Film Formation Potential Research Articles

Duplex stainless steel passive film electrical properties studied by in situ current sensing atomic force microscopy

The duplex stainless steel passive film electrical properties before and after passivation were investigated by current sensing atomic force microscopy and X-ray photoelectron spectroscopy (XPS). The current maps and band gap energies extracted from I–V curves show that the conductivity of passive film covering austenite and ferrite is different and decreases with increasing film formation potential due to the changes in the passive film thickness and composition, confirmed by XPS analysis. I–V curves reveal that the passive films exhibit p-type or n-type semiconducting properties depending on the film formation potential, attributed to different film chemical composition, supported by XPS results.

Effect of Chloride on Semiconducting Properties of Passive Films Formed on Supermartensitic Stainless Steel in NaHCO3 Solution

The effects of chloride ion on the electrochemical behavior and the semiconducting properties of the passive film on supermartensitic stainless steel in 0. 5 mol/L NaHCO3 solution were investigated using potentiodynamic polarization, the potentiostatic current transients and Mott-Schottky analysis. The results indicated that chloride ion narrowed passivation region and improved pitting susceptibility. The steady state current densities were independent of film-formed potentials, which was in good agreement with the assumption of the point defect model (PDM). The capacitance results showed the fact that the passive films had a multilayer character. The defect density decreased with increasing passive film formation potential. The chloride ion induced changes of the acceptor densities and donor densities of the passive films.

Passive and transpassive behaviour of Alloy 31 in a heavy brine LiBr solution

The passive and transpassive behaviour of Alloy 31, a highly alloyed austenitic stainless steel (UNS N08031), has been investigated in a LiBr heavy brine solution (400g/l) at 25°C using potentiostatic polarisation combined with electrochemical impedance spectroscopy and Mott–Schottky analysis. The passive film formed on Alloy 31 has been found to be p-type and/or n-type in electronic character, depending on the film formation potential. The thickness of the film formed at potentials within the passive region increases linearly with applied potential. The film formed at transpassive potentials is thinner and more conductive than the film formed within the passive region. These observations are consistent with the predictions of the Point Defect Model for passive and transpassive films on metals and alloys.

Passivity of AISI 321 stainless steel in 0.5 M H2SO4 solution studied by Mott–Schottky analysis in conjunction with the point defect model

The passivity of AISI 321 stainless steel in 0.5M H2SO4 solution, in the steady-state condition, has been explored using electrochemical impedance spectroscopy (EIS) and Mott–Schottky analysis. Based on the Mott–Schottky analysis in conjunction with the point defect model (PDM), it was shown that the calculated donor density decreases exponentially with increasing passive film formation potential. The thickness of the passive film was increased linearly with the formation potential. These observations were consistent with the predictions of the PDM, noting that the point defects within the passive film are metal interstitials, oxygen vacancies, or both.

Development of localized corrosion damage on low pressure turbine disks and blades: I. Passivity

Passivity on steel surfaces plays a crucial role in the development of pitting corrosion damage. In this work, the passivity on Type 403 stainless steel (SS), low pressure steam turbine (LPST) blade alloy, and A470/471 low alloy steel (LPST) disk/rotor steel has been studied in borate buffer solution. The highly defective barrier layers on Type 403 SS and A470/471 steel, formed at potentials in the passive region, exhibit n-type semiconductor behavior, due to the predominance of oxygen vacancies and/or cation interstitials as crystallographic point defects. The defective Cr2O3 barrier layer on the Type 403 SS surface has a greater donor concentration and a smaller thickness than does the barrier layer (defective Fe3O4) on the A470/471 steel surface. Increasing oxygen and chloride concentration in the electrolyte increase the donor concentration in the passive film on Type 403 SS. In the passive regions of Type 403 SS and A470/471 steel, the steady-state current density is nearly independent of, and the steady-state barrier layer thickness increases linearly with, increasing film formation potential. These experimental observations are interpreted in terms of the point defect model (PDM) for the passive state. Mechanistic analysis of electrochemical impedance spectroscopy (EIS) data by the impedance model developed from the PDM, is also performed, and the validity of the impedance model is demonstrated.

