THE GROWTH OF NONSTOICHIOMETRIC APATITES USING THE CONSTANT COMPOSITION METHOD

The kinetics of the crystal growth of calcium-deficient hydroxyapatite s with different stoichiometry (Ca-5-mu(HPO4)(mu)(PO4)(3-mu)(OH)(1-mu) ) have been investigated at 37 degrees C using the constant compositio n method. The growth was performed in solutions supersaturated only wi th respect to Ca-5(PO4)(3)(OH)(HAp) by inoculating with well-character ized seed crystals. The stoichiometry of the grown apatites was consis tent with values of 0 less than or equal to mu less than or equal to 0 .185. The deviation CL from HAp stoichiometry of the growing apatite i ncreased with increasing supersaturation degree (S). The constant comp osition method also provides relevant information about the solubility behaviour of the growing phase with a definite com position. From the decrease of the normalized growth rate j with decreasing S, an estima te could be made of the composition of the solution for which the grow th ceases. The determined solubility product of the grown apatite (4.2 8 x 10(-54) M(9)) was higher than the value obtained by the equilibrat ion of the seed material. The results were interpreted on the basis of differences in crystal lattice perfection.