Electrochemical investigations of pitting corrosion

By using chronopotentiostatic and stepwise potential change experiments with potentiokinetic and galvanostatic testing, the following types of pitting corrosion of stainless steels in chloride-containing solutions have been investigated: sulphate inhibition of pitting; 35%Cr-Fe alloy; Cr-Ni-Mo stainless steels. The circuit resistance was found to be of fundamental importance. The pit passivation potential depends on the intensity of a corrosion attack before potential change only in the case of inhibited solutions. In uninhibited solutions passivation and formation potentials are nearly equal only in the case of potentiostatic circuit conditions. The Cr-Fe alloy and the Cr-Ni-Mo stainless steels show a potential range of repassivating pitting. Of practical interest is the critical potential of stable pitting which decreases with increasing circuit resistance. The beneficial effect of Mo is only valid for the pitting potential obtained potentiostatically and not at higher circuit resistances. Considering the practical meaning of the addition of Mo it may be concluded that this element is probably essentially connected with repassivation of pits and conditioning effects of the passive layer.     

Microbiological corrosion of tanks in long-term storage of gas oil

Abstract

Investigations have been carried out to establish the causes of leakages occurring in long-term gas oil storage tanks. Samples of oil, water, etc. taken from the bottom of the emptied tanks and from blisters and pits found in the tank-bottoms have been examined and shown to contain sulphate-reducing bacteria. All of the evidence obtained points towards corrosion being due to the action of these bacteria rather than to any other corrosive effect.

Recommendations for the cleaning and repair of tanks are given.     

Accelerated corrosion test and corrosion failure distribution model of aircraft structural aluminum alloy

Based on corrosion damage data of 1 0 years for a type of aircraft aluminum alloy, the statistical analysis was conducted by Gumbel, Normal and two parameters Weibull distribution function. The results show that aluminum alloy structural member has the corrosion history of pitting corrosion--intergranular corrosion-exfoliation corrosion, and the maximum corrosion depth is in conformity to normal distribution. The accelerated corrosion test was carried out with the complied equivalent airport accelerated environment spectrum. The corrosion damage failure modes of aluminum alloy structural member indicate that the period of validity of the former protective coating is about 2.5 to 3 years, and that of the novel protective coating is about 4.0 to 4.5 years. The corrosion kinetics law of aluminum spar flange was established by fitting corrosion damage test data. The law indicates two apparent corrosion stages of high strength aluminum alloy section material： pitting corrosion and intergranular corrosion/exfoliation corrosion. The test results agree with the statistical fit result of corrosion data collected from corrosion member in service. The fractional error is 5.8% at the same calendar year. The accelerated corrosion test validates the corrosion kinetics law of aircraft aluminum alloy in service.     

The role of different surface damages in corrosion process in alkaline sour media

By applying different electrochemical methodologies to 1018 carbon steel/different electrolytic media interfaces, surfaces with generalised and blistered damages, commonly present in the oil refinery catalytic plants, were obtained. Afterwards, a freshly polished carbon steel surface as well as the damaged surfaces were characterised by electrochemical impedance spectroscopy and scanning electronic microscopy (SEM). The SEM results reveal that the damaged surfaces present films with different physical properties.In spite of the surface modification, the corrosion mechanism of these interfaces in a medium simulating catalytic plants condensates of the refineries in Mexico (0.1 M (NH₄)₂S, 0.4 mM NaCN (10 ppm CN⁻), pH=8.8) turned out to be the same. It was also found that the corrosion process presents the following steps: charge transfer resistance of steel oxidation in the metal/corrosion product film interface and the diffusion processes of Fe²⁺ and H^o ions through the corrosion product film. It was demonstrated that when there was no damage on the surface (freshly polished surface), a homogeneous film was formed instantaneously upon introducing carbon steel into the sour media. The corrosion process in this film occurs in three stages. On the surface with generalised corrosion the three stages are favoured, particularly that of atomic hydrogen process (inducing blistering). Meanwhile, the blistered surface presents a higher charge resistance of steel oxidation and the Fe²⁺ and atomic hydrogen diffusions through the corrosion products are slower than those presented on the other surface states.     

