Three complementary experimental techniques for in situ surface analysis have been combined for the first time in order to explore the chemistry and physics of a copper surface exposed to humidified air. Infrared reflection absorption spectroscopy, quartz crystal microbalance and atomic force microscopy provide a congruent picture of the processes occurring at the surface. At a given relative humidity, cuprous oxide forms according to an approximately logarithmic rate law. In addition, an aqueous adlayer of constant mass physisorbs on the surface. Increased relative humidity stimulates the physisorption of water and enhances the nucleation rate of oxide grains, thereby increasing the formation rate of cuprous oxide.
Good high-temperature corrosion resistance of Fe-Al alloys in oxidizing environments is due to the alpha-Al2O3 film which is formed on the surface provided temperature is above 900 degrees C and the Al-content of the alloy exceeds the critical value. Ab initio calculations combined with experiments on Fe-13Al, Fe-18Al, Fe-23Al and Fe-10Cr-10Al alloys show that the beneficial effect of Cr on the oxidation resistance is significantly related to bulk effects. The comparison of experimental and calculated results indicates a clear correlation between the Fe-Cr chemical potential difference and the formation of the protective oxide scales. (C) 2010 Elsevier Ltd. All rights reserved.
The resistance to environment-assisted cracking (EAC) of AISI 420 martensitic stainless steel (MSS) was investigated in 0.3 M NaCl solution (room temperature) at constant loads for 30 days. The steel tempered at 250 degrees C was superior to the 500 degrees C-temper, which showed corrosion pits favouring cracking. The fracture surface showed faceted grains, cleavage, striations, and inter- and transgranular cracks, suggesting a mixed stress corrosion cracking (SCC) and hydrogen embrittlement (HE) mechanism as the cause for EAC. Finite element modelling (FEM) indicated strain/stress localization at the mouth of deep pits and at the wall of shallow pits, displaying the favoured locations for pit-to-crack transition.
In this work, a novel in-situ grown layered double hydroxide (LDH) film co-intercalated with inhibitors (vanadates) and low surface energy substance (laurates) was immobilized on Al substrates. A long-term monitoring of electrochemical impedance spectra (EIS) of the various samples in 3.5 wt.% NaCl solution demonstrated the synergetic protection of the intercalated two functional species. Meanwhile, the X-ray diffraction (XRD) result of the samples after immersion in NaCl solution for a long time presented the anion-exchange process between vanadates/laurates and chlorides. The synergetic effect of the two species loaded film significantly contributed to the enhanced long-term corrosion protection of aluminum.
The interplay between atmospheric corrosion and antimicrobial efficiency of bare Cu and Cu5Zn5Al1Sn was studied upon exposures simulating high-touch surface conditions. The survival of the bacteria Bacillus subtilis during surface contact with Cu and Cu5Zn5Al1Sn was examined under different degrees of surface oxidation, tarnishing, wettability and copper ion release. Depending on surface conditions complete bacteria inhibition was obtained within 4 min on Cu and within 6-10 min on Cu5Zn5Al1Sn. The antibacterial efficiency increases slightly with copper release rate and is governed by complex interactions between the corroded metal surface, bacteria and extracellular polymeric substances produced by the bacteria.
The role of Sn on the atmospheric corrosion performance of binary Cu-Sn bronze alloys (4–6 wt.% Sn) compared with Cu metal used in outdoor architecture is elucidated in terms of microstructure, native surface oxide composition, patina evolution, corrosion rates, appearance and metal release. Results are presented for non-exposed surfaces and surfaces exposed at different urban and marine sites in Europe up to 5 years and based on multi-analytical findings from microscopic, spectroscopic, electrochemical and chemical investigations. Alloying influenced the corrosion, aesthetic appearance and patina evolution, differently for urban and marine sites, whereas no effects were observed on the release pattern.
The influence of chloride deposition on the formation, evolution and barrier properties of the patina formed on CuSZn5Al1Sn used for architectural cladding is explored via long-term marine field exposures and laboratory investigations. The presence of Cu2O, ZnO, Al2O3 and SnO2 within the inner part of the patina and intercalation of SnO2, Zn-5(CO3)(2)(OH)(6), Zn6Al2(OH)(16)CO3 center dot 4H(2)O, Zn-5(OH)(8)Cl-2 center dot H2O within its outer part, predominantly composed of Cu-2(OH)(3)Cl, significantly reduce the chloride-induced corrosion compared with Cu metal. The intercalation of zinc-rich corrosion products within the patina and not at the top-surface explain their marginal influence on the runoff process that mainly occurs at the outmost surface.
