Showing papers in "Materials and Corrosion-werkstoffe Und Korrosion in 2014"
TL;DR: The microstructure and bio-corrosion behavior of binary Mg-Zn alloys have been studied using scanning electron microscopy (SEM), electrochemical, and immersion tests.
Abstract: The microstructure and bio-corrosion behavior of binary Mg-xZn (x = 1.25, 2.5, 4) and ternary Mg-Ca-xZn (x = 1.25, 2.5, 4) alloys have been studied using scanning electron microscopy (SEM), electrochemical, and immersion tests. Microstructure analysis indicated that the binary Mg-Zn alloys are composed of primary α-Mg matrix and Mg12Zn13 phases, while, ternary Mg-Ca-Zn alloys are composed of α-Mg, Mg2Ca, and IM1 (Ca3MgxZn15-x) (4.6 & le; x & le; 12) phases or α-Mg, IM1 and IM3 (Ca2Mg5Zn13) phases. Electrochemical results showed that Mg-4Zn alloy has lowest corrosion rate among binary alloys. At constant Ca content of 0.8 wt.%, the addition of Zn up to 1.25 wt.% decreased the corrosion rate, while further addition of Zn increased the corrosion rate of ternary alloys. Immersion tests results demonstrated that the formation of Zn oxide layer in binary Mg-Zn alloy and evolution of eutectic phase (α-Mg+IM1+Mg2Ca) significantly retard the bio-degradation rate of the ternary alloys.
92 citations
TL;DR: In this paper, the composition and distribution of the corrosion layer was analyzed by microscopy and X-ray photoelectron spectroscopy, and the results indicated that Mg-Ag alloys have satisfactory corrosion properties and much better mechanical properties than pure magnesium as a functional biodegradable material.
Abstract: Binary magnesium–silver (Mg–Ag) alloys were designed as antibacterial material to treat infections in an implant site. The mechanical and electrochemical measurements were performed on three casting Mg–Ag alloys under cell culture conditions. The composition and distribution of the corrosion layer was analyzed by microscopy and X-ray photoelectron spectroscopy. In cell culture media, Mg–Ag alloys show higher, but still acceptable general corrosion rates while less susceptibility to pitting corrosion than pure Mg with increasing content of silver. This study indicates that Mg–Ag alloys have satisfactory corrosion properties and much better mechanical properties than pure magnesium as a functional biodegradable material.
76 citations
TL;DR: In this paper, the potential of an alumina-forming austenitic (AFA) stainless steel (OC-4, Fe-25Ni-14Cr-3.5Al-2.5Nb wt% base) as a candidate material for solar plant heat exchangers and pipes was investigated.
Abstract: In recent years, the study of renewable energies and its practical application has increased significantly. Solar energy feasibility entails the development of energy storage systems since solar power plants need to be working in unfavorable weather or night periods. The main heat transfer fluid (HTF) used on these plants is a salt mixture of 60% NaNO3/40% NaNO3 which must be kept above 220 °C to prevent freezing. This high operating temperature causes corrosion problems for steels in contact with the HTF, reducing the lifetime of the solar plants. The present research studies the potential of an alumina-forming austenitic (AFA) stainless steel (OC-4, Fe-25Ni-14Cr-3.5Al-2.5Nb wt% base) as a candidate material for solar plant heat exchangers and pipes. Corrosion behavior of OC-4, relative to 304 stainless steel and T22 steel, was studied by gravimetric analysis and electrochemical impedance spectroscopy (EIS). The AFA OC-4 exhibited better corrosion resistance in HTF at 390 °C than the currently used 304 austenitic stainless steel. © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
60 citations
TL;DR: In this article, the authors analyzed the effect of reactive element additions on the oxide scale formation in chromia-forming materials and found that minor element additions are necessary to increase their mechanical or chemical properties.