Bacterial corrosion of metals. II. Gravimetric investigations of the corrosion of nonferrous metals

The specific kinetic features of the bacterial corrosion of AK-4, AK-6, Д-16л, Д-16п, AMц-8 aluminum alloys; MA-8 magnesium alloy; and БpAЩMц 10-3-1.5 bronze were investigated with the use of tropical strains of bacteria. The protective effectiveness of anodic-oxide coatings applied to aluminum alloys, and that of TsIATIM-221 and AMG-10 compositions were also tested under these conditions.     

Technical note: Staining procedures for characterising biofilms in corrosion investigations

Abstract

Staining techniques with specificity for polysaccharides, anionically substituted polysaccharides, proteins, and polyphenols have been successfully adapted for use on gelatinous films found in certain pitted copper water pipes. The techniques are described and the results of their application both to films in pipes from service and to a range of controls are reported.     

Inhibition of aluminum corrosion in acid solution by environmentally friendly antibacterial corrosion inhibitors: Experimental and theoretical investigations

Protection of Metals and Physical Chemistry of Surfaces - The inhibition performance of penicillin G(I), methicillin(II) and nafcillin(III) on the corrosion of aluminum in a 1 M HCl solution has...     

Microbiological corrosion and measures to protect against such corrosion part VI. Corrosion of copper in the marine atmosphere: A technique

A technique is developed to enable one to study in a sufficiently objective way the processes of the microbiological corrosion of copper and its alloys in the marine atmosphere. This technique is recommended for diagnosing and forecasting corrosion processes in real conditions for the storage and transportation of products. Original Russian Text ? A.A. Gerasimenko, G.V. Matyusha, L.M. Petrova, 2007, published in Korroziya: Materialy, Zashchita, 2007, No. 3, pp. 33–37. Part V. see Corrosion: Materials and Protection, 2005, no. 8, pp. 45–47.     

Accelerated corrosion exposure in ultra thin sheets of 2024 aircraft aluminium alloy for GLARE applications

The effect of corrosion exposure on ultra thin (t < 0.4 mm) 2024-T3 aluminium sheet thickness is investigated. Microstructural analysis showed that for low accelerated corrosion exposure times, no surface deterioration existed and hence corresponding mechanical properties degradation was assumed to be incited by hydrogen diffusion and subsequent embrittlement. Medium exposure times resulted in cross-section reduction due to formation of sub-surface corrosion products, while crevice corrosion was evident for higher exposure times. Tensile specimens were pre-corroded for single or double sides and then mechanically tested. Decrease in mechanical properties was noticed for both L and T sheet rolling directions, even after a few minutes exposure, with transverse rolling direction having higher degradation values for same exposure times. It was noticed that a single sided corroded specimen needs approximately double exposure time to reach the same ductility decrease of a double sided specimen. Quantitative tensile properties degradation results are discussed; the results were correlated to observed corrosion degradation mechanisms. The stepwise ductile-to-brittle transition of tensile fracture mechanism with increasing corrosion exposure time was denoted via analysis of the ‘un-corroded’ region of tensile fracture surface. Single sided specimens exhibited quasi-cleavage fracture surfaces at the region below protected surface to corrosion.     

Modelling aerosol deposition rates on aircraft and implications for pollutant accumulation and corrosion

Abstract

Although corrosion of airframes is a major issue for both commercial and military air fleets, little work has been carried out on how the pollutants that promote corrosion on airframes are deposited (particularly in flight). In this study, a model has been developed that defines the efficiency of aerosol deposition on the leading edges of aircraft as a function of both aerosol size and airspeed. Deposition only occurs with aerosols in the medium size range, with small aerosols remaining in the airstream and large aerosols depositing on but then splashing off an airframe. However, the size range of particles that are deposited decreases with increasing airspeed. Modelling indicates that aerosols in the size range that can readily deposit in flight will remain stable on an airframe and will not be readily blown off. This knowledge of aerosol deposition efficiency enables calculations of total in-flight depositions while factoring in different locations, types of flights and environmental severity. It is estimated that deposition in flight through clouds may be quite significant, as cloud condensation nuclei are in a suitable range for deposition. The relative extents of aerosol deposition during flight and on ground are compared, and it is found that for certain combinations of airfield location and flight scenario, deposition during flight may be comparable to or exceed deposition on the ground.     

