Selective Oxidation as a Fundamental Principle in Metallic Protection

Abstract

IT is known that the oxidation or tarnishing of iron and copper can sometimes be diminished by alloying with small amounts of aluminium, beryllium, chromium and silicon, and that some oxide films confer protection or even passivity—especially when they are so thin as to be invisible. Little has been done, however, to obtain reliable protection by controlling the composition of the films. Miyake¹ has noted that, in the case of copper containing more than 3 per cent aluminium, the oxygen content of the atmosphere used for the first heating is an important factor. Sloman² has recommended the introduction of beryllium into silver to prevent tarnishing, but the efficacy of this addition has been questioned by Raub³, whose work suggests to us that some factor other than the composition of the alloy determines its behaviour.