title: Solid-state MAS NMR, TEM, and TGA studies of structural hydroxyl groups and water in nanocrystalline apatites prepared by dry milling.
abstract: A series of nanocrystalline calcium hydroxyapatites was prepared by dry milling and characterized using proton and31P MAS NMR, TEM, and TGA methods. The samples contained stubby rod-shaped crystals, which length and width varied in the 130-30 and 95-20 nm ranges, respectively. It was confirmed that concentration of structural hydroxyl groups in nanocrystalline apatites decreases with the decreasing crystal size. In the series of the studied apatites, the decrease was from 86 to ca. 50 % in reference to stoichiometric apatite. Water was found in the surface hydrated layer and in thec-axis channels, in which compartments existed as adsorbed and structural, respectively. Molecules of the adsorbed water were capable of moving from the crystal surface into the latticec-axis channels of apatite. This process introduced considerable structural disorder within and around those channels and reduced the content of the structural hydroxyl groups, particularly in the region underneath the apatite crystal surface.
authors.affiliation: Department of Inorganic and Analytical Chemistry, Faculty of Pharmacy, Medical University of Warsaw, ul. Banacha 1, 02-097 Warsaw, Poland.
authors.forename: Lukasz
authors.initials: L
authors.lastname: Pajchel
authors.forename: Waclaw
authors.initials: W
authors.lastname: Kolodziejski
keywords: Apatite; Hydroxyl groups; Milling; NMR; Nanocrystals; Structural water