par Doehaerd, Th;Goldfinger, Paul 
;Waelbroeck, F.G.
Référence Bulletin des Sociétés chimiques belges, 62, 9-10, page (498-544)
Publication Publié, 1953
;Waelbroeck, F.G.Référence Bulletin des Sociétés chimiques belges, 62, 9-10, page (498-544)
Publication Publié, 1953
Article révisé par les pairs
| Résumé : | The rate of effusion of carbon vapor from a graphite Knudsen cell was studied between 2400 and 2760°K. The resulting molecular (atomic) beam, defined by a collimator, was collected on glass plates. The amount and distribution of the deposit was determined by measuring its optical density. Measurable deposits have been obtained in 53 out of 65 experiments. In 10 experiments for known and in two for unknown reasons no measurable deposit could be detected. The aperture/total area ratio (ω) of the cell was varied between 1/100 and 1/23400. The establishment of the equilibrium vapor pressure of carbon has been thus observed, yielding for the condensation (or evaporation) coefficient f of carbon on hot graphite surfaces log f = −3,0 ± 0,5 The equilibrium vapor pressure was practically obtained in 33 experiments with ω = 1/3750 and 1/23400; the heat of sublimation of carbon Lc, calculated from these is : Lc = 141,7 kcal. A detailed discussion of the fortuitous and systematic errors is given. It is believed that the fortuitous errors are smaller than ± 4 kcal. which is the maximum deviation from the mean in 42 experiments. On the other hand the systematic errors could be as great as ± 6 kcal. The excellent agreement of our result with the value Lc = 141,26 kcal, resulting from the analysis of the CO spectrum and a well known thermochemical cycle, indicates that the systematic errors have probably been overestimated. However the possibility of Lc=135,74 keal which is also in agreement with the data on the CO spectrum, cannot be excluded. Copyright © 1953 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim |
