The application of DTA to hot corrosion studies of chromium and nickel powders and nimonic 80A

DTA has been successfully employed to study the hot corrosion behaviour of chromium and nickel powders and Nimonic 80A alloy samples in the presence of corrodants such as NaCl and Na₂SO₄. The DTA data indicate a large high-temperature exotherm due to oxidation in air; the onset of oxidation occurs at much lower temperatures when additional oxidants are added. The results also show that NaCl attacks chromium much more aggressively than does either Na₂SO₄ or the salt mixture. The reverse has been observed for nickel, i.e. enhanced corrosion in the presence of Na₂SO₄ and the mixtures. Both Cr and Ni are oxidized to their respective oxides, via chloride formation in the presence of NaCl, and via sulphide formation in the presence of Na₂SO₄. Sodium chromate formation was confirmed with chromium in addition to the above compounds in the presence of sodium salts. On the other hand, the DTA results on Nimonic 80A alloy samples indicate that the corrosion attack is negligible as long as the salt is in the solid form, but once the salt is molten it triggers catastrophic corrosion. The mechanism of hot corrosion is discussed.