Thickness Of Passive Film Research Articles

Corrosion mechanism of additively manufactured 316 L stainless steel in 3.5 wt.% NaCl solution

Additively manufactured stainless steel has received widespread attention due to its excellent mechanical properties, while its corrosion mechanism in Cl--containing environments is still vague. This work investigates the pitting and passivation behavior of additively manufactured 316 L stainless steel (AM SS316 L) in 3.5 wt.% NaCl solution and its comparison to wrought counterpart, by scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS) and electrochemical measurements. The results show that AM SS316 L exhibits a fine sub-grain structure with a diameter of approximately 5 μm, and dislocations and Mo elements enriched at the sub-grain boundary. Compared with the wrought 316 L stainless steel (SS316 L), a large number of sub-grain boundaries and high dislocation density in AM SS316 L promote the formation of a more compact and thicker passive film, consequently enhances its general corrosion resistance. However, the low hydroxide content in the passive film and the micro-galvanic corrosion effect between Mo-rich sub-grain boundaries and sub-grains reduce the self-repairing ability of the passive film, thus the pitting corrosion resistance of AM SS316 L.

Aqueous passivation of multi-principal element alloy Ni38Fe20Cr22Mn10Co10: Unexpected high Cr enrichment within the passive film

The aqueous passivation of a non-equiatomic Ni38Fe20Cr22Mn10Co10 - at.% (Ni40Fe20Cr20Mn10Co10 - wt.%) multi-principal element alloy (MPEA) was investigated in 0.1 M NaCl at pH 4 and compared to a conventional binary Ni76Cr24 – at.% (Ni78Cr22 – wt.%) alloy. The electrochemical behavior and oxide film characteristics were explored utilizing in-situ electrochemical and ex-situ surface-sensitive techniques. The passive film composition, thickness, and elemental valence states, as well as, the fate of each element were studied by in-situ atomic emission spectro-electrochemistry, ex-situ X-ray photoelectron spectroscopy, and atom probe tomography. The Ni38Fe20Cr22Mn10Co10 MPEA demonstrated slightly better corrosion resistance compared to the binary Ni76Cr24, alloy. Passive films on the MPEA contained primarily Cr, and small amounts of Ni, Fe, Co and Mn, while dissolution of Ni, Fe, Co was observed. Ni0 was enriched at the oxide/metal interface while Cr was depleted. Enrichment of Cr in the passive film occurred to a greater extent in the MPEA than for the Ni-Cr binary alloy. Enrichment factors were determined and the origins of enrichment are discussed.

Effect of deformed subsurface on the corrosion resistance of biomedical CoCrMo alloy in simulated physiological solution

In most cases, the microstructure of implants is stable and changeless after implanted into the body. However, the metallic joint replacements would be worn during patients’ movements. Their subsurface microstructures were deformed and changed. That may affect the corrosion resistance of the joint. Due to the complex surface situation on the worn joints, it was difficult to distinguish and evaluate the influence of the subsurface microstructure from surface roughness, wear debris, etc. In this study, a CoCrMo alloy used for artificial joints was treated by high-energy shot peening method to obtain a similar deformed surface to the worn joints, but without introducing other influencing factors. The corrosion rate of the deformed alloy which was treated for 4 h was down by 93.3% in the phosphate-buffered saline (PBS) solution compared with the untreated alloy. However, with the addition of bovine serum albumin (BSA) into PBS, the treated alloy showed the poorer corrosion resistance when its concentration was equal to or greater than 0.1 μmol L−1. The defects (grain boundaries and stacking faults), which were introduced into the alloy surface during peening process, could accelerate anodic dissolution, improve element diffusion and increase the number of active sites. These were beneficial for forming a more compact and thicker passive film which enhanced the corrosion resistance of the alloy. However, the deformation of subsurface could promote the adsorption of protein on the alloy surface. The adsorbed protein molecules would chelate with metallic ions and weaken the passive film.

Mechanistic study on initial passivation and surface chemistry of steel bars in nano-silica cement pastes

This work studied the passivation of steel bar in cement pastes prepared with and without nano-silica by using electrochemical measurements and surface characterization methods. The results showed that the passivation of steel bar in cement paste was dominated by the chemistry of the pore solution and the evolution over time, which are closely associated with the hydration process of the cement. The addition of nano-silica influenced the alkalinity of the pore solution in cement paste and modified the pore structure of the cement paste, which resulted in a different passivation process and a thicker passive film with a higher proportion of Fe2+ oxides. The intrinsic corrosion resistance of steel bars in concrete prepared with nano-silica was expected to be enhanced.

