Embrittlement of a Duplex Stainless Steel in Acidic Environment Under Applied Cathodic Potentials

Hydrogen-induced degradation of mechanical properties of a duplex stainless steel in 0.1N H₂SO₄ solution has been studied under in situ cathodic charging conditions. Significant reductions in percentage of elongation, toughness, and time to failure were noticed due to the ingress of hydrogen into the material at various applied cathodic potentials in the range of −200 to −800 mV (SCE). Cleavage fractures were identified mainly in the ferritic phases. Crack growth was observed to be inhibited by the austenite phase. However, depending on the severity of the environment, both the ferrite and austenite phases could be embrittled. At less negative potentials, presence of surface film and low hydrogen fugacity seemed to control hydrogen ingress in the metal. Addition of thiosulfate to the acidic solution further degraded the mechanical properties of the steel at the applied cathodic potential.     

Preparation of Mn−Zn ferrite from spent zinc-carbon batteries by alkali leaching,acid leaching and Co-precipitation

The treatment of spent zinc-carbon batteries for the recovery of valuable metals followed by conversion to Mn−Zn ferrite has been conducted employing two-stage alkali and acid leaching and co-precipitation method. In the first stage, leaching process was carried out with 4 M NaOH, which resulted in a recovery of 63.4 %Zn and 0.1% Mn. Electrowinning of alkali leaching solution containing 12.75 g/L Zn at a current density of 0.2 A/cm² produced Zn metal of 15 nm to 30 nm size and 99.9% purity. The second stage leaching of residue with 3 M H₂SO₄ and 6 vol.% H₂O₂ at a solid/liquid ratio of 1∶10 indicated the leaching efficiency of 98.0% Zn, 97.9% Mn and 55.2% Fe. The obtained leaching solution was finally adjusted to suitable mole ratios of Mn∶Zn∶Fe (1∶1∶4) by the addition of Zn and Fe sulfate salts followed by pH control to produce Mn−Zn ferrite powder. The characterization of the ferrite powder showed uniform nano-crystalline particles of about 20 nm size with spinel structure.     

Corrosion behavior of mild steel in the presence of scale inhibitor in sulfuric acid solution

Surfactants such as non-ionic polyethylene glycol tert-octylphenyl ether (Triton X-114) have been studied as efficient corrosion inhibitors in acid medium. In this study inhibition performance of Triton X-114 has been evaluated as corrosion inhibitor for mild steel in 0.5 mol l⁻¹ H₂SO₄. The electrochemical impedance spectroscopy (EIS), potentiodynamic polarization and linear polarization (LPR) techniques has been applied to determine the electrochemical behaviour of Triton X-114. The maximum efficiency of Triton X-114 was found as 96% at the concentration 5.0 × 10⁻⁵ mol l⁻¹. The adsorption isotherm of inhibitor on the mild steel surface was found to be in a good agreement with the Langmuir and the standard free energy value (ΔG _ads^°) was calculated as −50.1 kJ mol⁻¹, which shows that adsorption of Triton X-114 on the mild steel surface improves the inhibition characteristics in 0.5 M H₂SO₄.     

阴极保护下X65钢在模拟海水中的氢脆敏感性研究

采用阴极极化条件下的氢渗透实验和慢应变速率拉伸实验研究了X65钢在模拟海水中的氢渗透行为及其对断裂机理的影响。氢渗透实验结果表明,阴极极化过程中试样表面的钙镁沉积层能显著地降低氢扩散系数,采用Fourier方程、Laplace方程以及时间滞后法计算得出的有效氢扩散系数平均值为1.49×10-7cm2·s-1。结合变电位极化氢渗透测试结果、拉伸试样断口分析以及极化曲线测试,对阴极极化条件下X65钢的氢脆敏感性进行评估。结果显示,随着极化电位的降低,X65钢中的吸附氢浓度呈指数规律上升。当极化电位较高时,X65钢的裂纹扩展受阳极溶解和阴极析氢的双重作用控制。当极化电位较低,如-1200 mV时,钢中的吸附氢浓度急剧增加,脆性断裂区域的比例上升,X65钢发生氢致脆化失效。     

Strength and Corrosion Behavior of Fe–25Cr Alloys under Various Strain Rates in Ar and N2–0.1%SO2 at 973 K

The mechanical strength and corrosion behavior of Fe–25Cr alloys were studied in Ar and in N₂–0.1SO₂ at 973 K under strain rates of 2.7 × 10⁻⁴–10⁻⁶/s. A 0.1μm thick adhering Cr₂O₃ layer is formed on the alloy by pre-treatment in Ar. Scales formed in N₂–0.1SO₂ are thicker with poorer adherence to the metal substrate. The tensile strength is higher, about 9–19 MPa, in Ar than in N₂–0.1SO₂. However, the strain-rate sensitivities show similar values in both environments. Deformation is concentrated near the grain boundaries of the alloy, and it is more conspicuous at lower strain rates. Scale growth is rapidly increased by the deformation in N₂–0.1SO₂, and the scale growth rate increases with the increase in strain rates. The scale growth rate is higher at higher strain rates and the scale increases in sulfides.     

