Study of the variables affecting the corrosion of beryllium in carbon dioxide

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Australian Atomic Energy Commission.
Beryllium is a favoured canning and/or moderating material in the proposed Australian High Temperature Gas Cooled Reactor. With carbon dioxide as the most likely coolant a detailed knowledge of the corrosion of beryllium in this gas is required. Two separate investigations have proceeded simultaneously. First the effect of the following variables was studied; surface preparation of the specimen, temperature (100—725ºC), pressure (0—280 p.s.i.g.), velocity, and impurity content of the gas. The influence of irradiation has not yet been studied. Autoclaves, thermobalances, and dynamic loops were used. The results were statistically analysed and kinetic data obtained. In all cases specimens with etched surfaces yielded approximately 25 — 30 per cent, greater weight gains than specimens with ground or polished surfaces. On extruded material no "breakaway" oxidation was encountered below 650ºC in commercially dry gas (< 20 p.p.m. moisture). The rate of attack was to some extent affected by the pressure of the gas. Breakaway was only observed in one series of specimens at 650ºC. In this particular case the gas pressure was 280 p.s.i.g. However, it seems that surface temperatures of beryllium cans made from extruded material should be maintained below 650ºC in a reactor system using the commercially pure carbon dioxide as coolant. In the second approach a more basic study of the chemistry of the reaction was made as well as a detailed investigation into the variation caused by differences in the composition and fabrication of the metal. Spiral spring balances at atmospheric pressure were used. Extruded material made from beryllium powder oxidized in dry oxygen for a short period of time had greatly enhanced oxidation resistance when exposed to carbon dioxide. Some of the material exposed to wet carbon dioxide at 700ºC and atmospheric pressure did not exhibit "breakaway" oxidation. The weight gains after 1,000 hours exposure under these conditions were never greater than 0.5 mg/cmZ, Some comparisons were made between the reaction rates of beryllium with oxygen and carbon dioxide. In certain circumstances dry oxygen gave breakaway oxidation whereas carbon dioxide did not.
Beryllium oxides, Carbon dioxide, Corrosion, HTGR type reactors
Draycott, A., Nicholson, F. D., Price, G. H., & Stuart, W. L. (1961). study of the variables affecting the corrosion of beryllium in carbon dioxide. (AAEC/E83). Lucas Heights, NSW: Australian Atomic Energy Commission.