Abstract: Materials able to form protective chromia, Cr2O3, are most of time good candidates to be used at high temperatures in oxidizing atmospheres. Minor element additions are necessary to increase their mechanical or chemical properties. Among them, the reactive elements (RE) are highly efficient to improve the high temperature oxidation behavior of alloys. Their addition in small quantity is enough to greatly decrease the oxidation rates, but above all to drastically increase the oxide scale adherence to the base materials. That was the key point of what observed Pfeil 75 years ago. Since that date, many results have been published, many theories have been proposed, and many discussions have been engaged. Until now, the reasons why RE are so efficient are not fully understood, several hypotheses have been proposed in order to explain their beneficial effect on the oxide scale formation. According to the large amounts of published papers on this topic, there is probably no single theory envisageable to explain their role, whatever their nature, the tested materials and then the native oxide scale, as well as the nature of the oxidizing atmosphere. The decrease of the oxidation rate and the improvement of the oxide layer adherence are the final results due to RE additions. Generally, RE additions favor the nucleation and the growth of scales. They decrease the oxide grain size, and consequently could change scale plasticity and creep, which can modify the growth and/or thermal stresses generated within the scale during its growth or its cooling to room temperature. They prevent the detrimental sulfur effect and suppress dislocation climb in the metal and, then, limit cation transport (poisoned interface model). 75th Pfeil's patent anniversary seems good to make a pause in order to analyze what we really understood on the reactive element effect in chromia-forming materials.
53 citations
TL;DR: In this work, tetrakis hydroxymethyl phosphonium sulfate (THPS) was combined with D‐methionine for the mitigation of Desulfovibrio vulgaris biofilm in the full ATCC 1249 medium and a modified medium with only four ingredients, as well as MIC pitting of C1018 carbon steel.
Abstract: Biocorrosion is also known as microbiologically influenced corrosion (MIC). It is often caused by sulfate reducing bacteria (SRB) biofilms. More effective biocide treatment methods are desired due to environmental regulations and increasing costs. Recently, several publications revealed that some D-amino acids are signaling molecules for bacterial biofilm dispersal. In this work, tetrakis hydroxymethyl phosphonium sulfate (THPS) was combined with D-methionine for the mitigation of Desulfovibrio vulgaris (ATCC 7757) biofilm in the full ATCC 1249 medium and a modified medium with only four ingredients, i.e., magnesium sulfate, sodium lactate, ferrous ammonium sulfate hexahydrate, and yeast extract at concentrations 1/4 of those in the full medium, as well as MIC pitting of C1018 carbon steel. D-Methionine alone even at a concentration of 1000 ppm w/w and 50 ppm (active concentration) THPS alone were both found ineffective. However, a synergistic biocide combination consisting of 50 ppm THPS and 100 ppm D-methionine was highly effective and even better than 500 ppm THPS used alone. Although D-methionine alone has no biocidal effects, its biofilm dispersal effect can convert sessile cells to planktonic cells under a biocide stress. This is very useful in biofilm treatment because planktonic cells are much easier to treat than sessile cells using biocides.
53 citations
TL;DR: In this article, the inhibition of mild steel corrosion in 3% HCl solution by sulfamethoxazole (SZ) and norfloxacin (NF) were investigated at 25°C using weight loss measurement.
Abstract: The inhibition of mild steel corrosion in 3% HCl solution by sulfamethoxazole (SZ) and norfloxacin (NF) were investigated at 25 °C using weight loss measurement. The measurements reveal that the inhibition efficiency grows with increasing concentrations of inhibitors, and the inhibition efficiency decreases in the order NF > SZ. The adsorption of inhibitor molecule on mild steel surface follow Langmuir isotherm. Quantum chemical calculation was performed to correlate electronic structure parameters of SZ and NF with their inhibition performances. The molecular dynamics simulations were applied to find the equilibrium adsorption configurations and calculate the interaction energy between inhibitors and iron surface. The efficiency order of the studied inhibitors obtained by experimental results was verified by theoretical calculations.
51 citations
TL;DR: In this article, the elementary dissolution rates for Al, Mg, Cu, and Fe were measured as a function of time and potential using atomic emission spectroelectrochemistry (AESEC).
Abstract: Copper rich intermetallic particles are common in technical aluminum alloys. When exposed to an aggressive electrolyte, these particles undergo a transformation into a pure copper phase due to a selective dissolution or dealloying mechanism. In this work, the kinetics of this transformation have been investigated using synthetic intermetallic phases of Al2Cu, Al7Cu2Fe, and Al2CuMg in 2 M H2SO4 as commonly used in the anodization process. The elementary dissolution rates for Al, Mg, Cu, and Fe were measured as a function of time and potential using atomic emission spectroelectrochemistry (AESEC). From this data, it was possible to measure the degree of selective dissolution for the individual elements in the different potential domains. Mg and Fe dissolve simultaneously with Al during the overall polarization. Al dissolution is activated in the presence of Mg and inhibited in the presence of Fe. This work demonstrates the utility of atomic emission spectroelectrochemistry for the direct measurement of dealloying reactions and the indirect measurement of residual films.
