GROWTH OF PLASMA PYROLYTIC CARBON

At arc discharge in a methane ambient, the heat-up of the anodic and c athodic patches can under certain conditions be high enough to initiat e ps pyrolysis. Then carbon deposits grow onto the electrodes within t he patches. The anodic deposits have a column shape, while the cathodi c deposits are radical growths of a hemispherical nature. Because the temperature is relatively low for arc discharge within the patches, th e arc ion supply and the electric current limitation by means of the p ower supply are reasons why we have termed the process abnormal arc di scharge. The growth of carbon deposits within the arc patches is obser ved for the first time and includes three stages, nucleation, growth a long the shortest path between the anode and cathode and growth in a d irection subtending an angle to the shortest path between the anode an d cathode. An analysis of the thermal balance at the anodic and cathod ic patches has been conducted, while the parameters of the processes i nfluencing this phenomenon have also been discussed. The growth proces s observed is presented by a series of consecutive photos. At a work g as pressure of P = 30000Pa, an H-2/CH4 ratio of 90/10 and a discharge power of 36 W, the growth rate is 15 mm/h. In accordance with the clas sification for carbon obtained at methane pyrolysis, the growths are c onsidered as ''compact silver grey carbon.''