Formation and characterization of graphite-encapsulated cobalt nanoparticles synthesized by electric discharge in an ultrasonic cavitation field of liquid ethanol

Abstract Cobalt nanoparticles encapsulated in graphitic shells were successfully synthesized using an advanced and cost-effective synthesis method. The graphite-encapsulated nanoparticles were synthesized using an electric plasma discharge generated in an ultrasonic cavitation field of liquid ethanol, followed by the separation, drying and annealing of particles. Prior to annealing, the core-shell structured nanoparticles were characterized by high-resolution transmission electron microscopy and X-ray diffraction, which revealed the presence of a Co 3 C and carbon supersaturation in the face-centered cubic β-Co phase in the core of carbon nanocapsules; some cores were discovered in an amorphous state. The majority of carbon nanocapsules were found to be spherical particles, less than 10 nm in diameter. The annealed powder samples, in which cobalt carbides and amorphous inner cores transformed to crystallized α-Co and β-Co cores, showed coercivity values of 15.5 kA m −1 and saturation magnetization values of about 50 A m 2 kg −1 , which is approximately 32% of the value of bulk cobalt particles.