高度有序多孔阳极氧化铝模板的制备

为了得到纳米孔排列高度有序的多孔阳极氧化铝模板,以0.3 mol·L-1的草酸为电解液研究了模板的制备工艺.采用场发射扫描电子显微镜(FE-SEM)对多孔氧化铝模板的表面形貌进行表征,X射线衍射分析高纯铝及氧化膜的结构.实验结果表明,铝基体不经过高温退火处理,同样能够得到高度有序的氧化铝膜,简化了多孔氧化铝膜的制备工艺.分别讨论了阳极氧化电压和电解液温度对多孔阳极氧化铝膜的形貌及孔径的影响,并对一步法和两步法制得的多孔氧化铝膜进行比较,结果表明,两步阳极氧化法制备的多孔氧化铝模板的有序性优于一步氧化法.XRD分析证实,多孔氧化铝膜由非晶态的Al2O3组成.     

铝电解电容器高压电子箔点蚀机理的研究

采用极化曲线和场发射扫描电镜等方法,研究了铝电解电容器高压电子箔在高温强酸性溶液中的点蚀机理。结果表明:在开路状态下铝光箔在硫酸盐酸发孔溶液中可以产生点蚀,测到自腐蚀电位就是点蚀电位;形成隧道孔后,阳极极化曲线出现点蚀电位,且点蚀过电位与隧道孔长度之间存在线性关系。根据点蚀的微电池模型及其在阳极极化下微电池的腐蚀极化图,提出产生上述现象的原因是阳极极化时带孔铝箔的表面由阴极向阳极转变,其转变的临界点即所测到的点蚀电位。     

Alloy induced inhibition of fatigue crack growth in age-hardenable Al–Cu Alloys

Environmental fatigue crack propagation (EFCP) is alloy-inhibited in under aged Al–Cu–Mg and peak aged Al–Cu–Li alloys stressed in pure aqueous chloride solution. Counter to H diffusion and H-embrittlement rate limited step considerations which predict fatigue crack growth rate (da/dN) to be either independent of fatigue loading frequency (f) or increase with decreasing f, da/dN declines with decreasing f. The mechanism for such alloy induced inhibition and decreasing da/dN with decreasing f is reduced crack tip H production and uptake due to stabilization of the native aluminum passive film resulting from: (1) dissolution of anodic Cu-containing GP zones or precipitates (Al₂CuLi or Al₂CuMg) by dealloying, (2) crack surface Cu enrichment, and (3) enhanced crack wake cathodic reaction kinetics on Cu enriched sites that increase crack solution pH. Peak aged Al–Zn–Mg–Cu alloy 7075 does not exhibit alloy induced inhibition because the predominant anodic phase, Mg(Cu,Zn)₂, does not provide a source for Cu surface enrichment. Alloy induced inhibition is similar to ion-assisted inhibition by molybdate or chromate addition into bulk chloride solution which provides an alternate path to stabilize a crack tip passive film. Both alloy-induced and ion-assisted inhibition of EFCP are promoted by reduced f and crack tip strain rate which favor repassivation of the crack tip passive film over film rupture.     

Electrochemical impedance spectroscopic characterization of the oxide film formed over low modulus Ti–35.5Nb–7.3Zr–5.7Ta alloy in phosphate buffer saline at various potentials

Electrochemical impedance spectroscopic characterization of the low modulus Ti–35.5Nb–7.3Zr–5.7Ta alloy has been performed in phosphate buffer saline solution at 37 °C. Measurements were performed at various immersion intervals up to 720 h at OCP and also at various anodic potentials up to 2 V. The alloy exhibits a two time constant impedance response at the OCP and a one-time constant response at anodic potentials in the passive region. The thickness of the oxide film formed has been evaluated and the electrochemical interpretation of the results has been reported. Cyclic potentiodynamic profile of the alloy displays valve metal characteristics and the presence of a wide passive region that extends up to the maximum potential value of 2 V studied.     

