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The compositions of non-metallic phases in samples of medium-carbon steel, which differed in production technology and level of contamination with corrosive non-metallic inclusions, have been studied in detail by scanning electron microscopy. It is shown that the effect of non-metallic inclusions on the tendency of steel to local corrosion can be related to the degree of non-stoichiometry of their composition. A mechanism for the formation of non-stoichiometric inclusions during steel production using a modern technological scheme is proposed. [ABSTRACT FROM AUTHOR]

Linseed oil and poly(urea-formaldehyde)-based microcapsules with an 82% weight ratio of core/shell and a mean outer diameter of about 100 μm were synthesised by in-situ polymerisation. These microcapsules were dispersed in polyester paint and then primer-coated Galvalume sheets were painted with microcapsule loaded (MC) and neat (no microcapsules) paints. These painted samples were scribed and examined using various characterisation techniques to evaluate their self-healing properties. SST and CCT showed that the electrolyte diffusion was suppressed in the MC sample, whereas the neat sample was noticeably blistered due to under-film corrosion. Scanning Kelvin Probe microscopy, SKP supported this finding wherein the Volta potential of the neat sample increased in the positive direction indicating cathodic delamination, whereas no significant change occurred in the MC sample. SEM-EDAX revealed the surface morphology and composition of the samples. Furthermore, EIS showed that microcapsule addition increased the pore resistance and decreased the coating capacitance of the polyester paint. [ABSTRACT FROM AUTHOR]

In this work, the materials from different positions of 2219 aluminum‐alloy/304 stainless‐steel inertia friction–welded tank with long‐term storage of N2O4 are studied. The results show that the corrosion product layer composed of Fe3O4 and FeCr2O4 is covered on the surface of stainless steel. The corrosion product layer on the surface of stainless steel can effectively improve the protection effect. Severe corrosion occurred in both the sidewall and bottom aluminum alloy, with intergranular corrosion depths of about 30–50 μm observed in the cross section, accompanied by typical exfoliation corrosion. A Fe–Al‐dominated intermetallic compound layer is formed at the weld. A dynamic recrystallization zone and thermomechanical‐affected zone are included on the aluminum‐alloy side with intergranular corrosion depths of 4.3 and 13.3 μm, respectively. The granular Al matrix can be seen on the peeling surface of the aluminum alloy. Combining scanning Kelvin probe and potentiodynamic polarization curve results, the high potential of the stainless steel can further promote the corrosion of the aluminum alloy. [ABSTRACT FROM AUTHOR]

In this work, the materials from different positions of 2219 aluminum‐alloy/304 stainless‐steel inertia friction–welded tank with long‐term storage of N2O4 are studied. The results show that the corrosion product layer composed of Fe3O4 and FeCr2O4 is covered on the surface of stainless steel. The corrosion product layer on the surface of stainless steel can effectively improve the protection effect. Severe corrosion occurred in both the sidewall and bottom aluminum alloy, with intergranular corrosion depths of about 30–50 μm observed in the cross section, accompanied by typical exfoliation corrosion. A Fe–Al‐dominated intermetallic compound layer is formed at the weld. A dynamic recrystallization zone and thermomechanical‐affected zone are included on the aluminum‐alloy side with intergranular corrosion depths of 4.3 and 13.3 μm, respectively. The granular Al matrix can be seen on the peeling surface of the aluminum alloy. Combining scanning Kelvin probe and potentiodynamic polarization curve results, the high potential of the stainless steel can further promote the corrosion of the aluminum alloy. [ABSTRACT FROM AUTHOR]

The influence of inclusions corrosion behavior under multi-factor local corrosion mechanisms was researched by SKPFM, TOF-SIMS, EBSD, and in-situ corrosion tests. The model of the local corrosion behavior of CaO/CaS–MgO–Al2O3 inclusion under the multifactor mechanism was established. The structural defect area at the boundary of the inclusions acted as the anodic phase where corrosion occurs preferentially, and the CaS of the inclusion underwent a chemical dissolution process. TiN, TiS2 and TiO2 were gradually shed, and the MgO, Al2O3 and CaO inside the local corrosion area were not completely shed. The gap defect of inclusion was the preferred condition to induce local corrosion when the matrix contains galvanic corrosion effect, dislocation region and the gap defect, and the process of anodic dissolution occurred in the dislocation region. There was no gap defect, the environment could not completely provide the driving force for local corrosion, and the possibility of non-local corrosion existed. The existence of gap defect provided the condition for the existence of solution, and provided the double layer contribution of potential difference of inclusion/matrix and solution.

