Electronic Properties Of Passive Films Research Articles

Long-term stability and electronic properties of passive film of lean-duplex stainless steel reinforcements in chloride containing mortar

The corrosion behavior, semiconducting properties and chemical composition of the passive film formed on lean-duplex stainless steel LDSS 2001, LDSS 2304 and AISI 304 reinforcements embedded in OPC mortar containing chloride, 0, 0.4, 2 and 4 wt% Cl−; after 2.5 years were studied. The Ceff,film of LDSS 2001 remained constant at 3 × 10−5 F/cm2 for all Cl− concentrations. Flat-band potential, EFB,A, of LDSS 2001 increased with the Cl− concentration, suggesting a Cr2O3 film more prone to accept electrons, reducing the vacancy density. The enrichment in chromium in the passive film of LDSS 2001 after 2.5 years increases from 44% to 61%.

Electrochemical Properties of Passive Film Formed on Supermartensitic Stainless Steel in a Chloride Medium

The electrochemical behavior and the electronic properties of passive films formed on a super martensitic stainless steel (SMSS) used in oil and gas industries were investigated in aqueous 0.6 M and 2.1 M NaCl solutions with additions of sodium acetate and acetic acid (pH 4.5). Open-circuit potential transients, electrochemical impedance spectroscopy, cyclic voltammetry, and x-ray photoelectron spectroscopy were measured to characterize the passive film formed on SMSS. The electrochemical behavior of the steel in an aqueous solution of 0.6 M NaCl presented the highest pitting potential and the highest polarization resistance in relation to the NaCl/NaAc solution. The passive film of SMSS in an aqueous solution of NaCl presented a thickness of 18.40 nm, three times the thickness of the oxide film in NaCl/NaAc, and consisted of FeO, Cr2O3, MoO2, and spinels such as FeCr2O4 species that are a p-type semiconductor, but may also contain a small fraction of the Fe2O3 and MoO3 oxides. Additionally, it was shown that the passive layer after immersion in a saline solution also contains hydroxides such as FeOOH and Cr(OH)3.

Role of Molybdenum on the Electronic Properties of Passive Films on Stainless Steels

Potentiostatic polarization of different stainless steel grades with a mirror surface finishing was performed in order to investigate the role of Mo on stainless steels corrosion behaviour. In the attempt to gain more insight into transpassive dissolution mechanism, passive films were grown in neutral aqueous solution (pH ∼ 7) at different polarizing potentials ranging from passive to transpassive conditions. According to the photoelectrochemical characterization, Cr dissolution occurs even at low polarizing potentials in the case of AISI 304L, while higher band gap values were obtained for passive films grown on austenitic 316L and duplex SSs. Capacitance measurements suggest that the flat band potential values estimated for passive films grown on austenitic 316L and duplex SS are more noble if compared to that of AISI 304L at all polarizing potentials. This is rationalized by considering that passive films on 316L and duplex are doped with Mo during film growth, changing their electronics properties (band gap and flat band potential) with a consequent shift to more positive value of the potential for chromate formation and dissolution.

Molybdenum Addition Enhancing the Corrosion Resistance of Ni16Cr Alloy in Aqueous Solution

The influences of Mo on the structures and the electronic properties of passive films on Nil6CΧMo (Χ=0wt.%, 2wt.%, 5wt.%, 8wt.%, 12wt.% and 16wt.%) alloys in pH 1.0 sulfuric acid solution, pH 8.5 borate buffer solution and pH 13 sodium hydroxide solution were investigated using X-ray photoelectron spectroscopy (XPS), potentiodynamic polarization curve, Electrochemical impedance spectroscopy (EIS) and Mott-Schottky plot. The results showed that the addition of Mo can evidently refine the microstructure of Ni16Cr alloy, and the grain size sharply decreased with increasing Mo. Ni16Cr alloy was passivated in pH1 sulfuric acid solution, pH8.5 borate buffer solution and pH13 sodium hydroxide solution, each passive current density decreased and each passive potential region enlarged with the increment of Mo. XPS results showed that the passive films on Ni16CΧMo alloys were mainly composed of the inner Cr2s3 layer and the outer NiO layer with a little amount of Cr2S3, NiS and NiSO4. The resistances and compactness of the passive films on Ni16Cr alloy in the three solutions increased with the increased Mo, which implyed the enhanced protection of the passive film. Mott-Schottky plots revealed that the passive film on Ni16Cr alloy appeared the p-n heterojunction, the defect number of the outer film increased with the increment of Mo, while for the inner film, the defect number decreased with Mo, while the total protection of the passive films to the metal matrix was improved with increasing Mo.

