Corrosion in Liquid Metals

Practical problems are complicated by the fact that several of these forms can occur simultaneously. In fact, opposing actions may be required for individual effects that act in combination. The following categories can be used to classify relevant corrosion phenomena [16]  

Corrosion reactions can occur by a simple dissolution mechanism, whereby the containment material dissolves in the melt without any impurity effects. Material dissolved in a hot zone may be redeposited in a colder area, possibly compounding the corrosion problem by additional plugging and blockages where deposition has taken place. Dissolution damage may be of a localized nature, for example, by selective dealloying. The second corrosion mechanism is one of reactions involving interstitial (or impurity) elements such as carbon or oxygen in the melt or containment material. Two further subforms are corrosion product formation and elemental transfer. In the former the liquid metal is directly involved in corrosion product formation. In the latter the liquid metal does not react directly with the containment alloy rather, interstitial elements are transferred to, from, or across the liquid. 

Alloying refers to the formation of reaction products on the containment material, when atoms other than impurities or interstitials of the liquid metal and containment material react. This effect can sometimes be used to produce a corrosion-resistant layer, separating the liquid metal from the containment (for example, aluminum added to molten lithium contained by steel). Lastly, liquid metal can attack ceramics by reduction reactions. Removal of the nonmetallic element from such solids by the melt will clearly destroy their structural integrity. Molten lithium poses a high risk for reducing ceramic materials (oxides). 

Elliott P. Practical guide to high-temperature alloys. Materials Performance 1989 28 57-.  

Compilation and use of corrosion data for alloys in various high-temperature gases. Corrosion 99 Paper 99073. Houston, Tex., NACE International, 1999. 

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Tortorelli, P. F., Fundamentals of High-Temperature Corrosion in Liquid Metals," Metals Handbook, Ninth Edition, Volume 13, ASM International, Metals Park, OH, 1987, pp. 56-60. 

Corrosion testing in liquid metals and fused salts 19 84... 

Corrosion Testing in Liquid Metals and Fused Salts ... 

Corrosion by liquid metals is usually controlled by diffusion processes in the solid and liquid phases and, unlike aqueous corrosion, does not generally involve galvanic effects, and, even where electrochemical phenomena are known to occur, it has not, in general, been demonstrated that they have been responsible for a significant portion of the corrosion observed . In... 

Static test results may be evaluated by measurement of change of mass or section thickness, but metallographic and X-ray examination to determine the nature and extent of attack are of greater value because difficulty can be encountered in removing adherent layers of solidified corrodent from the surface of the specimen on completion of the exposure, particularly where irregular attack has occurred. Changes in the corrodent, ascertained by chemical analysis, are often of considerable value also. In view of the low solubility of many construction materials in liquid metals and salts, changes in mass or section thickness should be evaluated cautiously. A limited volume of liquid metal could become saturated early in the test and the reaction would thus be stifled when only a small corrosion loss... 

Properties. Most of the alloys developed to date were intended for service as fuel cladding and other structural components in liquid-metal-cooled fast-breeder reactors. Alloy selection was based primarily on the following criteria corrosion resistance in liquid metals, including lithium, sodium, and NaK, and a mixture of sodium and potassium strength ductility, including fabricabiUty and neutron considerations, including low absorption of fast neutrons as well as irradiation embrittlement and dimensional-variation effects. Alloys of greatest interest include V 80, Cr 15, Ti 5... 

An important aspect of corrosion in liquids is the nature of the corrosion product. If this takes the form of a soluble salt, then the metal will remain in contact with the liquid, and rapid corrosion can be expected (this is known as active corrosion). If the corrosion product is solid (often an oxide or hydroxide), then it will tend to form a barrier between the metal and... 

The nature of the lead-bismuth heat carrier substantially differs from that of alkali heat carriers. It is a powerful oxidant of structural materials at relatively low O2 concentration (< Kh mass %) in liquid metal [61] and is a corrosive dissolvent under lower concentrations. 

Migge, H., in Proc. 2nd. Intern. Conf. on Liquid Metal Technology in Energy Production (CONF-8M401-P2), Richland, Wash., USA, April 20-24, 1980, vol. 2, 18-9 Jansson, S. A., in Corrosion by Liquid Metals, Plenum Press, New York 1970, 523 Myles, K. M., Cafasso, F. A. J. Nucl. Mat. 67, 249 (1977)... 

IIZAWA, K., et al.. Transport of Radioactive Corrosion Product in Primary Systems of a Sodium Cooled Fast Reactor, Proc. Material Behavior and Physical Chemistry in Liquid Metal Systems 2, Plenum Press, ISBN 0-306-45069-0 (1995) pp. 9-26. 

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