The effect of blue light on atmospheric corrosion of Cu and on the antimicrobial properties was explored upon exposure mimicking the condition of hygienic surface disinfection. The results show that blue light illumination enhanced the formation of Cu2O, resulting in a slightly increased corrosion resistance of Cu without pre-deposited NaCl, whereas the enhanced formation of Cu2O, CuCl and/or Cu(OH)3Cl on copper with pre-deposited NaCl caused concomitant corrosion product flaking and a reduced corrosion resistance. The blue light induced enhancement of Cu corrosion led to increased surface roughness and more pronounced integration of bacteria within the corrosion products.
The complex stratified patina formed on Sn-bronze in chloride-rich atmospheres has been explored through long-term field exposures and short-term laboratory investigations using a multi-analytical approach. The stratified patina is composed of Cu2O- and Cu-2(OH)(3)Cl-rich sublayers intercalated by Sn-oxides, mainly SnO2. The stratification is triggered by events of high chloride deposition, resulting in repeated dissolution and solidification of sublayers, whereby redox reactions between the intermediate products of Sn- and Cu-chlorides play a crucial role. Sn-induced patina stratification is a major reason for enhanced patina flaking on Sn-bronze and its accelerated corrosion rate compared to Cu metal in marine environments.
The golden alloy Cu-5Zn-5Al-1Sn has found many applications because of its appearance and resistance to tarnishing. The microstructure and multi-component surface oxide of Cu-5Zn-5Al-1Sn have been investigated through a multi-analytical approach. Compared to commercial Cu metal, Cu-5Zn-5Al-1Sn has significantly smaller grains and higher fraction of coherent twin boundaries. The 5-10 nm thick oxide formed after diamond polishing has four identified sub-oxides all contributing to the overall corrosion resistance. Cu2O is mainly located in the outer part, followed by ZnO, SnO2 and Al2O3 closer to the alloy substrate. The latter three possess barrier properties, while Cu2O exhibits a more complex structure.
The pitting potential, intrinsic surface acidity, point of zero charge of passive film on Al are studied using first-principles calculations to establish their relationships. Influences of alloying elements Zn, Cr, Nb, Si, Mo and Sc on adsorption of NH3 and NaCl, pHpzc of Al2O3 and pitting susceptibility of Al are investigated. The efficiency for enhancing pitting resistance of Al is evaluated, yielding the ratios Si: Zn: Cr: Mo: Nb: Sc = 1.8: − 0.3: 1: 1.9: 1.4: 0.2. A model for the dependence of pitting potential on the concentration of alloying elements in Al alloy matrix is developed, based on effects of alloying elements on the surface charge of passive film. The effects of Sc on pitting potential and pHpzc of Al oxide are predicted based on the calculated results, which are supported by electrochemical measurement, XPS analysis and contact angle titration.
Initial corrosion and secondary spreading effects during NaCl particle induced corrosion on zinc was explored using in situ and ex situ FTIR microspectroscopy, optical microscopy, and SEM/EDAX. The secondary spreading effect which occurs upon introduction of humid air on NaCl deposited zinc surfaces was strongly dependent on the CO2 and SO2 content of the introduced air. Ambient level of CO2 (350 ppm) resulted in a relatively low spreading effect, whereas the lower level of CO2 (<5 ppm) caused a much faster spreading over a larger area. In the presence of SO2, the secondary spreading effect was absent which could limit the cathodic process in this case. At <5 ppm CO2, the corrosion is more localized, with the formation of simonkolleite (Zn5(OH)8Cl2 · H2O), zincite (ZnO) and sodium carbonate (Na2CO3), and a larger effective cathodic area. At 350 ppm CO2, the corrosion is more general and formation of simonkolleite, hydrozincite (Zn5(OH)6(CO3)2) and sodium carbonate was observed. Sodium carbonate was mainly formed in more alkaline areas, in the inner edge of the electrolyte droplet and in the secondary spreading area. Oxidation of sulphur and concomitant sulphate formation was enhanced in the presence of NaCl particles, due to the formation of a droplet, the separation of the anodic and cathodic areas and the accompanying differences in chemical composition and pH in the surface electrolyte.
