含重铬酸根硫酸溶液中磁场对铁自腐蚀状态及极化电阻 …

铁在含有一定浓度重铬酸根的硫酸中,自腐蚀状态下的阴极反应速率受重铬酸根阴极还原电子转移过程与扩散过程共同控制,外加磁场使铁的自腐蚀电位正移,且电位正移幅度随重铬酸根浓度增加而增大,在没有外加磁场时的自腐蚀电位下进行恒电位极化时,外加磁场后会出现阴极电流,磁致阴极电流随重铬酸根的浓度增大而显著增大,外加磁场会钤吸一定量重铬酸根的硫酸溶液中铁的极化电阻昱著下降,产场作用进行模型化,分析了磁场作用的动力     

磁场作用下铁在盐酸和氯化钠溶液中自腐蚀状态的变化

采用自腐蚀电位测量及恒电位极化法研究了磁场对铁在酸性与中性氯化的溶液中自腐蚀状态的作用。外加磁场使自腐蚀电位正移，撤去磁场使自腐蚀电位负移，没有磁场时在自腐蚀电位下极化然后外加磁场会导致磁致阴极电流；有磁场时自腐蚀电位下极化然后撤去磁场会导致磁致阳极电流。酸性溶液体系的磁致阴极电流值明显大于中性溶液体系，表现出磁场主要通过作用于析氢反应而影响自腐蚀状态。     

重铬酸根与磁场对铁在硫酸溶液中阳极极化行为的影响

采用动电位极化曲线法研究了外加磁场及不同浓度重铬酸根对Fe在0．5mol/L H2SO4溶液中阳极极化行为的影响,结果表明：浓度≤0．02mol/L的重铬酸根不改变阳极极化曲线的构型;重铬酸根浓度≥0.05mol/L时,阳极极化曲线上出现传质控制特征的斜率突变转折段,并且随重铬酸根浓度增大,斜率转折段在更负的电位、更小的电流密度下出现,外加磁场后,不同阳极电位区间内会表现出电流变小、不变及增大的现象,这与相应电位下阴、阳极反应贡献的相对大小以及各自的控制步骤类型有关,考虑阳极过程中可能发生的活性溶解、表面膜生成及表面膜溶解反应,以及极反应的影响,主要考虑磁场对阴、阳极反应中传质过程的作用,得出了外加磁场作用下的极化曲线模型,该模型较好地说明了磁场对不同电位区电流密度产生不同影响的实验事定。     

磁场对铜在含三价铁离子硫酸溶液中的腐蚀行为的影响

采用电化学测量方法研究了磁场对铜在含三价铁离子硫酸溶液中自腐蚀以及阴极极化行为的作用,磁场不影响该体系的自腐蚀状态。磁场加速铜电极上三价铁离子的阴极扩散过程,随磁场强度增大,阴极极限扩散电流密度增大;磁场强度恒定时,磁场对三价铁离子阴极扩散的作用系数随三价铁离子浓度增加而增大;引起极限扩散电流密度明显增加的临界磁场强度随三价铁离子浓度增加而减小。由于铜与铁在含有三价铁离子的水溶液中的热力学稳定性不同,不同的自腐蚀电位下阴极反应的控制步骤类型不同而导致磁场作用不同。     

漏磁场对鹰潭土壤模拟液中管线钢交流腐蚀行为的影响

目的 探究管体磁化产生的磁场对油气管道交流杂散电流腐蚀行为的影响。方法 采用自行设计试验装置模拟管道真实漏磁场,以开路电位、高频电位测量、动电位极化、电化学阻抗谱、表面分析技术及失重法,研究了鹰潭土壤模拟液中磁化和未磁化的X52管线钢试样交流腐蚀行为的差异。结果 磁化管体的磁场使交流腐蚀电位先负移后正移,交流幅值电位增大,极化电流增加,反应界面电容减小,法拉第电阻增大,交流平均腐蚀速率增大,对腐蚀产物形貌有一定影响,但对腐蚀形貌基本无影响。磁场作用机理分析表明,磁场产生的洛伦磁力驱动反应界面附近腐蚀介质运动而增加反应粒子的扩散速率及减小界面扩散层厚度,从而增大交流腐蚀速率。磁场梯度力在一定程度上抑制了阳极反应,促进了阴极反应。结论 漏磁场使管线钢交流杂散电流腐蚀速率大幅提升,但是不改变其均匀腐蚀的形貌,应提高开展过漏磁内检测的油气管道交流杂散电流评价标准。     

