Showing papers on "Corrosion published in 2004"

Ceramic materials for thermal barrier coatings

Abstract: This paper summarizes the basic properties of ceramic materials for thermal barrier coatings. Ceramics, in contrast to metals, are often more resistant to oxidation, corrosion and wear, as well as being better thermal insulators. Except yttria stabilized zirconia, other materials such as lanthanum zirconate and rare earth oxides are also promising materials for thermal barrier coatings.

Corrosion of Steel in Concrete: Prevention, Diagnosis, Repair

Abstract: Reinforced concrete has been developed and applied extensively in the 20th century. It combines the good compressive strength of concrete with the high tensile strength of steel and has proven to be successful in terms of structural performance and durability. However, there are instances of premature failure of reinforced concrete and prestressed concrete components due to corrosion of the reinforcing steel with very high economic implications of such damage. This book focuses on the chloride and carbonation induced corrosion of steel in concrete, presenting transport mechanisms and electrochemical concepts. Other types of corrosion of steel and degradation of concrete are also treated. The main emphasis lies on design and execution aspects related to durability of new and existing structures. New methods and materials for preventative measures, condition assessment and repair techniques are discussed. This makes this book an invaluable reference for any engineer and materials scientist involved in research and practice of corrosion protection, rehabilitation and maintenance of reinforced concrete structures and components. Owners, designers and contractors will profit by this updated state of the art. © 2013 Wiley-VCH Verlag GmbH & Co. KGaA.

Iron corrosion by novel anaerobic microorganisms

Abstract: Corrosion of iron presents a serious economic problem. Whereas aerobic corrosion is a chemical process, anaerobic corrosion is frequently linked to the activity of sulphate-reducing bacteria (SRB). SRB are supposed to act upon iron primarily by produced hydrogen sulphide as a corrosive agent and by consumption of 'cathodic hydrogen' formed on iron in contact with water. Among SRB, Desulfovibrio species--with their capacity to consume hydrogen effectively--are conventionally regarded as the main culprits of anaerobic corrosion; however, the underlying mechanisms are complex and insufficiently understood. Here we describe novel marine, corrosive types of SRB obtained via an isolation approach with metallic iron as the only electron donor. In particular, a Desulfobacterium-like isolate reduced sulphate with metallic iron much faster than conventional hydrogen-scavenging Desulfovibrio species, suggesting that the novel surface-attached cell type obtained electrons from metallic iron in a more direct manner than via free hydrogen. Similarly, a newly isolated Methanobacterium-like archaeon produced methane with iron faster than do known hydrogen-using methanogens, again suggesting a more direct access to electrons from iron than via hydrogen consumption.

Electrocatalytic corrosion of carbon support in PEMFC cathodes

Abstract: The influence of platinum on the corrosion of carbon catalyst supports has been characterized by on-line mass spectroscopy during cyclic voltammetry, with varying Pt mass fraction, catalyst type, and temperature. The generation rates increased with higher Pt mass fraction (0, 10, and 39% balanced by Vulcan XC-72). A peak observed at approximately for Pt/C was lowered to for PtRu/C. An Arrenhius plot indicated higher apparent activation energy for production at the positive potential limit of the cyclic voltammogram on 0% Pt (carbon-only) electrode than on 39% Pt/C electrode. It was concluded that platinum accelerated the corrosion rate of the carbon catalyst support. © 2003 The Electrochemical Society. All rights reserved.

Corrosion in high-temperature and supercritical water and aqueous solutions: a review

Abstract: The aim of the present article is to review some of the common corrosion phenomena and describe the predominant corrosion mechanisms in high-temperature and supercritical water. Corrosion in aqueous systems up to supercritical temperatures is determined by several solution-dependent and material-dependent factors. Solution-depending factors are the density, the temperature, the pH value, and the electrochemical potential of the solution, and the aggressiveness of the attacking anions. Material-dependent parameters include alloy composition, surface condition, material purity, and heat treatment. Corrosion phenomena that are observed include intergranular corrosion, pitting, general corrosion, and stress corrosion cracking. The solubility and dissociation of both attacking species and corrosion products play the most important role for corrosion in high-temperature water. Both solubility and dissociation processes are strongly influenced by the density, or the ionic product, respectively, of the solvent. High values of both parameters favor ionic reactions, and thus, accelerate electrochemical forms of corrosion. At low densities, water behaves like a non-polar solvent, and thus, ions associate. In these cases, the concentation of e.g. aggressive H + drops down and thus, solutions containing species such as HCl become neutral and thus less aggressive. Further, corrosion products plug the surface and material loss stops. Materials parameters have influence especially on the initiation of corrosion. In the present article, these factors are linked with the physical and chemical properties of high-temperature and supercritical water. An outlook is also given for future research needs.

