Corrosion performance of ferrous and refractory metals in molten salts under reducing conditions
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Corrosion performance of ferrous and refractory metals in molten salts under reducing conditions J. E. Indacochea, J. L. Smith, K. R. Litko, and E. J. Karell Argonne National Laboratory, Chemical Technology Division, Building 205, 9700 South Cass Avenue, Argonne, Illinois 60439-4837 (Received 14 May 1998; accepted 28 December 1998)
A lithium reduction technique to condition spent fuel for disposal has been developed at the Argonne National Laboratory. There is a need to ensure adequate vessel longevity through corrosion testing and, if necessary, materials development. Several ferrous alloys and tantalum specimens were submitted to a corrosion test at 725 ±C for thirty days in an argon atmosphere, using a lithium-chloride salt saturated with lithium metal and containing small amounts of lithium oxide and lithium nitride. The samples did not show dimensional or weight change, nor could corrosion attack be detected metallographically. The lithium-saturated salt system did not show any behavior similar to that of liquid lithium corrosion. From testing in other gas compositions, it appears that the presence of oxygen in the system is necessary to produce severe corrosion.
I. INTRODUCTION
The Chemical Technology Division of Argonne National Laboratory has developed a lithium reduction technique to condition spent oxide fuel for disposal. In this process the oxide is reduced to the metallic form by reaction with lithium dissolved in LiCl at 650 ±C. The Li2 O formed during the reduction process is soluble in the salt. The spent salt and lithium are recycled after the Li2 O is electrochemically reduced to lithium metal. Two environments for potential vessel corrosion exist in these processes. In the fuel reduction condition, the environment is predominantly lithium chloride with dissolved lithium metal and with no free oxygen. In the lithium electrowinning process, the environment is predominantly lithium chloride with a high oxygen activity. In each procedure there may be other factors, such as lithium nitride, that must be considered. In the electrowinning process, the oxygen from the Li2 O is liberated at an inert anode, and the lithium is collected on a porous metal cathode. The objective of this study was to find a material that can be used to improve the vessel longevity for this new technology. To date, there have been few corrosion studies that could be used for selection of corrosionresistant materials under these complex conditions. However, information on the corrosion behavior of metals for somewhat similar conditions, molten carbonate fuel cells, exists in the literature.1–3 State-of-the-art materials used for the separator plate are stainless steels and nickel-base alloys with a high-chromium concentration. The corrosion behavior of stainless steels and nickelbase alloys can often be improved by the addition of chromium, because it forms an oxidation resistant oxide layer on the surface of the base metal.1–3 1990
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