Investigations of the hydrogen evolution kinetics and hydrogen absorption by iron electrodes during cathodic polarization

The kinetics of the electrochemical reduction of hydrogen ions or water molecules on iron electrodes have been investigated using the electropermeation technique. The variation of permeation current density and cathodic potential with constant cathodic current density has been measured in various solutions, without or with promoters. The hydrogen activity on the cathodic side of the iron membranes was calculated from the H-permeation current. The exchange current densities of the three partial reactions of the cathodic hydrogen evolution were calculated from the obtained experimental data. In 0.1N H₂SO₄ without added promoters the chemical Tafel recombination predominates up to high cathodic current densities whereas in 0.1N NaOH or nearly neutral solutions without added promoters the electrochemical Heyrovsky recombination predominates already at comparatively low cathodic current densities. This is mainly due to the different exchange, current densities of the electrochemical recombination reaction with hydrogen ions or with water molecules. The promoter used enhances the hydrogenation of iron by inhibiting the recombination reactions stronger than the Volmer reaction.     

Investigations of the hydrogen evolution kinetics and hydrogen absorption by iron electrodes during cathodic polarization

The kinetics of the electrochemical reduction of hydrogen ions or water molecules on iron electrodes have been investigated using the electropermeation technique. The variation of permeation current density and cathodic potential with constant cathodic current density has been measured in various solutions, without or with promoters. The hydrogen activity on the cathodic side of the iron membranes was calculated from the H-permeation current. The exchange current densities of the three partial reactions of the cathodic hydrogen evolution were calculated from the obtained experimental data. In 0.1N H₂SO₄ without added promoters the chemical Tafel recombination predominates up to high cathodic current densities whereas in 0.1N NaOH or nearly neutral solutions without added promoters the electrochemical Heyrovsky recombination predominates already at comparatively low cathodic current densities. This is mainly due to the different exchange current densities of the electrochemical recombination reaction with hydrogen ions or with water molecules. The promoter used enhances the hydrogenation of iron by inhibiting the recombination reactions stronger than the Volmer reaction.     

Oxidation Behavior of TiAl<Subscript>3</Subscript>/Al Composite Coating on Orthorhombic-Ti<Subscript>2</Subscript>AlNb Based Alloy at Different Temperatures

This paper reports the oxidation behavior of TiAl₃/Al composite coating deposited by cold spray. The substrate alloy was orthorhombic-Ti-22Al-26Nb (at.%). The oxidation kinetics of the coating was tested at 650, 800, and 950 °C, respectively. The parabolic rate constant for the coating oxidized at 650 °C was k _p = 7.2 × 10⁻² mg·cm⁻²·h^−1/2 for the tested 1200 h. For the coating oxidized at 800 °C, the oxidation kinetics could be separated into two stages with k _p value of 39.8 × 10⁻² mg·cm⁻²·h^−1/2 for the initial 910 h and 17.7 × 10⁻² mg·cm⁻²·h^−1/2 for the stage thereafter. For the coating oxidized at 950 °C, the oxidation kinetics can be separated into three stages with k _p of 136.9 × 10⁻² mg·cm⁻²·h^−1/2 in the first 100 h, followed by 26.9 × 10⁻² mg·cm⁻²·h^−1/2 from 100 to 310 h, and 11.8 × 10⁻² mg·cm⁻²·h^−1/2 from 310 to 1098 h. XRD, SEM, and EPMA were used to study the microstructure of the coating. The results indicated that the oxidation took place throughout the entire coating instead of only at the surface. The aluminum phase in the composite coating was soon oxidized to Al₂O₃ in all tested cases. The aluminum in TiAl₃ phase was depleted gradually and oxidized to Al₂O₃ along with the degradation of TiAl₃ to TiAl₂ and TiAl as the temperature increased and time proceeded. AlTi₂N was also a typical oxidation product at temperature higher than 800 °C. The experimental results also indicated that the protection of the coating was attributed greatly to the interlayer formed between the coating and the substrate.     

