Papers by Author: D.J. Hadden

Abstract: A systematic study of the stability of potassium/carbonate co-substituted hydroxyapatite has been carried out, with samples synthesized by aqueous precipitation according to the chargebalanced mechanism: Ca10-xKx(PO4)6-x(CO3)x(OH)2 Samples up to x=1.0 were prepared and their stability determined by heating at a range of temperatures in both air and CO2 environments. Results showed that whilst samples up to x=1.0 can be prepared phase-pure, the stability of these materials is strongly dependent on sintering temperature with the full range of compositions only being stable at 600°C in CO2. The c unit cell parameter increases linearly with x, and, for a fixed composition, decreases linearly with temperature indicating loss of carbonate from the A-site. FTIR showed that samples contained carbonate at both A- and B-sites, and that carbonate content increased with x.

Abstract: Silicon-substituted hydroxyapatite (SiHA) bioceramics are widely used as bone replacement materials. There are various synthesis methods used to produce SiHA samples using different sources of silicon. This study aims to investigate the role of tetraethyl orthosilicate (TEOS) as the silicon source in the precipitation reaction synthesis of silicate-substituted HA. Four different synthesis methods were studied by changing the order of addition of the TEOS solution during the precipitation reaction. XRD and QXRD were used to determine the phase purity of the prepared samples. FTIR and SSNMR were used to assess silicon/silicate substitution in the prepared materials. Of the initial four methods used, only one resulted in a sample that was phase pure. The other three syntheses, which produced biphasic compositions, were modified and a further single phase sample was prepared. Results showed that the final composition is strongly dependant on how and when the TEOS was added during the precipitation reaction.