thermal diffusion

chemistry

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July 14, 2026

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Thermal diffusion is a phenomenon where a temperature gradient in a mixture of gases or liquids causes a separation of components, typically with heavier molecules concentrating in cooler areas. This effect, predicted theoretically before experimental verification, can be used to separate isotopes. While simple diffusion involves the net flow of matter from high to low concentration due to random molecular motion, thermal diffusion introduces a separation driven by temperature differences. The inverse effect, the diffusion thermoeffect, occurs when a concentration difference leads to a temperature difference.123

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gas
Diffusion and thermal diffusion
Both of these properties present difficulties for the simple mean free path version of kinetic theory. In the case of diffusion it must be argued that collisions of the molecules of species 1 with other species 1 molecules do not inhibit the interdiffusion…
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Both of these properties present difficulties for the simple mean free path version of kinetic theory. In the case of diffusion it must be argued that collisions of the molecules of species 1 with other species 1 molecules do not inhibit the interdiffusion…
Read More

gas
Thermal diffusion
If a temperature difference is applied to a uniform mixture of two gases, the mixture will partially separate into its components, with the heavier, larger molecules usually (but not invariably) concentrating at the lower temperature. This behaviour was predicted theoretically before it was…
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If a temperature difference is applied to a uniform mixture of two gases, the mixture will partially separate into its components, with the heavier, larger molecules usually (but not invariably) concentrating at the lower temperature. This behaviour was predicted theoretically before it was…
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Sydney Chapman
…thereby predicting the phenomenon of thermal diffusion and later confirming it experimentally (1912–17). His interest in geophysics was aroused while he served as chief assistant (1910–14, 1916–19) to Sir Frank W. Dyson, the Astronomer Royal at Greenwich, where he helped design a new magnetic observatory. This involvement led him to…
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…thereby predicting the phenomenon of thermal diffusion and later confirming it experimentally (1912–17). His interest in geophysics was aroused while he served as chief assistant (1910–14, 1916–19) to Sir Frank W. Dyson, the Astronomer Royal at Greenwich, where he helped design a new magnetic observatory. This involvement led him to…
Read More