Microstructural characterization of alumina-coated multi-walled carbon nanotubes synthesized by hydrothermal crystallization

Multi-walled carbon nanotubes (MWCNTs) were coated with a nano-sized α-alumina polycrystalline layer by hydrothermal crystallization under autoclave conditions followed by manipulative calcination. These nanocomposites were characterized for their microstructure and composition by X-ray diffraction (XRD), energy-dispersive X-ray spectroscopy (EDX), transmission electron microscopy (TEM), high resolution transmission electron microscopy (HRTEM) and scanning electron microscopy (SEM). The results show that the microcrystalline α-alumina layer with the thickness of 1–3 nm was rough and compact, which profited from well adhesion by boehmite sol, the lower temperature for the conversion of the hydroxide to oxide, and the slower speed for the calefaction process. In addition, the α-alumina-coated MWCNTs were dispersed uniformly in alumina particles.