Semiconductor properties of passive film and corrosion resistance of 2205 duplex stainless steel joint welded by laser hybrid welding

Purpose There are obvious differences in corrosion resistance of different 2205 welding joints with different ratios of austenite and ferrite, from the top to the bottom, the austenite content decreased gradually while the ferrite increased. In each region of welded joint, the pitting resistance number of ferrite is higher than that of austenite; pitting corrosion is more likely to occur in austenite phase first on the top region of the weld and in the secondary phase precipitates on the other regions of the weld. The fluctuation of the ratio of austenite and ferrite has a great influence on performance of passive film in 3.5 per cent NaCl solution. Design/methodology/approach To study the corrosion behavior of welded joint, the samples were obtained by laser hybrid welding. Pitting corrosion was studied in different area of welded joint. The Mott–Schottky curves of welded joints were measured to study the passive film on the different welded joint area. Findings Due to the difference of heat input and the limit of filler depth of the wire, the microstructure of duplex stainless steel laser welding joint has obvious difference in the thickness direction. In addition, there will be harmful secondary phase (such as chromium nitride and σphase) precipitates in the lower part of the joint. For the welded joint, the corrosion resistance decreases with the increase in the difference of the microstructure. Pitting corrosion usually takes the two phases as the nucleation point and grows up. The surface of 2205 duplex stainless steel laser hybrid welding joint cannot form a complete passive film in 3.5 per cent NaCl solution, and the more the ratios of austenite and ferrite deviate from equilibrium position (50:50), the worse the performance of passive film is. Originality/value In this paper, the authors attempt to establish the correlation between the semiconductor electronic properties of passive film and the difference of microstructures and the component in a joint welded by laser hybrid welding. The effect of passive film on the corrosion resistance of the weld was further investigated.

Improved corrosion resistance of 316LN stainless steel performed by rotationally accelerated shot peening

Rotationally accelerated shot peening (RASP) technology was used to produce nanocrystallines and twins on the surface of 316LN stainless steel. Electrochemical corrosion experiments were carried out on the RASP-processed 316LN SS specimens in the 3.5 wt% NaCl solution. Improved passivity and better electronic properties of passive films were observed on the RASP-processed specimens. The experimental results showed that the structure with nanocrystallines and a high density of twins produced by the RASP process can provide more nucleation sites, adhesion work and homogeneous capillary force to improve the uniformity and compactness of the passive film, resulting in a better corrosion resistance.

Effect of various ratios of nitric acid – chloride on electronic properties of passive films on AISI 304L stainless steel

AbstractIn this study, the electrochemical behavior of 304L SS stainless steel in various nitric acid/chloride ratios was investigated. The characteristics of the passive film, formed at the open circuit potential (OCP) and at the passive potential (0.65 V vs SCE) were also compared. OCP results show that a stable passive film formed over the surface with higher nitric acid/chloride ratios. Potentiodynamic polarization curves and electrochemical impedance spectroscopy (EIS) measurements showed that with higher nitric acid/chloride ratios, the film resistance increases (R1) for OCP, passive potential, and the critical current density (icrit) and corrosion rate (icorr) decreases. Mott–Schottky analysis revealed that the film formed at OCP shows n-type behavior for 0.01 N and 1 N concentration and shows p-type behavior for 0.1 N nitric acid concentration. At 0.65 V (vs. SCE) of film formation potential, the film formed in 1 N concentration shows n – type behavior. In 0.01 N and 0.1 N acid concentration, p-type behavior has been observed. Also, according to Mott–Schottky analysis, it was found that a lower defect density was found in 0.1 N nitric acid, for both the potentials. X-ray photoelectron spectroscopy spectra show evidence that the surface contains Fe and Cr as major elements. However, at OCP, Fe2O3was the main constituent of the passive film, whereas the passive potential film was rich in Cr2O3. In addition, nitrogen and chloride were adsorbed in the passive film at passive potential.