The effect of pressure on the permeation of hydrogen through steel

A cell is described which provides a means of studying the permeation of hydrogen through steel at elevated pressures. It has been shown that the significant factor in permeation is the partial pressure of hydrogen, p_H2, and not the applied pressure, P, and that reproducible results can be obtained provided the solution is agitated so that the hydrogen generated cathodically is dispersed into the bulk solution. The permeation of hydrogen through steel has been studied in 0.1 mol dm^?3 NaOH and in 0.05 mol dm^?3 H₂SO₄ under conditions of constant current density and applied pressure and at various constant partial pressures of hydrogen, and it has been shown that in all cases (?J/?p_H2) > 0. In 0.1 mol dm^?3 NaOH linear J vs $\text{i}{}^{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}$ and J vs p_H2 relationships have been observed, whereas in 0.05 mol dm^?3 H₂SO₄ although J vs $\text{i}{}^{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}$ is linear at low current densities the curves follow linear J vs log i and J vs log p_H2 relationships at higher current densities. The results in NaOH and H₂SO₄ have been explained in terms of the effect of p_H2 on the rate constants k₂, k_?2 of the chemical desorption step of the h.e.r. A decrease in k₂ and an increase in k₂ will increase the coverage, θ_H, with a consequent increase in the rate of permeation. The effect of p_H2 on permeation may be of significance in systems where the steel is enclosed so that hydrogen is discharged cathodically at high partial pressures, e.g. high-strength steels used for reinforcing bars and prestressing cables in concrete, which are adventitiously connected to a cathodic protection system.     

Measurements of hydrogen activity in iron during cathodic protection using a potentiometric concentration cell

A solid - state potentiometric sensor, based on the well - tried principle of the thermodynamic concentration cell, has been constructed. The sensor uses a conventional bi-electrode design with an entry side and an exit side at which the hydrogen is detected. The sensor has been used for the quantitative determination of the hydrogen activity (equivalent H₂ pressure) generated during cathodic protection. Thus, the background hydrogen pressure in uncharged steel is 10^?17.7 (2 × 10^?18 atm.) with a variation of about 20 times. During cathodic protection this value rises by large amounts. Thus, using a zinc anode, the equivalent hydrogen pressure rose by 10^10.3 (to 4.4 × 10^?8 atm.) in 3.5% NaCl and by 10^16.9 (to 0.16 atm.) in artificial sea water, indicating the much larger amounts of hydrogen present in the latter case. This compares, for example, with literature data of 0.11 μA cm^?2 and 0.60 μA cm^?2 for hydrogen permeation at ?1000 mV (SCE) in 3.5% NaCl and artificial sea water respectively. Hydrogen entry and exit was also considerably slowed in sea water. These differences are caused by local surface pH buffering and deposit formation.     

Mechanism of the initial stages of iron passivation in acidic sulfate solutions

Anodic and cathodic potentiostatic current transients of freshly formed iron (99.95%) electrodes in 0.5 M aqueous acidic (pH 1.7–3.2) sulfate solutions are examined. The initial stages of iron passivation are confirmed to be determined by the following several processes each prevailing in a definite period: the formation of surface charge-transfer complexes (H₂O) _δ+ ^ads (first 3–5 ms) and their transformation into adsorbed OH⁻ groups (subsequent 10–50 ms) with the concurrent adsorption of hydrogen atoms H_ads by iron.     

Electroplating of catalytically active nickel coatings from baths of various anionic compositions

The effect of the nature of bath anions (Cl⁻, SO₄²⁻ and CH₃COO⁻) on the characteristics of the electrochemical plating of nickel coatings, namely, parameters of the cathodic polarization curves, bath stability, and current efficiency, as well as the composition and morphology of deposits and their catalytic activity in the anodic oxidation of hypophosphite ions and cathodic evolution of hydrogen, is studied. The anionic composition of the baths is found to substantially affect not only the kinetics of the deposit growth, but also the properties of the deposit. The differences observed are determined by the complex-forming and buffering properties of the anions.     

Application of Mossbauer spectroscopy of conversion and Auger electrons for the study of transformations on Fe electrode under conditions of passive-transpassive transition

Using Mossbauer spectroscopy of conversion and Auger electrons and X-ray photoelectron spectroscopy peculiarities and regularities in formation of composition and structure of the products of oxidation of ⁵⁷Fe samples in solutions of 0.1 N NaOH, a mixture of 1 N NaOH and 6 N NaNO₃, 1 N H₂SO₄, 0.1 N H₃BO₃, and 0.5 mol/L Na₂B₄O₇ in relation to the nature of corrosion medium and charge densities of anode polarization (10…12000 mA/cm²) corresponding to the region of passive-transpassive transition has been studied.     

