Determination of the diffusivity of cation vacancy in a passive film of Ni using Mott-Schottky analysis and in-situ ellipsometry

The diffusivity of cation vacancies in a passive film formed on Ni in a pH 8.5 buffer solution was estimated based on the Point Defect Model with high field migration equations. The parameters required to calculate the diffusivity of the cation vacancies include the flux of cation vacancies, the acceptor density, and the thickness of the passive film as functions of the film formation potential and they were measured from potentiostatic polarization, a Mott-Schottky analysis, and in-situ ellipsometry, respectively. The passive current density, proportional to the flux of the point defects, linearly increased with an increase of the passivation potential, while the acceptor density was reduced with the potential. The thickness of the passive film appeared to increase very rapidly and the growth became stable in thousands of seconds, and increased linearly with an increase of the potential. The dependence of all parameters investigated in this study on the passivation potential corresponded well to the theory. The diffusivity of the cation vacancies in the passive film of Ni was determined to be 2.7×10^?18 cm²s^?1.     

中大口径弹药内表面喷涂工艺改进

目的改进弹药内表面喷涂方式及涂料种类,解决弹药装药环境适应性高低温贮存裂纹疵病的问题。方法采用高压无气喷涂技术进行弹体内表面喷漆,替代原有的空气喷涂。探讨涂料压力、涂料黏度、喷嘴移动速度等因素对涂层质量的影响,通过正交试验确定最佳工艺参数。采用直线加速器检测不同漆膜厚度的弹体装药环境适应性裂纹疵病情况。结果涂料压力为65 kg/cm2,涂料黏度为30 s,喷嘴移动速度为50 Hz,喷嘴孔径分别为0.51,0.71 mm时,弹药内表面漆膜具有较好的外观质量,漆膜厚度及附着力满足要求。膜层厚度为180μm的弹药经高、低温贮存试验,未出现裂纹。结论应用实践证明,高压无气喷涂工艺技术用于弹药卧式自动内表面涂装可行,具有一定的行业推广价值。     

Two‐step electrosynthesis of polypyrrole for corrosion protection of stainless steel

Smooth polypyrrole (PPy) films were successfully electrosynthesized on a stainless steel (SS, 1Cr18Ni9) surface by a self‐catalytic two‐step process. SS substrate dissolution during PPy electrosynthesis was effectively depressed. The redox properties and corrosion behavior of PPy film coated SS electrodes were investigated by cyclic voltammetry, electrochemical impedance spectroscopy (EIS), and potentiodynamic polarization. The reduction of PPy was found to include two reaction processes: an anion dedoping process and a cation insertion process. The PPy film was found to lose its electroactivity when polarized at high potentials due to peroxidation. EIS of SS/PPy mainly corresponds to PPy film response and charge transfer resistance decreases as film thickness increases, indicating that SS corrosion can be inhibited effectively by the PPy film.     

压载水舱高固体份环氧涂料的研究

目的提高压载水舱环氧涂料的耐阴极剥离性能。方法以双酚A型环氧树脂、酚醛环氧树脂、C9石油树脂和双酚F型环氧树脂为涂料的主要成膜树脂,采用四因素四水平的正交试验,对四种树脂的用量进行优化。固化剂采用聚酰胺固化剂和改性酚醛胺固化剂进行混合,以获得良好的物理化学性能。对涂料的颜基比及助剂进行了分析研究,以确定涂料各组分的用量。结果通过四因素四水平的正交试验,确定了涂料四种树脂的用量。当聚酰胺固化剂和改性酚醛胺固化剂的混合比例为2:1时,涂料具有较佳的抗阴极剥离性能。通过对颜填料不同颜基比(0.75:1~1.5:1)的研究,当涂料的颜基比为1:1时,涂料的耐阴极剥离性能最好。结论通过对涂料的成膜树脂、固化剂及颜基比的研究,制备的压载水舱环氧涂料具有优异的耐阴极剥离性能及良好的耐海水性、耐盐雾性及抗腐蚀蔓延性等性能,能够满足船舶压载舱的防腐需求。     

Wachstum und Auflösung anodisch erzeugter Oxidschichten auf Titan

Growth and dissolution of anodically obtained oxide layers on titanium Oxide films were grown by anodic polarization of titanium in various aqueous electrolytes. The field strength derived from film thickness and voltage is linearly related to the logarithm of the total current density. The current efficiency for film formation depends upon current density, pH-value, and film thickness. The dielectric constant of the film decreases with field strength from ε = 110 to ε = 7, but rises again at high field strengths and thick films. The dissolution rate of anodic oxide films on titanium was investigated as a function of pH-value, concentration of chloride, and temperature, respectively. Aging of the films in distilled water causes the dissolution rate to decrease by up to 3 order of magnitude.     