Enhancement of corrosion resistance of a biomedical grade 316LVM stainless steel by potentiodynamic cyclic polarization

The paper discusses the results on the use of a simple cyclic linear potentiodynamic polarization technique as a method of improving corrosion properties of passive oxide films formed on a biomedical-grade 316LVM stainless steel surface in phosphate buffer. The results demonstrate that the modification of 316LVM surface by cyclic potentiodynamic polarization between the potential of hydrogen and oxygen evolution results in the formation of a passive film that offers significantly increased corrosion resistance (both pitting and general) when compared to the naturally grown passive film. The effect of number of cycles and anodic potential limit on the resulting corrosion properties is discussed. The capacitance analysis demonstrates that the major difference between the electrochemically formed and naturally grown passive film is in the type of semiconductivity in the potential region where pitting on the unmodified surface occurs. The XPS analysis shows that this is due to the presence of Cr(VI)-species in the electrochemically formed passive film, which contribute to the increased density of metal vacancies, and thus to the increased pitting corrosion resistance of the passive film.     

电极极化对铝合金应力腐蚀断裂敏感性的影响

为了探讨极化对铝合金应力腐蚀断裂(SCC)敏感性的影响,采用慢应变速率拉伸技术研究了不同恒电位极化条件下7075T6,7075T7351,7075RRA铝合金的应力腐蚀行为.结果表明,在-1 200～-735 mV(vs SCE)电位范围内,无论是阳极极化还是阴极极化,甚至弱极化,都会增加7075铝合金在3.5% NaCl溶液中的应力腐蚀断裂敏感性,无论哪一种热处理状态的7075铝合金在极化电位下的ISSRT均明显高于腐蚀电位下的ISSRT.同时,有阴极极化时ISSRT值随电极极化增强而减小,阳极极化时ISSRT 值有随电极极化增强而增大的趋势.但不同热处理状态的7075铝合金受极化电位的影响程度不同.由此认为,阳极溶解和氢效应都是导致7075铝合金应力腐蚀开裂的重要因素,电化学保护方法并不适用于7075铝合金应力腐蚀断裂的防护.     

热氧化对Zr基块体金属玻璃腐蚀行为的影响

本文系统研究了空气中热氧化对Zr-Cu-(Nb)-Ag-Al-Be块体金属玻璃在含Cl~-溶液中腐蚀行为的影响。热氧化后:样品表面生成0.3~0.4μm厚的氧化层,层内Al和O富集;含Nb样品点蚀电位和自然腐蚀电位明显增大,不含Nb样品极化曲线却无明显变化;浸泡实验中样品表面的腐蚀坑密度显著降低,腐蚀坑内Cu富集、Zr贫化。X射线光电子能谱结果显示热氧化后含Nb样品表面含有Nb_2O_5和更低的Cu含量,而其它元素与不含Nb样品相似。因此,热氧化能更显著地改善含Nb样品耐蚀性能的原因可能是含Nb_2O_5的氧化膜更加致密,以及该氧化层能更有效阻碍Cl~-扩散。     

铝阳极氧化膜极限厚度的研究及氧化膜微观结构的表征

采用恒电压电解法研究了铝在硫酸中的阳极氧化过程.通过金相显微镜、扫描电镜(SEM)观测了铝阳极氧化膜的厚度和微观结构特征,并通过X射线能谱仪(XPS)分析了氧化膜的成分.结果表明:长时间氧化后,氧化膜厚度达到一个极限值,此值与外加电压、电解液浓度及温度有关;铝试样本身存在缺陷时,对氧化膜的制备产生一定的影响;阳极氧化膜的主要成分为Al和O,并含有杂质元素S.     

