Corrosion of iron archaeological artefacts in soil: Estimation of the average corrosion rates involving analytical techniques and thermodynamic calculations

Archaeological artefacts have been analysed in order to determine the average corrosion rate of low carbon steel after long burial periods. The method adopted consists of two steps. The first one is based on the thickness measurement of the corrosion products, which after density correction and sample age consideration, provides a corrosion rate. As the obtained value is a minimum, another step is required to evaluate a maximal limit. This is calculated by simulating the dissolution of the phases identified in the corrosion products, considering the burial conditions. Results show that it is possible to establish a reliable maximal limit for corrosion forms containing goethite and magnetite in oxidising conditions. The estimated average corrosion rates do not exceed 4 μm/year.