Corrosion Resistance In Aqueous Solutions Research Articles

Potential Dependent Mn Oxidation and Its Role in Passivation of Ni38Fe20Cr22Mn10Co10 Multi-Principal Element Alloy Using Multi-Element Resolved Atomic Emission Spectroelectrochemistry

The identity of passivating oxides on multi-principal element alloys is of great interest as their optimization offers the potential for exceptional corrosion resistance in aqueous solutions over a broad range of potential and pH. This study focuses on a non-equiatomic Ni38Fe20Cr22Mn10Co10 solid solution alloy and tracks the fate of each alloying element during linear sweep voltammetry, low and intermediate potential holds in the passive potential domain as well as during open circuit relaxation after anodic polarization in slightly acidified Cl− solution. Ni dissolves at all potentials investigated in this work, Fe and Co are incorporated into oxides or hydroxides in low concentrations whilst Cr and Mn are enriched at passive potentials. At low passivating potentials, Mn(II) dissolves and is incorporated in minor amounts in oxides containing large concentrations of Cr(III). Considerable enrichment in Mn(II)-species occurs relative to Cr(III) in the oxide at 0.1 V vs SCE. Electrochemical impedance spectroscopy suggests the presence of layered oxides with marginal passivation at high Mn(II) levels. The formation of these oxides depends on a combination of thermodynamic and kinetic factors as well as the sequence of passivation.

Junction Electrochemistry of InGaN Anode Materials in Solar Energy Conversion

The indium gallium nitride (InGaN) ternary alloy system offers an ideal semiconductor basis as a light absorber for driving chemical reactions such as the oxygen evolution reaction (OER) and hydrogen evolution reaction (HER). It is a direct bandgap semiconductor whose energy can be tuned for optimal solar absorption and overcoming kinetic overpotential losses, it can be grown epitaxially as a single crystal for high material quality, and it exhibits relatively high corrosion resistance in aqueous solutions for a III-V material. In this work, we report on the design, synthesis, and photoelectrochemical studies of InGaN in an anode configuration with a goal of using this material as a light absorber basis for driving solar fuels reactions such as the OER and the HER. Studies are shown reporting on how reactive vapor synthesis of GaN and InN with different structuring affects the light conversion properties and band diagram electrostatics in an electrochemical junction with ferrocene and cobaltocene redox pairs. This structure is extended to thin films of GaN and InGaN grown by molecular beam epitaxy for high efficiency light conversion, with the resulting electrochemical junction also made with ferrocene and cobaltocene. The effects of ternary alloying, doping, and the two different c-plane polarities (III-polar and V-polar) on the junction are investigated using the same electrochemical junction to evaluate the light conversion properties in relation to the electrostatics; specifically, tuning the bandgap energy for optimal light absorption, determining the c-plane polarity configuration for the electric fields to have the correct band alignment, and incorporating silicon doping to create a conductive substrate. The combination of these engineering techniques extends the depletion region of the active layer for high efficiency light absorption as similarly demonstrated for epitaxial phosphide films [1], and is utilized toward the goal of high performance solar energy conversion. [1] V. Parameshwaran, X. Xu, and B. Clemens, Journal of the Electrochemical Society, vol. 163, no. 8, pg. H714-H721 (2016).

