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ISSN: 0010-938X Subject:
engineering Published by Elsevier
No Issue Number
Novel benzimidazole derivatives as corrosion inhibitors of mild steel in the acidic media. Part I: Gravimetric, electrochemical, SEM and XPS studies
Publication date: Available online 9 May 2013 Source: Corrosion Science Author(s): Yongming Tang , Fan Zhang , Shengxiang Hu , Ziyi Cao , Zhenglei Wu , Wenheng Jing Three novel benzimidazole derivatives, 2-aminomethyl benzimidazole (ABI), bis (2-benzimidazolylmethyl) amine (BBIA) and tri (2-benzimidazolylmethyl) amine (TBIA), have been studied as inhibitors for mild steel in 1.0 M HCl. The three compounds prevent mild steel from corrosion by adsorption on the steel surface and forming insoluble complex with ferrous species. Inhibition efficiency increases with the increase in the number of benzimidazole segments in the molecules (TBIA > BBIA > ABI). Protection efficiency of the inhibitors depends on concentration of inhibitor, temperature and concentration of hydrochloric acid.
Oxidation protection of C/C composites with in situ bamboo-shaped SiC nanowire-toughened Si-Cr coating
Publication date: Available online 13 May 2013 Source: Corrosion Science Author(s): Hejun Li , Xi Yang , Yanhui Chu , Lu Li , Qiangang Fu , Lehua Qi An in situ bamboo-shaped SiC nanowire-toughened Si-Cr coating was prepared on the carbon/carbon composites by pack cementation and heat treatment with ferrocene as the catalyst. The microstructures and oxidation behavior of the coating were investigated. Results showed that the coating had a dense microstructure, without the penetrating microcracks, which was primarily attributed to the unusual toughening effect of the bamboo-shaped nanowires resulting from the mechanical interlocking between the nodes and the matrix. The coating exhibited good oxidation protection ability at high temperature. The weight gain of the samples was 0.79% after isothermal oxidation at 1500 °C for 185 h.
Oxidation and carburisation of Fe-6Al / Fe-6Al-3Si in dry and wet CO2 gases
Publication date: Available online 9 May 2013 Source: Corrosion Science Author(s): Jianqiang Zhang , Huan Li , Chunhua Kong , David J. Young Two model alloys, Fe-6Al and Fe-6Al-3Si (wt%), were reacted at 550°C in Ar-20%CO 2 gas for 864 h and Ar-20%CO 2 -5%H 2 O gas for 882 h, respectively. Non-protective multi-layered oxide scales were formed at the surface, together with an internal oxidation zone. In addition, internal carbides were formed near the surface and along alloy grain boundaries within the matrix, in the form of fine needles or short rods. TEM characterisation showed that for Fe-6Al alloy, the precipitates are aluminium enriched κ-carbide with a perovskite structure in an aluminium deficient ferritic matrix. Adding silicon to the alloy reduced the rate of oxidation but did not change the pattern of oxide formation and the κ-carbide structure. Using selective area diffraction, a new orientation relationship between κ-carbide and ferrite has been identified as [011] κ // [001] α , and (1 1)_k // (1 0) α
Key factors influencing the stability of silane solution during long-term surface treatment on carbon steel
Publication date: Available online 9 May 2013 Source: Corrosion Science Author(s): Xiaochao Xian , Minglu Chen , Lixin Li , Zhen Lin , Jun Xiang , Shuo Zhao The mixtures of bis-[trimethoxysilylpropyl]amine and vinyltriacetoxysilane were used for surface treatment of carbon steel, aiming to investigate the factors influencing the stability of silane solution during long-term experiment from two aspects. One is the concentrations of contamination ions, and the other is mass of silane consumed per cycle which is calculated according to concentration of Si measured by silicon molybdenum blue photometry. The results indicate that the accumulation of contamination ions, especially Fe 3+ , is the main factor leading to the condensation between the Si-OH groups in silane solution, which is responsible for the downward stability of silane solution.
Surface characterization of oxides grown on the Ti–13Nb–13Zr alloy and their corrosion protection
Publication date: July 2013 Source: Corrosion Science, Volume 72 Author(s): Laís T. Duarte , Sonia R. Biaggio , Romeu C. Rocha-Filho , Nerilso Bocchi Oxide films were formed on the biocompatible alloy Ti–13Nb–13Zr in a phosphate buffer at open-circuit potential ( E oc ), potentiodynamically up to 8 V, or by micro-arc oxidation (MAO) at 300 V. Their electrochemical properties were assessed in a phosphate buffer saline solution (PBS). EIS and SEM results showed that the E oc and potentiodynamically formed oxide films were compact and behave as a monolayer, while the MAO oxide was a bilayered film (compact inner and porous outer layers). Open-circuit potential and EIS resistance values indicated that the MAO oxide provides the best corrosion protection for the alloy in PBS.
Effect of titanium ions on the ion release rate and uptake at the interface of silica based xerogels with simulated body fluid
Publication date: July 2013 Source: Corrosion Science, Volume 72 Author(s): F. Taloş , M. Senilă , T. Frentiu , S. Simon The dissolution and surface layer changes of new x TiO 2 (100 − x )[4SiO 2 ·CaO·0.3P 2 O 5 ] sol–gel derived xerogels (0 ⩽ x ⩽ 20 mol%) have been investigated in Kokubo’s simulated body fluid (SBF). The ionic leaching rate was analysed by Inductively Coupled Plasma Atomic Emission Spectrometry (ICP-AES). ICP-AES results showed a relatively fast dissolution of titanium free sample, with a high release of phosphorous and calcium ions in the first hour of incubation while the release of silicon ions continuously increased up to 6 h of immersion. The titanium dioxide addition up to 20 mol% differently influences the release of phosphorus, calcium and silicon ions, i.e. TiO 2 strongly stabilises the phosphorus ions, to a lesser extent the calcium ions, and has almost no effect on the silicon ions release. The structural changes were evaluated using X-ray powder diffraction (XRD) and Fourier Transform Infrared Spectroscopy (FTIR). The XRD results show that all samples remain mainly amorphous after immersion in SBF. The changes occurred in the surrounding of phosphorous and silicon ions are well reflected in FTIR spectra and they were correlated with the samples stability in SBF.
Influence of metallurgical states on the corrosion behaviour of Al-Zn PVD coatings in saline solution
Publication date: Available online 8 May 2013 Source: Corrosion Science Author(s): A. Perez , A. Billard , C. Rébéré , C. Berziou , S. Touzain , J. Creus The objective of this study is to define the corrosion behaviour of different Al-Zn coatings, deposited by magnetron sputtering. The coatings exhibiting the best corrosion resistance are then characterized during long immersion tests in neutral 5 wt.% NaCl solution. The results show that the corrosion behaviour is strongly dependent on the zinc content. The evolution of the degradation mechanism is also related to the microstructure of the alloys. These alloys present very interesting properties for steel protection. Nevertheless, the zinc content has to be well defined in order to avoid a high dissolution of the coating.
Corrosion of Carbon Steel in Concentrated LiNO3 Solution at High Temperature
Publication date: Available online 13 May 2013 Source: Corrosion Science Author(s): Chunhuan Luo , Qingquan Su The corrosion of carbon steel in concentrated LiNO 3 solution at high temperature was investigated by a weight loss method. Results showed that increasing temperature and pH would increase the corrosion rate, and increasing concentration and adding Li 2 CrO 4 would reduce the corrosion rate. The corrosion in LiNO 3 solution was general corrosion and the corrosion products were composed of Fe 3 O 4 and Fe 2 O 3 . A compact passive layer comprising of Cr 2 O 3 , Fe 3 O 4 and Fe 2 O 3 was observed with adding Li 2 CrO 4 , and it could effectively depress the corrosion. The carbon steel corrosion in LiNO 3 solution was much smaller than that in LiBr solution.
Effect of Al content on the structure and oxidation resistance of Y and Al modified silicide coatings prepared on Nb–Ti–Si based alloy
Publication date: June 2013 Source: Corrosion Science, Volume 71
Several Y and Al modified silicide coatings containing different Al contents were prepared on an Nb–Ti–Si based alloy by pack cementation technique. The microstructure and oxidation resistance of these coatings were investigated. The existence of Al in the coatings was in the form of solid solutions in (Nb, X )Si 2 outer layer and forming Al-rich inner layer. A suitable content of Al in the coatings improved their oxidation resistance at 1250 °C for promoting the formation of SiO 2 preferentially, while an excess of Al in the coatings imposed an adverse effect for destroying the integrality of the SiO 2 scale.
Highlights
► Y and Al modified silicide coatings containing different Al contents were prepared. ► The microstructures of the coatings containing different Al contents were studied. ► The Al content in the coatings imposed a significant influence on their oxidation. ► The effect mechanism of Al on the oxidation of the coatings was investigated.
Characterization of AISI 4340 corrosion products using Raman spectroscopy
Publication date: Available online 13 May 2013 Source: Corrosion Science Author(s): E. Hazan , Y. Sadia , Y. Gelbstein Most of the currently available corrosion product characterization techniques require extensive samples preparation methods and cannot be employed under aqueous conditions. Raman spectroscopy possesses the advantage of characterization of the corrosion products under practical operation conditions, including aqueous, without any sample preparation procedures. The present study examines the corrosion characteristics of AISI-4340 steel at aqueous and atmospheric environments using Raman spectroscopy. FeO, Fe 2 O 3 , and Fe 3 O 4 were observed as the main corrosion products. The measured oxides thicknesses ratio were compared to the theoretic value obtained from Tammann equation.
In situ inhibitor synthesis from admixture of benzaldehyde and benzene-1,2-diamine along with FeCl3 catalyst as a new corrosion inhibitor for mild steel in 0.5M sulphuric acid
Publication date: June 2013 Source: Corrosion Science, Volume 71
Corrosion protection of mild steel in 0.5 M H 2 SO 4 solution was studied using combination of benzene-1,2-diamine and benzaldehyde with FeCl 3 to in situ synthesis of new inhibitor at different temperatures employing electrochemical, weight loss, quantum chemical studies and optical microscopy. The electrochemical results represent the combination of these components in the solution shows equal efficiency to the compound which was synthesized in the laboratory which is 2-phenyl-1H-benzo[d]imidazole. To indicate this compound was created on the metal surface, deposited layer was investigated by Fourier transform infrared spectroscopy (FTIR). Optical microscopy examinations demonstrate a decrease in corrosion attacks in presence of inhibitors.
Highlights
► Excellent inhibitive efficiency (97%) was obtained by in situ synthesis. ► Results from electrochemical and weight loss measurements are quite comparable. ► By increasing temperature the inhibition efficiency has not changed noticeably. ► FTIR results proved that 2-phenyl-1H-benzo[d]imidazole synthesized on the surface. ► Quantum chemical reveals benzene ring and N atoms are proper adsorption sites.
Effects of Zn2+ concentration and pH on the zinc phosphate conversion coatings on AZ31 magnesium alloy
Publication date: Available online 13 May 2013 Source: Corrosion Science Author(s): Nguyen Van Phuong , Kyu Hwan Lee , Doyon Chang , Sungmo Moon The effects of various Zn 2+ concentrations and pH levels (nine conditions in total) on the formation of zinc phosphate conversion coatings (ZPCCs) on AZ31 magnesium alloy were investigated, and corrosion resistances of the coated samples were evaluated by immersion test and potentiodynamic polarization experiment. The corrosion resistance of the coated AZ31 samples was found to increase with increasing Zn 2+ concentration and the lowest corrosion rate was obtained for the samples coated at pH of 3.07, independent of Zn 2+ concentration. The best coatings on AZ31 were obtained at [Zn 2+ ] = 0.068 M and pH 3.07.
