Transport and Dielectric Breakdown in Composites with Complex Inclusion Microstructures
Abstract
A series of experiments have been performed on the dielectric and breakdown properties of random continuum composites. The experiments are divided into two categories: those performed on samples with static interfaces (e.g. steel balls in paraffin wax) and those with dynamic interface (e.g. polystyrene microspheres in suspension). The critical parameter for the stainless steel spheres in wax departed considerably from the predicted parameter. Since the theory is based on the intrinsic conductivity of the metal being infinite, the departures for the stainless steel spheres were ascribed to this cause. The higher conductivity Cu "spheres" gave better values, but the critical concentration of the spheres was much lower than anticipated, possibly due to large departures from sphericity for the Cu "spheres". The dielectric breakdown measurements were performed for similar samples stainless steel particles in wax and compared with theory. The effect of a conducting defect is more drastic in dielectric breakdown than in capacitance. The statistics describing the dielectric and breakdown data are different. For the breakdown data the modified Gumbel distribution and the Weibull distribution have been suggested as possible distributions. 300 failure tests indicated that at least two breakdown mechanisms were present, and that the part ascribed to intrinsic breakdown is better described by the modified Gumbel distribution. Attempts were made to measure the dielectric properties of colloidal suspensions of polystyrene spheres. Several methods designed to reduce or correct for electrode polarization were performed. In a study of the effect of electrode material, we found that bare Pt electrodes were superior to conventionally recommended Pt black and sand blasted Pt electrodes. The experimental results for the real part of the dielectric constant still exhibited electrode polarization effects below 1 KHz. Other serious problems included time variation and the separation of AC and DC conductivities necessary for the extraction of the imaginary part of the dielectric constant. The experimental results were compared with the theory developed by Sen and Chew. Large discrepancies in the real part of the dielectric constant seemingly stemmed from the electrode polarization effect. The results for the imaginary part yielded characteristic frequencies proportional to the inverse square of the particle radius as expected from theory.
- Publication:
-
Ph.D. Thesis
- Pub Date:
- 1994
- Bibcode:
- 1994PhDT.......199B
- Keywords:
-
- ELECTRODES;
- Physics: Condensed Matter