The corrosion behavior of stainless steels and copper alloys exposed to natural seawater

The corrosion behavior of stainless steels, titanium and copper alloys exposed to flowing Pacific Ocean water was characterized using surface analytical and electrochemical techniques. Biofilm formation on stainless steels and titanium resulted in thin films of bacteria and diatoms that did not cause significant changes of the corrosion potential (E_corr) or surface properties. Rotating cylinder experiments indicated that both E_corr and corrosion rates for stainless steels and titanium were independent of mass transport. Four surface layers were identified on copper-containing materials: substratum metal; an inorganic chloride corrosion layer that contained alloying elements; a biofilm; and crystalline, spherical phosphate-rich deposits. All copper surfaces were colonized by bacteria independent of alloy composition. The complexity of the impedance spectra for copper-containing materials was attributed to formation of surface layers and contributions of charge transfer and mass transport controlled reactions mediated by the layers. Both anodic and cathodic reactions for copper-based materials were affected by mass transport.     

Use of SVET and SECM to study the galvanic corrosion of an iron-zinc cell

The work makes use of the scanning vibrating electrode technique (SVET) and the scanning electrochemical microscope (SECM) to investigate microscopic aspects of the electrochemical reactions that occur in an iron-zinc galvanic couple immersed in aqueous sodium chloride solution. Detection of the corrosion processes was made by sensing the phenomena occurring in solution. The SVET provided information on the distribution of ionic currents arising from the metal surface, whereas the SECM measured the concentration of chemical species relevant to the corrosion processes. The two techniques had comparable sensitivity for the corrosion of iron but significant differences were observed concerning the detection of corrosion of zinc.     

Galvanic corrosion behaviour of iron coupled to aluminium in NaCl solution by scanning eectrochemical microscopy

Scanning electrochemical microscopy (SECM) was used to sense the concentration of ions in 0.1M NaCl aqueous solution at the iron-aluminium couple. The SECM measured the concentration of ions relevant to the corrosion processes. The electrochemical behaviour of galvanic Fe/Al coupling was investigated as a function of time using SECM microelectrode tip. SECM amperometric line scan curves were obtained over the Fe/Al at a constant distance. In the first case the chemical species participating in the corrosion reactions at the sample are detected at the SECM-tip by applying appropriate potential values to the microelectrode. The release of Al³⁺ into the solution from local anodic surface, as well as the consumption of dissolved oxygen at the corresponding cathodic surface was successfully monitored. The results revealed that the galvanic couple where Fe/Al is close to each other will show lower corrosion rate due to the formation of corrosion products on the metal surface with further increase in exposure times.     

Mikrobielle Werkstoffzerstörung – Grundlagen: Grundvorgänge der Korrosion

Microbial deterioration of materials – fundamentals: Basic corrosion processes Microbial growth on metal surfaces induces a number of corrosion reactions which are due to changes in the conditions on the boundary layer. The corrosion systems in question are numerous and damage mechanisms correspondingly manifold. Metallic materials corrode according to known electrochemical mechanisms, whereby microorganisms act indirectly. They produce biofilms which are the cause of concentration cells (oxygen, pH, metal salts) and finally lead to local corrosion effects. Another widespread mechanism is based on the formation of sulphide by sulphide-reducing bacteria which stimulate electrochemical partial reactions. A third large group is attributed to the acid producing microorganisms which attack both metallic and inorganic materials. There is no indication that microorganisms are directly involved in the basic reactions of metal corrosion. The corrosion mechanism of inorganic materials, such as the concrete/sulphuric acid system, is of a purely chemical nature and involves processes, such as binding rupture by ion exchange, solvation, hydrolytic cleavage and chemical conversion. Contrary to this, microorganisms participate directly in the deterioration process of organic materials. For each natural polymer a microorganism exists which is capable of complete or partial decomposition of the polymer, whereby it, or additives (e.g. plasticizers). act as C and/or N sources. Explanations of mechanism are, therefore, transferred to the field of microbiology and physico-chemical interpretation is only partially possible.     

Elektrochemische Migration – eine typische Korrosionserscheinung in der Mikroelektronik

Electromigration – a typical corrosion phenomenon in microelectronics The most frequent failure of electronic components is electrochemical migration. As a consequence of the formation of humid films on contaminated printed circuit boards short cuts occur. To obtain an enhanced capacity the conductor spacings are reduced, promoting the danger of a fall out by short cuts. In this paper the main mechanisms of the electrochemical migration consisting of different reactions as metal solution, metal migration and metal deposition will be described in detail. Also methods to avoid electrochemical migration will be discussed.     

