ACTIVE, PASSIVE AND TRANSPASSIVE DISSOLUTION OF A NICKEL-BASE SUPER ALLOY IN CONCENTRATED ACID MIXTURE SOLUTION

The electrochemical and corrosion behaviour of a nickel base super all oy (C-263) has been investigated in tile deaerated binary and ternary solution mixture of concentrated phosphoric acid, acetic acid, sulphur ic acid, nitric acid or water using potentiostatic technique at 35 deg rees C. The possibilities of electropolishing of this ahoy in these so lution mixtures have been also explored. The alloy showed distinct act ive, passive and transpassive behaviour in the experimental solutions. The alloy remained active and turned passive in the negative potentia l region Transpassive dissolution of the alloy is observed and electro polishing is achieved in this region. The best electropolishing is obt ained in 50% H3PO4 + 40% CH3COOH + 10% H2SO4. Higher content of water in the electrolytic solution is not useful for electropolishing of the alloy. The experimental results also suggest that a current plateau i n the transpassive potential region is not a sufficient condition to a chieve electropolishing.