A Study of the Relation between Current Oscillations and Pitting

Anodic polarization behaviors of iron in pure H2SO4 and three mixed acidic solutions, H2SO4 NaCl，H2SO4 NaNO3 and H2SO4 NaCl NaNO3, were investigated. The potentiodynamie sweep curves showed that the current densities rose and dropped irregularly in H2SO4 NaCl solution at the more anodic potentials since the iron surface suffered pitting attack in the solution, but the pitting corrosion was inhibited effectively in the presence of nitrate ions. The surface morphological measurements indicated that pits appeared on the iron surface in H2SO4 NaCl solution and only a few unobvious corrosion spots were observed in H2SO4 NaCl NaNO3 sointian after the iron electrode was potentiostatically polarized at 1.3 V. The oscillatory properties of iron are associated with the susceptlbility of the iron to pitting. In H2SO4 NaCl solution, the regular potentiostatic current oscillations gradually evolved into the irreg-niar current fluctuations due to occurrence of the pitting; whereas in H2SO4 NaCl NaNO3 solution, the current oscillations took place regularly, like the oscillatory behavior in the pure H2SO4 solution. Thus, when the higher the oscillatory fre-quency, the more irregular oscillatory process and the more sensitive to pitting iron occurred.     

Pitting inhibition of stainless steel by surfactants: an electrochemical and surface chemical approach

Pitting corrosion of stainless steels causes tremendous damage in terms of material loss and resulting accidents. Organic surfactants have been tried as pitting inhibitors but the understanding of the inhibition mechanisms is mainly speculative. In the present study the inhibition of the pitting corrosion of 304 stainless steel by N-lauroylsarcosine sodium salt (NLS) in 0.1 M NaCl solutions at neutral pH was studied using an approach that combines surface chemical techniques with electrochemical ones. It was found that NLS increases the pitting resistance of 304 stainless steel, with possible complete inhibition at high NLS concentration (30 mM). Adsorption of NLS on 304 stainless steel particles was directly measured. NLS adsorbs significantly on 304 stainless steel with maximum adsorption density close to bilayer coverage. Electrophoretic mobility data for 304 stainless steel particles show that the surface of 304 stainless steel is negative in NaCl solution at neutral pH. The adsorption of NLS makes the interfacial charge even more negative. The relationship between pitting inhibition and adsorption density of NLS suggests that NLS does not adsorb preferentially on the pit nucleation sites and complete inhibition requires that the whole surface be covered completely by NLS. The inhibition mechanism of NLS is proposed to be due mainly to the blocking effect of a negatively charged NLS adsorption layer. This study shows that in addition to the adsorption amount of surfactant, interfacial charge also plays an important role in pitting inhibition.     

Pitting behavior on super 13Cr stainless steel in 3.5% NaCl solution in the presence of acetic acid

The pitting behavior was investigated on super 13Cr stainless steels in 3.5% NaCl solution in the presence of HAc. The electrochemical measurements including potentiodynamic polarization, electrochemical impedance spectroscopy (EIS), and chronoamperometric experiments were carried out, as well as the SEM surface analysis. The parameters such as E _corr and I _corr were obtained by fitting technique. Moreover, the equivalent circuit model was applied in the analysis of Nyquist plots, and ZsimWin software was used to analyze the EIS data. The results indicate that the pitting corrosion is accelerated with increasing the amounts of HAc. In addition, pitting nucleation and growth mechanisms were described in this work.     