MnO2조촉매가 코팅된 GaN 광전극의 광전기화학적 특성

수소를 생산하는 방법 중 하나로, 광전기화학적(photoelectrochemical; PEC) 물 분해 시스템은 높은 이론적 효율을 가진 친환경적이고 경제적인 방법이다. 광전극으로서 질화갈륨(gallium nitride; GaN)은 내화학성이 좋고 밴드갭이 물의 산화환원준위(<TEX>$V_{redox}=1.23$</TEX> V vs. SHE)를 포함하여 외부 전압 없이 수소를 생산할 수 있는 시스템을 구축할 수 있다. 그러나 이때 발생하는 높은 산소 발생 과전압은 시스템의 반응 효율을 저하시킨다. 산소 발생 과전압을 줄이기 위한 방법으로 광전극에 조촉매를 이용하는 방법이 많이 알려져 있다. 본 연구에서는 GaN 광전극에 입자 형태의 이산화망간(manganese dioxide; <TEX>$MnO_2$</TEX>)을 조촉매로 도입하여 PEC 시스템의 특성을 분석하고자 한다. <TEX>$MnO_2$</TEX>가 광전극에 잘 형성되었는지를 확인하기 위하여 표면분석을 수행하였고, potentiostat(PARSTAT4000)을 이용해 PEC 특성을 분석해 평가하였다. <TEX>$MnO_2$</TEX>가 코팅됨에 따라 flat-band potential(<TEX>$V_{fb}$</TEX>)과 onset voltage(<TEX>$V_{onset}$</TEX>)가 각각 음의 방향으로 0.195 V, 0.116 V 이동하는 것이 확인되었다. 광전류밀도 값에 대해서도 <TEX>$MnO_2$</TEX> 코팅 샘플이 더 높게 나타나며, 시간에 따른 광전류의 저하도 개선되었다. 이로부터 <TEX>$MnO_2$</TEX>이 조촉매로서 효과가 있음을 확인하였고, PEC 시스템 전반에 걸쳐 효율 향상에 기여할 수 있을 것으로 기대된다. Recently, hydrogen is regarded as important energy in the future, because it is clean and renewable. The photoelectrochemical (PEC) system, which produce hydrogen using water splitting by solar energy, is one of the most promising energy systems because it has abundant energy sources and good theoretical efficiency. GaN has recently been regarded as suitable photoelectrode that could be used to split water to generate hydrogen without extra bias because its band edge position include water redox potential (<TEX>$V_{redox}=1.23$</TEX> vs. SHE). GaN also shows considerable corrosion resistance in aqueous solutions and it is possible to control its properties, such as structure, band gap, and catalyst characteristics, in order to improve solar energy conversion efficiency. But, even if the band edge position of GaN make PEC reaction facilitate without bias, the overpotential of oxygen evolution reaction could reduce the efficiency of system. One of the ways to decrease overpotential is introduction of co-catalyst on photoelectrode. In this paper, we will investigate the effect of manganese dioxide (<TEX>$MnO_2$</TEX>) as a co-catalyst. <TEX>$MnO_2$</TEX> particles were dispersed on GaN photoelectrode by spincoater and analyzed properties of the PEC system using potentiostat (PARSTAT4000). After coating <TEX>$MnO_2$</TEX>, the flat-band potential (<TEX>$V_{fb}$</TEX>) and the onset voltage (<TEX>$V_{onset}$</TEX>) were moved negatively by 0.195 V and 0.116 V, respectively. The photocurrent density increased on <TEX>$MnO_2$</TEX> coated sample and time dependence was also improved. These results showed <TEX>$MnO_2$</TEX> has an effect as a co-catalyst and it would enhance the efficiency of overall PEC system.

A Comparison Between Hybrid Functional, GW Approach and the Bethe Salpether Equation: Optical Properties of High Pressure Phases of TiO&lt;SUB&gt;2&lt;/SUB&gt;

Titanium dioxide has good corrosion resistance in aqueous solutions and is a good candidate for photoelectrodes. The limitation of the anatase phase of TiO2 is its large band gap. High pressure pha ...

Structure and Resistance to Electrochemical Corrosion of NiTi Alloy

The NiTi alloy (50.6 at.% Ni) passivated for 30 min at 130°C by autoclaving has been studied towards corrosion resistance in aqueous solutions of 3% NaCl, 0.1 M H2SO4, 1 M H2SO4 and HBSS. Structure and thickness of the passive layer (TiO2, rutile) were examined by X-ray reflectivity method and high resolution electron microscopy. Corrosion behavior of this oxide layer was investigated by open circuit potential method and polarization curves. It was found that the corrosion resistance of the passivated NiTi alloy is strongly dependent on the type of corrosive environment. The higher corrosion resistance of the tested samples was revealed in sulfate solutions as compared to chloride ones. The highest resistance to electrochemical corrosion of the NiTi alloy was observed in 0.1 M H2SO4 solution. Susceptibility to pitting corrosion of the tested samples was observed which increased with the concentration rise of chlorine anions in solution. Electrochemical tests for 316L stainless steel carried out under the same experimental conditions revealed a weaker corrosion resistance in all solutions as compared to the highly corrosion resistant NiTi alloy.