Effect of microstructure on the passive behavior of selective laser melting-fabricated Hastelloy X in NaNO3 solution

The electrochemical dissolution characteristics of nickel-based alloys produced by selective laser melting (SLM) have received considerable attention in electrochemical machining (ECM). However, the passive behavior of Hastelloy X (HX) during ECM has not been systematically investigated so far. This study aimed to investigate the effect of microstructures on the passive behavior of SLM-fabricated HX, and compare it with that of wrought HX. The findings indicated that the XOY plane (perpendicular to build direction) with the refined microstructure exhibited a superior corrosion resistance. Compared to the wrought plane (the cross-sectional plane), the finer grain size, denser sub-grain boundaries, and dislocations all contributed to the formation of a more stable and thicker passivation film on the XOY plane of SLM HX in 10 wt% NaNO3 solution. An analysis of the Auger electron spectroscopy and X-ray photoelectron spectroscopy measurement results showed that a comparatively thick outer layer existed in the passivation film.

Surface modified zero-valent aluminum for Cr(VI) removal at neutral pH

Zero-valent aluminum has attracted considerable attention in degradation of organic contaminants and reduction of heavy metal ions due to its very low redox potential (E0(Al3+/Al0) = −1.662 V). Usually there is a passive oxide film on Al surface, inhibiting its electron transfer and leading to low reaction efficiency. In this work, metal Al surface was modified by loose fine Al2O3 (SM-Al) using a procedure of soaking Al powder in water for a time period and then heat-treating in vacuum. It was found that surface modification remarkably enhanced the reaction efficiency of zero-valent Al in reduction of Cr(VI) to Cr(III) ions in aqueous solution. The longer the soaking time of Al powder in water is, the higher the efficiency in removing Cr(VI) is. The effects of Al particle size and dosage, initial Cr(VI) concentration and reaction temperature on Cr(VI) removal were investigated as well. XPS analyses revealed that the decrease in thickness of Al surface passive oxide films and the promotion of surface covered loose Al2O3 phases on hydration of passive oxide films are two main reasons responsible for the rapid removal of Cr(VI) by SM-Al. Meanwhile, SM-Al exhibited an excellent recyclability and the reused SM-Al has a very fast reaction rate relative to as-prepared SM-Al, 80% of Cr(VI) can be removed even it was reused up to five cycles. The present study provides a new route to activate Al in removal of contaminants in aqueous solution.

Tribocorrosive Study of New and In Vivo Exposed Nickel Titanium and Stainless Steel Orthodontic Archwires

The surface, corrosion and wear properties of new and in vivo exposed nickel titanium (NiTi) and stainless steel (SS) archwires used in orthodontic treatment were investigated. Electrochemical and tribo-electrochemical tests in artificial saliva were performed in order to define corrosion properties and to estimate wear rate of new and in vivo exposed NiTi and SS archwires. The surface chemical analysis of the passive film on the NiTi and SS archwires before and after tribocorrosion tests was performed by Auger Electron Spectroscopy (AES). In vivo exposed NiTi and SS archwires had better electrochemical properties than new archwires due to the protective nature of oral deposits. Total wear and coefficients of friction were higher among in vivo exposed archwires and higher in NiTi archwires in comparison to SS archwires. The estimated thickness of the TiO2 passive film on as-received NiTi is 8 nm, while the passive Cr2O3 film on as-received SS is just 1–2 nm. On in vivo exposed NiTi archwire, a 60–80 nm thick organic film/dental plaque was observed, and on SS, it was thinner, at about 60 nm. This research shows the importance of combining AES with electrochemical testing, to characterize tribocorrosive properties of NiTi and SS orthodontic archwires.

The Coupling Effect of Lead and Polishing Treatments on the Passive Films of Alloy 690TT in High-Temperature and High-Pressure Water

In pressurized water reactors, the existence of lead contamination can promote the corrosion of Alloy 690TT. During the manufacturing, transportation and assembly processes, Alloy 690TT surface are easily scratched and it’s easily ignored. The effect of added lead on the scratched surface is different from that on unscratched surface. In the present study, Alloy 690TT were treated with mechanical polishing (MP) and electrochemical polishing (EP) to generate scratched and unscratched surfaces. With the addition of lead, the thickness of passive film on the MP sample increases by 8 times, while that on the EP sample only slightly increases. These chemical composition changes of passive films induced by lead result in the drop of their electrical resistivity, and the electrical resistivity of passive film on the MP sample is reduced by two orders of magnitude, while that on the EP sample decreases only 3 times. Nevertheless, the thickness and electrical resistivity of passive film on the MP sample are always greater than those of the EP sample. The toxic effect of lead on the MP sample is more severe than that of the EP sample, which may be closely related to their subsurface microstructure. Therefore, Alloy 690TT should better avoid being scratched in secondary circuit system of pressurized water reactors, as scratched behavior will result in a faster corrosion rate of Alloy 690TT with the presence of lead.