Test methods for on-site corrosion rate measurement of steel reinforcement in concrete by means of the polarization resistance method

Abstract: 1. SCOPE This Recommendation covers the description of nondestructive electrochemical test methods for the estimation in large size concrete structures of the instantaneous corrosion current density, ioorr, expressed in gA/cm 2, by means of the so-called Polarization Resistance technique, R o, in order to assess the condition of embedded steel reinforcement related to its corrosion. The values of i~orr, Can be used to assess the rate of degradation of concrete structures affected by reinforcement corrosion. However, they cannot give information on the actual loss in steel cross section which, at present, only can be assessed by means of direct visual observation. Values of the free corrosion potential or half-cell potential, Ecorr [V], of the embedded reinforcing steel and of the electrical concrete resistance, Re [f)], are obtained as preliminary steps of the Rp measurements. Values of the concrete resistivity, P [~m], can be calculated from Re values providing the geometrical arrangement of the electrodes enables this calculation. Both parameters, Ecorr and Re (or P) may be used to complement the reliability of the ico~r measurements.

Evaluation of cyto-toxicity and corrosion behavior of alkali-heat-treated magnesium in simulated body fluid

Abstract: Compared to other popular metallic biomaterials, magnesium has many advantages, which include high specific strength-to-mass ratio, non-toxicity and similar elastic modulus to that of human bone. However, the knowledge gap in corrosion resistance in physiological environment has prevented it from being a substitute for human hard tissues. In this paper, preliminary corrosion tests on magnesium specimens in Simulated Body Fluid (SBF) with and without Cl − ions have been investigated. Cytotoxicity tests were then carried out for developing a new biomaterial. The corrosion results showed that alkali and heat-treated magnesium has relatively high corrosion resistance in SBF, compared to untreated samples. Calcium-phosphate apatites were detected on the treated samples after they had been soaked in SBF for 14 days. In cytotoxicity tests, no signs of morphological changes on cells or inhibitory effect on cell growth were detected.

Corrosion resistance of aged die cast magnesium alloy AZ91D

Abstract: The corrosion behaviour of die cast magnesium alloy AZ91D aged at 160 ◦ C was investigated. The corrosion rate of the alloy decreases with ageing time in the initial stages and then increases again at ageing times greater than 45 h. The dependence of the corrosion rate on ageing time can be related to the changes in microstructure and local composition during ageing. Precipitation of the phase (Mg17Al12) occurs exclusively along the grain boundaries during ageing. The phase acts as a barrier, resulting in a decreasing corrosion rate in the initial stages of ageing. In the later stages, the decreasing aluminium content of grains makes the matrix more active, causing an increase in the corrosion rate. Electrochemical testing results also confirm the combined effects of the changes in and phases on the corrosion resistance of the aged die cast AZ91D alloy. © 2003 Elsevier B.V. All rights reserved.

General and localized corrosion of magnesium alloys: A critical review

Abstract: Magnesium (Mg) alloys as well as experimental alloys are emerging as light structural materials for current, new, and innovative applications. This paper describes the influence of the alloying elements and the different casting processes on the microstructure and performance of these alloys and corrosion. It gives a comprehensible approach for the resistance of these alloys to general, localized and metallurgically influenced corrosion, which are the main challenges for their use. Exposure to humid air with ∼65% relative humidity during 4 days gives 100–150 nm thickness. The film is amorphous and has an oxidation rate less than 0.01 µm/y. The pH values between 8.5 and 11.5 correspond to a relatively protective oxide or hydroxide film; however above 11.5 a passive stable layer is observed. The poor corrosion resistance of many Mg alloys can be due to the internal galvanic corrosion caused by second phases or impurities. Agitation or any other means of destroying or preventing the formation of a protective film leads to increasing corrosion kinetics. The pH changes during pitting corrosion can come from two different reduction reactions: reduction of dissolved oxygen (O) and that of hydrogen (H) ions. Filiform corrosion was observed in the uncoated AZ31, while general corrosion mainly occurred in some deposition coated alloys. Crevice corrosion can probably be initiated due to the hydrolysis reaction. Exfoliation can be considered as a type of intergranular attack, and this is observed in unalloyed Mg above a critical chloride concentration.

Electrochemistry and Corrosion Science

Abstract: Forms of Corrosion.- Electrochemistry.- Kinetics of Activation Polarization.- Kinetics of Concentration Polarization.- Mixed Potential Theory.- Corrosivity and Passivity.- Electrometallurgy.- Cathodic Protection.- Anodic Protection.- High-temperature Corrosion.