Corrosion Behavior of Reactive Sputtered Al_2O_3 and ZrO_2 Thin Films on Mg Disk Immersed in Saline Solution

Magnesium has attracted a lot of attention over the last few decades due to its light weight and potential use as biomaterial. However, the poor corrosion resistance of magnesium restricts its practical use for application where exposure to aggressive aqueous media is unavoidable. This paper describes the growth,characterization and corrosion analyses of Al2O3 and ZrO2 thin film coatings aimed at slowing down the fast degradation of Mg in saline solution. In this study, different thicknesses of Al2O3 and ZrO2 were deposited on pure magnesium(99.95%) disk using pulsed-DC reactive sputtering process. The microstructure and phase analyses were performed using scanning electron microscopy(SEM) and X-ray diffraction(XRD),respectively. The corrosion protection behavior of the Al2O3 and ZrO2 coated magnesium samples immersed in 0.9 wt% NaC l solution were evaluated using electrochemical measurement techniques, such as open-circuit potential(OCP), potentiodynamic polarization(PD) and electrochemical impedance spectroscopy(EIS). The microstructural analyses showed that the Al2O3 thin film coatings have circular grains between5 and 25 nm, while the ZrO2 coatings have bigger ellipsoidal grains. The results from the electrochemical corrosion analyses showed that the Al2O3 coated Mg disk had corrosion resistance of approximately 3 times that of ZrO2 coated Mg disk. It was also observed that increasing the thickness of the Al2O3 coating improved the corrosion resistance of the Mg disk. These results suggest that Al2O3 and ZrO2 coating can be used to effectively control the fast degradation of magnesium for medical implant applications.     

Effect of aluminium content on the anodic behaviour of copper-aluminium alloys in 3.5 wt% NaCl solution

Anodic behaviour of heterogeneous Cu-Al alloys in 3.5 wt% NaCl solution has been investigated as a function of aluminium content by potentiodynamic polarization, cyclic voltammetry and potentiostatic current transient experiments and compared to pure Cu and homogeneous Cu-Al alloys. The specimens were subjected to various anodic potentials and subsequent analyses by scanning electron microscopy (SEM) supplemented with energy dispersion spectroscopy (EDS). The pure Cu and single -phase Cu-Al alloys showed that a relatively thick protective CuCl film forms at active-passive transition potentials and transforms into CuO or Cu(OH)₂ at the passivation potential, resulting in high limiting current densities. However, the Cu-10 wt% Al alloy is passivated to Al(OH)₃, impeding the transformation of the thick CuCl layer which contains AlCl or Al(OH)₂Cl salt into CuO or Cu(OH)₂. At high applied anodic potential, the Cu₂(OH)₃Cl phase forms on the deteriorated passive film Al(OH)₃.     

Electrochemical repairing of pitted 18-8 stainless steel

In order to clarify the reaction essential of electrochemical repairing method, which was developed to repair the passive film on pits and suppress pitting corrosion on passive 18-8 stainless steel (18-8ss) after occurrence of pitting, the electrochemical characteristics, morphology and composition of passive film after different treatments were investigated by electrochemical impedance spectroscopy (EIS), Cyclic Voltammogram (CV), Scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS). The dynamic behavior of reactions occurred at lower potential (E _L = −200 mV) and higher potential (E _H = 1000 mV) of alternating electric filed was discussed respectively and the correlation between those reactions was analyzed. Based on above results, reaction essence of electrochemical repairing for pitted 18-8ss electrode was proposed: during the periodic action of alternating current, recycle reactions take place on the surface and the pit area of pitted electrode, i.e., metal dissolves into cations (occurs at E _L and form hydrous hydroxide, the hydrous hydroxide turns into metal oxide (occurs at E _H), a ‘bipolar mode’ passive film forms and Cr content is increased in repaired passive film. At the pit area, enclosed state of the pit is destroyed by the perturbing effect of alternating current in 1.0 M H₂S0₄ solution, thus the pit area will be repaired through above-mentioned process.     

Sn,Al对船用铜管耐蚀性的影响

研究了铜及Cu-2.80%Sn-1.06%Al合金在3.0%NaCl溶液及流动海水中腐蚀性能,利用金相、扫描电镜及电化学特征分析了它们的耐蚀特性。结果表明,纯铜在21mV时发生阳极溶解,在海水冲刷作用下保护膜很快遭到破坏,腐蚀速度大,Cu-2.80%Sn-1.06%Al合金由于其表面形成的Cu、Sn和Al的混合氧化物保护膜均匀、致密、质硬、在流动海水冲刷、摩擦作用下,保护膜稳定性好,腐蚀速度小。     

