Investigations on the influence of oxygen on corrosion of steel in concrete—Part I

The main objective of the research programme presented in the two parts of this article is determining the influence of oxygen diffusion through the concrete cover, on the corrosion process of the reinforcement in concrete structures. Altogether, 66 so-called “concrete corrosion cells”, i. e. reinforced concrete specimens with locally separated anodically and cathodically acting steel bars and different concrete compositions, have been used for the laboratory tests. Two testing methods have been used to investigate the influence of oxygen diffusion on the cathodic reaction under different environmental conditions: potentiostatic tests (presented in part I) and the determination of cathodic current density/potential curves (presented in part II). Using the results of these tests and a simplified equivalent electric circuit model for the corrosion process, it was possible to calculate the influence of oxygen diffusion on the corrosion rate of the reinforcement under defined conditions. The results of the laboratory tests and calculations show that the diffusion of oxygen is a significant limiting factor for the corrosion rate only when the concrete around the reinforcement is water saturated and most of the oxygen within the concrete near the reinforcement surface has been consumed by the cathodic reaction of the corrosion process. As a consequence, the corrosion rate is influenced by oxygen diffusion only through the concrete cover in structures which are submerged or exposed to long-term or cyclic water application that causes water saturation of the concrete for periods of several weeks. In the case of common outdoor structures being exposed to rain and not submerged or constantly water saturated due to other reasons, no reduction of the corrosion rate induced by limited oxygen diffusion is therefore to be expected.     

N-doped carbon-stabilized PtCo nanoparticles derived from Pt@ZIF-67: Highly active and durable catalysts for oxygen reduction reaction

Nano Research - The development of catalysts with high activity and durability for the cathodic oxygen reduction reaction (ORR) in both alkaline and acidic media is important for improving the...     

纳米镀锌层在NaCl溶液中的腐蚀行为研究

通过电镀的方法制备了不同晶粒尺寸的纳米镀锌层和微米镀锌层，应用极化曲线和交流阻抗的方法研究了它们在5％NaCl溶液中的电化学腐蚀行为，结果表明，纳米镀锌层较微米镀锌层腐蚀电流密度增加，纳米镀锌层的电化学腐蚀行为存在纳米尺寸纳应，镀锌层纳米化使参与反应的原子数增加，阳极交换电流密度提高，氧的阴极还原更为容易，阴极交换电流密度也提高。     

Effect of particle size on the electrochemical corrosion behavior of X70 pipeline steel

In this study, by using a standard quartz replace of sandy soil particles, the effect of soil particle size (0.1–0.25 mm, 0.6–1.0 mm) on the electrochemical corrosion behavior of X70 pipeline steel in sandy soil corrosive environment simulated by 3.5 wt% sodium chloride (NaCl) was investigated through polarization curve and electrochemical impedance spectroscopy (EIS) technology. The results indicated that the polarization resistance of X70 steel decreased with decreasing particle size. For all polarization curves, the right shift of cathodic branch with decreasing particle size, suggesting that the cathode oxygen reduction process is accelerated. The corrosion of X70 steel is controlled by the process of cathode diffusion and oxygen reduction. This can be attributed to the effect of gas/liquid/solid three‐phase boundary (TPB) zone on cathodic process of X70 steel, and the corrosion rate is mainly determined by the cathodic reaction. EIS of X70 steel consisted of two capacitive loops with 7, 60 and 90 days buried corrosion, and the charge transfer resistance of X70 steel increased with increasing particle size.     

Oxygen Coefficient of Uranium Oxides and Current Efficiency as Influenced by Electrolysis Parameters and Composition of Molten Salt Electrolytes in the Na2WO4-Na2W2O7-UO2WO4 System

The oxygen coefficient of uranium oxides, their structure, and current efficiency were studied as influenced by the electrolyte composition, deposition potential, and temperature of electrolysis. On passing from Na₂WO₄-UO₂WO₄ binary system to lower-melting ternary systems the dependences of the oxygen coefficient in the cathodic product on the electrolyte composition and electrolysis parameters remain essentially similar. Significant deviation of the experimental current efficiency with respect to uranium oxides from the theoretical value suggests significant chemical interaction between the cathodic product and electrolyte. The corrosion rate increases and the current efficiency decreases with increasing temperature and concentration of W₂O₇ ^2- ions. The structure of the resulting cathodic deposits is predominantly determined by their specific electrical conductivity, which is a function of the chemical composition of the electrolyte. The dendrite structure is typical for higher oxides.     