Atomic force microscopy of the dissolution of cubic Pt nanoparticle on a carbon substrate

Dissolution mechanism of cubic Pt nanoparticles has been studied with the use of atomic force microscopy on a carbon substrate in 0.1M NaClO4. The shape of the nanoparticles does not change in the double layer region. The height of the nanoparticles increases slightly at the onset potential of the oxide film formation. The nanoparticles are dissolved from the sides in the oxide film formation region, whereas the change of the height is negligible. These results differ from those of the cubic Pt nanoparticles on a Pt substrate, on which the dissolution proceeds at the upper terrace.

Structure-modifying alkaline and acidic pH-shifting processes promote film formation of soy proteins

The effect of pH-shifting, a process that induces the molten globule state in proteins, on the film-forming potential of soy protein isolate (SPI) at different temperatures was investigated. Partial unfolding at pH 1.5 or 12, followed by refolding at pH 7.0, was performed to alter the protein structure. Glycerin-plasticised films were prepared from pH-treated SPI at ambient temperature (20°C), or by heating at 50, 60, 70, or 80°C (30min). Tensile strength (TS), elongation at break (EAB), water vapour permeability (WVP), protein solubility (pH 3–7), and non-participating proteins of films were analysed, and the film microstructures were examined. The pH12-treated SPI spontaneously formed a transparent, slightly yellowish film at 20°C, which had the greatest EAB, while pH1.5-treated and native SPIs required preheating at 50 and 70°C, respectively, to form a film. Heating generally decreased solubility and WVP but increased TS. Films formed from both pH12- and pH1.5-treated SPIs were more elastic (up to 2-fold greater in EAB, P<0.05) than the film formed from untreated SPI despite slightly reduced TS and WVP. Electrophoresis revealed disulphide bonds between A and B subunits of glycinin being a dominant force in pH12- and pH1.5-treated SPI films, while noncovalent forces were abundant in untreated SPI films. The pH12-treated SPI film consisted of more interactive protein strands than other SPI films, which seemed to explain its superior elastic properties.

Characterization of passive film on 2205 duplex stainless steel in sodium thiosulphate solution

The electrochemical behaviour of passive film formed on 2205 duplex stainless steel in 0.1 M Na 2S 2O 3 solutions was investigated using potentiodynamic polarization, EIS, Mott–Schottky analysis and the compositions of oxide film in different passive regions were carried out by XPS. The results indicated that the impedance is dependent on the applied potential indicating the occurrence of a charge transfer reaction in a porous film. The doping densities evaluated from Mott–Schottky plots demonstrated that there existence of two donor levels in the space charge layer of the passive films. The donor density ( N D1 and N D2 ) values are in the range of 10 20–10 21 cm 3, and decreases exponentially with increasing film formation potential, which is in good agreement with the theoretical consequences of the PDM. The polarization curve and XPS results shows that in the passive regions the 2205 duplex stainless steel exhibits different electrochemical and semiconductor properties.

The semiconducting properties of passive films formed on AISI 316 L and AISI 321 stainless steels: A test of the point defect model (PDM)

The semiconductor properties of passive films formed on AISI 316L in 1 M H 2SO 4 in three temperatures and AISI 321 in 0.5 M H 2SO 4 were studied by employing Mott–Schottky analysis in conjunction with the point defect model (PDM). Based on the Mott–Schottky analysis in conjunction with PDM, it was shown that the calculated donor density decreases exponentially with increasing passive film formation potential. Also, the results indicated that donor densities increased with temperature. By assuming that the donors are oxygen ion vacancies and/or cation interstitials, the diffusion coefficients of the donors for two stainless steels are calculated.

Correlation between the plating regime of lead film deposition and electrode response after accumulation of organic compound. Microscopic study

The properties of the lead film electrode designed for adsorptive stripping voltammetric measurements of organic compounds were examined by electrochemical and microscopic techniques. The effect of Pb(II) concentration, the influence of deposition potential and time of the lead film formation on the determination of bleomycin at an in situ lead-coated glassy carbon electrode have been studied. Atomic force microscopy (AFM) was used to characterize the Pb crystallite growth on the glassy carbon surface. The morphology of the deposits was evaluated and its influence on the bleomycin responses was discussed.

