Mechanism of corrosion of tin-oxide electrodes

Conclusions The destruction of tin-oxide ceramic by glass takes place rapidly, despite the absence of marked penetration of molten glass into the pores of the material, i.e., the low impregnation is not an essential condition for high corrosion resistance.The corrosion is linked with the change in the structure of the material, expressed by the increase in its dispersion and the development of a large number of fine, weakly interbonded grains with subsequent penetration between them of glass, bloating, and breakdown into separate fragments.The least corrosion by lead glass is exhibited by tin oxide ceramic with clearly expressed crystals bonded by dense intergrain contacts, regardless of the total porosity.The most intense corrosion is typical of a material with badly formed intergrain faces, and a high open porosity. Even prolonged service at high temperatures in contact with glass does not lead to marked growth of the grains and their regular delimitation.The most resistant to corrosion turned out to be a material with a well-formed granular structure, with a pore volume of about 9.1 mm³/g, and pores measuring 10–20 m. In service it is completely impregnated with glass.Translated from Ogneupory, No. 2, pp. 24–29, February, 1989.     

Characterisation and corrosion studies of steel electrodes covered by polypyrrole/phosphotungstate using Electrochemical Impedance Spectroscopy

Polypyrrole/PW₁₂O₄₀³⁻ hybrid material was electrosynthesised on carbon steel electrodes in acetonitrile medium. The coatings obtained were characterised by Electrochemical Impedance Spectroscopy (EIS). On free-standing polypyrrole films the electrical response was mainly due to ion–ion charge transfer resistance, with a value of 175 Ω cm². A value of 2 × 10⁻⁵ S/cm was determined for the hybrid material conductivity. A charge transfer resistance about 7000 Ω cm² was obtained due to steel/oxide interface. Corrosion tests showed an important improvement in the protection against corrosion when the carbon steel electrodes were coated by these polymeric films.     

Modeling the rate of corrosion of carbon steel using activated diethanolamine solutions for CO_2 absorption

A mechanistic model is developed to investigate the influence of an activator on the corrosion rate of carbon steel in the absorption processes of carbon dioxide(CO_2). Piperazine(PZ) is used as the activator in diethanolamine(DEA) aqueous solutions. The developed model for corrosion takes into consideration the effect of fluid flow,transfer of charge and diffusion of oxidizing agents and operating parameters like temperature, activator concentration, CO_2 loading and pH. The study consists of two major models: Vapor–liquid Equilibrium(VLE) model and electrochemical corrosion model. The electrolyte-NRTL equilibrium model was used for determination of concentration of chemical species in the bulk solution. The results of speciation were subsequently used for producing polarization curves and predicting the rate of corrosion occurring at the surface of metal. An increase in concentration of activator, increases the rate of corrosion of carbon steel in mixtures of activated DEA.     

Modeling the rate of corrosion of carbon steel using activated diethanolamine solutions for CO2 absorption

A mechanistic model is developed to investigate the influence of an activator on the corrosion rate of carbon steel in the absorption processes of carbon dioxide (CO₂). Piperazine (PZ) is used as the activator in diethanolamine (DEA) aqueous solutions. The developed model for corrosion takes into consideration the effect of fluid flow, transfer of charge and diffusion of oxidizing agents and operating parameters like temperature, activator concentration, CO₂ loading and pH. The study consists of two major models: Vapor-liquid Equilibrium (VLE) model and electrochemical corrosion model. The electrolyte-NRTL equilibrium model was used for determination of concentration of chemical species in the bulk solution. The results of speciation were subsequently used for producing polarization curves and predicting the rate of corrosion occurring at the surface of metal. An increase in concentration of activator, increases the rate of corrosion of carbon steel in mixtures of activated DEA.     

