Editors’ Choice—Respirometric in Situ Methods for Real-Time Monitoring of Corrosion Rates: Part I. Atmospheric Corrosion

Abstract

A novel respirometric approach to monitor atmospheric corrosion kinetics is presented. Simultaneous real-time monitoring of the H2 evolution reaction (HER) and the O2 reduction reaction (ORR) is possible with a combination of optical O2 sensor measurements with gravimetric volume sensitive techniques or pressure sensor based techniques in closed chambers. The respirometric method is a universal, non-destructive tool applicable to any metal or alloy. It shows a high sensitivity for low corrosion rates and has a high time-resolution. Different examples of relevant engineering metals and alloys will be provided. Mass loss validation measurements carried out at the end of exposure show a good correlation with the total recorded cathodic charge. For metals with different oxidation states the average valency in the corrosion products can be calculated from the cathodic charge together with mass loss. The versatility of the novel monitoring technique is further demonstrated by studying the influence of wet-dry cycling, temperature steps or changes in the gas composition in situ. The rate of HER, ORR and total corrosion rate during these changing exposure conditions can be tracked directly on the same sample. Overall the new method contributes to bridging the gap between lab tests, accelerated testing and field exposure.

High rate oxygen reduction reaction during corrosion of ultra-high-purity magnesium

“…However, for magnesium possessing low degradation rate, ORR plays a significant role in total cathodic process. Strebl et al 15 estimated that during atmospheric corrosion of AZ91 alloy, ORR contribution to total cathodic reaction may reach 60% at certain relative humidity. Concomitantly, benefiting from the sealed construction of the eudiometer, ORR contribution to the total cathodic process was calculated based on the evolved hydrogen and weight loss after 24 h (Table 1).…”

“…Simultaneous measurements of local DO concentration and current density (by SVET) was performed. 13 Moreover, Strebl et al 14,15 provided the evidence for the contribution of ORR to cathodic processes on Mg alloy during atmospheric corrosion. In spite of these compelling evidences collected by different scientific groups, varying conditions and methods, the essential role of ORR during corrosion of Mg remains largely unexplored and poses a number of questions.…”

Corrosion Monitoring in Atmospheric Conditions: A Review

“…As the sensors allow for oxygen concentration measurements through the transparent wall of a closed container, three experimental setups were designed: the first with samples being placed in glass containers; the second using an oxygen barrier film with flexible dimensions for irregularly shaped artefacts; and the third using glass dishes glued to a large artefact's surface [199]. The approach was successfully applied to assess the effectiveness of historical iron and copper objects conservation [200][201][202][203][204][205][206][207]. However, all these measurements were restricted to the samples that corrode mainly by ORR or mainly by HER, whereas real systems often combine the two cathodic reactions with their contribution varying in time.…”

Respirometric In Situ Methods for Real-Time Monitoring of Corrosion Rates: Part II. Immersion

“…Figure 1: Classification of respirometric approaches to monitor immersion corrosion kinetics by the measurement principle and the degree of flow. Adapted from 23 .…”