EFFECT OF ALKYL PHOSPHATES ON THE FORMATION AND CRYSTALLIZATION OF CALCIUM PHOSPHATES IN AN AQUEOUS PHASE

摘要

The following conclusions may be drawn from the results presented here. 1. HAP was formed via ACP in the presence of alkyl phosphate of either form, the acid form (barely soluble in water) and the arginine salt form (easily soluble in water). 2. Transformation of ACP to HAP was accelerated with a concentration of alkyl phosphate irrespective of its torm. The acid form was more effective in the transformation and crystallization than the arginine salt form. 3. Particles of the insoluble acid adsorbed Ca~(2+) after the ion-exchange with H~+, while alkyl phosphate ion of the soluble arginine salt captured Ca~(2+) to form the precipitate. Both resulted in formation of the ---Ca--Pi--Ca--Pi--- clusters or embryos (i.e., heterogeneous nucleation). 4. Mean diameter of the secondary particles of HAP increased with a concentration of the acid (i.e., aggregation), whereas it decreased with that of the arginine salt(i.e., dispersion). Size of the secondary particle was, thus, regulated. 5. Negative charge or zeta potential of the particles was higher in the presence of the acid form than in the presence of the arginine salt form. The mechanism for aggregation/dispersion was discussed, taking the particle size and the adsorption amounts into consideration. 6. Arginine alone did not show any remarkable effects on the formation and dispersion of the particles up to 0.3 mM. It filled the role of solubilizing agent and/or a counter ion for an alkyl phosphoric acid.