Correlation of microstructure, electrical properties and electrochemical phenomena in reinforced mortar. Breakdown to multi-phase interface structures. Part II: Pore network, electrical properties and electrochemical response

Since reinforced mortar is a multi-phase composite material at different levels of aggregation, a combination of techniques, namely electrochemical impedance spectroscopy (EIS) (for investigating the electrochemical phenomena on the steel reinforcement) and microstructure analysis (for qualifying and quantifying the composite bulk material), was used to provide insight into the macro- and micro-level interactions, involved in conditions of corrosion and cathodic protection for the here investigated reinforced mortar specimens.

After 120days of exposure to the relevant conditions of chloride-induced corrosion and impressed current cathodic protection (CP), it was found that the accumulation, volume expansion and propagation of corrosion products bring about significant structural alterations in the cement matrix. Further, the current flow involved in CP applications, along with the protection itself, contributes to additional changes in the bulk material. In this study, the elements of the equivalent electrical circuit from EIS measurements are discussed in correlation to the evolution of porosity, pore size distribution and pore interconnectivity of the bulk matrix, during corrosion and CP application. The results indicate that different parameters in the EIS modeling concept correspond well to specific interface microstructures.

The outcomes of this combination of techniques will possibly provide implications for computer simulation of the corrosion process and CP applications as well as modeling of concrete performance in aggressive environments.     

含有硫酸盐还原菌的海泥中阴极保护电位对碳钢腐蚀的影响

对含有SRB海泥中的碳钢的阴极保护的可靠性进行了评价,重点研究了不同保护电位下碳钢的交流阻抗行为,并结合失重法、MPN法细菌计数,得出极化电位、腐蚀速度以及细菌活性之间的关系。3种极化电位下碳钢的腐蚀速度与交流阻抗谱表明,在本试验条件下,碳钢在-950 mV极化电位下受到了较好的保护,腐蚀速度稳定且相对较小。细菌计数表明在较高阴极极化电位下细菌的生长活性与稳定性低于在低电位下的。分析表明,合适的保护电位应该比-950 mV更负。     

Effects of bentonite content on the corrosion evolution of low carbon steel in simulated geological disposal environment

The effects of bentonite content on the corrosion behavior of low carbon steel in 5 mM NaHCO3+ 1 mM NaCl + 1 mM Na2SO4 solution were investigated by electrochemical measurements combined with X-ray diffraction(XRD) and scanning electron microscopy(SEM). In the initial immersion stage, the cathodic process of low carbon steel corrosion was dominated by the reduction of dissolved oxygen, while it transformed to the reduction of ferric corrosion products with the immersion time. The presence of bentonite colloids could suppress the cathodic reduction of oxygen due to their barrier effect on the diffusion of oxygen. However, the barrier performance of bentonite layer was gradually deteriorated due to the coagulation and separation of bentonite colloids caused by the charge neutralization of iron corrosion products dissolved from the steel substrate. More bentonite colloids could maintain the barrier effect for a long time before it was deteriorated by the accumulation of corrosion products. Conversely,it could lose the performance completely, and the corrosion behavior of low carbon steel reverted to the same as that in the blank solution.     

Cathodic protection of steel framed masonry structures: experimental and numerical studies

Many high-profile steel-framed masonry buildings are susceptible to extensive damage as a result of corrosion of the steel frame. This has resulted in serious consequences with respect to serviceability, safety, aesthetics and heritage. Cathodic protection (CP) is a proven method for preventing and protecting buried and submerged steel and reinforced concrete structures from corrosion. More recently, the method has been introduced to prevent and control corrosion in steel-framed masonry structures. However, despite several sizeable CP installations around the world, there are no formal guidelines for the design, installation and operation of such systems and much of the knowledge is based on empirical observations. This paper presents both experimental and numerical studies on the cathodic protection of representative steel framed masonry structures. These studies are considered essential in the understanding of the mechanisms of cathodic protection and the design of optimised cathodic protection systems for such structures.     

