Search

In recent times, Bangladesh has experienced increased environmental degradation in general, particularly industrial pollution. The effect of industrial pollution is huge and the country is affected badly in a socio-economic way. This article emphasizes the problem of industrial pollution with regard to the present status of the environment in Bangladesh. It contains a summary of the country’s major environmental problems, a compilation of varied information on industrial pollution, and its effects. In the end, this article gives a silver lining on the magnitude of the problem and strategies for handling industrial waste management in an environment-friendly way.

Steel rebars are widely applied in reinforced concrete structures due to their contribution to significant improvements in mechanical properties. However, the exposure to corrosive environments, such as solution containing chloride, may induce accelerated corrosion and jeopardize the sustainability and durability of reinforced concrete. The current work evaluated the chloride thresholds (in both wt% and [Cl-]/[OH-]) of steel rebar with different chromium contents (0, 4, and 23wt%) in synthetic concrete pore solution (SCPS) based on AC and DC electrochemical measurements, and chemical and structural characterizations. The study found thar the CT values varied slightly based on the different measurement methods and the values were compared with values obtained from the literature. The values are 0.01-0.1wt% (3.76), 0.1-1wt% (>23.8), and 2.9-3.5wt% (>23.8) for 615, 4% Cr, and SS23, respectively, where the values in parentheses are [Cl-]/[OH-]. Therefore, it is demonstrated that multiple measurements are necessary to determine a reliable CT value. Corrosion mechanisms giving rise to CT are included to illustrate the processes involved in establishing CT.

The failure of transpassive films on transition metal alloys was investigated. The results show that the failure of the transpassive film on 3D printing nickel-based superalloy in flowing NaNO3 solution is dominated by self-induced cracking of the film on niobium-segregated phases and the erosion-induced degradation on the film assisted by cation vacancy condensation at the metal/barrier layer interface. Secondary passivation induces the formation of a transpassive film, the nature of which has been debated for decades. The findings are consistent with a bi-layer structure comprising a point-defective barrier layer that grows into the substrate alloy and a precipitated outer layer.

Cl−-induced corrosion is one ineluctable problem we face when metals and alloys are exposed to marine environment. Herein, we give a mini review covering the aspects of combating Cl−-induced corrosion from the perspective of surface chemistry. Firstly, the interaction of Cl− with oxide surface is briefly reviewed. Then, we highlight some recent strategies for repelling, blocking and capturing Cl− by using surface chemistry control and surface modification via self-assembling at molecular levels.

It is known that the kinetics of redox reactions occurring on the surfaces of passive metals depend upon the properties of the passive film, ostensibly due to quantum mechanical tunnelling (QMT) of electrons and holes between the metal and the redox couple at the barrier layer/solution (bl/s) interface. In this paper, the tunnelling probability is used to inter-convert the exchange current densities for the redox reactions occurring at the bl/s interface and on the hypothetical bare metal surface. We review our previous work on combining QMT theory with the point defect model (PDM), which provides an analytical expression for the bl thickness as a function of voltage. By combining QMT theory and the PDM, we derive a modified form of the generalized Butler-Volmer equation that requires as input only the kinetic parameters for the redox reaction on the hypothetical bare surface and parameters contained in the PDM. The application of the theory is illustrated with reference to the corrosion of carbon steel in concrete pore solution, to calculating the corrosion potential of, and crack growth rate in, sensitized type 304 SS in boiling water reactor (BWR) coolant circuits, and the use of hydrogen oxidation on platinum to determine the thickness of the bl as a function of voltage and temperature. This illustrates a new, powerful technique for probing the formation of passive films on metal surfaces.