Painting rusted steel: The role of aluminum phosphosilicate
Publication date: Available online 14 May 2013 Source: Corrosion Science Author(s): S.N. Roselli , B. del Amo , R.O. Carbonari , A.R. Di Sarli , R. Romagnoli Surface preparation is a key factor for the adequate performance of a paint system. The aim of this investigation is to employ a wash-primer to accomplish the chemical conversion of rusted surface when current cleaning operations are difficult to carry out. The active component of the wash-primer was aluminum phosphosilicate whose electrochemical behavior and the composition of the generated protective layer, both, were studied by electrochemical techniques and scanning electron microscopy (SEM), respectively. Primed rusted steel panels were coated with an alkyd system to perform accelerated tests in the salt spray chamber and electrochemical impedance measurements (EIS). These tests were conducted in parallel with a chromate wash primer and the same alkyd system. Results showed that the wash-primer containing aluminum phosphosilicate could be used satisfactorily to paint rusted steel exhibiting a similar performance to the chromate primer.
Experimental investigation on the short-term impact of temperature and moisture on reinforcement corrosion
Publication date: July 2013 Source: Corrosion Science, Volume 72 Author(s): A. Michel , P.V. Nygaard , M.R. Geiker In this study, reinforced concrete specimens with and without mixed-in chlorides were conditioned at different relative humidities and subsequently subjected to varying temperatures. Results of the study confirmed that neither temperature nor moisture content have a major impact on the corrosion state and rate of passively corroding reinforcement. For actively corroding reinforcement, a temperature and moisture dependent corrosion rate was observed. The temperature dependency could be described by the Arrhenius equation with moisture dependent activation energies of approximately 10 kJ/mol at 75% RH and 35–40 kJ/mol above 85% RH.
Corrosion behavior of stainless steel 316 in sub- and supercritical aqueous environments: Effect of LiOH additions
Publication date: July 2013 Source: Corrosion Science, Volume 72 Author(s): Igor M. Svishchev , Ruth A. Carvajal-Ortiz , Kashif I. Choudhry , David A. Guzonas Corrosion control in nuclear power systems is examined via addition of LiOH to the coolant at pressurized water reactor (PWR) and supercritical water-cooled reactor (SCWR) operating conditions in stainless steel tubing. The loss of metal to the coolant is analyzed using the voltammetry method. The SEM/EDX analysis of metallographic cross-sections is performed. The results indicate that an adequate pH control is possible for water temperatures up to 500 °C. Above this temperature pH control becomes progressively more difficult as dielectric constant and density of water decrease. Significant hydrogen production is detected at 650 °C.
Evaluation of corrosion inhibition at sand-deposited carbon steel in CO2-saturated brine
Publication date: July 2013 Source: Corrosion Science, Volume 72 Author(s): Vedapriya Pandarinathan , Kateřina Lepková , Stuart I. Bailey , Rolf Gubner The adsorption of four CO 2 corrosion inhibitors on silica sand and their subsequent inhibition activity at sand-deposited steel has been investigated. The presence of a sand deposit affects the performance of inhibitors at carbon steel due to their competitive adsorption on sand. Sulfur-containing organic compounds show minimal adsorption on sand compared to pyridinium surfactants and provide the highest inhibition efficiency at the sand-deposited steel. The extent of inhibitor adsorption onto sand is discussed in relation to their chemical structures. The significance of determining the adsorption affinity to sand in the selection of inhibitors to mitigate under-deposit corrosion is demonstrated.
Formation of dicalcium phosphate dihydrate on magnesium alloy by micro-arc oxidation coupled with hydrothermal treatment
Publication date: July 2013 Source: Corrosion Science, Volume 72 Author(s): Limin Chang , Lifeng Tian , Wei Liu , Xiaoyue Duan A layer containing dicalcium phosphate dihydrate (DCPD) and β-Ca 3 (PO 4 ) 2 was prepared on magnesium alloy by hydrothermal treatment of micro-arc oxide (MAO) layer. The biocorrosion resistance of the oxide layers before and after hydrothermal treatment was analyzed by anodic polarization and electrochemical impedance spectroscopy (EIS) in Hank’s solution. The prepared MAO layers consisted mainly of MgO and MgAl 2 O 4 , and Ca and P inside the oxide layers existed with amorphous phase. Hydrothermal treatments not only made the amorphous Ca and P change into DCPD and β-Ca 3 (PO 4 ) 2 crystals, but also improved the biocorrosion resistance of magnesium alloys, especially the pitting corrosion resistance.
Microbial corrosion resistance of galvanized coatings with 4,5-dichloro-2-n-octyl-4-isothiazolin-3-one as a biocidal ingredient in electrolytes
Publication date: July 2013 Source: Corrosion Science, Volume 72 Author(s): Xiaofan Zhai , Maria Myamina , Jizhou Duan , Baorong Hou Electrodeposition of galvanized coatings from electrolyte containing 4,5-dichloro-2-n-octyl-4-isothiazolin-3-one (DCOIT) can increase microbial corrosion resistance. Coatings were found to inhibit the growth and metabolism of sulphate-reducing bacteria (SRB). Open circuit potentials and corrosion rates of coupons revealed DCOIT effectively influences the coating property. Energy diffraction spectrum and infrared absorption spectra were used to detect DCOIT on the coating surface. Scanning electron microscopy and X-ray diffraction revealed morphological and structural modifications. Electrochemical impedance spectroscopy and polarization techniques determined the corrosion behaviour of coatings in SRB. Results showed coatings formed from electrolytes with DCOIT have improved microbial corrosion resistance and bactericidal action.
2-Mercaptobenzimidazole as a copper corrosion inhibitor: Part I. Long-term immersion, 3D-profilometry, and electrochemistry
Publication date: July 2013 Source: Corrosion Science, Volume 72 Author(s): Matjaž Finšgar The high corrosion inhibition effectiveness of 2-mercaptobenzimidazole (MBIH) in 3 wt.% aqueous NaCl solution is reported using long term immersion tests, 3D-profilometry, electrochemical impedance spectroscopy, and potentiodynamic curve measurements. The high corrosion inhibition performance was proven after 180 days of immersion. The impedance spectra were characterized by two time constants relating to charge transfer and finite layer thickness or semi-infinite diffusion of copper ions through the surface layer, therefore Cu corrosion in solution containing MBIH follows kinetic-controlled and diffusion-controlled processes. Moreover, it is shown that MBIH is a mixed-type inhibitor.
2-Mercaptobenzimidazole as a copper corrosion inhibitor: Part II. Surface analysis using X-ray photoelectron spectroscopy
Publication date: July 2013 Source: Corrosion Science, Volume 72 Author(s): Matjaž Finšgar In Part I of this study, the high corrosion inhibition effectiveness of 2-mercaptobenzimidazole (MBIH) in 3 wt.% NaCl solution was unambiguously proven. In Part II, using angle-resolved X-ray photoelectron spectroscopy (XPS), the surface chemical structure and composition of adsorbed MBIH on Cu from the same solution was investigated. It was found that MBIH molecules are directed toward the Cu surface through their N and S atoms. The MBIH layer thickness is 1.9 ± 0.5 nm, as determined from a detailed analysis of the background in the XPS spectra. Tentative MBIH orientations on Cu were suggested based on the XPS measurements.
The high-temperature oxidation of bulk nanocrystalline 304 stainless steel in air
Publication date: July 2013 Source: Corrosion Science, Volume 72 Author(s): S.G. Wang , M. Sun , H.B. Han , K. Long , Z.D. Zhang The high-temperature oxidation of bulk nanocrystalline 304 stainless steel (BN-SS304) and its conventional polycrystalline counterpart (CP-SS304) in air at 900 °C for 24 h were studied by thermogravimetric analysis, X-ray photoelectron spectroscopy and scanning electron microscope. We studied the valence electron configurations of BN-SS304, CP-SS304 and their oxide scales by ultra-violet photoelectron spectroscopy. The high-temperature oxidation resistance of BN-SS304 was enhanced in both initial and isothermal oxidation, which was attributed to its larger work function and more chemical stability, its more chemically stable and compact oxide scale, its weaker O 2 adsorption and diffusion, its weaker Cr and Mn atoms diffusions.
Corrosion and electrochemical evaluation of an Al–Si–Cu aluminum alloy in ethanol solutions
Publication date: July 2013 Source: Corrosion Science, Volume 72 Author(s): Guang-Ling Song , Minghong Liu The corrosion of aluminum alloy AlSi8Cu3Fe(Zn) in ethanol and ethanol solutions containing 10 vol.% water and 10 vol.% acetic acid, respectively, was investigated by means of electrochemical impedance spectroscopy (EIS), polarization curve, immersion, optical microscopy, scanning electron microscopy and element mapping. The Al alloy in the ethanol and its solutions exhibited a capacitive loop in the measured Nyquist EIS spectra at high frequencies, which can be attributed to the ethanol’s dielectric response. Addition of 10 vol.% acetic acid increased the ethanol corrosivity more significantly than the same amount of water addition. The Al–Si–Cu–Mg precipitated zones in the alloy were susceptible to corrosion attack due to the micro-galvanic effect by the Cu-containing precipitates.
The influence of chromium content on the electrochemical behavior of weathering steels
Publication date: June 2013 Source: Corrosion Science, Volume 71
To investigate the influence of chromium content on corrosion characteristics of weathering steels, the electrochemical measurements were performed on the steels containing 0–9% Cr (wt.%) in NaHSO 3 aqueous solution. The results indicated that the open circuit potential of these steels shifted to the positive direction remarkably, because the additions of Cr improved the passivation capability of the steels. The corrosion current density of the steels containing more than 7% Cr (wt.%) decreased significantly after pre-rusted treatment, implying the corrosion resistance could be enhanced by the formation of protective goethite rust layer.
Corrosion behaviour of porous Ti–39Nb alloy for biomedical applications
Publication date: June 2013 Source: Corrosion Science, Volume 71
The presented work was aimed to describe the effect of porosity on the corrosion behaviour of Ti–39Nb alloy produced by the powder metallurgy technology, which represents a prospective material for medical applications. Corrosion properties of specimens with a porosity ranging from 0% to 33% were studied in simulated body environments, using electrochemical techniques and exposure tests. The results of measurements proved the occurrence of a localized form of corrosion in the material with a porosity of 24% and 33%. Distinct localization of the corrosion process was recorded in an environment containing fluoride ions.
In situ study of dew point corrosion by electrochemical measurement
Publication date: June 2013 Source: Corrosion Science, Volume 71
Dew point corrosion (DPC) is an electrochemical process in a dynamic electrolyte layer, which makes it difficult to carry out conventional electrochemical measurements and thus is not conducive to corrosion mechanism study. In situ electrochemical measurements including electrochemical impedance spectroscopy (EIS) and electrochemical noise (EN) are realized by a novel DPC simulation set-up and special electrode arrangements in this work. DPC of carbon steel is studied by in situ test method and ex situ test method, respectively. Different corrosion mechanisms are obtained from two methods. Thus, it is significant to study DPC by in situ test method so as to understand DPC essentially.
Atmospheric corrosion of two field-exposed AZ31B magnesium alloys with different grain size
Publication date: June 2013 Source: Corrosion Science, Volume 71
A fine-grained AZ31B alloy and a commonly hot-extruded AZ31B alloy with coarser grains were exposed to marine and urban environments for 1 year, and the atmospheric corrosion behavior of the AZ31B alloys was investigated. The fine-grained AZ31B alloy displays slightly higher corrosion resistance than the commonly hot-extruded AZ31B, particularly in urban environment. Magnesium carbonate hydrate and hydromagnesite are principal corrosion products of the two AZ31B alloys in both marine and urban environments. Besides, it is found that Al–Mn intermetallic particles have little influence on the atmospheric corrosion of the AZ31B alloys.