Investigation of structural, tribological and corrosion properties of electroless Ni–B coating deposited on 316L stainless steel

The AISI 316L type of stainless steel is a popular steel material, as it has excellent corrosion resistance in aqueous solutions at ambient temperatures. However, the application of the AISI 316L stainless steel is limited by its relatively low hardness and low wear resistance. In this study, the electroless Ni–B coating was deposited on the AISI 316L stainless steel, and its structural, tribological and corrosion properties were characterised. Microstructural analysis showed that the electroless Ni–B coating deposited on the AISI 316L steel substrate exhibited a typical cauliflower-like structure exhibits an amorphous growth. From this study, it may be concluded that this process cannot only improve the hardness and wear resistance of the 316L stainless steel, but can also provide cathodic protection without losing or sacrificing the original properties of the 316L stainless steel.

Structure and corrosion behavior of iron-based metallic glass coatings prepared by LPPS

Low pressure plasma spraying (LPPS) has been used to prepare coatings from the spraying powders of FeCrMoWSiBC at different hydrogen flow rates. X-ray diffraction (XRD), differential scanning calorimetry (DSC) and scanning electron microscopy (SEM) were used to study the microstructural characteristics of the spraying powders and as-sprayed coatings. Vickers hardness tester was used to measure the hardness of spraying powders and coatings. At the same time, the corrosion behavior of coatings was evaluated by potentiodynamic polarization test and immersion test. Along with the increase of hydrogen flow rate, the denseness of the as-sprayed coatings increases. Amorphous coatings were obtained at the hydrogen flow rates of 4 and 6Lmin−1, while partial crystallized coating was obtained at hydrogen flow rate of 8Lmin−1. In general, the as-sprayed coatings possess good corrosion resistance in aqueous solutions of 3.5% NaCl and 1N HCl. It is found that the denseness of coatings affects the corrosion resistance positively. Moreover, in this study, the partially crystallized coating shows better corrosion resistance than amorphous coatings. The partially crystallized coating even shows much higher hardness than amorphous coatings and spraying powders. This implies that such coating may find more promising application in engineering owing to desired corrosion resistance in association with good wear resistance.

ＷＣ‐Ｃｒ３Ｃ２‐Ｃｏ系超硬合金の腐食特性に及ぼすＣｏ含有量の影響

Though WC-Co cemented carbides are widely used for a variety of machining, drilling, metallic mold and other applications because of their high strength, high hardness and excellent wear resistance, their poor corrosion resistance in aqueous solutions reduces the scope of their application. In this experiment, three kinds of WC-Cr3C2-Co cemented carbides were used, and the influence of Co content on corrosion characteristics of them was investigated by the electrochemical methods such as the potenitodynamic polarization test and electrochemical impedance spectroscopy (EIS), and the observation by scanning electron microscopy (SEM). All of the three specimens showed the similar active, passive and over passive regions during the polarization test, though the passivation was retarded with increasing amount of Co content. EIS test indicated that all of the three samples had the similar capacitance semicircle in the first quadrant. After that, the second capacitance semicircle which involve a film formation following the first capacitance semicircle and the induction semicircle following the second capacitance semicircle were confirmed. From this EIS test result, it was confirmed that the charge transfer resistance (Rct) decreased with an increase in Co content.

Analytical characterization of the corrosion mechanisms of WC–Co by electrochemical methods and inductively coupled plasma mass spectroscopy

WC–Co hardmetals are used for their combined high hardness and toughness. However, their poor corrosion resistance in aqueous solutions reduces the spectrum of their application. The goal of this work was a systematic investigation of the corrosion mechanisms of the WC–Co composite with electrochemical methods and analytical chemistry solution analysis characterization. WC–Co, Co and WC samples were investigated by electrochemical impedance spectroscopy, potentiodynamic polarization and inductively coupled plasma mass spectroscopy (ICP-MS). Concerning the corrosion susceptibility, the solution pH dominates the effect of specific ions. In neutral and acidic solution, the corrosion process of WC–Co consists mainly of Co dissolution. WC dissolution becomes more significant at alkaline pH. Degradation is mainly the result of selective uniform dissolution of the phases (Co or WC) not of localized corrosion because of the poor passivating ability of Co (except in alkaline pH). Synergistic effects due to galvanic coupling between the Co binder and WC are accelerating Co dissolution and hindering WC dissolution in the hardmetals compared to the pure compounds. This although the Co binder phase contains W and C, making it more corrosion resistant than pure Co. A further influence of the locally separated anodic and cathodic reactions is that the cathodic reduction on WC induces local pH increase which causes chemical dissolution of WC detected only by ICP-MS.