Factors affecting cathodic-protection interference

A 3D theoretical simulation and analysis of DC stray-current corrosion (SCC) is introduced. The use of boundary element analysis system (BEASY) has allowed cathodic protection (CP) interference to be assessed in terms of the normal current density, which is directly proportional to the corrosion rate. Different real structures consisting of pipelines and/or well casings are simulated to investigate the factors affecting four types of CP interferences, namely, anodic, cathodic, combined and induced, with special emphasis on the cathodic one. The results reveal that the application of impressed current CP systems creates DC SCC on other nearby unprotected structures. This is an inherent potential problem with the application of such systems which dominates with decreasing soil conductivity, and/or increasing the anode current density and its proximity to the protected structures. On the contrary, SCC can be reduced by using multi-groundbed anodes. In addition, it is found that the cathodic interference is more serious than anodic one, and the combined and induced interferences can also cause severe corrosion. Finally, it can be concluded that the BEASY software is a very helpful tool for future planning before installing any structure, where it gives the possible CP interferences on any nearby unprotected metallic structures.     

Effects of phosphate on the chloride-induced corrosion behavior of reinforcing steel in mortars

The influence of phosphate as a corrosion inhibitor on the corrosion behavior of as-received and pre-rusted reinforcing steels in mortar specimens was investigated after 360 days exposure in 3.5% NaCl solution. This involved the use of electrochemical techniques for studying the steel surface reactions and microscopic observations of the steel–mortar interface. The electrochemical methods, including electrochemical impedance spectroscopy (EIS) and measurements of corrosion potential (E_corr) and linear polarization resistance (LPR), were employed to evaluate the corrosion tendency and general corrosion rate of steel. In addition, the pitting corrosion resistance of steel was also determined by cyclic polarization (CP) measurements. The results indicate that different from nitrite, which is generally accepted as an anodic inhibitor, phosphate may be a cathodic inhibitor according to its reduced corrosion rate and more negative E_corr at the same dosage as nitrite in mortar specimens. The study also reveals that the inhibiting efficiency of phosphate against general corrosion of both as-received and pre-rusted specimens is lower than 10%, which is inferior to nitrite in some respects. However, as indicated by cyclic polarization measurements, the presence of phosphate provides slightly higher pitting corrosion resistance in comparison to nitrite. Furthermore, it suggests that the corrosion inhibition mechanism of phosphate in mortars mainly depends on a dual effect occurring at the steel–mortar interface. Furthermore, it is confirmed that phosphate has little effect on the long-term mechanical properties of mortars.     

Corrosion behavior of TiN, TiAlN, TiAlSiN thin films deposited on tool steel in the 3.5 wt.% NaCl solution

TiN, TiAlN and TiAlSiN hard coatings were deposited onto AISI H13 tool steel by cathodic arc plasma method. X-ray diffraction (XRD) analysis confirmed that incorporation of Al and Si into TiN led to refinement of microstructure. From the results of potentiodynamic polarization test and electrochemical impedance spectroscopy (EIS) test conducted in an aerated 3.5% NaCl solution, the TiAlSiN film showed the best corrosion resistance with the lowest corrosion current density and porosity, the highest protective efficiency and total resistance (pore resistance plus charge transfer resistance).     

葡萄糖与甘氨酸反应产物对碳钢的缓蚀效果

为了解葡萄糖与甘氨酸反应产物对碳钢的缓蚀效果,采用失重法、电化学法并结合扫描电镜观察,研究了葡萄糖与甘氨酸反应产物(PGG)对碳钢在1 mol/L HCl溶液中的腐蚀抑制作用。结果发现:PGG对碳钢表现出很好的缓蚀效果,缓蚀效率随添加浓度的增加而增加,在最大浓度250 mg/L时,表现出最好的缓蚀效果,缓蚀效率为94.7%,且缓蚀效率随温度升高而降低。PGG同时抑制了碳钢腐蚀的阴极还原反应和阳极氧化反应过程,为混合型缓蚀剂,是通过多组分的物理和化学联合吸附,在碳钢表面上形成保护性覆盖层,将碳钢与酸溶液隔离,从而起到缓蚀作用,其吸附行为遵循Langmuir吸附等温模型。葡萄糖与甘氨酸反应产物(PGG)是碳钢在1 mol/L HCl溶液中的优良缓蚀剂。     

