Water irradiation by high-frequency ultrasonic wave: Effects on properties of passive film formed on stainless steel

In this paper an aqueous solution was irradiated with a 1.63 MHz ultrasonic wave. It is shown that if stainless steel can passivate under dynamic polarization in this medium, under static polarization, the latter does not show any repassivation behaviour with time. This is attributed to a diminution of the diffusion layer thickness that is developed at the electrode/electrolyte interface, which is associated with a production of H2 species by sonolysis and which maintains reductive conditions at the interface. The oxide film formed under ultrasonic irradiation for 1 h at a passive potential of +0.2 VSCE shows an early stage of passivation and an increased disordered state, which implies a considerable decrease in the corrosion resistance behaviour of the sample. The polarization resistance of the stainless steel Rp is divided by a value of 4.5 under ultrasonic conditions.