Highlights
► Two AZ31B alloys were exposed in marine and urban environments for 1 year. ► Grain refinement improves the atmospheric corrosion resistance of AZ31B alloy. ► Corrosion of AZ31B alloys is more severe in marine environment than urban environment. ► Al–Mn intermetallic phase has little influence on the atmospheric corrosion of AZ31B alloy.
Impact of surface condition on sulphide stress corrosion cracking of 316L stainless steel
Publication date: June 2013 Source: Corrosion Science, Volume 71
The effect of surface condition on crack initiation in 316L stainless steel during laboratory testing in sour (H 2 S) environments for oil and gas applications has been investigated using the four-point bend test method. The main focus was on the effect of the degree of surface damage introduced during specimen machining and the influence of heat tinting to simulate the welding process. Detailed mapping of the surface of the four-point bend specimens before and after the tests revealed a greater tendency for pits to form at pre-existing mechanical defects than at inclusions. Perhaps surprisingly, pitting was initiated more readily on the finer ground surface. The effect of heat tinting was (i) to increase the pit density and (ii) to facilitate cracking, shifting the material from the pass to the failure domain. In all cases cracks initiated at pitting sites. A clear time dependence was observed in both the evolution of pitting and the transition from pit to crack during the four-point bend test, implying that the standard 30 day test duration may not always be sufficiently conservative. Characterisation of pitting and cracking in the specimens using electron back-scatter diffraction (EBSD) and focused ion beam (FIB) milling revealed evidence of de-alloying local to the crack. The origin of the cracks could not be identified precisely but initiation in the thinned region of the metal caused by undercutting or intense localised dissolution along slip bands could both be important. Comparison of residual stress measurement using X-ray diffraction (XRD) and hole-drilling techniques demonstrated that near-surface residual stress measurement in austenitic stainless steels using XRD should be treated with caution due to the presence of a heavily deformed nanocrystalline layer on the surface arising from the machining process.
Highlights
► Heat tinting renders 316L stainless steel more susceptible to sulphide stress corrosion cracking. ► Pitting more likely at physical defects generated from specimen preparation than at inclusions. ► Cracks developed after 90 days that were not evident after the standard test duration of 30 days. ► Only shallow pitting observed due to constrained access of H 2 S to the pit recesses. ► Determination of near surface residual stress in austenitic stainless steels by XRD is unreliable.
Electrical mapping of AISI 304 stainless steel subjected to intergranular corrosion performed by means of AFM–LIS in the contact mode
Publication date: June 2013 Source: Corrosion Science, Volume 71
The paper presents results of the AFM-based approach to local impedance spectroscopy (LIS) measurements performed in a 20 × 20 μm grid within an austenite grain–grain boundary region for sensitized AISI 304 stainless steel (SS). Maps of electrical parameters obtained on the basis of localized impedance spectra were demonstrated, presenting their changes and correlation with the sample topography. Performed research revealed significant differences in the electrical distribution of the contact resistance considered as the passive layer resistance and contact capacitance considered as the passive layer capacitance determined for austenite grain interiors and austenite grain boundaries affected by intergranular corrosion.
Highlights
► Electrical differentiation of the austenite grain interior and its grain boundary. ► Austenite grains revealed higher localized impedance than its grain boundaries. ► Demonstration of electrical maps of the passive layer resistance and the passive layer capacitance. ► Relative changes of these parameters were determined within the localized grid.
Electrochemical formation and transformation of corrosion products on carbon steel under cathodic protection in seawater
Publication date: June 2013 Source: Corrosion Science, Volume 71
Carbon steel coupons were permanently exposed to seawater in the low water zone of two French harbors for 5 years before to be subjected to cathodic protection (potential about −0.95 V vs. Ag/AgCl/seawater) for 1 year. The application of cathodic polarization to the previously unprotected coupons induced the transformation of GR( ) into GR( ). Other coupons were permanently protected by cathodic protection during the 6 years immersion. A thin film of green rust and mackinawite was observed on the steel surface. This film was covered by a thicker layer of calcareous deposits.
Highlights
► Cathodic polarization of corroded carbon steel induces changes in the rust layers. ► Cathodic polarization transforms sulfated green rust into carbonated green rust. ► Residual dissolution of steel under cathodic polarization produces a thin rust layer. ► Green rust and FeS are formed on steel under cathodic protection in natural seawater.
Stress corrosion cracking of a recent rare-earth containing magnesium alloy, EV31A, and a common Al-containing alloy, AZ91E
Publication date: June 2013 Source: Corrosion Science, Volume 71
Stress corrosion cracking of the magnesium alloy Elektron 21 (ASTM–EV31A) and AZ91E was studied using constant load test in 0.1 M NaCl solution (saturated with Mg(OH) 2 ), and slow strain rate test using glycerol, distilled water and Mg(OH) 2 saturated, 0.01 M and 0.1 M NaCl solutions. Slow strain rate test indicated that EV31A was less susceptible to stress corrosion cracking than AZ91E. Under less intense loading of constant load, EV31A was found to be resistant to stress corrosion cracking. Fractography of EV31A specimens showed little evidence of hydrogen embrittlement. The superior resistance of EV31A is attributed to a more robust oxide/hydroxide layer.
Graphical abstract
Highlights
► Alloy EV31A and AZ91E were studied using SSRT and constant load techniques. ► Alloy EV31A showed higher resistance to SCC than alloy AZ91E. ► Crack initiation occurred from corrosion pits. ► Alloy AZ91E exhibited σ SCC as 60% of the σ YS in 0.1 M NaCl solution under CLT. ► The SCC resistance of EV31A is attributed to a protective film formed .
Effect of heat flux on ablation behaviour and mechanism of C/C–ZrB2–SiC composite under oxyacetylene torch flame
Publication date: Available online 9 May 2013 Source: Corrosion Science Author(s): He-jun Li , Xi-yuan Yao , Yu-lei Zhang , Ke-zhi Li , Ling-jun Guo , Lei Liu The ablation property of C/C–ZrB 2 –SiC composite under oxyacetylene torch flame with different heat flux was investigated. The ablation performance decreased with the increase of heat flux from 2400 to 4200 kW/m 2 and the ablation mechanism changed from chemical erosion to mechanical denudation. The good ablation resistance under 2400 kW/m 2 is attributed to the formation of SiO 2 – ZrO 2 mixture. When heat flux is 3200 kW/m 2 , the formation of ZrO 2 can partly prevent the diffusion of oxygen and provide ablation protection. But with heat flux increasing, the increase of mechanical denudation results in the reduction of ablation performance.
Enhanced Corrosion Resistance of High Strength Mg-3Al-1Zn Alloy Sheets with Ultrafine Grains in a Phosphate-buffered Saline Solution
Publication date: Available online 9 May 2013 Source: Corrosion Science Author(s): H.S. Kim , G.H. Kim , H. Kim , W.J. Kim The corrosion behaviour of ultrafine grained AZ31 Mg alloy sheets with very high strength, which were prepared by high-ratio differential speed rolling (HRDSR) technique, was studied in a phosphate-buffered saline solution. The corrosion resistance was greatly improved after HRDSR. This result was attributed to the enhanced stability of the Mg(OH) 2 layer due to the grain refinement and precipitation of various types of P-containing compounds on the stabilised Mg(OH) 2 layer. The HRDSR technique has a good potential to be used for the development of magnesium sheets with good combination of mechanical and biocorrosion properties.
Environmental factors affecting the corrosion behaviour of reinforcing steel. V. Role of chloride and sulphate ions in the corrosion of reinforcing steel in saturated Ca(OH)2 solutions
Publication date: Available online 8 May 2013 Source: Corrosion Science Author(s): S.M. Abd El Haleem , S. Abd El Wanees , A. Bahgat The corrosion behaviour of reinforcing steel in saturated naturally aerated Ca(OH) 2 solutions in absence and presence of different concentrations of NaCl, NH 4 Cl, Na 2 SO 4 and (NH 4 ) 2 SO 4 is followed by measuring of the open circuit potential complemented with SEM and EDS investigation. These salts cause breakdown of passivity and initiation of pitting corrosion. The rates of oxide film thickening by OH - ions and oxide film destruction by the aggressive ions follow a direct logarithm law and depend on the concentration and type of aggressive salts anions and cations. The values of the activation energies for oxide film thickening are calculated and discussed.
Practical Aspects on the Use of On-Site Double Loop Electrochemical Potentiodynamic Reactivation Technique (DL-EPR) for Duplex Stainless Steel
Publication date: Available online 7 May 2013 Source: Corrosion Science Author(s): Kioshy S. de Assis , A.C. Rocha , Isabel C.P. Margarit-Mattos , F.A.S. Serra , Oscar R. Mattos This work discusses on-site use of Double Loop Electrochemical Potentiodynamic Reactivation Technique (DL-EPR) for Duplex Stainless Steel. It is suggested that, instead of altering the standard parameters for each different material tested, the procedure adopted is to determine in laboratory all the parameters for a specific material tested beforehand and then use those results as standard criteria to be compared with the results obtained on-site. Analysis is performed at two commercial super-duplex steels, UNS S 32750 and UNS 32760 and in steel 22Cr6Ni2Mo with low nitrogen content. Then, a welded joint of UNS S 32750 steel is analysed.
Influence of alloyed chromium on the atmospheric corrosion resistance of weathering steels
Publication date: Available online 18 May 2013 Source: Corrosion Science Author(s): Yuhai Qian , Chaohui Ma , Dun Niu , Jingjun Xu , Meishuan Li The influence of alloyed chromium on atmospheric corrosion resistance (ACR) of weathering steels in simulated industrial atmosphere was investigated. The ACR of weathering steels was evaluated by determining the relative corrosion rate after periodic immersion wet/dry cyclic corrosion for 72 h. The presence of Cr improves the ACR of weathering steels. The beneficial effect of alloyed chromium is attributed to both its promotion of the formation of a protective rust layer, which acts as a barrier against corrosion process, and its enhancement of passivation capability, which decreases the anodic dissolution of substrate alloys.
Orientation Dependence of the Electrochemical Corrosion Properties of Electrodeposited Cu Foils
Publication date: Available online 9 May 2013 Source: Corrosion Science Author(s): Jenn-Ming Song , Yong-Sheng Zou , Chia-Chen Kuo , Shi-Ching Lin In this study, the electrochemical corrosion properties of electrodeposited Cu foils in a CuCl 2 -containing acidic etching solution were investigated. The main passive product was CuCl and a trace amount of Cu 2 O can also be detected. The (220)-oriented Cu foils exhibited higher corrosion potential and lower corrosion current density than those with (111) or (200) texture, suggesting a superior corrosion resistance against the etching solution. It is proposed that the preferred orientation and thus the differences in atomic stacking density on specific planes dominated the corrosion properties of the electrodeposited Cu foils instead of grain size or surface roughness.
Initial stages of corrosion pits on AISI 1040 steel in sulfide solution analyzed by temporal series micrographs coupled with electrochemical techniques
Publication date: Available online 10 May 2013 Source: Corrosion Science Author(s): Alexsandro Mendes Zimer , Matheus A.S. De Carra , Emerson Costa Rios , Ernesto Chaves Pereira , Lucia Helena Mascaro This work presents a study of the initial instants in the pitting corrosion of AISI 1040 steel, analyzed by temporal series micrographs coupled to an open circuit potential (E oc ) and polarization curves. During the E oc measurement, the pit induction time and the initial pit growth in MnS inclusions was detected in alkaline sulfide solution. The pit area behavior has two distinct rate of area changes in specific regions directly associated to current slope changes. Finally, it was possible to create a three-dimensional model of the pit depth evolution on the metal, using Faraday’s law and the bullet-shaped geometry.