Diffusivity of Point Defects in the Passive Film on Stainless Steel

The semiconductor properties of passive films formed on AISI 316 stainless steel in sulfuric acid solution were studied by employing Mott-Schottky analysis in conjunction with the point defect model. The donor density of the passive films, which can be estimated by the Mott-Schottky plots, changes depending on the film formation potentials. Based on the Mott-Schottky analysis, an exponential relationship between donor density and the film formation potentials of the passive films was developed. The results showed that the donor densities evaluated from Mott-Schottky plots are in the range 2-3 × 1021 cm−3and decreased with the film formation potential. By assuming that the donors are oxygen ion vacancies and/or cation interstitials, the diffusion coefficient of the donors, (), is calculated to be approximately 3.12 × 10−16 cm2/s.

The structure and electronic properties of passive and prepassive films of iron in borate buffer

The films that form on pure iron during potentiodynamic anodic polarization in aqueous borate buffer were investigated by surface enhanced Raman spectroscopy (SERS), and by electrochemical impedance spectroscopy and Mott–Schottky analysis at selected potentials. According to SERS, the passive film is a bilayer film with an outer layer of an as yet undetermined Fe(III)oxide/hydroxide, identified by a strong Raman peak at 560 cm −1 . The inner layer was a spinel compound. The capacitances of passive iron were frequency dependent and a constant phase element (CPE) best described the frequency dispersion. Current increases in cathodic polarization scans confirmed the accuracy of flatband potentials calculated from Mott–Schottky tests at two different film formation potentials. Both films were found to be n-type and flatband potentials of −846 and −95 mV vs. SHE and carrier densities of 1.6 × 10 22 and 8.3 × 10 20 /cm 3 were found for films grown at −500 and +1000 mV, respectively. The cathodic polarization curve of passivated iron exhibited a complex shape that was explained by the electronic properties of iron's passive and prepassive films. The reductive dissolution of the films abruptly began when the potential was lowered below their flatband potentials. It is suggested that the cathodic polarization behavior contributes to iron's susceptibility to localized corrosion.

The passivity of AISI 316L stainless steel in 0.05 M H2SO4

The passivity of AISI 316L stainless steel (AISI 316L) in 0.05 M H2SO4, in the steady-state condition, has been explored using various electrochemical techniques, including potentiostatic polarization, electrochemical impedance spectroscopy (EIS), and Mott–Schottky analysis. Based on the Mott–Schottky analysis in conjunction with the point defect model (PDM), it was shown that the calculated donor density decreases exponentially with increasing passive film formation potential. The thickness of the barrier layer was increased linearly with the film formation potential. These observations were consistent with the predictions of the PDM, noting that the point defects within the barrier layer of the passive film are metal interstitials, oxygen vacancies, or both. Also no evidence for p-type behavior was obtained, indicating that cation vacancies do not have any significant population density in the passive film.

Effect of the crystal face orientation and alloying with gold on the properties of thin anodic films of Ag(I) oxide: I. Photocurrent

The anodic formation of nano-size anodic films of Ag(I) oxide on polycrystalline silver and Ag-Au alloys, as well as on low-index monocrystalline silver faces in 0.1 M KOH, is studied. Based on the data of photocurrent measurements, the n-kind of the oxide film conductivity is determined. Replacing the polycrystalline silver with monocrystals, as well as adding a small amount of gold atoms to its lattice (X[Au] <= 4 at. %), results in substantial structure ordering of the oxide due to the decrease in the deviation from the stoichiometric composition. The structure-dependent parameters of Ag(I) oxide (the optical absorption coefficient α, the concentration of donor defects ND, the width of the spatial charge region W, and the Debye screening length LD) are determined by the silver crystal face orientation, the gold content, and the film formation potential. At E = 0.52 V, the series of changes in these characteristics correlate with the series of reticular density. An increase in E breaks the series and increases the deviation of the composition from the stoichiometric Ag2O composition.

