Electrochemical methods study on corrosion of 5% Al–Zn alloy‐coated steel under thin electrolyte layers

The corrosion behavior of a 5% Al–Zn alloy (GF) coated steel was investigated under cyclic wet–dry condition using electrochemical techniques. The wet–dry cycle was conducted by exposure to alternate condition of 1 h immersion in seawater and 7 h drying at ambient temperature. The polarization resistance, R_p of the coating was monitored during the wet–dry cycles by two points AC impedance method and the corrosion potential, E_corr was measured only when the coating was immersed in seawater. Simultaneously, the electrochemical impedance spectroscopy (EIS) of the coating was obtained after it was immersed in different cycles of wet–dry condition. The results obtained by two points AC impedance method had good agreement with those achieved from EIS technique, which proved that the two points AC impedance method was correct and an effective method for atmospheric corrosion study. The monitoring results indicated that the corrosion rate of GF coating firstly increased, then decreased slowly with time, and at last reached a relative steady state with local corrosion under the cyclic wet–dry alternate condition.     

碳钢与低合金钢耐大气腐蚀性研究

采用干湿复合循环实验、电化学交流阻抗和扫描电镜等方法研究了7种碳钢与低合金钢在试验环境中的腐蚀规律及腐蚀试验后带锈试样的电化学特征.结果表明,7种材料的腐蚀失重率随时间均遵从负指数规律：Y=Y0+Ae-t/B.电化学测试结果表明带锈试样进一步腐蚀的速度受阴极扩散过程所控制;7种材料带锈试样的阻抗值与材料的年腐蚀速率呈线性关系.     

EIS monitoring study of atmospheric corrosion under variable relative humidity

Electrochemical impedance spectroscopy (EIS) technique was used to investigate atmospheric corrosion in laboratory simulated environments with variable relative humidity (RH) and fixed Cl⁻ content. The results show the suitability of EIS for analyzing electrochemical corrosion behaviour at 5-100% RH. At 5-30% RH, EIS spectra reflected the character of the electrode, whereas at 40-100% RH, the model of EIS spectra was established with the help of surface analysis. From 70% RH, the film resistance (R_r) reflects the degree of corrosion and the charge transfer resistance (R_t) provides quantitative representation of the corrosion rate, which were verified by weight loss tests.     

Comparability and accuracy of time of wetness sensing methods relevant for atmospheric corrosion

The performance of three time of wetness (TOW) determination methods during outdoor exposure was examined. Two impedance-based TOW sensor types, RH, and temperature sensors were exposed to coastal marine and laboratory environments for up to three months. The sensor and ISO 9223 methods examined provided incomparable estimates. Inaccuracy of the ISO method originated from a humidity threshold well above the drying point of deposited aerosols and differences between surface and ambient RH. TOW sensor accuracy was linked to electrode configuration. Small electrode spacing was demonstrated to be required to capture the range of wetting events of importance to atmospheric corrosion.     

含铜低合金耐磨钢在盐雾环境中的腐蚀行为

对含铜和不含铜实验钢在中性盐雾试验箱中连续喷雾120、240、480和720 h,研究了在盐雾环境下Cu对低合金耐磨钢耐腐蚀性能的影响规律,通过失重法计算腐蚀速率,并利用XRD和SEM对腐蚀产物进行表征,利用动电位扫描、电化学阻抗谱 (EIS) 对比分析Cu在低合金耐磨钢腐蚀过程中起到的作用。结果表明：低合金耐磨钢的腐蚀产物主要包括γ-FeOOH、α-FeOOH、Fe₃O₄、γ-Fe₂O₃,前期腐蚀产物疏松多孔,后期产物致密难剥落,腐蚀速率先升高后下降,含铜实验钢的腐蚀速率明显低于不含铜实验钢,添加Cu后,实验钢的自腐蚀电位上升,阻抗谱容抗弧增大,电荷转移难度增加,说明Cu能有效降低实验钢腐蚀速率,增强其耐腐蚀性能。     

Research on intercrystalline corrosion,exfoliation corrosion,and stress corrosion cracking of Al–Zn–Mg–Sc–Zr alloy

