Solution Combustion Synthesis of Calcium Hydroxyapatite Nanoparticles

Nanoparticles of calcium hydroxyapatite, Ca10(PO4)6(OH)2, (HA) an important material for biomedical applications and other non-medical uses were synthesized by combustion in the aqueous system Ca-nitrate—diammonium hydrogen orthophos-phate-urea. The combustion behaviour and phase evolution with respect to the Ca/P atom ratio in the starting materials were investigated. Single-phase hydroxyapatite particles were obtained when the Ca/P ratio in the starting batch was 1.75. Below this ratio the products contained mainly hydroxyapatite and tricalcium phosphate (Ca3(PO4)2, TCP), the relative abundance of these phases being dependent upon the batch composition. In all these cases, the particles were equiaxed, nanosized (60—130 nm) and occurred as easily dispersible soft agglomerates of sizes ranging from 0.1 to larger than 100 μm. The products were characterized for phase contents, particle size distribution and morphology.