Semiconducting behavior and kinetics of passive film growth on AISI 321 stainless steel in sulfuric acid

AbstractIn the present study, the effects of aging and formation potential on the semiconducting behavior of AISI 321 stainless steel as well as the kinetics of the early stages of pitting are discussed. The donor and acceptor densities decrease with increasing formation potential. The steady-state passive film thickness and the coefficient of oxygen vacancies are estimated. The electrode polarization at higher anodic potentials causes the increase in the rate of pit initiation and slows down the growth rate of passive film. Also, the openness of the pits and their coalescence are highly promoted with the increase in the applied potential.

Role of Coke in the Passive Properties of Vitallium 2000 CoCrMo Casting Alloy in Simulated Oral Environment

The passive behaviors of Vitallium 2000 CoCrMo casting alloy in artificial saliva (AS) and Coke were studied by potentiodynamic polarization, electrochemical impedance spectroscopy, cyclic voltammetry, Mott–Schottky combined with scanning electron microscopy, Auger electron spectroscopy, and x-ray photoelectron spectroscopy surface analysis. The results show that with the increasing content of Coke, the self-corrosion current density of alloy increased sharply, the passive film corrosion resistance showed the best in AS and worst in Coke, and the Rp in Coke is reduced to half of that in AS. The thickness of passive films in AS, AS + Coke, and Coke is about 4.5, 3, and 2.5 nm, respectively. Passive films all exhibit n-type semiconductors; with more defects, the carrier density in Coke is 2.3 times more than that in AS. The Coke inhibits the oxidation of Co, Cr, and Mo, and the Co/Cr rate and Cr6+ concentration within the passive film increase. Coke weakens the formation process of protected oxides, thus reducing the stability of alloy’s passive film.

Box-behnken design to enhance the corrosion resistance of plasma sprayed Fe-based amorphous coating

Fe48Cr15Mo14C15B6Y2 (at. %) amorphous coatings under various spraying parameters were deposited on Q235 steel by atmospheric plasma spraying. Passive film thickness was estimated by power-law formula proposed by Hirschorn to investigate the corrosion properties of passive film on the coating surface. Box-behnken design (BBD) in combination with response surface methodology (RSM) was utilized to gain the thickest passive film (about 1.60 nm) in 3.5 wt% NaCl solution. XPS results indicated that passive film formed on the optimal coating comprised of Fe, Cr and Mo oxide species and certain amount of bounded water. Mott-Schottky curve further confirmed an enhanced corrosion resistance of the optimal coating due to a low carrier density under the magnitude of 1018 cm−3. The surface morphology after 20 days immersion suggested that no corrosion products were observed on the optimal coating surface and the passive film retained its stability to protect the metal substrate effectively.

Using Atomic Force Microscopy to Measure Thickness of Passive Film on Stainless Steel Immersed in Aqueous Solution

Employing atomic force microscopy (AFM) to measure passive film thickness on stainless steel (SS) in aqueous solution is proposed. SUS304 austenite and SUS329J4L duplex SS samples partly covered by gold were set in a minicell. To remove the original film, the SS surface but gold was etched using dilute sulfuric acid. After cleaning, open circuit potential (OCP), and distance from the sample surface to the top of the gold were measured. They were then immersed in either 1.0% NaCl; 5.0% NaCl; or aqueous solution with pH ranging from 1.0 to 10.0 and measured again. Differences between the first and subsequent measures of OCP suggested a passive film had formed in solution with pH ranging from 2.8 to 10.0. Similarly, differences among AFM measures revealed the observed film thickness increased with increase in pH and with decrease in chloride ions. Also, film thickness in water was greater than that in a vacuum. Comparison of AFM measurements of passive film on the austenite and sigma phases in sensitized SUS329J4L duplex SS revealed the film was thinner on the sigma phase containing more chromium. Taken together, these findings suggest the proposed method is applicable for measuring the thickness of passive films in aqueous solution.

