Dielectric breakdown model

Abstract: We introduce and discuss a fractal model for dielectric breakdown which exhibits a breakdown voltage and a region of stable prebreakdown structures. The model provides a unifying picture covering homogeneous space charge injection, treelike structures, and filamentary breakdown. A simple qualitative relation between the global form of the pattern and two simple physical parameters is found. The model illustrates the intricate relationship between local stochastic and global deterministic aspects of dielectric instablilities.

Abstract: Selective breakdown of mineralized particles by using high-voltage pulses (HVP) has been reported, yet its mechanisms are not fully understood, and the HVP setting factors affecting its efficacy in ore pre-concentration for the mining industry are not established. This study investigates the electro-dynamic mechanisms of electric breakdown by using the time-transient dielectric breakdown model and the finite-difference numerical method. Monte-Carlo method with random sampling is applied to calculate breakdown probabilities. The model and the selected parameters have been validated by the published experimental data of the electric breakdown of mineralized synthetic particles. The simulations of pulse rising time from 150 ns to 1 μs showed that the HVP breakdown threshold of rock particles gradually increased as the pulse rising time decreased. This suggests that to minimize the mis-breakdown of barren rocks in the HVP-enabled ore pre-concentration application, it is important to use a generator with a short pulse rising time. Shorter pulses also led to a higher probability of the internal breakdown of the mineralized particles. The simulations indicate that inhomogeneity of conductivity in an ore particle caused the streamers to bend toward the area of inclusion with high conductivity in a host rock matrix, which increased the probabilities of the breakdown of this mineralized particle. This phenomenon was more pronounced as conductivity rose. High-conductivity inclusions can reduce the minimum voltages required for the breakdown of the mineralized particles.

Abstract: We introduce a new theoretical approach that clarifies the origin of fractal structures in irreversible growth models based on Laplace equation and provides a systematic method for the calculation of the fractal dimension. A specific application to the Dielectric Breakdown Model (including therefore DLA) in two dimension is presented. The analogies and differences with respect to the Renormalization Group are discussed.

Abstract: High-performance energy storage dielectrics have been the key to solve energy problems in the context of energy crisis. Designing multilayered structures is an effective approach to break the paradox between high dielectric constant and high breakdown strength existing in polymer-based composite films to enhance energy storage performance. Herein, a designed sandwich-structured poly(vinylidene fluoride) (PVDF)-based composite film, with a characteristic of the inner PVDF layer filled with Na0.5Bi0.5TiO3 (NBT) whiskers and the outer layers of pure PVDF, is proposed. An ultrahigh discharged energy density of 30.55 J cm−3 and an outstanding discharged efficiency of 80.26% can be obtained in the optimized composition with the inner layer containing 6 vol% NBT whiskers, which outperforms all the previously reported PVDF-based composite films. Furthermore, it reveals that such a sandwich structure with NBT whiskers is able to adjust dielectric properties and reform electric field distribution, as evidenced by dielectric and insulation properties as well as the dielectric breakdown model by finite element analysis, which prompts the enhancement of polarization and breakdown strength synergistically, and thus, contributes to excellent energy storage performance. This work provides a strategy for developing high-end dielectrics for electrostatic energy storage applications.