The intercrystalline corrosion, exfoliation corrosion (EXCO), and stress corrosion cracking (SCC) of Al–Zn–Mg–Sc–Zr alloy were investigated by means of constant temperature immersion corrosion method, optical microscopy, transmission electron microscopy (TEM), and electrochemical impedance spectroscopy (EIS). The results show that intercrystalline corrosion, and EXCO susceptibility of Al–Zn–Mg–Sc–Zr alloy decrease gradually with increasing of aging time. Corrosion susceptibility order from low to high is as follows: OA > PA > UA > NA. The SCC susceptibility index of PA temper is more than OA temper at the same strain rate. According to TEM observation, with aging time prolonging, a part of η′ phases transform to η equilibrium phases, which become coarse gradually. The distribution discontinuity of the grain boundary precipitates increases. In addition, for Al–Zn–Mg–Sc–Zr alloy without EXCO, the EIS is comprised by a capacitive impedance arc at high frequency and an inductive impedance arc at low frequency. Once EXCO occurs, the EIS is composed of two capacitive impedance arcs at high frequency and at low frequency, respectively.     

大气中SO_2对金属银的电化学腐蚀行为

利用三电极电化学电池研究了大气环境中的SO2对金属银的腐蚀行为。通过电化学阻抗谱和极化曲线分析了金属银在不同厚度液膜、不同湿度、不同SO2气体浓度及不同暴露时间下的初期腐蚀行为。结果显示:电极表面液膜越薄,金属银的腐蚀电流密度越大;采用镜头纸控制银电极表面液膜厚度,随着大气环境湿度的增加,银的腐蚀速度减小;在自然大气环境中,随着大气中SO2浓度的增加,暴露时间的延长,银电极的阻抗值增大,这可能是由于银电极表面Ag2O、AgOH和亚硫酸银等反应产物膜的形成的原因。     

盐沉积条件下CO2对LY12铝合金大气腐蚀的影响

目的研究在有/无CO_2存在的恒温恒湿条件下,表面有沉积盐的LY12铝合金的大气腐蚀行为与腐蚀机理,搞清CO_2对其大气腐蚀的影响。方法将LY12铝合金表面分别沉积不同浓度的NaCl和MgCl_2,分别进行通/不通CO_2的恒温恒湿实验,借助扫描电镜(SEM/EDS)、X射线衍射(XRD)和X光电子能谱(XPS)等表面技术以及腐蚀失重分析方法,研究盐沉积条件下CO_2对LY12铝合金大气腐蚀的影响。结果在试验条件下,MgCl_2造成的LY12铝合金腐蚀都以点蚀为主,失重高于NaCl造成的。以MgCl_2为介质时,主要腐蚀产物都为(Mg1–xAlx(OH)_2)x+(Cl~–,CO~(2–))x×mH_2O(简写为LDH);以NaCl为介质时,主要腐蚀产物都为Al_2O_3或Al(OH)_3。两种介质的腐蚀产物都出现了Cu元素的富集。结论无论是否存在CO_2,Mg元素都参与了腐蚀产物的形成。合金元素Cu的存在及其富集,是造成CO_2对纯铝和LY12铝合金腐蚀行为不同影响的主要因素。     

应用电化学方法原位研究薄液膜下青铜的大气腐蚀行为(英文)

采用阴极极化曲线、开路电位和电化学阻抗谱,监测青铜在不同薄液膜厚度下的大气腐蚀行为。阴极极化曲线结果表明,阴极极限电流密度随着液膜的减薄而增大。电化学阻抗谱结果表明,在腐蚀初期,腐蚀速率随着液膜的减薄而增加,这主要是由于腐蚀速率是由阴极过程控制的;随着时间的延长,腐蚀程度随着液膜厚度的变化从强到弱的趋势为:150μm,310μm,100μm,本体溶液,57μm。开路电位和电化学阻抗谱实验较好地再现了原位电化学腐蚀信息,且电化学结果与物理表征具有良好的一致性。     

The effects of Cl ion concentration and relative humidity on atmospheric corrosion behaviour of PCB-Cu under adsorbed thin electrolyte layer

The effects of Cl⁻ ion concentration and relative humidity on atmospheric corrosion behaviour of PCB-Cu under adsorbed thin electrolyte layer were investigated by cathodic polarization curves and electrochemical impedance spectroscopy. Results indicated that the cathodic process of PCB-Cu corrosion was dominated by the reduction of oxygen and corrosion products. The cathodic current density increased with increasing relative humidity and Cl⁻ ion concentration. The corrosion rate was initially dominated by oxygen reduction, but at the later stage of corrosion, the anodic process began to affect the corrosion rate due to the accumulation of corrosion products.     

