The growth of non-stoichiometric apatites using the constant composition method

✍ Scribed by C. L. Dhondt; R. M. H. Verbeeck; E. A. P. Maeyer

• Book ID: 104628703
• Publisher: Springer
• Year: 1996
• Tongue: English
• Weight: 532 KB
• Volume: 7
• Category: Article
• ISSN: 0957-4530
• DOI: 10.1007/bf00119731

✦ Synopsis

The kinetics of the crystal growth of calcium-deficient hydroxyapatites with different stoichiometry (Cas_~(HPO4)~(PO4)3_~(OH)I_~) have been investigated at 37 °C using the constant composition method. The growth was performed in solutions supersaturated only with respect to CadPO~)3(OH) (HAp) by inoculating with well-characterized seed crystals. The stoichiometry of the grown apatites was consistent with values of 0 ~< t~ ~< 0.185. The deviation g from HAp stoichiometry of the growing apatite increased with increasing supersaturation degree (S). The constant composition method also provides relevant information about the solubility behaviour of the growing phase with a definite composition. From the decrease of the normalized growth rate jwith decreasing S, an estimate could be made of the composition of the solution for which the growth ceases. The determined solubility product of the grown apatite (4.28 x 10 -Sa M*) was higher than the value obtained by the equilibration of the seed material. The results were interpreted on the basis of differences in crystal lattice perfection.