High-temperature mass spectrometry—I. Free vaporization studies of graphites

Abstract

Some of the differences in the published data on the free vaporization of conventional (ATJ, ZTA, UT-6) and pyrolytic graphites have been resolved. Relative ion intensities, apparent rates of vaporization, and activation energies of vaporization have been measured for carbon species C 1 through C 5, for conventional graphites in the temperature range 2800°–3000°K, and for pyrolytic graphites in the temperature range 2600°–3260°K. Differences in the free evaporation behavior of the two types of graphites are discussed. For the first time, evidences for carbon evaporation from the new ‘white’ allotropic form of carbon are presented; some of the anomalous vaporization behavior observed with both types of graphites is attributed to the vaporization of carbon from this new allotropie form of carbon. Plausible explanations are presented to account for the differences in activation energies of vaporization for C 4 and C 5 molecules for pyrolytic and conventional graphites. For conventional graphites at temperatures above about 2950° ± 50° K, the rates of vaporization of carbon species were found to increase abruptly, and the total mass-loss appears to occur by vaporization of carbon and ejection of crystallites.