用丝束电极研究混凝土中钢筋腐蚀的不均匀性

用8×8阵列丝束电极模拟研究了混凝土中钢筋的腐蚀.将混凝土试样浸泡在10 %NaCl溶液中,通过测量铁丝束电极的自腐蚀电位和极化电阻,获得了在相同埋置深度和不同埋置深度时,铁丝腐蚀的电位、极化电阻和腐蚀速度分布等信息,研究了混凝土结构和氯离子浓度对它们的影响.结果表明,混凝土中铁丝腐蚀不均匀.自腐蚀电位和极化电阻较分散,电位随时间负移、极化电阻变小,丝束之间的电位差增大.随铁丝埋入深度增加,电位负移量、氯离子浓度和腐蚀速度都减小、极化电阻增加     

磁场对铁在含亚硝酸根的氯化钠溶液中不同电位下极化电流的影响

采用动电位扫描极化曲线、恒电位极化和电化学阻抗谱研究了磁场对铁在含亚硝酸钠的氯化钠溶液中电化学行为的影响。结果表明:外加0.4T磁场使得自腐蚀电位下电化学阻抗谱中容抗弧半径变小;外加磁场导致阳极极化曲线在初期出现阴极电流,并在钝化区内降低外测电流密度;外加磁场增加高电位极化下的阳极电流密度。     

空蚀对20SiMn在3%NaCl溶液中的电化学腐蚀行为的影响

利用带电化学测试系统的磁致伸缩空蚀试验机研究了 20SiMn低合金钢在3%NaCl水溶液中的电化学腐蚀行为，通过空蚀和静态条件下的自腐蚀电位变化以及交流阻抗谱和动电位极化曲线的比较，分析了空蚀加速20SiMn低合金钢电化学腐蚀的机理.结果表明，空蚀使20SiMn低合金钢的自腐蚀电位正移200 mV，并显著降低电荷转移电阻和线性极化电阻，使电化学腐蚀速率增大约54倍；随着空蚀的进行，电荷转移电阻和线性极化电阻减小，空蚀3 h后逐渐趋于稳定.     

NaNO2对20SiMn低合金钢在3％NaCl溶液中空蚀损伤的缓蚀作用

利用磁致伸缩空蚀实验机研究了20SiMn低合金钢在3%NaCl和3%NaCl＋NaNO2溶液中的空蚀行为.测量了静态和空蚀条件下的腐蚀电位变化、电化学阻抗谱和极化曲线.结果表明：NaNO2通过抑制腐蚀与空蚀间的交互作用，对20SiMn低合金钢在3%NaCl溶液中的空蚀损伤有良好的抑制作用，浓度为1%的NaNO2的缓蚀效率达到802%.添加NaNO2对20SiMn低合金钢在3%NaCl溶液中的电化学行为有显著影响.在3%NaCl溶液中，自腐蚀电位、线性极化电阻都随空蚀进行而逐渐负移和减小.与此相反，添加NaNO2后，20SiMn的自腐蚀电位、线性极化电阻都随空蚀的进行而逐渐正移和增大.3%NaCl+1%NaNO2溶液中的电化学阻抗谱特征与空蚀表面形貌的变化有较好的对应关系.     