A new strategy was proposed to prepare a composite film using mussel adhesive protein Mefp-1 and graphene to achieve corrosion protection and surface lubrication on carbon steel. The dispersibility of graphene in Mefp-1 solution was firstly investigated and deposition methods of Mefp-1/graphene film were proposed. In-situ confocal Raman micro-spectroscopy and electrochemical impedance spectroscopy measurements were utilized to study the corrosion inhibition effect in NaCl solution. Friction tests were conducted to study the tribological properties. Results show that the Mefp-1/graphene film exhibits strong adhesion to carbon steel, provides improved corrosion- and wear-resistance, and a significantly increased lubricity on carbon steel.
This paper focuses on the study of micro-galvanic corrosion of the Cu/Ru couple in KIO4 solution. Practical nobility across the Cu/Ru interface was evaluated by Volta potential mapping, and the morphological changes were monitored by in-situ atomic force microscopy measurements during exposure in a KIO4 solution. Chemical composition of precipitated corrosion product was analyzed by Confocal Raman spectroscopy immediately after the exposure. The results show that Cu is the anode of the Cu/Ru couple, and accelerated dissolution of Cu preferentially occurs near the Cu/Ru interface. However, subsequent formation of insoluble Cu(IO3)2·nH2O leads to precipitation, which impedes further Cu corrosion.
The corrosion resistance of a two-layer polymer (silane + parylene) coating on implant stainless steel was investigated by microscopic observations and electrochemical measurements Long term exposure tests in Hanks solution revealed that the coating of 2 mu m can be successfully used for corrosion protection However the addition of H2O2 simulating the inflammatory response of human body environment causes a dramatic destruction of the protective coating Analysis of the experimental data in terms of circuit models enables proposing a deterioration mechanism OH radicals formed at the metal surface attack the polymer thus the deterioration starts from the metal/polymer interface and progress towards the outward surface.
Samples of At, Cr, Ni, and Zr were sputter-coated with porous Pt-films with a particle size of 20-30 nm. Thermal oxidation of these samples was studied by gas phase analysis (GPA) and secondary ion mass spectrometry (SIMS). SIMS analysis on partly Pt-coated samples of At, Cr, Ni, and Zr at different oxide depths in areas with Pt and in areas away from Pt indicates an enhanced inward oxide growth in the Pt area and mm-ranged distance from Pt-area. Weight gain measurements on Pt-coated Ni samples show a reduced or increased oxidation rate depending on the amount of porous Pt-coating. Pt has two effects on the thermal oxidation of metals and the overall effect of Pt on the oxidation of metals depends on the mechanism of oxide growth in the absence of Pt.
In this study, the time-dependent corrosion protection ability of 10–15 µm thin polydimethylsiloxane -nanoparticle composite coatings was evaluated using mainly open circuit potential and electrochemical impedance spectroscopy measurements. The best result was obtained for the coating containing 20 wt% hydrophobic silica nanoparticles, where it was possible to achieve protection for almost 80 days in 3 wt% NaCl solution. The protective properties offered by this coating are suggested to be due to a synergistic effect of the hydrophobicity of the polydimethylsiloxane matrix and the prolonged diffusion path caused by addition of hydrophobic silica particles.
Selective dissolution of duplex stainless steel 2205 in acidic chloride solutions was studied in situ by electrochemical scanning tunnelling microscopy (STM). In 0.05 M H2SO4 + 1 M NaCl, no appreciable active dissolution was observed by in situ STM imaging at the corrosion potential (E-corr), but at potentials higher than E-corr + 1000 mV some selective dissolution at the austenite-ferrite boundary region occurred. In 4 M H2SO4 + 1 M HCl, STM images revealed active dissolution of ferrite grains at around E-corr + 50 mV. Dissolution of austenite grains started to occur at around E-corr + 150 mV, exhibiting steps of submicron scale on the edges.
To provide clarity on the poorly-understood mechanism of breakaway oxidation, corrosion of Fe9Cr1Mo steel in pressurised CO2 is quantified and modelled. The temperature range 400-640 degrees C, relevant to nuclear power plants, is emphasised. Attack is in the form of combined oxide scale growth and internal carburisation of the metal. Carbon activity in the metal at its surface exhibits a strong time dependence consistent with the kinetically-limited transport of carbon due to the slow Boudouard reaction. Breakaway is associated with the approach to saturation of the steel with respect to carbon. Diffusion modelling agrees well with steel carbide precipitation observations.