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Evaluation of coatings corrosion resistance with biocomponents as antifouling additives
Publication date: July 2013 Source: Corrosion Science, Volume 72 Author(s): Ulyana Kharchenko , Irina Beleneva The commercial enzymes complex and bacterial metabolites as antifouling additives were incorporated into a vinyl chloride–vinyl acetate copolymer UM50-based and epoxy resin-based paints. Fouling field tests, electrochemical impedance spectroscopy (EIS) and polarisation measurements showed that the addition of biocomponents into coatings did not always improve corrosion resistance. The EIS data demonstrated that the highest corrosion protection was observed when bacterial metabolites were added into UM50-based coatings and enzyme complexes into epoxy-based paint.
In situ infrared reflection spectroscopy studies of the initial atmospheric corrosion of Zn–Al–Mg coated steel
Publication date: July 2013 Source: Corrosion Science, Volume 72 Author(s): Dan Persson , Dominique Thierry , Nathalie LeBozec , Tomas Prosek NaCl induced atmospheric corrosion of ZnAl2Mg2 coated, electrogalvanised (EG) and hot dipped galvanised (HDG) steel was studied using in situ infrared reflection absorption spectroscopy, XRD and SEM. Initial corrosion leads to the formation of Mg/Al and Zn/Al layered double hydroxides (LDHs) on ZnAl2Mg2, due to the anodic dissolution of Zn–MgZn2 phases and cathodic oxygen reduction on Zn–Al–MgZn2, Al-phases and on zinc dendrites. In contrast to EG and HDG, were no ZnO and Zn 5 (OH) 8 Cl 2 ⋅H 2 O detected. This is explained by the buffering effect of Mg and Al which inhibit the ZnO formation, reduce the cathodic reaction and corrosion rate on ZnAl2Mg2.
Characterisation of complex alteration layers in medieval glasses
Publication date: July 2013 Source: Corrosion Science, Volume 72 Author(s): Tiziana Lombardo , Lucile Gentaz , Aurélie Verney-Carron , Anne Chabas , Claudine Loisel , Delphine Neff , Eric Leroy Silica–potash–lime stained-glasses from medieval age in Northern Europe are found in a poor conservation state. Their mechanisms of atmospheric corrosion are still not fully understood and need deeper investigation. A multi-scale analysis of K–Ca rich silicate glasses (ancient and model glass), showed modified layers characterised by a multilayer sequence consisting in the repetition of nm-thick laminae with different compositions. Crystalline phases (sulphates, carbonates and phosphates) are observed. The formation of these sequences is due chiefly to interdiffusion, followed by local dissolution phenomena. Precipitation of secondary phases is enhanced by the presence of fractures, which facilitate fluid circulation.
The inhibition effect of tannic acid on mild steel corrosion in seawater wet/dry cyclic conditions
Publication date: July 2013 Source: Corrosion Science, Volume 72 Author(s): Bei Qian , Baorong Hou , Meng Zheng The inhibition effect of tannic acid on mild steel corrosion in seawater wet/dry cyclic conditions was studied by weight loss and electrochemical methods. Result of the polarisation curves shows that corrosion current density decreases from 47.85 μA cm −2 to 6.67 μA cm −2 after tannic acid is added; charge transfer resistance remains stable in the electrochemical impedance spectra. Scanning electron microscopy, X-ray diffraction, and Fourier transform infrared reflection are performed to study the corrosion inhibition. The inhibition effect of the compound is attributed to ferric tannate film formation on the steel surface, which is relatively stable during wet/dry cycles.
Highlights
► Tannic acid has good inhibition effect for mild steel in wet/dry conditions. ► Significant difference in rust appearance is observed by means of SEM. ► Tannic acid acts as a cathodic-type inhibitor. ► The XRD and FT-IR analyses support the weight loss, EIS, and polarisation data.
Grain morphology and crystal structure of pre-transition oxides formed on Zircaloy-4
Publication date: Available online 15 May 2013 Source: Corrosion Science Author(s): Weijia Gong , Hailong Zhang , Yi Qiao , Hang Tian , Xiaodong Ni , Zhongkui Li , Xitao Wang Grain morphology and crystal structure of pre-transition oxides formed on a Zircaloy-4 alloy were investigated. The results show that monoclinic columnar grains align tightly in inner oxides, whereas porous monoclinic equiaxed grains exist in outer oxides. Small-sized tetragonal equiaxed grains are embedded in monoclinic columnar grains, with tetragonal phase content declining from the inner to the outer oxides. The crystallographic orientation relationship of (111) m // (10 0) α-Zr was identified, which explains well the formation of monoclinic texture on the zirconium substrate. This work advances the understanding of corrosion properties before transition of oxidation of zirconium alloys.
Decoupling the dual source of colour alteration of architectural titanium: Soiling or oxidation?
Publication date: July 2013 Source: Corrosion Science, Volume 72 Author(s): M.V. Diamanti , S. Aliverti , M.P. Pedeferri The advanced structural properties of titanium, together with its fascinating interference colours, have opened the way to architectural applications as façade claddings. Yet, several problems of soiling and gradual corrosion tend to alter its aesthetic properties. Atmospheric exposure tests on titanium and anodised titanium were performed, and surface colour was monitored with spectrophotometry to evaluate both corrosion and soiling extent. In all cases, a slight surface oxidation was observed, which decreased with increasing initial thickness of the anodic film. The use of lightness as main parameter to quantify soiling must be carefully considered, as lightness variations must also take into account the influence of oxide hue variation.
Microstructure and protection characteristics of the naturally formed oxide films on Mg–xZn alloys
Publication date: July 2013 Source: Corrosion Science, Volume 72 Author(s): Yingwei Song , En-Hou Han , Kaihui Dong , Dayong Shan , Chang Dong Yim , Bong Sun You The naturally formed oxide films on Mg–2Zn and Mg–5Zn alloys were investigated by atomic force microscopy (AFM), X-ray photoelectron spectroscopy (XPS) and electrochemical measurements. The oxide films on the both alloys present a similar chemical composition, consisting of surface layer of basic magnesium carbonate and MgO following with MgO and ZnO, but the oxide film on Mg–5Zn is thicker and contains more defects. The protection performance of the oxide film on Mg–5Zn is worse under open circuit potential but better in a suitable anodic potential scope compared with that on Mg–2Zn alloy.
Multilayer and multi-component oxidation protective coating system for carbon/carbon composites from room temperature to 1873K
Publication date: July 2013 Source: Corrosion Science, Volume 72 Author(s): Tao Feng , He-Jun Li , Xi Yang , Xiao-Hong Shi , Shao-long Wang , Zi-Bo He A multilayer B 2 O 3 -modified MoSi 2 –CrSi 2 –Si/B-modified SiC coating system was prepared on the surface of carbon/carbon (C/C) composites by a three-step pack cementation method. The microstructure, oxidation resistance and thermal cycling test of the multilayer coating were studied. The results show that the coating system exhibits good oxidation resistance from room temperature to 1873 K. It can protect the C/C composites from isothermal oxidation in air at 1173 K for 150 h or 1873 K for 900 h, respectively. It can also resist 30 thermal cycles between 1873 K and room temperature.
Microstructure and oxidation resistance of Si–Mo–B coating for C/SiC coated carbon/carbon composites
Publication date: July 2013 Source: Corrosion Science, Volume 72 Author(s): Yu-Lei Zhang , He-Jun Li , Zhi-Xiong Hu , Jin-Cui Ren , Ke-Zhi Li A self-sealing Si–Mo–B oxidation resistance coating was prepared on C/SiC coated carbon/carbon (C/C) composites by slurry and high temperature treatment method. The oxidation resistance of the coating increases at 1173 K and first increases then decreases at 1873 K with the increase of B content from 0 to 20 wt.%. The C/SiC/gradient Si–Mo–B multilayer coating can protect C/C composite from oxidation for 100 h at 1173 K and 125 h at 1873 K. The good oxidation resistance of the coating in broad temperature range could be attributed to its good self-sealing property.
Selective dissolution of amorphous and nanocrystalline Zr2Ni
Publication date: Available online 11 May 2013 Source: Corrosion Science Author(s): L. Mihailov , Murad Redzheb , T. Spassov Rapidly quenched Zr 2 Ni amorphous and nanocrystalline ribbons were subjected to electrochemical selective dissolution. The porous structure of the dealloyed materials showed a dependence on the alloy microstructure. The etching takes place with constant rate in three dimensions, indicating a surface controlled dissolution process. The etching rate of the amorphous alloy was found to be lower than for the nanocrystalline material. Partial crystallization of the de-alloyed amorphous ribbon has been observed. The electrocatalytic activity for Hydrogen evolution reaction of the selectively dissolved amorphous and nanocrystalline ribbons was found to be improved compared to the as-cast alloys.
Quantitative measurement of displacement and strain fields in the ZrO2 layer during the transition to nodular oxidation
April 2013 Publication year: 2013 Source: Corrosion Science, Volume 69
We have performed a microstructural characterization of the oxide layer formed on a Zr-based alloy during high-temperature oxidation, focusing in particular on the nodular oxide. A number of dislocations were observed at the nodular oxide layers, and there were many more dislocations in the nodular oxides than in normal oxides. Normal and nodular oxides were analyzed using high-resolution transmission electron microscopy, and their strain fields were mapped using a geometric phase analysis. Our results confirm that the stress built up in the oxide layer has a huge impact on the occurrence of nodular oxidation and the formation of dislocations.
Highlights
► Microstructure of nodular oxide formed on Zr alloy was characterized using HRTEM. ► Strain field in the ZrO 2 layer was measured quantitatively using GPA method. ► The stress built up in the oxide has a huge impact on onset of nodular oxidation. ► A number of dislocations in nodular oxide were caused by plastic deformation. ► The growth mechanism of nodular Zr oxide is proposed.
Atmospheric corrosion of AM60 Mg alloys in an industrial city environment
April 2013 Publication year: 2013 Source: Corrosion Science, Volume 69
This study investigates the atmospheric corrosion behaviour of ingot and as-extruded AM60 Mg alloys in a polluted city. The corrosion rate of the ingot samples was higher than that of the extruded samples. The size of dust particle conglomerates adsorbed on the sample surfaces was related to the pit sizes. The main corrosion products of both alloys included MgSO 4 ·6H 2 O and MgSO 3 ·6H 2 O. The extruded samples had more homogeneous structures and less second-phase contents compared with the ingot samples. As a result, the corrosion films formed on the extruded samples had better protective effects than those formed on the ingot samples.
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The conglomeration states of the dust particles had a great effect on the initial atmospheric corrosion behaviour of the AM60 Mg alloy. The larger pit like one in site A was caused by the conglomeration of many dust particles with rough surfaces, whereas the smaller pit like one in site B resulted from the unconglomerated particles or single ones with smoother surfaces. Consequently, the pit sizes were relative to the conglomerate states of the particles on the alloy. ► Atmospheric corrosion behaviour of AM60 Mg alloys was studied. ► The sizes of dust particle conglomerates were related to the sizes of pits. ► Corrosion rate of the ingot was higher than that of the extruded samples. ► The main corrosion products of both alloys were MgSO 4 ·6H 2 O and MgSO 3 ·6H 2 O. ► The extruded alloy with uniform microstructures showed a lower corrosion rate.
Hydrogen accommodation in Zr second phase particles: Implications for H pick-up and hydriding of Zircaloy-2 and Zircaloy-4
April 2013 Publication year: 2013 Source: Corrosion Science, Volume 69
Ab-initio computer simulations have been used to predict the energies associated with the accommodation of H atoms at interstitial sites in α, β-Zr and Zr–M intermetallics formed with common alloying additions (M = Cr, Fe, Ni). Intermetallics that relate to the Zr 2 (Ni,Fe) second phase particles (SPPs) found in Zircaloy-2 exhibit favourable solution enthalpies for H. The intermetallic phases that relate to the Zr(Cr,Fe) 2 SPPs, found predominantly in Zircaloy-4, do not offer favourable sites for interstitial H. It is proposed that Zr(Cr,Fe) 2 particles may act as bridges for the migration of H through the oxide layer, whilst the Zr 2 (Ni,Fe)-type particles will trap the migrating H until these are dissolved or fully oxidised.
