Hochohmige Stäube zeigen ein ausgeprägtes nicht‐ohmsches Verhalten. Die als spezifischer elektrischer Widerstand bekannte Messgröße ist stark abhängig von der Schichtdicke und der Polarität der Hochspannung. Der Stromstransport findet durch Überschussladungen beider Polaritäten statt, die zu hohen Raumladungsdichten führen und starke elektrostatische Felder induzieren. Die beobachteten Effekte können als Elektret‐Effekte interpretiert werden. Zur Untersuchung des elektrischen Verhaltens wurden hochohmige Staubschichten innerhalb einer Spitze‐Platte‐Anordnung einem elektrischen Feld mit überlagerter Korona‐Entladung ausgesetzt.
In case of electrical conduction through highly resistive dust layers, the generation of electrostatic adhesion force is strongly coupled to the mechanism of electrical (current) transport in the solid. High field strengths lead to a significant increase of the adhesive force. Here, more insight into the underlying mechanisms is given by experiments on the microscopic scale. An experimental arrangement is described which allows to study a particle pair subject to a strong electric field. Both the current and the force between the particles (150 μm) can be measured as a function of voltage and gap distance. The results show an extremely complex behaviour of the contact for the case of highly resistive particles. For current transport, both gas discharges and thermionic field emission are observed, depending on the width of the contact gap and the field strength. For both the force and the current across the gap, a strongly non-linear behaviour with pronounced time effects is observed.But additional problems are found with highly resistive dusts in electrostatic precipitators (ESPs). With dust resistivities beyond 10 11 Ω-cm, the precipitation process itself is disturbed by so called back corona (Masuda in [2,(3)(4)(5)). The current interpretation is that the current has to pass through the dust layer on the precipitation electrode. With high dust resistivity, a given current density will cause a strong voltage-drop across the dust layer and hence a strong electric field inside the dust layer. When a critical field strength is surpassed, an electric breakthrough occurs.
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