47 citations
TL;DR: In this paper, the oxidation behavior of two commercially available nickel-base alloys, Rene 80 and PWA 1483, was investigated for up to 500 h duration in synthetic air and synthetic air containing 2% SO 2 at 1050 °C.
Abstract: Modern gas turbine materials are subjected to increasing operating temperatures in service environments, which contain high concentrations of gaseous species originating from fuel impurities, e.g. sulfur. In the present study, the oxidation behavior of two commercially available nickel-base alloys, Rene 80 and PWA 1483, was investigated for up to 500 h duration in synthetic air and synthetic air containing 2% SO 2 at 1050 °C. In order to investigate the mechanisms of SO 2 attack, specimens of the two alloys after different oxidation times were characterized using a number of surface analytical techniques such as scanning electron microscopy, XRD, and glow discharge optical emission spectrometry. The corrosion reactions in the presence of SO 2 were found to be strongly alloy dependent and could not be explained simply in terms of the contents of the main scale-forming alloying elements, Cr and Al. Severe internal sulfidation was observed underneath the chromium-rich oxide scale on Rene 80, leading to breakaway oxidation after longer exposure times. For PWA 1483 sub-scale formation of a near-continuous alumina occurred, which resulted in substantial suppression of sulfidation. Consequently, no breakaway oxidation of PWA 1483 was observed up to 500 h exposure at 1050 °C in synthetic air with 2% SO 2 . The formation of a dense alumina sub-scale on PWA 1483 is believed to be correlated with the Ta-addition in this material. It is proposed thatTa can tie up Ti by forming a mixed oxide of the type TiTaO 4 . In this way, it prevents the incorporation of Ti into the chromia scale, which can lead to enhanced scale growth.
44 citations
TL;DR: In this paper, the influence of Ni on the corrosion behavior of Ni-containing weathering steel (Q415NH) was investigated under alternate dry/wet conditions, and the results suggested that the addition of Ni shifted the corrosion potential of the steel to the positive direction and lowered the corrosion current density.
Abstract: The influence of Ni on the corrosion behavior of Ni-containing weathering steel (Q415NH) was investigated under alternate dry/wet conditions. The results suggested that the addition of Ni shifted the corrosion potential of the steel to the positive direction and lowered the corrosion current density. Furthermore, the addition of Ni was in favor of the formation of a compact and homogeneous inner rust layer (composed of most α-FeOOH and little β-FeOOH), leading to enhanced corrosion resistance of the steel in the simulated marine atmosphere.
41 citations
TL;DR: In this article, the effects of SO2 additions on oxide formations and the interaction of other gases in oxvyfuel environments were investigated and the authors concluded that SO2 added to oxyclic acid compounds can affect oxide formation and interaction with other gases.
Abstract: This report is a description of research performed by the Julich Research Centre. Their conclusions outline the effects of SO2 additions on oxide formations and the interaction of other gases in oxvyfuel environments.
41 citations
TL;DR: In this article, an automated corrosion monitoring system using the electrical resistance technique was applied for assessment of the corrosivity towards carbon steel and zinc in different phases of a complex accelerated corrosion test recently introduced by VDA.
Abstract: An automated corrosion monitoring system using the electrical resistance technique was applied for assessment of the corrosivity towards carbon steel and zinc in different phases of a complex accelerated corrosion test recently introduced by VDA, an association of German car makers. It comprises salt spray, wet, dry, and freezing phases. The developed small and battery-driven atmospheric corrosion loggers provided high sensitivity allowing for sub-angstrom (<10−10 m) measurements of corrosion depth and good accuracy. The actual corrosion rate was affected by the exposure history due to a limited rate of wetting/drying and oxygen and ion transport to the reaction interface under a layer of corrosion products. The hysteresis was particularly strong for carbon steel. Except the freezing phase, the steel corrosion rate varied in a narrow range from 0.2 to 0.6 µm/h. For zinc, the corrosion rate varied from 0.001 to 0.1 µm/h in particular phases of the cycle with the maximum in the salt spray phase. Seventy-five percent of the metal corroded in the salt spray phase and in the following drying period representing only 13% of the total test time. The obtained data suggest that the proposed test cycle allowed for rather efficient drying of the zinc surface, which is believed to be crucial for the formation of corrosion products with certain protective ability observed also in field conditions.