Inhibition of steel corrosion by unsaturated aldehydes in solutions of mineral acids
April 2013 Publication year: 2013 Source: Corrosion Science, Volume 69
Effect of α,β-unsaturated aldehydes on the corrosion of mild steel in solutions of hydrochloric and sulfuric acids was investigated using gravimetric, voltammetric and chromato-mass spectrometry techniques. General regularities of corrosion and electrochemical behavior of these compounds in solutions of mineral acids are established. The role of the chemical transformation of α,β-unsaturated aldehydes in the inhibition of corrosion is shown.
Highlights
► The protective effect of aldehydes increases with increasing unsaturation. ► Aldehydes with an unsaturated α,β-bond shielded by a bulky group are not inhibitors. ► Aldehydes in solutions of H 2 SO 4 participate in the electrode reactions of steel. ► Cinnamic aldehyde can form protective film on the surface of the corroding steel.
Kinetics and mechanism of reaction between water vapor, carbon monoxide and a chromia-forming nickel base alloy
April 2013 Publication year: 2013 Source: Corrosion Science, Volume 69
The kinetic aspects of the competitive reaction of CO and H 2 O in the formation of chromia layer on a nickel base alloy at high temperature were studied by thermogravimetry combined to gas phase chromatography. It was shown that competitive adsorption occurred between both molecules and that whatever ratio, CO mainly reacted in the first instants of oxidation and H 2 O became the main long-term oxidant species. After an interfacial and diffusion mixed kinetic regime, the long-term oxidation rate was parabolic and did not depend on the water vapor content in the gas phase. The oxidation kinetics was well described by considering that the rate limiting step was the outwards diffusion of interstitial chromium cations in the oxide layer.
Highlights
► Competition of CO and H 2 O reactivity with a chromia forming alloys was studied. ► CO reacts only during a transient time lasting not more than 12 h. ► H 2 O is the most reacting species. ► The growth of chromia is rate limited by diffusion of interstitial chromium cations.
The effect of nickel and silicon addition on some oxidation properties of novel Co-based high temperature alloys
April 2013 Publication year: 2013 Source: Corrosion Science, Volume 69
Isothermal oxidation was carried out on γ′-strengthened Co–Al–W–B–Ni and Co–Al–W–B–Si superalloys at 800, 900, and 1000 °C. Ni-addition to Co–Al–W–B alloys leads to an absence of B within the inner oxide layer and at the grain boundaries, as indicated by ToF-SIMS. As a result, also inner Al 2 O 3 -formation is inhibited, which leads to inferior oxidation properties compared to Ni-free alloys. In contrast, Si-addition enhances formation of protective Al 2 O 3 at 900 and 1000 °C due to enhanced selective Al-oxidation. Si-containing phases at the oxide/alloy interface, at the grain boundaries, and within precipitates are of subordinate importance but may further improve oxidation resistance.
Highlights
► Isothermal oxidation in air on new γ′-strengthened Co-base superalloys. ► Ni-addition leads to an absence of B in the oxide layer and at the grain boundaries. ► Formation of protective inner Al 2 O 3 is inhibited compared to Ni-free alloys. ► Si-addition enhances the formation of protective inner Al 2 O 3 at T > 900 °C.
Super-hydrophobic film prepared on zinc and its effect on corrosion in simulated marine atmosphere
April 2013 Publication year: 2013 Source: Corrosion Science, Volume 69
Zinc–laurylamine complex film with super-hydrophobicity is fabricated on zinc surface with electrolysis method. Super-hydrophobicity of film results from papillae and ridge-like structures, which form due to uneven corrosion of zinc at high anodic potential. The film obtained can maintain super-hydrophobic property in solution system, and can inhibit corrosion effectively. However, saline water penetrates into super-hydrophobic film during deliquescence process of NaCl particle in simulated marine environment. This behavior is induced by capillary condensation in groove of film, and it declines the advantage of using super-hydrophobic film as corrosion barrier in marine atmosphere.
Highlights
► Super-hydrophobic film is fabricated on zinc surface with electrolysis method. ► The formation mechanism of super-hydrophobic film is proposed. ► The deliquescence process of NaCl on super-hydrophobic film is clarified. ► Failure mechanism of super-hydrophobic film in marine atmosphere is discussed.
Graphene: An effective oxidation barrier coating for liquid and two-phase cooling systems
April 2013 Publication year: 2013 Source: Corrosion Science, Volume 69
Graphene is studied as an oxidation barrier coating for liquid and liquid–vapor phase-change cooling systems. Forced convection heat transfer experiments on bare and graphene-coated copper surfaces reveal identical liquid-phase and two-phase thermal performance for the two surfaces. Surface analysis after thermal testing indicates significant oxide formation on the entire surface of the bare copper substrate; however, oxidation is observed only along the grain boundaries of the graphene-coated substrate. Results show that few-layer graphene can act as a protective layer even under vigorous flow boiling conditions, indicating a broad application space of few-layer graphene as an ultra-thin oxidation barrier coating.
Self-repairing oxides to protect zinc: Review, discussion and prospects
April 2013 Publication year: 2013 Source: Corrosion Science, Volume 69
Zinc is protected in the short term by chromate conversion coatings. The Cr (VI) based surface layer has the unique ability to self-repair which is attributable to the aqueous properties of its constituent ions. The thermodynamic feasibility of achieving chromium-like protection for the short term using other candidates is reviewed. Long-term protection of zinc is naturally affected by its own corrosion products (patina), which form a multilayered structure. The role of this patina in protecting the underlying metal is also reviewed, and processes within the patina, including the interaction between its various layers, are elaborated and discussed.
Early stage oxidation of Ni-Cr binary alloy (111), (110) and (100) surfaces: A combined density functional and quantum chemical molecular dynamics study
Available online 3 April 2013 Publication year: 2013 Source: Corrosion Science
First-principles and tight-binding quantum chemical molecular dynamics were used in this study. The chemisorption energies of O and OH on the Ni-Cr (110) surface are lower than those of other surfaces. The oxygen 2p orbitals hybridise with Ni 3d, 4s and small amounts of p orbitals for the (100) surface while Ni p orbitals have no contribution for the (110) surface, which might reduce the adsorption energy. Additionally, oxygen acquires the maximum depth into the Ni-Cr (110) surface. Applied strain increases the oxygen diffusivity. This study reveals that the Ni-Cr (110) surface is easier for oxygen diffusion accordingly oxidation accelerates.
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Characterisation of Oxide films Formed on Co-29Cr-6Mo Alloy Used in Die-casting Moulds for Aluminium
Publication date: Available online 8 April 2013 Source: Corrosion Science
Oxide films formed at 700 °C on Co-29Cr-6Mo alloy were characterised extensively to improve the corrosion resistance of the alloy to liquid Al, enabling its use in Al die-casting moulds. Film of duplex layer consisting of an outer CoO-rich layer and an inner Cr 2 O 3 -rich layer was observed in samples subjected to oxidation for 4 h. With an increase in duration of oxidation, CoO was gradually replaced by Cr 2 O 3 , resulting in a single-layered oxide film dominantly composed of Cr 2 O 3 . The oxide nano-film evolved with duration of oxidation treatment indicating the possibility of optimising films for Al die-casting moulds.
Pitting corrosion of 304ss nanocrystalline thin film
Publication date: Available online 6 April 2013 Source: Corrosion Science
Pitting corrosion behaviour of coarse crystalline (CC) 304ss and its nanocrystalline (NC) thin film have been investigated by electrochemical measurement and in-situ AFM observation in 3.5% NaCl solution. The results show two effects of nanocrystallization on pitting corrosion behaviour: (1) more frequent occurrence of metastable pits, but with lower probability of transition to stable pits, which is attributable to differences in morphologies of sulphur and manganese as well as outstanding repassivation ability of NC thin film; (2) nanocrystallization decreases stable pit generation rate and its propensity to form larger pit cavities, and modifies the morphology of stable pit cavity.
Corrosion and microstructure of the metal silicide (Mo1−xNbx)5Si3
May 2013 Publication year: 2013 Source: Corrosion Science, Volume 70
(Mo 1− x Nb x ) 5 Si 3 ( x = 0, 0.2,0.4) was fabricated by hot press sintering method. The microstructure, mechanical properties and corrosion behavior were studied. Results showed that the hardness, flexure strength and fracture toughness are improved compared with pure Mo 5 Si 3 with Nb content. The alloy exhibited good corrosion resistance in HCl solution due to the spontaneous formation of a compact and protective passive film as well as the high chemical stability and strong inter-atomic bonds inherent to the (Mo 1− x Nb x ) 5 Si 3 alloys phases. (Mo 1− x Nb x ) 5 Si 3 alloys displayed relatively low corrosion resistance in 1 mol/L NaOH solution due to continuously formed and dissolved of Na 2 MoO 4 , NaNbO 3 and Na 2 SiO 3 .
Highlights
► Corrosion and mechanical properties of (Mo 1− x Nb x ) 5 Si 3 alloys were studied. ► The alloys exhibited good corrosion resistance in HCl solutions. ► The secondary passivation behavior of alloy shows higher capacity for repassivation. ► Corrosion behavior of alloys are controlled by the properties of surface passive film. ► Chemical stability and strong bonds to alloys are beneficial to corrosion resistance.
Electrochemical and theoretical investigation of triazole derivatives on corrosion inhibition behavior of copper in hydrochloric acid medium
May 2013 Publication year: 2013 Source: Corrosion Science, Volume 70
The inhibition effect of three triazole derivatives namely 4-amino-4 H -1,2,4-triazole-3thiol (ATT), 4-amino-5-methyl-4 H -1,2,4-triazole-3thiol (AMTT) and 4-amino-5-ethyl-4 H -1,2,4-triazole-3thiol (AETT) have been investigated against the corrosion of copper in 0.5 M HCl solution. The investigations were analyzed using potentiodynamic polarization, electrochemical impedance, weight loss methods and quantum chemical studies. Potentiodynamic polarization measurements indicate that all three examined compounds are cathodic type inhibitors. Among the studied compounds, 4-amino-5-ethyl-4 H -1,2,4-triazole-3thiol exhibited the best inhibition efficiency 96.09% at 2.58 mM. The adsorption of these compounds obeyed the Langmuir adsorption isotherm. The electronic properties obtained using quantum chemical approach, were correlated with the experimental results.
Highlights
► Triazoles derivatives are good inhibitors for copper in 0.5 HCl solution. ► Polarization results explain that all inhibitors are cathodic-type inhibitors. ► EIS measurements are in good agreement with polarization measurements. ► Theoretical calculations provide good support to experimental results.
The influence of microstructure on the protective properties of the corrosion product layer generated on the welded API X70 steel in chloride solution
May 2013 Publication year: 2013 Source: Corrosion Science, Volume 70
In the present work, a novel heat treatment process was used to investigate the influence of microstructure alteration on the corrosion behavior of base metal (BM), heat affected zone (HAZ) and weld metal (WM) in welded pipe steel of grade API X70. The electrochemical impedance spectroscopy (EIS) measurements were carried out to study the protective properties of the corrosion product layer after 90 days immersion in a high-pH solution. The EIS results showed that, the corrosion resistance of HAZ and WM increased after heat treatment due to formation of fine and compact corrosion product layer with fewer defects.
Highlights
► Heat treated welded joint exhibits more effective corrosion products layer. ► Charge transfer resistances of heat treated welded joint sub-zones are close together. ► Defects of corrosion product layer affect corrosion behavior of welded joint sub-zones.
