Basic calcium phosphates with varying Ca/P ratio, 1.53-1.67 were prepared from lime suspension and phosphoric acid, or from calcium nitrate and ammonium phosphate solutions under various precipitation conditions, including agitation by ultrasonic vibration. Condensed phosphate formation has been studied by igniting the basic calcium phosphates, octacalcium phosphate and mixed phosphates with and without steam. Some precipitates have been examined by X-ray diffraction, infrared, petrographic microscopic techniques. These techniques did not reveal apparent separate phases in the precipitates.
Only one correlation between the amount of pyrophosphate equivalent formed and Ca/P ratio was found and it was independent of procedure and raw materials. The correlation is the case that calcined products consist of hydroxyapatite and calcium pyrophosphate only. The view is discussed that variation in Ca/P for some basic calcium phosphates is caused by simultaneous presence of hydroxyapatite with some other calcium phosphates. Constituents can be interlayered or poorly crystalline dicalcium phosphate, octacalcium phosphate and/or amorphous calcium phosphates without definite chemical identities mixed with hydroxyapatite.