Transient Currents in Silicone Oils Subjected to Voltage Steps with Polarity Reversal

We have studied the transient currents flowing in silicone oils subjected to voltage steps with polarity reversal. The experiments have been carried out, at room temperature, on two 50 cSt viscosity polydimethylsiloxane silicone oils (Rhône-Poulenc 604 V 50 and Dow Corning 561) in parallelplate conductivity cells as a function of the applied electric field strength (0.4 ≦ E (kV cm-1) ≦ 10), of the cell gap (0.022 ≦ d (cm) ≦ 0.3), of the oil viscosity (50 to 300 cSt) and of the oil purity. From our measurements we can assert that: (1) the peaks appearing on the waveforms corresponding to the commercial oils are due to some impurities present in these oils; (2) these peaks cannot be caused by the migration of a charged layer between the electrodes; (3) they are more certainly correlated to some dipole reorganization near the electrodes after each voltage polarity reversal.