Preparation of Various Barium Phosphates by Homogeneous Precipitation Method

Abstract

Various barium phosphates were prepared at 98 (± 1) °C by the homogeneous precipitation method using mixed solutions of BaCl₂, NaH₂PO₄ and urea (Ba²⁺/P mole ratio =1.00∼1.67), and investigated with respect to the effect of reaction conditions on the formation of various barium phosphates and the composition of barium apatite (Ba-Ap).
The barium hydrogenphosphate was o btained as the initial product in all of reaction conditions. Bariurn hydrogenphosphate was transformed to Ba-Ap by aging in concentrated solutions of Ba²⁺ ions, but the transformation was difficult in dilute solutions of Ba²⁺ ions. The barium carbonate once formed during the precipitation reaction remained in the product after the aging. Lowering the concentration of urea was preferred for the synthesis of various barium phosphates without BaCO₃. The single phase of BaHPO₄ was obtained by heating solutions with low Ba²⁺/P mixing ratios for a little while. On the othe r hand, both lowering the concentration of urea and heightening the Ba²⁺ /P mixing ratios, the single phase of Ba-Ap was obtained by heating solutions with low concentrations of urea and high Ba²⁺/P mixing ratios for a long time.
The incorporation of Cl^- ions or CO₃^2- ions into the crystal of Ba-Ap obtained was unavoidable. The incorporation of these ions, however, could be decreased by lowering the concentrations of urea and Cl^-ions and heightening the concentration of Ba²⁺ ions in the initial solution.
Consequently, it was clarified that the formation of various barium phosphates and the composition of Ba-Ap were influenced by various factors: concentrations of Ba²⁺ ions, Cl^- ions, urea or heating time, etc. The single phase of BaHPO₄, Ba-Ap or BaCO₃ could be obtained by the control of these factors.