Sol–gel synthesis, phase composition, morphological and structural characterization of Ca10(PO4)6(OH)2: XRD, FTIR, SEM, 3D SEM and solid-state NMR studies

• Influence of morphology and crystallinity of calcium hydroxyapatite on processing conditions.
• Different complexing agents used in the sol–gel processing.
• The amount of structural OH groups is significantly higher than from adsorbed water.
• The spatial 3D data from SEM images of CHAp samples were recovered.
• The non-classical spin coupling model perfectly described the CP kinetics in nano-CHAp.

Aqueous sol–gel chemistry route based on ammonium–hydrogen phosphate as the phosphorus precursor, calcium acetate monohydrate as source of calcium ions, and 1,2-ethylendiaminetetraacetic acid (EDTA), or 1,2-diaminocyclohexanetetracetic acid (DCTA), or tartaric acid (TA), or ethylene glycol (EG), or glycerol (GL) as complexing agents have been used to prepare calcium hydroxyapatite (Ca10(PO4)6(OH)2, CHAp). The phase transformations, composition, and structural changes in the polycrystalline samples were studied by infrared spectroscopy (FTIR), X-ray powder diffraction analysis (XRD), and scanning electron microscopy (SEM). The local short-range (nano- and mezo-) scale effects in CHAp were studied using solid-state NMR spectroscopy. The spatial 3D data from the SEM images of CHAp samples obtained by TA, EG and GL sol–gel routes were recovered for the first time to our knowledge.

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