Influence of Concentrated Neutral Salt Solutions on the Corrosion of Metals

Abstract

The H+ activity of diluted strong acids, such as or , rises by the addition of such neutral salts as , from 10−1 to 10 at constant concentration of the acid. The effect of this increase of activity on the anodic dissolution of Fe, Co, and Ni has been investigated. Fe and Co show the order with respect to the H+ activity, which was found by many other authors with respect to the H+ concentration when stationary measurements were accomplished. In accordance with the Heusler mechanism the order changed to at unstationary measurements. The cathodic process has the order with respect to the H+ concentration and 0.5 with regard to H+ activity changed by addition of neutral salts. The anodic dissolution is influenced by the nature of the cations .On the contrary the order of anodic dissolution of Ni is with regard to H+ concentration as well as to activity both at stationary and unstationary measurements. The cathodic process at Ni has the order with regard to H+ concentration and 0.5 with regard to H+ activity changed by addition of neutral salts. At the hydrogen ion discharge on the mercury electrode the order of reaction with regard to H+ concentration rises from 0.5 to 1 with increasing ionic strength according to the theory of Frumkin. The dependence upon at constant H+ concentration is complicated. The current density at constant potential passes through a maximum with increasing H+ activity and content of neutral salt. Height and position of this maximum with regard to the neutral salt concentration depend on the potential. A qualitative interpretation of the experimental results is proposed.