Rapid growth of onion-like carbon nanospheres in a microwave oven

Abstract

Onion-like carbon spheres (OLCSs) were synthesized by heating a mixture of naphthalene and graphite powder inside a kitchen microwave oven for ∼1 min under atmospheric conditions. Naphthalene, a hydrocarbon, provides carbon for growth, while graphite plays the crucial role of microwave absorber. The size of the OLCS particles was distributed over a wide range from a few 10s of nm up to a few μm. The OLCS particles self-assembled in a long range chain-like structure. The duration of microwave heating and the ratio of the precursor components were found to be important factors affecting the size and density of the particles. Alternative hydrocarbon sources and microwave absorbers were also examined for OLCS growth. Addition of ferrocene as a catalyst to the precursor mixture of naphthalene and graphite resulted in the formation of highly crystalline carbon-encapsulated iron (in the form of oxide/carbide) nanoparticles with a core–shell structure. The as-synthesized OLCS mixture containing graphite as the precursor was mixed with poly-alpha olefin oil (PAO4) as an additive. A significantly lower friction coefficient and wear rate were obtained with this mixture as compared to the neat PAO4 and PAO4+graphite mixture. Microwave heating was also employed to coat thin films of OLCSs on alumina/glass substrates. The conductivity of these films was measured using the four probe method. The microwave-assisted method used to produce OLCSs has several advantages like cost and energy efficiency, minimal preprocessing, etc. This technique can be of industrial importance for bulk productions of OLCSs and graphitic shell-encapsulated metal nanoparticles.