The effects of multiwall carbon nanotubes on the electrical characteristics of ZnO-based composites

In this experimental work, the effects of multiwall carbon nanotubes (MWCNTs) on electrical characteristics of zinc oxide-MWCNT-high-density polyethylene composite varistors have been investigated. All the samples were made at the temperature of 130 degrees C and pressure of 60 MPa by the hot-press method. Results show that increasing zinc oxide content in the mixture increases breakdown voltage up to 170 V, where the highest nonlinear coefficient (alpha similar to 13) corresponds to the samples with 95 wt% of ZnO. Results with regard to the effects of MWCNT as an additive reveal that increasing its content from 1 to 2.5% in the composites, the breakdown voltage decreases to 50 V, but the highest nonlinear coefficient (similar to 14) corresponds to the sample with 1.5% of MWCNT content. It is also revealed that, heat treatment of the sample at a constant temperature of 135 degrees C and different time intervals from 2 to 10 h, the sample with 6 h annealing time shows maximum breakdown voltages (V-b = 140 V) with the highest nonlinear coefficient (similar to 14). Investigation of the potential barrier height of samples shows a complete consistency with the breakdown voltage variations. The results have been justified regarding XRD patterns and SEM micrographs of samples.