Effect of SO2 in flue gas on coal ash hot corrosion of Inconel 740 alloy – A high temperature electrochemical sensor study

Our newly developed high temperature electrochemical sensor was applied to study the effect of SO₂ in flue gas on thin film coal ash corrosion of Inconel 740 superalloy at 750 °C. The response of electrochemical noise (EN), electrochemical impedance spectroscopy (EIS), and potentiodynamic polarization (PDP) test data from the sensor is compared with the results from a weight loss test. There is a good correlation between the electrochemical data and the actual degradation processes. The current noise analysis in time and frequency domains for the quantitative determination of hot corrosion rate in service is discussed.     

LY12铝合金在周浸试验中的腐蚀行为

用电化学阻抗谱（EIS）、扫描电子显微镜（SEM）和X射线能谱分析（EDAX）等检测技术,研究了LY12铝合金在周浸实验中的腐蚀行为及其机理。结果表明,LY12铝合金的腐蚀动力学符合幂函数规律。腐蚀历程为点蚀-晶间腐蚀-剥蚀（鼓泡）。EIS谱由高－中频容抗弧和低频收缩的感抗弧组成。     

Atmospheric corrosion of copper under wet/dry cyclic conditions

The polarization resistance of copper subjected to NaCl and an ammonium sulfate solution under wet/dry cycling conditions was monitored using an EIS impedance technique. The copper samples were exposed to 1 h of immersion using different solutions of pH, temperature and surface orientation and 7 h of drying. The copper plates corroded more substantially on the skyward side than those for a ground ward side. The degree of protection copper oxide provides decrease in an acidic medium (pH 4) more than in a neutral medium (pH 7). The corrosion rate of copper increases rapidly during the initial stages of exposure then decreases slowly and eventually attains the steady state during the last stages of exposure. The corrosion products were analyzed using X-ray diffraction. The corrosion mechanism for copper studied under wet/dry cyclic conditions was found to proceed under the dissolution-precipitation mechanism.     

湿度对Q235钢在污染土壤中腐蚀行为的影响

利用极化曲线技术、电化学阻抗测试技术、扫描电镜和表面能谱等方法,研究了Q235钢在不同湿度的污染土壤中的腐蚀行为。试验结果表明,湿度对Q235钢腐蚀的影响显著。随土壤湿度的增加,Q235钢在污染土壤中的腐蚀速率也增加,当含水量增大到20%时,腐蚀速率达到最大,然后腐蚀速率随着湿度增加而减小。Q235钢在湿度为20%的污染土壤中腐蚀后表面出现明显的裂痕和腐蚀坑。     

Cu,P,Cr 和 Ni 对低碳钢耐蚀性的影响简

选择Cu-P-Cr-Ni钢、Cu-P-Cr钢和Q235碳钢,在0.01 mol/L的NaHSO3溶液中进行周期浸润、阻抗谱和极化曲线实验,研究了Cu-P-Cr-Ni系合金钢相比Q235碳钢在模拟工业大气(SO2)环境下的耐腐蚀性能;利用SEM,EPMA面扫描和XRD分析腐蚀锈层的形貌、组成及Cu,Cr和Ni的元素分布情况。结果表明:Cu-P-Cr-Ni系钢的腐蚀诱发敏感性最低,其次为Cu-P-Cr钢,腐蚀速率分别为Q235碳钢的59.5%和52.8%;锈层分为内、外两层,致密的内锈层明显发生Cu的颗粒状、Cr的团聚状富集,外锈层主要有Cr的富集,Ni富集不明显。Cu和Cr等的富集可形成致密的内锈层,提高低碳钢的耐蚀性。     

An electrochemical impedance study on atmospheric corrosion of steels in a cyclic wet-dry condition