Correlation between Electrical Properties of the Passive Film on Carbon Steel and Inhibition Efficiency by Phosphate and Nitrite Ions

The electronic properties of passive films grown at open circuit potential for 24 h and 7 days in pore simulating solutions are correlated to the inhibiting effect of nitrite and phosphate ions in chloride-rich alkaline solutions. Electrochemical impedance and Mott-Schottky plots were used to investigate the electronic properties of the films grown. Changes in composition were analyzed by X-ray photoelectron spectroscopy. Both anions are excellent inhibitors. However, the donor density (ND) decreases when nitrites are incorporated and remains constant when phosphates are added. ND increases with ageing time. These differences are interpreted in terms of the composition of each surface layer.

(Olin Palladium Award of the Electrochemical Society Address) Corrosion Mechanisms at the Atomic or Nanometric Scale

In this Award Lecture I will emphasize a surface science approach that allows to reach a deep understanding of the mechanisms of corrosion at the atomic or nanometric scale. I will show the link between atomic/nanometric scale mechanisms and the macroscopic corrosion manifestations. The lecture will include the combined experimental approaches using advanced surface analytical and electrochemical methods with theoretical approaches based on atomistic modeling. The high resolution techniques used in combination with classical electrochemical methods will be presented, high resolution meaning high space resolution, as achieved by near field microscopies (Scanning Tunneling Microscopy and Atomic Force Microscopy), high energy resolution in electron spectroscopy for chemical analysis, and high mass resolution for surface molecular analysis by Time-of-Flight Secondary Ions Mass Spectrometry.The formation of the metal-water interface occurring when a metal surface is exposed to water, which has been investigated by in situ Scanning Tunneling Microscopy, will be presented.A major part of this address will be devoted to passivity of metals and alloys, a central issue in corrosion science and engineering since the formation of ultra-thin surface oxide films is the best of all means for protection of metallic materials against corrosion. I will discuss the growth mechanisms, the nanostructure, and the electronic properties of passive films, as well as passivity breakdown and initiation of localized corrosion, with emphasis on atomic and nanoscale data. Cathodic reactions on oxidized metal surfaces will then be discussed, with a theoretical approach of the di-oxygen reduction on surface oxide films on Al surfaces using DFT.Finally I will mention recent work on corrosion inhibition by adsorbed organic molecules, an area in which progress has been recently achieved by combining quantum chemical calculations (DFT) with experiments.

Electrochemical study of passive films formed on welded lean duplex stainless steel

Duplex stainless steel (DSS) has been considered as an excellent material of construction for applications where high corrosion resistance and high mechanical strength are required. The use of this material can minimize costs related to corrosion in different industries, for example, in the biodiesel industry. The objective of this study is to evaluate the electrochemical and electronic properties of passive films of thick welded joints of UNS S32304 lean duplex stainless steel (LDSS) fabricated by different welding processes, in acidified glycerin, a byproduct of the biodiesel industry. The electrochemical and electronic behavior of the passive films formed on UNS S32304 LDSS was evaluated using electrochemical impedance spectroscopy and Mott–Schottky measurements. The capacitance study shows that the passive films formed on welded DSS behave as n‐ and p‐type semiconductors above and below the flat band potential, respectively. Furthermore, the samples welded by the gas metal arc welding process exhibited better corrosion resistance than other welding process using the same filler metal.

Effects of pH value and temperature on the corrosion behavior of a Ta2N nanoceramic coating in simulated polymer electrolyte membrane fuel cell environment