Electrochemical impedance spectroscopy investigation on indium tin oxide films under cathodic polarization in NaOH solution

The electrochemical corrosion behaviors of indium tin oxide (ITO) films under the cathodic polarization in 0.1 M NaOH solution were investigated by electrochemical impedance spectroscopy. The as-received and the cathodically polarized ITO films were characterized by scanning electron microscopy, energy dispersive X-ray spectroscopy and X-ray diffraction for morphological, compositional and structural studies. The results showed that ITO films underwent a corrosion process during the cathodic polarization and the main component of the corrosion products was body-centered cubic indium. The electrochemical impedance parameters were related to the effect of the cathodic polarization on the ITO specimens. The capacitance of ITO specimens increased, while the charge transfer resistance and the inductance decreased with the increase of the polarization time. The proposed mechanism indicated that the corrosion products (metallic indium) were firstly formed during the cathodic polarization and then absorbed on the surface of the ITO film. As the surface was gradually covered by indium particles, the corrosion process was suppressed.     

Effect of scale formation and CP potentials on AC-induced pitting corrosion of low carbon steels

Journal of Materials Science - The effect of AC voltages, cathodic protection (CP) potentials and calcareous scale on the pitting corrosion of carbon steel 1010 was investigated by potentiostatic...     

Stress Corrosion Cracking of X80 Steel in the Presence of Sulfate-reducing Bacteria

The systematic laboratory studies on the roles of sulfate-reducing bacteria(SRB) in the stress corrosion cracking(SCC) susceptibility of X80 steel subjected to cathodic potential have been conducted in a nearneutral pH soil solution by slow strain rate tests.The cathodic potential and SRB increase individually the SCC susceptibility of the steel in the soil solution.The positive role of the SRB activities in SCC susceptibility depends on the prolongation of pre-incubation time,and the SCC susceptibility of the steel increases under more negative potentials.What’s more,the applied potentials and the presence of SRB work together in promoting the SCC susceptibility of the steel.But,the combined action becomes limited with decreasing cathodic potentials.The relationships between the plasticity loss and the permeable hydrogen concentration were established for the steel in the soil solution,regardless of under open circuit potential or cathodic potentials,in both the sterile and SRB inoculated conditions.The relationships are practically significant for the selection of safe cathodic protection(CP) potentials in the presence of SRB in soil environment.     

Corrosion Evolution of Low Alloy Steel in Deaerated Bicarbonate Solutions

Corrosion evolution during immersion tests(up to 43 days) of Ni Cu steel in deaerated 0.1 mol/L bicarbonate solutions was investigated by electrochemical measurements, scanning electron microscopy(SEM) and X-ray diffraction(XRD). Results show that Ni Cu steel transformed from the anodic dissolution in the early stage of immersion to a metastable passive state in the final stage as the open-circuit potential value shifted positively, which was aroused by the precipitation of corrosion products. This process was mainly promoted by the trace amount of oxygen. Simultaneously, dominant cathodic reaction transformed from the hydrogen evolution in early stage to reduction processes of corrosion products in later stages. Possible corrosion processes were discussed with the assistance of a corresponding Pourbaix diagram.     