Electrochemical impedance spectroscopy (EIS) is a powerful technique for the non-destructive, dynamic measurement of electrochemical corrosion behavior in condensed environments, and is a demonstrated, in situ method for monitoring oxide films formed on metal surfaces in liquid metals. To characterize this capability, the impedance properties of three kinds of oxide films (anodic titanium oxide films, deposited Fe2O3 films, and thermally oxidized Fe samples) in liquid metals were examined using the EIS technique. The results show that the impedance response is related to the oxide film thickness and quality. The impedance of thin oxide films ( 200 nm) shows that the oxide film without cracks is stable in LBE and protects the substrate from corrosion. EIS is a promising method for accessing the electrochemical behavior of oxide films on metals and alloys in liquid metals.

The effect of thermal oxide layer on He implanted 316L stainless steel was studied to evaluate experimentally how thermal oxidation affects the diffusion and distribution of He in the material. In the case of thermal oxidation of a He implanted sample, with an increase in oxidation time, the max swelling height increases logarithmically as a function of time and finally saturates for all samples except for the lowest dose of implanted He. Concerning TEM results, two void regions are identified. Similar to the calculation, the total irradiated depth was around 250 nm and the large void region was formed around 100–150 nm depth. On the other hand, the small void region was observed immediately under oxide layer from the thermal oxidation. In contrast, there were no voids in the altered zone near the metal/oxide interface in the non-thermal oxidized/He implanted sample. This description of the phenomena was justified using the Kirkendall effect and the Point Defect Model.

A simplified Point Defect Model incorporating reversible oxygen vacancy generation/annihilation at the metal/film interface has been used to investigate the impedance of anodized titanium in 0.5 M H2SO4, the oxygen vacancy profile in the anodic titanium oxide film, and the surface oxygen vacancy concentration. This simplified Point Defect Model (PDM), which considers the oxygen vacancy as the only point defect in the film, successfully accounts for the impedance of anodized titanium over the potential range explored. The results indicate that there is a thin region of the non-uniform oxygen vacancy concentration adjacent to the film/solution interface, which has an exponentially decreasing dopant ( $$ {V}_O^{\cdot \cdot } $$ ) concentration. The results of the investigation show that the surface oxygen vacancy concentration normalized to the bulk oxygen vacancy concentration is in the range of 0.05–0.15 and is essentially independent of potential.

The foundations of Fracture Impedance Spectroscopy (FIS) as a theoretical framework for analyzing and predicting fatigue and corrosion fatigue crack growth rate in real structures under complex loading waveforms from laboratory data obtained under simple, “pristine” loading conditions is presented. FIS is based upon an analogy between current flow (crack growth rate) in an electrical circuit in response to an applied, time-dependent voltage (time-dependent stress intensity factor). In this paper, the framework of the theory and its application for two different aerospace alloys are presented.

In this work, the nature of the electric field (E) in the defective oxide barrier layer on iron has been explored theoretically, within the classical regime, with the goal of ascertaining the validity of the postulates underlying the Point Defect Model (PDM). The analysis shows that if the thickness of the barrier layer under steady-state condition, L, is sufficiently small, the electric field strength and concentrations of point defects are essentially constants in the main part of this layer (with the exceptions in the very thin region near the metal/barrier layer (m/bl) and barrier layer/solution (bl/s) interfaces, depending upon the defect). A quantitative criterion was developed to decide when the barrier layer of the passive film can be considered to be sufficiently thin under these conditions. The potential drops inside the barrier layer and across the m/bl and bl/s interfaces can be represented as linear functions of applied voltage, V. This is the consequence of the change in thickness with applied voltage, with E being approximately (but with high accuracy) independent on the position inside the barrier layer and applied voltage. All conclusions stated above were derived from the solution of the system of mass transport equations for point defects and Poisson equation for the electric potential without applying any additional assumption except the small thickness of the barrier layer and without taking into account quantum (band-to-band) tunneling.

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.

