An alternate explanation for the abrupt current increase at the pitting potential

A critical transition potential is shown to be associated with the abrupt increase in the number of metastable pits and the onset of spatial clustering of pits amongst nearest neighbor defects in both commercial and model stainless steels. This critical transition potential is correlated with the parameter, E_pit commonly observed in near-neutral NaCl solutions when stainless steels form pits. The explosive growth of pit sites, the onset of clustering of pits, and E_pit all depend on the diffusion length associated with aggressive corrosion products formed at pits and thus on the stirring rate. E_pit is observed to increase significantly and pit sites remain random to high potentials in both experiments and modeling when the diffusion length is decreased below the nearest neighbor distance (NND) associated with surface defects such as non-metallic inclusions that form a random array of susceptible sites across the otherwise passive surface. This phenomenon is confirmed by experiments and modeling using model stainless steel alloys with decreased inclusions densities and, thus, increased defect NNDs. If the NND is greater than the lateral diffusion length, then E_pit will increase, clustering of pit sites will decrease and explosive growth in the number of pits will be suppressed at a given applied point.     

Critical pitting temperature for Type 254 SMO stainless steel in chloride solutions

The variation with time of the open circuit potential of high molybdenum containing stainless steel (Type 254 SMO) was measured in 4% sodium chloride solution in the temperatures range 30-100 °C. The plot of steady state potentials as function of temperature showed an inflection at 50 °C, attributed to the decrease of oxygen solubility in test solution above 50 °C. Potentiodynamic cycling anodic polarization technique was used to determine the critical pitting potential (E_pit) and the critical protection potential (E_prot) of the steel in 4-30% NaCl solutions at temperatures between 30 and 100 °C. By plotting the two values versus solution temperature, the corresponding critical pitting (CPT) and the critical protection (CPrT) temperatures were determined. Both parameters decreased with increasing chloride content. Above the CPT, E_pit and E_prot decreased linearly with log[Cl⁻]. The addition of bromide ions to the solution shifted both E_pit and E_prot towards positive values. In 4% NaCl, E_pit increased linearly with pH in the range 1-10. The combined effect of chloride ion concentration and pH on the morphology of the pits was examined by scanning electron microscopy (SEM) following potentiodynamic cycling anodic polarization.     

Electrochemical and Microscopic Study of Pitting Corrosion of Ultra-pure Iron

Abstract

Pitting corrosion of ultra-pure iron has been studied by both electrochemical and microscopic methods in borate buffer solution with various additions of potassium chloride.

Breakdown potential (E_b) has been determined by galvanostatic, potentiostatic and potentiokinetic measurements. It has been found that the effect of increasing Cl^? ion concentration is to shift E_b in the active direction by about 100 mV for a 10-fold change in concentration.

The pits were of a polyhedral shape independent of either the Cl^? ion concentration (0·01?0·5 N-Cl^?) or potential (E_b?+800 m V_S.C.E.). Only {110} planes were exposed within the pits.

Pit number was independent of time but increased with potential. At a constant potential the pits did not develop at the same rate and the number of larger pits increased with time. It has been also found that the pits grew in width only after they had approached the depth limit of ～ 0·1 mm.     

Initiation and repassivation of crevice corrosion of type 444 stainless steel in chloride solution

Effects of chloride ion concentrations, solution temperature, and crevice-forming materials on the crevice corrosion of type 444 stainless steel were investigated using a potentiostatic method. Critical crevice potential (E_crev) and repassivation potential (E_r) of the creviced alloy decreased with an increase in chloride concentration [Cl⁻], satisfying the logarithmic relationship between E and [Cl⁻]. In addition, E_crev and E_r of the alloy with silicone crevice former were measured to be higher than those of the alloy with an EPDM (Ethylene Propylene Diene Monomer) crevice former, suggesting that silicone was more effective in preventing water from penetrating crevices between a stainless steel sheet and the crevice former. In electrochemical current transient measurements with an applied potential, the intensity of current transients corresponding to the initiation of metastable pits increased abruptly near the E_r of the alloy, indicating that the stability of crevice corrosion is associated with the initiation of metastable pits.     

