Hirofumi Shimokawa

Conduction currents in silicone liquid films

Abstract The current response to the application of a stepped field on silicone liquid films has been measured over a wide range of time duration (10 −5 – 10 4 s), field strength (5 – 500 kV/cm), temperature (20 – 160 °C) and sample thickness (4 – 25 μm). Both the transient and the quasi-steady-state responses are considered. The results indicate that the activation energy for the transient current increases rapidly with increasing time corresponding to the rapid decrease of the current, and the Activation energy for the quasi-steady-state current does not vary with time. It is also found that the transient current depends on the sample thickness (i.e. bulk limited) and the quasi-steady-state current is electrode limited. These time-dependent behaviors of the conduction are discussed in terms of the thermally activated hopping of injected excess electrons from the metal-liquid contact.

High field conduction in dielectric liquid films in time range of 10−5 − 10−3 s

Abstract In order to develop more enough the investigation of electrical conduction in dielectric liquid films, partly reported previously by the authors, the transient conductivity at higher electric field has been studied. The measurement has been carried out under the conditions as follows; time duration (10 −5 − 10 −3 s), field strength (100 kV/cm - 1 MV/cm), temperature (room temperature - 150°C), a coefficient of kinematic viscosity (1 – 100 cSt) and sample thickness (3 – 5 μm). The results indicate that 1) the transient current i has been observed to decay according to i ∝ t -n where the exponent n is independent of the field strength, 2) the transient conductivity σ varies with field strength E as σ ∝ exp (bE) where b is a constant, and 3) the hopping distance of excess electrons obtained from conductivity-field curves depends on time and temperature, and these dependences correspond to time and temperature dependences of the activation energy respectively. The transient processes of excess electrons in dielectric liquids from these results are discussed.