铝阳极氧化膜的蚀孔形貌与蚀孔生长机理研究

用动电位极化法和扫描电镜研究了工业纯铝阳极氧化膜在NaCl溶液中的孔蚀行为．结果表明，蚀孔的生长控制机制随蚀孔的发展而发生变化，蚀孔生长的初期为扩散控制，然后向欧姆控制发展，在蚀孔生长的后期阶段又转为扩散控制．对蚀孔的形貌观察发现，小孔贯穿阳极氧化膜以后优先在基体中生长，形成“半球型”的蚀孔形貌，阳极氧化膜大部分保留在蚀孔上方形成“膜盖”，膜盖上只有一个直径很小的小孔作为蚀孔生长的扩散通道．讨论了蚀孔的生长机制．     

非晶态镍基合金表面亚稳态蚀孔生长的动力学特征

用恒电位下的电流-时间记录法研究了非晶态NiCrFeSiB合金在NaCI溶液中的亚稳态蚀孔的生长动力学行为。恒电位下亚稳孔蚀电流与时间的关系为I-I_0=k(t-t_0)~2,k表征亚稳小孔的生长速度。大量亚稳态蚀孔的k值服从对数正态分布,随电位升高,k的平均值和标准差都增大。亚稳蚀孔的峰值电流在恒电位下也服从对数正态分布且随电位升高而增大。文中提出一个亚稳态蚀孔生长的两阶段模型,解释了实验结果。     

钨酸根离子对304不锈钢亚稳态与稳态孔蚀形核与生长的影响

利用动电位回扫的方法研究了钨酸根离子(WO_4~(2-))对304不锈钢亚稳态孔蚀及稳定孔蚀的形核与生长阶段的影响。随着WO_4~(2-)浓度的增大,304不锈钢亚稳态孔蚀电位Em和稳定孔蚀电位Eb值均升高,即WO_4~(2-)浓度的增大,抑制了亚稳态孔蚀和稳定孔蚀的形核。WO_4~(2-)浓度增加导致亚稳态孔蚀的平均生长速度和电流峰值降低,从而降低了亚稳态孔蚀转化为稳定孔蚀的可能性,抑制了稳定孔蚀形核。WO_4~(2-)增加导致孔蚀回扫过程中的最大电流密度增大,再钝化电位Ep降低,即导致生长的稳定蚀孔更难于再钝化,其原因可能是钨酸盐膜在小孔孔口的沉淀会促进蚀孔生长的稳定性。     

粗糙度在316L不锈钢小孔初期生长过程中的作用

通过分析不同粗糙度下的316L不锈钢在0.01 mol/L Na Cl溶液中小孔腐蚀早期的电流波动,研究了粗糙度与不锈钢亚稳态孔蚀电位Em和稳定孔蚀电位Eb之间的关系,以及粗糙度(Ra)对亚稳态小孔生长机制的影响。结果表明,Em和Eb均随Ra的对数的增大而线性下降;Ra增大,亚稳孔的平均形核率和平均寿命增大,生长速率变化不大,但是同样的生长速率下粗糙表面的亚稳孔具有更强的可持续生长能力,加之高的形核频率导致强的腐蚀累积效应促进了亚稳态小孔向稳定孔的转变。     

PO43-对304不锈钢在氯离子水溶液中小孔腐蚀形核过程的影响

利用动电位循环扫描的方法研究了PO₄^3-对304不锈钢亚稳态孔蚀及稳定孔蚀形核与生长阶段的影响。随着PO₄^3-浓度的增大,亚稳态孔蚀电位E_m和稳定孔蚀电位E_b值均增大,即PO₄^3-浓度的增大,抑制了亚稳态孔蚀和稳定孔蚀的形核。PO₄^3-增加导致亚稳态孔蚀的平均生长速度和电流峰值降低,从而增大了亚稳态孔蚀转化为稳定孔蚀的难度,抑制了稳定孔蚀形核。但PO₄^3-增加导致孔蚀再钝化电位E_p降低,使充分发展的稳定蚀孔更难于再钝化,其原因可能是磷酸盐膜在小孔孔口的沉淀会促进蚀孔生长的稳定性。     

