Depassivation and repassivation of stainless steels by stepwise pH change

Immersion tests with different stainless steels have been performed, while the pH was stepwise decreased and then increased again. During 8.5-day exposure, the depassivation and repassivation pH values as a function of pitting resistance equivalent number were determined. There is always a gap between both pH values (depassivation and repassivation), indicating that for every steel, there are conditions where an existing passive layer can be maintained but cannot be rebuilt after depassivation. In such environments, the passive layer is thicker, consisting mainly of molybdenum and iron rich oxides, while chromium is dissolved. Usually, depending on conditions, the passive layer is more chromium-rich, especially the inner layer. This is relevant, for example, for acidizing jobs in oil and gas industry, proving that repassivation after acidizing will happen promptly, when the pH is increased again.     

Depassivation of steel reinforcement in case of pitting corrosion: detection techniques for laboratory studies

Methods for service life prediction of reinforced concrete structures exposed to chloride‐bearing environments require, amongst other parameters, the knowledge of the chloride threshold for pitting corrosion initiation (Cl_th). Nowadays, although the main factors influencing the chloride threshold are well known, it is often difficult to quantify a value of the chloride threshold, partly because of its intrinsic high variability, and partly because of the different test methods that have been used to measure it. All the experimental tests rely on the detection of steel depassivation and simultaneous measurement of chloride content or steel potential. This paper deals with the methods that can be used to detect steel depassivation in relation with the determination of the chloride threshold. Tests in concrete‐pore‐simulating solutions as well as tests in concrete will be considered, and advantages and limitations will be discussed.     

Potassium sorbate solutions as copper chemical mechanical planarization (CMP) based slurries

Copper depassivation and repassivation characteristics in potassium sorbate solutions, subsequent to mechanical abrading are reported. The identification of copper repassivation kinetics obtained subsequent to mechanical damage of copper protective films formed in sorbate based solutions is discussed. The repassivation rate of copper in sorbate based solutions was measured by means of a slurryjet system capable of measuring single particle impingments on microelectrodes. Copper repassivation rates measured by this slurryjet system in sulfate solutions containing 10 g L⁻¹ potassium sorbate were found to be in the range of 0.5-1.5 ms. An increase in the potassium sorbate concentration leads to a decrease in copper repassivation time at potentials ranging from 200 to 600 mV_Ag/AgCl. The impingement angle between the copper surface and a single abrasive particle has no impact on copper repassivation time nor peak current (I_max) values. XPS studies revealed that copper passivation in potassium based solution was due to the formation of a thin film which is constituted of: Cu₂O, Cu(OH)₂ and Cu(II)-sorbate, while copper(II)-sorbate is mainly present at the top levels of the passive film. It is therefore recommended that the use of potassium sorbate as a passivating component in conjunction with the addition of strong oxidizing agents in chemical mechanical planarization (CMP) slurry design should be considered.     

混凝土结构钢筋脱钝的随机可靠度分析

根据混凝土临界氯离子浓度和氯离子扩散系数与水灰比、环境温度等的关系式,计算出不同条件下受氯盐侵蚀混凝土结构50年内钢筋表面的氯离子浓度。在分析钢筋混凝土结构钢筋表面氯离子浓度随服役年限关系的基础上,用Monte Carlo方法对钢筋脱钝的随机可靠度进行分析。对保护层厚度、水灰比和环境温度等随机变量对海工混凝土结构钢筋脱钝概率的影响进行探讨。     

Initiation of chloride‐induced corrosion of steel in concrete: role of the interfacial zone

This paper provides a brief review of research aimed at characterising the steel–concrete interfacial zone (SCIZ) and its influence on the susceptibility of the metal to pitting corrosion when concrete is exposed to environments that cause ingress of chloride ions accompanied by leaching of hydroxyl ions. For reinforced concrete made from Portland cements, exposed to aqueous solutions of sodium chloride, the buffering effect of solid calcium hydroxide (portlandite) at pH ～12.6 has been shown to restrain the gradual decline in the hydroxyl ion concentration of the concrete pore solution phase at depths corresponding to the embedded steel. When the concrete is produced under laboratory conditions that are carefully controlled to exclude macroscopic defects from the SCIZ and the steel is cleaned before being embedded, this can lead to observed chloride threshold levels being consistently greater than 1% chloride by mass of cement. The buffering action of cement hydration products formed in the SCIZ is believed to be partly responsible for this high tolerance to chloride‐induced corrosion because it counters the generation of ‘anodic acidity’ that is a necessary condition for stable growth of pits to occur. Translating this behaviour of laboratory specimens to the performance of full‐scale reinforced concrete structures has often proved difficult in the past and there is a need for further research in this area, particularly in relation to the role of non‐traditional cements.     

Probabilistic Assessment of Reinforcing Steel Depassivation in Concrete under Aggressive Chloride Environments Based on Natural Exposure Data

The probability distributions of the critical threshold chloride concentration Ccr, the chloride diffusion coefficient D, and the surface chloride concentration Cs are determined based on the collected natural exposure data, and the probability estimation of reinforcement depassivation in concrete is presented using Monte-Carlo simulation. From sensitivity analysis of mean value for ccr, cs, and D on the depassivation probability of reinforcement, it is found that ccr, cs, and D respectively has the greatest, smaller, and the lowest effect on the probability of depassivation. Finally the effect of stress state of concrete on the reinforcement depassivation probability is analyzed. It is found that the influence of stress state becomes apparent as exposure time increases.     

混凝土中钢筋脱钝氯离子阈值的快速测定

基于金属极化理论,分析了外加电场电压对于钢筋钝化膜的影响。明确了外加电场电压的合理取值,并提出了连续通电条件下的钢筋脱钝判别依据。设计了电场加速条件下氯离子阈值快速测定以及自然渗透法氯离子阈值测定对比试验。结果表明,快速试验测试得到的氯离子阈值略小于自然渗透法得到的值,两者比值约为1.261,从而验证了该测定方法的可行性。     

一般大气环境下钢筋开始锈蚀时间的计算方法

在评估混凝土结构耐久性时,其关键是确定钢筋开始锈蚀条件.一般大气环境下混凝土中钢筋开始锈蚀的条件是混凝土碳化及钢筋脱钝.碳化残量是描述钢筋开始锈蚀的重要参数,其大小取决于部分碳化区长度、碳化速度及脱钝速度.以实际工程检测数据为主要依据,考虑不同环境条件,以碳化系数、保护层厚度和局部环境系数为主要参数,利用回归分析方法建立了碳化残量的计算公式,并由此计算钢筋开始锈蚀的时间.通过实际工程数据验证,表明本文给出的钢筋开始锈蚀时间计算方法,在工程应用上是可行的,从而为合理评定混凝土结构耐久性提供依据.     

混凝土内钢筋锈蚀初期行为研究

在混凝土内钢筋锈蚀初期,从结构开始使用到钢筋脱钝,占整个使用寿命的最大部分,因而对其锈蚀初期行为研究意义重大．对这一研究应着眼于钢筋脱钝临界点的把握．基于此对已有临界条件进行了归纳整理和初步研究．