Pyrolytic carbon films from Ethyl Chloride

Abstract

The formation of pyrolytic carbon films during the gas phase decomposition of ethyl chloride at 450 °C has been followed by measurement of the electrical conductance. On fresh glass surfaces there was observed an initial induction period of approximately 30 min after which the conductance rose steadily, the rate of change decreasing as ethylene accumulated in the system. The time of induction varied with surface treatment and has been attributed largely to the removal of some substance (e.g. water or oxygen) from the glass surface. Pressure measurements indicated no appreciable induction effect for the simultaneous decomposition of the ethyl chloride to ethylene and hydrogen chloride. The films of carbonized material were semiconductive and their electrical resistance was estimated to be very much greater than that of graphite. (One film had an estimated specific resistance of 12Ω cm at room temperature.) The electrical properties of the films were found to vary greatly with changes in the film thickness, the temperature, the applied voltage, and the pressure of the gases in contact with them. For these reasons the conductance measurements did not provide an accurate estimate of the amount of carbon deposited although they did provide information concerning the physical and chemical nature of the deposit. The behaviour of the films was consistent with the presence of a high concentration of " foreign " atoms, groups, and/or molecules at the intercrystal boundaries, as suggested by other workers. The efficiency of these Elms in suppressing heterogeneous reactions is discussed in terms of the formation of a continuous non-polar coating on the surface of the glass.