Date

2022-9-02

Author

Yücel, Nurdan

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Characterization of corrosion layers on iron artifacts and their iron oxide phases are important for long term prediction of complex iron corrosion mechanisms in different atmospheric conditions for improvements in corrosion resistance of iron products as well as maintenance and conservation treatments of iron artifacts. Exposed iron components in the Ottoman period historical buildings visually seem to be in quite a good state of preservation, in spite of their longterm exposure to atmospheric conditions. The purpose of this study was to investigate metallurgical and corrosion properties of iron components used in some Ottoman period historical buildings to derive information on their technological and corrosion characteristics. In this study, some iron components taken from the hammam buildings (Gazi Mihal Hammam constructed around 1450 and Kılıç Ali Paşa Hammam around 1580) representing the the Classical Period and other iron components from some historical dwellings in Foça, Izmir and in Tekkekoy, Samsun representing late Ottoman period (19th cc) were examined. The metalurgical properties of the artifacts were investigated in terms of their Brinell hardness measurements, elemental composition by spark emission spectrometry and the microstructure of the main metal bodies by using a metallographic microscope and digital microscope. The corrosion layers were examined on polished and ethced cross-sections using µ-Raman spectrometer and SEM-EDX. Powdered samples scraped from the corrosion layers were studied by XRD and FTIR. All iron objects examined have corrosion layers on their surface where the corrosion products are mainly goethite and rarely hematite formed in open air environments namely urban, rural (interior, exterior) and burial environment. The goethite formation on the iron objects is favorable in open air atmospheric conditions during repeated wet-dry cycles at around pH 7-8. The corrosion layers of the objects are further classified as perfect, medium and imperfect corrosion layers depending on their thickness and compactness. They are mostly composed of nano-sized goethite particles with good crystallinity and are free of impurities. The perfect corrosion layers have finer nano-sized particles with good crystallinity that is thought to be an indication of good stability for goethite in comparison to its amorphous state. The protective ability of the corrosion layer is closely related with fine size of goethite particles and its compactness. Nano-sized goethite particles appear to have the super-paramagnetic property affecting the compactness of corrosion layer on the iron object. The microstructural properties of the historical objects seem to have some influence on perfect corrosion layer formation. Objects having perfect corrosion layers have finer ferrite grain size. Some elements in the composition of the objects such as manganese, carbon, silicon, phosphorous, sulfur, chromium and nickel were further discussed for their influence in the formation of protective corrosion layer.

Subject Keywords

historical steel, corrosion products, goethite formation, microstructure, raman spectroscopy

URI

https://hdl.handle.net/11511/99727

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Graduate School of Natural and Applied Sciences, Thesis