Preparation of fibrous hydroxyapatite particles by homogeneous precipitation and microwave-assisted hydrothermal heating

Preparation conditions of fibrous hydroxyapatite (Ca10(PO4)6(OH)2: HAp) particles were examined by two-step chemical routes: (i) the preparation of fibrous octacalcium phosphate (Ca8H2(PO4)6·5H2O: OCP) particles by homogeneous precipitation, using 0.0333 ~ 0.0500 mol∙dm Ca(NO3)2, 0.0200 ~ 0.0300 mol∙dm 3 (NH4)2HPO4, 0.04 ~ 0.40 mol∙dm 3 urea ((NH2)2CO; precipitant) and conc. HNO3, and (ii) the microwave-assisted hydrothermal heating of OCP particles at 130oC for 1 ~ 3 h. The fibrous HAp particles with the mean long-axis length of 307 m were obtained when the calcium phosphate solution containing 0.0333 mol∙dm Ca(NO3)2, 0.0200 mol∙dm 3 (NH4)2HPO4 and 0.12 mol∙dm 3 (NH2)2CO, was heated under flux at 80oC for 24 h, followed by the microwave-assisted hydrothermal heating at 130oC for 3 h. The mean long-axis length decreased down to 255 m, after the heating under reflux and microwave-assisted hydrothermal heating of the calcium phosphate solution containing 0.050 mol∙dm Ca(NO3)2, 0.030 mol∙dm 3 (NH4)2HPO4 and 0.20 mol∙dm 3 (NH2)2CO. Instead, the microwave-assisted hydrothermal heating of OCP particles in the HAp-dissolved solution, i.e., the dissolution of HAp powder by bubbling CO2 gas, helped increasing the mean long-axis length to 437 m. (Received Dec 7, 2017; Accepted Jan 16, 2018)