Semiconductor Properties Of Passive Films Research Articles

Corrosion and passive behavior of AlxCrFeNi3−x (x = 0.6, 0.8, 1.0) eutectic high entropy alloys in chloride environment

The corrosion and passive behavior of the as-cast AlxCrFeNi3−x (x = 0.6, 0.8, 1.0 in molar ratio) high entropy alloys in 3.5 wt% NaCl solution at room temperature was investigated by the electrochemical impedance spectroscopy, potentiodynamic polarization measurement, Mott-Schottky measurement, X-ray photoelectron spectroscopy tests, and scanning Kelvin probe force microscopy. The increase of the Al content resulted in the decrease in corrosion resistance, which might be attributed to the reduction of stability and protection of passive films caused by composition difference. Furthermore, the p-type and n-type semiconductor properties of passive films were discussed.

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.

The semiconductor properties of passive films and corrosion behavior of stainless steel reinforcing bars in simulated concrete pore solution

The vulnerability of concrete reinforcing steels to corrosion when depassivation occurs, typically in the presence of chloride, makes it important to understand the nature of the steels’ passive films. In Part I of the study, electrochemical techniques and Mott–Schottky analysis were used to investigate these films formed on five different grades of stainless steel and carbon steel reinforcing bars exposed to simulated concrete pore solution. The influence of the steel composition and surface finish on Mott–Schottky plots and the electronic properties are discussed in relation to the steels’ corrosion resistance. A p-type semiconductor behavior was observed in the stainless steel alloys in the cathodic potential regions and an n-type in the anodic potential regions. The n-type behavior is similar to that observed in the carbon steel. The electronic and electrochemical properties of the austenitic grades were superior to the duplex grades. The molybdenum-containing grades, 316LN and 2205, did not show the expected superior properties compared to molybdenum-free grades, 304L and 2304. Also, the replacement of nickel by manganese in the 24100 alloy was not found to be detrimental. The as-received bars showed electronic and electrochemical properties that are more realistic to field conditions than those of the polished cross-sections.

Effects of passive films on corrosion resistance of uncoated SS316L bipolar plates for proton exchange membrane fuel cell application

The effects of passive films on the corrosion behaviors of uncoated SS316L in anode and cathode environments of proton exchange membrane fuel cells (PEMFCs) are studied. Potentiodynamic and potentiostatic polarizations are employed to study the corrosion behavior; Mott-Schottky measurements are used to characterize the semiconductor properties of passive films; X-ray photoelectron spectroscopy (XPS) analyses are used to identify the compositions and the depth profiles of passive films. The passive films formed in the PEMFC anode and cathode environments under corresponding conditions both behave as n-type semiconductor. The passive film formed in the anode environment has a single-layer structure, Cr is the major element (Cr/Fe atomic ratio>1), and the Cr/Fe atomic ratio decreases from the surface to the bulk; while the passive film formed in the PEMFC cathode environment has a bi-layer structure, Fe is the major element (Cr/Fe atomic ratio<0.5), and in the external layer of the bi-layer structure Fe content increases rapidly and gradually in the internal layer. SS316L shows better corrosion resistance owing to both the high content of Cr oxide in the passive film and low band bending in normal PEMFC anode environments.

Studying the Structure and Semiconductor Properties of Passive Film on 316SS by XPS and Capacitance Measurement

In borate buffer solution, anodic oxide passive film was formed on 316SS at 0.6 VSCE. Chemical composition and semiconductor properties of the film were studied by XPS and capacitance measurement. It’s determined from the results that the film has duplex structure with inner oxide layer and outer hydroxide layer. The inner layer behaves as p-type semiconductor, while the outer layer shows n-type semiconductor. A p-n junction is formed at the interface of outer and inner layer, and it plays an important role in the protective effect on the metal matrix.

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.

The non-linear fitting method to study the semiconductor properties of passive films of INCONEL alloy G3

The structure and semiconducting behavior of passive films formed on nickel base alloy G3 in borate buffer solution after polarization at different times and potentials were studied by XPS analysis and capacitance measurement in this paper. The results indicated that the formed passive films had double layer structure, i.e., outer layer hydroxide as p-type semiconductor and inner layer oxide as n-type semiconductor. Due to the series connection of two space charge capacitances, the measured Mott–Schottky plots were non-linear. A non-linear fitting method was proposed to determine the carrier densities in the outer and inner layers. The carrier densities of passive film formed at different polarization times and potentials were also discussed. The results indicated that both the outer and inner layers were compact and could protect the substrate simultaneously.