Mechanisms of alloy degradation in a fireside N-S-O-C-H-Cl-Na-K atmosphere at 880 °C were elucidated using SEM-EDS, chemical equilibrium calculations, and XRD. Alloys 310S, 800H/HT, and 600 were studied after 0, 8000, and 16,000 h exposure in a boiler co-firing biomass waste. For 310S and 800H/HT it was shown that nitrogen formed internal Cr nitrides lowering the Cr activity and inhibiting internal alloy Cr permeation, and that NaCl and Na 2 SO 4 reacted with Cr oxide to form chromate and to accelerate the S and the Cl pickup. Alloy 600 showed no nitride or major chromate formation.
The influence of environmental conditions and corrosion layer characteristics have been investigated on the runoff rate of copper and zinc, used as roofing material. For this purpose, a rain device has been constructed, capable of simulating rain episodes of varying intensity and pH, and used on new and aged copper and zinc panels of varying origin and corrosion product composition. The setup, using artificial rain with a composition resembling the southern and central part of Sweden, has proven to result in realistic runoff rates for all materials investigated. During a rain event, easily soluble corrosion products will be removed in the first rain volume, commonly referred to as the first flush, followed by a more or less constant runoff rate during subsequent rain. The magnitude of the first flush depends on environmental conditions prior Co a rain episode, e.g., length of dry periods and extent of dry deposition, as well as on rain volume and rain intensity. A defect-rich and porous corrosion layer increases the magnitude of the first flush. The total metal runoff quantity increases with decreasing pH for both copper and zinc. In agreement with previous findings outdoors, an effect of patina age can be seen on copper. The laboratory data can be used to explain variations in runoff rate between different sampling periods observed in field data.
The present investigation highlights corrosion protection of carbon steel by a waterborne acrylate-based matrix coating, with and without reinforcement by cellulose nanocrystals, by using electrochemical impedance spectroscopy in 0.1âM NaCl solution over a period of 35 days. Interactions between cellulose nanocrystals and the matrix coating were demonstrated by Fourier transform infrared spectroscopy. The results show that both coatings have high barrier performance but different protective characteristics during long-term exposure. The differences can be attributed to the reinforcement effect of cellulose nanocrystals caused by hydrogen bonding interactions between cellulose nanocrystals and the matrix coating.
Different surface treatments, with and without silver (Ag), of a Ti6Al4V alloy for increased bone bonding ability were investigated and compared with non-treated surfaces. Studies were conducted at 37 degrees C in phosphate buffered saline (PBS, pH 7.4) of varying hydrogen peroxide (H2O2) and bovine serum albumin (BSA) concentrations. Increased levels of metal release and corrosion were observed in the presence of both H2O2 and BSA due to complexation with Ti and Al in the surface oxide, respectively. Ag release was enhanced by the presence of BSA. Galvanic effects by Ag were minor, but possibly observed in the most corrosive environment.
Release rates of chromium, nickel and iron from grade 304 stainless steel with three different surface finishes, BA, 2B and 2D, have been determined after exposure to artificial lysosomal fluid. Metal release rates are discussed in relation to corrosion resistance, compositional changes of the outermost surface film of the stainless steel and to measurements of the effective surface area and roughness. The total metal release decreased in the following sequence: 2D > 2B approximate to BA, and was primarily related to the electrochemically active surface area. No direct correlation was observed between corrosion resistance and metal release rates.
Release rates of individual alloy constituents have been determined from seven grades of stainless steels exposed to two synthetic body fluids, used as surrogates for different areas of potential exposure in the lung: "Gamble's solution", (pH 7.4) that represents the interstitial fluid of the deep lung, and artificial lysosomal fluid (ALF) that represents the more acidic (pH 4.5-5) milieu of particles following their phagocytosis by macrophages. Total metal release rates from all grades of stainless steel investigated were low (< 5 mu g cm(-2) week(-1)). The more acidic environment of ALF resulted in significantly higher total metal release rates (0.3-4.6 mu g cm(-2) week(-1)) compared to Gamble's solution (< 0.1 mu g cm(-2) week(-1)).
A range of ex situ and in situ analytical techniques were applied to gain insights into the formation and properties of the pre-formed Mefp-1 film on magnesium-1.0 wt.% calcium (Mg-1.0Ca) alloy. The results revealed that the Mefp-1 film pre-formed at pH 4.6 shows a net-like structure, whereas it is more packed at pH 8.5. in situ scanning micro-reference electrode technique results demonstrated the Mefp-1 films formed at both pH can effectively inhibit the localised corrosion of Mg-1.0Ca alloy. Moreover, the film pre-formed at pH 4.6 provides an increasing corrosion inhibition to Mg-1.0Ca alloy during 7 days of exposure.
