Corrosion of Bronzes on Shipwrecks

Abstract Data on corrosion of metals are normally derived from two sources, namely, immersion/exposure tests and controlled electrochemical experiments. Because of inherent problems associated with the extrapolation of short-term measurements to long-term performance, many field workers are skeptical of the value of electrochemical data. In order to compare these two methods, corrosion rate data obtained for bronzes using (1) chemical analysis of corrosion products and (2) instantaneous corrosion rate measurements are presented. The material was examined after 170 years' immersion in tropical waters northwest of Western Australia where the American China Trader “Rapid” foundered in 1811. The nature of the corrosion products and the microenvironment will be discussed in terms of pH, oxygen access, Eh gradients, and the microstructure of the objects. Problems associated with non-uniform surfaces and slow rates of attaining a steady state will be discussed. Corrosion rates from the two methods are in good ag...