Effect of tensile stresses on the Δ<Emphasis Type="Italic">E</Emphasis> effect in ferromagnetic Fe<Subscript>64</Subscript>Co<Subscript>21</Subscript>B<Subscript>15</Subscript> ribbons

Effect of elastic tensile stresses on the Δ E -effect magnitude in ferromagnetic Fe₆₄Co₂₁B₁₅ amorphous ribbons subjected to magnetic annealing and dc treatment was studied. In the case of relatively low tensile stresses, the maximum magnitude of the negative Δ E effect in the ribbons under study is shown to increase whatever their treatment. The subsequent increase in elastic tensile stresses leads to a decrease in the maximum value of the negative ΔE effect. The maximum sensitivity of the ΔE effect to the applied elastic tensile stresses is characteristic of samples subjected to magnetic annealing. The results obtained are explained using a conception of the effect of magnetic domain structure and mechanisms of its transformation induced by magnetic field and elastic tensile stresses on the ΔE effect in amorphous ferromagnetic ribbons.     

Effect of temperature on the ΔE effect in Fe75Si10B15 amorphous metallic wires

The influence of temperature on the dependences of the ΔE effect of Fe₇₅Si₁₀B₁₅ metallic amorphous wires, which were subjected to thermomagnetic treatment at temperatures of from 370 to 470°C, on the magnetic field has been studied. It was shown that, at all temperatures of thermomagnetic treatment at relatively low heating temperatures, the negative ΔE effect is observed. The increase in the heating temperature of the wire during measurements of the ΔE effect at temperatures of 30–330°C leads to a decrease in both the magnitude of negative ΔE effect and the field of reaching the maximum ΔE effect magnitude. The dependence of the induced anisotropy field on the heating temperature of the wire has been determined. The obtained results are explained based on the concept of magnetoeleastic interactions between the core of wire and its near-surface area.     

Electrochemical corrosion and impedance study of SAE1045 steel under gel-like environment

To present simulative study on corrosion of metal by sewage sludge, three kinds of gel-like systems based on SiO₂ gel and polyacrylamide gel are proposed. Comparative results of electrochemical polarization and impedance studies together with coupon test of SAE1045 steel under these gel-like surroundings and deionized water are investigated. Obvious pitting corrosion characteristic of the steel can be seen in gel-like systems with decreasing I_corr and more negative value of E_corr. It is considered to be caused by electric field concentration effect at defected sites in covering layer on the surface of the steel formed by gel particles.     

The aspect ratio of surface grooves and metastable pitting of stainless steel

The metastable pitting behavior of 316L stainless steel with different surface roughness in 0.01 M NaCl solution was studied using potentiostatic and potentiodynamic polarization methods and statistical treatments. As surface roughness decreased, the nucleation rate of metastable pits decreased. The peak current of metastable pits also decreased, but the average growth rate of metastable pits showed a slight increase. The aspect ratio of surface groove, w/d, was suggested to characterize the openness of surface grooves, in which w is the width of the groove at the opening and d the depth of the groove. Bigger w/d value indicates more smooth surface, and it is more difficult for micro-pit to nucleate. Under certain conditions of solution and potential, there is a critical w/d value. Metastable pits may nucleate only on those surfaces whose w/d values are less than the critical value. As the aspect ratio w/d increases, the nucleation rate of metastable pits decreases linearly, and both metastable pitting potential E_m and pitting potential E_p move in the positive direction.     

