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

Abstract

A technique that monitors the impedance of a 250 µm diameter aluminium electrode as a function of time with a 2 µs resolution as sand particles are impinged on the solid/liquid interface is reported. The detection of individual particles as they approach an electrode, before any erosion/corrosion was registered, is demonstrated. This study shows that at least two types of erosion mechanisms are possible; direct or 'primary' impact and tumbling or 'scrape' events.The primary impact events are correlated to the acoustic emission from the environment which is shown to be significant for these events, whereas scrape events appear to produce far weaker acoustic emission signatures under the conditions employed. The velocities of the particles are reported and are of the order of 6-8 m s -1 at the jet mouth. However, high-speed imaging of the particles as they strike the substrate indicates a significant deceleration prior to impact and an order of magnitude reduction in kinetic energy compared to that as it exits the jet.

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

“…Particles (sand pre-filtered through an aperture of the same size as employed in the jet) were added to the flow system via a loading port situated between the pump and the jet. Typically these sand particle are non-spherical and have approximate diameters centred around 250 µm [13]. To determine the electrochemical characteristics of the electrode as a particle approaches/impacts, a high-speed impedance approach was adopted.…”

“…As part of these investigations, the study of passive electrode interfaces exposed to an erosive event is of interest. Examples of these environments include cavitation [7][8][9][10][11] and particle impingement [12][13][14]. In many cases, the effect of the erosive mechanism on the surface has been quantified ex situ.…”

“…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].…”

“…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]. 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.…”

An Overview of Major Experimental Methods and Apparatus for Measuring and Investigating Erosion-Corrosion of Ferrous-Based Steels

“…Acoustic emission sensors are always used in combination with ER probes to build the relationship between the total metal loss rate and sand impingements [65,75,80,88,89]. It is seen from Figure 9 that an acoustic sensor was applied at the downstream of the elbow in previous study [80] to provide the sand impact rate.…”