Upon performing electrochemical measurements, XPS and TEM characterizations, the influence of sulfide on the passive behavior of Super 13Cr martensitic stainless steel was deciphered. Mechanism interpretation is performed by optimizing the Point Defect Model based upon the impedance data. It is revealed that the passive film display n-type semiconductivity, and the donor density dropped with increasing concentration of sulfide ion. Sulfide ion can induce a current peak at −250 mVSCE (Epeak). The addition of Na2S generates a continuous outer layer which is comprised of Cr(OH)3, FeS2 and FeS at potential lower than Epeak, and Cr(OH)3 at potential higher than Epeak. This result leads to the thinner barrier layer and lower charge transfer resistance, implying a weaker protection of the substrate by the passive film.

The thickness of the anodic titanium oxide film formed on titanium in 0.5 M H2SO4 at 22 °C was measured by ellipsometry, and the Forouhi interband single-layer model was used to analyze the data. The anodizing constant was determined experimentally to be 2.75 nm/V, which is in good agreement with literature data, and indicates that the anodizing constants for barrier layers of anodic oxide films formed on a wide variety of metals and alloys lie within the range of 2.2–3.0 nm/V. Using a value for the polarizability of the barrier layer/solution interface obtained via electrochemical impedance spectroscopy (EIS) together with the anodizing constant, the electric field is estimated to be a voltage-independent 1.82 × 106 V/cm. For the anodic oxide film formed on titanium in 0.5 M H2SO4 solution by galvanostatic polarization, the thickness was maintained to be virtually constant even though the oxygen vacancy concentration (donor density) analyzed by the Mott-Schottky relation varied over a wide range, as a function of the film formation rate (current density), with higher donor densities being found for lower current densities. The increase in the donor density leads to a decrease in the modulus of the impedance.

The kinetic parameters of the formation of the anodic titanium oxide film on Ti in 0.5 M H2SO4 have been determined using potentiostatic polarization, electrochemical impedance spectroscopy (EIS), and the Mott-Schottky analysis (MSA). The findings are interpreted in terms of the point defect model (PDM). The oxygen vacancy is found to be the dominant point defect under all conditions studied with the metal interstitial being the minority defect. From MSA, the oxygen vacancy concentration was found to exponentially decrease from 5.03 × 1020 to 3.91 × 1019 cm−3 as the film formation voltage was increased from 2.24 to 10.24 VSHE. Using a value for the electric field strength of 1.734 × 106 V/cm, as determined by previous modeling with the PDM together with a fitted expression for the donor density and film formation potential, the oxygen vacancy diffusivity was found to be 2.6 × 10−16 cm2/s.

For 9–12Cr ferritic–martensitic steels in supercritical water, the dependencies of the thicknesses of three oxide layers (diffusion, inner, and outer layers) on each of seven principal independent variables were separately investigated using three supervised artificial neural networks (ANN) and fuzzy curve analyses. The latter were employed to evaluate the relative significances of independent variables, indicating that on the whole, temperature and exposure time are the most important variables, while the oxide dispersion strengthening (ODS) comes in the first place for the thickness of the diffusion layer. A thicker diffusion layer occurs easily at intermediate temperature approximately 600 °C and/or on ODS steels, due to higher growth rate of the barrier layer than that of the outer layer. The periodic growth of the diffusion layer, including the “shrinking”/“thickening” stages, was revealed by ANN prediction, which may be the basic cause of periodic pore-assembled layers within the inner layer. Finally, the physicochemical basis of classical point defect model was extended to describe the growth of oxide scales for explaining the ANN predictions at the atomic level. The growth of the inner layer into the metal is attributed to the inward transport of oxide ions (actually via outward transport of oxygen vacancies), while the outward transport of cations through the inner layer via a cation vacancy mechanism or as interstitials results in the thickening of the outer layer. The periodic variation in oxygen potentials at the diffusion/inner layer interface is responsible for the periodic growth of the diffusion layer. The iron caves at the inner–diffusion interface left behind by the generation reaction of cation interstitials may be the intrinsic sources of pores within the inner layer.

