CORROSION AND CREEP BEHAVIOR OF TANTALUM IN FLOWING SODIUM

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Abstract
The corrosion behavior of commercial tantalum in high-purity flowing sodium from 700 to 1200 deg F and the effect of sodium exposure on the creep strength of tantalum at 1200 deg F were investigated. The tests were conducted in forced-convection flow loops constructed of Type 315 stainless steel. With continuously gettered sodium systems (probably containing less than 10 ppm oxygen) operating for periods up to 50 days, weight losses sustained by 1200 deg F specimens corresponded to only about 0.1 mil of metal removed per year. Maximum weight losses, encountered with a continuously coldtrapped (about 40 ppm oxygen) sodium system, were equivalent to about 3 mils per year for 1200 deg F specimens. For the most part, metallographic examinations revealed no deleterious corrosion effects; however, one particular group of arc-cast tubing specimens suffered severe intergranular attack in sodium with about 80 ppm oxygen. In addition to the corrosion findings, the corrosion tests yielded information about the partition of interstitials, particularly oxygen, in the sodium -- tantalum system. Oxygen, for example, showed a tendency for migration from tantalum to high-purity sodium considerably stronger than wonld be predicted from limited thermodynamic data available. In the creep experiments, the oxygen content of themore » sodium was maintained at the <10 ppm level by continuous gettering. In general, the results demonstrated that sodium exposure at 1200 deg F had very little, if any, effect on tantalum creep strength. Baseline data necessary to establish this were obtained in supplementary helium-atmosphere creep tests. (auth) « less

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