Instrumented micro-indentation of NiTi shape-memory alloys

We study the instrumented Vickers micro-indentation of single-crystal Ti–50.9 at% Ni shape-memory alloys with systematically varied surface normal orientations ([100], [210], [111] and [221]) and Ti₃Ni₄ precipitate sizes (0 nm, 10 nm, 50 nm, 100 nm, 300 nm and 500 nm). Based on transmission electron microscopy observations, indentation of solutionized NiTi induces inelastic deformation via dislocation activity and a stress-induced martensitic transformation. The room-temperature hardness, Hv, and recoverable energy, E_r, of NiTi are shown to be a maximum for very small precipitate sizes, decrease for intermediate precipitate sizes, and increase for large precipitate sizes. The maximization of Hv and E_r at small precipitate sizes (10 nm) is attributed to the relatively high resistance to both dislocation motion and a recoverable stress-induced martensitic transformation. The decreases in Hv and E_r at intermediate precipitate sizes (50–300 nm) are attributed to a decrease in the resistance to dislocation motion and a measured increase in the transformation temperatures with respect to the indentation temperature. The increases in Hv and E_r at large precipitate sizes (500 nm) are attributed solely to measured decreases in the transformation temperatures with respect to the indentation temperature, since the resistance to dislocation motion remains constant as the precipitates grow from 300 nm to 500 nm. For nearly all heat treatments, the [100] and [221] surfaces demonstrate the highest and lowest values of Hv and E_r, respectively, an effect attributed primarily to orientation of favorable slip systems.     

High temperature dependence of the cubic phase content and optical properties of BN thin films

The temperature dependence of the cubic phase content and optical properties of Boron nitrogen (BN) thin films was studied in this paper. The BN thin films were deposited on fused silica and Si substrates by radio frequency bias magnetron sputtering. The BN film properties before and after annealing were characterized by Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy and UV-visible transmittance and reflection spectra. The results indicate that annealing temperature has a significant effect on the optical absorption edge, optical absorption coefficient α, refractive index n, and optical conductivity σ of BN films. The optical absorption edge shift to the high energy with annealing temperature increase indicates that the film optical band gap E_g becomes large. The change in the optical absorption properties results from the stress relaxation and phase transformation owing to the high temperature annealings. The dependence of α on the photon energy is fitted by the Urbach tail model in order to determine the Urbach energy E₀. In addition, it is found that refractive index n exists clearly different dependences on temperature in visible and ultraviolet regions, and the optical conductivity σ threshold moves to high energy with increasing annealing temperatures in the threshold region.     

Influence of temperature on ΔE effect in amorphous Fe64Co21B15 ribbons

The work presents the results of investigation of the influence of thermal cycling on ΔE effect as a function of the external magnetic field in amorphous Fe₆₄Co₂₁B₁₅ ribbons after thermomagnetic treatments in the temperature range of 250–350°C. The influence of the temperature of subsequent heating of ribbons in the temperature range 30–300°C on the absolute maximum value of the negative ΔE effect has been determined. The heating results in a displacement of maximum absolute value of negative ΔE effect to the region of lower magnetic fields. Based on the obtained results, it has been established that the dependence of the field of uniaxial anisotropy induced by thermomagnetic treatment on heating temperature in amorphous Fe₆₄Co₂₁B₁₅ ribbons is close to linear.     

Effect of Nb addition on microstructure evolution and nanomechanical properties of a glass-forming Ti–Zr–Si alloy