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.     

黄铜在酸碱盐腐蚀介质中的腐蚀研究

利用SEM、EPMA、电化学曲线测量、XPS等检测技术,研究了HSn62-1黄铜在pH值为2的H2SO4溶液、pH值为13的NaOH溶液和3.5％(质量分数)的NaCl溶液中的腐蚀形貌、腐蚀产物、腐蚀类型,并针对不同的腐蚀机制,建立了化学反应模型,对腐蚀机制进行了分析.结果表明,HSn62-1在H2SO4溶液中腐蚀失重明显,且其溶解方式为选择性溶解,其腐蚀是以析氢腐蚀为主的混合腐蚀机制;在NaCl溶液和NaOH溶液中的腐蚀为溶解-再沉积机制,溶解速度较为缓慢,在NaCl溶液中为析氢腐蚀,在NaOH溶液中为吸氧腐蚀.     

Analysis of hot water pipeline system leakage

An analysis of the catastrophic corrosion of the hot water pipeline system was made. The cause was oxygen, dissolved in water due to the malfunctioning of the degassing device in the water preparation phase. Because of differential aeration, cathodic and anodic areas formed underneath the oxide deposit on the bottom side of the pipeline. The consequence of the thus activated pitting corrosion was pipeline perforation. It is imperative to regularly test the water for dissolved oxygen and monitor its pH value.     

Investigations on the influence of oxygen on corrosion of steel in concrete—Part 2

In Part I of this article, potentiostatic tests on reinforced concrete specimens under different environmental conditions have been described. The results of these tests have shown that it is possible to define four cases related to the humidity, in which different dominant parameters influence the corrosion rate for the reinforcement, discussed in detail in Part I. The main result is that the diffusion of oxygen is only a significant limiting factor for the corrosion rate when the concrete around the reinforcement is water-saturated and most of the oxygen within the concrete near the reinforcement has been consumed by the cathodic reaction of the corrosion process. As a consequence, the corrosion rate is only influenced by oxygen diffusion through the concrete cover in structures which are submerged or exposed to long term or cyclic water application, thereby causing water saturation of the concrete around the reinforcement for periods of several weeks. In Part II of this article, the determination of cathodic current-density/potential curves is described. Using the results of these tests and a simplified equivalent electric circuit model for the corrosion process, it is possible to calculate the influence of oxygen diffusion on the corrosion rate of the reinforcement quantitatively for defined conditions. One interesting consequence of this work is that the thickness of the concrete cover does not influence the corrosion rate by reducing the oxygen diffusion rate significantly when the concrete is not water-saturated. However, a sufficiently thick concrete cover is essential due to several other reasons (ingress of chlorides, carbonation, etc.).     

Parameters of Oxidation-Reduction Processes in Ozonized Acid Media

We have studied the cathodic processes on a platinum electrode in ozonized sulfuric acid solutions of different concentrations. The kinetic parameters of corrosion processes have been determined. The cathodic processes on a platinum electrode in the presence of ozone are more intense by a factor of 1.5 than in the presence of oxygen. Ozone increases the possibility of chemical reaction with the help of generation of OH⁻ ions. In addition, we have proposed a scheme for the action of ozone in acid media.__________Translated from Fizyko-Khimichna Mekhanika Materialiv, Vol. 40, No. 5, pp. 43–47, September– October, 2004.     

石墨表层对四面体非晶炭膜中受激电子的石墨建序化作用

对渗气阴极真空电弧法制备的四而体非晶炭(ta-c)膜实施氧等离子体刻蚀,消除其表面石墨层后,发现:原沉积膜中ta-C石墨表层的消除会影响其受激电子的石墨建序化.应用发射电子能耗谱,表面增强拉曼光谱和表面敏化X光吸收光谱等测量方法,测定了其表层的淌除(程度).样品的氧等离子体刻蚀阻迟了受激电子的石墨化作用,可能归因于多相成核过程中石墨晶核的缺失之故.     

