Pressure gradient flow electrical conduction in polar liquids

Abstract

Polar liquids like nitro-, chloro- and bromobenzenes find possible applications in electrostatic generators, impulse voltmeters etc. In this work natural conduction in these liquids has been studied at electric fields of 50 V/cm to 50 kV/cm and at temperatures of 0 to 200°C. An all?glass vacuum system has been designed to distill these liquids under a vacuum of 5 × 10?? torr. On fractional freezing and continuous distillation the conductivities of these liquids improved considerably. Since bromobenzene showed a photo?conductive effect it was distilled in complete darkness. Nitro-, chloro- and bromobenzenes showed minimum conductivities of 6.6 × 10?²?, 2 × 10?²? and 1.25 × 10?²¹ mho/cm respectively, after about one hundred hours of distillation. Many theories have been proposed to explain the conduction in insulating liquids under broad classification of dissociation and emission theories. In liquids with high dielectric constants the agreement between the various theories and the experimental result is poor. A modification of the thermionic emission theory has been suggested in this work and the current I and stress E are shown to be related in the form: log I = (e³E½ / 2kT) (1 + e?¹?) in which e is the electronic charge, ? the dielectric constant, k the Boltzmann constant, T the absolute temperature and n a constant characteristic of the liquid. The experimental results in nitro-, chloro- and bromobenzene confirmed this equation. The results in several other liquids by many previous workers also show good agreement. The conduction currents in these liquids increased with the temperature according to I = exp(C ? Ea/kT) in which Ea is the activation energy for electron release from its quasi?stable traps. The activation energies for nitro-, chloro- and bromobenzene were found to be 0.50 ± 0.05, 0.58 ± 0.06 and 0.38 ± 0.04 eV respectively. Data are not available in the literature for comparison. Ionic mobilities in these liquids have been deduced from the time variation of the current following application of a voltage to the liquids. These are found to be 12 × 10??, 6 × 10?? and 9 × 10?? cm²/V·sec in nitro-, chloro- and bromobenzenes respectively at an electric stress of 3 kV/cm. These are about a tenth of the values obtained in non?polar liquids. The mobilities varied inversely with the electric stress in all the three liquids.