Electric Conduction, Adhesion Forces and Discharge Processes in a Particle-Particle-Contact - Highly Resistive Materials

在高电阻粉尘层中，通过颗粒-颗粒-接触进行导电的情况下，静电粘附力的产生与固体中的电传输机制密切相关。高场强导致粘接力显著增加。对于电阻率，观察到明显的非欧姆行为，具有强烈的时间效应。该项目的目的是通过微观尺度的实验和模拟来研究潜在的机制。我们以前的研究表明，高电阻粒子层中的电荷输运机制与电极材料中的机制相对应。在电流传输过程中，正负电荷载流子被注入到材料中，形成显著的静电空间电荷。时间效应可以用电荷注入机制和粒子体积中电荷的固定来解释。在接触间隙和孔隙中，电荷通过热离子场发射和气体放电机制进行输运。即使在微观层面上产生强大的静电附着力，宏观空间电荷过剩也会导致高阻粉尘层因静电斥力而发生机械失效。在项目的继续进行中，应改进并继续进行对单颗粒-颗粒接触的成功测量。在这里，电流吸收和接触力作为粒子直径、接触间隙距离、粒子材料和施加电压的函数被测量（时间分辨）。电荷在接触间隙的输运机制应通过观察光和气体离子的发射来验证。在该项目的模拟部分，正在开发一个包含固体和接触间隙中电荷传输机制的模型。通过局部电势、场强、载流子密度和电流密度，可以得到间隙内的传导或放电机制和接触力。在这里，时间效应的适当建模也是一项重要任务。模拟结果将用单粒子实验结果进行验证。最后，我们将尝试模拟链状粒子排列作为宏观粒子层的模型。此外，将进行粒子层和大质量层（介电）材料的实验。

In case of electrical conduction across the particle-particle-contacts in highly resistive dust layers, the generation of electrostatic adhesion force is strongly coupled to the mechanisms of electrical transport in the solid. High field strengths lead to a significant increase of adhesive forces. For the electrical resistivity, a pronounced non-ohmic behaviour with strong time effects is observed. Aim of the project is to investigate the underlying mechanisms by experiments and simulations on the microscopic scale. Our previous investigations have shown that the mechanisms of charge transport in highly resistive particle layers correspond to those in electrete materials. During current transport, positive and negative charge carriers are injected into the material, and significant electrostatic space charges are formed. The time effects are explained by the mechanisms of charge injection and by the immobilization of charges in the particle volume. In the contact gaps and pore spaces, charge transport can occur by the mechanisms of thermionic field emission and gas discharge. Even though strong electrostatic adhesion forces are generated on the microscopic level, the macroscopic space charge excess can lead to a mechanical failure of highly resistive dust layers by electrostatic repulsion. In the continuation of the project, the successful measurements on single particle-particle contacts shall be improved and continued. Here, the current uptake and the contact force are measured (time-resolving) as a function of particle diameter, contact gap distance, particle material and applied voltage. The mechanism of charge transport across the contact gap shall be verified by observing the emission of light and gas ions. Within the simulation part of the project, a model incorporating the mechanisms of charge transport in the solid and in the contact gap is being developed. Via local potentials, field strengths, charge carrier densities and current densities, the conduction or discharge mechanisms in the gap and the contact force are to be obtained. Here as well, the appropriate modelling of time effects is an important task.The simulations will be verified using results from the single particle experiments. Finally, we will try to simulate chain-like particle arrangements as a model for macroscopic particle layers. Additionally, experiments on particle layers and on massive layers of (dielectric) materials will be made.