Characterization of manganese sulfide inclusion surfaces in 1018 carbon steels and interfacial studies of graphene coated copper surfaces

Abstract

Manganese sulfide inclusions are known to be sites of localized corrosion in steels, however little is know concerning the physical and chemical properties of inclusion surfaces. Some inclusions have been observed to be more corrosively active than others. In an effort to distinguish between active and inactive inclusions, this work utilizes surface sensitive electron spectroscopies and microscopies to characterize manganese sulfide inclusion interfaces in 1018 carbon steels. A method was developed to measure variations in surface potential with a high degree of spatial resolution using an Auger microscope. It was found that manganese sulfide inclusion surfaces are heterogeneous and possess discrete manganese oxide and copper sulfide phases. Valence band Auger spectroscopy was used to distinguish between various Mn and Fe chemical species. Surface potential measurements indicate that inclusions are more noble than the surrounding steel surface. TEM analysis indicates a high defect content at the inclusion/steel interface. It is hypothesized that active and inactive inclusions can be distinguished via the availability of sulfur. Graphene on copper surfaces were characterized for use as a protective coating against corrosion using surface sensitive spectroscopies. A feature in the copper Auger transition was found to be unique to graphene, and used to identify its presence and degree of substrate coupling. Localized oxidation of the copper substrate was observed to correlate with low surface potential regions, believed to be intercalated oxygen, which enhances the reactivity of the graphene overlayer. Intercalated Cl was observed to inhibit substrate oxidation, and reduce the reactivity of the graphene overlayer. The intercalation of water was observed to occur at room temperature, and molecularly adsorb to the copper surface at temperatures up to 200 C, indicating that graphene inhibits dissociation of water. Distribution of intercalated water was observed using Auger spectroscopy. It is suggested that doping of graphene is an effective strategy for use as an anticorrosive coating on heterogeneous surfaces.