Separation of Isotopes in the Thermal Diffusion Column

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Abstract
Gas liquid and solid mixtures undergo a slight demixing in the presence of a temperature difference. This phenomenon, known as thermal diffusion, is illustrated in Figure 1 for the isotopes of neon in the gas phase and for isotopically substituted carbon disulfide in the liquid phase. The separation effect, which is quite small even for relatively large temperature differences, was of no practical significance prior to the invention by Clusius and Dickel of the thermogravitational thermal diffusion column in 19381. In the thermal diffusion column (Figure 2) the fluid is confined between closely spaced vertical walls maintained at different temperatures. A convection current is set up with the fluid rising along the hot wall and descending along the cold wall. Thermal diffusion takes place In the horizontal direction. The combined effects of vertical countercurrent thermogravitational circulation and horizontal thermal diffusion lead to large separations in the vertical direction. The equivalent of several hundred separation stages can be obtained in apparatus no more than a few meters in length.