PostprintThis is the accepted version of a paper published in Electrochimica Acta. This paper has been peerreviewed but does not include the final publisher proof-corrections or journal pagination.Citation for the original published paper (version of record):Bettini, E., Kivisäkk, U., Leygraf, C., Pan, J. [Year unknown!] Study of corrosion behavior of a 22% Cr duplex stainless steel: influence of nano-sized chromium nitrides and exposure temperature.
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AbstractChromium nitrides may precipitate in duplex stainless steels during processing and their influence on the corrosion behavior is of great importance for the steel performance. In this study, the influence of nanosized quenched-in chromium nitrides on the corrosion behavior of a heat treated 2205 duplex stainless steel was investigated at room temperature and 50 °C (just above critical pitting temperature). The microstructure was characterized by SEM/EDS and AFM analyses, and quenched-in nitrides precipitated in the ferrite phase were identified by TEM analysis. Volta potential mapping at room temperature suggests lower relative nobility of the ferrite matrix. Electrochemical polarization and in-situ AFM measurements in 1 M NaCl solution at room temperature show a passive behavior of the steel despite the presence of the quenched-in nitrides in the ferrite phase, and preferential dissolution of ferrite phase occurred only at transpassive conditions. At 50 °C, selective dissolution of the austenite phase was observed, while the ferrite phase with the quenched-in nitrides remained to be stable. It can be concluded that the finely dispersed quenched-in nitrides do not cause localized corrosion, whereas the exposure temperature has a strong influence on the corrosion behavior of the duplex stainless steel.
Passivity determines corrosion resistance and stability of highly-alloyed stainless steels, and passivity breakdown is commonly believed to occur at a fixed potential due to formation and dissolution of Cr(VI) species. In this work, the study of a 25Cr-7Ni super duplex stainless steel in 1 M NaCl solution revealed that the passivity breakdown is a continuous degradation progress of the passive film over a potential range, associated with enhanced Fe dissolution before rapid Cr dissolution and removal of the oxide. The breakdown involves structural and compositional changes of the passive film and the underlying alloy surface layer, as well as selective metal dissolution depending on the anodic potential. The onset of passivity breakdown occurred at 1000 mV/ Ag/AgCl , and Fe dissolved more on the ferrite than the austenite phase. With increasing potential, the passive film became thicker but less dense, while the underlying alloy surface layer became denser indicating Ni and Mo enrichment. Rapid Cr dissolution occurred at ≥1300 mV/ Ag/AgCl .
Sandvik Materials Technology, SwedenIn this study, preferential sites for metal dissolution during anodic polarization were investigated for a biomedical CoCrMo alloy. As-cast and heat treated materials were compared through a combination of complementary techniques. Scanning Kelvin probe force microscopy mapping suggested the matrix areas adjacent to the carbides to be preferential sites for metal dissolution. By means of in situ electrochemical-optical microscopy it was observed that localized dissolution initiated from the matrix areas adjacent to carbides and grain boundaries in both materials at high anodic potential. By using scanning electron microscopy and transmission electron microscopy/energy dispersive spectroscopy analysis, submicron-sized carbides were found along the grain boundaries, and significant Cr depletion was detected across the grain boundaries for both materials, providing an explanation for the initiation of metal dissolution. A slightly higher metal dissolution was observed for the as-cast sample at high anodic potential, probably due to a more heterogeneous microstructure. (C) 2012 The Electrochemical Society. [DOI: 10.1149/2.056209jes] All rights reserved
A full biouse of crops for multiple end-uses would contribute to a more economically attractive and thereby more sustainable use of the crop. The purpose of this paper was to evaluate options to develop materials from residuals of rapeseed, originating from the biodiesel (RME) production. Compression molding of rapeseed flour and rapeseed cake residuals was evaluated together with additions of different amount of plasticizer (glycerol), as well as use of various pressing temperatures and times. The results were promising and led to a compact and hard, although somewhat brittle material. The potential to produce materials from the rapeseed residuals from RME production is thus high. Glycerol content was the most important factor increasing tensile strength in the material followed by pressing time. No clear protein polymerization was detected in the produced materials. Thus, despite the promising results, methods to obtain increased protein polymerization should be searched for. Therefore, binding agents, additives, or pretreatment of the rapeseed residuals are needed, or the proteins have to be purified, in order to generate a better polymerization of the proteins.
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