溶融炭酸塩中におけるNiおよびFeの腐食の電気化学的研究

抄録

Electrochemical studies of corrosion of Ni, Fe and their alloys have been made in molten carbonate at 973 K by using potentiodynamic polarization and polarization resistance methods. It was concluded that metallic corrosion in molten carbonate was well explained by the mixed potential theory. Partial cathodic reaction for metallic corrosion in molten carbonate was found to be the reduction of the peroxide ion (O₂²⁻) formed by the reaction of carbonate ion with dissolved oxygen. The anodic dissolution current of Ni in molten carbonate increased with increasing pressure of CO₂ gas, namely, with decreasing oxide ion activity. The rate of metallic corrosion in molten carbonate was controlled by cathodic reaction rates at high P_CO2, whereas, at low P_CO2 it was controlled by anodic reaction rates.
The instantaneous rate of corrosion of Ni, Fe and their alloys in molten carbonate was estimated by the electrochemical polarization resistance method. The results of corrosion monitoring by this method indicated that Fe-base alloys with high Cr content (more than 25%) exhibited a little better corrosion resistance than Fe, but high Mo content alloys exhibited very poor corrosion resistance in molten carbonate. The results well correspond with those obtained from anodic polarization curves.