and Applied Sciences, Thesis