Preparation of cadmium hydroxyapatite particles using acetamide

Well-crystallized needle-like cadmium hydroxyapatite (CdHap) particles were prepared by a two-steps wet method with acetamide (AA). Cd5H2(PO4)4·4H2O, which is a precursor of CdHap, was synthesized from aqueous solutions containing Cd(NO3)2·4H2O, (NH4)2HPO4 and AA in the first step and then transformed into CdHap by dissolution and recrystallization in the second step. The crystal phases of the products depended on the synthetic conditions, such as AA concentration of the starting solution in the first step ([AA]) and aging period (ta), solution pH and solution volume (Vs) in the second step. CdHap particles, obtained at [AA] = 8.0 mol dm−3, ta = 7 days, pH 9.0 and Vs = 500 cm3, were agglomerates of needle-like particles with ca. 10 μm width and ca. 100 μm length and had a Cd/P molar ratio of 1.69. The transformation from the precursor into CdHap was completed at [AA] ≥ 6.0 mol dm−3, ta ≥ 7 days, pH = 9–9.5 and Vs ≥ 500 cm3.