Compositional analysis of passivating surface film formed on carbon electrode in organic electrolytic solution using in-situ spectroelectrochemical technique

In-situ spectroelectrochemical technique has been applied to investigate passivating surface film on porous carbon electrode and plasma enhanced chemical vapour deposited (PECVD) carbon film electrode in organic electrolytic solution consisting of ethylene carbonate (EC) and diethyl carbonate (DEC) solvent, and 1 M LiPF₆ and LiAsF₆. Water impurity with the concentration of 0 M, 0.02 M, 0.05 M, and 0.1 M H₂0 was added to 1 M LiPF₆-EC/DEC solution. In-situ Fourier transform infra-red (FTIR) spectra of the surface film on both electrodes with the constituents of ROCO₂Li, Li₂CO₃, and Li_xPF_y suggested that the reduction of EC to ROCO₂Li runs via a one-electron transfer pathway as a result of diffusion of water through the surface film, and then Li2CO3 formation proceeds simultaneously by the chemical reaction of ROCO₂Li with water. From the measured potential dependence of the amount of the salt reduction products, it is suggested that the surface film formed in 1 M LiPF₆EC/DEC solution gives a poorer passivity as compared with that formed in 1 M LiAsF₆-EC/DEC solution, which is due to the considerable interference of LiPE₆ salt reduction with the compact sedimentation of ROCO₂Li on the electrode. In-situ FFIR spectra of the surface film showed that all the peak intensities of the three constituents significantly increase with increasing water content under application of the negative potentials with respect to open circuit potential (OCP). From these experimental results, the dependence of the passivity of the surface film on the carbon electrode on the water concentration of the electrolyte, as well as on the lithium salt type, was discussed in view of the salt and solvent reactivities.     

The characterization of the thin oxide film formed over Fe3C at 300°C

The oxide formed over polished iron-carbon alloys at 300°C and in a 100 Torr dry oxygen atmosphere was primarily due to the oxidation of the ferrite phase, but a thin protective oxide film ( 150 Å) was formed on the carbide phase. The protective nature was attributed to the existence of a kinetic barrier of CO and CO₂ at the carbide-oxide interface. The initial oxide film formed on the carbide phase comprised many small, randomly oriented crystallites; approximately 70 Å in size, of -Fe₂O₃. This film then underwent a grain growth process via a strain-induced grain boundary migration accompanied by a phase transformation from -Fe₂O₃ to -Fe₂O₃. This transformation produced a tensile stress in the oxide film which was later relieved by the generation of cracks along the newly grown grain boundaries. These cracks exposed fresh carbide surface, released the gas barrier at the carbide-oxide interface, and provided rapid diffusional paths for further oxidation. As a result, the oxide film (-Fe₂O₃) was reduced to Fe₃O₄ and raised ridges appeared at the crack sites. Once the cracks were healed, the film again became protective.This research was supported by grant number DA-18-035-98(A) from the Chemical Research Laboratory, Edgewood Arsenal, Department of the Army. This paper is based on work performed as part of a thesis submitted by H. J. Kim to Lehigh University in partial fulfillment of the requirements for the Ph.D. degree in Metallurgy and Materials Science.     

The coloured film formed on stainless steel in hot chromic/sulphuric acid solution

The coloured film formed on stainless steel in a hot concentrated solution containing chromic and sulphuric acids has been studied by producing ultramicrotomed sections and examining them by transmission electron microscopy. The sections of the film, for a given treatment time, are relatively uniform in thickness and texture, with no well-defined parallel-sided pores. The film is composed of crystallites of size within the range 6–14 nm giving rise to a tortuous network of interlinking pathways of effective length about twice the film thickness.     

Characterization of the passive film formed on weathering steels

Raman spectroscopy, infrared spectroscopy and electrochemical reduction techniques were used to characterize the passive film formed on weathering steels. Test pieces of weathering steel were exposed to an industrial environment for 4.5 and 8 yrs. In both cases the passive film was composed predominantly of 8-FeOOH with 10–20% γ-FeOOH and possibly some α-FeOOH. Raman spectra from different depths of the surface were identical which implied that the film composition was homogeneous.     