Some aspects of corrosion and film formation of austenitic stainless steel type 316LN using electrochemical impedance spectroscopy (EIS)

Corrosion and passive film characteristics of 316LN stainless steel with different degrees of cold work (0–25%) were studied using electrochemical impedance spectroscopy (EIS) and potentiodynamic anodic polarization techniques in deaerated acidic and alkaline (pH = 8) media. EIS measurements were conducted at open circuit potential (OCP) as well as after passivation in these media. Using the capacitance data from EIS measurements, film thickness was calculated. A definite correlation was observed between film thickness and corrosion rate after passivation. Analysis of the series capacitance and series resistance data from the EIS spectra showed that the films formed at OCP and after passivation were of semiconducting type. The nature of the semiconducting type of films was determined to be n-type using the ratios of anodic and cathodic transfer coefficients (α_a/α_c).     

Electrochemical Polarization and Passivation of Tin in neutral solutions of chloride,bromide and iodide ions

Passivation of commercial grade tin (99.5%) was studied in 0.1 M KCl, KBr and KI solutions using the potentiodynamic technique involving cathodic and anodic polarization at various scan rates. While low scan rates (0.1 mV/sec) lead to the complete deterioration of the anode in chloride solutions, higher scan rates of 1 and 5 mV/sec lead to the appearance of two anodic peaks. These peaks disappear at still higher rates (10 mV/sec). In bromide solutions, two anodic peaks appear with scan rates of 1 and 5 mV/sec, and only one peak is observed with 50 mV/sec. A white precipitate is formed in both chloride and bromide solutions during anodic scanning. No gas evolution (O₂, Cl₂ or Br₂) could be detected up to anode potentials of 3–4 V (SCE). At scan rates of 1 mV/sec and higher values, pitting does not occur, and thick anode films are formed. The film is gray in chloride solutions, and yellowish gray in bromide solutions. Values of the corrosion potential Ecor are recorded for the forward and reverse scanning. The corrosion cd Icor is calculated both by the Tafel extrapolation procedure and by the linear polarization technique. The latter gives more accurate results. In Cl^? and Br^? solutions, the first anodic peak associated with passivation is more anodic than the equilibrium potentials for the tin/tin oxides or hydroxides. Passivation is explained as a result of the formation of the sparingly soluble salts Sn(OH)Cl, Sn(OH)Br which appear both in the precipitate and in the anode film. The passivating films are constituted at least partially of these basic salts, and contain a proportion of the oxides and hydroxides of Sn. From the effect of scan rates on the characteristics of the anodic peaks, it appears that the formation of thick anode films is governed by the diffusion kinetics for porous films. Of the three possibilities considered as explanations for the second anodic peak (oxidation of impurities, oxidation of halides to oxyacids, and structural changes in the film) the latter appears to be the most probable one. Thick anodic films are not formed in iodide solutions (scan rates 1, 5, 10 mV/sec), and the anode surface remains very bright. Dense evolution of I₂ occurs during anodic polarization, and apart from I₂ which dissolves in solution, the latter remains clear. Only one peak is observed in the forward anodic scanning. The polarization resistance technique gives Icor = 0. Thermodynamic calculations show that I₃^?, HIO, IO^?, HIO₃, IO₃^?, HIO₄, and IO₄^? occur in 0.1 M KI solutions at potentials less anodic than the potential of the anodic peak (1.32 to 1.37 V, vs SCE). This peak potential is more anodic than the quilibrium potential for I₂ evolution.     

Extremely high pitting resistance of NiTi shape memory alloy thin film in simulated body fluids

In this paper the corrosion behavior of NiTi thin films fabricated by sputtering from Ni and Ti targets has been studied by cyclic potentiodynamic polarization tests in Hank's and Ringer's solution at 310 K. For comparison, bulk NiTi Shape Memory Alloy (SMA) has also been studied to elucidate the different corrosion behavior of bulk and thin film material. The electrochemical experiments reveal that thin film NiTi SMA has comparable corrosion current density (i_corr), much higher pitting corrosion potentials and wider passive range than the bulk NiTi. We show that NiTi SMA vapour deposited thin films are less susceptible to pitting corrosion than the bulk.     