Microbial consortium influence upon steel corrosion rate, using polarisation resistance and electrochemical noise techniques

The microbiologically influenced corrosion (MIC) is a process, which affects the oil industry, particularly the hydrocarbons extraction, transport and storage. MIC evaluation has been normally based upon microbiological tests, and just a few references mention alternating methods, such as the electrochemical techniques, which can be used as criteria for their evaluation.In this work, two different electrochemical laboratory techniques, polarisation resistance and electrochemical noise were used, in order to determine the corrosion behaviour of a microbial consortium, obtained from a gas transporting pipeline, located in the southeast of Mexico.The bacteria population growth was found to be different for sessile and plancktonic microorganisms. Moreover, long incubation times were required to reach the maximum concentration of sessile bacteria.The electrochemical techniques used in this study exhibited a similar tendency on the corrosion rate behaviour with time, and values above 0.3 mm year⁻¹ were observed at the end of the experiments.The experiments were complemented with surface analysis. Scanning electron microscope observation of APIXL52 steel coupons, exposed to the consortium action, revealed bacteria presence, as well as a damaged steel surface. A type of localized corrosion was observed on the metal surface, and it was associated to the bacteria effect.     

Mass transfer and flow rate measurements for a system of two rotating disc electrodes with an axial electrolyte inlet

Limiting currents and volume flow rates in the self pumping regime were measured on a model rotating electrolyzer with a variable geometry. The volume flow rate depends not only on the radius of the inlet orifice, outer disc radius, and angular velocity, but also on the interelectrode distance. Experimental mean current densities are compared with those calculated by the finite-element method, from an equation based on the theory of similarity of the diffusion layer, and from the theory of the rotating disc electrode with a ring.Notation a ₁–a ₄ constants - c ₀ bulk concentration - D diffusion coefficient - F Faraday constant, 96 487 C mol^–1 - h interelectrode distance - I current - mean current density - k ₁,k ₂ constants - n number of transferred electrons - Q volume rate of flow - r radial coordinate - r ₀ inner radius of electrode - r ₁ outer radius of electrode - r _v radius of inlet orifice - r _d outer radius of disc - R radius of measuring tube - u _max maximum velocity of liquid - z normal coordinate - dynamic viscosity - kinematic viscosity - density - angular velocity     

Predeterminate model of corrosion rate of steel in concrete

The predeterminate model of corrosion rate of steel in concrete, the influence of concrete carbonation exponent and cover thickness to steel corrosion rate, and relationships among steel diameter, cover thickness and exposure time to steel corrosion rate are mainly studied. It is shown that (1) the steel corrosion rate increases when the concrete carbonation exponent increases. (2) The steel corrosion rate decreases when a mild carbon steel with circular diameter in concrete increases. The more the concrete carbonation exponent becomes larger, the more the effect of steel diameter obviously appears. (3) The steel corrosion rate increases when the concrete cover thickness decreases. (4) The steel corrosion rate obviously increases when the exposure time decreases. The results of present studies are discussed in comparison with earlier findings.     

Characterization of solid embeddable reference electrodes for corrosion monitoring in reinforced concrete structures

Metal-metal oxide (MMO), graphite and laboratory-made Ag/AgCl electrodes were electrochemically characterized to be used as reference electrodes embedded in concrete structures. Electrodes were studied in both, aqueous solutions of pH ranging from 7 to 13.5 and embedded into cement mortars; and the electrochemical studies were carried out in the absence and presence of chloride ions. Potential evolution, polarization behaviour, galvanostatic pulse response and impedance characteristics of the electrodes were carried out in aqueous solutions. Besides, the electrochemical stability of the electrodes embedded in mortar was studied for an exposure period of 2 years. It was found that the MMO pseudo-reference electrode is pH-sensitive, the graphite pseudo-reference electrode is oxygen sensitive and the Ag/AgCl pseudo-reference electrode is chloride sensitive. In spite of the fact that any of them can be used to determine the corrosion rates of rebars because they do not depend on the absolute potential and/or the long-term stability of the reference electrode when using traditional electrochemical techniques, long-term drifts in the electrode potentials may lead to misinterpretations of the rebar state. In this context graphite electrodes are recommended because they provide conservative results regarding the active/passive state of the rebars.     

