Molten-salt corrosion

This chapter is closely related to the chapter titled Electrochemical Techniques in Corrosion Engineering and Research, Vol 4, Chapter 7 . Hence, no detailed description of the techniques will be given here however, examples are provided for use of electrochemical techniques for molten salt corrosion studies. 

Impedance spectroscopic measurements are randomly used in molten salt corrosion studies. In general, most of the impedance spectra emphasize diffusion-controlled kinetics for the active corrosion of metals in molten salts. This behavior is expected, as the activation energy for charge-transfer reactions is easily reached at higher temperatures. 

Vanadium in a fuel forms various metal compounds with low melting points, and causes molten-salt corrosion of steel called vanadium attack. Another example of high temperature corrosion is sulfidation. Carbon monoxide, carbon dioxide, and hydrocarbons form metal carbides at high temperatures and this is called carburization. Nitriding involves chemical reaction of nitrogen with metal. 

However, since gases generally have limited solubility in molten salts, corrosion will be restricted to a narrow region in the three-phase boundary. 

G. Gao, F.H. Stott, J.L. Dawson, and D.M. FarreU, Electrochemical monitoring of high-temperature molten-salt corrosion. Oxidation o/MefaJs 33 79-94,1990. 

In discussing molten salt corrosion tests, the task is to develop guidelines that may be used to develop tests for various situations. Since no standardized tests for molten salt-induced corrosion are available, the tests to be described are presented by way of example. Tests for other situations could, in principle, be devised by following procedures used in these examples. It is also important to emphasize that this chapter is not concerned with the various mechanisms for molten salt corrosion, but only the conditions that cause attack. 

Electrochemical cells can also be used to attempt to obtain data on the mechanisms of the salt-induced corrosion processes. Cyclic voltammetry has been used [78-22] to obtain information on the oxidation and reduction reactions that may occur during molten salt corrosion. Chronopotentio-metric investigations with platinum as the working electrode in cells can also be used to determine and control the compositions of molten salts, as well as to measure the solubilities of various oxidation products in melts [25-28,30]. 

R. E. Tressler, T. M. Yonushonis, and M. D. Meiser, Crack Propagation in Molten Salt Corrosion of Si3N4, private communication, 1976. 

Molten-Salt Corrosion on stainless steels due to molten fluorides (LiF, BeF2, etc.). 

Corrosion damage from molten salts can occur in a wide variety of materials and by different mechanisms. It has been pointed out that although many studies have been performed, quantitative data for materials selection and performance prediction are rarely available [15]. Molten salt corrosion is usually applicable to materials retaining the molten salt, as used in heat treating, solar and nuclear energy systems, batteries, fuel cells, and extractive metallurgical processes. Some factors that can make molten salts extremely corrosive include the following ... 

ORNL LORD Hastelloy-N Molten-Salt Corrosion Test Loop Will Be Operational March 2003... 

Liu, K., Xu, L., Liu, Z., 2015. Impact of temperature on the molten salt corrosion of Hastelloy-N alloys. Nuclear Techniques 38. 

MOLTEN-SALT CORROSION OF NICKEL-BASE ALLOYS... 

Only minor spalling of the scales was observed in powder form during the molten salt corrosion for most of the coated cases. The scales in general showed no tendency towards spalling or cracking and were found to be intact. 

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