Characterizing the microstructure and mechanical and electrochemical properties of novel ceramic/polymer sandwich structural coatings

In this study, a polymer bond layer was incorporated between the chemically bonded composite sol–gel coating (CB-CSG) and stainless steel substrate to form sandwich structure coatings for improving the coating's corrosion resistance in aqueous solutions. The low processing temperatures of CB-CSG coatings and a specified high temperature polymer (siloxane) make it possible to prepare polymer/CB-CSG composite coatings with an unusual combination of mechanical properties and corrosion resistance. Compared with non-polymer CB-CSG coatings, the ceramic/polymer sandwich coatings exhibit lower hardness and elastic modulus due to the infiltration of polymer into the CB-CSG ceramic coatings. However, the polymer layer of the sandwich structure coatings may remarkably reduce the residual stress in the coatings. Electrochemical characterization and salt spray tests indicate that the polymer layer is very efficient for improving the overall corrosion resistance.

Protective Properties of a Sol-Gel Coating on Zinc Coated Steel

Galvanised and galvannealed steels are widely used due to their good corrosion resistance in aqueous solutions. However, when additional protection is required, organic coatings, corrosion inhibitors or conversion coatings are used to improve their corrosion protection. In this work, sol-gel coating was used to improve the corrosion behaviour of these two materials. This paper analyses the final protective properties of a sol-gel coating prepared by basic catalysis and its dependence on the sintering temperature and time of treatment. The influence of the sintering conditions on the galvanised and galvannealed substrates is a decisive factor for the coating quality and for the barrier affect against the aggressive media. While heat treatment time is the controlling factor for the galvannealed steels, the temperature is determining in the case of the galvanised. Corrosion mechanisms for sol-gel galvanised steels did not changed with respect to the uncoated steel. However for galvannealed steel, after coating the mechanism is not purely cathodic.

Corrosion Behavior of a Superduplex Stainless Steel in Chloride Aqueous Solution

Super duplex stainless steels (SDSS) have been widely used as structural materials for chemical plants (especially in those engaged in phosphoric acid production), in the hydrometallurgy industries, and as materials for offshore applications due to their excellent corrosion resistance in chloride environments, compared with other commercial types of ferritic stainless steels. These alloys also possess superior weldability and better mechanical properties than austenitic stainless steels. However, due to their two-phase structure, the nature of which is very dependent on their composition and thermal history, the behavior of SDSS regarding localized corrosion appears difficult to predict, especially in chloride environments. To improve their final properties, the effect of the partition of the alloying elements between the two phases, and the composition and microstructure of each phase are the key to understanding the localized corrosion phenomena of SDSS. This paper concerns the effects of the SDSS microstructure and heat treatment on the SDSS corrosion resistance in aqueous solutions, containing different amounts of NaCl at room temperature.

Effect of Co and W on the corrosion behaviour of 1% Cr steel in flowing synthetic seawater

AbstractThe aqueous corrosion characteristics of 1% Cr‐steel alloyed with small amounts of Co and W in synthetic seawater was studied by using immersion weight‐loss tests, electrochemical corrosion tests (potentiodynamic tests and electrochemical impedance spectroscopy (EIS) measurements) and analytical techniques. 1% Cr steels containing Co or W from 0.2 to 0.4 wt.% showed higher corrosion resistance than the 1% Cr steel in the immersion and potentiodynamic tests. EIS measurements showed that the Nyquist plot presented one time constant. Furthermore, the Co‐ and W‐bearing steels present higher Rp values than the 1% Cr steel through all the test period. The better corrosion resistance of the Co‐and W‐bearing steels is attributed to the protectiveness of the surface layer. The corrosion products were examined using electron probe microanalysis (EPMA) and X‐ray photoelectron spectroscopy (XPS). The results of EPMA indicated that Cr was concentrated in the inner region of the rust layer, while Co and W were distributed all over the rust layer. XPS results showed that Co existed as a trivalent oxide in the rust layer and W in the rust appeared in the form of a WO4 compound. These compounds act as a factor for corrosion resistance in aqueous solutions.

