Title: The Construction and Operation of a Thermal Diffusion Column, Author: David L. Prosser, Location: Thode / The first observation of the phenomenon of thermal diffusion was made by Soret in 1878. He found that a concentration gradate was set up in a liquid solution when a temperature gradient existed in the solution. Hence the lighter molecules or ions in the solution moved toward the hotter part of the solution faster than the heavier particles, which distributed the homogeneity of the solution. Two gases or gaseous isotopes were separated in the same way by a temperature gradient. A rigorous mathematical and theoretical treatment was given to thermal diffusion by Enskog in 1911, and independently by Chapman in England in 1917. In 1918 first experimental data was obtained by Chapman and Dootson. Mullikan discussed the use of the thermal diffusion process for the separation of gaseous isotopes, but concluded that other methods at that time superior. However, he did not consider the new twist given to the application of thermal diffusion by Clusius and Dickle which consisted of thermal diffusion in conjunction with convection currents which increased the effect of thermal diffusion enormously. In order to produce this effect, they used a specially designed column consisting of two concentric tubes mounted vertically, the inner one of which was a hot wall and the outer one a cold wall. A temperature gradient was set up radially from the cold wall to the hot wall. Then the convection currents carried the light molecules, concentrating at the hot wall, up the tube and brought the heavier molecules, at the cold wall, down the cold wall. This effect is sometimes called thermal syphoning. The separated stab;e isotopes of hydrogen, carbon, nitrogen, oxygen and sulphur, are of considerable importance in isotope exchange and trace work. These isotopes can be separated with relative ease by chemical exchange methods which are particularly suited for the production of relatively large amounts of material at medium concentrations. The thermal diffusion the mod, on the other hand, the method first used by Clusius and Dickel, is one of the best methods for producing small quantities of highly enriched isotopes. It would be most economical, therefore, to concentrate those isotopes by chemical exchange in a first stage in order to produce the large quantities of enriched material at medium concentrations, which will be required for he most chemical and medical tracer work, and to enrich a much smaller amount of material still further by a second stage thermal diffusion unit for the few experiments where very high concentrations are desirable or necessary. High concentrations of the isotopes will be required in experiments where high dilution of the "tagged" material is encountered and for experiments designed to study the physical and chemical properties of the separated isotopes. Thermal diffusion columns have been set up at McMaster University to make possible the further enrichment of the isotope which have already been concentrated by chemical exchange methods. Several years ago the heavy isotopes of oxygen and sulphur were separated in this laboratory in distillation and chemical exchange methods, respectively. The latter involved the exchange between sulphur dioxide and bisulphite ion in solutions. Our thermal diffusion columns will be used first to further enrich O^18 samples now on hand. Of the elements mentioned above, deuterium has been an article of commerce for some time, and 775 percent N^15 produced by chemical methods is now on the market. In the latter car, it might be of interest to produce a small quantity of high concentrations. Further, the Houdry Catalytic Corporation has plans to produce O^13 at two concentrations, twelve percent and sixty percent, in a two stage system, the latter stage being a thermal diffusion unit. Here again there may be experiments where high concentrations are desirable. At the present time, however, the isotopes of oxygen and sulphur are not available commercially, but can be procured from several universities (McMaster) only at low concentrations. Four thermal diffusion units have been completed. One of there units has already been tested on the separation of the nitrogen gas as a working substance. The results are not most encouraging and incite an enrichments factor of seven for the nitrogen isotopes using four units or 36 feet of column. Details of the thermal diffusion column and of the test runs made with one unit are discussed below. / Thesis / Master of Science (MS)
| Identifer | oai:union.ndltd.org:mcmaster.ca/oai:macsphere.mcmaster.ca:11375/20059 |
| Date | 05 1900 |
| Creators | Prosser, David L. |
| Contributors | Chemistry |
| Source Sets | McMaster University |
| Language | English |
| Detected Language | English |
| Type | Thesis |
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