To improve the corrosion resistance and electrical conductivity of Ti-6Al-4V bipolar plates used in polymer electrolyte membrane fuel cells (PEMFCs), a novel electro-conductive Ta2N nanoceramic coating was developed by reactive sputter-deposition using a double cathode glow discharge plasma technique. The microstructure of the coating consisted of fine equiaxed Ta2N grains with an average grain size of ∼13nm, which exhibited a strong (101) preferred orientation. To explore the influence of both pH values and temperatures on the corrosion resistance of the coating, the electrochemical behaviors and electronic properties of passive films grown on the Ta2N coating were systematically investigated using different electrochemical techniques in simulated PEMFC operating environment. It was shown that either increasing the acidity or the temperatures of the solution, the corrosion potential (Ecorr) decreased and the corrosion current density (icorr) increased. At a given temperature or pH value, the Ta2N coating had a higher Ecorr and lower icorr as compared with uncoated Ti-6Al-4V. The results of EIS measurements showed that with increasing temperature or acidity of the solution, the resistance of the passive film (Rp) formed on the Ta2N coating decreased slightly, being of the order of magnitude of 107Ωcm2, which was an order of magnitude higher than that of uncoated Ti-6Al-4V. The interfacial contact resistance (ICR) values were found to increase with increasing pH value or decreasing solution temperature, and the ICR values of the Ta2N coating were markedly lower than that of uncoated Ti-6Al-4V, due to the thinner thickness of passive films. Furthermore, the Ta2N-coated Ti-6Al-4V is more hydrophobic than bare Ti-6A1-4V, which was favorable for both the simplification of water management and improving corrosion resistance in PEMFC operating environment.

Borate 완충용액에서 알루미늄의 산화피막의 생성과정과 전기적 성질에 대한 대기의 영향

In a borate buffer solution, the growth kinetics and the electronic properties of passive film on aluminum were investigated, using the potentiodynamic method, chronoamperometry, and multi-frequency electrochemical impedance spec- troscopy. The corrosion of aluminum was heavily influenced by the degree of oxygen concentration because of the increasing reduction current. The oxide film formed during the passivation process of aluminum has showed the electronic properties of n-type semiconductor, which follow from the Mott-Schottky equation. It was found out that the passive film (Al(OH)3) of Al formed in the low electrode potential changes to Al2O3 while the electrode potential increases. The growth kinetics data as measured by chronoamperometry suggests a mechanism in which the growth of the film of Al2O3 is determined by field-assisted trans- port of ions through the film.

Electronic properties of passive films from the multi-frequency Mott–Schottky and power-law coupled approach

The electronic properties of the passive film formed on pure chromium in an acidic sulfate medium at 30°C was studied by using the multi-frequency Mott–Schottky approach and the point defect model. Conversely to common Mott–Schottky experiments, the relevance of the multi-frequency Mott–Schottky analysis relies on the determination of the space charge capacitance from a large frequency range impedance diagram. To analyze the Constant-Phase-Element behavior commonly observed for the impedance diagrams which characterize the passive film, the power-law model was used and allowed to determine the space charge capacitance. The consistency of the results showed that it was relevant to combine the power-law model to the predictive point defect model. The aim of this study is to extract the semi-conductive parameters of a passive film from impedance measurements using a sensitive analytical method.

The effect of simulated concrete pore solution composition and chlorides on the electronic properties of passive films on carbon steel rebar

Effects of simulated concrete pore solution composition, pH, and added chlorides on electronic properties of passive films on carbon steel rebar were investigated using Mott–Schottky (M–S) analysis. Passive films showed n-type semiconductive behavior with two discrete donor species and high donor densities. Deep donor densities increased with increasing passivation time. Less protective films resulted in lower space charge capacitances and lower flatband potentials. Sulfates had little influence on electronic properties. Chlorides caused a loss of linearity of M–S plots. This loss of linearity required higher chloride levels and longer exposure times to occur in higher pH solutions.

Metastable pitting and its correlation with electronic properties of passive films on Sn–xZn solder alloys

The potentiostatically formed passive films on Sn–xZn solder alloys in NaCl solution was investigated by potentiostatic polarization and electrochemical impedance spectroscopy (EIS). Metastable pitting is quantitatively assessed in terms of pit size and frequency, which are found increase with Zn content. EIS results indicate the presence of transport behavior of charge species within the films. The Mott–Schottky analysis reveals that the passive films all behave as a highly disordered n-type semiconductor. The electronic properties of the passive films are greatly associated with metastable pitting susceptibility. The correlation between the stability and the electronic properties of the passive films is discussed.

