Low Temperature Transformation of the Surface of Copper Oxide Filled Ptfe Via Treatment in a Hydrogen Plasma
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LOW TEMPERATURE TRANSFORMATION OF THE SURFACE OF COPPER OXIDE FILLED PTFE VIA TREATMENT IN A HYDROGEN PLASMA DOV B. GOLDMAN Olin Corporation,
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ABSTRACT The surface conductivity of PTFE-copper oxide filled composites containing between 10 and 25% of the oxides increases significantly after treatment in a low pressure hydrogen plasma at temperatures below 100 0 C. The plasma-reduction of copper oxides (CuO and CuO/Cu 2 O mixture) was investigated and compared with thermal reduction at different hydrogen partial pressures. INTRODUCTION Preparation of conductive surfaces of polymers or polymer matrix composites can be carried out via reduction of a metal oxide mixed with a polymer matrix. Reduction of the oxide can be performed in a liquid chemical solution [I] or using a reducing gas, e.g. hydrogen. The gas-oxide reaction normally occurs at elevated temperatures. It is desirable to conduct the reaction at the lowest possible temperatures. Plasma treatment the offers such an opportunity [2-41. This work demonstrates feasibility of a low temperature transformation (T ! 100 0 C) of copper oxide-filled PTFE surfaces from an electrically insulating to a conducting state by using an RF hydrogen plasma. EXPERIMENTAL Preparation of the composites consisted of mixing PTFE (Teflon® 8, E.I. du Pont de Nemours & Company) powder with copper oxide (Cu2 O, J.T. Baker, technical grade) , followed by compaction and sintering into 50mm diameter and 4mm thick discs. The samples contained 10, 15, 20, and 25% by volume of the oxide. The sintering was conducted at 370 °C in air. Samples of Cu 2 0 or CuO ("Baker Analyzed" reagent) about 0.5mm thick layer on a PTFE substrate were prepared to study reduction of the oxides in plasma. The oxide powder was poured over the PTFE After compaction the two-layer powder in the compacting mold. samples were sintered under the same conditions as the composites. The samples had the same dimensions as the samples of the composites. High purity grade hydrogen, and prepurified grade nitrogen (both from Matheson) were used in the experiments. The temperature-controlled reduction of the oxide powders was conducted in a flow-through apparatus as described in [5] and a Perkin-Elmer model TSG-2 TG analyzer. XRD analysis with CuKa radiation identified the phases in the reactions. The plasma treatment was conducted in a plasma desmear apparatus Model 400 manufactured by Advanced Plasma Systems [6]. Samples were suspended between the electrodes as shown in Fig. 1. A Plasmaloc 2 RF power supply (E.N.I.) operated at 42kHz was used. The power was varied between 1200 and 1400 W. The sample temperature was measured using an iron-constantan thermocouple attached to the sample surface. Sample heating was carried out Mat. Res. Soc. Symp. Proc. Vol. 131. s1989 Materials Research Society
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Fig 1. Schematic diagram of the plasma chamber. 1 - sample; 2 .2 rthemocouple; 3 - coupled -
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