Experimental study of the sublimation of graphite at high temperatures

Abstract

The equilibrium vaporization of pyrolytic graphite was studied using rf induction heating and a time-of-flight mass spectrometer. rf induction heating was demonstrated for the first time as a compatible and practical heating technique for high temperature mass spectrometry. Relative ion intensities were measured for C1(g), C2(g), C3(g), and C4(g) in the temperature range 2320 K-3000 K and partial vapor pressures were obtained. The vapor pressures of C2 and C3 in the temperature range 2400 K-3000 K can be represented by logP(C2) (atm) = 9.971 − 44 230/T(K) and logP (C3) (atm) = 9.944 − 40 670/T(K). Heats of vaporization obtained by the second and third law methods are as follows: SpeciesSecond law ΔH°298(kcal/mole)Third law ΔH°298(kcal/mole)C1170.3 ± 1.1C2206.0 ± 1.3202.7 ± 0.6C3194.4 ± 1.2202.1 ± 1.5C4242.7Thermodynamic functions calculated by Strauss and Thiele were used forC3. JANAF thermodynamic data were used for all other species. The entropy change in the vaporization of C3 determined from this work is 45.55 eu at 2740 K.