Understanding in compositional phases of carbon steel rust layer with a long-term atmospheric exposure

Available research mainly hold opinion that the rust layer on plain carbon steels under atmospheric condition contains a higher amount of gamma-FeOOH, but that on weathering steels contains a large amount of alpha-FeOOH. However, the performed investigations were almost done in a short exposure duration with no more than 15 years. In this work, the compositional phases of rust layer on plain carbon steel exposed to an indoor atmosphere for about 40 years have been characterized. Interestingly, alpha-FeOOH has been identified as the main phase, indicating that alpha-FeOOH can also be the dominant phase of rust layer even for plain carbon steel after a long-term atmospheric exposure.