The Effects of Ni and NaNO₃ on the Corrosion Behaviors of Cast Iron in Concentration Caustic Soda Solutions

Abstract

The results obtained are as follows:
(1) In pure concentration caustic soda the corrosion weight loss of cast iron decreases by the addition of NaNO₃. On increasing its content, the corrosion weight loss decreases.
(2) The corrosion weight loss of cast iron containing 1%Ni is maximum as the passive film becomes unstable. When the Ni content increases more than 1%, the corrosion rate decreases gradually.
(3) Ni cast irons in concentration caustic soda solutions containing less than 0.1%NaNO₃ show a larger anodic dissolution than that of cast iron. An increase in NaNO₃ content has a favorable effect on the diminution of the active current density of Ni cast irons.
(4) Ni added to cast iron has the same excellent inhibition effect to the dissolution of FeO₂⁻ and FeO₄⁻ ions as Fe-Ni alloy.
(5) 3%Ni cast iron is a most suitable material in concentration caustic soda solution containing the oxidizing agent as NaNO₃.