机械镀锌镀层钝化与耐蚀性能研究

    对机械镀锌层分别用三价铬、稀土和六价铬进行了钝化处理,利用盐雾试验和电化学测试对不同钝化膜的耐蚀性与电化学行为进行了比较研究.盐雾试验结果表明,稀土与三价铬钝化处理的效果均已超过传统的六价铬钝化,比六价铬钝化膜的耐蚀性提高了一倍以上;稀土钝化膜的耐蚀性最好,三价铬钝化膜的耐蚀性仅次于稀土钝化膜的.电化学测试表明,三价铬、稀土和六价铬钝化膜都能够不同程度地抑制腐蚀的阴极电极反应,抑制阴极反应程度最大的是稀土钝化膜,其次是三价铬钝化膜,最小的是六价铬钝化膜.三价铬与稀土钝化工艺的环保和良好的防腐效果使其具有良好的应用前景.     

The science of pipe corrosion: A review of the literature on the corrosion of ferrous metals in soils

The paper reviews the literature that may assist in forming a multiscale model of corrosion in soils. This model should take into account macro-environmental processes (rainfall, etc.), soils processes (water movement, oxygen transport, etc.), processes within the oxides, and the electrochemical activity occurring at the metal surface. The literature reviewed includes traditional corrosion research such as surveys and historical analysis of buried pipelines, scientific exposures of buried metal, results from buried sensors, and laboratory studies aimed to duplicate soil exposures. Also included are wider studies on water and solute movement in soils, and oxygen transport through soils.     

Mechanismen der Korrosionsinhibition im Vergleich zu den Inhibitionsmechanismen anderer Elektrodenreaktionen

Corrosion inhibition mechanisms as compared to the inhibition mechanisms of other electrode reactions The corrosion inhibition is a special case of the inhibition of electrochemical electrode reactions. During any reaction of this nature - with or without impressed current - partial reactions may be inhibited by boundary face, electrolyte film or membrane inhibitors. The boundary face inhibitors are most efficient in acid or alkaline media, while membrane inhibitors are most efficient in approximately neutral media. The former — because of electrosorption at the metal/electrolyte boundary face - affect the electrochemical charge exchange or heterogeneous chemical partial reactions, while membrane inhibitors inhibit all the partial reactions by building a threedimensional surface layer. The electrolyte film inhibitors inhibit mass transfer to or from the metal/electrolyte boundary face, or they inhibit homogeneous chemical partial reactions either mechanically (by colloids or suspensions) or electrochemically (by modifying the surface charge of the metal and thus the tranfer velocity of ions by increasing attraction or repulsion). The use of passivators is restricted exclusively to corrosion inhibition. The passivating layers formed by them are much thinner and denser than the layers formed by membrane inhibitors. The passivators act like boundary surface inhibitors.     

The hydrogen evolution reaction on iron corroded in dilute and very dilute solutions of sulfuric acid

Permeation transients for hydrogen, generated by corrosion of iron in dilute solutions of sulfuric acid, were recorded with an improved electrochemical permeation apparatus.The mechanism of the hydrogen evolution reactions is coupled discharge hydrogen recombination for all methods of hydrogen generation, low current anodic polarization, cathodic polarization and corrosion.The experimental hydrogen transient was compared with that predicted theoretically.It is concluded that electrochemical hydrogen permeation is a sensitive tool for investigating processes on metal surfaces which are of engineering importance.     

海洋微生物腐蚀的电化学研究方法

海洋微生物引起的腐蚀对海洋结构物造成了日益严重的危害,其特征是微生物附着于金属表面并形成聚合物膜－－生物膜,该生物膜改变了膜内的环境条件,并伴有微生物对电化学反应的催化过程,因此加速了金属的腐蚀。本文介绍了监测腐蚀电位,氧化还原电位、极化电阻、强极化技术,电化学阻抗谱、,电化学噪声、电化学表面成象,双区电池等方法在微生物腐蚀研究中的应用,指出了这些方法的使用条件和优缺点,为了保持微生物本身物活性,     

Effect of the Crevice Former on the Corrosion Behavior of 316L Stainless Steel in Chloride-Containing Synthetic Tap Water

To restrain the failure of the plate heat exchanger (PHE) in customer boiler working fluid, the effect of crevice former type on the corrosion behavior of the 316L stainless steel plate was investigated using electrochemical methods and surface analyses in chloride-containing synthetic tap water (60 °C). The localized corrosion under metal–metal crevice condition was initiated more easily than that under the metal-gasket crevice condition due to the restricted mass transport at the gasket crevice mouth. However, the anodic current under the metal–metal crevice condition was lower than that under metal-gasket crevice condition at a higher anodic potential, indicating that that the metal dissolution under EPDM crevice would be higher than that under metal crevice under the accelerated corrosion condition. Because narrow crevice gap that was formed under gasket accelerated the anodic dissolution at the crevice mouth, the perforation tendency under metal-gasket crevice condition is much higher than that under metal–metal crevice condition. As a result, the crevice geometry, especially the crevice gap, mainly affected the corrosion behavior of PHE material.     

