Search results

The purpose of this paper is to explore and develop specific models of the kinetics of isothermal depolarization currents (IDC) and the corresponding methods for the diagnostics of the physical parameters of localized electronic states (LES) in heterogeneous materials and corresponding polycrystalline semiconductor materials and heterogeneous insulators with a conductive phase.

Analysis of the kinetics of isothermal depolarization on the basis of the models allowed the authors to establish a sufficient level of their information content. This also allowed the possibility of applying for research and testing of heterogeneous structures of electronic technique.

Optimal conditions (full charge of LES on one side of the object and full discharge on the other side) and the correction factors, allowed the researchers to find concentration of these states using the developed models.

This paper uses a particular method to determine and test the parameters of LES, including operations of determining the time constant of IDC signal from its frequency spectrum, finding the ionization energy and the capture coefficient of electrons from the temperature dependence of this time constant, determining the concentration based on the integration of the time dependence of current density of IDC in the time interval that boundaries are determined from the limited range of frequencies of the signal IDC spectrum has been proposed, validated and verified by numerical experiments.

The purpose of this paper is to develop the models of the dielectric permittivity dispersion of heterogeneous systems based on semiconductors to a level that would allow to apply effectively the method of broadband dielectric spectroscopy for the study of electronic processes in ceramic and composite materials.

The new approach for determining the complex dielectric permittivity of heterogeneous systems with semiconductor particles is used. It includes finding the analytical expression of the effective dielectric permittivity of the separate semiconductor particle of spherical shape. This approach takes into account the polarization of the free charge carriers in this particle, including capturing to localized electron states. This enabled the authors to use the known equations for complex dielectric permittivity of two-component matrix systems and statistical mixtures.

The presented dispersion equations establish the relationship between the parameters of the dielectric spectrum and electronic processes in the structures like semiconductor particles in a dielectric matrix in a wide frequency range. Conditions of manifestation and location of the different dispersion regions of the complex dielectric heterogeneous systems based on semiconductors in the frequency axis and their features are established. The most high-frequency dispersion region corresponds to the separation of free charge carriers at polarization. After this region in the direction of reducing of the frequency, the dispersion regions caused by recharge bulk and/or surface localized states follow. The most low-frequency dispersion region is caused by recharging electron traps in the boundary layer of the dielectric matrix.

Dielectric dispersion models are developed that are associated with: electronic processes of separation of free charge carriers in the semiconductor component, recapture of free charge carriers in the localized electronic states in bulk and on the surface of the semiconductor and also boundary layers of the dielectric at the polarization. The authors have analyzed to situations that correspond applicable and promising materials: varistor ceramics and composite structure with conductive and semiconductor fillers. The modelling results correspond to the existing level of understanding of the electron phenomena in matrix systems and statistical mixtures based on semiconductors. It allows to raise efficiency of research and control properties of heterogeneous materials by dielectric spectroscopy.

Introduces the fourth and final chapter of the ISEF 1999 Proceedings by stating electric and magnetic fields are influenced, in a reciprocal way, by thermal and mechanical fields. Looks at the coupling of fields in a device or a system as a prescribed effect. Points out that there are 12 contributions included ‐ covering magnetic levitation or induction heating, superconducting devices and possible effects to the human body due to electric impressed fields.

Last month we published abstracts and summaries of some of the papers presented at the Congress, which was held at the Imperial College of Science and Technology from April 10–15 under the auspices of the International Union of Pure and Applied Chemistry. In this issue we publish further abstracts and summaries together with illustrations of many of the corrosionists attending and photographs of some of the many visits which were arranged to works and laboratories. The Congress attracted over 800 delegates.

Introduction The U.M.I.S.T. Corrosion and Protection Centre was established in April 1972. In the first article in this series we outlined the reasons for this move, and the approach adopted by the Centre to undergraduate and postgraduate education and training in corrosion science and engineering. In this article we shall describe some of the researches in corrosion and protection currently in progress in the Centre.

Presented herein is information developed by a panel of the Sub‐Committee on Corrosion of the American Institute of Petroleum concerned with the mechanism of corrosion inhibition, temperature limitations, detergent action and chemical composition of the high‐molecular‐weight organic inhibitors commonly used in process streams. Included is a literature survey on the mechanism of corrosion inhibition; refinery experiences with inhibitors as developed by a questionnaire; and information contributed by manufacturers of inhibitors. Other data pertinent to corrosion and inhibitor problems are discussed.