Structural, morphological and magnetic properties of nickel-carbon nanocomposites prepared by solid-phase pyrolysis of Ni phthalocyanine

Abstract

Nickel-carbon nanocomposites have been synthesized by the solid-phase pyrolysis of nickel-phthalocyanine at temperatures in the range 600–1100 °C and synthesis duration time up to 300 min. Nickel nanoparticles of various size have been obtained, which are embedded in carbon nanotubes (CNT), nanofibers and encapsulated in the graphite-like shell. A formation of metallic nanoparticles with diameters in the range 5–40 nm takes place at pyrolysis temperatures lower than 700 °C. The temperature of ~700 °C is a threshold for the beginning of the CNTs growth. At these temperatures, the CNTs have diameters ~20 nm and the aspect ratio ~100. A rise of the pyrolysis temperature leads to the increase of the CNTs average diameters. An analysis of the formation mechanisms of the metal-carbon nanocomposites has made it possible to determine that the CNT growth is caused by catalytic properties of nickel. In the process of interaction of Ni with amorphous carbon at high temperatures, nanoparticles form around themselves the graphitelike shells. Investigations of magnetic characteristics have shown that the main mass of Ni ferromagnetic nanoparticles has a single-domain and a vortex (pseudosingle domain) nature. We have detected the presence of superparamagnetic Ni nanoparticles and carbon paramagnetic centers in the nickel-carbon nanocomposite.