The initial micro-galvanic corrosion behavior of Mg‒30wt%Ca alloy only containing Mg2Ca and α-Mg was studied by immersion testing in a 0.9% NaCl solution at 37 °C. The quasi-in situ SEM and TEM results show that Mg2Ca corroded easier than α-Mg, indicating that Mg2Ca acted as an anode. The work function (Φ) for Mg2Ca calculated by first-principles is significantly lower compared to that for α-Mg. The Volta potential measured by a scanning Kelvin probe force microscope reveals that the Mg2Ca had a relatively low Volta potential (ψ) value. The lower Φ and ψ values for Mg2Ca indicate a lower electrochemical nobility, which is consistent with the experimental phenomenon.

The localized corrosion behavior of different inclusions in a simulated solution of coastal industrial pollution is investigated in this study. It is indicated in the results that the Al2O3–MnS composite inclusions of ordinary carbon Q345B steel have microcracks and induce severe lattice distortions in the surrounding matrix. The MnS in the Al2O3–MnS composite inclusions dissolves preferentially to induce pitting corrosion. The microcracks and severe lattice distortion of the surrounding matrix accelerate the corrosion propagation. The preferential dissolution of CeAlO3–Ce2O2S inclusions induces pitting in No. 2 steel. The inherent physical and chemical properties of the inclusions and the chemical corrosion of the simulated fluid are vital in the initiation and expansion of pitting corrosion. The TiN in the test steel exhibits excellent resistance to pitting corrosion, and the double‐layer composite inclusions completely covered by TiN do not form corrosion pits in the simulated solution and do not cause the dissolution of the adjacent matrix. The coordinated addition of Ti–Ce can reduce the size of the inclusions and improve the probability of complete cladding of TiN. [ABSTRACT FROM AUTHOR]

The initial micro-galvanic corrosion behavior of Mg‒30wt%Ca alloy only containing Mg 2 Ca and α-Mg was studied by immersion testing in a 0.9% NaCl solution at 37 °C. The quasi-in situ SEM and TEM results show that Mg 2 Ca corroded easier than α-Mg, indicating that Mg 2 Ca acted as an anode. The work function (Φ) for Mg 2 Ca calculated by first-principles is significantly lower compared to that for α-Mg. The Volta potential measured by a scanning Kelvin probe force microscope reveals that the Mg 2 Ca had a relatively low Volta potential (ψ) value. The lower Φ and ψ values for Mg 2 Ca indicate a lower electrochemical nobility, which is consistent with the experimental phenomenon. [ABSTRACT FROM AUTHOR]

A scanning Kelvin probe (SKP) was used to study corrosion of X52 pipeline steel under a CO2-containing solution droplet simulating the water condensate generated in interior of wet gas pipelines. The Volta potential measured by SKP was indicative of the feature of corrosion occurring under the droplet. Three potential zones were observed from the droplet center towards the transition and the side of the droplet, which were -0.1 V, -0.4 V and 0.1 V (Kelvin probe, kp), respectively, after 4 h of testing. The droplet side had the highest Volta potential, which was attributed to corrosion scale generation and precipitation due to a limited solution volume and achieved solubility limit of FeCO3 scale. The transition zone possessed the most negative Volta potential due to a higher corrosion activity than the droplet center with more supply and dissolution of CO2, while the droplet center had the thickest solution. The SKP measurements could estimate the volume evolution of the solution droplet with time at a relatively accurate scale. The solution droplet could maintain its topographic feature, i.e., a spherical cap shape, within 4 h of testing in this work. The increase in droplet concentration due to solution evaporation during testing affected the Volta potential, but slightly only.

