Wire beam electrode : a new tool for studying localised corrosion and other heterogeneous electrochemical processes

Heterogeneous electrochemical processes are very common in industry and are important, but difficult topics in electrochemical and corrosion science studies. Traditional electrochemical techniques which employ a conventional one-piece electrode have major limitations in studying heterogeneous electrochemical processes since the one-piece electrode has major difficulties in measuring electrochemical parameters from local areas of the electrode surface. In order to overcome this problem, a multi-piece electrode, namely the wire beam electrode, has been developed. This new electrode enables the measurement of electrochemical parameters from local areas over a working electrode surface and thus it can be used to study heterogeneous electrochemical processes. This paper describes how this new electrode was applied in studying several typical heterogeneous electrochemical processes including water-drop corrosion, corrosion under non-uniform organic films and cathodic protection.

A novel crevice corrosion experiment using a wire beam electrode

This paper describes a new experiment for studying crevice corrosion. A wire beam electrode was employed in this experiment to measure electrochemical parameters directly from crevice area and these parameters were used to calculate instantaneous crevice corrosion kinetics. A clear correlation between calculated corrosion depth map and real corrosion appearance was obtained.

An auto-switch for multisampling of a wire beam electrode corrosion monitoring system

An auto-switch device has been designed, constructed, and tested for multisensor corrosion measurements. The auto-switch is able to connect/disconnect the selected wire beam electrode and/or electrode pairs under computer control. A computer controlled analog switch-array consisting of 100 inputs has been used as an essential part of the switch bank. The switch-bank is an essential component of a corrosion-monitoring instrument that is expected to find wide application in industry. The performance of the switch-bank is discussed and its effect on the signals is illustrated.

Monitoring pitting-crevice corrosion using the WBE-noise signatures method

An electrochemically integrated multi-electrode array namely the wire beam electrode (WBE) and noise signatures analysis have been applied in novel combinations to study crevice corrosion behaviour in the presence of pits. Characteristic electrochemical noise signatures were found to correlate with characteristic changes in WBE current distribution maps, which indicate corrosion rates distributions, corrosion patterns and the degree of pitting and crevice corrosion. Specifically, two characteristic noise patterns were observed: (i) the characteristic noise pattern of quick potential changes towards more negative direction with no recovery (termed noise signature I) was found to correspond with the initiation and stabilization of the anode inside crevice; and (ii) the characteristic noise pattern of the cyclic potential oscillation at a constant frequency (termed noise signature II) was found to correspond with the stable anodic dissolution in the occluded cavity site in WBE current distribution maps. A new parameter namely the localization parameter (LP) has been proposed to describe the degree of localization. The LP for crevice corrosion was found to be low compared to that for pitting corrosion.

Inhibiting localized corrosion of aluminum and aluminum alloy by rare earth metal compounds : behaviors and characteristics observed using an electrochemically integrated multi-electrode array

An electrochemically integrated multi-electrode array namely the wire beam electrode (WBE) has been used to characterize the behavior of cerium chloride (CeCl3) and lanthanum chloride (LaCl3) in inhibiting localized corrosion of AA2024-T3 and AA1100. CeCl3 has been found to inhibit AA2024-T3 corrosion in 0.005 M sodium chloride (NaCl) solution by suppressing galvanic corrosion activities and by creating a large number of insignificant anodes. It has also been shown to inhibit localized corrosion of AA1100 in 0.5 M NaCl solution by promoting the random distribution of minor anodes. LaCl3 has been found to inhibit localized corrosion of AA2024-T3 at 1000 ppm, although its efficiency dropped significantly when its concentration decreased to 500 ppm. The addition of CeCl3 and LaCl3 to corrosion testing cells at later stages was unable to effectively suppress existing corrosion anodes.

Visualising dynamic passivation and localised corrosion processes occurring on buried steel surfaces under the effect of anodic transients

A new method of visualising dynamically changing electrode processes has been demonstrated by mapping localised corrosion processes occurring on buried steel surfaces under the effect of anodic transients. Dynamically shifting external electrical interferences such as anodic transients are known to affect the efficiency of cathodic protection (CP) of underground pipelines; however unfortunately conventional techniques including electrochemical methods have difficulties in measuring such effects. In this paper we report that the wire beam electrode has necessary temporal and spatial resolutions required for measuring and visualising the dynamic effects of anodic transients on CP, passivation and localised corrosion processes occurring on buried steel surfaces. For the first time a critical anodic transient duration has been observed and explained as the incubation period for the breakdown of passivity and the initiation of localised corrosion.