The possibility of using a high voltage atmospheric pressure discharge for chemo" thermal processing of surfaces is demonstrated by experimental study.

At the present time the process of interaction of a nonequilibrium plasma with a material surface for the purpose of changing physicochemical properties is being used ever more widely. Among the large number of discharge types used for creation of the nonequilibrium pla~:ma, special attention has been given to uhf, hf, and glow discharges [1-6], a characteristic feature of which is their use of reduced pressures. Instruments based on use of other discharge forms, for example, the high voltage atmospheric pressure discharge, have been studied little. Theoretical studies of plasmochemical processes [i] have shown that these occur at greatest efficiency under nonequilibrium conditions with an electron temperature of TE = 1-2 eV, which corresponds to values of the gas discharge parameter E/N ~ 2"i0 -Is V'cm =, characterizing the ratio hf the electric field intensity E to the gas density N in the discharge zone. in this case the energy contribution to the system Q < 1.5 eV/moi (Q = Di/G). The processes of CO 2 dissociation and nitrogen oxidation in an atmospheric pressure high voltage discharge were studied in [7, 8]. The goal of the present study is to investigate the atmospheric pressure high voltage discharge and its use for chemothermal processing. A diagram of the experimental equipment used for realizing the atmospheric pressure high voltage discharge is shown in Fig. i. Initiation of the high voltage discharge in chamber 4 occurs by a method similar to that of [9], in which a dependent atmospheric pressure discharge is maintained by gas injection from the pre-ionizer. Under the conditions o:f our experiments after discharge ignition in chamber 4 the pre-ionizer i was shut off after 5-10 sec. The length of the discharge zone I in the chamber between electrodes 3 and 5 was varied by moving electrode 5. In our study of the atmospheric pressure high voltage discharge the geometric parameters of the discharge zone were varied over the ranges: d = 1.0-9.0 mm, interelectrode distance i = 15-100 mm. The discharge burn voltage compris~d U = 2-15 kV, with a current I = 30-70 mA, and gas flow rate of 100-600 liter/hr. By w~rying the gas discharge parameters, discharge zone length, and gas flow rate during the experiments the temperature of the gas flow at the exit of the discharge zone was changed ov~r the limits t = 350-1450~ Temperature was measured by a platinuar-platin um/rhodium tl~ermocouple. The properties of the low temperature plasma maintained by the external electric lield define the current-voltage characteristic (CVC) of the discharge. Typical CVC's of th~ atmospheric pressure high voltage discharge are shown in Fig. 2. It is evident from tke figure that with increase in gas flow rate at one and the same load current the burn vcltage increases. With increase in current for constant flow rate the gas temperature increases, its resistance decreases, and the voltage falls. For identical load currents, gas flow rates, and one and the same reactor geometrical characteristics the lowest discharge voltages occur for nitrogen, and the highest for carbon dioxide. The curves are all decreasing, i.e., the discharge studied was independent.