WC系サーメット溶射材のNa_2SO_4水溶液下における腐食疲労(S14-1 溶射材の疲労,S14 金属材料の疲労特性と破壊機構)

WC thermally sprayed coating is widely used in industry for its high wear resistance properties. Unfortunately, WC-Co coatings are plagued by low corrosion resistance in aqueous solutions. In this study, first, two kinds of coatings (WC-12Co & WC-10Co-4Cr) were deposited on SS400 steel by high-velocity flame spraying. Second, fracture behavior was investigated through corrosion fatigue testing in a Na_2SO_4 aqueous solution (R=0∫=14Hz). Improvement of corrosion fatigue was also examined. COrrosion fatigue fractures were found to associated with corrosion pits formed at the interface between the coating and the substrate. Thermal spraying of Al-Zn as an undercoat between the WC thermally sprayed coatings and the substrate appears to be an efective method for improving corrosion fatigue strength.

ＷＣ系サーメット溶射した軟鋼の腐食疲労破壊挙動

WC-12Co thermally sprayed coating, formed by high velocity oxygen-fuel spraying, is widely used in industry for its high wear resistance properties. Unfortunately, WC-12Co coatings are plagued by low corrosion resistance in aqueous solutions. Previous studies have shown that adding Cr to the coating improves corrosion resistance, but the effect on corrosion fatigue fractures remains unknown.In this study, first, two kinds of coatings (WC-12Co & WC-10Co-4Cr) were deposited on SS400 steel by high-velocity flame spraying. Second, fracture behavior was investigated through corrosion fatigue testing in an Na2SO4 aqueous solution (R=0, f=14Hz). The cause of the corrosion fatigue fractures was found to be corrosion pits formed at the interface between the coating and the substrate. The corrosion fatigue life for WC-10Co-4Cr was longer than that for WC-12Co in low cyclic stress areas (stress amplitude σa<75MPa). This extended corrosion fatigue life is assumed to be due to decreased corrosion response, because the passivation film on the surface of the WC-10Co-4Cr coated materials was quickly restored, even after it had been mechanically broken.

Influence of Hydrogen in Iron and in Two Stainless Steels on Aqueous and Gaseous Corrosion

The influence of hydrogen in Fe, 301 stainless steel (SS 301), and Avesta 353MA on corrosion resistance in aqueous solutions was studied. The oxidation kinetics of uncoated and Pt-coated Fe was also investigated in at 500 and 700°C. Electrochemical and weight loss measurements were used to evaluate the corrosion resistance in aqueous solutions, and the high-temperature oxidation rate was determined by measuring the pressure decrease in a closed volume. Observations of a high dissolution rate of Fe and SS 301 in deionized water, as well as a high oxidation rate in can be explained by an increased metal cation transport in the oxide film induced by hydrogen in the metal. However, hydrogen up to a certain concentration in Avesta 353MA was found to increase the resistance to localized corrosion in chloride solution. Pt coating on Fe was found to decrease the oxidation rate and improve scale adherence. The presented results are discussed in view of recent findings of balanced metal cation and oxygen anion transport in protective metal oxides. © 2002 The Electrochemical Society. All rights reserved.

Corrosion Behavior of Thermally Sprayed WC Coating in Na&lt;SUB&gt;2&lt;/SUB&gt;SO&lt;SUB&gt;4&lt;/SUB&gt; Aqueous Solution

WC-Co thermally sprayed coating, formed by high velocity oxygen-fuel flame spraying, has had the problem of low corrosion resistance in aqueous solutions. Furthermore, much remains unknown regarding corrosion reactions on coating surfaces and the formation of passivation films. This study focused on changes of the corrosion surfaces of two thermally sprayed coatings, WC-12Co and WC-10Co-4Cr, with immersion time. The chemical composition of the corrosion surfaces was analyzed by electron spectroscopy, and the relation with passivation film stability is discussed. For WC-12Co, the thermally sprayed coating was immersed in Na 2 SO 4 solution. The W and Co components were dissolved by extended anodic reaction. Oxides of W and Co were then formed on the surface of the thermally sprayed coating. However, these oxides appeared to have little effect on the corrosion. Passivation film, which mainly consists of Cr 2 O 3 , was formed on the surface of WC-10Co-4Cr thermally sprayed coating immediately after immersion, and limited the dissolving of coating components into the aqueous solution. However, it is suspected that this film did not completely cover the entire coating surface. It is probably a thin porous film formed as islands.