The effect of molybdenum on corrosion of low-temperature nitrided stainless steels in sulphate–chloride solution

Resistance of stainless steels to pitting corrosion is strongly enhanced by nitriding at 380–450°C. In this work, anodic behaviour of steels with 0.13, 2.1, 4.5 and 6.1 wt% Mo was studied before and after nitriding at 450°C for 30 h which gave 13.0–15.8 wt% N at the surface. Electrochemical measurements were carried out in 0.1 M Na₂SO₄ + 0.4 M NaCl at pH 3.0. Nitriding of steels with lower Mo contents (0.13 and 2.1 wt% Mo) enhanced the resistance to pitting corrosion; steels with higher Mo contents retained their high resistance to pitting but underwent an activation. Nitrogen increased anodic reactivity in initial stages of polarisation, and it also increased the passivation rate. X-ray photoelectron spectroscopy analysis showed that anodic films on nitrided steels contained oxides at the outer surface and Cr–N species deeper from the surface. The enhanced resistance to pitting corrosion of low-temperature nitrided steels is explained by the increased anodic reactivity which leads to the formation of a salt-type film with Cr/Fe oxides and Cr–N species.In Honour of Professor Kurt Schwabe.     

Anodic behavior of tungsten in water—organic solutions of sodium chloride

The anodic behavior of tungsten in water-amino alcohol solutions of sodium chloride is studied potentiostatically and potentiodynamically on a rotating disk electrode. The introduction of monoethanol amine (MEA) into an aqueous NaCl solution leads to anodic activation of tungsten. From the dependence of the current density on the disk electrode rotation rate, it is determined that the anodic dissolution obeys the diffusion kinetics equations. The delivery of MEA molecules to the electrode is the slow stage of the reaction. The dissolution rate and the tungsten surface quality after the treatment are the highest at 6 M MEA. The effect of physicochemical properties of solutions on the anodic reaction is shown     

合金元素及模拟热处理对2205双相不锈钢之孔蚀性质影响

本文研究了Ｎｉ元素及不同模拟焊后热影响区（ＨＡＺ）组织对２２０５双相不锈钢孔蚀性质之影响。结果发现：在研究成分范围内，不同Ｎｉ含量对于底材电化学极化曲线之影响不大，其Ｅｎｐ和Ｅｎｐ均在１１００￣１２００ｍＶ之间。     

Q235碳钢缝隙腐蚀的电化学噪声研究

应用电化学噪声和电化学阻抗技术研究Q235碳钢在NaHCO3+NaCl溶液中的缝隙腐蚀行为.结果显示,缝隙腐蚀过程可以被清楚地划分为3个阶段:孕育期、快速转换期和稳定发展期.电化学噪声的特征和噪声电阻在各阶段有着显著的变化.缝隙外、内表面积比(r)对缝隙腐蚀的孕育和发展有着十分重要的影响:r越大,孕育期越长.但是,在缝隙腐蚀稳定发展期,r较小时,缝隙外电极表面处于活性溶解状态,缝隙内外电位差很小,缝隙内腐蚀速率较小;倘如r很大时,则缝隙外电极表面处于钝态,缝隙内外电位差大,最终将导致严重的缝隙腐蚀.     

Examinations on the morphology of tarnish layers grown on stainless 18–10 chromium nickel steels

18-10 chromium nickel steels are generally valid as well weldable. However, during thermal joining oxides are formed in the heat affected zone, whose structure and composition essentially differs from the morphology of passive layers. The steel qualities X6 CrNiTi 18-10 (materials no. 1.4541) and X5 CrNiMoTi 17-12-2 (materials no. 1.4571) were examined on their tarnish growing behaviour by means of XPS/sputtering, transmission electron microscopy and atomic force microscopy. Information on the pitting corrosion resistance of annealed metal sheets was received by ageing them in iron chloride solution and by measuring the current density-potential curves under quasi-stationary conditions in artificial sea water.     

Development of pitting corrosion of stainless steel 403 in sodium chloride solutions

Pitting corrosion of stainless steel 403 in the NaCl solutions is studied. It is shown that the experimental results obtained under the potentiostatic conditions do not provide sufficient information on the behavior of steel under the conditions of free corrosion. The corrosion experiments take long time, their results exhibit poor reproducibility; however, they are necessary for obtaining reliable data on the corrosion behavior of steel. The development of corrosion process is reflected in the variation of corrosion potential with time. The effect of concentration and temperature of NaCl solutions on the development of pitting corrosion is studied. The peculiarities of the distribution of pits over the test specimen surface are revealed. In 1 M NaCl solution at 20°C, few pits arise. Some of them repassivate; some pits grow, initially, in diameter and depth and, then, almost only in depth. The examples of through pit formation on the specimens 4 mm thick are presented.     

