Question

Which of the following ions that accelerate the dissolution rate of metals or alloys in a crevice?

(a) H^+, OH^–

(b) H^+, Cl^–

(c) OH^–, Cl^–

(d) OH^–, Cl^– and H^–

The question was posed to me in semester exam.

My doubt stems from Eight Forms topic in section Eight Forms of Corrosion of Corrosion Engineering

Answer 1

The correct answer is (b) H^+, Cl^–

Explanation: H^+ and Cl^– ions accelerate the dissolution rate of metals and alloys in the crevice. These are produced by hydrolysis of metal chlorides. It accelerates corrosion because hydrogen ion decreases pH value (more acidic) and chloride ion attacks the metallic surface in the crevice.