Effect of hydration pretreatment on tunnel etching behaviour of aluminium foil
May 2013 Publication year: 2013 Source: Corrosion Science, Volume 70
Hydrous oxide films composed of pseudoboehmite and bayerite have been fabricated on the aluminium surfaces by hydration pretreatment in hot distilled water and ammonia solutions, respectively. After tunnel etching process, the specific surface area of aluminium foil with hydrous oxide film has been significantly improved, compared with that of aluminium foil with thermal oxide film. This effect can be attributed to the role that the hydrous oxide film contains plenty of water channels and defects, which allow the chloride ions to penetrate the film easily and reach the aluminium surface, thereby nucleating pits.
Highlights
► The hydrous oxide film is composed of pseudoboehmite and bayerite. ► The hydrous oxide film provides water channels for pit nucleations. ► The hydrous oxide film may contain vast defects when adding ammonia. ► The specific surface area of etched foil with hydration pretreatment is improved.
The initial stage of atmospheric corrosion on interstitial free steel investigated by in situ SPM
May 2013 Publication year: 2013 Source: Corrosion Science, Volume 70
The initial stage of atmospheric corrosion on interstitial free steel was investigated by ab initio calculation and scanning probe microscopy under different operation modes. Water droplets are adsorbed preferentially on grain boundaries at 95% relative humidity due to their higher surface energy, which is confirmed by ab initio calculation. Atomic force microscopy observation indicates that corrosion preferentially occurs at grain boundaries after immersion under a thin film of NaCl electrolyte, because of the lower relative nobility of grain boundary, which is proved by scanning Kelvin probe force microscope. These results indicate that water adsorption is crucial for initializing atmospheric corrosion.
Highlights
► The initial stage of atmospheric corrosion on interstitial free steel was studied. ► Water droplets are adsorbed preferentially on the grain boundaries. ► Ab initio calculations prove the grain boundary has higher surface energy. ► AFM image indicates the corrosion preferentially occurs at grain boundary. ► SKPFM image proves the grain boundary has lower relative nobility than the grain.
Anodic behaviour of the Cu82Al8Ni5Fe5 alloy in low-temperature aluminium electrolysis
May 2013 Publication year: 2013 Source: Corrosion Science, Volume 70
A Cu 82 Al 8 Ni 5 Fe 5 wt.% alloy was evaluated as an inert anode in the electrolysis of an Al 2 O 3 -saturated, KF 35.6 –NaF 12 –LiF 3 –(AlF 3 ) 49.4 melt (790 °С) for 73 h. It was shown that metal consumption at the alloy/scale interface led to the formation of a ring-like gap that was filled with oxygen-free electrolyte. It was hypothesised that the electrochemical transfer of the alloy components through the gap occurred and the chemical oxidation of the alloy particles after the dissolution-deposition process took place in the scale. It was concluded that the rate of scale formation was governed by the percentage of current that had passed through the gap.
Highlights
► A Cu 82 Al 8 Ni 5 Fe 5 wt.% alloy performed as a dimensionally stable anode for 73 h. ► A gap filled with oxygen-free electrolyte was formed at the alloy/scale interface. ► Electrochemical transfer of alloy components through the gap occurred. ► It is concluded that Al in the alloy did not protect the alloy from oxidation. ► 2% of current consumed by the secondary electrochemical process after 73 h.
High temperature erosion–oxidation of Cr3C2–NiCr thermal spray coatings under simulated turbine conditions
May 2013 Publication year: 2013 Source: Corrosion Science, Volume 70
Most erosion–oxidation research has been directed at high erodent flux, low impact velocity conditions typical of fluidised bed conditions. Few works have investigated erosion–oxidation under high temperature, high impact velocity, and low erodent flux conditions found within turbines. This work addresses the gap in knowledge of the high temperature erosion–oxidation mechanism of Cr 3 C 2 –NiCr coatings under long-term simulated turbine conditions. The same generic mechanism was observed under erosion-affected-oxidation and oxidation-affected-erosion conditions. The carbide and Cr 3 C 2 –NiCr phase interface was preferentially oxidised. An internal oxidation front progressed into the coating in advance of the slower erosive mass loss front at the surface.
Highlights
► Long-term simulated turbine erosion–oxidation of Cr 3 C 2 –NiCr thermal spray coatings. ► Preferential internal oxidation of carbide phase and Cr 3 C 2 –NiCr phase interfaces. ► Internal oxidation front moved into composite in front of surface erosive mass loss. ► Long term composite erosion response influenced by internally oxidised material.
Electrochemical corrosion and bioactivity of titanium–hydroxyapatite composites prepared by spark plasma sintering
May 2013 Publication year: 2013 Source: Corrosion Science, Volume 70
The corrosion resistance and bioactivity of titanium–hydroxyapatite (Ti–HA) composites prepared by mechanical alloying (MA) followed by spark plasma sintering were investigated. Potentiodynamic polarization tests showed that Ti composites containing 0–10% HA exhibited higher corrosion resistance than commercially pure Ti. An increase in HA concentration (20–30%) decreased corrosion resistance owing to the craterlike defects induced by ceramic particle detachment. Increasing MA time significantly reduced defect density and improved corrosion resistance. Bioactivity test on Ti HA composites in simulated body fluid revealed the growth of a nano-HA layer, which indicates the high potential of Ti–HA composites for application in biomedical implants.
Highlights
► We investigated corrosion resistance and bioactivity of Ti–HA composites. ► The surface microstructure related with corrosion behavior was studied by FE-SEM. ► Superior corrosion resistance was obtained for Ti containing 0–10% HA. ► Higher HA content decreased the corrosion resistance. ► Bioactivity test in SBF showed the growth of nanohydroxyapatite layer and particles.
Potentiostatic oxidation of AgCu50 alloy in alkaline solution in the presence of chlorides
May 2013 Publication year: 2013 Source: Corrosion Science, Volume 70
SEM and EDS analyses of AgCu50 alloy were performed after potentiostatic oxidation in an alkaline solution in the presence or absence of chloride ions. Oxidation in pure alkaline solution was favoured on the portion where a eutectic mixture was present on the surface. There was an essential difference between SEM images obtained in pure alkaline solution and in the presence of chloride, when voluminous deposits covering the whole eutectic area and expanding towards the middle of primary crystals appeared. EDS analysis confirmed that both oxides and chlorides of silver form in parallel. Chlorides disturb the protective performance of copper oxides.
Highlights
► An AgCu (50 mass.%) alloy was investigated during anodic oxidation. ► Oxidation was performed with and without the presence of chlorides. ► Oxidation in pure alkali begins on the area of the eutectic mixture. ► In the presence of chloride ions, oxides and chlorides form simultaneously. ► Voluminous deposits appear on the eutectic area and on silver spots inside α crystals.
Decanoate conversion layer with improved corrosion protection for magnesium alloy
May 2013 Publication year: 2013 Source: Corrosion Science, Volume 70
A novel decanoate conversion layer (DCL) with improved hydrophobicity for the corrosion protection of Mg alloy is fabricated and tested. XRD, EDX and FTIR results suggest that DCL comprises (CH 3 (CH 2 ) 8 COO) 2 Mg and Mg(OH) 2 . The contact angle of DCL increases with increased cycling number and reaches ca. 120° at the 30th cycle. The corrosion protection of DCL is much better than that of a decanoate inhibition layer, and close to that of a chromate conversion layer. With increased thickness, improved compactness and hydrophobicity, the decanoate conversion is proven to be a green and effective way to protect Mg alloys from corrosion.
Highlights
► A decanoate conversion layer is achieved using cyclic voltammetric method. ► The corrosion protection of the decanoate inhibition layer can be improved greatly. ► The decanoate conversion layer is thicker, more compact with high hydrophobicity. ► The decanoate conversion layer is of environmental friendliness and effectiveness.
Facile chromaticity approach for the inspection of passive films on austenitic stainless steel
May 2013 Publication year: 2013 Source: Corrosion Science, Volume 70
A chromaticity approach for the inspection of passive films on 304 stainless steel is explored by measuring the redness degree of the colouration reaction product of phenanthroline. The measurement exhibits good capability in evaluating film quality. The measured values are dependent on the structural integrity of the passive films. Based on the electrochemical examination and XPS spectra, this approach is discussed from the view point of the inhibition of the passive films on the release of ferrous from the matrix during its reaction with phenanthroline. The preferential dissolution of Fe-rich oxides in the films can affect the measurement.
Highlights
► A passive film inspection composed of colouration reaction and colour measurement. ► This inspection is of good capability to evaluate the quality of passive films. ► The measured value consists well with electrochemical behaviour of passive films. ► The measurement is dependent on the barrier of passive film on colouration reaction. ► Reducing dissolution of Fe-rich oxides in passive film affects the measurement too.
High temperature oxidation of AZ31+0.3wt.%Ca and AZ31+0.3wt.%CaO magnesium alloys
May 2013 Publication year: 2013 Source: Corrosion Science, Volume 70
Magnesium alloys of AZ31 + 0.3 wt.%Ca and AZ31 + 0.3 wt.%CaO were cast and oxidized between 450 and 650 °C in atmospheric air. The initially added Ca and CaO enabled to cast the alloys in air without using environmentally hazardous SF 6 gas, by forming a thin CaO-rich barrier layer at the surface during casting. A thin CaO-rich barrier layer was also formed at the surface during oxidation in air, thereby increasing the oxidation resistance of the AZ31 alloy considerably. The initially added Ca and CaO reacted with Al to become Al 2 Ca along the grain boundaries of the AZ31 alloy during casting.
Highlights
► AZ31 + 0.3 wt.%CaO alloys were cast and oxidized between 450 and 650 °C in air. ► Initially added CaO particles increased the oxidation resistance of Mg alloys. ► Oxidation-resistant, environment-friendly CaO-added Mg alloys were developed.
Influence of Creq/Nieq on pitting corrosion resistance and mechanical properties of UNS S32304 duplex stainless steel welded joints
May 2013 Publication year: 2013 Source: Corrosion Science, Volume 70
Pitting corrosion resistance and mechanical properties of 2304 duplex stainless steel with different Cr eq /Ni eq values after plasma-arc welding and welding thermal simulation were systematically studied. The results showed that the lower the Cr eq/ Ni eq value in the experimental range, the better the microstructure after welding or welding thermal cycle. High pitting resistance equivalent number in the chemical composition brought in low weight loss rate and high critical pitting temperature for base metal. Furthermore, as the Cr eq /Ni eq value decreased, the degradation of pitting corrosion resistance after welding thermal cycle reduced.
Highlights
► Influence of Cr eq /Ni eq on properties of DSS UNS S32304 was studied firstly. ► Both simulated HAZ and practical PAW welded joints were investigated and compared. ► Both chemical and electrochemical methods were applied. ► The lower Cr eq /Ni eq , the better microstructure and pitting corrosion resistance.
Internal oxidation of Sm(CobalFe0.22Cu0.08Zr0.02)7.5 alloy at 700°C
May 2013 Publication year: 2013 Source: Corrosion Science, Volume 70
The internal oxidation zone (IOZ) of a Sm(Co bal Fe 0.22 Cu 0.08 Zr 0.02 ) 7.5 alloy formed in air at 700 °C was characterized using transmission electron microscopy (TEM). It shows that the internal oxides are varied in composition and size with depth, from mainly fine FeSmO 3 in shallow area to larger Sm 2 O 3 in deeper area. The internal oxidation also causes the formation of a thin phase transformation zone between the IOZ and the alloy. The internal oxidation mechanism, together with the oxidation-induced phase transformation of the magnetic matrix phases of the alloy, is fully disclosed.
Graphical abstract
Highlights
The internal oxidation of the magnet mainly formed Sm 2 O 3 but FeSmO 3 in a shallow depth, as seen in the scanning transmission electron microscopy and corresponding X-ray mappings of Fe, Sm and O. ► Sm is internally oxidized into FeSmO 3 in shallow internal oxidation zone. ► Larger Sm 2 O 3 particles occur in deeper internal oxidation zone. ► The internal oxidation causes degradation of the magnetic matrix phases. ► Formation of Sm–Cu compound in a thin layer ahead of the internal oxidation zone.
