Thermal Diffusion Factors for the Noble Gases

Abstract

With an all-metal "Trennschaukel" of the type recently developed by Clusius and Huber, consisting of 22 tubes interconnected by single capillaries, and with the gas oscillating with a period of 15 sec, we have measured the thermal diffusion factor $\ensuremath{\alpha}$ for all of the noble gases as a function of temperature in the range 230\ifmmode^\circ\else\textdegree\fi{}K-600\ifmmode^\circ\else\textdegree\fi{}K. The reduced thermal diffusion factors ${\ensuremath{\alpha}}_{0}$ for krypton and xenon are positive even at the lowest temperature and increase so markedly with temperature as to indicate the advisability of operating isotopeseparating columns with these gases with the cold wall at a somewhat elevated temperature. For neon the $\ensuremath{\alpha}$ vs $T$ curve has but a slight positive slope, while for helium $\ensuremath{\alpha}$ actually decreases as $T$ increases in this range. The values of ${R}_{T}$ (=ratio of observed $\ensuremath{\alpha}$ to its theoretical first-approximation value based on rigid elastic sphere molecules) agree quite well with those estimated from viscosity data except for helium. The intermolecular potential is best represented by a modified Buckingham (exp-six) potential with appropriately chosen parameters.