Current transients of passive iron observed during micro-indentation in pH 8.4 borate buffer solution

Micro-indentation test of passive iron electrode in deaerated pH 8.4 borate buffer solution was carried out to investigate the rupture and repair of passive film. During driving a conical diamond micro-indenter with a load of 0.1 N order downward to the electrode and driving upward from the electrode, a couple of anodic current peaks were observed. The first current peak spiked during loading was responsible for partial exposure of iron substrate to the solution due to rupture of the passive film when the indenter tip contacted. The second peak emerged during unloading when elastic deformation recovered, which was ascribed to repair at the ruptured sites. The second peak current was larger than the first one. Both peaks were sensitively influenced by electrode potential or concentration of sulfate ions containing in solution. The model for a series of rupture and repair processes of the passive film by micro-indentation was proposed to discuss the current transients.     

A numerical model for current transients during micro-indentation of passive iron surface

During in situ micro-indentation of passive iron in pH 8.4 borate solution, a couple of anodic current peaks emerged; the first peak during loading and the second peak during unloading. The current transients, associated with rupture and repair of the passive film, were influenced by the indentation conditions. For instance, the current peak height, the current peak area and the time required for complete repassivation are strongly dependent on indentation rate. A numerical model was proposed to correlate the current transient during loading with mechanical deformation of the passive surface. The comparison between the current transient measured experimentally and that estimated from the load transient suggested that the ruptured area of passive film was about 10% of the surface area deformed by the contact with the indenter.     

Mechano-electrochemistry of a passive surface using an in situ micro-indentation test

Depassivation–repassivation of iron surfaces in boric–borate solutions were investigated by using the micro-indentation test. A pair of current peaks due to repair of the passive film following rupture of the film were observed during a series of indenter drives, i.e., loading and unloading of the indenter. The shape of the current peak depended on environmental conditions (conductivity and pH of the solution) and substrate conditions (mechanical processing history, alloyed element) as well as indentation conditions (repetition, maximum depth, and maximum load). Plastic deformation of the surface was accompanied by surface depassivation, while no depassivation occurred during the elastic deformation, indicating that the passive film on iron has a ductile property. The solution conditions did not affect the scale of depassivation but affected the rate of repassivation. Dislocations in the substrate made surface depassivation difficult but enhanced reactivity during the repassivation. The test also revealed that type-312L stainless steel has high corrosion resistance in a concentrated NaCl solution.     

Effect of stress on the passivation of Si-DLC coating as stent materials in simulated body environment

DLC coating can be used for vascular stents to prevent the stainless steel substrate from eluting Ni and Cr by plastic deformation and corrosion environment. The stress corrosion cracking (SCC) of Si-diamond-like carbon (Si-DLC) coated on 316L stainless steel was studied in a simulated body environment of a deaerated 0.89 wt.% NaCl electrolyte at 37 °C. This paper investigated the effect of Si-DLC coating on the SCC of 316L SS by slow-strain-rate test (SSRT), constant load test (CLT), and electrochemical impedance spectroscopy (EIS). The EIS data were monitored for the elastic and plastic regions under CLT to determine the electrochemical behavior of the passive film during SCC phenomena. The Si-DLC coated steel exhibited more ductility than uncoated steel and less susceptibility to SCC in this environment. According to X-ray photoelectron spectroscopy (XPS) analysis, the film repassivation occurs due to the presence of the silicon oxide layer on the Si-DLC film surface.     

Influence of Experimental Setup and Plastic Deformation on the Shaft-Loaded Blister Test

In the shaft-loaded blister test (SLBT), plastic deformation often occurs at the contact area between the shaft tip and adhesive layer, leading to a larger displacement (blister height) than if the film was loaded elastically. As a consequence, incorporating the displacement variable into the analysis can result in misleading values of the applied strain energy-release rate, G. In this work, the influence of plastic yielding at the contact area on G of a thin film was investigated as a function of some common SLBT experimental variables, namely, substrate hole diameter, film thickness, and shaft-tip diameter. Test specimens consisted of plies of pressure-sensitive adhesive tape adhered to a rigid glass substrate. G was calculated from the following Equations: (1) load-based, (2) hybrid, (3) displacement-based, and (4) combination. Decreasing the film thickness, increasing the hole diameter, or decreasing the shaft-tip diameter lead to more plastic yielding at the contact area as well as to an increase in blister height. The increased blister height resulting from plastic deformation leads to disagreement among the values of G calculated from the different Equations when the displacement variable was included in the calculation. However, the load-based equation, which does not include the displacement, was determined to be independent of plastic yielding and the “correct” equation for calculating G. In addition, the film tensile rigidity (Eh) was calculated using an experimental compliance calibration. The effects of film thickness on the mechanical behavior of the film (bending plate vs. stretching membrane) as well as methods to determine the displacement resulting from plastic deformation are also discussed.     