油气运输管道防腐层的抗阴极剥离性能

研究了3种聚乙烯防腐层(3PE、热收缩带、热收缩套)在不同阴极保护电位下,阴极剥离过程中阴极保护电流的变化情况,以及它们在不同条件下的抗阴极剥离性能。结果表明:3种防腐层的阴极剥离距离,会随着阴极保护电位的负移、时间的延长及温度的升高而增大;在过负的阴极保护电位下,3种防腐层阴极剥离时的阴极保护电流呈现出了不同的波动性,3PE防腐层抗阴极剥离的性能优于聚乙烯热收缩带(套)。     

Anodic oxidation and kinetics of titanium in 1 M chloride solutions

The anodic behaviour of titanium was investigated in 1 M chloride solutions of pH ranging from 0.0 to 12.0 by using electrochemical techniques combined with chemical analysis. No active region appears in solutions of pH above 2.0. In the passive region, the amount of titanium dissolved into the solution during 1 h oxidation decreases with increasing pH, and no dissolution occurs at pH 10.5. The thickness of passive films estimated from the electric charge accumulated on the surface increases linearly with the potential. The kinetic analysis between the anodic current and the film charge indicates that the growth of the passive film obeys the inverse logarithmic rate law, and the kinetic parameters are calculated.     

Cathodic disbonding of an unpigmented epoxy coating on mild steel under semi- and full-immersion conditions

Cathodic disbonding of an unpigmented epoxy coating around a defect was studied with samples fully- and semi-immersed in 3.5 wt.% NaCl solution. Disbonding and the growth of blisters were monitored by scanning acoustic microscopy, which showed growth of blisters within the disbond for both type of samples. Scanning Kelvin probe potential maps suggest that blisters first form at local anodes. For semi-immersed samples, disbonding of the immersed part and the non-immersed part propagate with parabolic kinetics at identical rates, similar to fully-immersed samples. This implies that ion transport is along the coating–metal interface in both cases.     

Impedance studies of the inhibitive effect of benzotriazole on the corrosion of copper in sodium chloride medium

Impedance studies of a copper electrode in chloride medium with or without benzotriazole (BTA) were made over a wide frequency range (10^?2?10²KHz). The impedance characteristics of the Cu-BTA surface film were established under various experimental conditions. The results indicate that the film was of a dielectric nature having a dielectric constant of ca. 20. It was found that the film thickness increased and the corrosion rate decreased by increasing the BTA-concentration or with ageing. It was assumed that, at the stationary state, the rate of dissolution of Cu-BTA film blanced that of the slow transport of Cu ions through the film. Good support for these results was obtained from the data of potentiostatic polarization and weight loss measurements.     

Influence of deposition technique on the protective properties of epoxy films

The electrochemical impedance spectra, the anodic polarization curves and the time dependence of paint capacitance and paint resistance have been used in this paper to evaluate the protective properties of epoxy films on carbon steel substrate. The coatings were formed using four deposition techniques (brushing, immersion, cathodic and anodic electrodeposition) with the aim to determine the effect of deposition type on the anticorrosive performances of epoxy paint. Interpretation of Nyquist and Bode impedance spectra with the immitance analysis Equivcrt. programme has established an electrical equivalent circuit with two time constants fitted to describe the electrodeposited epoxy/carbon steel system in the 3 % sodium chloride solution and an electrical equivalent circuit with four time constants fitted in case of epoxy films applied by brush or immersion. The anodic polarisation measurements show nobler corrosion potentials and smaller dissolution current densities for the carbon steel in the presence of the electrodeposited films in comparison with epoxy coatings applied by brush or with the immersion technique. The values of the porosity, water uptake, and ionic transport through the film emphasize the higher performances of the electrodeposited films, characterized by uniformity, porosity absence, low water permeability and few conductive pathways.     

