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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: Continuous Hydrothermal Flow Synthesis and Characterisation of Nano-bioceramics and their Rapid Consolidation Using Spark Plasma Sintering

Author: CHAUDHRY, Aqif A

Year: 2008

Supervisor(s): Asa Barber

The existing methods of synthesis of calcium phosphate bioceramics are multi-step, time consuming and require strict control over synthesis conditions. Therefore, there is a requirement of a one-step, rapid synthesis technology which allows control over particle properties. The continuous hydrothermal flow synthesis (CHFS) technique addresses all such issues but it has not been used to synthesise calcium phosphate based nano-bioceramics.

The work in this thesis involves the use of CHFS technology to synthesise calcium phosphate bioceramics. It was demonstrated that the rapid crystallizing environment in a CHFS system resulted in phase-pure crystalline hydroxyapatite (HA). Traditionally required long ageing times and heat-treatment were avoided. Furthermore, variations in the CHFS system parameters were correlated with properties of the synthesised nano-bioceramics.

The CHFS system was also used to substitute biologically beneficial ions (CO32-, SiO44-, Mg2+ and Zn2+) into HA. Some ionic substitutions affected thermal stability and phase composition. For example, increase in magnesium contents in solution resulted in precipitation of a phase pure Mg-Whitlockite phase.

Conventional consolidation methods of HA powders require several hours of exposure to elevated temperatures which results in large grains, phase decomposition and poor mechanical properties. Spark Plasma Sintering on the other hand is capable of very high heating and cooling rates. Phase-pure and ion-substituted calcium phosphates and zirconia-hydroxyapatite phase mixtures were spark plasma sintered to high densities with these materials displaying good mechanical properties.