铅阳极膜的半导体性能

利用微分电容法结合Mott-Schottky理论研究铅电极1.28V(vsSCE)下硫酸溶液中所形成阳极腐蚀膜的半导体性质,同时对测试频率、成膜时间及成膜溶液pH值等影响膜半导体性能的因素也做了分析。结果表明:铅阳极膜具有n型半导体特性,施主密度ND随测试频率的增加而减小,随极化时间的延长而增加,随溶液pH值的增加而减小。溶液pH值的改变可以显著影响膜的平带电位EFB,两者间呈线性关系,拟和斜率为60.43。     

Electrochemical characterization for polybithiophene film on porous oxide layer of 304 stainless steel formed by square wave passivation

A bilayer coating was prepared by electrodepositing a polybithiophene (PBT) film on the top of square wave passivated 304 stainless steel (304SS). The structure of the PBT layer was characterized by FTIR spectroscopy and suggested to be composed of α–α coupling thiophene units. The electrochemical properties of the coating were investigated in 1 mol/L sulfuric acid solution by anodic polarization and electrochemical impedance spectroscopy measurements. The results indicated that the bilayer could provide an effective barrier and maintain the metal substrate in a passive state during the immersion time. The interfacial shear strength of the polythiophene film on untreated and passivated 304SS were 0.81 and 5.1 MPa, respectively. The better result given by treated one may be due to PBT growing within the pores formed on the square wave passivated 304SS.     

New functionalized 3-(alkyl)thiophene derivatives and spectroelectrochemical characterization of its polymers

Three novel 3-[ω-(p-methoxyphenoxy)alkyl]thiophene monomers were synthesized and electrochemically polymerized on ITO electrodes by potentiodynamic or potentiostatic methods. Potentiostatic deposition provided films with better stabilities and had smaller quantities of soluble oligomers formed during polymerization. We also observed that derivatives with shorter alkyl chains in the substituted thiophene are difficult to polymerize by electrochemical methods. Spectroelectrochemical characterization of the polymer films obtained showed that their colors depend on the alkyl chain length in the substituted monomer. This demonstrates that the electrochromic behavior of these polymers can be tailored by means of the chemical synthesis of the monomers. The electrochromic properties presented by these new polymers motivate their future application in electrochromic devices.     

Electropolymerization of PANI coating in nitric acid for corrosion protection of 430 SS

A smooth and adherent polyaniline (PANI) coating was electropolymerized in HNO₃ solution by cyclic voltammetry in order to protect the ferritic and economic 430 stainless steel (SS) from corrosion. The corrosion resistance was evaluated in 3.5 wt.% NaCl solution by anodic polarization, potentiodynamic polarization, and electrochemical impedance spectroscopy. The PANI coating shifts the corrosion potential of SS to the passive region and provides a strong and steady corrosion resistance. A low growth rate leads to a compact PANI coating that acts as a good physical barrier. However, the strong corrosion inhibition is mainly attributed to the dense oxide layers formed by the catalytic effect of PANI at the polymer/metal interface. The composition of the oxide layers was analyzed via depth profiling using X-ray photoelectron spectroscopy alternating with sputtering. Compared with layers formed on uncoated SS, the iron and chromium oxide layers under the PANI are thinner and denser, absorbing less oxygen, and providing a stronger corrosion inhibition.     

柠檬酸对腐蚀铝箔高压阳极氧化膜微观结构与电化学性能的影响(英文)

将高压铝电解电容器用腐蚀铝箔与沸水反应,然后再在硼酸溶液或硼酸-柠檬酸混合酸溶液中进行530V高压阳极氧化制得耐压薄膜,应用透射电镜(TEM)、X射线衍射(XRD)研究不同电解液所形成的高压阳极氧化膜的微观结构与结晶程度,利用电化学交流阻抗(EIS)、LCR数字电桥与小电流充电测试阳极氧化膜的电化学性能。结果表明:高压阳极氧化膜具有明显层状结构,内层结晶程度较高、外层结晶程度较低;与单纯硼酸溶液所形成的氧化膜相比,混合酸液所形成的阳极氧化膜的外层结晶程度与晶粒平均尺寸较大,抗电场强度与比电容均比较高,但相变使得氧化膜外层微观缺陷密度增多,氧化膜比电阻与耐电压值有所降低。     

Electropolymerization mechanism of N-methylaniline

A poly(N-methylaniline) (PNMA) film was obtained by chronoamperometry on tin oxide (TO) in dimethylformamide DMF containing 0.5 M sulphuric acid. The PNMA film formation was monitored by in situ UV–vis spectroscopy. A detailed electropolymerization mechanism and reaction pathway of N-methylaniline (NMA) is proposed based on mass spectroscopy (MS) and NMR analysis. The NMA repeating units (both in the film and in the soluble part) were found to be partially dealkylated during electropolymerization. NMA was also electropolymerized in different solvents such as propylene carbonate (PC) and acetonitrile (ACN). Our results show that protonation is not a necessary condition to initiate the electropolymerization of NMA, but it may play a key role for the propagation of longer conjugated chains. The influence of solvents on the film formation and the function of protons are discussed in this paper.     