We report here on the prediction of corrosion fatigue crack growth rate (CFCGR) for Aluminum Alloy 2024-T351 in aqueous environments under cyclical sinusoidal loading. Using the General Corrosion Fatigue Model (GCFM) described in Part I, the CFCGR was calculated as a function of environmental variables, including the electrochemical potential, NaCl concentration, loading frequency, stress intensity factor range, and temperature, in addition to the contribution from mechanical fatigue. Based on the influence of the environment, the changes in the potential drop down the crack enclave and the corrosion current density in a 1:1 electrolyte were also calculated from which the CFCGR was estimated. Corrosion fatigue crack growth in this alloy is readily understood in terms of the competition between environmental factors as described by the differential aeration hypothesis and the hydromechanics (advection) of the system resulting from the cyclical opening and closing of the crack.

By anodic potentiostatic polarization and electrochemical impedance spectroscopy (EIS) measurements, the effect of temperature (200 °C, 250 °C, and 300 °C) on the electrochemical behavior of Alloy 690 was investigated in oxygenated borate buffer solution containing H 3 B O 3 (2000 ppm B ) + L i O H (2 ppm L i ). The steady state passive current density was independent of the film formation potential at each temperature, indicating that the passive film is n-type in electronic character based on the predictions of the Point Defect Model (PDM). The passive current density increased and the absolute value of impedance decreased with increasing temperature, indicating a corresponding decrease in corrosion resistance. A mixed potential model (MPM), containing the PDM for describing the anodic passive dissolution of the alloy and the generalized Butler–Volmer equation for the cathodic oxygen reduction reaction was optimized on the experimental EIS data in order to extract model parameters, including kinetic parameters for the generation and annihilation of point defects in the barrier layer of the passive film. Metal ( C r , N i , F e ) interstitials, which were found to have a higher concentration than oxygen vacancies, dominate the point defect structure of the barrier layer of the passive film at each temperature, thereby accounting for the n-type behavior of the passive film. With increasing temperature, the film thickness and defect density also increased, resulting in the decreased corrosion resistance of film. This indicates that the defect density of passive film plays a more important role on corrosion behavior of alloy than the film thickness.

Passivity breakdown on 436 ferritic stainless steel (FSS) has been investigated in solutions containing different concentrations of chloride at 25 °C and interpreted in terms of the point defect model (PDM). The measured near-normal distributions of passivity breakdown potentials for 436 FSS under experimental conditions are in good agreement with the calculated results according to the PDM. The linear dependence of breakdown potential on the square root of potential scanning rate, which was described by the PDM, provides the estimation of the critical concentration of condensed vacancies at the metal/film interface, which leads to the passivity breakdown. This value is in good agreement with that calculated from the microstructure properties of the alloy substrate and the barrier layer of the passive film. This study demonstrates the validity of the PDM in describing the passivity breakdown on 436 FSS in NaCl solutions.

The defect structure of passive film continues to keep mysterious and pose to challenge, especially for copper. In this paper, we applied the Density functional theory (DFT) using Heyd-Scuseria Ernzerhof (HSE) functional to explore the relationship between band structure and defect type and concentration for ultrathin passive film using Cu2O slab model. The results showed: (1) oxygen vacancies almost have no effect on band gap or conductivity; (2) VCu1 induce an ultra-shallow acceptor state (0.02 eV) in band gap, which convert the original direct gap to indirect; (3) VCu2 does not change the direct gap character but the acceptor energy level induced is a little higher (0.45 eV) than VCu1; (4) two linear relational expressions were derived, Eg = − 5.4 ∗ CV + 2.18 for VCu1 and Eg = − 15.6 ∗ CV + 2.18 for VCu2, according to the variation of band gap with copper vacancy concentration. Then combining calculation results with photo-electrochemical experimental data, we concluded the approximate concentration range of defects in passive films: the compositions of passive films formed at −0.35, −0.23 and −0.12 V range from Cu1.96O to Cu1.83O with 2.24% VCu2 + a % VCu1 (0 ≤ a