外加磁场对铁磁材料电火花小孔加工的影响

针对电火花加工中电蚀产物排出困难、加工效率低、电极损耗严重等问题,研究了外加磁场对铁磁性材料电火花小孔加工的影响,分析了铁磁性电蚀微粒在加工区域受外加磁场磁力作用的影响规律,实验研究了在不同电极材质条件下,外加磁场对加工速度、电极损耗的影响。结果表明:采用磁场电火花复合加工方法在铁磁材料工件上加工小孔,其加工速度和电极损耗都比普通电火花加工有明显改善。     

含S阴离子对低碳钢孔蚀的影响

用电化学极化法研究了SO2-4,SO2- 3,S2O2-3,CNS-和S2- 5种含S阴离子对低碳钢在0.1 mol/L NaNO2 +005 mol/L NaCl溶液中的孔蚀行为的影响.CNS-,SO2-3,SO2-4和S 2O2-3离子促进碳钢孔蚀形核,影响大小顺序为S2O2-3＞SO2- 4＞SO2-3＞CNS-;S2-离子则抑制孔蚀形核.S2-,S2O2- 3和SO2-3离子促进小孔生长;而SO2-4抑制小孔生长.CNS-离子对 小孔生长的作用不明显.将各种含S阴离子对孔蚀形核和生长影响作用的大小进行了比较, 并讨论了作用机制.     

铝合金孔底电位的研究

<正> 一、引言 铝合金是广为应用的结构材料之一,但常因发生小孔腐蚀而影响其使用寿命。因此研究铝合金孔蚀的再钝化过程既有理论意义,又有实用价值。孔底电位是孔内其他电化学参数的综合反映,从测得的孔底电位,可分析蚀孔生长过程中孔内的状态及在再钝化过程中变化情况。 及认为随着小孔变深,孔底与金属表面的欧姆电位降增大,孔底电位负移到钝化区从而发生再钝化。而Strehblow的观点暗示了在再钝化过程中孔底电位将从活化区正移到Flade电位以上的钝化区,即认为蚀孔内表面是处于活性溶解区。Okada     

铝箔在HCl中交流电腐蚀的起始成孔效应

研究了在5.5mol/LHCl高纯铝箔交流电腐蚀的起始成孔对后续蚀孔发展以及表面扩大率影响。50Hz交流电直接腐蚀时,在小于0.2A/cm2时产生大的圆孔,大于0.2A/cm2时产生覆盖有厚膜的小孔,并导致小孔堵塞。用交流预腐蚀发孔,得到覆盖有透明钝化型薄膜的小孔,孔径较大,并为后续的交流电腐蚀继承和延续。起始蚀孔的几何尺寸和表面膜形态决定后续蚀孔的尺寸和表面膜。     

金属亚稳态孔蚀行为的电化学研究

综述了国内外近期在亚稳态孔蚀行为的研究方法,亚稳态小孔形核、生长的统计规律 ,亚稳态蚀孔生长和再钝化过程的机制及控制因素,亚稳态蚀孔向稳定蚀孔转变的临界条件等方面的 研究进展,并对进一步的研究作出了展望。     

The mechanism of electrograining aluminium sheet in nitric/boric acid electrolyte

Aluminium sheet is roughened commercially in various electrolytes to form a pitted substrate suitable for lithographic printing plates. Although studies on hydrochloric acid systems have been published, little has been reported on the equally important nitric acid based electrolytes.

Observations were made using high resolution scanning electron microscopy on a commercial lithographic sheet alloy (AA1050A) that had been a.c. electrograined for very short times in a nitric/boric acid electrolyte. These were combined with electrochemical information to elicit the mechanism by which a.c. electrograining proceeds.

It was determined that graining is governed by anodizing processes. Pitting proceeds at flaws in the oxide film. At the start of the anodic cycle the exposed metal, which may be in existing pits or new sites, is anodized forming an oxide layer that replicates the shape of the pit, thus forming a cup shaped structure. As the temperature rises the rate of dissolution overtakes the barrier film growth rate, which causes detachment of the anodic oxide cup and effectively direct metal dissolution occurs. When the potential falls, repassivation of the pit occurs.

Repetition of this process causes a successive increase in pit diameter as each oxide cup is formed and the cups are forced out of the pit in a stacked formation. As the pit grows the oxide film on the surrounding metal surface peels back around the periphery of the pit.

The cathodic half cycle influences pit initiation.     

