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In this study, a flame-generated nm-range SiO2 aerosol (approx. 170 nm median aggregate diameter) is fed into an electrostatic precipitator with an operating temperature of 200 °C. While a highly porous layer of SiO2 nanoparticles (NPs) is deposited by electrostatic precipitation, a decrease of current uptake is observed initially, indicating exceptionally high values of the electric field within the layer (> 100 kV/mm) and of the layer resistivity (> 1013 Ω∙cm). Later a strong (13- to 17-fold) increase of current uptake is observed. Aerosol charge measurements show that charges of opposite polarity are emitted from the NP layer. Investigation of the NP layer by SEM shows that charge-emitting structures with a polarity-dependent morphology develop on an originally homogeneous NP layer. Based on the experimental evidence, the mechanisms of charge emission and structure formation are discussed. Charge emission from the precipitated dust layer is known as back corona in the field of electrostatic precipitation. It appears that the mechanisms of back corona observed with SiO2 NP layers are quite distinct from those observed with µm-range particles. While gas discharges inside the NP layer are suppressed due to small pore size, back corona inside the NP layers is apparently initiated by thermionic field emission of free electrons and secondary electron multiplication within the NP layer.

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 m) 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.