Influence of structural transformations over the electrochemical behavior of Ti anodic films grown in 0.1 M NaOH

In this work, the structural transformation during the anodic growth of Ti oxide films and its influence on the resistive properties of the film are studied. The voltammetric characterization of Ti/0.1 M NaOH indicates that the oxide film composition depends on potential. Depending on the anodic switching potential, the oxide film can produce up to three cathodic peaks, and the peaks can be related to different Ti oxides. During the early stages of potentiostatic formation, the oxide film seems to have the same initial structure regardless of the film formation potential; however, after increasing growth time, the oxide structure depends on the formation potential. The evaluation of the resistive properties of Ti oxide films determined by electrochemical impedance spectroscopy shows that despite the chemical transformations within the film, there is a linear dependence between the capacitance of the Ti oxide film with formation potential.

Study of passive films formed on mild steel in alkaline media by the application of anodic potentials

In this paper, iron oxide thin layers formed on mild steel substrates in alkaline media by the application of different anodic potentials were studied in order to characterize their morphology, composition and electrochemical behaviour, in particular under conditions of cathodic protection. The surface composition was evaluated by X-Ray Photoelectron Spectroscopy (XPS) and Auger Electron Spectroscopy (AES). The morphology of the surface oxides was studied via Atomic Force Microscopy (AFM). The electrochemical behaviour of the surface oxides was studied using Electrochemical Impedance Spectroscopy (EIS). The results showed that the surface film is composed by Fe 2+oxides and Fe 3+ oxides and/or hydroxides. The contribution of Fe 2+ species vanishes when the potential of film formation increases in the passive domain. Two distinct phases were differentiated in the outer layers of the surface film, which proves that film growing is topotactic in nature.

Studying on the Point-Defect-Conductive Property of the Semiconducting Anodic Oxide Films on Titanium

By using electrochemical measurement techniques and based on the point-defect model (PDM), this work studied the point-defect-conductive property of the n-type semiconducting anodic oxide film formed on titanium under steady-state condition within the passive potential region of ca. in solution. The point-defect transport property was characterized by the steady-state current density through the film and the diffusion coefficient of the point defects in the film. It was demonstrated that with the increase of the film formation potentials, (and ) show an exponentially dependent increase on the potential. This behavior of the oxide films formed on titanium is to some extent different from that of some other n-type anodic oxide films. The influence of potential on the changes in structure and crystallization of the oxide film on titanium was proposed to be taken as a reason for the potential-dependence of (and ) observed in this work. It was also shown that within the passive potential region most of any change in the applied potential does appear predominantly as a change in the potential drop within the oxide film (only of that drops across the film/solution interface). Additionally, a question about the values of the polarizability of the oxide film/solution interface used and estimated within the frames of the PDM was raised and discussed at the end of this paper.

Evaluation of film-forming potential of a natural gum

Films were prepared using 5 parts of 10% w/w of mucilage of gum of Moringa oleifera with different proportions of plasticizers: polyethylene glycol (PEG 400) (0.1, 0.15, 0.2, and 0.3), glycerin (0.15), and propylene glycol (0.2). The films were casted on glass plates and dried under controlled evaporation. Films prepared with 0.15, 0.2 part of PEG 400; 0.15 part of glycerin and propylene glycol showed satisfactory drying after 24 h. They were evaluated for following parameters water uptake, tensile strength, folding endurance, and water vapor transmission rate. The results obtained are comparable with films made from other polymers, and the gum can be used for preparing polymeric drug delivery systems and as film coating agent.

Evaluation of film-forming potential of a natural gum

Evaluation of film-forming potential of a natural gum

Characterization of Thin Anodically Grown Oxide Films on AISI 304L Stainless Steel

The passivity and protective nature of the passive films are essentially related to ionic and electronic transport processes, which are controlled by the optical and electronic properties of passive films. Corrosion properties of passive films anodically formed on 304L stainless steel in borate/boric acid solution have been examined using electrochemical impedance spectroscopy (EIS). An electrical equivalent circuit based on the impedance analysis, which describes the behavior of the passive film on stainless steel more satisfactorily than the proposed models, is presented. The semiconducting properties of the passive films were also investigated by photoelectrochemistry. Effects of film-formation potential, film-formation time, and applied potential on the electronic properties were studied. Depending on the operating conditions, the optical bandgap values were estimated to vary from 2.1 to . Both film resistance and bandgap were found to decrease with applied potential. Therefore, correlation between the two significant parameters was determined.