1,720,977 research outputs found
Acoustoelectrochemical characterisation of cavitation and its use in the study of surface processes
No full textEThOS - Electronic Theses Online ServiceGBUnited Kingdo
Cavitation, shockwaves and electrochemistry: an experimental and theoretical approach to a complex environment
No full textThe investigation of bubble events generated and driven in an acoustic environment is reported.
An electrochemical approach is combined with a number of other chemical and physical
observations of the systems studied. In particular laser scattering through the bubble cloud,
high-speed imaging and luminescent measurements of multibubble sonoluminescence (MBSL)
within the environment below an operating ultrasonic transducer (specifically a piston like
emitter operating at ~ 23 kHz) is discussed in detail. The investigation of this complex
environment highlights the contribution to the system from cluster events, shockwaves, transient
bubble clouds and the electrochemical sensors employed in their investigation. Implications for
the chemical and physical properties of the unusual environments explored will be highlighted
with the need for a combined approach to these systems emphasised. In addition, the inertial
zone, created by the sound source employed, is used to study erosion/corrosion processes at a
stainless steel microelectrode
An activated fluid stream - New techniques for cold water cleaning
No full textElectrochemical, acoustic and imaging techniques are used to characterise surface cleaning with particular emphasis on the understanding of the key phenomena relevant to surface cleaning. A range of novel techniques designed to enhance and monitor the effective cleaning of a solid/liquid interface is presented. Among the techniques presented, mass transfer of material to a sensor embedded in a surface is demonstrated to be useful in the further exploration of ultrasonic cleaning of high aspect ratio micropores. In addition the effect of micropore size on the cleaning efficacy is demonstrated. The design and performance of a new cleaning system reliant on the activation of bubbles within a free flowing stream is presented. This device utilised acoustic activation of bubbles within the stream and at a variety of substrates. Finally, a controlled bubble swarm is generated in the stream using electrolysis, and its effect on both acoustic output and cleaning performance are compared to the case when no bubbles are added. This will demonstrate the active role that the electrochemically generated bubble swarm can have in extending the spatial zone over which cleaning is achieved.</span
An electrochemical and high-speed imaging study of micropore decontamination by acoustic bubble entrapment
No full textElectrochemical and high-speed imaging techniques are used to study the abilities of ultrasonically-activated bubbles to clean out micropores. Cylindrical pores with dimensions (diameter × depth) of 500 ?m × 400 ?m (aspect ratio 0.8), 125 ?m × 350 ?m (aspect ratio 2.8) and 50 ?m × 200 ?m (aspect ratio 4.0) are fabricated in glass substrates. Each pore is contaminated by filling it with an electrochemically inactive blocking organic material (thickened methyl salicylate) before the substrate is placed in a solution containing an electroactive species (Fe(CN)6(3-)). An electrode is fabricated at the base of each pore and the Faradaic current is used to monitor the decontamination as a function of time. For the largest pore, decontamination driven by ultrasound (generated by a horn type transducer) and bulk fluid flow are compared. It is shown that ultrasound is much more effective than flow alone, and that bulk fluid flow at the rates used cannot decontaminate the pore completely, but that ultrasound can. In the case of the 125 ?m pore, high-speed imaging is used to elucidate the cleaning mechanisms involved in ultrasonic decontamination and reveals that acoustic bubble entrapment is a key feature. The smallest pore is used to explore the limits of decontamination and it is found that ultrasound is still effective at this size under the conditions employed
Electrochemical ‘Bubble Swarm’ Enhancement of Ultrasonic Surface Cleaning
No full textAn investigation of surface cleaning using a swarm of gas bubbles within an acoustically activated stream is presented. Electrolysis of water at Pt microwires (100 µm diameter) to produce both hydrogen and oxygen bubbles is shown to enhance the extent of ultrasonic surface cleaning in a free flowing water stream containing an electrolyte (0.1 M Na2SO4) and low surfactant concentration (2 mM SDS). The surfactant was employed to allow control of the average size of the bubble population within the swarm. The electrochemical bubble swarm (EBS) is shown to perturb acoustic transmission through the stream. To optimise the cleaning process both the ultrasonic field and the electrochemical current are pulsed and synchronized but with different duty cycles. Cleaning action is demonstrated on structured surfaces (porcine skin and finger mimics) loaded with fluorescent particles. This action is shown to be significantly enhanced compared to that found with an inherent bubble population produced by the flow and acoustic regime alone under the same conditions.</span
The study of surface processes under electrochemical control in the presence of inertial cavitation