TL;DR: In this article, natural hydroxyapatite (HA) was coated on NiTi alloy using electrophoretic deposition method to improve the corrosion resistance and biocompatibility.
Abstract: Natural hydroxyapatite (HA) was coated on NiTi alloy using electrophoretic deposition method to improve the corrosion resistance and biocompatibility. Coating process was performed at 120 s in various applied voltages of 40, 60, and 80 V. Sintering process was done at 800 °C under inert gas for 2 h. Electrochemical behavior of the coated samples was investigated in simulated body fluid by using electrochemical impedance spectroscopy and polarization tests. Furthermore, the nickel ions release from NiTi and HA coated-NiTi samples were analyzed by atomic absorption analysis. Ultimately, scanning electron microscopy micrographs and X-ray diffraction patterns were used to evaluate the morphology and phase analysis of HA coatings. The results show that the sample coated at 60 V reveals a uniform, dense coating accompanied with a higher corrosion resistance. Moreover, after 4 weeks, nickel ions release was reduced to 0.205 µg/cm2 for coated sample at 60 V.
TL;DR: In this paper, the microstructure and corrosion behavior in simulated body fluid of as-cast and heat treated Mg-xZn (x = 3 and 6) alloys for different heat treatment times were studied.
Abstract: Microstructure and corrosion behaviour in simulated body fluid of as-cast and heat treated Mg–xZn (x = 3 and 6) alloys for different heat treatment times were studied. The results revealed that as-cast Mg–3Zn alloys consist of Mg12Zn13 phase and α-Mg matrix, while Mg–6Zn is composed of Mg51Zn20, Mg12Zn13 compounds and α-Mg matrix. After heat treatment of Mg–6Zn alloy at 340 °C, the Mg51Zn20 phase decomposed to the matrix and Mg12Zn13 while, the microstructure of Mg–3Zn remained unchanged. The results also indicated that heat treatment at 340 °C has little influence on the corrosion behaviour of Mg–3Zn. In contrast, heat treatment improved the corrosion resistance of the Mg–6Zn alloy as the decomposition of the Mg51Zn20 phase decreased micro-galvanic corrosion. The corrosion resistance of both as-cast Mg–3Zn and Mg–6Zn alloys marginally improved with increasing heat treatment times.
TL;DR: In this paper, a nano-zinc oxide-containing polyurethane-based coatings were prepared by incorporating 3'wt% nano-ZnO in the electrocoating composition.
Abstract: In this investigation nano-zinc oxide-containing polyurethane-based coatings were prepared by incorporating 3 wt% nano-ZnO in the electrocoating composition. The paint films were deposited on phosphated steel panels through electrodeposition. The films were then rinsed by DI water and baked for 20 min at 165 °C in an electrical laboratory oven. The cured films were exposed to ultraviolet (UV) radiation under humid condition. Variation of chemical nature, color, surface roughness, gloss, and corrosion resistance of the coatings were investigated as a function of UV exposure period. It was found that in presence of nano-ZnO particles, photodegradation reactions of the aromatic polyurethane network are delayed for a longer time. Specular gloss and surface roughness values of the exposed films are in accordance to this observation too. It was found that deep cracks are formed in the films in which no nano-ZnO is present. The higher electrical resistance value of the nano-ZnO stabilized films was found to be due to the protective effect of the particles against photodegradation of the polyurethane binder.
TL;DR: In this article, the authors examined the influence of the ternary elements on the corrosion behavior using standard electrochemical techniques and proposed a relation between the NiTi-based alloys and their localised corrosion resistances.