Electrochemical investigation of the effects of hydrogen on the stability of the passive film on iron

The effects of hydrogen on the stability of passive films on iron were investigated by electrochemical methods: open circuit potential decay, cathodic galvanostatic reduction, electrochemical impedance spectroscopy, and breakdown potential measurements. The results show that hydrogen decreases the final static open circuit potential, the cathodic charge for reduction and the charge transfer resistance of the passive film, indicating that hydrogen decreases the stability of the passive film. The charge transfer resistance of the passive film formed on the charged specimen does not change with increasing the film formation potentials, suggesting that increasing film formation potentials under hydrogen charging conditions cannot improve the stability of the passive film. Hydrogen decreases the breakdown potential of the passive film, especially at lower chloride ion concentrations, confirming that hydrogen promotes the susceptibility of the passive film on iron to pitting corrosion. The reasons why hydrogen decreases the stability of the passive film were discussed.     

Influence of Experimental Setup and Plastic Deformation on the Shaft-Loaded Blister Test

In the shaft-loaded blister test (SLBT), plastic deformation often occurs at the contact area between the shaft tip and adhesive layer, leading to a larger displacement (blister height) than if the film was loaded elastically. As a consequence, incorporating the displacement variable into the analysis can result in misleading values of the applied strain energy-release rate, 𝒢. In this work, the influence of plastic yielding at the contact area on 𝒢 of a thin film was investigated as a function of some common SLBT experimental variables, namely, substrate hole diameter, film thickness, and shaft-tip diameter. Test specimens consisted of plies of pressure-sensitive adhesive tape adhered to a rigid glass substrate. 𝒢 was calculated from the following Equations: (1) load-based, (2) hybrid, (3) displacement-based, and (4) combination. Decreasing the film thickness, increasing the hole diameter, or decreasing the shaft-tip diameter lead to more plastic yielding at the contact area as well as to an increase in blister height. The increased blister height resulting from plastic deformation leads to disagreement among the values of 𝒢 calculated from the different Equations when the displacement variable was included in the calculation. However, the load-based equation, which does not include the displacement, was determined to be independent of plastic yielding and the “correct” equation for calculating 𝒢. In addition, the film tensile rigidity (Eh) was calculated using an experimental compliance calibration. The effects of film thickness on the mechanical behavior of the film (bending plate vs. stretching membrane) as well as methods to determine the displacement resulting from plastic deformation are also discussed.     

Multiscale Simulation of Indentation,Retraction and Fracture Processes of Nanocontact

The process of nanocontact including indentation and retraction between a large Ni tip and a Cu substrate is investigated using quasicontinuum (QC) method. The multiscale model reveals that significant plastic deformation occurs during the process of nanocontact between Ni tip and Cu substrate. Plastic deformation is observed in an area as large as 20 nm wide and 10 nm thick beneath Ni tip during the indentation and retraction. Also, plastic deformation at a deep position in the Cu substrate does not disappear after the neck failure. The analysis of generalized planar fault energy curve shows that there is a strong tendency for deformation twinning in Cu substrate. However, deformation twinning will be retarded during indentation due to the high stress intensity caused by stepped surface of Ni tip. The abrupt drop of load curve during tip retraction is attributed to the two different fracture mechanisms. One is atomic rearrangement near the interface of Ni tip and Cu substrate at the initial stage of neck fracture, the other is shear behavior of adjacent {111} planes at the necking point. A comparison of the critical load and critical contact radius for neck fracture is also made between theoretical values and our numerical results.     

Galvanostatic response of the passive film on iron in acid media

The galvanostatic technique applied to the passive system as it is described here enable access to the region between zero current and the steady state passivation current in the potentiostatic polarization diagram. It allows us to visualize the electric field applied to the passive film out of its steady state value. A good correlation with the impedance behaviour of the passive iron is observed in the entire frequency range. The long time domain of the potential/time curves reveals an exceptional degree of linearity in a wide range of current applied. In this region the passive film may be represented by a capacitor whose charge is defined not only by the applied potential but also by the actual film thickness. The hydrodynamic conditions affect the galvanostatic transient in the case of the Fe/H₃PO₄ passive system.     

