An attempt to classify the morphologies presented by different rust phases formed during the exposure of carbon steel to marine atmospheres

The scientific literature contains very little knowledge on the morphology of the different rust phases formed upon exposure of carbon steel to the atmosphere. In recent years this topic has attracted the attention of many researchers working on atmospheric corrosion, but the various morphologies seen in microscopic observations and reported in many publications lack a rigorous characterisation and identification in terms of the rust phases that give rise to them. The aim of this paper is to advance in this respect with a dual purpose: firstly to try to make a classification of the numerous different types of morphologies seen in the microscopic observation of rusts formed on carbon steel exposed to marine atmospheres, and secondly to identify some of these morphologies, perhaps the most common, using the powerful SEM/Micro-Raman spectroscopic technique. This work distinguishes several main types of morphology: globular, acicular, laminar, tubular and toroidal, and the variants existing within each group. The rust phases most commonly found are the oxyhydroxides lepidocrocite, goethite and akaganeite and the iron oxide magnetite.