Carbon encapsulated nickel(Ni@C) nanoparticles were synthesized via one step reducing flame spray pyrolysis approach and mixed with HDPE to prepare polymer based positive temperature coefficient(PTC) conductive composites.The as-prepared Ni@C nanoparticles possessed a core/shell structure with carbon shell located outside and nickel core located inside.The mean size of Ni@C nanoparticles was 30~50 nm

and the carbon shell was about 2.9 nm in thickness.The carbon content of Ni@C was about 3.4% calculated from TG analysis.The existence of carbon shell has significantly prevented the agglomeration of metallic nickel particles.Investigations of composite structure were carried by using an optical microscope on slides of composites and section SEM analysis.Results showed the Ni@C had a good spatial distribution in the HDPE matrix

and the PTC conductive composite performed a low percolation threshold of 10 wt% and a high PTC intensity of 8 in magnitude.