Influence of the electrolysis conditions and composition of electrolytes in the M2WO4-M2W2O7-UO2WO4 system (M = Li, Na, K, Cs) on the oxygen coefficient of uranium oxide

The oxygen coefficient (O/U atomic ratio) of the cathodic product prepared by potentiostatic electrolysis of tungstate melts was studied in relation to the electrolyte composition, deposition potential, temperature of electrolysis, and cation of the solvent salt. With increasing temperature, the oxygen coefficient of the cathodic product increases. With shifting the deposition potential toward more negative potentials, with increasing concentration of W₂O ₇ ^2? anions, and with decreasing concentration of UO₂WO₄ in the tungstate electrolytes, uranium oxides with smaller oxygen coefficients are formed. The oxygen coefficient decreases with increasing radius of the salt cation, other conditions being equal. The abnormal behavior of melts based on Li₂WO₄ is probably due to lower activity of O^2? anions capable to form strong Li₃O⁺ complexes with lithium cations in the melt. The experimental results can be accounted for using the model of the ionic composition of uranyl-containing tungstate melts based on the concepts of complexation and stepwise solvolysis of uranyl ions.     

Utilization of Peroxide Reduction Reaction at Air–Liquid–Solid Joint Interfaces for Reliable Sensing System Construction

The utilization of hydrogen peroxide (H₂O₂) cathodic reaction is an ideal approach to develop reliable biosensors that are immune to interferences arising from oxidizable endogenous/exogenous species in biological solutions. However, practical application of such a detection scheme is limited due to the significantly fluctuating oxygen levels in solutions, as oxygen can be reduced at similar potentials. Herein, this limitation is addressed by developing a novel electrode system with superhydrophobicity‐mediated air–liquid–solid joint interfaces, which allows the rapid and continuous transport of oxygen from the air phase to the electrode surface and provides a fixed interfacial oxygen concentration. Using cathodic measurement of the enzymatic product H₂O₂, the sensing platform is applied to detect glucose, a model analyte, achieving a remarkably high selectivity (≈2% signal modulation due to common biologic interferents), sensitivity (18.56 µA cm^?2 mm ^?1), and a dynamic linear range up to 80 × 10^?3m . The utility of H₂O₂ reduction reaction at triphase interface to achieve reliable sensing platforms is general, and hence has broad potential in the fields of medical research, clinical diagnosis, and environmental analysis.     

The cooperative electrochemical oxidation of chlorophenols in anode-cathode compartments

By using a self-made carbon/polytetrafluoroethylene (C/PTFE) O2-fed as the cathode and Ti/IrO2/RuO2 as the anode, the degradation of three organic compounds (phenol, 4-chlorophenol, and 2,4-dichlorophenol) was investigated in the diaphragm (with terylene as diaphragm material) electrolysis device by electrochemical oxidation process. The result indicated that the concentration of hydrogen peroxide (H2O2) was 8.3 mg/L, and hydroxyl radical (HO) was determined in the cathodic compartment by electron spin resonance spectrum (ESR). The removal efficiency for organic compounds reached about 90% after 120 min, conforming to the sequence of phenol, 4-chlorophenol, and 2,4-dichlorophenol. And the dechlorination degree of 4-chlorophenol exceeded 90% after 80 min. For H2O2, HO existed in the catholyte and reduction dechlorination at the cathode, the mineralization of organics in the cathodic compartment was better than that in the anodic compartment. The degradation of organics was supposed to be cooperative oxidation by direct or indirect electrochemical oxidation at the anode and H2O2, HO produced by oxygen reduction at the cathode. High-performance liquid chromatography (HPLC) allowed identifying phenol as the dechlorination product of 4-chlorophenol in the cathodic compartment, and hydroquinone, 4-chlorocatechol, benzoquinone, maleic, fumaric, oxalic, and formic acids as the main oxidation intermediates in the cathodic and anodic compartments. A reaction scheme involving all these intermediates was proposed.     

Cu-Zr-Al-Ti块体非晶合金的制备及腐蚀行为研究

制备出新型Cu46 Zr46 Al4 Ti4块体非晶合金.利用X射线衍射仪和差示扫描量热仪对其非晶态进行表征,采用电化学方法和扫描电子显微镜研究了非晶合金在3.5％ NaCl溶液中的电化学行为.结果表明,Cu46Zr46-Al4 Ti4样品为完全非晶,玻璃转变温度Tg、晶化温度Tx和过冷液相区△Tx都有所降低,断裂强度提高了约11％.Cu46 Zr46 Al4 Ti4的腐蚀电流密度降低了1个数量级,电化学反应电阻R1大大增加.分析表明,Ti通过抑制阴极过程从而降低了非晶合金的腐蚀速度,其机理可能是Ti的加入降低了活性阴极的面积或增加了氧的离子化过电位.     