Modeling of electrochemical noise transients

Starting from the elementary corrosion reactions on a passive metal surface a model is developed for the origin of electrochemical noise. The ion currents flowing at the electrochemical reactions are described by the electrons remaining in the metal and then interpreted as a measuring signal. The measurable sum current is composed of the superimposition of the electron currents of the partial reactions. Due to the inhomogeneity of the metal surface, local metal dissolutions take place in preferential areas until the area is consumed or repassivated after short times. The short‐time surplus of free electrons leads for every metal dissolution event to a current transient, which itself consists of the partial currents of the elementary anodic and cathodic reactions. Due to the different reaction speeds, there are temporary charge disequilibria and thus measurable noise transients. In model calculations the influence of the diffusion of the oxygen on the sum signal as well as the variation of the anodic current is shown. Furthermore, the results show that a measurable noise signal can only arise under certain conditions. This signal arisen directly at the metal surface is not, however, ascertainable without further amplification. In the measurement amplifiers filter stages play an important role for signal conditioning. The influence of the measuring technique is shown at the filtration of a simulated test signal in different frequency domains. It is discussed how the signal distortion affects the detectability of the partial reactions described at the beginning and in which way the noise signal is estimated. Indications for the layout of suitable measuring parameters are given.     

深度轧制技术制备的纳米晶金属板材腐蚀性能研究进展

概述了目前已提出的几种纳米晶金属材料制备技术和不同纳米晶金属材料腐蚀研究进展。介绍了深度轧制技术制备纳米晶金属板材,阐述了该技术制备的纳米晶金属板材(工业纯铁、304不锈钢和工业纯铝)腐蚀性能研究进展。与相应的普通金属材料相比,深度轧制技术制备的这三种纳米晶金属材料在不同腐蚀环境(溶液、熔盐和高温气体)中耐腐蚀性能(局部腐蚀和均匀腐蚀)提高。大量纳米晶及其相应普通金属材料的腐蚀实验结果表明,传统的材料微观结构参量(成分及其分布、晶粒尺寸、位错密度和残余应力等)不是腐蚀性能的本征参量。提出了从金属材料价电子结构和氧化膜电子结构角度理解金属材料腐蚀性能及其相关腐蚀机理,并在现有工作基础上提出金属材料电化学腐蚀本征参量的概念。     

Mechanism of the corrosion exfoliation of a polymer coating from a carbon steel

A mechanism of the atmospheric corrosion of a carbon steel under polymer (paint and varnish) coatings is studied. The potential distribution around an artificial coating defect was measured in situ with a scanning Kelvin probe (SKP). The potential gradient between the steel surface at the defect and under the coating determines the mechanism of the subfilm corrosion. Measuring the galvanic currents in a steel under coating-steel at defect model system revealed the spatial separation of partial electrochemical reactions. The separation was additionally confirmed by the elemental analysis of the metal surface upon removing the coating. The mechanism of corrosion exfoliation is shown to differ depending on the kind of rate, which determines the electrochemical reaction at the coating defect. In the presence of aqueous NaCl electrolyte, the defect acts as an anode, which results in the cathodic exfoliation of the coating. In the case of drier corrosion in an atmosphere at a humidity of 95%, the steel at a defect acts as a cathode with respect to the surrounding interface, which leads to the development of anodic zones around the defect.     

Corrosion protection of AA 2024-T3 by bis-[3-(triethoxysilyl)propyl]tetrasulfide in sodium chloride solution.: Part 2: mechanism for corrosion protection

The corrosion protection of AA 2024-T3 by films of bis-[3-(triethoxysilyl)propyl]tetrasulfide (bis-sulfur silane) was studied in a neutral 0.6 M NaCl solution using potential transient, potentiodynamic polarization and electrochemical impedance spectroscopy (EIS) techniques. The results showed that a highly crosslinked or dense interfacial layer that developed between the silane film and the aluminum oxide is the major contribution to the corrosion protection of AA 2024-T3. The formation of this interfacial layer heavily restricts pit growth underneath via retarding the transport of corrosion products, as well as effectively blocks a number of cathodic sites available for cathodic reactions.     