The passive film formed on 2205 duplex stainless steel in pH 8.59 borate buffer solutions was studied by photo-electrochemical techniques and Mott-Schottky analysis. The passive film displays both n-type and p-type semiconductor character in different potential regions of the passive state. The band gap energy of barrier layer of the passive film was 2.4∼2.75 eV. Additionally, the composition of passive film was analyzed by AR-XPS; at -400∼100 mVSCE and above 600 mVSCE Fe2O3, Fe3O4, FeOOH and CrO3 dominate the passive film, showing n-type semi-conductivity; while at 100∼600 mVSCE the passive film comprises FeO, Cr2O3 and Cr(OH)3, exhibiting p-type semi-conductivity.

Electrocatalysts serving in electrochemical cells differ from general chemical catalysts by way of their special double-layer structure and a rarely discussed interface potential drop as described by the Butler–Volmer (BV) equation. In the present study, we explored the relationship between a material's properties and electrocatalytic performance for the oxygen evolution reaction (OER) by combining the BV equation with first-principle calculations, and concluded that the band gap and conductivity of the material function as descriptors of its electrocatalytic activity as well as Gibbs adsorption free energy. Furthermore, 13 kinds of modification methods, all aimed at developing an earth-abundant catalyst Co3O4 with heteroatoms doped in three different crystal sites, were designed and evaluated by a series of predictive first-principle calculations. Special attention was focused on modification with carbon element doping, which notably narrowed the band gap, lowered the polaron migration barrier, and reduced the Gibbs free energy. The selected configuration of the modified electrocatalyst was accomplished by plasma-enhanced chemical vapor deposition with a low-energy input to assure the appropriate doping site of carbon atoms. A remarkable catalytic activity of 235 mV overpotential at 10 mA cm−2 for OER on carbon-doped Co3O4 nanosheets demonstrated the rationality and feasibility of theoretical prediction by comparing this performance with that of the unmodified sample of 423 mV. The theoretical study and calculation prediction proposed here, which is also applicable for other catalysts and even other electrochemical reactions would be helpful for designing new materials or novel modification methods via reducing the failure rate and cost.

The destructive role of chloride ions on the defect structure of barrier layers (bl) is vitally important for understanding the initial breakdown of passive films on metals. Here photo-electrochemical and density functional theory (DFT) were applied to investigate the influence of chloride on the defect structure of the bl in passive films. The results show a bl with a narrow band gap, in which the valence band maximum (VBM) increased upon introducing chloride into the electrolyte. DFT calculations indicate that an increase in the copper vacancy concentration, due to cation extraction at the bl/solution interface could increase the VBM while oxygen vacancy generation results in a decrease in the conduction band minimum (CBM). The combination of these results verifies the aggressive role of chloride as proposed by the Point Defect Model (PDM) where an enhancement of the cation vacancy concentration across the bl occurs in response to the absorption of Cl− into oxygen vacancies on the bl.

The plasma electrolytic oxidation is an innovative method for the surface treatment of titanium and its alloys. This review provides an overview of the historical development of the process and summarizes the current state of the art. The chemical as well as the electro- and plasma-chemical basics of the layer forming mechanisms, which comprises the substrate/electrolyte interface before discharge initiation and the different types and stages of plasma electrolytic discharge phenomena are explained within the context of titanium-based materials. How these phenomena can be influenced by the use of suitable electrolytes and controlled by the electrical regime is described. Subsequently, the microstructures and composition of the layers are described in detail, and the properties for specific applications are then discussed. The resistance of a PEO coating to corrosive environments, tribological factors, and alternating mechanical stress is viewed critically, and the extensive functional properties such as physiological compatibility, photocatalytic activity, and decorative properties are revealed. Finally, examples of various practical applications in the medical engineering, aviation, automotive, and environmental technology fields, as well as other branches of industry, are presented., M. Aliofkhazraei acknowledges comments received from Prof. A. Yerokhin during intial steps of preparation of this review paper. D.D. Macdonald gratefully acknowledges the support of the FUTURE (Fundamental Understanding of Transport Under Reactor Extremes), an Energy Frontier Research Center funded by the U.S. Department of En- ergy (DOE), Office of Science, Basic Energy Sciences (BES). E. Matykina would like to thank the support of the RTI2018-096391-B-C33 (MCIU/ AEI/FEDER, UE) and S2018/NMT-4411 (Regional Government of Madrid and EU Structural and Social Funds). S.V. Gnedenkov ac- knowledges the support of the Russian Science Foundation (No. 20-13- 00130).

