Positive and negative corona discharges in flowing carbon dioxide

The effect of the gas flow rate (10-320 cm(3) min(-1)) on the process of ozone formation in both positive and negative corona discharges has been studied using a coaxial cylindrical system of electrodes fed by dry CO2. The source of ozone is electron impact dissociation of carbon dioxide to liberate oxygen atoms and their subsequent formation of oxygen molecules, which may then form ozone by the well-known Chapman mechanism. Small increases in flow rate were found to cause a major increase in the discharge current measured in the negative corona discharge. This effect was found to correspond to observed changes in the ozone concentration within the discharge and is a consequence of dissociative electron attachment to ozone leading to negative ion formation in the discharge. In contrast no direct effect of ozone on the positive corona discharge current was observed. The observed increase in average positive ion mobility in the positive corona is ascribed to the conversion of O-2(+) ions into more mobile O-2(+) ions. Considerably higher ozone concentrations (up to 100 ppm) were found in the negative corona discharge. The effect of the geometry of the system was also explored by using three different stainless steel outer electrodes with diameters of 10, 15 and 27 mm. Ozone concentrations were found to decrease significantly with increasing radius of the outer electrode at the same average input energy density.