Influence of electromagnetic fields on the microstructure of precipitated calcium phosphate nanometric-grains

Extremely low frequency electromagnetic fields (EM-ELF) of 3 mT and 1300 Hz in frequency were applied during spontaneous precipitation processes of ca lcium phosphates mixtures front their super-saturated aqueous solutions of calcium chloride and sodium phosphates. At the temperature of 37 degrees C and at an aqueous solution with pH 7.4, for any total precipitation time ra nging between 15 min and 5 h, the precipitated solid phase is formed by oct acalcium phosphate (OCP) and by non-stoichiometric hydroxyapatite (ns-OHAp) . The EM-ELF forces do not produce any effect in changing the chemical comp osition of the precipitated mixture. For any precipitation time the powders obtained under the action of the EM-ELF fields are characterised by a spec ific surface area values which are lower then the ones corresponding to sam ples obtained without EM-ELF applied by a percentage ranging between 18 and 36%. The crystallites sizes of both samples range between 10 and 20 nm, bu t the EM-ELF samples are characterised by an aver age crystallites size whi ch is about the 40% bigger than that of one concerning the specimen precipi tated without anl, EM-ELF applied. Experimental evidences are given to supp ort the hypothesis that the action of the EM-ELF fields is active at the be ginning of the precipitation process when the calcium phosphate particles a ve still in a colloidal-like status. Critical discussions, based on a theor y that the authors previously described, establish that the dimension of th e particles on which the applied exogenous field can have an effect is of t he order of 0.1 nm. (C) 1999 Elsevier Science Limited. All rights reserved.