In exposure of copper to water molecules there will be relatively strong bonds (reversible traps) between copper and hydrogen. One copper-hydrogen bond corresponds to the thermal energy of a temperature of approximately 250 degrees C and this explains an unusual temperature influence on hydrogen uptake in the metal and in corrosion of copper in pure water-vapour without O-2. This unusual temperature influence is exemplified in exposure of copper at 180 degrees C and 500 degrees C where Cu corrodes more at 180 degrees C than at 500 degrees C.
This paper reports on hydrogen pressures measured during ~19,000. h immersion of copper in oxygen-free liquid distilled water. Copper corrosion products have been examined ex-situ by SEM and characterized by XPS and SIMS. XPS strongly indicates a corrosion product containing both oxygen and hydrogen. SIMS shows that oxygen is mainly present in the outer 0.3. μm surface region and that hydrogen penetrates to depths well below the corrosion product. Thermal desorption spectroscopy shows that the reaction product formed near room-temperature is less stable than that formed in air at 350. °C.
This short communication presents Thermal Desorption Spectroscopy (TDS) of hydrogen desorption from various metals and alloys [Au, Pd, Cu, Ni, Zr, Y, stainless steel and ODS (oxide dispersion strengthened) alloy] after long-term exposure (up to 20 years) to ambient humid air at room-temperature. Of the metals studied only gold does not contain a measurable level of hydrogen. For polycrystalline metals there is a strong correlation between the amount of hydrogen in the metal and the tendency for oxidation of the metal.
This paper considers the corrosion of copper in water by (1) short term open system weight measurements and (2) long term closed system immersion in distilled water (13 800 h) without O-2 at 21-55 degrees C In the latter experiments the hydrogen gas pressure is measured above the immersed copper and approaches similar to 10(-3) bar at equilibrium This pressure is mostly due to copper corrosion and greatly exceeds that in ambient air Accordingly this measured hydrogen pressure from copper corrosion increases with temperature and has the same dependency as the concentration of OH- in the ion product [OH-] [H+].
The effects of porous Pt on the oxidation of Cr at 800degreesC have been studied with the (OSIMS)-O-18 technique, gas phase analysis and XPS. In oxide areas with Pt a pronounced inward oxygen transport takes place and a substantial oxide growth near the Cr substrate is observed. In oxide grown on areas without Pt the counts of CrO ions in SIMS and the binding energy of O (1s) in XPS depend on the distance from the area with Pt. The experimental observations are believed to be a consequence of a high dissociation efficiency of O-2 on areas with Pt in combination with a high diffusivity of O in external and internal oxide surfaces on areas both with and without Pt.
Since corrosion commonly occurs heterogeneously over a surface, studies on a microscopic level are desired to obtain a complete picture of the process. Here, we demonstrate the capability of nano-FTIR microscopy to spectroscopically determine the nature of different corrosion products and their spatial distribution with a resolution of 20 nm, two-three orders of magnitude better than conventional IR microscopy. A copper surface was exposed to a humid atmosphere containing formic acid, and in addition to cuprite the corrosion product copper formate was observed to form inhomogeneously in particles of some tens to a few hundreds of nm.
The initial oxidation of iron and the effect of different O-2/H2O mixtures have been investigated through ESEM in situ exposure and analysis at 500 degrees C. In dry and wet air a two-layered magnetite forms beneath a thin, fine-grained hematite layer. while only a two-layered magnetite forms in H2O. The two-layered magnetite is separated by a straight interface (in all environments), which is suggested to be the original metal surface. The presence of low levels of water vapour (similar to 1% H2O) produces a thicker hematite layer (compared to dry air), exhibiting a large number of whiskers. At least four different factors are suggested to influence the local growth rate: the surface of the metal grain, the thickness of the hematite layer, the oxide grain size and the exposure environment. The ESEM in situ exposures have in addition been shown to have high quality and reproducibility.
