CORROSION BY URANIUM HEXAFLUORIDE METHODS FOR STUDYING CORROSION (in French)
The chemical properties of uranium hexafluoride have prompted the development of new methods for studying the corrosion of metals by this gas. The corrosion process is characterized by the reactions between an anhydrous gaseous phase and a solid phase, which is comparable to the dry oxidation of metals. After a critical review of the principal methods used in this field, discontinuous gravimetry is chosen in which samples are weighed before and after attack by hexafluoride. Polished samples, rwn simultaneously, are examined micrographically. Specimen dimensions were chosen to achieve optimum conditions for microbalance weighing. Methods of preparation and surface condition of the specimens were carefully defined. Corrosion was effected by H-shaped tubes; the tubes, including joints, unions, seats, and butterfly valves, were made entirely of metal. The apparatus was sufficiently vacuumtight to permit routire degassing under a vacuum of 10/sup -6/ mm Hg at temperatures up to 400 deg C. After degassing, hexafluoride is introduced into ths apparatus and triple distilled; the tube is kept warm. Incorporated at ths end of one of the legs of each tube is a condensing attachment which, with the help of local cooling, permits a reservoir of solid hexafluoride to be maintained, with consequent constancy of gas pressure. When a tube is removed for examination, it is again pumped out to remove residual hexafluoride. It is opened in an inert atmosphere in a glove box and the specimens manipulated out of contact with air to avoid alteration of the corrosion products. Microweighing and micrographic examination are carried out. Progressive elimination of the deposits revealed etch pits, which often affected the shape of grain-boundary grooves or micropits. Their growth in depth was found to follow parabolic timelaws similar to those characteristic of dry oxidation curves. The precautions taken in preparing specimens and distilling the hexafluoride resulted in excellent reproducibility of the results. The sensitivity of the microbalance was sufficient to follow the formation of a fluoride monolayer. The ensemble of corrosion apparatus and methods of measurement was selectsd as being one of the most easily adaptable to the technology of uranium hexafluoride in that it gave great sensitivity and allowed serial experimentation on a vast scale. The ensemble is readily adapted to the study of numerous variables, such as time, temperature, and pressure. (auth)
- Research Organization:
- Center d'Etudes Nucleaires, Saclay, France
- NSA Number:
- NSA-15-013293
- OSTI ID:
- 4072303
- Journal Information:
- J. Nuclear Materials, Vol. Vol: 3; Other Information: Orig. Receipt Date: 31-DEC-61
- Country of Publication:
- Country unknown/Code not available
- Language:
- French
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