The glass-forming Ti₇₅Zr₁₀Si₁₅ alloy is regarded as a potential material for implant applications due to its composition of non-toxic, biocompatible elements and some interesting mechanical properties. The effects of partial substitution of 15 at.% Ti by Nb on the microstructure and the mechanical behaviour have been investigated by X-ray diffraction, scanning electron microscopy with energy-dispersive X-ray analysis, transmission electron microscopy and nanoindentation techniques. Copper mold casting and melt-spinning methods have been applied to study the influence of the cooling rate on the properties of both alloys, Ti₇₅Zr₁₀Si₁₅ and Ti₆₀Zr₁₀Nb₁₅Si₁₅. As a result of different cooling rates, significant microstructural variations from multiphase crystalline states in cast rods to nanocomposite structures in ribbons were observed. The limited glass-forming ability (GFA) of the Ti₇₅Zr₁₀Si₁₅ alloy results for melt-spun ribbons mainly in nanocomposite structures with β-type nanocrystals being embedded in a glassy matrix. Addition of Nb increases the glass-forming ability. Raising the overheating temperature of the melt prior to melt-spinning from 1923 K to 2053 K yields for both alloys a higher amorphous phase fraction. The mechanical properties were investigated using compression tests (bulk samples) and the nano-indentation technique. A decrease of hardness (H), ultimate stress and reduced Young's modulus (E_r) is observed for Ti₆₀Zr₁₀Nb₁₅Si₁₅ rods as compared to Ti₇₅Zr₁₀Si₁₅ ones. This is attributed to an increase of the fraction of the β-type phase. The melt-spun ribbons show an interesting combination of very high hardness values (H) and moderate reduced elastic modulus values (E_r). This results in comparatively very high H/E_r ratios of >0.075 which suggests these new materials for applications demanding high wear resistance.     

Electrochemical studies of packed iron powder electrodes: Effects of common constituents of natural waters on corrosion potential

Using a powder disk electrode (PDE) made with micron-sized, high purity iron metal we investigated how the corrosion of this material is affected by solution conditions that are relevant to the degradation of contaminants in environmental remediation applications. Changes in corrosion potential (E_corr) with time showed that low pH, high concentrations of chloride, and natural organic matter led to breakdown of the passive film. Bicarbonate caused E_corr to decline rapidly into the active potential region, but then E_corr rose back into the passive region over 10s of hours. The rate of decline in E_corr was greatest at higher pHs, suggesting a specific effect of rather than a general effect of pH.     

Detection of back-side pit on a ferrous plate by magnetic flux leakage method with analyzing magnetic field vector

We have developed a magnetic flux leakage (MFL) system using magnetic resistive (MR) sensors for detecting two dimensional magnetic field components, and an induction coil that generates low magnetic field strengths and extremely low frequencies. The signal at each scanned measurement point (i) was divided by the signal strength M_mes,i and phase α_i by a lock-in amplifier. Using the strength M_mes,i and phase α_i, we calculated the imaginary part of the signal using the common phase β. By optimization of the common phase β to the imaginary part, the analyzed scanning data curve was shown to be effective in estimating the size (depth and diameter) of back-side pits on a ferrous plate. Comparing the two dimensional magnetic field components of leakage, the imaginary part of the y-component parallel to the induced magnetic field was found to be suitable for detecting the back-side pits.     

Cumulative quantum mechanics (CQM). Part I: Prerequisites and fundamentals of CQM