The magnesium alloy AZ91D was exposed in three different types of atmospheric environment, viz. urban, rural and marine exposure sites. Corrosion rates, corrosion products formed, and the influence of the microstructure on the corrosion behaviour of the alloy were investigated. The corrosion rate of AZ91D exposed in the marine environment was 4.2 mu m/year, and in the rural and urban environments 2.2 and 1.8 mu m/year, respectively. The main corrosion product found was magnesium carbonate hydromagnesite (Mg-5(CO3)(4)(OH)(2)center dot 4H(2)O), which was formed at all three exposure sites. The corrosion attack started in the alpha-phase in larger grains at the boundary between the alpha-phase and the eutectic alpha-/beta-phase. Microgalvanic elements were formed with the eutectic alpha-/beta-Mg phase as cathodic site and the alpha-Mg grains as anodes. The Al-Mn particles played a minor roll in the initiation process, even though these particles are the most noble in the microstructure and thus the driving force for a corrosion attack around these particles could be expected to be high. A close resemblance was observed between the corrosion mechanisms operating under the field-exposure conditions described here and the mechanisms operating under the previously reported laboratory conditions.
Magnesium alloy AZ91D was exposed in humid air at 95% relative humidity (RH) with a deposition of 70 mu g/cm-2 NaCl. The corrosion products formed and the surface electrolyte were analysed after different exposure times using ex situ and in situ FTIR spectroscopy, X-ray diffraction and Ion Chromatography. The results show that magnesium carbonates are the main solid corrosion products formed under these conditions. The corrosion products identified were the magnesium carbonates hydromagnesite (Mg-5 (CO3)(4) (OH)(2)4H(2)O) and nesquehonite (MgCO3 3H(2)O). The corrosion attack starts with the formation of magnesite at locations with higher NaCl contents. At 95% RH, a sequence of reactions was observed with the initial formation of magnesite, which transformed into nesquehonite after 2-3 days. Long exposures result in the formation of pits containing brucite (Mg(OH2)) covered with hydromagnesite crusts. The hydromagnesite crusts restrict the transport of CO2 and O-2 to the magnesium surface and thereby favour the formation of brucite. Analysis of the surface electrolyte showed that the NaCl applied on the surface at the beginning was essentially preserved during the initial corrosion process. Since the applied salt was not bound in sparingly soluble corrosion products a layer of NaCl electrolyte was present on the surface during the whole exposure. Thus, Na+ and Cl- ions can participate in the corrosion process during the whole time and the availability of these species will not restrict the atmospheric corrosion of AZ91D under these conditions. It is suggested that the corrosion behaviour of AZ91D is rather controlled by factors related to the microstructure of the alloy and formation of solid carbonate containing corrosion products blocking active corrosion sites on the surface.
beta-Mg17Al12, eta-Al8Mn5 and an alpha-magnesium phase have been synthesized from pure components by controlled solidification procedures. These phases have been studied using different electrochemical techniques including the scanning Kelvin probe (SKP). From the results; it was possible to determine the nobility and the rate of the cathodic reaction of the different phases. Measurements have also been made on an AZ91D Mg-alloy using scanning Kelvin probe force microscopy (SKPFM) and field emission gun scanning electron microscopy (FEG-SEM). The results show that the Volta potentials measured with the scanning Kelvin probe (SKP) on bulk intermetallics are comparable with those recorded with the SKPFM on the AZ91D alloy. It is shown that SKPFM provides information on the local nobility of the different intermetallic particles and phases on the submicron scale. Both the eta-Al8Mn5 phase and the beta-Mg17Al12 phase in AZ91D showed a more noble potential than the alpha-magnesium phase. It is also shown that the aluminium-rich coring along the grain boundaries results in measurable changes in the Volta potential. Finally, the role of the beta-Mg17Al12 phase and the eta-Al8Mn5 phase in the corrosion behaviour of AZ91D is discussed in term of local nobility, surface coverage of the cathode and the cathodic activity of the different phases.
Corrosion properties of aluminum alloy AA6063-T5 were investigated in molybdate-containing NaCl solutions. Electrochemical, microscopic, and spectroscopic experiments were utilized to examine the mechanism of corrosion inhibition by molybdates. SEM-EDX, magnetic force, and intermodulation electrostatic force microscopy data suggested that the inhibition initiation preferentially occurred over Fe-rich cathodic IMPs. Spectroscopic measurements demonstrated that the formed surface layer consists of mixed Mo(VI, V, IV) species. This layer provided inhibition with an efficiency of similar to 90% after 4 h of exposure. High efficacy of similar to 70% was achieved even after one week of exposure. A two-step oxidation-reduction mechanism of corrosion inhibition by aqueous molybdates was proposed.