Effects of Solution Hydrodynamics on Corrosion Inhibition of Steel by Citric Acid in Cooling Water

Corrosion is a major problem in cooling water systems, which is often controlled using corrosion inhibitors. Solution hydrodynamics is one of the factors affecting corrosion inhibition of metals in these systems. The present work focuses on the study of the combined effects of citric acid concentration (as a green corrosion inhibitor) and fluid flow on corrosion of steel in simulated cooling water. Electrochemical techniques including Tafel polarization and electrochemical impedance spectroscopy were used for corrosion studies. Laminar flow was simulated using a rotating disk electrode. The effects of solution hydrodynamics on inhibition performance of citric acid were discussed. The citric acid showed low inhibition performance in quiescent solution; however, when the electrode rotated at 200 rpm, inhibition efficiency increased remarkably. It was attributed mainly to the acceleration of inhibitor mass transport toward metal surface. The efficiencies were then decreased at higher rotation speeds due to enhanced wall shear stresses on metal surface and separation of adsorbed inhibitor molecules. This article is first part of authors’ attempts in designing green inhibitor formulations for industrial cooling water. Citric acid showed acceptable corrosion inhibition in low rotation rates; thus, it can be used as a green additive to the corrosion inhibitor formulations.     

Role of chlorides in hot corrosion of a cast Fe–Cr–Ni alloy. Part II: thermochemical model studies

In many high temperature applications severe degradation of alloys is caused by thin deposits of molten salts, especially alkali metal sulfates, alkali metal chlorides and mixtures of these salts. Calculations of multi-component thermochemical equilibria in systems involving (initially) metal/salt/gas as a function of local oxygen activity can help identify the important hot corrosion reactions. Such calculations for four pure salts (KCl, NaCl, Na₂SO₄, and K₂SO₄) and a mixture of these salts in contact with an Fe–20%Cr alloy at 800 °C are presented. The results predict that the compositions of gas, oxide, (sulfide, when sulfate was input) and salt phases depend strongly upon the salt chosen and upon the local oxygen activity. In some cases the equilibrium salt composition is significantly changed by reactions with metal or oxide phases. The calculated results for the salt mixture were compared with experimental data from part I of this paper. The model calculations have led to the identification of two new factors that support faster hot corrosion rates in an alkali chloride + sulfate salt compared to that in alkali sulfate alone. First, alkali chlorides, unlike sulfates, support a continuous salt pathway from ambient to the metal/scale interface, allowing oxidant to be efficiently transported to oxidize metal. Secondly, under oxidizing conditions alkali chlorides have a higher solubility of dissolved Fe- and Cr-containing species than that in alkali sulfates. Both of these factors support higher transport rates, which according to the fluxing theory of hot corrosion will lead to faster corrosion.     

The corrosion and electrochemical behaviour of zinc in binary mixtures of dimethylformamide and water

The results of corrosion and electrochemical studies on zinc in dimethylformamide and water mixtures at 30°C indicate that the dissolution of zinc is cathodically controlled with the metal being anodically more active in the region of the higher percentage of water. Stirring and the dissolved oxygen influence only the cathodic reactions.     

Role of magnesium ions in reducing high temperature aqueous corrosion of carbon steel

Carbon steel is used as the primary heat transport system piping material in pressurized heavy water reactors. The carbon steel surfaces corrode during the high temperature operation. Enhanced wall thinning of the piping in locations of high velocity and neutron activation of corrosion products pose serious operational difficulties. Magnesium ion modified water chemistry resulted in significant reduction in the corrosion and corrosion release of carbon steel. The changes induced by magnesium ions in the various processes at the metal–oxide, oxide–solution interfaces, and subsequent restructuring of the oxide were identified by in situ electrochemical impedance spectroscopy.     

Corrosion of metals and alloys in molten glasses. Part 1: glass electrochemical properties and pure metal (Fe, Co, Ni, Cr) behaviours

Corrosion of pure metals Fe, Ni, Co, Cr in molten glass was studied at 1050 °C by electrochemical techniques and thickness losses measurements. These two techniques are in good agreement. The electrochemical apparatus was used to determine the formal potential of some redox couples, to identify the corrosion reactions and to evaluate the corrosion rates.Among tested metals, only chromium is a passivable material. The passivation is due to the formation of a chromium oxide (Cr₂O₃) protective layer at the glass/metal interface. Then superalloys used in molten glass must contain a high chromium level to resist to corrosion.