Detection of Currents from a Model Pit Using the Scanning Vibrating Electrode Technique

Abstract

The scanning vibrating electrode technique (SVET) is a versatile technique for determining the location and intensity of anodes and cathodes and mechanisms in corroding systems. A model anode has been used to assess current profiles above such features in a variety of electrolytes and using various scanning parameters. The model anode has a current profile in between the theoretical determined results for equi-potential and equicurrent discs. It has been shown that low concentration electrolytes (<0.1% NaCl) and low scan heights (<80 µm) are unsuitable for SVET testing.

Concentration Effects on the Spatial Interaction of Corrosion Pits Occurring on Zinc in Dilute Aqueous Sodium Chloride

“…It has previously been pointed out that estimates of current density can give rise to large errors when the SVET is used in a dilute solution. 46,47 These errors arise from deviation from Ohm's law, caused in turn by a non-uniform ion distribution stemming from localized electrochemical reactions at the specimen surface. 46 However, the experimental work on which these findings were based involved SVET measurement made over polarized platinum surfaces immersed in NaCl.…”

“…This in turn minimized the risk that SVET calibration could be influenced by local changes in electrolyte pH induced by water electrolysis or by any other non-uniform ion distribution stemming from localized electrochemical reactions at the platinum surface. 47 Given all these safeguards it is likely that the J a(t) values obtained using Equation 3 and shown in Figure 8 are substantially accurate. Nevertheless, wherever possible, quantities calculated from SVET data will be compared with the same quantities calculated by other means.…”