Positron annihilation spectroscopic study of hydrothemally synthesized fine nanoporous hydroxyapatite agglomerates

Nanoporous hydroxyapatite (Ca10(PO4)6(OH)2) powders in the form of agglomerates with micrometer dimension were synthesized through hydrothermal wet chemical route. The fine agglomerates were characterized by X-ray diffraction, infrared spectroscopy, scanning electron microscopy and transmission electron microscopy (TEM). Here we use positron annihilation lifetime spectroscopy (PALS) to indicate significant nanoporosity of agglomerates. The longest lifetime component τ4, which is ascribed to the annihilation of ortho-positronium (o-Ps) localized at mesopores, provides information about the pore size. τ4 varied at 300 K between 93 and 111 ns. The mean size of mesopores D is determined to vary between 6.8 and 11.6 nm. The spectra were also analyzed allowing a size distribution.