查看更多>>摘要：Understanding elemental corrosion currents and visualizing corroding topographies provides a detailed insight into corrosion mechanisms at the nanoscale. Here, we develop a strategy to understand the elemental composition, corrosion resistivity, and local stability of passive materials. Specifically, we utilize a pulse voltammetry approach in a novel electrochemical atomic force microscopy (AFM) cell and complement this data by real-time dissolution currents based on spectroelectrochemical online analysis in an inductively coupled plasma mass spectroscopy (ICP-MS) flow cell. We study the oxide properties and their protective behavior when formed under different applied potentials using Alloy 600 as a model sample. Both AFM and ICP-MS data show that passive films formed on Alloy 600 at around +0.3 to +0.4 V in neutral 1 mM NaCl solution are most stable during anodic corrosion at +1.0 V, while AFM further demonstrates that local dissolution occurs, indicating locally varying defect levels in the passive film. In combination with both techniques, our approach provides real-time elementally resolved and localized information of passive film quality under corrosive conditions, and it may prove useful for other corroding materials.
Ningshen, S.Philip, JohnMannepalli, SrinivasShankar, A. R....
15页
查看更多>>摘要：Type 316N (0.07% N) stainless-steel welds prepared by shielded metal arc welding were evaluated for their pitting corrosion susceptibility in an acidified chloride environment and a neutral chloride environment in as-welded and thermally aged conditions at 823 and 923 K for 4, 10, 24, and 100 h. After 100 h thermal aging at 823 K, 46% of delta ferrite was transformed into carbide and 81% delta ferrite was transformed into carbide and sigma phases at 923 K for 100 h. On thermal aging at 823 K (0-10 h) and 923 K (10-100 h), the changes in the degree of alloy depletion (DOA) and pitting potential were marginal due to the presence of nitrogen. Thermally aged samples at 823 K beyond 24 h showed a significant decrease in pitting potential in acidic and neutral chloride media, whereas at 923 K, the pitting potential decreased significantly up to 10 h. The results of DOA and passive current density from the double-loop electrochemical potentiokinetic reactivation (DLEPR) test and the electrochemical reactivation test (ERT) correlated well with the observed secondary phases. The role of alloy depletion in terms of the parameters DLEPR, ERT, microstructure, and nitrogen alloying on pitting corrosion is discussed.
Tavares, Sergio S. M.de Sampaio, Marcelo T. G.Perez, Geronimode Almeida, Brigida B....
10页
查看更多>>摘要：The corrosion behavior of a 17Cr multiphase martensitic stainless steel quenched (1000 degrees C, water cooling) and tempered at different temperatures was determined using the double-loop electrochemical potentiokinetic reactivation (DL-EPR) test. The specimen tempered at 550 degrees C showed the highest degree of sensitization. For the specimen treated at 600 degrees C, a healing process was observed, followed by a second sensitization at 625 degrees C coincident with an increase in the austenite volume fraction. This phase was quantified using the magnetic method and an increase in this phase was observed with the tempering temperature. The DL-EPR results were correlated with surface aspects obtained by atomic force microscopy.
查看更多>>摘要：The effect of temperature and UV irradiation on the corrosion behavior of 304 stainless steel exposed to a simulated marine atmosphere was studied. The corroded samples were analyzed in detail through potentiodynamic polarization, in situ electrochemical impedance spectroscopy, Mott-Schottky measurements, scanning electron microscopy, and X-ray photoelectron spectroscopy. The results showed that the corrosion rate of 304 SS was significantly inhibited by UV irradiation, and the inhibition effect increased at a higher temperature. The UV irradiation not only changed the corrosion products morphologies formed on the 304 SS surface but also the relative content of the corrosion products was changed. In particular, UV irradiation can promote the formation of Cr2O3 in corrosion products, especially at a higher temperature, thus improving the corrosion resistance of 304 SS.
查看更多>>摘要：In this study, the galvanic corrosion behavior of the side surface of titanium-clad steel plate (TCSP) and below the defects, which penetrate through the titanium layer of TCSP, have been focused on. Electrochemical corrosion tests and infinite focus three-dimensional measurement results revealed that galvanic corrosion on the side of TCSP will lead to widespread pitting of the steel, and the distribution positions of pits in splash, tidal, and submerged zones are different. Severe corrosion occurs below the defects in the titanium layer of TCSP, and the larger the defect, the deeper the corrosion depth, but TCSP with smaller defects have larger corrosion width on the Ti-Stl line (the joint between the titanium and steel). This shows that the size of the defect will influence the density of corrosion products and the effect of TCSP defect internal corrosion on titanium layer peeling is extremely limited.
