A Study of the Effect of Chloride lon on Films Formed on lron in Sodium Nitrite Solutions

The effect of chloride ion on the potential of iron in sodium nitrite solutions has been measured. This has been related to the surface composition and topography by the techniques of electron diffraction and electron microscopy. The effect of initial surface preparation has also been investigated. It is shown that in the absence of chloride ion the potential is noble and steady and that the surface remains practically unchanged. A film of is shown to be present by electron diffraction. When chloride ion is added to the system the potential becomes unsteady and less noble. Inclusions of a second phase grow in the oxide layer. This is shown to be or lepidocro‐cite. The lower and unsteady potential is probably due to the decrease in resistance of the anodic areas, which correspond to the inclusions in the oxide layer.