Cathodic Corrosion of Chromium in Molten Na₂SO₄

Abstract

The corrosion behavior of chromium under catholic polarization in molten Na₂SO₄ at 1173K has been investigated. The loss of chromium under catholic polarization in the molten salt increased with an increase in the quantity of electricity for the cathodic reaction. In order to examine the mechanism of catholic corrosion of chromium in the molten salt, direct observation of the chromium electrode under catholic polarization and identification of corrosion products were conducted. A black turbidity near the chromium electrode was observed in the melt during catholic polarization, suggesting a generation of corrosion product from the electrode. It was found that the corrosion product consisted of Cr₂O₃. Investigation of the cathodic polarization reaction showed that a two-electron reduction reaction of SO₄^2- occurred under catholic polarization in molten Na₂SO₄. Consequently, it was proposed that catholic corrosion for chromium in molten Na₂SO₄ occurred by a chemical reaction of the chromium with SO₃^2- and O^2- which appeared as catholic products.