Surface cleaning of metals in air with a one atmosphere uniform glow discharge plasma

Abstract

Summary form only given, as follows. We report the use of active species generated in a one atmosphere uniform glow discharge plasma reactor with a parallel-plate configuration to clean the surface of as-received metal samples from the machine shop floor. The unmagnetized air plasma in this reactor had the following characteristic operating and plasma parameters: RF frequency, 1-4 kHz; RMS electric field, 9 kV/cm; RMS voltage, 4 kV; plasma number density, 10/sup 10//cm/sup 3/; and plasma power density of tens of milliwatts/cm/sup 3/. The experimental arrangement used to expose our 7 by 10 cm metal samples. The lower parallel-plate electrode is a flat copper plate, covered by a pyrex sheet. The upper electrode is formed by the bare metal sample plate, with the side to be cleaned facing the plasma. To assure plasma uniformity between the electrodes, it was helpful to direct a flow of air on the edges of the plasma volume. The cleanliness of the metal samples was determined with the standard sessile water drop test. In their as-received condition, the metal samples yielded a contact angle of 90/spl deg/ or more, indicating a non-wettable surface, presumably because of (adherent layers of hydrocarbon machine oils. After from 3 to 10 minutes of plasma exposure, however, the water-drop test yielded a contact angle well below 10/spl deg/, a very wettable surface. The metal surfaces would remain wettable for hours, until the surfaces became re-contaminated by exposure to the atmosphere.