Dissolution of copper and copper-nickel alloys in aerated dilute HCl solutions

Abstract

The dissolution of pure Cu, 90 10 and 70 30 CuNi alloys and of Monel 400 in strongly aerated 0.1 m HCl is studied by the weight loss technique at 25°C and 60°C. All four materials behave in a similar manner. The weight-loss/time curves are formed by an initial, low rate, induction period representing the dissolution of Cu in the monovalent state, CuCl 2 −. The nickel of the alloys dissolves simultaneously, but in quantities higher than present in the solid metal. Air oxidizes Cu + to Cu 2+. When enough of Cu 2+ accumulates in solution, the dissolution of Cu is auto-catalyzed through the reaction Cu+Cu 2+=2Cu +. This conclusion is supported by the results of experiments in which extra Cu 2+ ions are added to the solution. The rate of dissolution along the induction period increases and the period itself decreases and disappears as more Cu 2+ ions are added to the acid. A rise in temperature accelerates the dissolution reaction both along the induction as well as the catalyzed stages. The activation energies of dissolution are material dependent and vary between 3 and 11 K cal/mole. The corrosion rate (CR) of the four materials along the induction period varies with the [Cu 2+] of the solution according to CR = A[Cu 2+] n where A and n are constants. The value of n depends on the Cu content of the alloy. The corrosion rates along the catalyzed reaction are independent of the [Cu 2+].