Influence of Cr on the electronic properties of passive film on B30 alloy in NaOH solution

The influence of Cr on the electronic properties of the passive film on B30 alloy in NaOH solution was studied via electrochemical impedance spectra(EIS), potentiodynamic curve and Mott-Schottky plot. The Cr doped in the passive film on B30 alloy was detected by X-ray photoelectron spectroscopy(XPS). XPS results show that Cr2O3 appeared on the passive film, which implied the enhanced anti-corrosion of B30 alloy. The passive film showed a p-type semi-conductive character. The acceptor density(NA) was in an order of magnitude of 1022 cm−3, and NA decreased with the increment of Cr. EIS results show that the film resistance(Rf) increased with increasing the amount of Cr. The diffusion coefficient(D0) was calculated to be in a range of 10−16−10−17 cm−2/s on the basement of point defect model(PDM).

Semiconductive Properties of Passive Films on Carbon Steel Rebar in Highly Alkaline Environments

In the highly alkaline environment of concrete, carbon steel rebar is protected against corrosion by a passive oxide/oxyhydroxide film. Understanding the characteristics of this passive film, and how it depassivates, is the key to mitigate problems associated with steel corrosion in concrete. Although a large number of electrochemical and analytical studies have been conducted on the passivity of steel in concrete, current mechanistic models do not explain all experimental observations about the chloride-induced depassivation process. One area that is not studied extensively is the electronic properties of passive films which show semi-conductive properties; a better understanding of these properties will provide additional information to improve the mechanistic models for chloride-induced depassivation of carbon steel in concrete. The present study uses Mott-Schottky (M-S) analysis along with other electrochemical techniques to study the electronic properties of passive films that form on carbon steel exposed to simulated concrete pore solutions. Both passivation and chloride-induced depassivation processes are investigated, and changes in electronic properties during these processes are monitored. The main parameters of the study include the concrete pore solution composition, pH, and chloride amount. Challenges of using M-S analysis to study the electronic properties of passive films will also be discussed.

Modeling Electronic Properties of the Passive Films on Carbon Steel in Simulated Concrete Pore Solutions

The performance of five existing models for predicting the electronic properties of passive oxide films on carbon steel that are exposed to synthetic alkaline media representing concrete pore solutions was investigated. It was found that the two donor band model, which is based on the presence of two discrete donor bands each with a Gaussian distribution of energy states for an n-type semiconductor, most accurately predicts experimental measurements. The model supports the experimental data that show an increase in the deep donor density and width of the deep donor band with increasing passivation time. A comparison of films formed in different passivating solutions revealed the potential of this model to predict the passive film electronic properties in environments not yet studied experimentally.

Electrochemical Characterization of Passive Films on Ni-Based Alloys in Acidic and Neutral Solutions

The present work reports the structure, chemical composition and electronic properties of passive films formed on Alloy 600 and Alloy 690 in borate buffer and sulfuric acid solutions. Photoelectrochemical response from passive films varied depending on the alloy substrates and the solutions. XPS analysis revealed that the passive films formed on Alloy 600 and Alloy 690 consisted of an outer hydroxide layer and an inner oxide layer in the borate buffer solution as well as the sulfuric acid solution. The chemical composition of the layers was relatively different depending on the solutions, that is, more Fe was incorporated into the passive films formed in the borate buffer solution. [doi:10.2320/matertrans.M2014384]

Borate 완충용액에서 니켈 산화피막의 생성 과정과 전기적 성질

Borate 완충용액에서 Ni의 부동화 피막의 생성과정(growth kinetics)과 부동화 피막의 전기적 성질을 변전위법, 대 시간 전류법 그리고 단일 주파수 또는 다중 주파수 전기화학적 임피던스 측정법으로 조사하였다. 이때 생성되는 산화피막은 Mott-Schottky 식이 적용되는 p-형 반도체 성질을 보였으며, 낮은 전극전위에서 생성되는 Ni의 부동화 피막 <TEX>$Ni(OH)_2$</TEX>는 전극 전위가 증가하면서 NiO, NiO(OH)로 변화되는 것을 알 수 있었다. In a borate buffer solution, the growth kinetics and the electronic properties of passive film on nickel were investigated, using the potentiodynamic method, chronoamperometry, and single- or multi-frequency electrochemical impedance spectroscopy. The oxide film formed during the passivation process of nickel has showed the electronic properties of p-type semiconductor, which follow from the Mott-Schottky equation. It was found out that the passive film (<TEX>$Ni(OH)_2$</TEX>) of Ni formed in the low electrode potential changes to NiO and NiO(OH) while the electrode potential increases.