Solid-phase steam-assisted synthesis of hydroxyapatite nanorods and nanoparticles

This article reports a novel and facile solid-based steam-assisted conversion method for the synthesis of hydroxyapatite (HAP, Ca₁₀(PO₄)₆(OH)₂) nanorods and nanoparticles. After steam treatment at 180 °C for 20 h, the wet solid of brushite (CaHPO₄·2H₂O), which was precipitated from reaction between calcium nitrate [Ca(NO₃)₂] and diammonium hydrogen phosphate [(NH₄)₂HPO₄], was transformed to HAP nanorods with dimension of 100–300 nm in length and 56 ± 10 nm in diameter through a solid–gas reaction. By the same steam treatment, the dried brushite was converted to nanoparticles of HAP with small aspect ratio and particle size of 70 ± 18 nm. As compared with commercial HAP material, the nanostructured HAP materials exhibited superior sinterability in terms of density and hardness as well as excellent thermal stability. This simple, organic-free and cost-effective synthesis route with low reactant volume offers high potential for large-scale production of nanostructured HAP.