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 Semiconductor Character of Passive Film of 304L Stainless Steel(SS), 316L SS and Nickel Alloy 800 Formed in Zinc Contained High-Temperature and High-Pressure Water

The semiconductor properties of passive film formed on 304L stainless steel (SS), 316L SS and Alloy 800HT in high-temperature and high-pressure water with zinc addition have been investigated by using Polarization curve, Mott-Schottky analysis and photocurrent method. The donor density, flat band and band gap of semiconductor behavior are analyzed to investigate the impact of zinc addition to the passive film. Analysis of the experimental results indicated that passive film formed on 316L and 800HT with zinc addition showed different electrochemical, photo-electrochemical and semiconductor properties. The results indicated that corrosion resistance of passive film from in high-temperature and high-pressure water with zinc addition was obviously better than that without zinc addition.

Effects of dissolved oxygen on electrochemical and semiconductor properties of 316L stainless steel

The effects of dissolved oxygen on the electrochemical behavior and semiconductor properties of passive film formed on 316L SS in three solutions with different dissolved oxygen were studied by using polarization curve, Mott–Schottky analysis and the point defect model (PDM). The results show that higher dissolved oxygen accelerates both anodic and cathodic process. Based on Mott–Schottky analysis and PDM, the key parameters for passive film, donor density N d, flat-band potential E fb and diffusivity of defects D 0 were calculated. The results display that N d(1−7 × 10 27 m −3) and D 0(1−18 × 10 −16 cm 2/s) increase and E fb value reduces with the dissolved oxygen in solution.

Effect of solution concentration on semiconducting properties of passive films formed on austenitic stainless steels

The semiconductor properties of passive films formed on AISI 316L in three acidic solutions were studied by employing Mott–Schottky analysis in conjunction with the point defect model (PDM). Based on PDM, the key parameters for passive film growth are the diffusivity and density of the defects within the film. The results indicated that donor densities are in the range 1–4 × 10 21 cm −3 and increased with solution concentration. By assuming that the donors are oxygen ion vacancies and/or cation interstitials, the diffusion coefficient of the donors in three acidic solutions are calculated to be approximately 1–5 × 10 −16 cm 2/s.

Influence of yttrium as a minority alloying element on the corrosion behavior in Fe-based bulk metallic glasses

The role of yttrium in corrosion behavior in an HCl solution was studied systematically by comparing bulk FeCrMoCB metallic glasses with and without yttrium. The corrosion resistance was very sensitive to minor yttrium addition. The material exhibits a detrimental effect on corrosion resistance at 0.5 at.% yttrium addition while a beneficial effect at more yttrium additions. Such effects are argued to be associated with variations of the semiconductor properties of passive film ( i.e. defects concentration and band structure of passive film), induced by minority yttrium alloying element doping. It was shown that there exhibits a bi-layer structure of passive film on Fe-based metallic glasses. The outer layer with high valence cations is responsible for the dissolution behavior of the passive film, whereas the inner layer with doped oxides connects with the semiconductor properties. This result presents us an important hint that the corrosion resistance of metallic glasses can be improved by elaborately tailoring the defect structure of passive film via proper additions of minor alloying elements.

Semiconductor properties and protective role of passive films of iron base alloys

Semiconductor properties of passive films formed on the Fe–18Cr alloy in a borate buffer solution (pH = 8.4) and 0.1 M H 2SO 4 solution were examined using a photoelectrochemical spectroscopy and an electrochemical impedance spectroscopy. Photo current reveals two photo action spectra that derived from outer hydroxide and inner oxide layers. A typical n-type semiconductor behaviour is observed by both photo current and impedance for the passive films formed in the borate buffer solution. On the other hand, a negative photo current generated, the absolute value of which decreased as applied potential increased in the sulfuric acid solution. This indicates that the passive film behaves as a p-type semiconductor. However, Mott–Schottky plot revealed the typical n-type semiconductor property. It is concluded that the passive film on the Fe–18Cr alloy formed in the borate buffer solution is composed of both n-type outer hydroxide and inner oxide layers. On the other hand, the passive film of the Fe–18Cr alloy in the sulphuric acid consists of p-type oxide and n-type hydroxide layers. The behaviour of passive film growth and corrosion was discussed in terms of the electronic structure in the passive film.