The role of surface oxides on annealed high-strength steels in hot-dip galvanizing
May 2013 Publication year: 2013 Source: Corrosion Science, Volume 70
Oxidized alloying elements on the surface of annealed advanced high-strength steels deteriorate zinc wetting during hot-dip galvanizing. The present work describes reactions taking place during immersion of a steel strip in a zinc bath and gives new insight in changes of the surface oxides during hot-dipping. By using different advanced analysis techniques a direct proof for the occurrence of an aluminothermic reduction of Mn-oxides by Al dissolved in the zinc bath is shown. Furthermore, the morphology – rather than the chemical composition – of the surface oxides is crucial for obtaining a satisfactory galvanizability, mandatory for efficient corrosion prevention.
Highlights
► Reactions proceeding between the liquid zinc and steel surface oxides during hot-dip galvanizing were investigated. ► Surface oxides change during immersion in the zinc bath, improving galvanizability. ► The changes of oxides in the zinc bath were characterized by SEM, TEM and XPS. ► A direct proof for the occurrence of an aluminothermic reduction of MnO is shown for the first time. ► The morphology of surface oxides is most essential for a satisfying galvanizability.
Determination of residual stress in alumina scale by photostimulated Cr3+ luminescence piezospectroscopy
May 2013 Publication year: 2013 Source: Corrosion Science, Volume 70
Residual stresses in the scales of water-quenched and air-cooled Pt 84 :Al 11 :Cr 3 :Ru 2 (at.%) specimens oxidized in air at 1150 °C for up to 100 h were measured using luminescence piezospectroscopy. Scanning electron microscopy equipped with energy dispersive spectroscopy, optical microscopy, X-ray diffraction and Raman spectroscopy showed that well-adhering, irregular and protective external α-Al 2 O 3 scales developed on all specimens. Room-temperature residual stresses were compressive and became independent of oxidation times above 10 h exposure. Stress measurement results suggest that the air-cooled specimens possessed better adhesion than the water-quenched specimens, while both displayed lower stress values than those of the Ni- and Fe-based superalloys.
Highlights
► We examine two alloys having similar compositions but quenched in different media. ► Oxidation at high temperatures results in formation of scales with residual stresses. ► The residual stresses were found to be compressive. ► Current alloy displayed lower stresses compared to other alumina forming alloys.
Oxidation protection and behavior of C/C composites with an in situ SiC nanowire–SiC–Si/SiC–Si coating
May 2013 Publication year: 2013 Source: Corrosion Science, Volume 70
An in situ SiC nanowire–SiC–Si/SiC–Si protective coating was prepared on C/C composites by pack cementation and heat treatment. SiC nanowires suppressed the cracking of the coating by nanowire pullout and bridging and microcrack deflection, avoiding the oxidation of C/C composites. Results showed that the oxidation of the samples was a continuous weight gain process. The oxidation behavior was fitted to the parabolic–linear model and the final weight gain was 1.8% during thermogravimetric analysis from 50 to 1600 °C. The oxidation behavior was fitted to the parabolic model and the final weight gain was 0.51% during isothermal oxidation at 800 °C.
Electrochemical behaviour of the β-phase intermetallic (Mg2Al3) as a function of pH as relevant to corrosion of aluminium–magnesium alloys
May 2013 Publication year: 2013 Source: Corrosion Science, Volume 70
The intermetallic phase Mg 2 Al 3 was synthesised in bulk form to permit electrochemical characterisation. Polarisation testing was performed in 0.01 M NaCl across the pH range of 2–10, which is relevant to instances where the Mg 2 Al 3 phase populates Al-alloys (i.e. 5xxx series). Mg 2 Al 3 is capable of sustaining high dissolution rates, but this is pH dependent. As such, the range of currents sustained over the E-pH space are reported and are of general use for reconciling localised corrosion or corrosion model feedstock in other works.
Highlights
► Electrochemical characteristics reported for Mg 2 Al 3 over a wide pH range. ► Addressees the role of Mg 2 Al 3 in corrosion of Al-Mg alloys. ► Anodic current density of Mg 2 Al 3 reported as function of potential and pH.
Comments on the “Reply to comments on the paper ‘On the nature of inhibition performance of imidazole on iron surface’” by J.O. Mendes and A.B. Rocha
May 2013 Publication year: 2013 Source: Corrosion Science, Volume 70
Two DFT-GGA studies reported almost an order of magnitude different adsorption energies of imidazole on Fe (1 0 0), −0.7 vs. −5.9 eV, which inevitably leads to conclusion that one of them is wrong. But which? In their Reply to my Comments, Mendes and Rocha explained that the difference emerges due to different treatment of magnetization, which should be constrained to bulk value. In these Comments, it is rigorously demonstrated that different treatments of magnetization lead to similar adsorption energies (−0.75 ± 0.1 eV) and that magnetization should be treated self-consistently. The issue is therefore firmly settled.
Reply to comments on the paper “On the nature of inhibition performance of imidazole on iron surface” by J.O. Mendes, E.C. da Silva, A.B. Rocha
May 2013 Publication year: 2013 Source: Corrosion Science, Volume 70
Corrosion resistance of novel silane-functional polybenzoxazine coating on steel
May 2013 Publication year: 2013 Source: Corrosion Science, Volume 70
A novel silane-functional polybenzoxazine (PB-TMOS) coating, with silane groups that can bond to the substrate, was prepared through a dip-coating and thermal curing method. The coating properties were investigated by Fourier transform infrared spectroscopy, solid-state nuclear magnetic resonance spectroscopy, static contact angle measurement, electrochemical and accelerated corrosion tests. The corrosion resistant performance of PB-TMOS coated specimens was considerably enhanced by the high hydrophobicity and water resistance resulted from the dual cross-linking network of polybenzoxazine and Si–O–Si in PB-TMOS matrix.
Highlights
► Polybenzoxazine coating shows good corrosion resistance for stainless steel. ► The coating is prepared only by thermal cure method without hydrolytic process. ► Dual crosslink network of the coating is studied by FTIR and 29 Si NMR spectra. ► Adhesion between coating and substrate is improved by the Fe–O–Si bond.
In situ investigation of sacrificial behaviour of hot dipped AlSi coating in sulphate and chloride solutions
May 2013 Publication year: 2013 Source: Corrosion Science, Volume 70
The electrochemical behaviour of the cut-edge of hot-dipped aluminium–silicon-based alloy coated steel is studied in immersed conditions in sulphate and in chloride media. Preliminary studies performed on steel-pure Al bi-electrode demonstrate that a significant galvanic current can develop at short times ( t < 1000 s) only in chloride solutions. In situ measurements of current density and pH distributions over cut-edge coated steels immersed in chloride solutions revealed a quasi-steady state current between the coating and the steel substrate, resulting from local (pitting like) dissolution of the aluminium–silicon-based alloy coating. In sulphate solutions, the coating is not at all sacrificial and remains passive.
Highlights
► The sacrificial behaviour of a HDG Al–Si coating is studied on steel sheets. ► The electrochemical behaviour of Al and Al–Si coatings are compared. ► Pure Al is sacrificial only at short times ( t < 10 3 s) and in chloride solutions. ► HDG Al–Si coatings are sacrificial only in chloride solutions.
Corrosion behavior of reinforced no-fines concrete
May 2013 Publication year: 2013 Source: Corrosion Science, Volume 70
The CO 2 induced corrosion behavior of no-fines concrete manufactured with three different strength classes and reinforcements is compared. The main results showed that black steel corrodes with rates three times higher with respect to those monitored in the other reinforcements, with higher corrosion rates in lower strength class concretes. The corrosion rates of steel covered by cement grout and galvanized reinforcements are not affected by concrete strength class since they protect themselves with the cement grout coating or zinc passivation, respectively. Among the reinforcements considered in this work, galvanized steel shows the best corrosion behavior.
Highlights
► In no-fines concrete, black steel shows the worst CO 2 induced corrosion behavior. ► Corrosion rates of black steel are higher in lower strength class concretes. ► Corrosion of steel covered by cement grout is not affected by concrete strength. ► Corrosion of galvanized steel is not affected by concrete strength. ► Galvanized steel shows the best corrosion behavior.
Role of magnesium ions in reducing high temperature aqueous corrosion of carbon steel
May 2013 Publication year: 2013 Source: Corrosion Science, Volume 70
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.
Highlights
► Corrosion of carbon steel reduced by 40% in the presence of magnesium ions. ► Uptake of magnesium ions in the corrosion product oxide confirmed by LRS and XPS. ► Altered corrosion processes seen in EIS studies. ► Mg modified oxide at inner oxide–solution interface alters anodic reaction kinetics. ► Electrical conductivity of Mg modified oxide alters cathodic reaction kinetics.
Effect of hydrogen on pitting susceptibility of 2507 duplex stainless steel
May 2013 Publication year: 2013 Source: Corrosion Science, Volume 70
The effect of hydrogen on pitting corrosion susceptibility of duplex stainless steel was investigated. Pits are observed on the hydrogen-charged specimen after 6 days of immersion in 6% FeCl 3 solution, while no pits on the uncharged specimen even after more than 30 days of immersion, which indicates that hydrogen promotes pitting initiation and pit growth. Moreover, pitting susceptibility increases with hydrogen charging current density. The pitting tends to nucleate initially inside the austenite or at ferrite/austenite boundaries, and then appears in the ferrite, because of different behaviors of hydrogen in two phases, such as solubility and diffusivity of hydrogen.
Highlights
► The effect of hydrogen on pitting corrosion susceptibility of duplex stainless steel (DSS) was investigated. ► Hydrogen promotes pit initiation and accelerates pit growth in DSS. ► Higher hydrogen concentrations give rise to higher pitting susceptibility. ► Pitting is more severe in acidic solution than in neutral one. ► Pits nucleate initially inside the austenite phase or at ferrite/austenite boundaries.
Corrosion and scaling as interrelated phenomena in an operating geothermal power plant
May 2013 Publication year: 2013 Source: Corrosion Science, Volume 70
This study refers to an experimental research and contributes to a better understanding of corrosion and scaling in an operating geothermal power plant (Soultz-sous-Forêts, France). An in situ physicochemical monitoring program has been performed in order to characterise the processed brine. In situ and laboratory corrosion experiments were performed using conventional and candidate metals (mild steels, CrNiMo alloys, and non-ferrous metals). Mild steels exhibit long-term corrosion rates below 0.2 mm/year, accompanied by scaling formation offering protection. Conventional stainless steels 430F and 316L undergo pitting corrosion, while higher alloyed materials were identified to be suited for geothermal service.
Highlights
► In situ physicochemical monitoring was performed in the geothermal power plant of Soultz, France. ► Long-term uniform corrosion rates of mild steels are <0.2 mm/year. ► Localised corrosion (filiform corrosion) can occur with considerable penetration depths (>1 mm). ► Corrosion scales (e.g. siderite) form and contribute to materials resistance. ► Steel grades 430F and 316L suffer pitting corrosion in test environments.
Hot corrosion properties of composite coatings in the presence of NaCl at 700 and 900°C
May 2013 Publication year: 2013 Source: Corrosion Science, Volume 70
Cyclic hot corrosion tests have been carried out on three coatings (one NiCoCrAlY and two composite coatings) at 700 and 900 °C. The kinetic curves and evolution of microstructure show that the composite coating with a Cr-base interlayer performs best. The Cr 2 O 3 scale is more effective to protect the coating at 700 °C than that at 900 °C. The corrosion process is accelerated by NaCl via forming volatile MCl x and inducing the formation of molten voids in the coating or extra oxidation at the interface of fusant/oxide scale, determined by the temperature and the compositions of the coating.
