Crystallization of Lead Phosphate in Gel Systems

Oratai Saisa-ard, Kenneth J Haller
2012 Engineering Journal  
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. Individual crystallites from the pure gel layer show equant habit while those from the PO4 3− gel layer show plate-like habit. Vibrational spectra indicate that the PO4 3-ion is distorted and its symmetry is lower than free ion symmetry. Powder diffraction patterns of the pure gel products show
more » ... phases of PbHPO4, Pb3(PO4)2, and Pb5(PO4)3OH (PbHAp) consistent with saturation index predictions obtained from the PHREEQC program. Formation of the microscopic crystalline products was accompanied by a decrease in pH from 8 (theoretical for all layers mixed) to 3 for all reactions studied, consistent with PbHPO4 being the major product. PbHAp does not appear in the phosphate gel layer because of the higher Pb:P ratio required for the PbHAp phase relative to the Pb3(PO4)2 phase. PbHAp crystals from the gel crystallization method are first reported in this work as microcrystalline product deposited on the surface of the dominant phase formed in the pure gel layer.
doi:10.4186/ej.2012.16.3.161 fatcat:rsuqenxnpzbmrbqunmx76polq4