A mixed potential model (MPM) comprising the Point Defect Model (PDM) and the Generalized Butler Volmer Equation (GBVE) was successfully developed to study the passivity of HDSS 2707. The results show that the dominant point defect within the passive film is the Min+, thereby rendering n-type semiconductor behavior of the barrier layer. The anodic current is independent of the film formation potential whereas it increases with increasing temperature and follows the Arrhenius law. The partial cathodic current of hydrogen reaction is affected by the applied voltage. The anodizing constant of the passive film is calculated to be 2.91 nm/V.

Employing Li-ion batteries (LIBs) in portable electronics has become a necessity in the modern world but, due to the short application time for any given battery (1-3 years), the quantity of spent LIBs (SLIBs) waste is becoming substantial. Herein, a novel strategy for recycling SLIB graphite and reforming it as a valuable catalyst material for electrochemical oxygen reduction reaction was proposed. SLIB graphite has been used as a precursor material for graphite oxide, which was thereafter doped with nitrogen to prepare nitrogen-doped graphene (NG-Bat). The prepared NG-Bat was characterized by various physical characterization methods and the electrochemical properties of the resulting catalyst material were investigated in alkaline media. It was found that NG-Bat prepared from SLIB had superior physical and electrochemical properties in comparison to commercial nitrogen-doped graphene. The findings clearly demonstrate the importance of the recycling of SLIB graphite and its great potential to be re-applied for various applications.

The disposal of Belgium's High Level Nuclear Waste (HLNW) in the proposed Boom Clay repository requires careful consideration of the nature of the near-field environment, because of the presence of potentially corrosive species. The near-field environment is expected to be in contact with both carbon steel and highly alloyed iron-based alloys, such as stainless steels, although it is recognized that the canister material has yet to be specified in the Belgian programme. This chapter summarizes the chemistry of sulphur in the form of potential/pH and volt-equivalent diagrams calculated as a function of pH and temperature. It discusses little known feature of potential-pH diagrams; that of the formation of thermodynamically metastable oxide or sulphide phases on a metal surface.

The effect of chloride concentration on the passivity breakdown of carbon steel in deaerated pH = 13.5 alkaline solution was investigated. The results show that chloride plays an important role for the pitting corrosion of carbon steel. When NaCl ≤ 1 M , the carbon steel is passive but for 1 M < NaCl < 2 M , the carbon steel transfers from passive to passivity breakdown. When NaCl ≥ 2 M , passive film breakdown occurs and the passivity breakdown potential (E b ) of carbon steel is linearly-dependent on the logarithm of the chloride activity in the alkaline solution. As predicted by the PDM, the near-normal distribution of E b is well indicated by the near straight line in the cumulative distribution probability. The analysis in this study gives us a method to calculate the E b of carbon steel in alkaline solution and its distribution for any given chloride concentration.

Passivity breakdown on HDSS 2707 has been studied and the electrochemical data are interpreted in terms of the Point Defect Model. Pitting parameters of HDSS 2707 are determined, including the polarizability at bl/s interface, the defect annihilation rate, and the defect diffusion coefficient. The breakdown potential is demonstrated to be linearly related to log [Br-], pH, and the square root of potential scan rate (v1/2), and follows a near-normal distribution. The critical vacancy concentration calculated from the PDM is consistent with that estimated crystallographically from the chromic barrier layer, and the dominant point defect is further confirmed by Mott-Schottky measurements.