Highlights
► Composite coating with the Cr-base interlayer performs best during hot corrosion. ► Cr 2 O 3 is more effective to protect the coating at 700 °C than that at 900 °C. ► Degradation of the coating was accelerated by NaCl via forming volatile MCl x . ► The formation of molten voids and outside extra oxidation are induced by MCl x . ► Temperature and the content of Al/Cr affect the specific corrosion mechanism.
Corrosion inhibition performance of polypyrrole Al flake composite coatings for Al alloys
May 2013 Publication year: 2013 Source: Corrosion Science, Volume 70
Polypyrrole (PPy) was deposited on Al flakes in the presence of oxyanions (molybdate, phosphate or vanadate) as inhibiting dopants and the PPy modified Al flakes were incorporated into an epoxy primer as protection pigments for AA 2024-T3. The protection performance of the PPy Al flake coating was assessed by electrochemical evaluations including Scanning Vibrating Electrode Technique (SVET), Electrochemical Impedance Spectroscopy (EIS) and salt spray test. The oxyanion doped PPy Al flake coating shows enhanced protection performance for AA 2024-T3. An oxygen scavenger protection mechanism is suggested for PPy in the composite coating, and the roles of Al flake and oxyanions in the formulation are discussed.
Highlights
► Oxyanion incorporation enhances protection property of the PPy Al flake coatings. ► An oxygen scavenger protection mechanism is proposed for PPy in composite coatings. ► Al flake improves dispersion of PPy in the composite coating. ► Vanadate as inhibiting dopant in the composite coating shows good performance.
Effect of aging time on corrosion inhibition of cationic surfactant on mild steel in sulfamic acid cleaning solution
May 2013 Publication year: 2013 Source: Corrosion Science, Volume 70
The stability of the 1 M sulfamic acid solutions containing a gemini cationic surfactant (12-4-12) or its monomeric counterpart (DTAB) during 23 days of storage were studied by electrochemical impedance spectroscopy (EIS), X-ray diffraction (XRD) and surface tension measurements. The EIS studies indicated that in comparison to DTAB solution, 12-4-12 solution considerably retained the corrosion inhibition during the storage period. The surface tension of DTAB solution was increased around 10 mN/m during storage while the surface tension of 12-4-12 solution was almost unchanged. The higher stability of 12-4-12 acidic solution than that of DTAB was also depicted by XRD results.
Highlights
► Stability of surfactants in sulfamic acid solution regarding corrosion inhibition. ► Stability of surfactants in sulfamic acid solution regarding surface tension. ► Evaluation of surface energy of mild steel in aged and fresh acid solutions. ► Evaluation of surface morphology of mild steel in aged and fresh acid solutions. ► Characterization of the aged solutions by XRD.
Methods for making alloy 600 resistant to sensitization and intergranular corrosion
May 2013 Publication year: 2013 Source: Corrosion Science, Volume 70
Thermomechanical processing (TMP) and strain annealing were performed on alloy 600. The degree of sensitization (DOS) and susceptibility to intergranular corrosion (IGC) were assessed by electrochemical potentiokinetic reactivation and weight loss tests respectively. The grain boundary character distribution was established by orientation imaging microscopy. It was shown that as the fraction of special boundaries increased with TMP/strain annealing, the DOS and IGC rates decreased drastically. Alloy 600 with fraction of special boundaries above 85% showed only uniform corrosion. The DOS and IGC values indicating resistance to sensitization and IGC and the methods to achieve such values have been highlighted.
Highlights
► Grain boundary engineering of alloy 600 for 85% special boundaries established. ► Intergranular corrosion resistance of alloy 600 in G28 test improved by thermo-mechanical processing. ► Double loop – electrochemical reactivation test values less than 0.78 shown to correspond to uniform corrosion in G28 test. ► Corrosion rate less than 1.27 mm/y in G28 shown to be due to uniform corrosion. ► Corrosion rates over 1.57 mm/y in G28 shown to be a result of grain dropping.
Corrosion and wear of zinc in various aqueous based environments
May 2013 Publication year: 2013 Source: Corrosion Science, Volume 70
The corrosion and corrosive wear resistance of zinc sliding against 440C martensitic stainless steel counterface, were studied in aqueous based solutions having different NaCl and sodium molybdate dihydrate concentrations respectively. The main objective was to investigate the effect of aqueous based environments and corrosion inhibitors on the interface and tribological characteristics of this tribosystem, as in several cases the formation of a thin corrosion product layer can act as a lubricating film. The experimental results indicated that sodium molybdate dihydrate acted as a corrosion inhibitor, decreasing significantly the corrosion susceptibility of zinc. However, during the corrosive wear of zinc under free corrosion conditions, the addition of sodium molybdate dihydrate inhibitor did not improve the tribological properties of zinc, as higher friction coefficients of the tribosystem were recorded. This observation indicates that aqueous lubrication cannot be applied in this tribosystem, even though an inhibitor was used to minimize the effect of Cl − halide ions. In addition, the observed wear mechanisms of zinc were mainly plastic deformation and abrasion. These wear mechanisms coexisted with pitting and dissolution–precipitation corrosion phenomena on the surface of this material.
Highlights
► Use of aqueous based solutions as possible liquid lubricants. ► Effect of NaCl concentration in aqueous solutions on corrosion and wear of zinc. ► Effect of Na 2 MoO 4 .2H 2 O inhibitor on corrosion and wear behavior of zinc. ► Investigate surface phenomena occurring during corrosive wear of zinc.
SiC/SiC–YAG–YSZ oxidation protective coatings for carbon/carbon composites
May 2013 Publication year: 2013 Source: Corrosion Science, Volume 70
SiC/SiC–YAG–YSZ coatings were prepared by pack cementation, chemical vapor deposition and slurry painting on carbon/carbon (C/C) composites. The microstructures and oxidation behavior of coatings were investigated. The results show that the coatings displayed good oxidation and thermal shock resistance due to a dense glassy layer with silicates formed on the coating of SiC–YAG–YSZ. The weight gain rate of coated C/C composites was 1.77% after oxidation for 150 h at 1773 K. SiC in outer coating can promote the formation of oxygen diffusion barrier and lead to the optimum oxidation resistance for the coatings, compared with YSZ and YAG.
Graphical abstract
Highlights
SiC as the major phase in outer coating can promote the formation of oxygen diffusion barrier and lead to the optimum oxidation resistance for the coatings, compared with YSZ and YAG. ► SiC/SiC–YAG(Y 3 Al 5 O 12 )–YSZ(Y 0.16 Zr 0.92 O 2.08 ) coatings were prepared on C/C composites. ► The coatings exhibit good oxidation and thermal shock resistance at 1773 K. ► SiC in outer layer can promote the formation of a dense glassy layer with silicates.
Effect of permanganate concentration on the formation and properties of phosphate/permanganate conversion coating on AZ31 magnesium alloy
May 2013 Publication year: 2013 Source: Corrosion Science, Volume 70
This study investigated the role of permanganate in phosphate solutions in the formation and corrosion resistance of phosphate/permanganate coatings on AZ31 magnesium alloys. Experimental results showed that permanganate was reduced to manganese (IV) oxide together with the dissolution of magnesium during the conversion coating treatment. Adding more permanganate to the phosphate solution resulted in a thinner coating with a compact magnesium oxide layer contacting the AZ31 plate. Moreover, the thinner coating had fewer cracks and displayed higher polarization resistance and corrosion resistance than the thicker counterpart formed in the solution with less permanganate.
Highlights
► Phosphate/permanganate coating on an AZ31 displays a three-layered structure. ► Permanganate ions reduce the size of cracks on phosphated AZ31 Mg alloy. ► Cracks of phosphate/permanganate coating deteriorate its corrosion protection. ► Permanganate ions reduce the phosphate/permanganate coating growth rate.
An investigation of the influence of physical vapour deposited aluminium layers on the kinetics of organic coating disbondment on iron
May 2013 Publication year: 2013 Source: Corrosion Science, Volume 70
A high-throughput method of investigating organic coating delamination from iron substrates incorporating interfacial thin metallic films of varying thickness is presented. Physical vapour deposited aluminium is demonstrated as a means of limiting underfilm oxygen reduction and slowing rates of corrosion-driven cathodic disbondment. A wedge of graded thickness is deposited on an iron surface and over-coated with a model organic layer. After initiating corrosion by applying corrosive electrolyte to a penetrative defect, rates of corrosion-driven delamination are determined by in situ scanning Kelvin probe measurements, enabling the influence of a range of Al thicknesses to be studied on a single sample.
Highlights
► Thin PVD-deposited aluminium was investigated as a cathodic blocking layer on iron. ► A high-throughput method was used to study the influence of Al layer thickness. ► Samples comprising a wedge of increasing Al layer thickness were organic coated. ► In situ scanning Kelvin probe data was used to quantify rates of underfilm corrosion. ► Organic coating delamination was halted using Al thicknesses 15 nm or greater.
The passivation behaviour of copper-containing high-performance ferritic stainless steels in the cathode environment of polymer electrolyte membrane fuel cells
May 2013 Publication year: 2013 Source: Corrosion Science, Volume 70
The passivation behaviour of copper-containing high-performance ferritic stainless steels in the cathode environment of polymer electrolyte membrane fuel cells was investigated using electrochemical tests and XPS surface analyses. The addition of copper to the alloy deteriorated the corrosion resistance at a passive region of 0.6 V SCE . With an increase of the copper content, the passivity of the alloy degraded due to an increase of the formation of Cr-containing inclusions, and a decrease of the Cr oxide and hydroxide in the passive film.
Highlights
► A greater content of Cu in the alloy enhanced the active corrosion resistance. ► A greater content of Cu in the alloy decreased the passive corrosion resistance. ► A greater content of Cu in the alloy increased the number and area of inclusions. ► A greater content of Cu in the alloy decreased the Cr oxide and hydroxide in film. ► The passivity of Cu added alloy degraded due to the inclusions and the Cr species.
Evolution of hydrogen at dissolving magnesium surfaces
May 2013 Publication year: 2013 Source: Corrosion Science, Volume 70
The origin of hydrogen evolved at dissolving magnesium surfaces, including those subjected to anodic polarisation, remains a topical issue. In this work, a critical appraisal of existing theories is presented, along with data from simultaneous polarisation and hydrogen collection tests. The observations invalidate mechanisms invoking the presence of univalent Mg + . A combined experimental and thermodynamic analysis suggests that the ability of magnesium to support the cathodic reaction is enhanced during dissolution as the result of an increase in the exchange current density for the hydrogen evolution reaction, This mechanism can also explain high rates of hydrogen evolution in aluminium pits.
Highlights
► H 2 generation rate at dissolving Mg surface increases with Mg dissolution rate. ► Total H 2 volume for given net anodic charge decreases as current density increases. ► Findings are not consistent with univalent Mg ion mechanism of H 2 generation. ► New model presented for increased generation of H 2 with increased potential. ► Surface catalytic activity and i 0, HER presumed to increase with Mg dissolution rate.
Characterisation of AISI 1005 corrosion films grown under cyclic voltammetry of low sulfide ion concentrations
Publication date: Available online 3 May 2013 Source: Corrosion Science Author(s): N. Perini , P.G. Corradini , V.P. Nascimento , E.C. Passamani , M.B.J.G. Freitas The mechanism of AISI 1005 corrosion in sulfide ion solutions has been investigated using cyclic voltammetry, electrochemical impedance spectroscopy, X-ray diffraction (XRD) and Mössbauer spectroscopy (MS). The proposed mechanism occurs with the initial formation of oxygenated ferrous species followed by adsorption of HS - species, precipitation of iron monosulfides and their partial conversion to bisulfide iron. This mechanism was demonstrated by XRD results that revealed Fe-O and Fe-S phases and by MS results that detected pyrite as the major proportion (94%) of the iron species in the corrosion product.
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