Abstract: The goal of this study is to compare the corrosion behaviour of selected ternary nickel titanium (NiTi)-based alloys (Ni45Ti50Cu5, Ni47Ti50Fe3 and Ni39Ti50Pd11) with a binary, pseudoelastic Ni50.7Ti49.3 alloy. We examine the influence of the ternary elements on the corrosion behaviour using standard electrochemical techniques. All measurements were done in a physiological solution (0.9% NaCl) simulating a body temperature of 37 ± 1 °C. The influence of Cu and Pd addition on the surface oxide film was characterised by X-ray photoelectron spectroscopy (XPS). The results revealed that, the localised corrosion resistance of these ternary alloys is lower than the binary NiTi alloy. By comparing the different NiTi-based alloys, the following relation has been proposed for their localised corrosion resistances: NiTiCu < NiTiFe < NiTiPd < NiTi. Depth profiling by XPS showed that the surface oxide film on all the investigated NiTi-based alloys is mainly of TiO2, however, the NiTiPd and NiTiCu alloys showed metallic ternary element distributed within TiO2 layer.
TL;DR: The performance of ZnMg and ZnAl coatings for corrosion protection of steel crucially depends on a number of factors as mentioned in this paper, such as the degree of alloying.
Abstract: The performance of ZnMg and ZnMgAl coatings for corrosion protection of steel crucially depends on a number of factors. One is the degree of alloying. For instance, under standard testing conditions very promising inherent resistance against paint delamination even without conversion treatment was reported for highly Mg-alloyed zinc coatings. However, it will be shown in this work that under certain conditions very fast delamination may occur. For the much lower alloyed ZnMgAl coatings that are at the main focus of current research, as well as for lower alloyed ZnMg microstructural aspects of their corrosion performance will be discussed in more detail.
TL;DR: In this article, the anticorrosion potential of Kappaphycus alvarezii on mild steel in both 1'M HCl and H2SO4 media has been studied using weight loss method at three different temperatures, electrochemical measurements, and surface analyses.
Abstract: The anticorrosion potential of Kappaphycus alvarezii on mild steel in both 1 M HCl and H2SO4 media has been studied using weight loss method at three different temperatures, electrochemical measurements, and surface analyses. The results revealed the inhibitive effect of K. alvarezii. The inhibition efficiency was found to increase with increasing concentration of the algal extract but decreased with increase in temperature which is attributed to the physisorption. The adsorption of the extract on the mild steel surface obeys the Temkin adsorption isotherm. Further, scanning electron microscope (SEM) and atomic force microscope (AFM) analyses supported the inhibitive action of this red alga by the formation of protective layer over the mild steel surface.
TL;DR: In this article, the corrosion performance of PANI/M(with template) and MCM-41 (without template) particle was evaluated using electrochemical impedance spectroscopy (EIS) and salt spray test.
Abstract: Mesoporous MCM-41(M(with template)) whose pore channels were filled with cationic surfactant n-hexadecyltrimethyl-ammonium bromide (CTAB) and a (hydrophobic) poly(propylene glycol) nucleus terminated by two primary hydroxyl groups (Pluronic F-127, molecular weight = 11500) inside the pore channels and on the outer surface of the particle, MCM-41 (M(without template)) whose mixture template inside the pore channels and on the outer surface of the particle were calcinated, were used as new fillers for waterborne epoxy. The corrosion studies were carried out on steel plates coated with formulations containing polyaniline prepared with M(with template) and M(without template). Correspondingly, corrosion performance of the coatings was studied by electrochemical impedance spectroscopy (EIS) in 3.5% NaCl aqueous solution and salt spray test. Coatings prepared from polyaniline (PANI)/M(without template) particles synthesized by in situ polymerization were found to exhibit excellent corrosion resistance much superior to PANI/M(with template) in aggressive environments due to the different interfacial structures between the fillers and the matrix.
TL;DR: Cerium-based conversion coatings were deposited on Al 7075-T6 and characterized to determine the effect of different surface pre-treatments on the corrosion rate and surface morphology as discussed by the authors.
Abstract: Cerium-based conversion coatings were deposited on Al 7075-T6 and characterized to determine the effect of different surface pre-treatments on the corrosion rate and surface morphology. The methods of potentiodynamic polarization and scanning electron microscopy were employed. The experimental results suggest that cerium-based conversion coating is corrosion resistant in NaCl solution. Corrosion current decreased with alkaline cleaning and acid activation of aluminum surface before cerium oxide deposition. Alkaline cleaning and activation improved deposition of cerium-based conversion coatings compared to only alkaline cleaning. Analysis of the surface morphology of the coatings showed that the coatings deposited on the alkaline cleaning and acid treated panels exhibited lower visible cracks compared to coatings on only alkaline cleaned panels.
