The Mechanism of Dezincification and the Effect of Arsenic. I.

Abstract

Copper formed by dezincification of brass shows, in microsections, a dense layer at the surface roughly proportional in thickness to the depth of dezincificatton. The underlying copper frequently shows growth rings of alternate, more or less dense copper layers, sometimes incorporating bands of cuprous oxide, and a narrow band of dense copper is usually observed adjacent to the advancing corrosion front. These features are explained, and have been reproduced in laboratory experiments, on the basis of a redeposition theory of dezincification.

The first step in either dezincification or pitting corrosion of brass is dissolution of both copper and zinc, the copper forming cuprous chloride. In pitting corrosion the cuprous chloride is precipitated and subsequently hydrolysed or oxidised to secondary corrosion products. In dezincification, it is reduced to copper close to the point at which it first forms.

Beta- and non-arsenical alpha-brass both reduce cuprous chloride to copper (the beta much more readily), but arsenical alpha does not. These differences between the three types of brass are reflected in their relative susceptibility to dezincification. The reasons for these differences will be reported in Part II of the paper.