Chemical interactions between aqueous vanadium species and aluminium alloy AA6063-T5 were investigated in vanadate-containing NaCl solutions. Confocal Raman and X-ray photoelectron spectroscopy experiments were utilised to gain insight into the mechanism of corrosion inhibition by vanadates. A greenish-grey coloured surface layer, consisting of V+4 and V+5 polymerized species, was seen to form on the alloy surface, especially on top of cathodic micrometre-sized IMPs, whereby suppressing oxygen reduction kinetics. The results suggest a two-step mechanism of corrosion inhibition in which V+5 species are first reduced to V+4 or V+3 species above cathodic IMPs, and then oxidized to mixed-valence V+5/V+4 polymerized compounds.
Corrosion and corrosion inhibition of WE43 magnesium alloy were investigated in NaCl solutions containing different amounts of sodium molybdate. Electrochemical, microscopic, and spectroscopic experiments were utilized to examine the mechanism of corrosion inhibition by molybdates. Electrochemical data showed that Na2MoO4 inhibitor provides reliable inhibition at concentrations at and above 100 mM. Raman and XPS spectroscopy demonstrated that the formed surface layer consists of mixed Mo(V, IV) species. This layer provided inhibition with an efficiency of 91-99 % after 24 h of exposure. A two-step oxidation-reduction mechanism of corrosion inhibition of the WE43 alloy by aqueous molybdates was proposed.
When acid-containing gases condense on a steel surface a phenomenon called dewpoint corrosion can occur. In this case severe attack can appear and the attack cannot be predicted from traditional immersion test data. Dewpoint corrosion can for instance be found in refinery overhead condensers and in waste incineration plants. An experimental set-up consisting of a closed glass loop has been constructed in which stainless steel samples are exposed to condensing conditions simulating a formed condensate of about 1% HCl. In the loop three stainless steels have been tested. For all three materials higher corrosion rates were found in the loop than obtained in immersion tests but in the same range as can be predicted from service experience.
A general reaction scheme has been deduced which describes the evolution of the copper patina, including altogether eight compounds, formed upon exposure to outdoor atmospheric environments. The scheme is based on data obtained from altogether 39 exposure sites, using a recently developed method for quantitative X-ray powder diffraction analysis of up to 8 year old patina still adhering to the copper substrate. In all cases, cuprite forms initially and continuously throughout the atmospheric exposure. Three main sequences have been identified on sheltered copper, representing different reaction routes in sulfur- or chlorine-dominated environments. In less sulfur-polluted environments, posnjakite forms on the cuprite as a precursor to brochantite. In more sulfur-polluted environments, strandbergite is a precursor to antlerite. Both reaction routes may operate simultaneously and the main route may change from the more sulfur-polluted to the less polluted route, as a result of decreased pollutant levels. In chlorine-dominated environments the initial cuprite formation is followed by nantokite and atacamite. By far the most dominating sequence on unsheltered copper includes cuprite, followed by posnjakite and brochantite formation.
The corrosion protection of copper by four bioorganic compounds; adenine, purine, cysteine and histidine, in hydrocarbon media has been examined by in situ ellipsometry, atom absorption spectroscopy and a standard corrosion test. Adenine and purine were found to irreversibly bind to the copper surface. The amount of dissolved copper was severely lowered and the copper surface appeared unaffected. It was concluded that adenine and purine exhibited a surface passivating effect, whereas the effect of cysteine and histidine was significantly lower. The influence on oxidation stability of the medium by addition of the compounds was examined and found to be minor.
The copper patina colour has been systematically explored through a large set of short- and long-term exposed copper metal samples. The initial brown-black appearance is attributed to semiconducting properties of cuprite (Cu2O) and fully attained at thickness 0.8 +/- 0.2 mu m. The characteristic green-blue appearance is due to the colour forming Cu(II)-ion in the outer patina layer which needs to be 12 +/- 2 mu m to fully cover the inner cuprite layer. No significant influence of atmospheric environment on patina colour is discerned. The green-blue patina colour on historic copper was attained after shorter exposures than in modem copper due to more inhomogeneous microstructure.