Corrosion of duplex stainless steels (DSS) usually initiates at a specific phase, causing preferential phase-dissolution in aqueous environments. Although the scanning Kelvin probe force microscopy (SKPFM) can characterise the phase-corrosion at a micro- or even nanoscale, conventional data-processing methods are insufficient to analyse massive data to derive mechanistic information, and sometimes, even cause a misunderstanding of corrosion evolution. Here we utilised root mean square, power spectral density and fractal evaluations to analyse the time-dependent topographic and Volta potential results obtained by SKPFM during corrosion progression of 2205 DSS in a chloride solution. Corrosion of the DSS preferentially occurs in the ferrite phase and at the ferrite/austenite boundaries in the initial stage. The corrosion changes from the initial galvanic mechanism to mass transfer control with increased time. By using proper numerical tools, the Volta potential results are more insightful of analysing corrosion than the topographic profiles. [ABSTRACT FROM AUTHOR]

The mechanism of step-like corrosion pit induced by TiN inclusion in Ti-stabilized interstitial free steel was systematically investigated. There was neither micro-crevice nor local stress in the steel matrix adjacent to the TiN inclusion, but a significant Volta potential difference was detected between the conductive TiN and steel matrix. The corrosion pits induced by the TiN inclusion had a step-like structure, composed of an inner pit and a shallow ring-like corroded region (RCR). Three stages, initiation, transition, and propagation stages, involved in the formation of the step-like corrosion pits were observed. The three stages were manifested with the initiation of inner pit, the deepening of inner pit, and RCR formation, respectively. The inner pit was triggered by the Volta potential difference in the initiation stage. In the transition stage, the extreme gradients of H+ and Cl− occurred through the hydrolysis of Fe2+ and electromigration of Cl− in the deepening inner pit. Finally, the extreme gradients of aggressive ions between the inner pit and NaCl bulk solution resulted in the formation of RCR surrounding the inner pit in the propagation stage.

The limited wide applicability of commercial Mg alloys is mainly attributed to the poor corrosion resistance. Addition of alloying elements is the simplest and effective method to improve the corrosion properties. Based on the low-cost alloy composition design, the corrosion behavior of commercial Mg-3Al-1Zn (AZ31) alloy bearing minor Ca or Sn element was characterized by scanning Kelvin probe force microscopy, hydrogen evolution, electrochemical measurements, and corrosion morphology analysis. Results revealed that the potential difference of Al2Ca/α-Mg and Mg2Sn/α-Mg was (230 ± 19) mV and (80 ± 6) mV, respectively, much lower than that of Al8Mn5/α-Mg (430 ± 31) mV in AZ31 alloy, which illustrated that AZ31-0.2Sn alloy performed the best corrosion resistance, followed by AZ31-0.2Ca, while AZ31 alloy exhibited the worst corrosion resistance. Moreover, Sn dissolved into matrix obviously increased the potential of α-Mg and participated in the formation of dense SnO2 film at the interface of matrix, while Ca element was enriched in the corrosion product layer, resulting in the corrosion product layer of AZ31-0.2Ca/Sn alloys more compact, stable, and protective than AZ31 alloy. Therefore, AZ31 alloy bearing 0.2wt% Ca or Sn element exhibited excellent balanced properties, which is potential to be applied in commercial more comprehensively. [ABSTRACT FROM AUTHOR]

Electrochemical corrosion thermodynamics of an X52 pipeline steel under plastic stresses was studied by measurements of corrosion potential and Volta potential with a scanning Kelvin probe in an anaerobic near-neutral pH and an aerobic high pH corrosive environments, where the steel was under active dissolution and passivity, respectively. The stress-corrosion thermodynamics of the stressed steel in both environments was studied by Volta potential measurements. While the corrosion potential shifts negatively due to a stress-enhanced corrosion activity in both solutions, the shift of Volta potential is more indicative of the corrosion thermodynamics under identical stresses. Volta potential measurements provide a more promising method than corrosion potential to indicate the stress corrosion thermodynamics of the steel. The relationships between Volta potential and corrosion potential in both active and passive solutions deviate from linearity in the presence of stress. However, the difference between the two potentials increases linearly with stress. [ABSTRACT FROM AUTHOR]

Oils and iron fines deposit on carbon steel during cold rolling and are removed by an electrolytic cleaning line (ECL). Sometimes localized contamination is observed on the ECL samples. No reliable tests are available for on-line measurement and the off-line tests demand samples with a large surface area. SKP addresses this issue effectively. SKP shows ∼390 mV potential difference between the clean and the uncleaned surface, with the cleaned surface potential being more positive. This indicates that the oil on the steel acts as a Lewis base, whereas the steel surface acts as a Lewis acid. Hence, the potential of the sample increases after cleaning. FTIR confirmed the absence of oil peaks on the cleaned samples. Deposition of an optimum thickness of the silicate layer is another important aspect of the ECL. It was measured by AES which displayed 2.3 nm of the silicate layer deposited on the cleaned steel surface. [ABSTRACT FROM AUTHOR]

