Structural and proton transport studies on nanocrystalline [Ca10(PO4)6(OH)2] (HAp), HAp–Nafion® composite, and natural human bone

Abstract

AbstractNanocrystalline hydroxyapatite, Ca10(PO4)6(OH)2 (HAp) is synthesized from hydroxide gels at room temperature using sonochemical technique. The as‐synthesized material is characterized by X‐ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), selected area electron diffraction (SAED), Fourier transform infrared (FT‐IR), and solid‐ state (1H and 31P) NMR techniques. Hexagonal structure with space group P63/m is evident from powder XRD. Microscopic analysis with SAED indicates the nanocrystalline nature of the compound. Average particle size of 30 nm with excellent phase purity in good stoichiometric ratios of HAp is observed. The prevalence of protons as hydroxyls in apatitic structure of HAp is evident from FT‐IR and solid‐state NMR. The microstructure and proton conducting properties of the synthesized material are compared with the natural human bone powder having similar constituents. The sonochemically prepared HAp, and HAp‐Nafion® composite exhibited excellent AC conductivities ∼10−5 S cm−1 at 650 °C and ∼10−5 S cm−1 at 160 °C, respectively, may find application as an electrolyte for low temperature solid oxide fuel cells (LT‐SOFCs) and high temperature polymer electrolyte fuel cells (HT‐PEFCs) applications.