A novel high efficiency method for the synthesis of graphite encapsulated metal (GEM) nanoparticles

Graphite encapsulated metal (GEM) nanoparticle is a composite material with a core-shell structure; it can retain its novel properties even under severe environments. In recent years, many researchers have dedicated their efforts to improving the synthesizing efficiency of GEM by the arc-discharge method; although some progress has been made, the results remain unsatisfactory. To solve the problem, and under the guidance of the two-step mechanism model, it is clear that the carbon-to-metal ratio within the coalescence region of the arc-discharge must be effectively controlled. Thus, an injection of liquid ethanol was used as the carbon source to replace the synthetic diamond powder; the results showed that the encapsulation efficiency of ferromagnetic GEM was dramatically increased, i.e., 70–80% for Ni-GEM and Co-GEM, and for Fe-GEM it was quadrupled to about 50%. Furthermore, high encapsulation efficiency also prevents the common problem of spontaneous combustion of the as-made Fe-GEM powders. Some evidence as well as observations, indicates that the ethanol jet provides a large quantity of carbon in the arc-discharge area in a relatively short time. Although the detailed mechanism of this phenomenon is not well-understood, it shows that the production rate could be increased by a factor of ten or higher than it was previously. In this study, a simple and novel liquid ethanol injecting method has been developed; experiments have also demonstrated that this is an effective method for the synthesis of ferromagnetic GEM nanoparticles.

► A simple liquid ethanol injection process has been developed for the arc-discharge method.
► The liquid ethanol carbon source is better than other solid or gas carbon sources in the synthesis of GEM nanoparticles.
► Controlling the carbon-to-metal ratio is the key to the synthesis of GEM nanoparticles.