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

Abstract

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^-3 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 130°C for 1-3 h. The fibrous HAp particles with the mean long-axis length of 307 μm were obtained when the calcium phosphate solution containing 0.0333 mol・dm^-3 Ca(NO₃)₂, 0.0200 mol・dm^-3 (NH₄)₂HPO₄ and 0.12 mol・dm^-3 (NH₂)₂CO, was heated under flux at 80°C for 24 h, followed by the microwave-assisted hydrothermal heating at 130°C for 3 h. The mean long-axis length decreased down to 255 μm, after the heating under reflux and microwave-assisted hydrothermal heating of the calcium phosphate solution containing 0.050 mol・dm^-3 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 μm.