The effect of carbon within corrosion pits of iron in chloride solutions

Iron artificial pits have been used in this work to investigate the effect of a carbon-based black layer that can form within a pit during iron dissolution in HCl solutions. Commercial purity iron (99.5%) and high purity iron (99.99+%) have been compared, and a black layer has been observed only in the 99.5% iron pit. It has been found that the formation of a black layer within an iron artificial pit is potential dependent: it can form at applied voltages below 0.2?V(SCE), but not at 0.6?V(SCE). The presence of a black layer can decrease the rate of mass transport inside a pit, which may help to maintain the aggressive acidic solution in an active pit. This effect has been characterised quantitatively via potentiostatic and potential step methods. In addition, the black layer has also been found to induce a small extra resistance in the solution.     

The growth of 2-D pits in thin film aluminum

Pitting in chloride solutions of 1000–2000 Å thick films of Al evaporated onto quartz substrates was studied. The anodic dissolution and hydrogen evolution current densities in the pit were both constant with time. The anodic current density and the pit morphology were, however, dependent on the pit growth potential. At low potentials, the pit current density increased linearly with potential, the pit surface was extremely rough, and pit growth was determined to be under ohmic control. At higher potentials, the pit current density was independent of potential and the pits became round and smooth, indicating that mass transport was rate limiting.     

Partial currents of anodic oxidation of copper in alkaline media according to RRDE data. II. Experiment

Anodic oxidation of copper in aqueous alkaline media is studied using the method of chronoamperometry on a rotating ring–disk electrode in a wide range of potentials. Partial currents of processes of anodic oxide formation, active copper dissolution, and chemical dissolution of Cu(I) oxide taking into account the possibility of its chemical growth are calculated. The current of chemical oxide dissolution is registered at all the studied potentials. In the cathodic range of potentials, anodic dissolution of copper is thermodynamically impossible, but, after the disk electrode polarization is switched off, oxide is formed via the chemical route. In the range of potentials where anodic copper dissolution is thermodynamically possible, the current of anodic oxide formation prevails over the currents of the other partial processes. The dependence of partial currents on time within the studied time interval (120 s) is not systematic, while their dependence on the disk polarization potential is very significant: the rate of oxide formation repeats the shape of the cyclic voltammogram, the rate of active copper dissolution through the oxide pores increases with potential, and the rate (and rate constant) of chemical dissolution of Cu(I) oxide are maximum at the potentials of its anodic formation. If the thermodynamic activity of the oxide layer does not reach unity within the anodic oxidation period, then the rate constant of chemical copper oxidation exceeds the rate constant of chemical oxide dissolution. The result is chemical oxidation of copper by traces of molecular oxygen in the solution.     

Plasma nitriding of 42CrMo low alloy steels at anodic or cathodic potentials

The nitriding of low alloy steel has been carried out at anodic potential in a space enclosed by an active screen that consists of two cylinders with different diameter. These two cylinders made up a hollow cathode in a discharge system. The difference in diameter of the two cylinders is about 8-10 mm to maintain strong discharge between them. They can also be heated rapidly to the required temperature for treatment. The sample to be nitrided was held at the same potential as that of the anode used in the discharge and heated through heat radiation from the hot cylinders and by electron bombardment. Electrons bombarded the surface of the sample even though the intensity of bombardment was low because of the anodic sheath. To illustrate the effect of the anodic potential on the nitriding a comparison was made between nitriding at anodic and cathodic potential (general plasma nitriding). The phase composition, the compound layer thickness and the surface topography of the nitrided layer, as well as its properties, were investigated using X-ray diffraction, scanning electron microscopy and microhardness tester. In particular, the corrosion properties of the untreated and plasma nitrided samples were evaluated using anodic polarization tests in 3.5% NaCl solution. The results showed that anodic plasma nitriding not only increased the surface hardness but also improved the corrosion resistance of the low alloy steel.     