TL;DR: In this paper, the surface and cross-sectional morphologies, phase composition, and chemical composition of oxide coatings are studied by scanning electron microscopy (SEM), electron dispersion X-ray spectroscopy (EDX), XRD, and XPS.
Abstract: The need of corrosion protection for metals in aggressive environments is an issue of prime importance for widespread applications. In this article, we demonstrate the properties of oxide coatings prepared in molybdate/silicate and aluminate/silicate composite electrolytes via plasma electrolytic oxidation (PEO) on Mg–Li alloy. To understand the nature of the two coatings, the surface and cross-sectional morphologies, phase composition, and chemical composition of the coatings are studied by scanning electron microscopy (SEM), electron dispersion X-ray spectroscopy (EDX), X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS). The corrosion resistances of oxide films are evaluated using potentiodynamic polarization and electrochemical impedance spectroscopy (EIS) in 3.5 wt% NaCl solution. In contrast to Mg–Li alloy substrate, the anti-corrosion properties of the two coated alloys are both remarkably improved. Furthermore, molybdate instead of aluminate as an additive in the electrolyte brings forth a denser and compact coating, which can provide longer corrosion protection for Mg–Li alloys. Thereby a surface protection method based on PEO in molybdate/silicate electrolyte is a promising means for producing a dark brown ceramic coating on the surface of Mg–Li alloys with the capability to corrosion protection.
TL;DR: In this article, a scanning Kelvin probe (SKP) was used to investigate the corrosion potential behavior in the electrolyte droplets, and the effects of chromate-, vanadate-, and cerous-based corrosion inhibiting salts were also examined.
Abstract: Pitting corrosion of polished and etched AA7075-T6 in the presence of 3.5 wt% NaCl electrolyte was investigated both with standard full immersion testing, and under evaporating electrolyte droplets in a fixed humidity environment. The effects of chromate-, vanadate-, and cerous-based corrosion inhibiting salts were also examined. A scanning Kelvin probe (SKP) was used to investigate the corrosion potential behavior in the electrolyte droplets. During immersion testing, widespread pitting at intermetallic particles was observed in uninhibited solution. Similar but less severe attack was observed with additions of 0.03 mM vanadate and cerous ions. At higher concentration of vanadate, small numbers of very large pits were found, while higher concentrations of cerous ions provided very good inhibition. Chromate provided nearly complete inhibition of corrosion in all concentrations of immersion testing. In droplet testing, corrosion potentials measured by SKP were associated with metastable pitting, inhibition/passivation, and a form of corrosion attack in which pitting at the edge of the test droplet resulted in the formation of an adjacent, secondary droplet. A model is described for the formation of the secondary droplet and associated attack, by deliquescence of water vapor due to an excess of ions from the anode diffusing to the edge of the droplet.
TL;DR: In this article, phase analysis and composition of the spalled oxide scales and subscale alloy substrates revealed that eskolaite (Cr2O3) forms the protective scale, while SiO2 (cristobalite) is locally formed below the chromia scale.
Abstract: The oxidation behavior of Cr–Cr3(Si1−XGeX) alloys with the composition range Cr85GeXSi1−X (0 < X < 15) was studied at 1350 °C. Thermogravimetric measurements showed improved oxidation kinetics by alloying up to 2 at% of Ge, but a significant weight loss was observed when higher Ge was added. Phase analysis and composition of the spalled oxide scales and subscale alloy substrates revealed that eskolaite (Cr2O3) forms the protective scale, while SiO2 (cristobalite) is locally formed below the chromia scale. Addition of up to 2 at% altered the morphology of locally formed silica and subsequently affected the spallation of chromia scale. The morphological observations of the different chromia scales are discussed for all alloys oxidized at 1350 °C.
TL;DR: In this paper, the authors compared the fraction of each sample's surface undergoing the incubation stage or the propagation stage (higher levels of sample damage due to direct attack of the base alloy) of type II hot corrosion damage was determined.