Improvement of the experimental setup for investigations on microbially influenced corrosion of stainless steels

A new type of MIC testing facility has been developed based on the data gained through MIC-experiments, and the analysis of the potential shift caused by MIC. A parallel trial experiment was also conducted lasting more than two months. The results demonstrated that the facility enables one to undergo a detailed investigation of responses to MIC behavior. This allows for the collection of a substantial amount of data required for the investigation of MIC. The experiment also demonstrated that the improved facility offers more flexibility to MIC experiments. The facility can maintain predefined conditions allowing experiments to be conducted without outside environmental influence.     

Diphenolic Schiff bases as corrosion inhibitors for aluminium in 0.1 M HCl: Potentiodynamic polarisation and EQCM investigations

The effects of novel synthesised two Schiff bases on the corrosion of aluminium in 0.1 M HCl were investigated using potentiodynamic polarisation and electrochemical quartz crystal microbalance measurements. Results show that inhibition efficiencies increase with increase in inhibitor concentration. This reveals that the inhibition occurs through adsorption of the inhibitor molecules on the metal surface. Adsorption of these inhibitors follows Temkin adsorption isotherm. The correlation between the inhibitor performances and their molecular structures has been investigated using quantum chemical parameters obtained by MNDO (modified neglect of diatomic overlap) semi-empirical method. Calculated quantum chemical parameters indicate that Schiff bases adsorbed on aluminium surface by chemical mechanism.     

钢芯铝绞导线大气腐蚀产物层的结构及腐蚀机理

在模拟大气腐蚀环境中,采用干/湿NaHSO3+NaCl水溶液盐雾试验研究钢芯铝绞(ACSR)导线腐蚀产物的相组成及腐蚀层结构,讨论其腐蚀机理。结果表明:ACSR导线中单股铝线或镀锌钢芯线的腐蚀主要表现为点蚀,腐蚀产物组成复杂,主要为锌和铝的氢氧化物、硫酸盐与氯化物的复式盐;在腐蚀初期,内外层铝股线及钢芯线表面镀锌层开始形成点蚀坑,逐步形成连续的腐蚀层;由于镀锌层和内层铝股线之间构成原电池,因为牺牲阳极效应,镀锌层腐蚀速率最大;而内层铝股线受到保护,腐蚀速率最小,外层铝股线腐蚀速率居中。     

Multianalytical in-situ investigations of the early stages of corrosion of copper, zinc and binary copper/zinc alloys

A new experimental infrared reflection absorption spectroscopy (IRRAS) set-up for in-situ investigation of corrosion phenomena occurring in the metal–atmosphere interface was developed. It was applied in combination with in-situ tapping-mode atomic force microscopy (TM-AFM) and phase detection imaging (PDI) to study the early stages of corrosion of pure copper and pure zinc as well as to determine the influence of increasing zinc contents in brass. Additionally, ex-situ secondary ion mass spectrometry (SIMS) investigations were carried out on the samples after exposure.The investigations were accomplished in synthetic air with 80% relative humidity (RH) and synthetic air with 80% RH and 250 ppb SO₂. The experiments showed that an increase of the zinc content in the brass alloy yields to an increase of the dimension of the corrosion features formed on the metal surface during weathering. Large features on top of smaller features were observed with TM-AFM on the surfaces exposed to SO₂-containing humidified air, which could be identified by IRRAS as metal sulphur compounds. Furthermore, an increased amount of physisorbed water on the metal surfaces was determined with IRRAS in dependence of the increasing zinc content in the brass samples.     

Electrochemical investigations of organic,corrosion protective barrier coatings – limiting factors of small signal perturbation techniques

After a short introduction into the application of organic barrier coatings for corrosion protection the expectable parameters of the tested materials are discussed and the principle limitations are shown. Electrochemical impedance spectroscopy (EIS) is an already well known and also widely used technique, here only a very fundamental approach will be given. Relaxation voltammetry (RV) is a new electrochemical technology in the time domain. RV allows a two‐step data interpretation: first a very direct and easy accessible extraction of the coating resistance and coating capacity from the raw data. Second, a much more detailed interpretation of electrochemical processes in the coating in terms of dielectric relaxation, diffusion and charge transfer is presented and discussed in this paper.     