Adsorption and corrosion inhibition effect of 2-((5-mercapto-1,3,4-thiadiazol-2-ylimino)methyl)phenol Schiff base on mild steel

In this study, the inhibition effect of 2-((5-mercapto-1,3,4-thiadiazol-2-ylimino)methyl)phenol Schiff base (MTMP) on mild steel corrosion in 0.5 M HCl solution was studied. For this aim, electrochemical techniques such as potentiodynamic polarization curves, weight loss (WL), electrochemical impedance spectroscopy (EIS) and linear polarization resistance (LPR) were used. It was shown that, the MTMP Schiff base has remarkable inhibition efficiency on the corrosion of mild steel in 0.5 M HCl solution. Polarization measurements indicated that, the studied inhibitor acts as mixed type corrosion inhibitor with predominantly control of cathodic reaction. The inhibition efficiency depends on the concentration of inhibitor and reaches 97% at 1.0 mM MTMP. The remarkable inhibition efficiency of MTMP was discussed in terms of blocking of electrode surface by adsorption of inhibitor molecules through active centers. The adsorption of MTMP molecules on the mild steel surface obeys Langmuir adsorption isotherm.     

硫酸盐还原菌的生长过程及其对D36钢海水腐蚀行为的影响

通过测定海水中硫酸盐还原菌(SRB)的生长曲线及其不同生长阶段的硫离子浓度、D36钢电极体系的氧化还原电位、自腐蚀电位、极化曲线和电化学阻抗谱,研究了硫酸盐还原菌对该体系钢电极腐蚀行为的影响。结果表明,海水中D36钢氧化还原电位和自腐蚀电位主要由体系中硫酸盐还原菌代谢产物硫离子的浓度所决定;体系的阳极和阴极反应速率均在硫酸盐还原菌增殖期增加,而且阳极反应速率衰亡期和残余期保持不变。     

Microstructural study and electrochemical behavior of low alloy steel weldment

Submerged arc welding (SAW) was applied to SA516 (Grade 70) pressure vessel and boiler steel. The microstructural and electrochemical corrosion study of base metal (BM), weld zone (WZ) and heat affected zone (HAZ) was carried out to understand the effect of welding cycle by optical microscopy, X-ray diffraction (XRD), potentiodynamic polarization and linear polarization resistance (LPR) method to correlate corrosion kinetic parameters with microstructural changes in tap water and 0.5% (w/v) NaCl solution under plain and aeration conditions at room temperature. From microstructural study, the morphology of ferrite in WZ and HAZ showed different electrochemical behavior and corrosion rate than that of BM.     

Synthesis of a new family of Schiff base nonionic surfactants and evaluation of their corrosion inhibition effect on X-65 type tubing steel in deep oil wells formation water

Some new Schiff base nonionic surfactants were synthesized and characterized using FTIR and ¹H NMR spectroscopy. The corrosion inhibition effect of the synthesized surfactants on X-65 type tubing steel in deep oil wells formation water has been studied by polarization, electrochemical impedance spectroscopy (EIS) and weight loss measurements. Polarization data indicate that the selected surfactants act as mixed type (cathodic/anodic) inhibitors. EIS results show that the change in impedance parameters with the concentration of the surfactants studied is indicative of the adsorption of surfactant molecules on carbon steel surface. The adsorption of the inhibitors was well described by the Langmuir adsorption isotherm. Effect of temperature on the efficiency of the corrosion inhibition process was studied and the values of activation energy, enthalpy of activation and entropy of activation were calculated and discussed. The corrosion inhibition efficiency of the surfactants is correlated with surface tension measurements data. The protective film formed on the carbon steel surface was studied by scanning electron microscopy (SEM) and energy dispersive analysis of X-rays (EDX) techniques.     

Corrosion inhibition and adsorption behavior of 2-((dehydroabietylamine)methyl)-6-methoxyphenol on mild steel surface in seawater

The inhibition effect of a Dehydroabietylamine Schiff base derivative, namely 2-((dehydroabietylamine)methyl)-6-methoxyphenol (DMP) against mild steel corrosion in seawater was evaluated using weight loss and electrochemical techniques (potentiodynamic polarization and electrochemical impedance). The experimental results showed that DMP is a good corrosion inhibitor and the inhibition efficiency increased with the increase of DMP concentration, while the adsorption followed the Langmuir isotherm. X-ray photoelectron spectroscopy, scanning electron microscopy, theoretical calculation of electronic density, molecular electrostatic potential and molecular dynamics were carried out to establish mechanism of corrosion inhibition for mild steel with DMP in seawater medium. The inhibition action of the compound was assumed to occur via adsorption on the steel surface through the active centers in the molecule. The corrosion inhibition is due to the formation of a chemisorbed film on the steel surface.     

