Plasma-Surface Interactions Induced by Pulsed Corona Discharge in Water

Summary form only given. Pulsed high voltage discharges generated directly in water initiate a variety of chemical and physical effects including the high electric field, intense ultraviolet radiation, overpressure shock waves, and, of particular importance, formation of various chemically active species (OH, H and O radicals, H 2 O 2 ). These reactive species and physical conditions in turn have been shown to be effective at degrading a variety of organic compounds; in the destruction and inactivation of microorganisms; and also in the modification of surface properties of polymeric materials. Recent research has showed that plasma chemical activity of electrical discharge in water can be enhanced by the addition of solid particles into the discharge reactor. Several types of materials have been tested such as activated carbon, silica gel, alumina, titanium oxide or zeolites. However, despite observed synergistic effects there is only limited knowledge about the role of these materials in the plasma assisted processes in water. It is apparent, that presence of these materials can affect chemical activity of the discharge in various ways including in addition to the simple adsorption processes also plasma induced catalytical reactions on their surface. Consequently, plasma-surface interactions can also alter the electrical discharge properties through the formation of non-equilibrium surface layers and local electric field at the solid surfaces. These processes were determined important particularly during generation of pulsed electrical discharge in water using ceramic-coated electrodes prepared by thermal plasma spraying technology. It has been found that characteristics of these discharges strongly depend on type of ceramic material and also chemical composition of the aqueous solution. In the present study, comparison is made for two types of ceramics-oxide (corundum) and silicates (almandine). The possible mechanisms of plasma-surface interactions will be discussed with regard to the polarity of applied power and chemical composition of the aqueous solution.