Atmospheric microwave discharges for plasma treatment of fibers

Summary form only given. Many contemporary plasma applications require the treatment of irregular shaped substrates such as filamentary or fiber-like objects. Additionally, for reasons of simplicity, efficiency and low process costs, it is desirable to develop plasma sources and associated processes that can continuously process a moving web or strand of materials at atmospheric pressure; i.e. without a high vacuum environment. Thus the article describes the development and testing of atmospheric plasma sources and associated processes that enable the treatment of individual fibers and/or bundles of fibers. Graphite fibers are chosen as the example substrate material. Specifically, a 2.45 GHz, atmospheric discharge plasma source is described. It is able to continuously treat single or multiple graphite fibers or even treat graphite fiber tows. Small cylindrical discharges are created in gases that flow through a small 1-3 mm diameter quartz tube placed axially inside a tunable, cylindrical microwave applicator. The fibers are subjected to plasma treatment as they are passed through the discharge. The reactor design process involved an initial ANSOFT HFSS numerical analysis of the material/discharge loaded reactor excited with a variety of different electromagnetic modes. Based on this analysis, two modes, the TE/sub 112/ and the TM/sub 102/ modes were experimentally evaluated with input power levels of 20-200 W, and with a variety of gases, such as mixtures of argon, nitrogen, methane, etc. The experiments have demonstrated a controllable, atmospheric plasma source capable of heating and treating fibers from 300-850/spl deg/C without the need of an associated vacuum system. Experimental operating parameters, such as substrate temperatures, plasma densities, discharge power densities, etc versus input power, gas flow rate, and gas mixture are presented.