A facile urea-assisted hydrothermal synthesis and systematic characterization of hydroxyapatite (HA) with calcium nitrate tetrahydrate and diammonium hydrogen phosphate as precursors are reported. The advantage of the proposed technique over previously reported synthetic approaches is the simple but precise control of the HA crystals morphology, which is achieved by employing an intensive, stepwise, and slow thermal decomposition of urea as well as varying initial concentrations of starting reagents. Whereas the plate-, hexagonal prism- and needle-like HA particles preferentially growth along the c-axis, the smaller and fine-plate-like HA crystals demonstrate crystal growth along the (102) and (211) directions, uncommon for HA. Furthermore, it was established that the hydrothermally derived powdered products are phase-pure HA containing CO3
2− anions in the crystal lattice, that is, AB-type carbonated hydroxyapatite. Transmission electron microscopy (TEM) and electron diffraction (ED) of selected samples reveal that the as-prepared HA crystals are single-crystalline and exhibit a nearly defect-free microstructure. The hardness and elastic modulus of the hexagonal prism-like HA crystals have been investigated on a nanoscale using the nanoindentation technique; the observed trends are discussed.
In this report, we describe a novel solvothermal procedure for the synthesis of nanosized particles of barium titanate (BaTiO 3 ). We have been able to synthesize large amounts of nearly uniform sized BaTiO 3 nanocrystals in the size range of 5-37 nm. The advantages of our technique over other previously reported hydrothermal/ solvothermal approaches are the high yield and the simple but precise control of the size of the particles, which is very conveniently achieved by changing the water content of the reaction mixture in a measured way. The particles are systematically characterized by powder X-ray diffraction (XRD), Raman scattering, scanning electron microscopy (SEM), transmission electron microscopy (TEM), electron diffraction (ED), high-resolution TEM (HRTEM), disc centrifugation, thermogravimetric and differential thermal analyses (TGA-DTA), infrared spectroscopy (IR), and inductively coupled plasma-optical emission spectrometer (ICP-OES). The as-synthesized BaTiO 3 nanopowders contain BaCO 3 byproduct as well as internal OHgroups and residual solvent species that can be removed by acid washing following heating. However, it is shown that this procedure results in the substantial change of the chemical composition and strong degradation of real microstructure of nanosized BaTiO 3 particles.
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