查看更多>>摘要：Organic repair coatings are applied to repair areas of previously coated low-carbon steel samples, and the samples are exposed to the splash zone in an offshore environment (Helgoland, North Sea) for 57 months. The volume loss of the steel underneath the delaminated coating is estimated with a three-dimensional optical stripe line projection. The samples show a small variation in the degree of delamination (22%) only. The steel volume loss values, in contrast, range between 164 x 10(6) and 320 x 10(9) mu m(3), which is a variation of 196%. The degree of delamination of the scribed coatings does not mirror the corrosion of the steel underneath the delaminated sections. The coating with the widest degree of delamination exhibits the lowest steel volume loss due to corrosion. A good scribe performance of a coating is, therefore, no guarantee for a low corrosion loss nor for a low local corrosion depth in the steels to be protected.
查看更多>>摘要：The acid-resistant steel represented by 09CrCuSb (ND) steel that is widely used in flue gas treatment systems is easily prone to mixed-acid dew point corrosion in the low-temperature flue gas environment. To improve the corrosion resistance of ND steel in a low-temperature dew point corrosion environment, here, a chromium-myristate hybrid (CMH) superhydrophobic coating is proposed as a low-temperature dew point corrosion protective coating for the ND steel substrate. This superhydrophobic coating is deposited on the ND steel substrate (preplated dark nickel as a transition layer) by one-step direct current electrodeposition. The electrochemical analysis from potentiodynamic polarization and electrochemical impedance spectroscopy and the immersion test show that the CMH superhydrophobic coating can significantly improve the corrosion resistance of the ND substrate. Therefore, the present study provides a feasible strategy for preventing the mixed-acid dew point corrosion of ND steel in the low-temperature zone.
查看更多>>摘要：The effect of 1.5% Cr on the corrosion resistance of low-alloy steel in a simulated mine environment was studied. To clarify the effect of Cr on the corrosion of low-alloy steel in the wet environment at the initial stage of corrosion, salt spray corrosion tests were performed to simulate the corrosion process in the field, and the bare steel and corrosion products were characterized. The results showed that the addition of 1.5% Cr reduced the surface potential and the kinetic tendency of the corrosion reaction, making the corrosion rate at the initial stage of the test lower than anticipated. An increase in Cr content significantly elevates the level of alpha-FeOOH. The corrosion product film (CPF) had a bilayer structure, with alpha-FeOOH of Cr-rich and Cr(OH)(3) were found in the inner layer and at the junction of the inner and outer layer. The CPF had a dense structure that effectively reduced electrochemical reaction activity and improved corrosion resistance.
Osterminski, KaiGehlen, ChristophZausinger, Christoph
8页
查看更多>>摘要：The aim of this study is to elucidate suitable methods of corrosion monitoring for chloride-induced rebar corrosion in cracked concrete. Depolarization gradients and transients provide evidence for the electrode kinetics at the steel-concrete interface and the geometry of the macrocell. In the present study, a set of cracked, short-term chloride-exposed, reinforced concrete specimens is investigated in terms of their corrosion activity. Primarily, the depolarization behavior was observed by short-term high-frequency measurements, allowing for cost-effective measurement campaigns and robust results. All measurement intervals are split apart via a gradient analysis to enable a congruent, numerical transient analysis. Since the geometry of macrocells in rebar corrosion follows the model of a series of ohmic resistances with a parallel connection of a diffusion-controlled capacitor and an ohmic resistance, the transient of each depolarization curve with unit time in seconds provides evidence for the present electrode kinetics and macrocell geometry. According to the time, which is consumed until a certain state of depolarization is reached, transient modeling can be used to predict corrosion activity as a function of chloride ingress.
Torres, VianeyMayen-Mondragon, RodrigoGenesca, Juan
10页
查看更多>>摘要：The corrosion behavior of a galvanic coupling consisting of a 7075-T6-aluminum alloy and a low-carbon low-manganese microalloyed dual-phase steel was studied in a 3% NaCl aqueous solution at room temperature. Corrosion behavior of the individual materials was assessed from potentiodynamic polarization and electrochemical impedance spectroscopy measurements conducted on the individual couple components. The corrosion rate of the individual samples was found to be seven times larger on the microalloyed steel than on the aluminum alloy. From a comparison of corrosion current densities, the galvanic couple was found to sustain a nonsignificant galvanic effect-the latter in contrast to what may be determined considering differences in their respective corrosion potentials. According to the applied mixed-potential theory and the zero-resistance-ammeter measurements performed directly on the galvanic couple, the aluminum-alloy acted as the anodic member of the galvanic couple. Such behavior was justified by kinetic parameters rather than thermodynamic ones, considering the favorable rate of the oxygen reduction reaction on the microalloyed steel surface.
NSTL
Wiley