Detrimental role of LiOH on the oxide film formed on Zircaloy-4

To understand the degradation behavior of Zircaloy-4 corroded in LiOH aqueous solution, X-ray diffraction was performed to analyze the crystal structure of Zircaloy-4 oxide formed in three different media. Second ion mass spectrometry (SIMS) was utilized to measure the penetration of Li⁺ and OH⁻ into the oxide film when Zircaloy-4 is exposed in LiOH aqueous solution. It was found that the SIMS depth profile of OH⁻ in the oxide film is in accord with that of Li⁺, which indicates that there exists OH⁻ in the oxide film. Based on the results, it is put forward that OH⁻ diffuses faster than O⁻² in the oxide films, which can enhance the corrosion rate of Zircaloy-4 and the transformation from tetragonal zirconia (t-ZrO₂) to monoclinic zirconia (m-ZrO₂). OH⁻ plays a detrimental role on the oxide film formed on Zircaloy-4.     

Corrosion behavior and surface film characterization of TaNbHfZrTi high entropy alloy in aggressive nitric acid medium

Corrosion behavior of TaNbHfZrTi high-entropy alloy (HEA) was investigated in nitric and fluorinated nitric acid at ambient (27 °C) and boiling (120 °C) conditions. The alloy passivated spontaneously during potentiodynamic polarization in 11.5 M HNO₃ at ambient condition. The corrosion rate was negligible in boiling 11.5 M HNO₃, exposed for 240 h. Scanning electron microscopic (SEM) studies did not show any significant corrosion attack. The high corrosion resistance of TaNbHfZrTi HEA was attributed to its single phase bcc structure. X-ray photoelectron spectroscopic (XPS) analysis revealed that the protective passive film formed in boiling nitric acid was predominantly composed of Ta₂O₅, in contrast to the presence of ZrO₂ and HfO₂ in air-formed native film. Potentiodynamic polarization studies indicated a pseudo-passivation behavior of the HEA in 11.5 M HNO₃ + 0.05 M NaF at ambient condition. In boiling fluorinated nitric acid, SEM images of TaNbHfZrTi HEA displayed a severely corroded morphology indicating the instability of the metal-oxides of the alloying elements. XPS investigations confirmed the presence of ZrF₄, ZrOF₂ and HfF₄ along with un-protective oxides of Ta, Nb and Ti on the film, resulting in decreased corrosion resistance of TaNbHfZrTi HEA in fluorinated nitric acid.     

Passive film formed on nickel in a neutral solution

A bright nickel was passivated in the pH 8·39 boric acid-borate buffer solution. The oxide formation reactions were mainly investigated by means of polarization experiments, alternating anodic and cathodic polarization, potential decay experiments and colorimetric analysis. From the results, the chemical composition and structure of passive films formed on nickel were discussed. The experimental results are summarized as follows.1. A considerable amount of nickel ions dissolved during the anodic formation of passive films. The dissolution ceased because of the formation of NiO₂. 2. The passive films on bright nickel has a duplex structure consisting of NiO and Ni₃O₄. At higher potentials, NiO₂ was produced on them. NiO and Ni₃O₄ were formed directly from Ni, and NiO₂ was transformed from Ni₃O₄. 3. NiO and NiO₂ were reversibly produced and reduced, but Ni₃O₄ was very difficult to be reduced. 4. It was observed that there was a reversible charging and discharging layer at the potential where Ni₃O₄ formed. The electric capacity was calculated to be about 100 μF/cm², assuming that roughness factor was 2. It would be reasonable to think that a space charge was established on nickel surface.     

Electrochemical behaviour of an inhibitor film formed on copper surface

The potential dependence of adsorption and kinetic properties of inhibitor film formation on copper surface was studied in acidic environment by using surface sensitive techniques: electrochemical quartz crystal microbalance (EQCM) and electrochemical scanning tunneling microscopy (EC-STM). The investigated inhibitor was 5-mercapto-1-phenyl-tetrazole (5-MPhTT) in 1 mmol dm⁻³ H₂SO₄ solution. The QCM investigations were done to study the electrode mass changes in absence and presence of 5-MPhTT at rest potential. The apparent mass and current variation as a function of the electrode potential was registered in order to study the protective film and its breakdown. Results revealed that the anodic current density and the electrode mass loss is twice less in presence of 5-MPhTT. We also present results of an in situ STM study on the surface morphology and anodic dissolution of Cu(1 1 1) electrodes in inhibited/uninhibited electrolytes. The images gave information about the nature of the protective layer. The results were analyzed and discussed.     