腐蚀产物膜对X80钢在库尔勒土壤模拟溶液中腐蚀行为的影响

采用扫描电镜和X射线衍射对X80钢在库尔勒土壤模拟溶液中浸泡1个月后的表面腐蚀产物膜进行观察和测试,通过动电位极化和交流阻抗等电化学方法研究了腐蚀产物膜对X80钢腐蚀行为的影响。结果表明:腐蚀产物膜明显加速了X80钢在模拟溶液中的阴极还原过程,腐蚀也由原来的活化控制转变为扩散过程控制。腐蚀产物膜可分内外两层,外层产物膜由Fe2O3,Fe(OH)3和FeO(OH)组成,疏松,易脱落,没有保护作用。内层产物膜为Fe3O4,与基体结合得虽然较为紧密,但存在着微裂纹和微小孔洞等缺陷,这些缺陷增大了阴极还原的有效面积,减少了荷电离子的传输阻力,促进了腐蚀微电池的形成,从而使覆盖有腐蚀产物膜的X80钢表现出更大的腐蚀速率。     

极化电位对高锰铝青铜表面钙质沉积层的影响研究

采用恒电位极化和电化学阻抗谱(EIS)技术研究了青岛天然海水中不同极化电位下高锰铝青铜的保护电流密度和表面状态随时间的变化过程,利用扫描电镜(SEM)和能谱X射线(EDX)分析了阴极极化产物的微观形貌和元素组成。结果表明,极化168 h后,-0.8 V和-0.5 V两种极化电位下,高锰铝青铜表面都能够形成明显的钙质沉积层,主要成分都是CaCO_3;-0.8 V的极化电位下,高锰铝青铜虽然表面形成了铁锰氧化物,但其稳定保护电流密度更低,钙质沉积层膜电阻和电荷转移电阻值更高,钙质沉积层结构也更加致密。因此,-0.8 V的极化电位比-0.5 V的极化电位对高锰铝青铜具有更高的阴极保护效率。     

Electrochemical,Morphological and Anti-corrosive Characteristics of Pyrazine Derivatives for Mild Steel Corrosion in Aggressive Medium: A Comparative Study

The anti-corrosive characteristics of 2,5-dimethylpyrazine (2,5-DMP) and 2,6-dimethylpyrazine (2,6-DMP) on the corrosion of mild steel in 0.5 M sulfuric acid have been studied by gravimetric method and electrochemical techniques (potentiodynamic polarization, linear polarization resistance and electrochemical impedance measurement) to observe the adsorption of these pyrazine derivatives at the metal/solution interface. The results obtained have revealed that 2,5-DMP performs more efficiently in comparison with 2,6-DMP showing an efficiency of 97.12% at a concentration of 10^?2 M. The polarization curves clearly indicate that both chemicals act as a mixed-type inhibitors showing a predominance toward the cathodic reaction. Langmuir’s isotherm model was found to adequately describe the adsorption of both these inhibitors onto the mild steel surface. The calculated value of the free energy for the adsorption process, \(\Delta G^\circ_{\text{ads}}\), reveals a strong chemisorbed bond as well as a spontaneous adsorption process between the tested inhibitors and the mild steel surface. Surface morphological analysis of the MS specimens treated with these inhibitors has been conducted using energy-sispersive atomic X-ray spectroscopy. The results obtained have shown a good agreement with the results obtained from electrochemical techniques. Quantum chemical calculations have also been performed using hyperchem 8.0.6 package to supplement the findings from the preceding techniques.