The Consumption of the Positive Arc Carbon

The consumption of the positive electrode of an arc between solid carbons in air results partly from evaporation and partly from oxidation. The oxidation is operative chiefly on the sides of the carbon, tapering the end of the electrode-and thus producing a tip with a diameter 1/2 to 5/8 that of the original carbon. The consumption of the flat tip, or crater, however, is due almost entirely to evaporation. The evaporation rate is controlled by the pressure of carbon vapor at the crater surface and the mechanism of diffusion away from it. This diffusion was computed on the assumption that it is similar to that occurring in the evaporation from liquid drops of the same diameter as that of the carbon crater, and it was shown that the linear electrode consumption should be inversely proportional to the crater diameter. This was borne out approximately by measurements of consumption rates made near the overload current. The absolute values of the consumption rates are consistent with the hypothesis that the surface temperature of the positive crater is at or near the sublimation temperature of carbon.

Print ISSN

0097-5834

Published

1942-03

Content type

Original Research

DOI

10.5594/J09916