Transient film formation on chalcopyrite in acidic solutions

The transient time-dependent region characteristic of the anodic passive film formation on chalcopyrite in sulphuric acid solutions was studied by galvanostatic measurements. The occurrence of two passivation subregions was observed. Both followed the Sato–Cohen (logarithmic) model for the growth of anodic passive films. The experimental electric field for the two passivated steps was approximately 10⁵ V cm^?1. The electric field for the first step, at lower potentials, decreased with increasing ionic strength, but was pH independent. In the second step, the electric field decreased with increasing pH. The Tafel relationship was followed for constant electrical charge passed. The transition points between first and second step had almost the same electrical charge for different current densities and the electrical charge of the transition point decreased with increasing pH. The effects of temperature and iron/copper ion additions were also studied.     

An SECM observation of dissolution distribution of ferrous or ferric ion from a polycrystalline iron electrode

The dissolution of iron as ferrous or ferric ion from a polycrystalline iron electrode during anodic polarization in pH 2.3 sulfate solution was evaluated by using scanning electrochemical microscopy (SECM). A graphite reinforcement carbon (GRC) microelectrode was employed as a probe electrode of SECM to detect ferrous or ferric ions dissolved from the iron electrode in the active-dissolution, passive or trans-passive region. The probe current above the iron electrode surface subjected to active-dissolution showed the dissolution distribution of ferrous ion, depending on the substrate grains. It was found that the active-dissolution rate of iron as ferrous ions from the grain on which the thicker film was formed in the passive region, was lower than that from the grain on which the thinner film was formed in the passive region.     

Surface analyses of anodic oxides films formed on Fe-3% Ti alloy

Surface analyses of the anodic oxide films formed on Fe—3% Ti alloy in deaerated pH 3.0 phosphate solution were performed with Auger electron spectroscopy (AES) and ellipsometry to evaluate the role of allying titanium in the corrosion resistance of iron.The 3%-addition of titanium reduced significantly the passivity-maintaining current density of iron as well as the maximum-active current density. Auger analysis revealed that titanium was enriched markedly in the anodic oxide films formed on Fe—3% Ti alloy and that a significant amount of phosphorus was distributed in the whole range of film thickness. Both the amount of titanium enriched in the film and the film thickness (20–40 nm) ellipsometrically obtained were proportional to the amount of electric charge required for passivation. Atomic absorption analysis of the solution indicated that the formation of a titanium-enriched film resulted from a preferential dissolution of iron as ferrous ions.From the measurement of the potential decay curves of the Fe—3% Ti alloy and pure iron electrodes passivated for different hours, it was concluded that the titanium-enriched layer promoted the passivity by suppressing, though incompletely, the active dissolution, whereas the substantial passivity of the alloy was attributed to the iron oxide film of barrier type formed at the interface of titanium-enriched layer/alloy substrate.     

Ion migration in anodic barrier oxide films on iron in acidic phosphate solutions

A kinetic study was carried out of the ionic current in the anodic barrier oxide layer on iron at the steady state in the passive potential region in acidic phosphate solutions. It is found that the ionic current follows the classical high field ion conduction equation in which the current is expressed as an exponential function of the electric field in the barrier layer. From the kinetic constants appearing in this equation and their temperature dependence, the diffusion coefficient and the activation energy for diffusion of moving ions in the layer were estimated and compared with those of high temperature diffusion in iron oxides. It is suggested that the ionic current is carried by oxygen ions than by iron ions in the barrier oxide film.     

Electron conduction in passive films on nickel

The electron conduction properties of the passive film on nickel in acid solution were studied by differential capacitance of nickel electrode in the passive condition, and by redox reactions of the Fe²⁺/Fe³⁺ and Q/H₂Q systems. A large capacitance value of the passive electrode, which is possibly comparable to that of the double layer, can be ascribed to the space charge capacitance in the passive film which is highly nonstoichiometric. The redox reaction currents of these systems may be sustained by tunnelling of charge carriers through the space charge layer in the passive film, if it can be accepted that the tunnel effect commences when the electric field strength in the space charge layer is of the order of 10⁶ V/cm. Consequently, the passive film can not be an insulator, at least in acid solutions.     

