AbstractThe attack of Cl−, Br−, and I−on the passive layer of iron has been studied by XPS. A pronounced thinning of the oxide is found. The effect decreases in the sequence of ions mentioned above and increases with the halide concentration. With the rotating ring disc technique no increase in Fe3+dissolution was detected before pit nucleation. Apparently the oxide thinning is a relatively slow process leading to the breakdown of passivity which occurs locally or generally depending on the kind and concentration of the ha