Microsecond resolution of cavitation bubble dynamics using a high-speed electrochemical impedance approach

Abstract

A new method to detect the uncompensated resistance, the capacitance and the Faradaic current at an electrode exposed to ultrasonic cavitation is presented. The method enables these parameters to be resolved with a 2 microsecond resolution and relies on the detection of the impedance of an electrode recorded as a function of time with a suitable AC excitation signal (here 500 kHz). Data obtained from an aluminium electrode, held under potentiostatic control, is used to illustrate the technique with particular relevance to the effects of cavitation bubbles generated by ultrasound. Analysis of the data recorded shows that the cavitation bubbles form close to the surface of the electrode and collapse, causing damage to the passive film formed at the aluminium surface. The capacitance, uncompensated resistance and Faradaic signals are used to explore the dynamic processes and show expansion and collapse of bubbles prior to erosion/corrosion. The close proximity of the bubbles to the surface is deduced from the reductions in capacitance and increases in resistance prior to bubble collapse, which is then shown to trigger the onset of a Faradaic signal, thus confirming the erosion/corrosion mechanism previously assumed.

Particle induced surface erosion – Tumbling and direct impact; a high-speed electrochemical, acoustic and visual study

“…The pump (Hailea HX8810, not shown in Figure 1) took electrolyte from the main reservoir (~2.5 dm 3 ) and pumped it through the jet after passing a loading port where sand was added to the flow system. The high-speed impedance system has been described in detail elsewhere [28].…”

“…This particle deceleration is also supported by simulations of impinging jets [33,37]. In order to characterise the impacts of the particle before, during and after impact onto the surface of an electrode, a high-speed electrochemical impedance technique was employed [28]. Here an AC perturbation was applied to the electrode and the current response monitored as a function of time while the jet, containing, sand particles, was directed at the electrode surface.…”

“…particle collision with an electrode). However, it has recently been shown that the measurement of impedance of an electrode exposed to cavitation can be performed with a time resolution of 2 µs [28]. This study showed that the growth and collapse of cavitation bubbles, produced by continuous ultrasound, could be followed prior to any conventional electrochemical signal (e.g.…”

In-situ detection of single particle impact, erosion/corrosion and surface roughening

“…Although useful this does not give any other information on the event that caused the erosion itself. To circumvent this limitation, a technique based on high-speed impedance [16,17] analysis has been developed [13,18]. In this case, the uncompensated resistance and the effective capacitance of the electrode (through the measurement of the electrode impedance), was acquired with a 2 µs resolution throughout either cavitation erosion (via bubble dynamics) or sand particle impact [13].…”

“…In this case, the uncompensated resistance and the effective capacitance of the electrode (through the measurement of the electrode impedance), was acquired with a 2 µs resolution throughout either cavitation erosion (via bubble dynamics) or sand particle impact [13]. These studies showed that in the former case, bubble growth and collapse preceded the erosion/corrosion event [18] while in the latter case particle approach and impact as well as tumbling [13] could be detected prior to the erosion/corrosion process. These observations are powerful in that the full mechanism can be probed rather than just the aftereffects on their own.…”