CORROSION AND PROTECTION AT THE N.P.L

Work on oxidation of metals at N.P.L. has been devoted largely to an investigation of the mechanism of breakaway oxidation of iron-chromium alloys. Much research on oxidation has been based on the view that alloying additions can improve protection either by modifying the defect structure of the oxide so as to slow down the diffusion processes involved in oxide growth, or by forming a different and more protective oxide by selective oxidation so that a small alloying addition serves to ensure protection. Unfortunately, however, the protective films are liable to fail after a certain period, leading to a large and possibly catastrophic increase in rates of oxidation. The causes of this change are complex, but may include build-up of stress in the growing oxide, changes in diffusion mechanism, and nucleation of new phases. It was decided to concentrate attention at N.P.L. on this loss of protective action for the following reasons: