Surface ageing of dielectric materials in a controlled atmosphere: A Raman microprobe study

This paper takes a novel approach to the problem of characterising electrical ageing in solid dielectrics through ex-situ experiments that seek to reproduce the chemistry of electrical treeing in bulk. Plaque specimens of a range of polymers, including polyethylene, polystyrene, polyether ether ketone and silicone rubber, were subjected to surface ageing via corona discharge in air or in a closed cell where the atmosphere can be controlled and adjusted. The residual products on both the sample surface and the high voltage electrode were characterised by Raman microprobe spectroscopy and the resulting fingerprints were compared with those previously identified within electrical trees. Analysis of the electrodes aged in air and nitrogen revealed varying evidence of sp² hybridized carbon, and fluorescence, both of which are products previously associated with the processes involved in electrical treeing. The significance of the results is discussed with respect to electrical treeing.