Complex Capacitance Analysis on Electrochemical Properties of Passive Film Formed on Rebar in Concrete

Reinforced concrete structures have been widely used for the social infrastructures because the rebar embedded in concrete shows high corrosion resistance due to the formation of passive film formed on the rebar. The monitoring of the conditions of the passive film formed on the rebar is important to ensure the proper maintenance and management of reinforced concrete structures. An electrochemical impedance spectroscopy (EIS) is a useful method to evaluate the corrosion state of reinforced concrete nondestructively1, 2). In the present study, the stability of passive film formed on the rebar was evaluated in the concrete simulated environment by the EIS. A saturated calcium hydroxide solution was used to simulate the environment in concrete. The chloride ion concentration was adjusted to 3.8 mmol dm-3 and 16 mmol dm-3 by adding sodium chloride to a saturated aqueous solution of calcium hydroxide. The electrochemical impedance measurement was carried out by a three electrode system. A rod electrode made of cylindrical carbon steel (SR345) that has the same composition as rebar SD345, as is often used in actual structures, was adopted as a working electrode. A saturated KCl silver / silver chloride electrode and a platinum wire were used as a reference electrode and a counter electrode respectively. The electrochemical impedance was measured every 12 hours during immersion. The 3D impedance was measured in order to investigate the time-dependent change of the thickness of the passive film. An electrochemical measurement system (HZ-7000, Hokuto Denko Corporation) was used as the measurement device. The measurement frequency range was 10 kHz to 10 mHz with 5 points per logarithmic sweep. By plotting the admittance and capacitance calculated from the impedance of carbon steel on the complex plane, the resistance and capacitance of the passive film formed on the carbon steel were evaluated. The changes of thickness of passive film formed on the carbon steel with time were discussed. References 1) J. L. Dawson et al., Proceedings of NACE Corrosion / 78, Paper No. 125 (1978). 2) Yoshinao Hoshi et al., Electrochemistry, 87, 78-83, (2019) 3) Masayuki Itagaki et al., Electrochemistry, 75, 649-655, (2007).

Long term semiconducting and passive film properties of a novel dense FeCrMoCBY amorphous coating by atmospheric plasma spraying

The long term electrochemical corrosion behavior and passive film properties of a novel dense Fe48Cr15Mo14C15B6Y2 (at.%) amorphous coating were investigated using electrochemical measurement, Mott-Schottky test, effective capacitance model and XPS technique. The coating exhibited a superior corrosion resistance with a relative low current density of 5.305 × 10−6 A cm−2 even after 1000 h immersion in 3.5 wt% NaCl solution. The film composition changed slightly and made no difference to the corrosion behavior. Noting that point defect density in the passive film and film thickness played a dominant role in the corrosion resistance of the amorphous coating in chloride electrolyte. The enhanced long term corrosion resistance of the coating may be attributed to an inactive mass transport behavior in the passive film in the early immersion age.

Determining the electric-field strength in a passive film via photo-induced electric fields

The nature of the electric-field strength in the passive film on tungsten is explored using photo-electrochemical techniques. A theoretical expression for the photo-stimulated growth of the film has been derived. Rotating ring-disk electrode (RRDE) experiments indicate that photo-corrosion of a tungsten electrode is negligible under super-band gap light illumination. XPS results show that tungsten is in the maximum possible oxidation state (VI) in the film and hence no higher oxidation state is available. The photo-stimulated transient film growth of tungsten in pH 8.5 ± 0.1 boric-borax buffer was recorded as a function of film formation potential (1 VSCE, 2 VSCE, 3 VSCE, 4 VSCE, 5 VSCE, 6 VSCE) and light intensities (50, 200, 1000 mW/cm2). Steady state passive film thickness measurements of the passive film on tungsten indicate that super band gap, UV light suppresses the electric field in the barrier layer, and hence stimulates anodic oxide film growth. The data obtained in this study demonstrate that the electric field strength in the steady state is independent of the applied potential and film thickness, as postulated in the Point Defect Model.

Corrosion protection of a novel SiO2@PANI coating for Q235 carbon steel

In this work, hydrophobic polyaniline-silica nanocomposites were prepared by the growth of the silica spheres in polyaniline solution. Silica spheres were encapsulated into the polyaniline shell (SiO2@PANI), and then mixed with silicone for protecting Q235 carbon steel in 0.1 M sulfuric acid solution. The coatings with special morphology present hydrophobicity (CA=115°), outstanding anti-permeability, good mechanical properties, and strong adhesion. Specifically, silicone-SiO2@PANI coating with a SiO2/PANI weight ratio of 4:1 shows a high corrosion resistance of 2.24×107 Ω cm2 even after 180 days of immersion in corrosive medium. The long-lasting corrosion protection of the coating may be attributed to the excellent physical barrier property and the formation of a thick passive film.