Abstract: CMSX-4 and IN738LC, industrial gas turbine (IGT) aerofoil alloys with low (6.5 wt%) and high (16 wt%) chromium contents respectively, were exposed to type II hot corrosion conditions (700 °C, SOX in air, alkali sulphate/chloride deposits) for up to 1000 h. By comparing detailed pre- and post-exposure dimensional metrology from the samples, the fraction of each sample's surface undergoing the incubation stage (lower levels of sample damage due to the presence of a protective scale) or the propagation stage (higher levels of sample damage due to the direct attack of the base alloy) of type II hot corrosion damage was determined. Corrosion pit development under type II conditions may be described as an extreme event. As such, the transition from incubation to propagation may be modelled using Weibull statistics, which were found to give a good fit to the spread of incubation lifetimes in the exposed IN738LC samples. Much shorter incubation lifetimes were found for the lower chromium content alloy (CMSX-4). Propagation rates for CMSX-4 were found not to be constant over time. Instead, when exposed to the higher deposition fluxes, the propagation rates fell after long exposure times as the resultant deposit/corrosion product inhibited the transportation of reactive species. This improved, quantitative understanding of the transition from incubation to propagation damage under type II hot corrosion conditions will assist in the development of quantitative hot corrosion damage models, enhancing IGT component lifetime prediction.
TL;DR: In this paper, the authors investigated the oxidation behavior of a combination of commercial and model alloys with and without the presence of synthetic coal ash at 600 and 650°C, respectively, and showed that higher CO2 contents with oxy-firing do not increase the rate of oxidation.
Abstract: Because of higher CO2, and possibly H2O and SO2, levels in the boiler, there are concerns about increased corrosion rates after retrofitting current coal fired boilers from air-firing to oxy-firing to assist in CO2 capture. The oxidation behavior of a combination of commercial and model alloys were investigated both with and without the presence of synthetic coal ash at 600 and 650 °C. At 600 °C, a CO2–H2O environment showed the most rapid oxidation rate for Fe-based alloys with <20% Cr and varying the CO2 content or adding a 0.15% O2 buffer had little effect on the mass change. However, at 650 °C, the O2-buffered CO2–H2O environment showed a similar rate of oxidation as 100% H2O, again requiring more than 20% Cr for a thin protective Cr-rich oxide to form. With synthetic coal ash, increasing the CO2, H2O, and/or SO2 levels in the gas phase tended to show a lower oxide thickness after a 500 h exposure at 600 °C, compared to the base line air-firing condition. At 650 °C, no systematic increase in the reaction rate was observed when switching from the air firing to the oxy-firing gas. These simulations suggest that higher CO2 contents with oxy-firing do not increase the rate of oxidation.
TL;DR: In this article, the dew point corrosion and viscous ash deposits at different temperature ranges are proposed to instruct engineering application for a boiler of a 1000MW pulverized coal-fired power plant for 150'h.
Abstract: Characteristics of the deposits and oxide films formed on 316L stainless steel in situ tested on a boiler of 1000 MW pulverized coal-fired power plant for 150 h were examined. The results show that the deposits are mainly composed of outer fly ash, middle sulfate, and chloride and fluoride in the inner layer. Oxide films are mainly Fe2O3 and Fe3O4. Two models of coupling mechanism of dew point corrosion and viscous ash deposits at different temperature ranges are proposed to instruct engineering application.
TL;DR: In this article, high purity chromium was reacted at 950°C in flowing mixtures of N2H2-H2O, N2-O 2-H 2O and Ar-O2, and the results were interpreted in terms of inward oxygen transport via a hydrogen bearing species, and uptake by the scale of this species.
Abstract: High purity chromium was reacted at 950 °C in flowing mixtures of N2-H2-H2O, N2-O2-H2O and Ar-O2. All gases produced an outer scale of Cr2O3. In addition, an underlying layer of Cr2N grew during reaction with N2-O2. As a result, the overall chromium consumption rate was significantly faster in N2-1O2 than in Ar-1O2 (gas compositions in vol%). Additions of water vapour to N2-1O2 slowed the rate of nitride growth, and nitridation was completely suppressed at a level of 10% H2O(g). Conversely, water vapour additions accelerated chromia growth rates. Reaction in N2-H2-H2O led to chromia scaling at rates faster than in dry N2-O2, but no nitride formation occurred. The results are interpreted in terms of inward oxygen transport via a hydrogen bearing species, and uptake by the scale of this species in a way which excludes nitrogen.
