In situ mass spectrometric analysis of the deterioration of polymer surfaces by low pressure AC discharges

Mass spectra of positive ions extracted from low-pressure (300-500 Pa) AC discharges to polymer surfaces show that polyethylene and polypropylene emit significant amounts of water when exposed to dry air of air-SF₆ coronas, and that this is due to the action of oxygen. This suggests that water trees in polymers may grow without externally supplied water if microdischarges and oxygen are present. The discharge conditions used, pd≈2.5 Pa-m, are near the Paschen minimum and correspond to a void of 25-μm thickness at atmospheric pressure. This is the width at which a partial discharge will initiate at the lowest voltage. The corona ion source mass spectrometer has proved to be a very sensitive device for in situ measurement of the interaction between a gas discharge and a surface