Influence of magnetic field on the properties of freshly precipitated calcium phosphate: implication in adhesion to glass surface

Abstract

Static magnetic field (MF) (S–S, B = 0.1 T) effects on spontaneous precipitation of calcium phosphates from equilimolar aqueous solutions of CaCl2 and Na2HPO4, or a mixture of Na2HPO4 and NaH2PO4 solutions ([Ca] = [P] = 10−2 M) at 25°C were studied. Besides the zeta potential and pH measurements as a function of time after the solution mixing, in situ deposition of calcium phosphates on glass surface was also investigated. The deposits were photographed at 400× magnification using an optical polarizing microscope equipped with a camera. It was found that MF effects on the properties of in situ precipitated calcium phosphates appeared in terms of changes in nucleation and precipitation rates, pH and zeta potential. The largest changes in the studied parameters occurred during 20 min from the moment of nucleation and precipitation. In the first system (CaCl2 and Na2HPO4 solutions) the magnetic field increases the precipitation rate, which results in a faster pH decrease relative to the reference system. However, in the second system (CaCl2 and a mixture of Na2HPO4 and NaH2PO4 solutions) the initial pH of the slurry is lower in comparison to the above system and in the absence of the MF it decreases at a slower rate. Based on the optical microscope photographs, it was found that the MF ordered the structure of calcium phosphates crystals precipitated in both systems, but to a higher degree when the sediment was precipitated from the mixture of phosphates. From the X-ray diffractograms of the samples it can be concluded that the MF does not change the chemical composition of the precipitated mixture of calcium phosphates, although in the second system it enhances the transformation of dicalcium phosphate into octacalcium phosphate.