The effect of photo-illumination on the corrosion resistance of stainless steels

The effect of photo illumination on passivity breakdown was experimentally studied for commercial grade 304 stainless steel. The breakdown on this stainless steel was found to be inhibited at low illumination intensities, while accelerated at high illumination intensities. The low intensity inhibition is attributed to either the alteration of the electronic properties (defect structure) of the passive film or to the passivation of manganese sulfide inclusions by elemental sulfur. The high intensity enhancement of pitting is attributed to accelerated photo dissolution of the manganese sulfide inclusions. The passive film is modeled as a {dollar}rm psp+{dollar}-n{dollar}sp+{dollar} junction to explain the inhibition effect. In this model, the electric field is buffered by the tunneling of electrons and quenched by the optical generation of electron hole pairs. The enhanced photo dissolution of the manganese sulfide is experimentally verified using manganese sulfide powder and theoretically explained using semiconductor electrochemistry and defect chemistry.