There is proposed a formulation of the fundamentals of cumulative quantum mechanics (CQM) that allows one to describe the resonance cos-waves with the ψ _n function of an electron (ψ _n (r) ～ cos(k _n r)/r ^k ) unlimited (with k ≠ 0) in the resonator center in hollow quantum resonators with any type of symmetry (plane—k = 0, spherical—k = 1, and cylindrical—k = 0.5). Irregular in the center of a resonator, the cos solutions are regularized in the resonator center by the geometric normalization coefficient corresponding to the symmetry type and being χ(r) = 2 ^k π^1/2 r ^k at k ≠ 0 (if k = 0, then χ = 1). The stratification of the probability of finding the particle in the quantum resonator volume is similarly determined by the energy of a particle or a full set of squares of the corresponding quantum numbers ((n ? 1/2)² for cos-waves and n ² for sin-waves) for any type of the resonator symmetry. An analytical CQM model of the polarization resonance electron capture (dynamic localization due to the self-formation of a potential barrier cumulating this electron into a molecule) is proposed. When there occurs the polarization capture of an electron by the allotropic hollow forms of carbon (fullerenes and nanotubes), the electron energy E _n > 0. The problem on the Vysikaylo polarization effect of the first type (or the problem on polarization cumulation of the de Broglie waves of electrons with characteristic dimension of ～ 1 nm) is reduced to the problem of G.A. Gamov: “a quantum particle in a box with a potential barrier on its boundary.” The energy spectrum of states localized by the barrier, E _n > 0 (a metastable IQ particle is a partially open quantum dot, line, or pit), as in the case of E _n < 0 (a stable FQ particle is a closed quantum dot, line, or pit) is determined by the effective internal dimensions of a box (R + r _ind) with the polarization forces effectively acting at a distance r _ind from the polarizable molecule. The CQM allows one to describe with E _n > 0 both the limited cumulation of ψn(r)-functions for de Broglie-Fresnel generalized interference and the unlimited cumulation of ψn(r)-functions to the center of a quantum resonator with Vysikaylo-de Broglie-Fraunhofer generalized interference in hollow polarizable spherically or cylindrically symmetric quantum resonators for de Broglie electron waves. In the framework of the CQM, there have been analytically calculated the eigen quantum pairs: ψ _n (r)-functions, respectively stratified profiles of the probability of a particle’s location in the resonator cavity, W _n (r) and E _n > 0, the eigen energies of the electrons localized in the quantum resonator (C₆₀ and C₇₀, etc.) by polarization forces. It is proved that, alongside with the classical energy spectrum for asymmetric ψ _n -functions (sin-waves) with E _n ～ n ² for hollow quantum resonators, there exist quantum resonances for symmetric ψ _n -functions (cos-waves) with E _n ～ (n ? 1/2)², which can be realized in the experiments.     

Origin of the n-type field effect in polyaniline and oligoaniline thin films

We analyse the n-type field effect recently reported for protonated, layer-by-layer self-assembled polyaniline and oligoaniline thin films. An agreement is obtained between the experiments and a model, valid for three-dimensional variable-range hopping in a parabolic Coulomb gap. The results suggest that the wave-function decay length ξ and/or the dielectric constant ε vary with the position of the Fermi level (E_F), with a positive derivative dln[ξ(E_F)ε(E_F)]/dE_F in the order of a few eV⁻¹. The apparent discrepancy between the p-type doping and n-type field effect is explained by the electron-hole asymmetry characteristic for aniline derivatives.     

Ba(Ti1 − xSnx)O3 (x = 0.13) nanomaterials produced by low-temperature aqueous synthesis

BaTi_0.87Sn_0.13O₃ (BTS₁₃) nanopowder was prepared by low-temperature aqueous synthesis (LTAS) method. The evolution of the structure and microstructure of the precursor precipitate, heated at temperatures up to 1000 °C was studied by TGA, FT-IR, SEM and XRD techniques. The dried precipitate showed a microstructure consisting of nano-sized grains (∼40 nm) with great tendency to agglomeration. BaTi_0.87Sn_0.13O₃ single phase was obtained at 800 °C. The ceramics prepared from as-obtained BTS₁₃ powders (60-70 nm) show good dielectric and ferroelectric characteristics. The dielectric constant was about 4800 and the dielectric loss (tan δ) was 0.229 at 1 kHz and at the Curie temperature (31 °C). The remanent polarization (P_r) and the coercive field (E_C) of Ba_0.97Ho_0.03TiO₃ ceramics, at 1 kHz, were P_r = 13 μC/cm² and E_C = 0.89 kV/cm. The ferroelectric parameters E_C and P_r decrease with increasing frequency in the domain 100 Hz to 10 kHz.     

