Solubility study of the initial formation of calcium orthophosphates from aqueous solutions at pH 5-10.
In unsaturated stock solutions with various concentrations of calcium and phosphate and pH of 4-5, supersaturation with respect to brushite, hydroxy- and fluorapatite, octacalcium phosphate and amorphous tricalcium phosphate was established at 20 degrees C by increasing pH in two series of portions, one containing low concentrations of fluoride, one fluoride-free. The precipitate as identified by X-ray diffraction was compared to the ion-activity products in the liquid. Brushite and amorphous tricalcium phosphate were formed at low supersaturation with respect to the salt in question; apatite formation required a high degree of supersaturation. Octacalcium phosphate was not observed presumably due to moderate supersaturations with respect to this salt. Fluoride had no effect on brushite and tricalcium-phosphate formation; only apatite was influenced slightly through a fluorapatite precipitation. The salts were often formed in mutual competition.
Larsen
M J
MJ
Jensen
S J
SJ
D001031:Apatites / Q000138:chemical synthesis; D002130:Calcium Phosphates / Q000138:chemical synthesis*; D011232:Chemical Precipitation; D005459:Fluorides; D006863:Hydrogen-Ion Concentration; D012995:Solubility
D001031:Apatites; D002130:Calcium Phosphates; C485828:alpha-tricalcium phosphate; C485830:tetracalcium phosphate; C485838:calcium phosphate, monobasic, anhydrous; C020243:calcium phosphate; C485829:calcium phosphate, dibasic, anhydrous; D005459:Fluorides