Hot Corrosion of Nimonic 105 in Sodium Sulfate-Sodium Chloride Melts⁽¹⁾

The corrosion behavior of Nimonic 105 in molten Na₂SO₄, NaCl, and mixtures of these two salts, at 900 C, in laboratory air and under O₂ + SO₂/SO₃ atmospheres has been evaluated by potentiodynamic, potential decay, and free corrosion potential measurements. In addition, the corrosion products were examined using several electron-optical techniques, and by other analytical methods. Pure Na₂SO₄ in air did not seem to be very corrosive towards Nimonic 105. Addition of NaCl to the molten Na₂SO₄ resulted in increased dissolution of Nimonic 105, which was in general nonuniform, alloy constituents nickel and cobalt dissolving more than others. Evidence of internal attack and enhancement of dissolution of the Ni alloy by SO₃ was significant only when the corrosion conditions were prolonged. In pure NaCl, catastrophic corrosion occurs, which has been attributed to the depletion, dissolution, and vaporization of some alloy species.