The results of a systematic study on the adsorption of polylysine molecules of different lengths on the surface of a 1,2-dimyristoyl-sn-glycero-3-phospho-L-serine (DMPS) monolayer in the liquid (LE) and condensed (LC) states are presented. A compressibility diagram and the Volta potential were recorded with the Langmuir monolayer technique and further analyzed with the empirical approach. The structure of the monolayer films with adsorbed polypeptides was studied with synchrotron X-ray reflectometry. Two- and three-layer slab models describe the reflectivity data fairly well and reveal both the significant structural changes and the dehydration of the polar groups induced by all polylysines used at the maximal coverage of the monolayer interface in both the LE and LC states. On the one hand, in the LE phase of the monolayer (area per molecule A ≅ 70 Ǻ2), the integrated electron density of the lipid headgroup region is approximately half the density contained in the clean monolayer. This indicates both significant compaction and dehydration in the polar groups of the lipids, caused by the adsorption of polypeptides. On the other hand, in the LC state (A ≅ 40 Ǻ2), the degree of the hydration of the polar region is similar to that for the initial DMPS monolayer. However, both the electron density and the thickness of the head group region differ significantly from the values of these parameters for the clean monolayer in the LC state.

The corrosion behavior of 5.5%Cr–8.5%Cr steels in a CO2 environment was studied. To clarify the effect of Volta potential on uniform corrosion and pitting corrosion, weight loss test, electrochemical measurement, scanning electron microscope, energy dispersive spectrometer, confocal laser scanning microscope, and scanning Kelvin probe force microscope were conducted. The results show that there is a linear relationship between the surface potential of the steel substrate and the self‐corrosion potential. The increase of the Cr content reduces the surface potential and increases the self‐corrosion potential, reducing the thermodynamic tendency of corrosion. The Al‐oxide inclusions show lower potential than the substrate, and their sensitivity to pitting corrosion is affected by the potential difference with the substrate. The larger the potential difference, the easier it is tantamount to induce pitting corrosion. [ABSTRACT FROM AUTHOR]

The atmospheric corrosion of a metal under a thin electrolyte layer is caused due to the adsorption of the thin electrolyte layer on metal surfaces. As the electrolyte layer is considerably thin, the application of a traditional three-electrode system is considerably difficult; therefore, localized electrochemical technologies are of great use in this field. Herein, different localized electrochemical techniques for atmospheric corrosion under a thin liquid film were discussed. In particular, the applications of scanning Kelvin probe microscopy, wire-beam electrodes, and micro-droplet electrodes were introduced and comprehensively explained. In addition, the key parameters of the tests, which show the relation between thin film/droplet size and corrosion kinetics, were summarized. Furthermore, the issues that currently exist in this field and the potential for improvement was proposed in this research.

The variation rule of the Volta potential on deformed copper surfaces with the dislocation density is determined in this study by using electron back-scattered diffraction (EBSD) in conjunction with scanning Kelvin probe force microscopy (SKPFM). The results show that the Volta potential is not linear in the dislocation density. When the dislocation density increases due to the deformation of pure copper, the Volta potential tends to a physical limit. The Volta potential exhibits a fractional function relationship with the dislocation density only for a relatively low shape variable.

General corrosion rates and inhibition efficiencies (obtained from weight loss measurements) of samples with different surface roughness after immersion for different time in 3 wt. % NaCl solution with various concentrations of inhibitor at 333 K (the scatter band in the Figure was standard deviation). The results exhibited that surface roughness had no effect on corrosion rates of samples in the absence of inhibitor. However, the corrosion rates and inhibition efficiencies for samples with different surface roughness were distinct in solutions with inhibitor. However, when the samples were simultaneously immersed in the solution with 1.22 × 10−5 mol/l inhibitor for 1 h, the inhibition efficiencies for samples with rougher surface and smoother surface were 43.1% and 91.8%, respectively. When the samples with different surface roughness were simultaneously immersed in the solution with 1.22 × 10−4 mol/l inhibitor for 240 h, the rougher samples had a larger corrosion rate, and the inhibition efficiencies for rougher samples and smoother samples were 98.8% and 99.4%, respectively. • Surface roughness had an effect on the corrosion of X70 steel with inhibitor. • Samples with smoother surface showed higher inhibition efficiencies. • Fe-inhibitor complex on the smoother surfaces were more ordered. • Smoother surface with higher EWF was more attractive to react with the inhibitor. Effect of surface roughness on the inhibition behavior of X70 steel corrosion in CO 2 -saturated brine by a thioureido imidozaline inhibitor was investigated. Results showed that samples with different surface roughness had the same corrosion rate/corrosion current density in the absence of inhibitor. However, the inhibition efficiencies for samples with different surface roughness were distinct in the presence of inhibitor, and smoother samples exhibited higher inhibition efficiencies. Smoother surface with a higher electron work function was more attractive to react with the inhibitor molecules and then formed a more protective inhibitor film, compared to rougher surface. [ABSTRACT FROM AUTHOR]