渗铝钢在Na_2S溶液中的腐蚀行为研究

用热浸镀方法制备了一种渗铝钢 ,并通过静态腐蚀失重试验、电子探针微观分析和X 射线衍射分析对渗铝钢、工业纯铝、碳钢在不同浓度Na2 S溶液中的腐蚀行为进行了研究。结果表明 ,随着溶液中Na2 S浓度的升高 ,渗铝钢因表层 (Al2 O3+Al)发生溶解而形成均匀腐蚀 ;而碳钢则发生不均匀腐蚀和点蚀 ;纯铝在低浓度Na2 S溶液中发生点蚀 ,在高浓度时则发生严重的剥蚀。     

吗啉多元胺对混凝土钢筋的阻锈作用

迁移性阻锈剂对钢筋混凝土中的金属材料有很好的保护作用,国内这方面的研究报道较少.采用动电位极化曲线和电化学阻抗谱研究了吗啉多元胺在模拟混凝土空隙液及混凝土中对钢筋的保护作用.在含有2 000mg/L NaCl的模拟液中,吗啉多元胺可以提高钢筋的抗点蚀能力.吗啉多元胺的加入导致混凝土钢筋的腐蚀电位正移,对钢筋的阴极和阳极电化学过程均有抑制作用,它是一种混合型缓蚀剂.吗啉多元胺能够在混凝土中扩散迁移,在钢筋表面形成吸附膜,阻挡侵蚀性离子对钢筋表面的侵入,抑制钢筋腐蚀电化学反应的进行.     

Inhibitive effect of some thiadiazole derivatives on C-steel corrosion in neutral sodium chloride solution

Electrochemical techniques were used to investigate the effect of concentration of three new thiadiazole derivatives (I–III) on the corrosion behavior of C-steel in 0.5 M NaCl solution through the analysis of electrochemical measurements including open circuit potential (OCP), Tafel polarization and electrochemical impedance spectroscopy (EIS). Polarization curves showed that the compounds studied act as anodic type inhibitors, where the inhibition efficiency increases with increase in inhibitor concentration and decreases with rise in temperature. An adherent layer of inhibitor molecules on the surface is proposed to account for their inhibitive action in which the organic molecules adsorb on the active anodic sites following Langmuir isotherm. The thermodynamic parameters of adsorption and corrosion processes were determined and discussed. The results also indicated that pitting potential at higher anodic polarization of C-steel in 0.5 M NaCl solution becomes more positive the higher the concentration of the additive, suggesting that these inhibitors acts as retarding catalyst for pitting corrosion. EIS data confirm well the electrochemical dc results and the results are all in good agreement with the calculated quantum chemical HOMO and LUMO energies of the tested molecules, as well as with surface examination via scanning electron microscope.     

Effect of pre-existing oxide film on the electrochemical fabrication of nanoporous alumina film

Different thickness of barrier-type oxide film was intentionally grown on the Al metal surface and the effect of barrier film on the formation of nanoporous aluminum oxide film during anodization was investigated to control the nanopore structure. Analysis of potential transients during anodization indicated that anodic oxide film is initially overlaid on the barrier film but the anodic film is more facile to dissolve than barrier film. As the thickness of barrier film increases, both nanopore diameter and density decrease but the pore length is irrespective of barrier-film thickness.     

Electrochemical and XPS studies of corrosion behavior of Ti–23Nb–0.7Ta–2Zr–O alloy in Ringer's solution

Corrosion behavior of a newly developed multifunctional β-type Ti–23Nb–0.7Ta–2Zr–O (mol%, TNTZO) alloy in Ringer's physiological solution was evaluated by open circuit potential, potentiodynamic polarization and X-ray photoelectron spectroscopy (XPS) techniques. Corrosion property of Ti–6Al–4V was also measured for comparison. The results showed that the TNTZO alloy possesses much better corrosion property than the Ti–6Al–4V alloy, corroborated by a high corrosion potential and broad passive region, which is attributed to the stable and inert passive TiO₂ film modified by the oxides of Nb, Ta and Zr on the surface of the TNTZO alloy.