黄铜在酸碱盐腐蚀介质中的腐蚀研究

利用SEM、EPMA、电化学曲线测量、XPS等检测技术,研究了HSn62-1黄铜在pH值为2的H_2SO_4溶液、pH值为13的NaOH溶液和3.5%(质量分数)的NaCl溶液中的腐蚀形貌、腐蚀产物、腐蚀类型,并针对不同的腐蚀机制,建立了化学反应模型,对腐蚀机制进行了分析。结果表明,HSn62-1在H_2SO_4溶液中腐蚀失重明显,且其溶解方式为选择性溶解,其腐蚀是以析氢腐蚀为主的混合腐蚀机制;在NaCl溶液和NaOH溶液中的腐蚀为溶解-再沉积机制,溶解速度较为缓慢,在NaCl溶液中为析氢腐蚀,在NaOH溶液中为吸氧腐蚀。     

Hillock formation,hole growth and agglomeration in thin silver films

Thin silver films deposited onto quartz substrates by cathodic sputtering showed hillock growth on annealing in vacuum and in atmospheres of oxygen, helium and argon. Further heating in an oxygen atmosphere caused hole growth and finally led to agglomeration in the films, whereas no hole formation or agglomeration was observed on annealing the films in vacuum and in helium or argon atmospheres. The phenomenon of hillock formation observed in the present case has been explained on the basis of thermal stress relaxation occuring by diffusion creep, with the additional effect of the high surface diffusion of silver atoms on an oxygen-covered silver surface. The hole growth observed as a result of annealing in an oxygen atmosphere could be suitably explained by surface diffusion of silver atoms while the agglomeration occurs during the process of achieving a minimum energy configuration.     

Reaction of tantalum oxide with calcium chloride–calcium oxide melts

Tantalum oxide is a suitable precursor for electro-deoxidation, where a cathodic potential is applied to the oxide, immersed in a molten salt, to remove oxygen from the oxide leaving tantalum metal. The electro-deoxidation reactions take place in a melt of CaCl₂–CaO and, unlike the reduction of other metal oxides where little or no reaction occurs between the melt and oxide until the application of a cathodic potential, tantalum oxide readily reacts with the calcium oxide to form CaTa₄O₁₁, CaTa₂O₆ and Ca₂Ta₂O₇. These phases have completely different morphologies which convert a robust pellet into a collection of poorly connected particles.     

质子交换膜燃料电池氮掺杂碳基催化剂研究进展

简要介绍了近年来氮掺杂碳基催化剂在质子交换膜燃料电池阴极氧还原方面的应用发展状况,详细总结了最近几年有关氮掺杂碳基催化剂制备及机理方面的研究结果,包括氮源前驱体种类、金属前驱体种类、金属的含量、碳源前驱体种类、热处理工艺等影响催化剂氧还原活性的主要因素,并指出了目前研究中的难点以及未来的发展方向。     

Multi-walled carbon nanotube-based glucose/O2 biofuel cell with glucose oxidase and laccase as biocatalysts

This study describes a multi-walled carbon nanotube-based glucose/O2 biofuel cell with glucose oxidase and laccase as the anodic and cathodic biocatalysts, respectively. Upon being functionalized with L-a-phosphatidylcholine, one kind of lipid, multi-walled carbon nanotubes can serve as a support for glucose oxidase to form a three-dimensional, conducting and uniform bioanode that possesses a good bioelectrocatalytic activity toward the oxidation of glucose biofuel with solution-phased ferrocene monocarboxylic acid as the mediator to shuttle the electron transfer between glucose oxidase and multi-walled carbon nanotubes. In a similar way, the lipid-functionalized multiwalled carbon nanotubes can also be used to support the cathodic biocatalyst, i.e., laccase, and, more remarkably, to facilitate the direct electron transfer of laccase. As a result, the prepared biocathode is very active toward the reduction of oxygen without using any electron-transfer mediators. The biofuel cell has a 0.45 V open circuit potential and 34 microA/cm2 short circuit current density in phosphate buffer (pH 6.0) separated with Nafion-117 membrane with anodic compartment containing 15 mM glucose and 2 mM ferrocene monocarboxylic acid and with cathodic compartment being saturated with O2 at room temperature. A maximum power density of 3.2 microW/cm2 is obtained with ca. 0.2 V potential output.