Quantitative characterization by micro-electrochemical measurements of the synergism of hydrogen, stress and dissolution on near-neutral pH stress corrosion cracking of pipelines

Occurrence of stress corrosion cracking of pipelines under a near-neutral pH condition depends on the synergism of stress, hydrogen and anodic dissolution at the crack tip of the steel. In this work, micro-electrochemical techniques, including localized electrochemical impedance spectroscopy and scanning vibrating electrode technique, were used to characterize quantitatively the synergistic effects of hydrogen and stress on local dissolution at crack-tip of a X70 pipeline steel in a near-neutral pH solution. Results demonstrate that, upon hydrogen-charging, the anodic dissolution of the steel is enhanced. The resistance of the deposited corrosion product layer depends on the charging current density. There is a non-uniform dissolution rate on the cracked steel specimen, with a highest dissolution current density measured at crack-tip. For a smooth steel specimen, the synergistic effect factor of hydrogen and stress is equal to 5.4, and the total effect of hydrogen and stress on anodic dissolution of the steel is 7.7. In the presence of a crack, the hydrogen effect factor, stress effect factor and the synergistic effect factor are approximately 4.3, 1.3 and 4.0, respectively. The total effect factor is up to 22.4, which is very close to the 20 times of difference of crack growth rate in pipelines in the presence and absence of the hydrogen involvement recorded in the field.     

铝在海水中蚀孔生长的特点

<正> 铝及其合金是海洋工程中的常用材料之一。铝在海水中全面腐蚀率极小,约0.03～0.05mm/a,孔蚀是其主要破坏形式。铝设备在海水中的使用寿命取决于耐孔蚀性能。 对铝的蚀孔生长,前人做了一些工作,考察了诸如电位、电流、时间及某些离子对蚀孔生长速度的影响;进行了一些动力学的研究。蚀孔生长过程中孔内Cl~-浓度升高和pH降低,已得到公认,但目前见到的数据极少。闭塞区内溶液的变化对铝孔蚀的影响研究     

在南海海域铜合金8年腐蚀行为研究

研究了7种铜合金在南海榆林站海水中8年的腐蚀行为结果表明,7种铜合金的平均腐蚀深度与时间关系符合H=aTb规律,其平均腐蚀速度随时间而下降,利用EPMA、X衍射分析了HSn62—1、QSn6.5-0.1腐蚀膜成分、结构与耐蚀性的关系.     

Electrochemical corrosion behavior of X80 pipeline steel in a near‐neutral pH solution

In this work, the electrochemical corrosion behavior of X80 pipeline steel was investigated in a near‐neutral pH solution using electrochemical impedance spectroscopy (EIC) and photo‐electrochemical (PEC) measurements as well as X‐ray photo‐electron spectroscopy (XPS) technique. The effects of hydrogen‐charging and stress were considered. The results show that the steel is in an active dissolution state, and a layer of corrosion product is formed and deposited on the electrode surface, which is subjected to further oxidation to form ferric oxide and hydroxide. Photo‐illumination enhances anodic dissolution of the steel when it is under anodic polarization due to destroying of the corrosion product film. When the steel is under cathodic polarization, the cathodic current density decreases upon laser illumination due to the photo‐oxidation of hydrogen atoms generated during cathodic reactions, which behaves as an anodic reaction to offset the cathodic current density. Hydrogen‐charging and stress decrease the corrosion resistance of the steel and enhance the dissolution rate of the steel.     

孔蚀发展过程动力学分析

根据物质守恒、电荷守恒关系和电化学动力学,对球形、柱形蚀孔且其孔内存在和不存在沉积层,共四种典型状态下蚀孔的发展过程进行动力学分析,得到孔蚀电流、蚀孔深度和孔径随时间的变化关系。结果表明:孔蚀电流随时间发展共有四种特征函数,t~(1/2)、t、t~2和t~*ln(t),每一函数均对应特定的蚀孔发展状态.此四种函数构成一般蚀孔电流随时间关系的基集合,线性组合后得到普遍性孔蚀发展动力学方程。详细讨论了孔蚀发展与诸影响因素的关系,孔内沉积层存在与否及性能如何对蚀孔发展有显著影响,对球形孔的影响大于对柱形蚀孔。进而分析缓蚀剂抑制孔蚀发展的可能途径和效果,确定了孔蚀发展缓蚀剂须具备的条件;模型的正确性得到三方面结果的证实:实测304不锈钢在NaCl介质中孔蚀发展过程的电流关系,由建立的动力学方程给予了很好的解释。模型得到的孔蚀电流增长的最大方式是时间二次方,最小方式是平方根,与大量的文献结果吻合。孔蚀深度随时间仅有两种变化关系,幂函数和指数函数,与孔蚀深度的统计研究结果一致。