Open-Circuit TSD Method and Anomalous Air Gap Current in Teflon® FEP

The paper shows an extension of the technique of open-circuit thermally stimulated discharge (TSD), consisting of simultaneously measuring the current and its charge on the external circuit as a function of temperature. The current is measured with a strongly damped meter which fails to give a time-resolved record of fast current pulses. The charge is recorded with a capacitive integrating system. Using this arrangement it was possible to show that the noise usually appearing in the current curve of negatively charged Teflon FEP is due to microbreakdown events in the sample. Moreover, positive charges were detected, which were ejected from the surface of virgin, uncharged FEP samples, whenever a positive bias voltage was applied in the measuring circuit. The effect of this current on the measurements with charged FEP is also discussed.