The influence of ambient concentrations of carbon dioxide on the atmospheric corrosion of magnesium has been studied by atomic force microscopy (AFM) and scanning electron microscopy (SEM), revealing the development and growth of corrosion products. The surfaces investigated by AFM were prepared by ultramicrotomy, using a diamond knife, to generate a smooth finish without using water or lubricant. Sputter-deposited Mg films were also studied with mechanically polished samples used to monitor the overall corrosion process. The exposures were performed at 22.0 degreesC in a synthetic environment with precise control of relative humidity (95%) and CO2 (0 or 350 ppm). Corrosion is localized in the absence of CO2 and is related to noble inclusions in the metal matrix. After corrosion product removal, relatively deep pits are evident. In contrast, pitting is inhibited in the presence of CO, with relatively uniform corrosion product development; further, the noble inclusions have no effect on the distribution of corrosion. The inhibitive effect of CO2 is also observed in the long-term exposures, showing that CO2 reduces the average corrosion rate. Mechanisms are introduced to explain the effects of CO2 and the roles of the noble inclusions on the corrosion behaviour.
A native passive film on 25Cr-7Ni super duplex stainless steel was analyzed using synchrotron hard X-ray photoemission electron microscopy, focusing on variations between individual grains of ferrite and austenite phases. The film consists of an oxide inner layer and an oxyhydroxide outer layer, in total 2.3 nm thick. The Cr content is higher in the outer than the inner layer, ca. 80 % on average. The Cr content is higher on ferrite than austenite, whereas the thickness is rather uniform. The grain orientation has a small but detectable influence, ferrite (111) grains have a lower Cr content than other ferrite grains.
Data on metal release from stainless steel particles can be used in the assessment and quantification of the potential impact of stainless steel on health and the environment. To elaborate a test method suitable for the study of metal release from particles, the experimental parameters particle loading, agitation and separation of particles from the solution were investigated through exposure of 316L powder particles in two artificial biological media. The results suggest that a small particle loading, bi-linear shaking and centrifugation for separation of particles from the solution give the most reproducible results. They also show that metal release rates are strongly influenced by the physico-chemical properties of the test medium and the effective surface area of particles during exposure
This paper summarizes the results from an extensive field exposure program implemented to study possible seasonal dependencies of copper corrosion rates and runoff rates. Two-year exposures in one urban and one rural environment were performed at four different starting seasons. An extensive multi-analytical approach was undertaken of all exposed samples. Seasonal differences in corrosion product formation was observed during the first month of exposure and attributed mainly to differences in relative humidity conditions. Seasonal differences in corrosion rate at the rural site could be discerned throughout the whole two-year exposure, again, mainly attributed to differences in relative humidity, No seasonal effect could be observed at the urban site indicating that other parameters influenced the corrosion kinetics at this site. While corrosion rates exhibit a continuous decrease with exposure time. the yearly runoff rates are independent of time. Depending on starting months the yearly copper runoff rates ranged from 1.1 to 1.7 g m(-2) y(-1) for the urban site, and from 0.6 to 1.0 g m(-2) y(-1) for the rural site. These seasonal variations were primarily attributed to differences in precipitation quantity and environmental characteristics. Runoff rates are significantly lower than corrosion rates as long as the adhering copper patina is growing with exposure time. A full risk assessment requires not only information on the total amount of copper in the runoff, but also on its chemical speciation, Under present conditions, 70-90%,, of all copper in runoff water collected immediately after leaving the surface is present as the most bioavailable form, the hydrated cupric ion, Cu(H2O)(6)(2+).
Release rates of chromium and nickel from pickled and skin passed 304 and 316 stainless steel have been determined during a one-year field exposure in an urban environment (Stockholm, Sweden) and through complementary exposures in artificial rain. Measured annual release rates from 304 stainless steel are 0.25-0.3 mg Cr/m(2) and 0.3-0.4 mgNi/m(2), and slightly higher from 316 stainless steel, 0.35-0.4 mgCr/m(2) and 0.7-0.8 mgNi/m(2). The release rates decrease as the rain pH increases and exhibit no direct influence by rain intensity. Variations in release rates are thought to be a result of a non-uniformly attack.
The effect of exposure direction and inclination on the runoff rates of both zinc and copper has been studied by field exposures on model roofs. Runoff rates decrease with higher inclinations from horizon and are higher for exposures directed towards the prevailing wind direction. At a given pollution concentration, the metal runoff is largely governed by the precipitation volume impinging on the surface. In this study the field exposure results were compared to laboratory tests on zinc and copper panels with different inclinations. Current literature mainly describes runoff rates for zinc and copper panels inclined 45 degrees facing south. Calculations of the average runoff rate using the runoff rates obtained on the model roofs as well as market information show that the effect of inclination, orientation and degree of sheltering are important parameters to consider while estimating runoff rates from existing buildings.