Corrosion of Aluminium

Abstract: Aluminium and its alloys Aluminium corrosion Atmospheric corrosion of aluminium Corrosion in water The action of mineral products The action of organic products The effect of different environments appendices

Corrosion of Aluminum and Aluminum Alloys

Abstract: ALUMINUM became an economic competitor in engineering applications toward the end of the 19th century. The reason aluminum was not used earlier was the difficulty of extracting it from its ore. When the electrolytic reduction of aluminum oxide (Al2O:3) dissolved in molten cryolite was independently developed by Charles Martin Hall in the United States and Paul T. Heroult in France, the aluminum industry was bom. The emergence of three important industrial developments in the late 18008 and early 1900swould, by demanding material characteristics consistent with the unique qualities of aluminum and its alloys, greatly benefit growth in the production and use of the new metal. The first of these was the introduction of the first internal-combustion-engine-powered vehicles. Aluminum would play a role as an automotive material of increasing engineering value. Secondly, electrification would require immense quantities of lightweight conductive metal for long-distance transmission and for construction of the towers needed to support the overhead network of cables that deliver electrical energy from sites of power generation. Within a few decades, a third important application area was made possible by the invention of the airplane by the Wright brothers. This gave birth to an entirely new industry which grew in partnership with the aluminum industry development of structurally reliable, strong, and fracture-resistant parts for airframes, engines, and ultimately, for missile bodies, fuel cells, and satellite components. However, .the aluminum industry growth was not limited to these developments. The first commercial applications of aluminum were novelty items such as mirror frames, house (address) numbers, and serving trays. Cooking utensils were also a major early market In time, aluminum applications grew in diversity to the extent that virtually every aspect of modem life would bedirectly or indirectly affected by use. Today, aluminum is surpassed only by steel in its use as a structural material.

Effect of coating time and heat treatment on structures and corrosion characteristics of electroless Ni-P alloy deposits

Abstract: Mild steel was electroless coated with nickel–phosphorus alloy from a bath containing sodium hypophosphite and glycin–citrate complexing agents. The effect of coating time on phosphorus content, thickness, structure and hardness of the deposits were analyzed. Corrosion parameters such as current density, corrosion potential and corrosion rate were obtained from tafel polarization curves and immersion corrosion tests in aerated 3.5% NaCl solution. The X-ray diffraction (XRD) patterns, anodic polarization curves and scanning electron microscopy (SEM) of heat-treated specimens obtained in various coating times were also studied. The X-ray diffraction patterns showed that by changing the coating times, amorphous or crystalline structure could be obtained. The coatings containing 11.1–13.1% phosphorous were amorphous, and showed better corrosion resistance than microcrystalline structure. The heat-treated specimens obtained in different coating time had more hardness and corrosion resistance than unheated samples. According to the polarization studies and scanning electron microscopy images, the heat-treated samples with 10.8 and 10.1% phosphorous show the intergranular corrosion, while the coatings with 11.7 and 12.2% of phosphorus have the least corrosion rate. Immersion corrosion test data at the 4-month interval had good agreement with electrochemical polarization results.

Iron Corrosion Scales: Model for Scale Growth, Iron Release, and Colored Water Formation

Abstract: This paper was presented in part by V. L. Snoeyink as the Simon W. Freese Lecture at the 2002 Canadian Society of Civil Engineers/Environmental and Water Resources Institute of ASCE Environmental Engineering Conference in Niagara Falls, Ontario, Canada, July 22, 2002. The interactions of corroded iron pipe surfaces with water are of importance because they can lead to serious water quality degradation and material deterioration. A conceptual model has been developed in this paper to describe the formation and growth of iron scales, and their reactions that lead to colored water problems. Most corrosion scales have characteristic structural features, such as a loosely held top surface layer, a shell-like layer ~s!, and a porous core. According to this model corrosion scales are expected to grow from inside the scale via the corrosion reaction, i.e., the conversion of iron metal to ferrous ion. The average oxidation state of iron increases with distance from the pipe wall. The scale structure and scale reactions permit the ferrous iron to be released to the bulk water, where it undergoes conversion to particulate ferric iron, which is the cause of colored water. Scale structure and composition play important roles in the reactions of iron scales that lead to iron release, and water quality control to decrease the porosity of the scale is an important means of reducing iron release. It is anticipated that the conceptual model presented here will be used as a basis for changing water quality to minimize colored water formation, and as a guide for further research.