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Chemistry

Research project: High-speed AC Impedance: Bubble and Particle dynamics

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Conventional electrochemistry is a powerful technique but the complex and often-dynamic environment generated in ultrasonic systems or in an environment, containing moving particles is often too complex to be fully understood using this approach.

To avoid this problem we have developed a high-speed AC impedance technique with the ability to follow dynamics on the µs timescale and give added information regarding the processes that occur at the solid/liquid interface.

The figure shows the impact of a set of particles onto an electrode surface characterised using an AC impedance approach.  Here, the particles cause changes in the uncompensated resistance and effective capacitance at the electrode surface.  The insulating sand particles employed (~300 µm diameter) are entrained in a jet (~5 m s-1) which hit the electrode surface at ~ 1 m s-1.  Increases in uncompensated resistance (purple) and reduction in apparent capacitance (black) preceded the conventional anodic current transient (green).  This shows how particles can be followed as they approach the surface and characterised in relation to their erosive effects.  These studies revealed a number of interesting effects.  First, particle erosion could be caused by direct impact onto the surface.  Second, tumbling effects, which produced little detectable acoustic emission, could be observed.  Third, the effect of an individual particle on the roughness of the interface could be assessed in situ for the first time.

The approach is very powerful1–3 and has clear potential for the elucidation of the mechanisms present in complex environments.  It also can be used to look at different particles including conducting particles or cavitation bubbles.

1  P. R. Birkin, T. M. Foley, J. L. Barber and H. L. Martin, Microsecond resolution of cavitation bubble dynamics using a high-speed electrochemical impedance approach ChemComm COMMUNICATION, Chem. Commun., 2016, 52, 11406–11409.

2 P. R. Birkin, R. Lear, L. Webster, L. Powell and H. L. Martin, In-situ detection of single particle impact, erosion/corrosion and surface roughening, Wear, 2021, 464–465, 203527.

3 P. R. Birkin and J. L. Barber, Particle induced surface erosion – Tumbling and direct impact; a high-speed electrochemical, acoustic and visual study, Wear, 2019, 428–429, 147–153.

 

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