Semiconductor properties of passive films formed on sputter-deposited Fe–18Cr alloy thin films with various additive elements

The semiconductor properties of passive films formed on an Fe–18Cr alloy with various additive elements in a borate buffer solution were studied using electrochemical impedance spectroscopy and photoelectrochemical response. The photocurrent was plotted as a photoelectrochemical action spectrum that could be separated into two components, which were mainly derived from Cr oxide (Eg = 3.4 eV) and Cr hydroxide (Eg = 2.4 eV). The band gap energy, Eg; of each component was almost constant, independent of the species and amount of additive elements. The photoelectrochemical response showed positive photocurrent for most potential in the passive region, which indicates that the passive film behaved as an n-type semiconductor. In addition, the Mott–Schottky plot of the capacitance showed positive slope, which also means that the passive films behaved as an n-type semiconductor. The donor density of the passive films, which can be estimated by the Mott–Schottky plots, changes depending on the film formation potentials and a variety of additives.

Large Area Photocurrent Behavior and Laser Spot Scanning of Passivated Stainless Steels

The semiconductor properties of passive films on different stainless steels were investigated by photoelectrochemical methods. Photocurrent‐potential measurements together with data for the susceptibility of the materials to localized corrosion revealed that above a critical potential value photocurrents as well as the pit initiation rate decrease with increasing potential. The occurrence of could be explained by a Cr(III)/Cr(VI) oxidation in the passive film starting at this potential. By applying a laser spot scanning technique it was possible to resolve local variations in the photocurrent response of the passive films studied. Microscopic investigations revealed that sites which exhibit an enlarged photocurrent coincide with inclusions present in the bulk material of the steels.

Semiconductor properties of passive films on Zn, ZnCo, and ZnNi substrates and ZnO single crystals

The semiconductor properties of passive films formed in alkaline aqueous solutions of Zn, ZnCo, ZnNi substrates and ZnO single crystals, were studied by electrochemical and photoelectrochemical methods. The substrate doping with Co and Ni leads to a homogeneous distribution of these elements in the passive oxide layer. The density and energy distribution of shallow donor states were determined from deviations of the ideal Mott-Schottky behaviour observed by electrochemical impedance measurements and from optical quantum efficiency experiments. The flat band potentials were found to be practically the same measured on passive oxide layers on zinc substrates and on ZnO single crystal electrodes showing a typical Nernstian pH-dependence. The doping elements Co and Ni seem to generate deep donor levels as indicated by impedance measurements.

The effects of polarization potential and concentration of hydrochloric acid on the photopotential of passive films formed on titanium in hydrochloric acid solution

The effects of polarization potential and concentration of hydrochloric acid on the photopotential of the passive film formed on titanium in hydrochloric acid solutions were investigated. The photopotentials measured for titanium at open circuit condition after potentiostatic polarization at potentials in the passive region showed negative values, and increased in the negative direction with an increase in polarization potential. The increase in concentration of hydrochloric acid for the solution led to an increase in passive current density and a lowering of the photopotential. The results were interpreted on the basis of Oshe's model, and discussed from the viewpoint of semiconductor properties of passive film.

Semiconductor Properties of Passive Films on Zn, Zn‐Co, and Zn‐Ni Substrates

The semiconductor properties of passive films formed in alkaline aqueous solutions on Zn, Zn‐Co, and Zn‐Ni substrates were studied by electrochemical and photoelectrochemical methods. Substrate doping with Co and Ni leads to a homogeneous distribution of these elements in the passive oxide layer. The density and energy distribution of shallow donor states were determined from deviations from the ideal Mott‐Schottky behavior observed by electrochemical impedance measurements and from optical quantum efficiency experiments. The doping elements Co and Ni seem to generate deep donor levels, as indicated by impedance measurements. The inhibition effect of these doping elements on the corrosion rate of passive layers on Zn is interpreted in terms of transport processes within the oxide film.

Fe-Cr合金の不働態皮膜の半導体的性質の光電分極法による解析

Fe-Cr合金の不働態皮膜の半導体的性質の光電分極法による解析