Effects of mechanical properties, residual stress and indenter tip geometry on instrumented indentation data in thin films

In this work, an axisymmetric two-dimensional finite element model was developed to simulate instrumented indentation testing of thin ceramic films deposited onto hard steel substrates. The level of film residual stress (σ_r), the film elastic modulus (E) and the film work hardening exponent (n) were varied to analyze their effects on indentation data. These numerical results were used to analyze experimental data that were obtained with titanium nitride coated specimens, in which the substrate bias applied during deposition was modified to obtain films with different levels of σ_r. Good qualitative correlation was obtained when numerical and experimental results were compared, as long as all film properties are considered in the analyses, and not only σ_r. The numerical analyses were also used to further understand the effect of σ_r on the mechanical properties calculated based on instrumented indentation data. In this case, the hardness values obtained based on real or calculated contact areas are similar only when sink-in occurs, i.e. with high n or high ratio Y/E, where Y is the yield strength of the film. In an additional analysis, four ratios (R/h_max) between indenter tip radius and maximum penetration depth were simulated to analyze the combined effects of R and σ_r on the indentation load-displacement curves. In this case, σ_r did not significantly affect the load curve exponent, which was affected only by the indenter tip radius. On the other hand, the proportional curvature coefficient was significantly affected by σ_r and n.     

A newly synthesized glycine derivative to control uniform and pitting corrosion processes of Al induced by SCN anions - Chemical, electrochemical and morphological studies

A newly synthesized glycine derivative (termed GlyD), 2-(4-(dimethylamino)benzylamino)acetic acid hydrochloride, was used to inhibit uniform and pitting corrosion processes of Al in 0.50 M KSCN solutions (pH 6.8) at 25 °C. For uniform corrosion inhibition study, Tafel extrapolation, linear polarization resistance and impedance methods were used, complemented with SEM examinations. An independent method of chemical analysis, namely ICP-AES (inductively coupled plasma atomic emission spectrometry) was also used to test validity of corrosion rate measured by Tafel extrapolation method. GlyD inhibited uniform corrosion, even at low concentrations, reaching a value of inhibition efficiency up to 97% at a concentration of 5 × 10⁻³ M. Results obtained from the different corrosion evaluation techniques were in good agreement. This new synthesized glycine derivative was also used to control pit nucleation and growth on the pitted Al surface based on cyclic polarization, potentiostatic and galvanostatic measurements. The pitting potential (E_pit) and the repassivation potential (E_rp) increased by the addition of GlyD. Thus GlyD suppressed pit nucleation and propagation. Nucleation of pit was found to take place after an incubation time (t_i). The rate of pit nucleation and growth decreased with increase in inhibitor concentration. Morphology of pitting was also studied as a function of the applied anodic potential and solution temperature. Cross-sectional view of pitted surface revealed the formation of large distorted hemispherical and narrow deep pits. GlyD was much better than Gly in controlling uniform and pitting corrosion processes of Al in these solutions.     

Pitting and pitting control of Al in gluconic acid solutions - Polarization, chronoamperometry and morphological studies

The anodic behaviour of Al in gluconic acid (HG) solutions was studied. Al was found to pit in such solutions. Surface and cross-sectional views of the SEM images recorded beyond the breakdown potential (E_b) revealed the occurrence of intense pitting attack with the formation of large hemispherical pits. The effect of adding some environmentally acceptable inorganic inhibitors (tungstates, molybdates or silicates) on the pitting corrosion behaviour of Al in HG solutions was also studied. Measurements were carried out under the influence of various experimental variables based on polarization and chronoamperometric techniques. These measurements were complemented by ex situ scanning electron microscopy (SEM) and energy dispersive X-ray (EDX) examinations of the electrode surface. The presence of these compounds in HG solutions decreased the passive current density (j_pass) and increased E_b. In HG solutions, chronoamperometric measurements showed that the anodic current density first decreased, due to growth of a passive oxide film, then increased with time after a pit incubation time, t_i and finally attained a steady-state value. Value of t_i was shortened and simultaneously the steady-state current was elevated, corresponding to an increase in the rate of pit initiation and growth, with increasing applied anodic potential and HG concentration. The rate of pit nucleation () was found to decrease to an extent depending on the type and concentration of the introduced inhibitor. The inhibitory effect of these compounds decreased in the order:  >  > .