The corrosion rates of steels with different nickel contents (0, 2.5, 10 and 20 wt%) were monitored by the AC impedance method under a cyclic wet-dry condition, which was conducted by exposure to alternate conditions of 1 h immersion in a 0.05 M NaCl solution and 7 h drying at 60% RH and 25 °C. The corrosion rates of the ordinary carbon steel and the 2.5% Ni containing steel were greatly accelerated by the wet-dry cycles, while those of steels containing at least 5% Ni were only slightly affected. AC impedance tests indicated that the addition of 5% Ni greatly reduced the corrosion rates of the steel exposed to the cyclic wet-dry environments containing chloride ions, in good agreement with one year exposure tests in the atmospheric marine environments. Within the wet-dry cycle for the carbon steel, a gradual increase in the corrosion rate and a shift of the corrosion potential to negative values were observed at the initial stage of the drying period. These indicated that the anodic metal dissolution rate was accelerated by a slight increase in the chloride ion concentration. At the intermediate stage of drying, the corrosion rate rapidly increased and the corrosion potential remained constant. This can be attributed to the acceleration of both the anodic metal dissolution process and the cathodic oxygen reduction process which is usually controlled by the rates of O₂ transport through the thin electrolyte film. At the final stage, just before the surface dried out, the corrosion rate rapidly decreased, shifting the corrosion potential to the noble direction. At this stage, the anodic process was greatly inhibited. The corrosion testing system employed in this study is very useful for the rapid evaluation of the corrosion performance of metals in atmospheric marine environments and for mechanistic study.     

Experimental determination of time taken for openly exposed metal surfaces to dry

Abstract

The time taken for wetness sensors on zinc plates, openly exposed to the atmosphere, to dry was analysed at four sites in southern Australia. The sites cover a range of environmental conditions from inland to marine. A number of typical drying patterns were observed, and it was found that these patterns could be related to the environmental severity and the probable presence of various salt contaminants. Therefore, at the marine site drying was frequently slow (>4 h) and appeared to be controlled by the presence of salts with a low deliquescent relative humidity (DRH) such as MgCl₂. In contrast, at the inland sites drying was generally more rapid, which was consistent with either the drying of a clean surface or that of a surface controlled with salts of high DRH such as NaCl. The present paper presents histograms of drying rate for each site and the relationship between the distributions in drying rate and the environmental conditions is discussed. The relevance of the present study to modelling of atmospheric corrosion and to the design of cyclic tests to duplicate atmospheric corrosion is also discussed.     

模拟海洋大气环境对XCS-lode钢与30CrNi3Mo钢腐蚀行为的影响

采用盐雾腐蚀试验方法,研究了模拟海洋大气环境下XCS-lode钢与30CrNi3Mo钢的腐蚀性能,通过极化曲线及电化学阻抗谱(EIS)试验研究了两种钢在腐蚀行为上的差异.结果表明:XCS-lode钢相比30CrNi3Mo钢具有更高的自腐蚀电位,XCS-lode钢腐蚀产物膜的阻抗明显大于30CrNi3Mo钢,XCS-lo...     

LC4CS铝合金大气腐蚀模拟加速实验方法的研究

采用周期降雨模式的加速腐蚀方法对LC4铝合金进行试验,通过正交试验分析干燥时间、降雨时间、润湿时间、相对湿度、去极化剂、加速剂、人造雨水pH值等7项因子对试验模拟性和加速性的影响规律,得出优化的试验控制参数：人造雨水成分为0.05%NaNO3+0.8%Na2S2O8+4%NaCl,pH为4;单循环时间30 min;单循环中干燥时间2 min;单循环中降雨时间30 s;保湿阶段相对湿度70%.      

Corrosion behaviour of HVOF-sprayed Co–Cr–W–C coating in NaCl solution

Stellite 6 (Co–Cr–W–C) coating was deposited on carbon steel substrate by high-velocity oxyfuel spraying. The electrochemical corrosion behaviour of the coatings was investigated in 3.5% NaCl solutions at 25°C by means of polarisation studies and electrochemical impedance spectroscopy (EIS) measurements. The immersion time before corrosion tests was 0.5 and 24?h. The results showed that the corrosion rate of the coatings was lower than that of the steel substrate by one order of magnitude. An active–passive behaviour was observed during anodic polarisation of the coatings at both immersion times. The degree of substrate attack after polarisation tests of coated samples was not considerable. EIS measurement showed that two-time constants were observed in Nyquist plots of the coatings.