The Kelvin probe method has become very common in the study of the atmospheric corrosion since it was suggested that the method can be applied to the surface potential measurement as a non contacting method. The accuracy of the method is insufficient in detecting and discussing the corrosion initiation from the inclusions less than few microns. We applied the Kelvin force method (KFM) which is one of the AFM methods for the study of corrosion. First we examined the effect of the gap between the tip and specimen and found that the gap of less than 20 nm does not affect the potential distribution. The potential distribution of iron corroded in air was measured accurately. The irregularity of potential was caused by the small dust particles or scratches that become the nucleation sites of corrosion. A series of AFM observations show the atmospheric corrosion proceeded by micro-galvanic cell.
