AC Microdischarges in Porous Ceramics

Generation of microdischarges inside porous ceramics by AC high voltage has been investigated. Electrical and optical measurements were performed to explore the physical properties of the microdischarges. The effect of pore size, discharge power and gas mixture on the discharge properties and development is described. Introduction Research of various types of non-thermal plasmas generated by electrical discharges at atmospheric pressure has received a fast development in the last two decades. Streamer and pulsed coronas, and various types of dielectric or ferroelectric barrier discharges are mostly used. They are typical with nonequilibrium character and a large amount of thin filamentary channels, called microdischarges. The microdischarges produce a large density of energetic electrons and free radicals at relatively low energy consumption; therefore they represent a potential method for car exhaust cleaning [1-3]. In the recent years, there appeared a few pioneering works dealing with the generation of microdischarges in narrow cavities and capillaries of porous dielectric materials. The objective of the paper was to investigate the physical properties of these microdischarges by 50 Hz AC high voltage power supply by the electrical and optical methods. Experimental Setup The experimental set-up (Figure 1) includes a discharge reactor and electrical and optical circuits. The discharge reactor consisted of a porous ceramics placed between two stainless steel mesh electrodes inside the quartz cylinder. The ceramics were composed of alumina, and their diameter and thickness were 31 and 7 mm, respectively. The pore sizes of the ceramics were from 2 to 200 μm. (Figure 2). The whole reactor was placed in a Faraday cage to reduce induced noise signals. AC regulated high voltage power supply was used to generate the discharge. The voltage on the reactor was measured by a high voltage probe Tektronix P6015A and the discharge current was measured using a current probe Pearson Electronics 2877 (1V/A), both linked to the digitizing oscilloscope Tektronix TDS2024 (200 MHz, 2.5 GS/s). The total power including power losses in the electrical circuit was measured by the digital wattmeter Metex 3860M. Optical emission spectroscopy system consisted of a dual fiber-optic compact spectrometer Ocean Optics SD2000 with CCD detector used for fast scanning in the UV and VIS-NIR region (200-500 and 400-1050 nm). The photographs of discharge were taken by the digital camera Nikon E4300. All experiments were carried out in mixtures of nitrogen and oxygen at atmospheric pressure and at room temperature. The total gas flow rate ranged from 0.4 to 2 l/min. Figure 1. Experimental set-up WDS'07 Proceedings of Contributed Papers, Part II, 134–138, 2007. ISBN 978-80-7378-024-1 © MATFYZPRESS