The influence of magnetism on precipitation of calcium phosphate

The precipitation of calcium phosphate upon rapid mixing of solutions of CaCl2 and KH2PO4-K2HPO4 was followed by pH and other quantitative measurements and the examination of the precipitate in the polarizing microscope. The experiments were carried out at 25 degrees C in the presence and absence of a static magnetic field of 0.27 T. It was found that the magnetic field increased dissolution of metastable precursor phases and increased nucleation of more stable phases. This was a general tendency for the transformation sequence: ACP --> brushite --> OCP --> HAP at initial pH approximate to 6.5 and total concentrations C-Ca = C-P = 25, 50 or 100 mM. Crystallization upon slow diffusion of ions from a solution of CaCl2 into silica hydrogel containing dissolved KH2PO4-K2HPO4 was followed by recording the number and positions of appearing brushite crystals and Liesegang rings. The experiment was performed in the presence and absence of magnetic fields in the range 0.08-0.3 T and the following conditions: room temperature, initial pH of the gel between 5.5 and 6.8, and C-Ca = C-P = 50mM. Magnetism increased nucleation of brushite in the experiments at low initial pH. The dependence on field strength was not significant, and no effect was found in experiments with high initial pH. (C) 2000 Elsevier Science B.V. All rights reserved.