Full text linkIn some circumstances, the erosive effects of inertial (transient) cavitation have been usefully employed in the acceleration of chemical processes that are dependent on surface reactions. However, in other situations the erosion of materials can be detrimental. For example, problematic erosion/corrosion phenomena have been well documented. It will be demonstrated here that the employment of inertial cavitation can be beneficial to the study of surface processes and indeed has a number of advantages. These include rapid erosion and the removal of small quantities of the surface. To highlight these effects, high-temporal resolution of the re-oxidation transients produced from a passivated microelectrode placed within a cavitation cloud will be reported. These will be compared to the multi bubble sonoluminescence (MBSL) output of the cell
Electrochemical measurements of the effects of inertial acoustic cavitation by means of a novel dual microelectrode
No full textA novel dual microelectrode system has been developed to study the effects of cavitation at the solid/liquid interface. By sealing lead and platinum microelectrodes in close proximity, the mass transfer and surface effects from the same inertial cavitation event have been recorded simultaneously for the first time. A number of advantages of the system have been outlined. In addition supporting evidence for an erosion/corrosion mechanism on the lead electrode is reported
An activated fluid stream – new techniques for cold water cleaning
No full textElectrochemical, acoustic and imaging techniques are used to characterise surface cleaning with particular emphasis on the understanding of the key phenomena relevant to surface cleaning. A range of novel techniques designed to enhance and monitor the effective cleaning of a solid/liquid interface is presented. Among the techniques presented, mass transfer of material to a sensor embedded in a surface is demonstrated to be useful in the further exploration of ultrasonic cleaning of high aspect ratio micropores. In addition the effect of micropore size on the cleaning efficacy is demonstrated. The design and performance of a new cleaning system reliant on the activation of bubbles within a free flowing stream is presented. This device utilised acoustic activation of bubbles within the stream and at a variety of substrates. Finally, a controlled bubble swarm is generated in the stream using electrolysis, and its effect on both acoustic output and cleaning performance are compared to the case when no bubbles are added. This will demonstrate the active role that the electrochemically generated bubble swarm can have in extending the spatial zone over which cleaning is achieved
Experimental and theoretical characterisation of sonochemical cells. Part 2: cell disruptors (ultrasonic horns) and cavity cluster collapse
No full textCavitation theory is used to predict the acoustic pressure at the boundary of the inertial/non inertial threshold for a range of bubble sizes. The sound field generated from a commonly employed sonoelectrochemical cell is modelled. The model is tested with a calibrated hydrophone far from the transducer to avoid spatial averaging. This allows the model to provide the absolute pressure amplitude as a function of axial distance from the source. An electrochemical technique for detecting both inertial and non-inertial cavitation within the solution is employed. This technique uses a dual microelectrode to map the boundary between the regions where inertial cavitation occurs (associated with surface erosion), and where it does not. This zone occurs close to the transducer for the microelectrode employed (<1.5 mm). Further characterisation of the inertial cavitation zone is achieved by imaging of multibubble sonoluminescence (MBSL). The pressures at the boundary between inertial and non inertial cavitation that are determined from the electrochemical and imaging experiments are compared to a sound field model and cavitation theory. Qualitative arguments for the invasive nature of the electrode into the sound field are proposed. Evidence for cavity cluster collapse and shock wave emission is presented and discussed in relation to luminescence, the electrochemical experiments and cavitation theory
Electrodeposition of copper in the presence of an acoustically excited gas bubble
Full text linkCopper has been electrodeposited in the presence of an acoustically excited gas bubble (Ar bubbles with radii 1.5 mm held below a copper plate). Under the conditions employed, an acoustic pressure amplitude of 69.5 Pa is sufficient to excite multiple surface wave modes on the bubble wall. This is observed using high-speed imaging. This oscillation generates significant micromixing, which brings fresh electrolyte to the electrode surface leading to an enhanced deposition current. Scanning electron microscopy reveals radial streaming patterns in the resulting copper deposit. Experiments carried out using a lower acoustic pressure amplitude of 50.5 Pa (such that only the Faraday wave is excited) exhibit a lesser degree of streaming and mass transfer enhancement. No significant spatially averaged current enhancement is seen if the bubble is only undergoing breathing mode oscillation
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