The Volta potential is an electron-sensitive parameter and describes the thermodynamic propensity of a metal to take part in electrochemical reactions. It has found widespread acceptance among corrosion researchers due to its connection to the corrosion potential and its easy measurability in local scale, being often used to study localised corrosion phenomena and micro-galvanic activities. The principle object of this paper is to provide a comprehensive, fundamental insight into the meaning of the Volta potential and to define a polarity convention of measured potentials by the scanning Kelvin probe force microscopy (SKPFM) in order to assess local nobilities in microstructures. Conditions to relate the Volta potential with the mixed-potential theory are discussed and a possible connection to corrosion phenomena explained. The limitations of the Volta potential as well as the SKPFM technique are also aimed to be explained, with some practical information to maximise the output of high quality data. [ABSTRACT FROM AUTHOR]

Abstract A significant enhancement in corrosion resistance by Y microalloying was achieved for the Mg–8Sn–1Zn–1Al (wt%) alloy in the extruded condition. Average corrosion rates obtained by immersion tests in 0.6 M NaCl solution at 25 °C were 4.2 and 12.7 mm y−1 for the alloys with and without microalloying with 0.04 wt% Y, respectively. Microstructural investigations indicated that the enhanced corrosion resistance is a result of a transition in a type of second-phase particles toward lowering the difference in electrochemical nobility between the α-Mg and these particles, thereby reducing the susceptibility of the alloy to microgalvanic corrosion. Graphical abstract Unlabelled Image [ABSTRACT FROM AUTHOR]

Abstract As a promising candidate for wearable power sources, it is essential to explore new-type of triboelectric nanogenerator (TENG) to further enhance the output power under realistic environments. Here, we report a new-type of sliding-mode TENG with its potential enhanced through direct metal-to-metal contact with a ground connection. When the positively charged Al layer contacts the grounded Al, the electron flow is promoted to the ground by a large potential difference between the two metals. This induces the charge transfer between bottom electrodes, enhancing the electric potential, confirmed by COMSOL simulations. This new-type of TENG generates a maximum power of 0.13 W under a low frequency of 3 Hz on an external load of 1 MΩ, corresponding to energy conversion efficiency of approximately 22.2%. Performance of the working-mode are also systematically investigated in free-rotating disk-type and patch-type TENGs, which offered a lot of convenience and feasibility for energy harvesting from the wearable energy sources. Graphical abstract fx1 Highlights • TENG with the direct metal-to-metal contact with the ground connection is reported. • The key feature of the TENG is that the bottom plate is composed of three parts. • This TENG could deliver a maximum power of 0.13 W under a low frequency of 3 Hz. • Free-rotating disk-type TENG generated an output power of 6.1 mW at 1000 rpm. • The patch-type TENG effectively generated an output under the bidirectional motion. [ABSTRACT FROM AUTHOR]

Volta potential of a material can be easily determined by using scanning Kelvin probe (SKP), but up to now there is no standard method established. This study focuses on finding an alternative or even a standard material for SKP probes. Re, Ni, and Mo are analyzed regarding their suitability for serving as tips in SKP measurements. For comparison purposes, a commonly used NiCr probe is analyzed too. Linearity, the sensitivity to humidity changes as well as the lateral and Volta potential resolution are determined for various probe materials. Linearity is excellent for all tested probes. SKP measurements carried out under humidity variations shows dissimilar results for all different metal probes. Lateral and Volta potential resolution are the best for Re and Ni tips. There may be a correlation between the work function of a material and its suitability for serving as a probe in Kelvin measurements − the higher the work function, the better the resolution of Volta potentials. Based on the results, it can be concluded that pure Re and Ni are more suitable for serving as SKP probes than NiCr alloy. [ABSTRACT FROM AUTHOR]