Effect of chromium content and sweep rate on passive film growth on iron-chromium alloys studied by EQCM and XPS

Growth of passive films on Cr and Fe-Cr alloys with Cr concentrations ranging from 15% to 54% was studied in situ with the electrochemical quartz crystal microbalance (EQCM). Mass change and current transients were measured as the response to a potential change in the passive region from 0 to 800 mV (SHE) in a pH 1.5 sulfate electrolyte. From these measurements, the thickness change as well as integral and differential growth fractions were calculated. The growth fraction expresses the fraction of oxidized metal that remains in the film. It was found that higher Cr contents gave thicker films and an increase in the growth fraction. The thickness change curves were compared to film growth models assuming rate control at either a film interface or in the film itself through high field conductivity. The integral growth fraction for the potential change experiment was found to vary approximately linearly with the Cr bulk composition. The fraction of dissolved Cr calculated from EQCM data matched well with previous solution analysis results.     

用微量元素涂料改善球铁件热节组织的试验研究

对RE、Tc、Bi、Sb等微量元素以涂料形式对球铁件厚大热节部位进行微合金化,以改善其组织的可能性进行了试验研究,结果表明:多元微量元素涂料可有效地消除碎块状石墨,提高球化率,改善球铁组织,涂料层厚度影响微合金化程度而应严格控制,该工艺具有简便。无炉料污染、可代替冷铁以确保复杂铸件组织均一等优点。     

有机涂层耐阴极剥离的影响因素研究进展

有机涂层在服役期间,阴极剥离是使其失效的主要形式之一。综述了国内外海水、淡水、土壤环境中,有机涂层耐阴极剥离影响因素的研究进展。介绍了有机涂层阴极剥离过程,阐述了影响涂层耐阴极剥离的因素——树脂、颜填料、助剂以及表面处理、涂层厚度和缺陷等,并指出了耐阴极剥离有机涂层主要研究方向的发展趋势。     

A critical review of the protection of metals by paints

The literature has been reviewed in order to categorize the reasons why paint films protect metals, and how they eventually degrade. The early work is examined which showed that the rate-controlling process in the corrosion degradation of some painted metals was the diffusion of ions through the paint film. The processes of water and oxygen permeation, being faster than on unpainted samples, were not rate controlling for these paint films. Later work is then discussed which indicates the importance of other factors, e.g. oxygen permeation may well be rate determining with some paint films; in some cases ionic diffusion rates are so low that, although they may be the slowest process, they cannot be rate controlling; and although water permeability in most cases cannot be the rate-controlling step because it is too fast, it may well be the rate-controlling factor in the loss of adhesion. It is demonstrated that the rate-controlling factor for one type of painted metal is not necessarily the same as for another and therefore it can be sometimes misleading to extrapolate the results of one system to that of another.     

提高铝药筒阴极电泳涂漆良品率

目的通过优化铝药筒预处理及阴极电泳涂漆工艺参数,设计专用挂具等,提高涂漆制品良品率。方法分析铝药筒不良品漆膜疵病,依据阴极电涂漆的基本原理,明确电泳漆相关工艺参数对铝药筒电泳涂漆及漆膜性能的影响,调整施工槽液温度为29~31℃,施工电压为170~175 V,槽液固体份为13%~15%,槽液电导率为900~1300μs/cm,阳极液电导率为500~700μs/cm,漆膜烘干温度为175℃,烘干时间为29~30 min。对铝药筒的预处理工艺进行分析,明确铝药筒预处理基体发黑、漆膜结合性不良的影响因素。结果经过试验,降低除油液中碱的含量10~15 g/L,降低热水洗的温度10℃左右,可以确保油污去除彻底且基体金属不过腐蚀、不发黑。同时,根据铝药筒的材质及结构特点,对其设计专用挂具,确保涂漆导电一致性。调整电泳漆相关工艺参数后,漆膜厚度一致性得到控制,解决了药筒色差明显、漆膜结合性差等问题,产品外观质量明显提高,装配漆膜无脱落现象。结论通过优化预处理及电泳涂漆工艺参数,加强过程监控,采用改进后的挂具等手段,大幅度提高了铝药筒阴极电泳涂漆的良品率。     

The effect of applied voltage on the cathodic electrodeposition process

The effect of applied voltage on the final film thickness and the rate constant during the cathodic electrodeposition process has been investigated by a constant voltage method. It was shown that the film thickness increases linearly with applied voltage and this was explained analytically. The rate constant increases exponentially with applied voltage.     