Dual-chambered bio-batteries using immobilized mediator electrodes

Methylene blue was immobilized on 304L stainless steel to investigate a potential cost-effective, durable, and high performance composite electrode for use with microbial applications, such as bio-batteries and microbial fuel cells. The composite electrodes were tested in dual-chamber bio-batteries with pure cultures of Escherichia coli K-12 or Shewanella oneidensis MR-1 and the results were compared to those obtained using bare graphite electrodes. The maximum power generated using the composite electrodes was 39.35 mW m^?2 in bio-batteries using E. coli K-12, and 60.05 mW m^?2 in bio-batteries using S. oneidensis MR-1. Compared to graphite electrodes, the bio-batteries using composite electrodes showed a 6- and 2.5-fold increase in the maximum power density, using pure cultures of E. coli K-12 and S. oneidensis MR-1, respectively. The composite electrodes did not inhibit bacterial growth in the bio-batteries and were shown to improve performance (both in terms of power output and current density) over conventional graphite electrodes.     

Electrochemical studies of pyrite oxidation and reduction using freshly-fractured electrodes and rotating ring-disc electrodes

Oxidation and reduction processes on coal- and mineral-pyrite surfaces have been investigated to better understand the reactions that control the hydrophobicity and flotation behavior of pyrite. The incipient oxidation and reduction reactions were studied using fresh surfaces of pyrite that were created by in situ fracturing electrodes potentiostated at a predetermined potential. Chronoamperometry immediately after fracture and subsequent cyclic voltammetry have established that fresh fracture surfaces of pyrite instantaneously assume a unique potential (referred to as the “stable” potential) at which neither oxidation nor reduction takes place. For Peruvian and Chinese pyrites, the stable potential is −0.28 V (standard hydrogen electrode, SHE) at pH 9.2 and 0 V at pH 4.6. The initial oxidation of pyrite begins at potentials slightly positive of the stable potential and is believed to produce a hydrophobic sulfur-rich species, most likely a polysulfide or metal-deficient sulfide. A rotating ring-disc electrode (RRDE) was employed to study the kinetics and mechanisms of surface reactions on pyrite over moderate potential ranges. Two distinct soluble reduction products (ferrous hydroxide and HS⁻) and one distinct soluble oxidation product (ferrous hydroxide) were observed on pyrite in alkaline solutions. It is concluded that the initial oxidation of pyrite and the oxidation of ferrous to ferric hydroxide occur in a similar potential range. When the electrode is oxidized, e.g. by polishing, prior to experiments, the initial oxidation of pyrite is masked by the oxidation of ferrous hydroxide, making it difficult to study the oxidation of pyrite itself.     

Electrolytic decomposition of amaranth dyestuff using diamond electrodes

The electrolytic decomposition of an amaranth dyestuff solution using several combinations of electrodes with diamond and platinum is reported. It is observed that a portion of the amaranth is decomposed on the cathode surface while the other portion is decomposed to lower molecular weight components on the anode surface. The decolourizing rate is higher at diamond electrodes used as the anode and the cathode than with other combinations. This electrode combination also shows a rapid decrease in total organic carbon concentration. Acetic acid and oxalic acid are detected as the intermediate substances, and CO₂ gas is generated as a final product corresponding to the decrease in the oxalic acid concentration.     

Effect of surfactants on the rate of mass transfer at gas-evolving electrodes

The effect of sodium lauryl sulphate surfactant on the mass transfer coefficient of the cathodic reduction of ferricyanide ion and the anode oxidation of ferrocyanide ion at hydrogen- and oxygen-evolving electrodes, respectively, was studied. Also, the effect of sodium lauryl sulphate on the gas hold-up and cell voltage was studied. The presence of surfactant in the electrolyte was found to decrease the mass transfer coefficient by an amount ranging from 7.6 to 81% depending on the operating conditions. Gas hold-up and cell voltage were found to increase in the presence of surfactant.Nomenclature C concentration - F Faraday constant (96 487 C mol^–1) - I _I limiting current under natural convection - I current consumed in ferricyanide reduction or ferrocyanide oxidation during electrolysis with gas evolution - K mass transfer coefficient - V gas discharge rate - Z number of electrons involved in the reaction - gas hold-up     

