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Queen Mary University of LondonQueen Mary University of London
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School of Engineering and Materials Science
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PhD Thesis: Development of an enstatite glass-ceramic for biomedical applications

Author: BUCKLAND, Thomas

Year: 1999

Supervisor(s): Serena Best

The mineral enstatite, MgSiO3, is known to exist in three polymorphs, orthoenstatite (OE), clinoenstatite (CE) and protoenstatite (PE). CE and PE are recognised as possessing desirable mechanical properties. The production of an enstatite material via glass-ceramic processing technology was identified as being a potential route to a low cost, highly effective novel biomaterial.

An MgO-SiO2-Na2O glass system was investigated using differential thermal analysis, X-ray diffraction and scanning electron microscopy in order to determine the effects of varying TiO2 additions on the mechanisms of nucleation and crystallisation. It was found that a critical level of TiO2 was required in order to produce effective bulk nucleation. Nucleation in a 7wt% glass was found to occur via an amorphous phase separation (APS) mechanism, a process for which an optimum temperature was determined. The APS induced micro precipitation of CE and PE within the parent glass. Subsequent heating of nucleated glasses to 1200°C resulted in ripening and coalescence of the micro precipitates into a fine (<1 µm), highly acicular microstructure, whose phase composition consisted of CE, PE, rutile and quartz. The activation energy for crystallisation was ~500 kJ.mol-1. The heating rates employed during crystallisation influenced the material microstructure and controlled the ratio of CE:PE obtained. Stress-induced transformation from PE to CE occurred in all samples save those crystallised at rapid heating rates.

Hence, a new glass-ceramic system has been investigated and found to possess a highly acicular microstructure, whose major crystalline phase consists of polymorphs of enstatite. An envelope of optimum compositional and processing parameters has been determined and the microstructural development and kinetics of the system characterised. In addition, new data on the stability relationships of the enstatite polymorphs have been obtained.