The effects of austenite spacing, hydrogen charging, and applied tensile strain on the local Volta potential evolution and micro-deformation behaviour of grade 2507 (UNS S32750) super duplex stainless steel were studied. A novel in-situ methodological approach using Digital Image Correlation (DIC) and Scanning Kelvin Probe Force Microscopy (SKPFM) was employed. The microstructure with small austenite spacing showed load partitioning of tensile micro-strains to the austenite during elastic loading, with the ferrite then taking up most tensile strain at large plastic deformation. The opposite trend was seen when the microstructure was pre-charged with hydrogen, with more intense strain localisation formed due to local hydrogen hardening. The hydrogen-charged microstructure with large austenite spacing showed a contrasting micro-mechanical response, resulting in heterogeneous strain localisation with high strain intensities in both phases in the elastic regime. The austenite was hydrogen-hardened, whereas the ferrite became more strain-hardened. SKPFM measured Volta potentials revealed the development of local cathodic sites in the ferrite associated with hydrogen damage (blister), with anodic sites related to trapped hydrogen and/or micro voids in the microstructure with small austenite spacing. Discrete cathodic sites with large Volta potential variations across the ferrite were seen in the coarse-grained microstructure, indicating enhanced susceptibility to micro-galvanic activity. Microstructures with large austenite spacing were more susceptible to hydrogen embrittlement, related to the development of tensile strains in the ferrite. [ABSTRACT FROM AUTHOR]

In this work, first-principle density functional theory (DFT) was used to calculate the work function and Volta potential differences between aluminum alloy matrix and two intermetallic phases (Mg2Si and Al2Cu) with varying surface terminations as a function of adhering monolayers (ML) of water. The calculated data were compared with experimental local Volta potential data obtained by the scanning Kelvin probe force microscopy (SKPFM) on a commercial aluminum alloy AA6063-T5 in atmospheric environments with varying relative humidity (RH). The calculations suggest that the surface termination has a major effect on the magnitude and polarity of the Volta potential of both intermetallic phases (IMP’s). The Volta potential difference between the IMP’s and the aluminum matrix decreases when the surface is gradually covered by water molecules, and may further change as a function of adhering ML’s of water. This can lead to nobility inversions of the IMP’s relative to the aluminum matrix. The measured Volta potential difference between both IMP’s and their neighboring matrix is dependent on RH. Natural oxidation in ambient indoor air for 2 months led to a nobility inversion of the IMP’s with respect to the aluminum matrix, with the intermetallics showing anodic nature already in dry condition. The anodic nature of Al2Cu remained with the introduction of RH, whereas Mg2Si became cathodic at high RH, presumably due to de-alloying of Mg and oxide dissolution. The DFT calculations predicted an anodic character of both IMP’s in reference to the oxidized aluminum matrix, being in good agreement with the SKPFM data. The DFT and SKPFM data were discussed in light of understanding localized corrosion of aluminum alloys under conditions akin to atmospheric exposure. [ABSTRACT FROM AUTHOR]

In this study, a combination of scanning tunneling microscopy (STM), scanning tunneling spectroscopy (STS), atomic force microscopy (AFM), scanning Kelvin probe force microscopy (SKPFM), and density functional theory is applied to investigate the evolution of Volta potential and electronic properties of TiO 2 /Cu 2 O coupled oxides in presence of chloride-containing corrosive solution. Volta potential and the band gap of Cu 2 O are increased in presence of chloride ion due to paratacamite (Cu 2 (OH) 3 Cl) formation whereas the opposite is seen for TiO 2 due to the formation of H 4 TiO 4 . The results shows a good correlation between the measured Volta potential difference and the observed corrosion behavior. [ABSTRACT FROM AUTHOR]

CO 2 corrosion behavior of carbon steel with different microstructures (H steel: coarse laminar pearlite; T steel: globular and shot rod shaped pearlite) was analyzed in 3 wt.% NaCl solution at 60 °C with imidazoline-based inhibitor by electrochemical and weight loss methods. Electrochemical measurements showed that, compared to H steel, the inhibitor film adsorbed on T steel had a higher pitting corrosion resistance and the inhibition efficiency for T steel was larger at each concentration of inhibitor. Weight loss results exhibited that both steels suffered general corrosion in absence of inhibitor; however, localized corrosion was observed on the samples with insufficient concentration of inhibitor. H steel suffered more severe localized corrosion than T steel, it was related to that H steel had a higher density of dislocations in the pearlite area and the larger driving force for galvanic corrosion. The localized corrosion on H steel mainly distributed on the laminar pearlite area. [ABSTRACT FROM AUTHOR]

