Magnesium sulphate solutions, attack

Nickel-iron alloys are more resistant than iron to attack by solutions of various salts. In alternate immersion tests in 5% sodium chloride solution Fink and De Croly determined values of 2-8, 0-25 and 0-5 g m d for alloys containing 37, 80 and 100% nickel compared with 46 g m d for iron. Corrosion rates of about 0.4 g m d are reported by Hatfield for Fe-30Ni alloy exposed to solutions containing respectively 5 Vo magnesium sulphate, 10 Vo magnesium chloride and 10% sodium sulphate the same alloy corroded at a rate of about 1.2 g m d in 5% ammonium chloride. 

Whether anhydrous or in solution (beryllium or magnesium sulphate), these sulphates have no action on aluminium. Calcium and barium sulphate are insoluble. It is well known that plaster, which mainly contains calcinated calcium sulphate (gypsum) does not attack aluminium (see Section G.4.2). 

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