Electrochemical polarization and passive film analysis of austenitic Fe–Mn–Al steels in aqueous solutions

The corrosion behaviour of the Fe–25Mn–5Al–0.15C alloy in different aqueous solutions of pH −0.8 to 15.3 and the corrosion protection mechanism induced by the presence of Al have been investigated by electrochemical measurements and AES/XPS analysis. The corrosion behaviour of Fe–25Mn–5Al steel has been compared with that of mild steel, cryogenic 9% Ni steel and 1Cr13 stainless steel. The addition of 25 wt.% Mn to mild steel is very detrimental to the corrosion resistance in aqueous solution. Fe–25Mn steel is difficult to passivate, even in such neutral aqueous electrolytes as 1 mol l −1 Na 2SO 4 solution. With increasing Al content of Fe–25Mn–Al steels, the aqueous corrosion resistance increase and the anodic polarization curves exhibit a stable passivation region in 1 mol l −1 Na 2SO 4, 50% HNO 3 and 10–50% NaOH solutions as Al content increases to about 5 wt.%, but it shows no passivation in either 10% HCl or 3.5% NaCl solution. The corrosion resistance of Fe–25Mn–5Al steel in the aqueous solutions tested is comparable to that of mild steel. The outermost surface and the main part of the passive film formed on the surface of Fe–25Mn–5Al steel in 30% NaOH solution are probably the bound water and a mixture of aluminium, iron and manganese oxides including metallic iron and aluminium, respectively.

Corrosion studies on aluminium reinforced with uncoated and coated carbon fibres

Knowing materials behaviour under conditions of electrochemical attack is an important necessity for engineering applications, especially in marine environments. The considerable deterioration of the electrochemical corrosion resistance which results from the reinforcement of aluminium with carbon fibres demands preventative measures. In order to retain usual life times of applications, suitable corrosion protection has to be implemented. The present study deals with an internal corrosion protection process resulting from the use of suitable fibre coatings, viz. a pyrolytic carbon (pyC) coating and a nickel fibre coating. However, neither the ceramic pyC coating nor the metallic nickel coating effect an improvement of the corrosion resistance in aqueous solutions of 3.5 wt% NaCl or 3.5 wt% Na 2SO 4. Although, the simple immersion test confirmed the lowest anodic matrix dissolution for metal-matrix composites (MMCs) formerly containing nickel-coated fibres, the polarisation of the MMCs to more positive potentials causes greatly accelerated electrochemical dissolution. Furthermore, the observed segregation of elemental nickel to the sample surface after the immersion tests in both electrolytes indicate additional susceptibility to galvanic coupling. MMCs reinforced with carbon fibres obtaining a pyrolytic carbon coating show evidence of strongly accelerated electrochemical corrosion. Because the microstructure and the surface area of the pyrolytic carbon differs from that of the carbon fibres, a probable reason for the enhanced corrosion susceptibility may be the higher reactivity of the pyC coating. This result stresses the importance of taking into account the features of the carbon of the reinforcing component and to distinguish between different carbon types. Special emphasis should be placed on the processing of pyC coatings in order to generate pyC coatings with few active sites and low reactivity.

Corrosion Protection of Copper by a Self‐Assembled Monolayer of Alkanethiol

A self‐assembled monolayer of 1‐dodecanethiol (DT) was formed on a copper surface pretreated using different methods. The corrosion protection abilities of the monolayer were evaluated in an air‐saturated 0.51 M NaCl solution using various techniques including electrochemical impedance spectroscopy, polarization, coulometry, weight loss, and x‐ray photoelectron spectroscopy. It was found that the corrosion resistance of the monolayer was improved markedly by using a nitric acid etching method. A minimum concentration of M DT was needed to form a protective monolayer. The DT‐monolayer retarded the reduction of dissolved oxygen and inhibited the growth of copper oxide in the NaCl solution. In comparison with other inhibitors, such as benzotriazole (BTA) and mercapto‐benzothiazole (MBT), the DT‐monolayer showed much better corrosion resistance in aqueous solution.