In this paper, Kelvin method is introduced, which can be utilized to measure a contact potential difference between two dissimilar metals. The basic principle of the Kelvin method for measuring contact potential differences is described. Some measured results in some corrosion systems are also explained. [ABSTRACT FROM AUTHOR]

Localized attack can negatively affect the mechanical properties and durability of high strength low alloy steels. The present work investigates the effect of inclusions on the susceptibility to pitting attack of 42CrMo4 QT steel (quenched and tempered condition). A detailed characterization of the microstructure of the steel was performed by field emission scanning electron microscopy and energy dispersive X-ray spectroscopy in order to evaluate the morphology and chemical composition of the inclusions. The initiation of pitting corrosion at the inclusion sites was investigated with a localized approach combining topographic and surface potential maps obtained by means of the scanning Kelvin probe force microscopy technique and the morphology of inclusion sites after the immersion in an aggressive electrolyte. The effect of different inclusion types (clusters combining Al 2 O 3 and MnS and containing Ca and Mg or single MnS based inclusions) is discussed in the present work taking into account their galvanic coupling with the surrounding steel matrix and the existence of gaps at the periphery of the inclusions promoting the formation of an occluded cell. [ABSTRACT FROM AUTHOR]

The effect of Sn content on the mechanical properties and corrosion behavior of Mg-3Al-xSn alloys was investigated by SEM-EDXS, XRD, electrochemical measurements, and scanning Kelvin probe force microscopy (SKPFM). The results showed that when the Sn content was 1.4 wt%, Sn dissolved in the α -Mg matrix and then precipitated as an intermetallic compound (Mg _2 Sn). The combined results of mass loss, hydrogen evolution, and electrochemical measurements indicated that Mg-3Al-1Sn had a low corrosion rate. The SKPFM results showed that the Volta potential of Mg _2 Sn particles, Al-Mn, and β -Mg _17 Al _12 phases were 100, 80, and 50 mV higher than the matrix, respectively. Therefore, the Mg _2 Sn phase that formed in Mg-3Al-xSn served as a local cathode due to its high potential, which accelerated microgalvanic corrosion along with the secondary local cathode (Al-Mn). The Sn solution strengthening and secondary phase strengthening (fine Mg _2 Sn particles) improved the mechanical properties of the Mg-3Al-xSn alloys.

Microstructure and corrosion behaviour of a Mg-9Al alloy with minor alloying additions (Mn, Y, Nd, Ca and Sn) are evaluated. All of the additions form Al-rich intermetallics with varying amounts of Fe, while Ca and Sn are also incorporated into the eutectic β-phase (β-Mg 17 Al 12 ). Special attention is given to the surface potential values of the microconstituents, which are related to the formation of microgalvanic couples. Scanning Kelvin Probe Force Microscopy (SKPFM) measurements revealed that all the alloying elements, except Sn, reduced the potential difference between the secondary phases and the matrix, which is the main reason for the improvement of the corrosion resistance of Mn-, Y- and Nd-modified alloys. The beneficial effect of Ca is additionally related to the microstructure refinement and an increased area fraction of the β-phase. [ABSTRACT FROM AUTHOR]

The morphology and elemental composition of cross sections of eight historic copper materials have been explored. The materials were taken from copper roofs installed in different middle and northern European environments from the 16th to the 19th century. All copper substrates contain inclusions of varying size, number and composition, reflecting different copper ores and production methods. The largest inclusions have a size of up to 40 μm, with most inclusions in the size ranging between 2 and 10 μm. The most common element in the inclusions is O, followed by Pb, Sb and As. Minor elements include Ni, Sn and Fe. All historic patinas exhibit quite fragmentized bilayer structures, with a thin inner layer of cuprite (Cu2O) and a thicker outer one consisting mainly of brochantite (Cu4SO4(OH)6). The extent of patina fragmentation seems to depend on the size of the inclusions, rather than on their number and elemental composition. The larger inclusions are electrochemically nobler than the surrounding copper matrix. This creates micro-galvanic effects resulting both in a profound influence on the homogeneity and morphology of historic copper patinas and in a significantly increased ratio of the thicknesses of the brochantite and cuprite layers. The results suggest that copper patinas formed during different centuries exhibit variations in uniformity and corrosion protection ability. [ABSTRACT FROM AUTHOR]