Title: 0705 - Machinability of Fluor-Mica Glass-Ceramics of High Mica Volume Fraction
Tina Behraznia, Queen Mary University of London
Ali Alzahrani (Presenter)
Queen Mary University of London
Andy Bushby, Queen Mary University of London
Robert Hill, QMUL
Objectives: Barium-Mica glass-ceramics can be machined with conventional tipped tooling without resorting to expensive diamond tooling. The objective of this study is to investigate barium-mica based glass-ceramics for potential use in CAD/CAM dental applications, with specific reference to the parameters which determine the microstructure and governs hardness and machinability.
Methods: Barium-Mica glass was batched and synthesised via melt-quench route and cast into monolithic shape, annealed then subsequently heat-treated at two different crystal growth temperatures (1175 oC and 1200oC) for various holding times, in order to prepare glass-ceramics with a wide range of micro-structure. Further, the developed microstructures were quantified via SEM, in the back scattered mode, whereby the volume fraction and aspect ratio of the crystals were determined using Image J software, and admixed X-powder diffraction method. The hardness of the prepared glass-ceramics was measured by indentation along with a machinability test to measure the required force during machining of the samples.
Results: Heat-treatments of the base glass, resulted in the development mica-based glass-ceramics with different interlocking ‘House of Card's microstructures, governed by the crystal growth time-and temperature (T-T). Wherein the volume fraction, aspect ratio and connectivity of crystals are associated with the formation of the microstructure. Further, the volume fraction of the crystals was found almost identical for all the samples heat treated at different T-T. While, the crystal grain length and width increase as a function of crystal growth T-T resulting in aspect ratio range from 2.74 to 6.80 µm, which allow control over the end glass-ceramics machinability and hardness parameters. Hardness and machinability were found to decreased and increase on the bases of aspect ratio and effective crystallinity from 4.72 Gpa to 1.70 Gpa (± 0.5) and from 4.02 up to 17 N (± 3) respectively.
Conclusions: The final barium-mica glass-ceramic developed in this study may have the potential to be used as achair-side dental glass-ceramics material.
The submitter must disclose the names of the organizations with which any author have a relationship, the nature of the relationship, and the clinical or research area involved. The following is submitted: NONE