恒电量微扰下涂装金属体系极化电位响应式的理论推导

恒电量微扰下的过渡过程可用一组线性微分方程组表示,求解的关键是确定其初始条件值。在恒电量扰动瞬间,有溶液电阻和忽略溶液电阻的暂态过渡过程的机制不同,因而极化电位随时间变化的函数关系也不一样。有溶液电阻时,电荷的转移和传输不能瞬间完成,需要一定的传递时间,即极化电位不会发生突变;而无溶液电阻时,依据基尔霍夫定律,在恒电量扰动瞬间,极化电位必将发生突变。同时电路受恒电量控制,无论突变瞬间或电量传递的整个过程都必须遵守电荷守恒原理。以此建立恒电量激励下过渡过程的初始条件。     

Streaming potential measurements on stainless steels surfaces: evidence of a gel-like layer at the steel/electrolyte interface

Electric charges at the surface of a passive stainless steel are generally considered as concentrated either in the passive film itself, or at the metal/passive film interface, or in the electrical double layer at the film solution interface. Rest potential time dependence after immersion of a passive surface in aqueous electrolytes suggests however that slow processes occur in the onset of the surface charge. Specific experiments, such as streaming potential measurements and electrochemical impedance spectroscopy in a thin electrolyte cell, were carried out for understanding better this phenomenon. An AISI 304 type austenitic stainless steel with polished or bright annealed surface finishes was immersed in NaCl aqueous solutions with various pH and chloride concentrations. The streaming potential time evolution shows two steps: a first rapid one (∼2 min) is attributed to the onset of the surface charge. The second step is much slower (approximately several hours) and possibly due to an interphase layer between the passive film and the solution. Following this idea, the whole kinetics is controlled by cation migration across the interphase when the pH is larger than the isoelectric pH (pH_iep), while chloride ions are incorporated in the interphase when pH < pH_iep. Impedance measurements allow determining both the kinetics of charge transport and the thin cell conductivity. When glass is used as reference material for the cell walls instead of stainless steel, the Nyquist plots show a high-frequency response. For stainless steel cell walls, a low-frequency response is observed, attributed to a slow charge reorganisation inside the interphase layer. The charge distribution at metal/electrolyte interface is discussed in terms of a gel-like layer which possibly takes place at the passive film/electrolyte interface.     

Impedance studies of the growth of porous magnetite films on carbon steel in high temperature aqueous systems

The growth of porous magnetite on carbon steel in high temperature chloride solution has been studied using the a.c. impedance technique. At both 200 and 250°C the reciprocal of the polarization resistance, which is proportional to the corrosion rate, at first increases with time, but eventually tends to a constant value. Accordingly, the early stages of corrosion are autocatalytic, but at longer times a linear rate law is observed. The early autocatalytic stage is attributed to the gradual development of a highly aggressive solution within the porous film due to cation hydrolysis and transport of chloride ions from the bulk solution into the pores. The frequency dispersion of the impedance of the growing film has been successfully accounted for by a finite transmission line model. Numerical analysis has shown that the total impedance is a sensitve function of the film thickness and of the impedances along the pore wall and at the base of the pore. These analyses have demonstrated that the a.c. impedance technique is well suited for studying the corrosion of metals and the growth of porous films in high-temperature aqueous systems.     

阳极钝化电位对黄铜表面钝化膜半导体性能的影响

目的研究黄铜在不同阳极钝化电位下形成的钝化膜的半导体性能。方法通过动电位极化曲线获取黄铜在硼酸盐缓冲溶液中的维钝电位区间,并选取3个钝化电位值对黄铜进行钝化处理,采用电化学阻抗谱和Mott-Schottky半导体理论研究阳极钝化电位对钝化膜半导体性能的影响,并进一步利用PDM模型进行点缺陷扩散系数的计算。结果黄铜在硼酸盐缓冲溶液中有明显的钝化区间,不同钝化电位对应的Mott-Schottky直线斜率均为负值,且点缺陷扩散系数均为10-14数量级。随着阳极钝化电位的正移,钝化膜的阻抗值不断增加,受主密度降低,平带电位变小,空间电荷层厚度增加。结论黄铜在不同钝化电位下形成的钝化膜均表现出p型半导体的特性,膜中载流子以空穴为主,随着阳极钝化电位的正移,钝化膜的导电性能变差,耐蚀性能增强,对基体的保护作用更好。