Motoi Hara1 and Yutaka Shinata1
1Department of Metallic Engineering for Materials, Mining College, Akita University, Akita
The hot corrosion behavior of Ni-20%Cr-2%W alloy in molten Na2SO4-NaCl mixtures has been examined in comparison with that of Ni-20%Cr alloy by the measurement of corrosion loss, the observation of corrosion morphology and the electrochemical measurement. Particular attention was given to the influence of salt composition and melt temperature. Corrosion loss of Ni-20%Cr-2%W alloy markedly increased accompanying the formation of thick corrosion layer in molten Na2SO4-10% and -25%NaCl mixtures in the neighborhood of 1090 K. Such a hot corrosion was not observed for the alloys tested in the composition range higher than 75%NaCl or the temperature range higher than 1173 K. The anode and cathode reactions for Ni-20%Cr-2%W alloy in the vicinity of the corrosion potential became active with lowering of the corrosion potential in molten Na2SO4-25%NaCl at 1073 K, in which the corrosion loss of the alloy increased. This fact indicates that the hot corrosion of the alloy causted in the particular melt proceeded by an electrochemical process. In addition, the electrochemical studies suggested that the anode and cathode reactions for the hot corrosion of the alloy were preferential dissolution of chromium from the alloy and reduction of the dissolution product, respectively. Such an electrochemical corrosion occurred for the alloy in the melt seemed to be attributed to an inhibition of the formation of a protective surface oxide consisting of Cr2O3 by tungsten in the alloy.
hot corrosion, nickel-base alloy, tungsten, sodium sulfate, sodium chloride, molten salt, polarization curves
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