Sol-gel silica electret films were coated on silicon substrates by a spin coating technique. The process of preparing the films is described and the electret behavior of the films is discussed. The films were corona charged at room temperature. Then, isothermal decay of the surface potential at room temperature and open-circuit thermally stimulated discharge (TSD) experiments were carried out. The results showed that the main peak of the TSD current spectra was situated at approximately 250-degrees-C and charge deposited in the film indicated good stability for the negative charged sample. After storage at room temperature for 50 days, the surface potential of the sample still retained at approximately 90% of the initial value. We found activation energies of 1.3 and 0.7 eV for negative and positive corona charged samples. Our experimental results suggest that the sol-gel process could be useful in electret and electronic technique applications.
A Monte Carlo simulation is carried out in SF6 in uniform electric fields with 7 and 14% overvoltages and at two gas densities at each overvoltage. The electron motion and avalanche growth is simulated by tracing individual paths and the effect of space charge is included by solving the Poisson equation. The streamer propagation, electron, positive and negative ion distribution and space charge fields are studied in detail as more time has lapsed after voltage application. The simulated streamer shape explains for the first time the dark space in SF6 streamers observed experimentally. It is found that the mechanism of streamer propagation in an attaching gas is different from that in a non-attaching gas. The maximum field enhancement is just behind the streamer or between two successive streamers in SF6. The anode directed streamer propagates with a velocity of 10(7) to 10(8) cm/s, dependent on the percentage of overvoltage and the gas number density.
HV outdoor insulators are always subjected to pollution of different nature and severity and the performance of a HV insulator under polluted conditions is quite different from that under pollution-free conditions. The present paper is concerned with the field distribution around a post-type insulator for different severities of surface pollution. The capacitive-resistive field distribution around the polluted insulator is calculated by a charge simulation method. The field calculations are carried out for power frequency voltage and also for lightning and switching impulse voltages. The effects of uniform or partial surface pollution and the presence of dry bands on the field distribution around a polluted post insulator are presented and discussed in detail. >
A comprehensive set of data of electron swarm parameters in nitrogen, oxygen and air are calculated by the Monte Carlo technique. It is shown that for mixtures of gases the calculated values differ considerably from those obtained using the simplified procedure of partial addition of the parameters of the constituent gases
The radiation-charged electret ionization-chamber uses an electret formed in situ by applying a bias voltage to the chamber electrodes while the chamber is being irradiated with X-rays. An electrometer permits measurement of the charge on the electret surface before and after the use of the chamber as a dosimeter. The authors present measurements of dosimeter range, sensitivity, and energy dependence as functions of bias potential, electrode separation, guard-ring size, and various materials. Reproducibility permits detection as low as 55 mu Gys with range up to 100's of cGys depending on the design of the chamber, with charge retention properties similar to those of electrets formed from corona discharge.<>