An atomic emission spectroelectrochemical study of passive film formation and dissolution on galvanized steel treated with silicate conversion coatings

The effect of a silicate conversion coating, which was applied on electrogalvanized steel (EG) and hot dip galvanized steel (HDG), on zinc passivation and dissolution is investigated by atomic emission spectroelectrochemistry (AESEC) using anodic/cathodic cycles in a neutral borate buffer solution. We are able to decompose the total zinc oxidation rate into a soluble (dissolution) and insoluble (passivation) component. It is found that the silicate conversion coating reduces the soluble component with no measurable effect on the insoluble component. The results imply that zinc passive film formation occurs unhindered underneath the silicate film but the film effectively blocks zinc dissolution.     

Surface characterization of passive film formed on nitrogen ion implanted Ti-6Al-4V and Ti-6Al-7Nb alloys using SIMS

The aim of this paper is to study the effect of N⁺ ion implantation on corrosion and phase formation on the implanted surfaces of Ti-6Al-4V and Ti-6Al-7Nb alloys. Nitrogen ion was implanted on Ti-6Al-4V and Ti-6Al-7Nb alloys at an energy of 70 and 100 keV, respectively using a 150 keV accelerator at different doses ranging from 5 × 10¹⁵ to 2.5 × 10¹⁷ ions/cm². Electrochemical studies have been carried out in Ringer’s solution in order to determine the optimum dose that can give good corrosion resistance in a simulated body fluid condition. The implanted surfaces of such modified doses were electrochemically passivated at 1.0 V for an hour. Secondary ion mass spectroscopy was used to study and characterize titanium oxide and titanium nitride layers produced on implanted surface and to correlate them with the corrosion resistance. The nature of the passive film of the implanted-passivated specimen was compared with the unimplanted-passivated as well as as-implanted specimens.     

Electropolymerization and characterization of poly(N-methylaniline) and poly(N-butylaniline) in mixtures of aqueous and organic solvents

Electropolymerization of N-methylaniline (NMA) and N-butylaniline (NBA) was studied on glassy carbon and optically transparent tin oxide electrodes in mixtures of aqueous and organic solvents. Five different organic solvents, dimethyl formamide, dimethyl sulfoxide, tetrahydrofuran (THF), propylene carbonate (PC) and acetonitrile (ACN) were mixed with aqueous 1.0 M HClO₄ solutions. Our results show that NMA and NBA can be electropolymerized in aqueous–organic solvent mixtures with maximum 30 and 50% (v/v) organic solvents, respectively. The choice of organic solvent strongly influences the film formation. With addition of 10–20% THF, ACN and PC to the aqueous polymerization solution, the film formation was highly improved. The poly(N-methylaniline) and poly(N-butylaniline) films were characterized with cyclic voltammetry, in situ UV–vis spectroscopy, size exclusion chromatography and with electrical conductivity measurements.     

On rearrangement of spectrum of epitaxial graphene formed on thin metallic film

A simple model has been applied to the investigation of electron states of epitaxial graphene formed on the surface of dimensionally quantized film. It has been shown that quantum dimensional effects in the substrate influence the electron spectrum of graphene, i.e., Fermi velocity is renormalized and energy forbidden gap is generated in the density of states. The gap and Fermi velocity have been estimated for various values of interaction constant and substrate parameters.     

TEM and X-ray diffraction investigation of the structural characteristics of the microporous oxide film formed on polycrystalline Ti

The microporous TiO₂ layer in the vicinity of the Ti–TiO₂ interface is formed by a great amount of tiny crystallites. Bigger anatase and rutile crystals stand in the outer region of the oxide. The orientation of a proportion of the TiO₂ crystals is influenced by the underlying textured Ti substrate.     

Structure of corrosion film formed on copper exposed to controlled corrosive environment

This paper describes a transmission electron microscopy (TEM) investigation of copper coupons exposed to a corrosive mixed flowing gas environment (MFG). A focused ion beam (FIB) lift-out technique was used to extract electron transparent specimens for TEM investigation. A duplex corrosion film comprising cuprite (Cu₂O) and chalcocite (Cu₂S) developed on the copper substrate. The oxide demonstrated a dense morphology with evidence of chlorine in the oxide layer showing that chlorine plays an important role in the corrosion of copper transforming the protective Cu₂O layer to a non-protective layer. The outer layer of the Cu₂S demonstrated a porous morphology allowing easy penetration of water and gases.