Potential dependence of normalized friction coefficient of passive iron surface evaluated by nano-scratching in solution

Nano-scratching in solution was performed to the single-crystal iron (1 0 0) surface passivated at 0.0-1.0 V (SHE) in pH 8.4 borate buffer solution to evaluate the friction coefficient of the iron (1 0 0) surface kept in the passive state and its potential dependence. The friction coefficient obtained with nano-scratching for the passive iron surface depended on normal force, i.e., normal displacement, which resulted mainly from the geometry of the diamond tip. In order to avoid the effect of the tip geometry on friction coefficient, the normalized friction coefficient was newly defined with dividing friction coefficient by geometrical factor. The normalized friction coefficient obtained with nano-scratching in solution for the iron (1 0 0) surface kept in the passive sate was significantly larger than those obtained with nano-scratching in air after passivation. The normalized friction coefficient obtained with nano-scratching in air after passivation was almost independent of potential in the passive region. On the other hand, the normalized friction coefficient obtained with nano-scratching in solution increased with increasing potential in the passive region.The difference between normalized friction coefficients obtained with nano-scratching in solution and in air was discussed by taking into account a series of mechano-electrochemical reaction (film rupture, active dissolution and repassivation) which would take place at the moving front of the diamond tip during nano-scratching in solution. The large potential dependence of the normalized friction coefficient obtained with nano-scratching in solution was explained in terms of the increase in repassivation rate at the film rupture sites with increasing potential in the passive region.     

Plastic deformation of ZnO thin films through edge and screw dislocation movements

Columnar wurtzite grains were formed in sputtered ZnO thin films deposited on a plastic polyethylene terephthalate substrate. Selected-area diffraction patterns reveal that the columnar grains in the sputtered films present two preferred growth planes, namely, the basal (0002) and prismatic (100) growth planes. The diffraction patterns obtained also confirm that the microstructure of sputtered indium tin oxide thin films is amorphous in nature. Tensile tests indicate that the fracture strain of the ZnO thin film occurs between 1.73% and 2.14%, while the fracture strain of the indium tin oxide thin film occurs between 0.24% and 0.67%. Thus, the fracture toughness of the sputtered ZnO thin film is greater than that of the sputtered indium tin oxide thin film. High-resolution transmission electron microscopic images demonstrate that edge and screw dislocations could be identified in the sputtered ZnO thin films. Moreover, edge and screw dislocation movements may, respectively, be observed in the basal- and prismatic-oriented ZnO columnar grains of the sputtered ZnO thin films. Our results indicate that movements of the edge and screw dislocations in the basal- and prismatic-oriented ZnO columnar grains account for the plastic deformation of the investigated ZnO thin films under tensile stress.     

在玻璃上合成有取向的silicalite-1分子筛膜及其生长机理

引言 分子筛膜具有规则的微孔结构、良好的化学和热稳定性,在气体分离、催化膜反应器、化学传感器以及分子筛改性电极等方面有广泛的应用前景[1-2],是催化和分离新材料领域的研究热点之一.     

Contact angle characteristics and breaking strength of paint plastic film

The advancing contact angle of water on plastic film coatings on metal was measured against both the air and the metal side surfaces after their being peeled off from the metal substrate. The plastic used was a methacrylate copolymer, and it was baked on cadmium, aluminum, nickel, iron, and gold. Contact angle for the air side was about 74° at 25°C. for all metals, but the values on the metal side differed considerably, ranging from 76° for gold to 50° for cadmium. At the same time the static breaking strengths of the same films were investigated by applying a knife-edge vertically to the film with increasing load and measuring the weight at which the electric resistance through the film became zero. Increasing film thickness gave increasing strength, but further thickening made the film weaker with a tendency for crack formation. The film–metal combinations of larger contact angle difference generally also showed the higher breaking strength.     

Plastic Deformation and the Fracture Surface Energy of Sodium Chloride

A correlation between plastic deformation at crack tips in sodium chloride and the measured value of the fracture surface energy is presented. Plastic deformation can either aid or hinder crack growth, depending on the mode of deformation at the crack tip. If plane-stress deformation occurs, crack motion is hindered by step formation, dislocation generation, and plastic blunting of the crack tip. If plane-strain deformation occurs, crack motion is aided by stress fields that arise from the deformation. The specific surface free energy of sodium chloride, {100} plane, is estimated to be less than 0.37 J/m².     

Wiederbefeuchtung bei der Pressfiltration

During press filtration, the filter cake experiences a plastic deformation. However, a filter cake expansion may occur once the pressing forces are released, which is confirmed by experiments with an aqueous coal suspension. Rewetting of the cake occurs when a liquid film is present during cake swelling, which deteriorates the cake dryness significantly. However, this can be prevented when the liquid film is successfully removed, and lower pressures suffice for mechanical cake drying.