Triazolothiadiazine derivatives as corrosion inhibitors for copper,mild steel and aluminum surfaces: Electrochemical and quantum investigations

Protection of Metals and Physical Chemistry of Surfaces - The corrosion inhibition activity of triazolothiadiazine derivatives namely...     

The role of alloying elements in commercial alloys for corrosion resistance in oxidizing‐chloridizing atmospheres. Part II: Experimental investigations

In an extensive study the role of the alloying elements in commercial alloys for corrosion resistance was studied in air without and with 0.1 and 2 vol.% Cl₂, respectively. In the first part of this paper [1] the thermodynamic fundamentals were discussed on the basis of the new concept of the quasi‐stability diagrams. The second part which is presented here reports the results from investigations at 650, 800 and 1000°C and testing times up to 1000 hrs where 14 commercial alloys were tested with regard to their corrosion behavior. The materials were selected so that the role of the alloying elements Mo, C, Si, Al, N, Fe, Ni and Cr would be evident from the results. The exposure tests were followed by extensive microstructural analyses of the corrosion scales and the metal subsurface zones so that type, mechanism and extent of corrosion could be characterized in great detail. At the end a ranking was possible of the different materials and with regard to the detrimental or beneficial role of the different alloying elements. The present results thus provide a much deeper insight into materials resistance in oxidizing‐chloridizing environments at high temperatures.     

Electrochemical investigations regarding the bioavailability of silver after potentiodynamic corrosion load of precious metal alloys Part 2: Dental alloys

The spectrum of commercial dental alloys has been essentially expanded during the last years. The toxicological effects of dental alloys depend mainly on their element specific corrosion behaviour in the oral cavity. The present study demonstrates the electrochemical boundary conditions regarding the possible formation of AgCl-corrosion products, for which cytotoxic effects has been established, by means of specially adapted electrochemical in-vitro test programs. The prevalence of the developed corrosion mode was proved for two electrolytes and four daily used dental alloys containing different amounts of silver. The results show, that a biological relevant assessment of the released silver ions in both electrolytes, induced by anodic metal dissolution, is only reliable if the measurement takes into account the silver ions within the electrolyte as well as the superficial immobilized amount of silver chloride corrosion products. Thus especially from a biological point of view, interface processes like the formation of immobilized corrosion products seem to be a relevant parameter for the complete testing of biocompatibility of metallic biomaterials. To sum up it can be concluded, that the dental alloys investigated in the course of this study have not shown any adverse susceptibility to corrosion with respect to the clinical practice and can therefore be classified as well biocompatible.     

Adsorption properties and inhibition of mild steel corrosion in hydrochloric solution by some newly synthesized diamine derivatives: Experimental and theoretical investigations

New diamine derivatives, namely 2-[{2-[bis-(2-hydroxyethyl)amino]ethyl}(2-hydroxyethyl)amino]ethanol (DAME) and 2-[{2-[bis-(2-hydroxyethyl)amino]ethyl}(2-hydroxyethyl)amino]propanol (DAMP) were synthesised and their inhibitive action against the corrosion of mild steel in 1 M HCl solution were investigated at 308 K. The detailed study of DAME is given using gravimetric measurements and polarization curves method. Results show that DAME is a good inhibitor and inhibition efficiency reaches 91.7% at 10⁻³ M. Tafel polarization study revealed that DAME acts as a mixed-type inhibitor. The inhibitor adsorption process in mild steel/DAME/hydrochloric acid system was studied at different temperatures (308-353 K) by means of weight loss measurements. The adsorption of DAME on steel surface obeyed Langmuir’s adsorption isotherm. The kinetic and thermodynamic parameters for mild steel corrosion and inhibitor adsorption, respectively, were determined and discussed. The comparative study of inhibitive performance of the two diamine derivatives revealed that DAME is more effective than DAMP. Quantitative Structure-Activity Relationship (QSAR) approach has been conducted in attempt to correlate the corrosion inhibition properties of these diamine derivatives with their calculated quantum chemical parameters.