Polydimethylsiloxane and alumina trihydrate system subjected to dry-band discharges or high temperature part II: electrical insulation

This is the second of a two-part series on the chemical, morphological and electrical changes of the polydimethylsiloxane (PDMS) and alumina trihydrate (ATH) material system subjected to dry-band discharges. The PDMS/ATH system allowed track formation (tracking) leading to dielectric breakdown in the IEC 60587 internationally standardized tracking test. However, the carbon concentrations in the formed track were merely ∼1% wt., and thus dielectric breakdown based on electrical conductivity of carbon deposited in the track could not be reasonably explained. This second paper describes electrical conduction in the track of the PDMS/ATH system as well as the track-propagation mechanism in little presence of carbon. The discharge behavior during the track propagation was studied in detail in association with the behavior of the electrolytic solution as discharge onset media and with gas byproducts emitted from the system subjected to dry-band discharges. A hypothesis regarding tracking of the PDMS/ATH system, which has previously been believed to be a highly tracking resistant system, is proposed herein. Gas byproducts created a space where electrical insulation was reduced and induced discharges to the surface. As a result, the emission of gas byproducts was more strongly promoted and the gas byproducts played the role of media creating discharges that connect carbon particles dispersed in the track.