ULTRASONICALLY INDUCED CAVITATION STUDIES OF ELECTROCHEMICAL PASSIVITY AND TRANSPORT MECHANISMS .1. THEORETICAL

High intensity ultrasound causes the formation of cavitation bubble which collapse in a manner that, in the presence of a solid surface, form high velocity fluid microjects directed toward the surface. The intense fluid agitation at surface in a focused ultrasound field enhances transport of momentum, heat, and mass and influences the behavior and integrity of surface films on metal electrodes. A mathematical model is proposed to determine the reaction and transport between liquid microjets and a reactive solid surface. The conditions were estimated under which oxide depassivation and repassivation occur as a function of ultrasonic intensity, surface film thickness and fluid microjet surface coverage. The model was based on the concept that cavitation induces sufficient momentum and mass transfer rates (water hammer pressures) at a surface to create oxide film stresses leading to depassivation The model was used in a companion paper (1) to evaluate experimental data on the corrosion behaviour of iron in sulfuric acid.