Characterization of Tricalcium Phosphate Powders Prepared by Spray-Pyrolysis Technique

Abstract

Crystalline tricalcium phosphate (TCP) was directly prepared by the spray-pyrolysis technique from ethanol-nitric acid solution of calcium nitrate and phosphoric acid. The concentration of the solution ([Ca²⁺]+[PO₄^3-]) was 0.05-1.0mol/l. The spray-pyrolysis temperature ranged from 1100° to 1400°C. TCP powders of the α form were obtained under all experimental conditions studied. When the temperature of the powders being produced in the reaction zone was lower than the β→α phase transformation temperature, metastable α-TCP was obtained, though the β phase is thermodynamically stable. On the other hand, stable α-TCP was obtained when the temperature of the powders was higher than the transformation temperature. With increasing spray-pyrolysis temperature and decreasing solution concentration, the temperature at which α→β phase transformation started in as-prepared α-TCP increased and the fraction of the phase transformation decreased. For the stable α-TCP obtained from the solution of 0.05mol/l at spray-pyrolysis temperatures above 1250°C, no transformation to β phase was observed by heat-treatment in the stable temperature range of β-TCP for 1h.