Birkin & Leighton 1 AN INVESTIGATION OF SURFACE RE-FORMATION IN THE PRESENCE OF INERTIAL (TRANSIENT) CAVITATION (GR/N30989/01)

AN INVESTIGATION OF SURFACE RE-FORMATION IN THE PRESENCE OF INERTIAL (TRANSIENT) CAVITATION (GR/N30989/01) P. R. Birkin and T. G. Leighton 1. Background There is an international need to understand the influence of inertial (transient) cavitation on the erosion of surfaces. Electrochemical data, relevant to this area, has been concentrated on the bulk effects observed for relatively large electrode surface areas (e.g. mm diameters compared to μm diameters as employed here). However, in many of these examples the exact acoustic conditions are not reported at the electrode surface. This is due in part to the diverse nature of sonoelectrochemistry, relying on aspects of chemistry, electrochemistry and acoustics. In general the understanding of the acoustic environment of a sonochemical cell is complex and relies on the characterisation of the transducer/cell/cavitation interaction that can be generated within the system as a whole. This fundamental problem often results in poor reproducibility between experiments and laboratories even though the same chemical environment and system is being employed (assuming no differences in the chemistry occur). During this project, the authors set out to systematically and quantitatively identify the sources of these problems and formulated an experimental approach to rectify them considering both the chemistry and acoustics involved. 2 The project set out to investigate surface erosion caused by cavitation using an acoustoelectrochemical approach to this complex problem. In order to achieve these goals, a controlled and well characterised acoustic cell was employed with the ability to generate inertial and non-inertial cavitation. Within this cell a further series of experiments were undertaken to follow fast surface reformation on a number of different metal/solution interfaces. Two complementary techniques were used to obtain supporting data: High speed imaging; and the quantification and imaging of luminescence produced through so called ‘multibubble sonoluminescence’ [MBSL]. The project was successful in producing and characterising a sonochemical cell, which was then investigated using electrochemical, luminescent and high speed imaging technology with relevance to the study of surface processes. Further to this, a novel electrode (dual electrode) was developed that enabled the assessment of a complex cavitation environment to be investigated for both inertial and non-inertial events. The methodology used in this project relied on microelectrodes (typically 25 μm in diameter) to study surface erosion. This procedure has enabled high temporal and spatial resolution to be achieved. While some results have yet to be published, the authors (PRB & TGL) have produced a series of high quality publications outlining some of the major results of the project (including 5 peer reviewed published papers (or in the process of publishing), with more [~5] in preparation for high quality journals (e.g. Proc. Royal Soc.)). This success has led to 2 further grant awards to the sum of £110k (including an industrially sponsored grant) all of which rely on well-characterised experimental procedures. In addition to these achievements, while the EPSRC paid for only one PhD student, the grant has (at no extra cost to the EPSRC) provided the platform to support a further PhD student.