TL;DR: In this paper, the effect of activation treatment with nickel acetate on the microstructural evolution and corrosion resistance of the zinc phosphate coating on mild steel was studied, and the chemical composition and morphology of the coatings were analyzed via scanning electron microscopy (SEM) and energy-dispersive spectroscopy (EDS).
Abstract: Zinc phosphating is a chemical conversion process that has been widely used in industry for corrosion protection and primer for painting. In this investigation, the effect of activation treatment with nickel acetate on the microstructural evolution and corrosion resistance of the zinc phosphate coating on mild steel was studied. The chemical composition and morphology of the coatings were analyzed via scanning electron microscopy (SEM) and energy-dispersive spectroscopy (EDS). The corrosion resistance of the coatings was evaluated using polarization curves and electrochemical impedance spectroscopy (EIS) in an aerated 3.5% NaCl solution. Surface morphology observations revealed that the activation treatment increased the population density and refined the grain size of the coating.The electrochemical results showed better barrier protection characteristics and corrosion resistance for activated phosphate coatings compared with inactivated coatings.
TL;DR: In this paper, a ternary Ti-15Zr-5Nb alloy was elaborated with the aim to satisfy the most stringent requirements of a good implant material, showing a more compact, resistant passive film formed on the new alloy surface.
Abstract: A new ternary Ti–15Zr–5Nb alloy was elaborated with the aim to satisfy the most stringent requirements of a good implant material. The alloy has α + β bi-phase microstructure (by XRD and optical microscopy) and presents a proper combination between Young's modulus, elasticity and good ultimate tensile strength and 0.2% yield strength (from stress–strain tensile curve), indicating a good suitability as implant material. Electrochemical behaviour in artificial Carter-Brugirard saliva of different pH values (3.96, 7.84, and 9.11) and composition (un-doped and doped with 0.05 M NaF) that simulate the severe functional conditions in the oral cavity was evaluated. All electrochemical parameters of the new alloy revealed more favourable values than those of the CP Ti and Ti–6Al–4V ELI alloy, showing a more compact, resistant passive film formed on the new alloy surface. The corrosion rates and corresponding ion release rates for the new Ti–15Zr–5Nb alloy exhibited very low values (hundreds of times smaller) in comparison with similar commercial biomaterials. Electrochemical impedance spectra distinguished bi-layered passive film formed by inner, barrier layer and outer, porous layer. X-ray photoelectron spectra and scanning electron microscopy (SEM) observations proved that in time, protective compounds were deposited from saliva on the alloy surface, enhancing its corrosion resistance.
TL;DR: In this paper, the corrosion inhibition of 2-amino thiazole (AT) for 45# steel in 0.1 M HCl solution was studied by means of weight loss, potentiodynamic polarization, electrochemical impedance spectroscopy (EIS), and scanning electron microscopy (SEM) methods.
Abstract: The corrosion inhibition of 2-amino thiazole (AT) for 45# steel in 0.1 M HCl solution was studied by means of weight loss, potentiodynamic polarization, electrochemical impedance spectroscopy (EIS), and scanning electron microscopy (SEM) methods. Quantum chemical calculations based on the density functional theory (DFT) method were performed on AT. The results showed that the corrosion inhibition efficiency of 2-amino thiazole was excellent, and its corrosion inhibition efficiency could reach 90.34% at 500 mg/L. The results obtained from the weight loss experiment and electrochemical experiments were in good agreement. Potentiodynamic polarization study showed that the 2-amino thiazole was a mixed-type inhibitor. And the slow-release process was controlled by electro transfer steps. The electronic properties obtained by quantum chemical approach were correlated with the experiment results.
TL;DR: In this article, the hot-dip galvanizing coating ZnAl2Mg2 was tested against the reference material Zn Al0.2 in nonstandardised salt spray test.
Abstract: In this work the hot-dip galvanising coating ZnAl2Mg2 was tested against the reference material ZnAl0.2 in nonstandardised salt spray test. In those tests the samples were exposed to the sodium salts of sulphate, nitrate, phosphate and acetate. The corrosion products formed on the alloys were analysed with XRD. Additionally the corrosion behaviour of the samples was investigated by studying cross-section cuts with SEM. With this information the corrosivity of the different anions in relation to chloride ions and their corrosion behaviour could be determined.