日本金属学会誌

J. Japan Inst. Metals, Vol. 59, No. 9 (1995),
pp. 960-966

Corrosion Behavior of Chromium in Molten NaNO3

Motoi Hara, Toshiyuki Nagahara,Yoshiyuki Sato and Tokiko Nakagawa

Department of Materials Engineering and Applied Chemistry, Mining College, Akita University, Akita

Abstract:

The corrosion behavior of pure chromium in molten NaNO3 has been examined by the measurement of corrosion loss and the electrochemical measurement. Particular attention was given to the influence of melt temperature. Corrosion losses of pure chromium in the temperature range lower than 723 K were small, whereas those in the temperature range higher than 823 K were extremely large. It was found that a surface oxide consisting of Cr2O3 was formed on the chromium after the corrosion test in the low temperature range. In the high temperature range, on the contrary, the formation of the surface oxide was not found, and the specimen surface showed a feature of vigorous dissolution. Such a temperature dependence of the corrosion behavior corresponded to that of the electrochemical behavior. That is to say, the anodic polarization curves measured at the low temperatures showed the spontaneous passivation behavior, while those at the high temperatures showed a large rise in anodic current density from the low corrosion potential. As the result of the corrosion test of oxides in molten NaNO3, it was found that Cr2O3 dissolved vigorously in the high temperature range. Consequently, it was thought that the high corrosion rate of chromium in molten NaNO3 at high temperature was attributed to a dissolution of the surface oxide consisting of Cr2O3 and a consequent electrochemical corrosion reaction of chromium.


(Received May 9, 1995)

Keywords:

corrosion, chromium, molten salt, sodium nitrate, electrochemical study, chromium oxide


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