Polarization currents in high temperature polymers in 10/sup -6/-10s time range

While considerable data are available on the steady state currents under dc voltages in polymers, transient current measurements are relatively few. The transient currents resulting from the application of a step voltage are studied in aramid paper (Nomex(R)), aramid paper-mica composites and Fluoropolymer (Tefzel(R)) films. Experimental results are obtained in the temperature range of 50-200/spl deg/C at electric field strengths of 1.32 MVm/sup -1/ to 20 MVm/sup -1/. The currents are recorded in the time scale extending from 2/spl mu/s to 2s as measured from the edge of the step voltage. Initially transient currents decay with time. At 0.1s, currents in fluoropolymer start to increase with time, while the currents in aramid paper and composite continue to decrease. Possible mechanisms are considered. The conductivity is observed to be related to relaxation time.