Crystallization of Lead Phosphate in Gel Systems
Lead phosphate crystals were grown in agarose gel at room temperature. Nucleation and crystal growth rates were controlled by changing the density of the gel medium including pure and phosphate gel. Crystalline products in the pure gel layer show equant habit while products formed in the PO43- gel layer show plate-like morphology. Microscopic crystalline products were accompanied by a decrease in pH from 10 to 3 for all reactions studied. Vibrational spectrum indicates that the PO43- ion is distorted and its symmetry is lower than free ion symmetry. Powder diffraction patterns in the pure gel show mixed phases of PbHPO4, Pb3(PO4)3, and Pb5(PO4)3OH consistent with predictions obtained from the PHREEQC program, similar phases appear for product formed in phosphate gel except Pb5(PO4)3OH phase because the higher Pb:P ratio required for the PbHAp phase relative to the Pb3(PO4)2 phase.
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