Mechanical properties and corrosion behavior of selective laser melted 316L stainless steel after different heat treatment processes

Irregular grains, high interfacial stresses and anisotropic properties widely exist in 3D-printed metallic materials, and this paper investigated the effects of heat treatment on the microstructural, mechanical and corrosion properties of 316 L stainless steel fabricated by selective laser melting. Sub-grains and low-angle boundaries exist in the as-received selective laser melted (SLMed) 316 L stainless steel. After heat treatment at 1050 °C, the sub-grains and low-angle boundaries changed slightly, and the stress state and strength decreased to some extent due to the decrease of dislocation density. After heat treatment at 1200 °C, the grains became uniform, and the dislocation cells vanished, which led to a sharp decline in the hardness and strength. However, the ductility was improved after recrystallization heat treatment. The passive film thickness and corrosion potential of the SLMed 316 L stainless steel decreased after heat treatment, and the pitting potential also decreased due to the accelerated transition from metastable to steady-state pitting; this accelerated transition was caused by the presence of weak passive films at the enlarged pores after heat treatment, especially for an adequate solid solution treatment.

Corrosion behavior of deformed low-nickel stainless steel in groundwater solution

Abstract Effect of deformation on the corrosion behaviour of 201 low-nickel stainless steel in a simulated groundwater solution was studied via electrochemical tests. The open-circuit potential, pitting potential, polarization resistance and the thickness of passive film decreased with the magnitude of deformation. The carry density of passive film significantly increased as the deformation increasing. In general, the deformation shows a negative effect on the corrosion resistance of the low-nickel stainless steel, which causes the stainless steel more susceptive to pitting in the groundwater. Moreover, the number of pitting initially increased with the magnitude of elastic deformation, while the depths of pitting were extended whereas the number of pitting does not be significantly influenced by the increasing plastic deformation.

Impact of the electrolyte salt anion on the solid electrolyte interphase formation in sodium ion batteries

Aiming at a more comprehensive understanding of the solid electrolyte interphase (SEI) in sodium ion batteries (NIBs), a detailed X-ray photoelectron spectroscopy (XPS) investigation of the few-nanometer thick passivation film formed on hard carbon (HC) in contact with various Na+-ion conducting electrolytes is reported. The electrolytes investigated include 1 M solutions of NaPF6, NaClO4, NaTFSI, NaFSI, and NaFTFSI, all dissolved in a common mixture of ethylene carbonate (EC) and diethylene carbonate (DEC) (EC/DEC = 1/1 wt. ratio). For comparison, the study of analogous Li-based electrolytes containing LiPF6 and LiFSI as representative electrolyte salts is also reported. The anion and cation of the electrolyte salt appear to play a key role in determining the overall SEI layer composition, including its depth evolution and thickness. The SEI building species formed on hard carbon by solvent reduction upon sodiation are found to decrease with the various salts in the order: NaPF6 > NaClO4 ≈ NaTFSI > NaFTFSI > NaFSI. The comparison of lithiated and sodiated HC electrodes shows that the SEI layer is more homogeneous and richer in organic species upon the use of Na-based electrolytes. Surface and depth-profiling XPS analysis on HC electrodes charged in the various electrolyte formulations provides in-depth insights on the differences and similarities of the SEI (composition, thickness, depth evolution, etc.) evolving from the variation in the chemical structure of the cations and anions of the respective salts.

In-situ synchrotron GIXRD study of passive film evolution on duplex stainless steel in corrosive environment

This paper presents new findings about the passive film formed on super duplex stainless steel in ambient air and corrosive environments, studied by synchrotron grazing-incidence X-ray diffraction (GIXRD). The passive film, formed in air, was seen to be a nano-crystalline mixed-oxide. Electrochemical polarisation to the passive region in aqueous 1 M NaCl at room temperature resulted in an increase of the passive film thickness, preferential dissolution of Fe, and partial loss of crystallinity. After termination of polarization to the transpassive regime, reformation of the mixed-oxides was observed, showing a thicker, semi-crystalline, and more defective nature (more vacancies) with further new oxides/hydroxides.