LY12铝合金表面稀土转化膜腐蚀行为的研究

通过金相观察和Ｘ射线射能谱分析研究了ＬＹ１２铝合金表面两种稀土转化膜的腐蚀行为,在ＮａＣｌ溶液中稀土转化膜的腐蚀以点腐蚀开始,点蚀处基体含Ｃｕ量高。根据Ｍａｎｓｆｅｌｄ点腐蚀模型等效电路提出了利用电化学阻抗谱研究稀土转化膜在ＮａＣｌ溶液中腐蚀程度的新方法,转化膜在ＮａＣｌ淀粉 中浸泡时间较短、腐蚀不太严重的情况下,等效电路中的Ｗａｒｂｕｒｇ阻抗Ｗ可以忽略,简化等效电路得出了计算转化膜表面点腐蚀百分     

利用小波变换检测电化学噪声信号波形

简述了应用小波变换检测点蚀电化学噪声信号的基本原理,对在3.5％ NaCl溶液中工业纯铝发生点蚀的电化学噪声信号检测分析表明：小波变换能够提取发生点蚀的电化学噪声信号和测量系统噪声在多惊讶分辨空间中的波形特征,根据表征该特征的小波系数模极大值在不同尺度下的传播特性,可实现对点蚀电化学噪声信号波形的检测。     

Surface remelting of 316 L + 434 L sintered steel: microstructure and corrosion resistance

This study presents arc surface remelting of three types of sintered stainless steels carried out in order to constitute a homogeneous microstructure in the surface layer which is free from open and interconnected porosity. The main aim of this treatment was to improve functional properties of the sinters analysed, especially their resistance to pitting corrosion. The sinters were obtained from powders of 316 L and 434 L steels. The PM austenitic-ferritic stainless steels are used mainly in the automotive industry, but their general application is still limited due to relatively poor corrosion properties when compared to casts or wrought components. This study used the gas tungsten arc welding (GTAW) process as a method of economical surface treatment. The effect of surface treatment was evaluated based on macro- and microstructural observations, energy-dispersive X-ray spectroscopy (EDX) analysis, X-ray phase analysis, measurements of surface roughness and electrochemical examinations. It was found that a cellular or mixed cellular and dendritic structure was formed in the remelted zone of the sinters after remelting. X-ray analysis demonstrated that application of remelting contributes to formation of the austenitic phase in the surface layer. The corrosion resistance of the remelted surface layers was evaluated using polarization tests in 0.5 M NaCl solution. It was found that arc surface remelted layers exhibit much better anticorrosive properties than sinters without surface treatment. Microstructural observations of the surface of specimens after electrochemical tests showed only a few single pits in the remelted layer, while the surface of initial sinters was much more corroded.     

Surface analytical examinations of welded nickel alloys by XPS, SNMS and SEM/EDX

Tarnish layers are formed in the heat affected zone during the welding of steels and nickel based alloys. They commonly consist of oxides of the alloying elements. The corrosion behaviour of welded components is generally influenced by the thickness and composition of the oxide films. In the following the corrosion behaviour of annealed samples cut from NiMo28 and NiMo16Cr16Ti is investigated, correlating XPS, SNMS and SEM/EDX data to their pitting corrosion potentials.Dedicated to Professor Dr. rer. nat. Dr. h.c. Hubertus Nickel on the occasion of his 65th birthday     

Performance of glucose electrooxidation on Ni–Co composition dispersed on the poly(isonicotinic acid) (SDS) film