外加电位下X80双相管线钢在模拟沿海土壤环境中的应力腐蚀行为

采用交流阻抗谱、极化试验、慢应变拉伸试验研究了不同外加电位下在模拟沿海土壤环境中X80双相管线钢的应力腐蚀行为,对拉伸断口和极化后试样进行SEM表面形貌及能谱分析。结果表明,与慢扫极化(模拟的非裂尖区域)相比,X80双相管线钢快扫极化模拟的裂尖腐蚀电位较负且腐蚀电流较大。-750 mV外加阴极电位处于裂尖自腐蚀电位范围,不足以起到阴极保护的作用,对应力腐蚀仍十分敏感。外加电位为-1050 mV时,阴极反应速率显著大于阳极反应,阴极反应产生的氢被金属吸收且扩散,慢应变拉伸未经颈缩即发生断裂,为准解理断裂。外加阴极电位为-900 mV,阴极电流有效抑制了阳极溶解反应,因此管线钢在模拟沿海土壤溶液中慢应变拉伸抗拉强度和断面收缩率都最高,断口表现为韧性断裂,侧面裂纹细小,阻抗模值最大,应力腐蚀敏感性最小。     

Probing into the effects of a magnetic field on the electrode processes of iron in sulphuric acid solutions with dichromate based on the fundamental electrochemistry kinetics

The effects of an applied magnetic field on the electrode processes of iron in sulphuric acid solutions with dichromate have been investigated by electrochemical measurements. Open circuit potentials, cathodic and anodic polarisation curves, values of polarisation resistance were measured in the presence or absence of a 0.4 T horizontal magnetic field (HMF). A potentiostatic polarisation plus magnetic field perturbation technique was used to study the effect of the magnetic field on open circuit corrosion. Cathodic reaction rates at open circuit potentials for iron in sulphuric acid solutions containing dichromate ions are controlled by both the electron-transfer process and the diffusion process. A magnetic field made the open circuit potential move in the positive direction, and changes of the open circuit potentials due to the magnetic field increase with increasing dichromate concentration. When iron was potentiostatically polarised at open circuit potentials in the absence of a magnetic field, a cathodic current was observed after a magnetic field was imposed. Such cathodic currents induced by the magnetic field increases with increasing dichromate concentration. The positive shifts of open circuit potential, the decrease of polarisation resistance, and the occurrence of cathodic currents induced by the magnetic field are caused by the accelerating effect of magnetic field on the cathodic diffusion process. Measured current densities showed lower, equal, or higher values in the presence of the magnetic field than those in the absence of a magnetic field at certain anodic potentials. This effect of the magnetic field is related to the contribution of the cathodic and anodic reactions to the measured current and the types of rate-determining steps for each reaction at certain potentials. The applied magnetic field significantly decreased the polarisation resistance. The experimental results in this paper are formulated based on the fundamental electrochemistry kinetics after introducing a coefficient term of the magnetic field effect on the mass transfer process of reactive ions.     

The corrosion inhibition of Ti-alloy (VT-9) in mixture of H<Subscript>2</Subscript>SO<Subscript>4</Subscript>-NaF by organic compounds

This investigation deals with corrosion behavior of high strength titanium alloy in concentrated sulphuric acid solution containing different concentrations (500, 1000, 1500 ppm) of fluoride ion (F⁻) using various organic compounds (MPA, L-OH, NFP) as inhibitor, potentiodynamically. The open circuit potential values noted before and after each experiment, varied appreciably. These values were negative before polarization but after completion of the experiment turned positive and remained stable over long period of time. It is observed that cathodic current density values increase with increasing cathodic potential (more negative) and fluoride ion. The values of cathodic Tafel slopes derived from the curves (∼110 − 140 mV/dec I) indicate hydrogen evolution reaction (h.e.r). The corrosion potential (E _corr) varied slightly with addition of inhibitors. The corrosion current densities (I _corr) increased with increasing fluoride ion concentration, but these values decreased appreciably when inhibitor (MPA) was used. SEM micrograph reveals reduction of pits in the presence of inhibitor (MPA). So this concludes that organic compound was used in this case acts as a good inhibitor. The article is published in the original.     

