CRYSTALLINITY CONTROL OF HYDROXYAPATITE AND THE RELATED CALCIUM PHOSPHATES BY MECHANICAL GRINDING (MG)

摘要

Crystallinity of hydroxyapatite (HAp) and the related calcium phosphates for regenerating hard tissue was controlled by the MG method and subsequent heat treatment. The HAp, fluorapatite (FAp) and α- and β-tricalcium phosphates (α-TCP,β-TCP) were used as initial materials. Variations in crystallinity and crystal structure were examined by the XRD method during MG and the following heat treatment. Crystallinity based on crystallite size and crystal elastic strain decreased with grinding time and the rate in decrease depended on type of calcium phosphates; crystallographic diffraction peaks disappeared more rapidly in HAp than that in FAp. Change in the morphology of powder during MG was influenced by primary particle size of the first-stage product; the α-TCP and β-TCP powders composed of large particles were predominantly shattered into small particles and then gathered together during MG, while the crystal strain in the HAp and FAp powders was mainly accumulated without significant refinement of crystallite size. Recovery process of crystallinity in the milled powders was investigated. The crystallinity of the HAp and FAp powders recovered depending on annealing temperature. The novel phase of β'-TCP with higher ordering than β-TCP appeared during heat treatment from amorphous state of α-TCP or β-TCP obtained during MG. The MG and subsequent heat treatment were finally concluded to be an effective process for controlling crystallinity and changing crystal structure on calcium phosphate powders.