Investigating atmospheric corrosion behavior of carbon steel in coastal regions of Mauritius using Raman Spectroscopy

Low carbon steel was exposed at two sites in Mauritius, namely Port Louis and Belle Mare. The site at Port Louis is basically an industrial marine one whereas the one at Belle Mare is a purely marine site. Though the corrosion loss trend at both sites follow the power law, the corrosion loss at Port Louis was found to be higher than that at Belle Mare. This study has been performed to investigate the surface characteristics of the rust layers of the samples exposed at the two sites, through Raman spectroscopy and SEM, so as to get a better insight into the mechanism of the atmospheric corrosion process. For Port Louis, it was observed that there was not much change in the corrosion products in the rust layer over the 3 years period. The structure was less compact than that at Belle Mare with the presence of lepidocrocite and akaganeite as commonly observed corrosion products. The corrosion rate at Port Louis is, therefore, expected to follow the same trend over the long term. For Belle Mare, the corrosion products changed significantly after 3 years of exposure. Though lepidocrocite and akaganeite were observed on the surface after 0.2 years of exposure, magnetite was the most probable corrosion product in the more compact rust layer after 3 years of exposure. This compactness of the rust layer is expected to have reduced the corrosion rate as compared to that of Port Louis. Significant changes in the corrosion rate at Belle Mare are, therefore, expected over the medium and the long term

Characterisation of iron archaeological analogues using micro diffraction under synchrotron radiation. Application to the study of long term corrosion behaviour of low alloy steels

Last progresses in synchrotron radiation focusing allow the characterisation on microscopic samples. The use of X Ray micro diffraction ($\mu$XRD) in two corrosion studies (indoor atmospheric corrosion and in soil corrosion) concerning iron archaeological artefacts is presented. This analytical method permits to locate and identify very precisely the constitutive phases of the corrosion products. For the atmospheric corrosion study, semi quantitative data were presented to assess the proportion of the different identified phases in the rust layers. For the in soil corrosion study, the precise distribution of corrosion products formed on the nine analysed artefacts is given

Study of red pigments from the 'Genyornis' Panel, Arnhem Land, Australia: what are the origins of the haematite? ?[Etude des pigments rouges du panneau du 'Genyornis' Terre d’Arnhem, Australie: origines de l’hématite?]

Western Arnhem Land’s rock art is world famous yet very poorly dated. Understanding its history over tens of thousands of years has major implications for understanding Aboriginal cultural history in Australia. In particular, very little is known about the composition of paints and the techniques used to make Rock Art. Here we investigate the pigments and rock surfaces of an undated rock painting that has been argued in the literature to represent the extinct megafaunal bird Genyornis newtoni, thought to have become extinct across Australia 40-45 000 years ago. Small flakes of pigmented and unpigmented rock were sampled from the so-called ‘Genyornis’ panel in order to address three major questions concerning: i) the constituents of the pigments used and their modes of preparation (mixing with extender(s) or binder(s); grinding; heat treatment); (ii) the geological formations which provided such pigments; and (iii) the antiquity of paintings on the rock walls. Following macroscopic observations, pigment compositions were analyzed by scanning electron microscopy coupled with energy-dispersive X-ray spectrometry (SEM-EDX) and Raman microspectroscopy. Complementary structural information was obtained using X-ray diffraction (XRD). Both unprepared samples and cross-sections of resin-embedded samples were analyzed to obtain morphological, chemical and structural characterizations. Iron oxides (hematite Fe2O3 and goethite FeOOH) were identified in the paint layer. A white alumino-phosphate-rich matrix was identified as a weathering, microstratigraphically basal bedrock layer on the rock wall. The punctual presence of gypsum (CaSO4, 2H20) was observed as an underlayer below the pigment and could be explained by the weathering process of the quartzite support. This study highlights the difficulty of obtaining information on ancient pigments significantly modified through time in a relatively open site and distinguishing poorly crystallized iron oxides, which result from the weathering of rocks and the sub-micronic iron oxide crystals in the leached paint layer