The initiation of single corrosion sites on iron by focused laser illumination

An experimental method has been developed for selective depassivation of small regions on an otherwise passive metal surface with the use of a focused laser radiation. A nitrogen pumped dye laser provided a pulsed beam which was focused to a diameter of approximately 5 μm. The method was used to create corrosion sites on iron immersed in a solution of 0.1 M Na₂B₄O₇ containing NaCl in the range of 0.01 to 0.03 M. It was found that the corrosion rate was controlled by transport through a covering of corrosion products which precipitated over the site. The corrosion current from single sites increased with the square root of time, and with a proportionality factor that depended upon both the applied potential and chloride ion concentration.