Different hydrothermal corrosion results between two sides of sodalime float glass and the possible corrosion mechanism

Sodalime float (SF) glass is widely used in our societies and industries. Hydrothermal corrosion method is one of the effective ways to prepare a superhydrophobic glass, but there is still lack of knowledge about hydrothermal corrosion behavior and mechanism of SF glass. We have hydrothermally treated SF glass at 180 °C for different time, and tried to reveal the aqueous corrosion process of SF glass. We have characterized the morphologies and chemical compositions of samples, and found that (1) the two sides of SF glass have different corrosion resistances, and (2) a multilayer structural coating with a nanoflake layer (Mg-rich gel layer), a nanowire layer (Ca-rich gel layer), and a porous layer (etched layer) is formed on the air-side of SF glass. Based on the experimental results, we have proposed an aqueous corrosion mechanism of SF glass. The insights of the hydrothermal corrosion behaviors and mechanism provide helpful guidelines to glass surface structural control and functionalization.     

高固体分低腐蚀蔓延环氧底漆的研究

为了延长涂层的使用寿命,改善涂层被划伤后因水分子渗入、涂层附着力降低而导致的腐蚀蔓延情况,选用环氧树脂、固化剂、活性粉料、附着力促进剂及其他助剂制备了一种高固体分、低腐蚀蔓延的环氧底漆。分别讨论了固化剂、活性粉料及附着力促进剂对漆膜耐蚀性的影响,结果发现采用改性曼尼希碱固化剂,以6%磷酸锌、6%氧化锌、3%三聚磷酸铝和1%钼酸锌复配作为活性粉料,并且在加入0.5%附着力促进剂的情况下所制备的底漆的固含量达到80%以上,斯托默黏度仅95 KU,有利于施工。经中性盐雾试验120 h后,其漆膜的划线单侧腐蚀≤1 mm,1 032 h后的腐蚀宽度约为1.26 mm,腐蚀蔓延水平较低。     

两类酸化用缓蚀剂性能评价

针对在油气井酸化作业过程中出现的腐蚀问题,应用缓蚀剂是一种高效,经济和便捷的办法.通过静态常压失重法测试缓蚀剂A和B的缓蚀性能,缓蚀剂A为咪唑啉类缓蚀剂,缓蚀剂B为双季铵盐类缓蚀剂.实验采用地层螯合酸和现场取回的过滤海水配制酸性溶液.结果表明,3组不同含量的缓蚀剂A均达到二级标准,3组不同含量的缓蚀剂B均达到一级标准,...     

The distribution of potential and electrochemical reaction rate in molten polysulphide electrodes

A simple mathematical derivation is given of the distribution of potential in a porous carbon electrode saturated with molten sulphur/sodium polysulphide. The equations show how the spatial distribution of reaction products in the sodium/sulphur cell depends on the relative electrical resistivities of the melt and the carbon matrix and, also, the electrode thickness. This distribution is shown to be of particular significance, as far as polarization and utilization are concerned, if the formation of passive films occurs.     

Prediction of reinforcement corrosion using corrosion induced cracks width in corroded reinforced concrete beams

This paper studies the evolution of reinforcement corrosion in comparison to corrosion crack width in a highly corroded reinforced concrete beam. Cracking and corrosion maps of the beam were drawn and steel reinforcement was recovered from the beam to observe the corrosion pattern and to measure the loss of mass of steel reinforcement. Maximum steel cross-section loss of the main reinforcement and average steel cross-section loss between stirrups were plotted against the crack width. The experimental results were compared with existing models proposed by Rodriguez et al., Vidal et al. and Zhang et al. Time prediction models for a given opening threshold are also compared to experimental results. Steel cross-section loss for stirrups was also measured and was plotted against the crack width. It was observed that steel cross-section loss in the stirrups had no relationship with the crack width of longitudinal corrosion cracks.