铝合金稀土转化膜碱性成膜工艺T3/T7的研究

采用正交实验方法得出了最佳成膜工艺T3/T7,利用线性极化、极化曲线测试、中性盐雾实验等对该工艺形成的膜层耐蚀性进行了研究,并对表面膜层的性能进行了一系列测试.结果表明:在NaCl水溶液中的全面腐蚀速度可降低10～20倍,可通过504h的中性盐雾试验;经该工艺处理后铝合金腐蚀的阴阳极过程都受到明显阻滞,且自然腐蚀电位负移,点蚀电位相对于自然腐蚀电位明显正移,T3/T7处理明显的改善了铝合金在氯化物介质中的耐点蚀性能     

Relationship between electrochemical characteristics and SCC of X70 pipeline steel in an acidic soil simulated solution

Stress corrosion cracking (SCC) of X70 pipeline steel in simulated solution of the acidic soil in Yingtan in China was investigated using slow strain rate test (SSRT), SEM and potentiodynamic polarization technique. Experiment results indicate that X70 steel is highly susceptible to SCC as applied potential reduces, which is manifested in loss of toughness and brittle fracture. Constant polarization current can detect the occurrence of SCC. The lower the polarization current is the sooner stress corrosion cracking occurs. The SCC mechanisms are different at varying potentials. When potential is higher than open circuit potential, anodic process controls SCC, whereas when potential is far lower than open circuit potential, cathodic process controls SCC, and between these two potential regions, a combined electrochemical process controls the SCC. Stress or strain has a synergistic effect with electrochemical reactions to accelerate the cathodic hydrogen evolution process, which makes the X70 pipeline steel to be more susceptible to SCC.     

Corrosion behaviour of hot-pressed austenitic stainless steel in H2SO4 solutions at room temperature

The corrosion behavior of hot-pressed stainless steel (HPSS) of Type 316 was investigated. Samples of HPSS with porosity of 10–30% were prepared. The influence of the porosity factor on corrosion behaviour was investigated by potentiodynamic polarization, open circuit potential, identification of corrosion products by EDAX and SEM observation.It was found that porosity of the HPSS is the main factor affecting corrosion resistance. High porosity results in low corrosion resistance. The open circuit potential of the HPSS is about ? 200 mV (VSCE) as compared to 200 mV for the wrought 316 stainless steel. The potentiodynamic measurements indicate that cathodic concentration polarization is achieved at a relatively low current density and secondary active-passive transition is observed at a relatively high current density in HPSS as compared to wrought 316 stainless steel.It is suggested that the main mechanism affecting the low corrosion resistance of HPSS in H₂SO₄ is the evolution of hydrogen concentration cells due to electrolytic stagnation in the interconnected open pores. As a result the surfaces of the interconnected open pores act as an active anode and the engineering sample surface acts as an active cathode.     

Effect of potential on the corrosion behavior of a new titanium alloy for dental implant applications in fluoride media

The effect of fluoride ion concentration and pH on the corrosion behavior of TCA (60 Ti 10 Ag 30 Cu), which is a new Ti alloy with low melting point, pure Titanium (Ti), and TAV (TiAl6V4) was examined using open circuit potential (OCP) and electrochemical impedance spectroscopy (EIS) at different potentials. Results show that the corrosion resistance of TCA and Ti decrease at anodic potentials compared with results obtained at OCP. At one potential the corrosion resistance decrease depends on NaF concentration and pH. TAV shows less resistance against corrosion in fluoride containing saliva. TCA has potentials more positive than Ti and TAV due to surface enrichment of Cu and Ag as Ti dissolves which accelerates the cathodic reaction. Fluoride ion may not hinder the growth of oxide layers on the surfaces of the electrodes. It will have influence on the properties of the oxide layer causing them to be not protective against corrosion in acid media containing fluoride ions.     

铝合金牺牲阳极极化性能研究

阳极开路电位下由于氧化膜的存在导致阳极不易溶解,当对阳极施加外加电流后,双电层电容逐渐增大,极化电阻逐渐减小,氧化膜逐渐破裂;随着极化电位的增大,阳极发出电流迅速增大,此时极化电阻逐渐减小,最后基本稳定不变;极化电阻较小的阳极材料有着较好的电化学性能,这与4 d加速实验的评价结果相吻合。