Papers by Author: F.R. Baxter

Abstract: This paper studies the effects of porosity, sintering atmosphere and composition on the polarisation behaviour of calcium phosphate (CaP) ceramics. Hydroxyapatite (HA) and α- tricalcium phosphate (α-TCP) materials were prepared as both dense discs and as porous samples with interconnecting porosity. Materials were sintered in either air or water vapour at 1300°C and poled at a variety of temperatures, applied electric fields and time periods to optimise the polarisation properties of the materials. Thermally Stimulated Depolarisation Current (TSDC) measurements were used to investigate the degree of polarisation of the HA and α-TCP ceramics. A high depolarisation current was observed for both the porous HA and α-TCP ceramics. Sintering in water vapour also increased the depolarisation current due to reduced dehydration reactions, which result in a greater concentration of hydroxyl ions.

Abstract: Hydroxyapatite (HA) and barium titanate (BT) powders were mixed and sintered to form hydroxyapatite – barium titanate (HABT) ceramics. These materials were then poled and their piezoelectric properties were measured. The microstructure of unpoled samples was examined using scanning electron microscopy (SEM).The piezoelectric constants (d33 and d31) of the ceramics were found to be dependent on the proportion of BT in the ceramic In materials containing less than 70% BT, no piezoelectric effect was found. Above this value, the piezoelectric constant increased with the addition of BT up to a value of 108pCN-1 for pure BT. Values of d33 for ceramics containing more than 80% BT are above values previously shown to have a positive influence on bone growth in vivo. SEM analysis indicated that the grain size within the materials decreased as the proportion of BT in the material was reduced. Examination of the microstructure of the ceramics indicated the presence of electrical domains in the 100% BT and 95% BT ceramics. Domains were not visible below 95% BT. The reduction in grain size may influence the reduction in piezoelectric activity within the materials but cannot be considered to be the only cause.