Insulator-conductor transition in carbon nanotube and graphene nanoplatelates reinforced plasma sprayed alumina single splat: Experimental evidence by conductive atomic force microscopy

Abstract

Splats are the most fundamental and paramount unit of any plasma sprayed coating and splats are having the potential to manipulate the overall property of the same. Current study shows the insulator-conductor transition of alumina (Al2O3) splat by the hybrid addition of carbonaceous nanofillers, namely carbon nanotubes (CNTs) and Graphene nanoplatelets (GNPs) into it. Reinforcement of CNTs and GNPs changed the splat shape from fragmented to nearly disk shaped as well as from porous splat to densified one upon the reinforcement. Further, Current mapping over the splats were carried out using conductive atomic force microscopy (cAFM). Current map for Al2O3 splat showed fully black region, evincing its insulating nature; whereas hybrid addition of CNTs and GNPs into the splat dramatically improved the electrical conductivity of Al2O3 splat, coining its non-conductive map to conductive one. This transition was attributed to electron tunneling mechanism, which is a function of electron hopping distance of these conductive nanofillers. The electron hopping distance of the matrix got minimized when CNTs and GNPs were simultaneously added to Al2O3 splat, due to their higher aspect ratio. This led to the formation of a 3-dimensional conductive channels for the electron transport in the matrix, converting the whole splat as conductive.