溶融硫酸塩中における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 chloride containing sulfate and molten sulfate at 973 K by using potentiodynamic polarization and polarization resistance methods. It was concluded that metallic corrosion in these melts was well explained by the mixed potential theory. The oxidant for metallic corrosion in these melts was found to be SO₃ and SO₂ generated by the dissociation of sulfate ion. In contract to the corrosion in molten chloride or carbonate, the corrosion in sulfate was accelerated not by oxygen but by water. The acceleration of corrosion by water is attributable to SO₃ and SO₂ generated by the reaction of water with sulfate.
With increasing concentration of sulfate in molten chloride, the anodic dissolution current decreased, but the cathodic reduction current increased. The complicated corrosion behavior of metals in molten chloride containing sulfate is attributable to these opposite effects of sulfate on anodic and cathodic reactions, respectively.
The instantaneous rate of corrosion of Ni, Fe and the their alloys was well estimated by the electrochemical polarization resistance method. The corrosion resistance of alloys increased greatly, when the alloy contains chromium more than 20%. Alloying with molybdenum sometimes deteriorated the corrosion resistance. Electrochemical techniques are a very useful method for obtaining mechanistic data as well as for monitoring the rate of hot corrosion.