Poly(isonicotinic acid) (PINA) film was electrosynthesized on carbon paste electrode (CPE) by using the repeated potential cycling technique in aqueous solution containing isonicotinic acid (INA), sulfuric acid and sodium dodecyl sulfate (SDS). Then, nickel and cobalt ions were incorporated by immersion of CPE/PINA prepared in the presence of SDS (CPE/PINA(SDS)) in a solution with different proportions of nickel chloride and cobalt chloride. The electrochemical characterization of mixed hydroxides containing cobalt and nickel at the surface of the modified electrode is presented. The modified electrodes were successfully used in the electrocatalytic oxidation of glucose. Finally, the electrocatalytic oxidation peak currents of glucose exhibited a good linear dependence on concentration, and its quantification can be done easily. The good analytical performance, low cost and straightforward preparation method make this novel electrode material promising for the development of an effective glucose sensor.     

Voltammetric Study and Detection of Methane on Nickel Hydroxide–Modified Nickel Electrode

Abstract

The nickel hydroxide–modified nickel (NMN) electrode was prepared by cyclic voltammetry. The modified electrode exhibited better catalytic effect toward electrochemical oxidation of methane in 1.0 mol · L^?1 NaOH solution. The catalytic activation of nickel hydroxide on the nickel electrode surface was investigated in different supporting electrolyte solutions by the cyclic voltammetry method in detail, and the related electrochemical oxidation of methane at the NMN electrode was first proposed by amperometric i‐t curve method under the experiment conditions. The results indicated that in the 1.0 mol · L^?1 NaOH solution, the anodic peak current increased with the increased concentration of methane.     

Porous nickel deposits formed in the oxidation of alcohols in an alkaline medium

Highly porous nickel matrices with varied content of nickel were formed on a glassy graphite electrode by the electrochemical deposition method. The nickel deposits were studied by pulsed chronoamperometry, impedance spectroscopy, and cyclic voltammetry on a rotating disk electrode in a 1 M KOH solution and in alkaline solutions containing methanol or ethanol. The process in which a hydroxide film is formed on the nickel surface in an alkaline solution and the influence exerted by this process on the catalytic oxidation of alcohols on nickel in an alkaline medium are discussed.     

Effect of halides on the electrochemiluminescence of heavy metals at an aluminum electrode

The effect of halides on cathodic electrochemiluminescence spectra of mercury-like ions at an aluminum electrode is studied. A method of changing the solution in concordance with the potential change is proposed to inhibit pitting corrosion arising in the anodic oxidation of aluminum in chloride-containing solutions. This method allows tin, lead, thallium, and mercury to be rapidly determined in model solutions and seawater.     

Corrosion resistance of nickel coatings deposited from low-temperature nickel-plating electrolytes

The corrosion resistance of nickel coatings on a copper substrate, plated from low-temperature electrolytes based on acetates, tartrates, and isobutyrates, was studied by the methods of electrochemical impedance spectroscopy (EIS) and polarization curves. The tests were performed in a 0.3% NaCl solution. The nickel coatings exhibit high chemical activity, dissolving in the NaCl solution. The electrochemical step is the limiting step of the corrosion process.     

镍修饰WO3膜光电化学氧化水的研究

在强碱性溶液中低电压低电流条件下在W基底上经阳极氧化得到致密WO3层,而后在酸性条件下在WO3表面经光辅助电化学还原沉积镍,所获得的复合电极具有优异的光电化学氧化水的活性和稳定性.SEM,EDX,XPS和TEM等表征表明复合电极中具有体心立方结构的W基底经阳极氧化形成了具有单斜结构的WO3层,表面修饰的镍物种以Ni(OH)2形式存在.光电化学实验表明WO3层对可见光具有良好的光响应,表面修饰镍后,光电氧化水的起始电位显著降低,电极的稳定性也得以提高.     

Determination of corrosion current density on bulk nickel and nickel powder by the rate of cathodic depolarizer consumption

The method of “compensating additives” is used to determine the corrosion current of nickel and nickel powder in 0.5 M NaCl solution containing 0.01 M HCl. Comparing the corrosion currents measured on bulk nickel and nickel powder, the specific electrochemically active surface area of nickel powder is estimated.