Some properties of carbonate-containing hydroxyapatite powder prepared by spray-pyrolysis technique using urea as a foaming agent

The effect of urea addition on the formation of hydroxyapatite (HAp) through the spray-pyrolysis technique was examined. The crystalline phases of the powders prepared from the spraying solution without urea were HAp and a small amount of p-tricalcium phosphate; however, only carbonate-containing HAp was formed from the solutions with urea concentrations of 1.00 mol . dm(-3) or higher. The SEM observations showed that the particle size of the as-prepared powder decreased with increasing urea concentration in the spraying solution. This reduction of the particle size may be due to the foaming action of CO2 generated by the decomposition of urea. The relative density of the sintered body which originated from the solution with an urea concentration of 5.00 mol . dm(-3) was comparable to that from the calcined and crushed powder which was obtained by spray-pyrolysing the solution without urea. The calcining and crushing operations before the fabrication of the sintered body may be omitted when the powders are prepared from starting solutions containing some urea.