The effect of power ultrasound on surfaces has been well documented. Indeed the presence of cavitation generated by flow, sound or some other technique is well known to have a detrimental effect on a surface. However, this characteristic can be used to quantify the presence of erosive mechanisms in this environment.
In order to achieve this, a passivated electrode surface can be deployed. Typical examples of this include Pb coated with an electrochemically generated PbSO4 film, a stainless steel electrode and an aluminium electrode. In all these cases it is possible to use electrochemical control of the surface to monitor the erosion of the interface as a function of time and space. For example, if we consider a Pb system, under appropriate conditions of potential and solution composition, the surface of this electrode can be coated with an insoluble PbSO4 layer. In the event of an erosive event (such as the collapse of an inertial cavitation bubble close to the solid/liquid interface), material is removed from the surface. The electrode is held under electrochemical control and hence the initial PbSO 4 surface reforms. The associated electrons are registered as an anodic current at the electrode surface. The figure shows the sequence of events and the associated time periods. Note the electrochemical data is post the erosion event. However, the electrochemical current time transient registered is relatively fast depending on the system. For example, an erosion event recorded at passivated surfaces are on the order of 10-100’s µs in duration.