Percolation Phenomena and Critical Exponent of Dielectric Breakdown Strength of Carbon Black-Polyethylene Composites

Abstract

This paper addresses the critical exponent of dielectric breakdown strength of composites made with carbon black and polyethylene below the percolation threshold for the first time. At first place, the percolation threshold p_c is determined based on the critical exponents of resistivity and relative permittivity of the composites. Dielectric breakdown strength E_B of the composites below p_c is measured by using an impulse voltage in the range of 10 kV to 40 kV in order to avoid the effect of joule heating. Although the observed data of E_B seem to be well fitted to the straight line with the slope of 0.9 on a double logarithm of (p_c -p) and E_B, a method of least squares gives the slopes of 0.72 ± 0.12 and 0.96 ± 0.05 for the composites made with BP2000 and Asahi-Thermal, respectively. It has been found that finite carbon black clusters play an important role in the dielectric breakdown of the composites.