Segregation of hydrogen at internal Ag/MgO (metal/oxide)-interfaces as observed by small angle neutron scattering

The chemical composition of metal/oxide (M/O)-interfaces was studied for an internally oxidized Ag–1at.%Mg-alloy with small MgO nanoprecipitates in a dilute Ag matrix. This composition was varied by exposing the sample to oxygen (p(O₂) = 2 × 10⁴ Pa), hydrogen (p(H₂) = 10⁵ Pa) or vacuum (p<10⁻⁴ Pa). By means of small angle neutron scattering (SANS) we were able to show that hydrogen segregates at the internal Ag/MgO-interfaces. The average hydrogen occupancy at the Ag/MgO-phase boundary can be determined to be Θ_H=(7.1±0.5)×10¹⁴ H/cm². In addition it could be shown that for each segregated hydrogen atom one Ag atom is displaced from the M/O-interface. The amount of hydrogen at the interfaces is in agreement with a model of structural vacancies at densely packed interface planes. To the best of our knowledge these are the first SANS-measurements that provide information about the segregation of hydrogen and deuterium at internal interfaces.     

Analysis of electrochemical impedance of polypyrrole|sulfate and polypyrrole|perchlorate films

PPy|SO₄ and PPy|ClO₄ films have been synthesized and investigated in K₂SO₄, ZnSO₄ and NaClO₄ aqueous solutions by electrochemical impedance spectroscopy (EIS), cyclic voltammetry (CV) and electron probe microanalysis (EPMA) methods. On the basis of obtained data and calculated impedance parameters as the potential functions, the role of different processes (diffusion of ions, double-layer charging, adsorption and charge transfer) in oxidized, partially reduced and reduced PPy films is estimated. The lowest pseudocapacitance values (from n × 10⁻⁶ to n × 10⁻⁴ μF cm⁻² for 1 μm film), independent of solution concentration, were established for PPy|SO₄ in ZnSO₄. This phenomenon is related with strongly aggravated film reduction process in the solution of double-charged cations. In the case of PPy|ClO₄ in NaClO₄ and PPy|SO₄ in K₂SO₄,where the mono-charged cations participate in redox process, the capacitance values are in the range from: n × 10⁻³ to n × 10⁻² μF cm⁻² and even somewhat higher for PPy|ClO₄ system at oxidized state. The calculated effective diffusion coefficients of ions D remain inside the range from n × 10⁻¹² to n × 10⁻¹⁴ cm² s⁻¹ for PPy|SO₄ in 0.1 M K₂SO₄ and PPy|ClO₄ in 0.1 M NaClO₄ aqueous solution. In the case of PPy|SO₄ film in ZnSO₄ solution the D values are essentially lower.     

Moisture-induced delayed spallation and interfacial hydrogen embrittlement of alumina scales

While interfacial sulfuris the primary chemical factor affecting Al₂O₃ scale adhesion, moisture-induced delayed spallation appears as a secondary, but impressive, mechanistic detail. Similarities with bulk metallic phenomena suggest that hydrogen embrittlement from ambient humidity, resulting from the reaction Al_alloy+3(H₂O)_air=Al(OH)⁻ ₃+3H⁺ may be the operative mechanism. This proposal was tested on pre-oxidized René N5 by standard cathodic hydrogen charging in 1N H₂SO₄, as monitored by weight change, induced current, and microstructure. Cathodic polarization at −2.0 V abruptly stripped mature Al₂O₃ scales at the oxide-metal interface. Anodic polarization at +2.0V, however, produced alloy dissolution. Finally, with no applied voltage, the acid electrolyte produced neither scale spallation nor alloy dissolution. Thus, hydrogen charging was detrimental to alumina scale adhesion. Moisture-induced interfacial hydrogen embrittlement is concluded to be the cause of delayed scale spallation and desktop thermal barrier coating failures.     

Effects of temperature and pH level on the corrosion behavior of amorphous Co69Fe4.5Nb1.5Si10B15 alloy

The corrosion behavior of the amorphous Co₆₉Fe_4.5Nb_1.5Si₁₀B₁₅ (at.%) alloy ribbon in H₂SO₄ solutions (0.001 M or 0.07 M), NaCl solution (0.07 M), and HCl + NaOH solution were examined as functions of solution temperature and pH. The corrosion potential decreased when either the temperature or pH of the solutions increased. The corrosion resistance of the Co₆₉Fe_4.5Nb_1.5Si₁₀B₁₅ alloy in the 0.07 M NaCl solution was higher than the 0.001 M or 0.07 M H₂SO₄ solutions for a given temperature. The corrosion rate increased exponentially with an increase in temperature and was inversely proportional to the pH in the range of 10^?6 A/cm²～10^?4 A/cm².     

Effects of dopant content on optical and electrical properties of In<Subscript>2</Subscript>O<Subscript>3</Subscript>: W transparent conductive films

The In2O3:W (IWO) films with different W content were deposited on glass substrate using direct current sputtering method. The structure, surface morphology, and optical and electrical properties were investigated. Results showed that both the carrier concentration and carrier mobility were increased with the doping of W. The IWO film with the lowest resistivity of 1. 0× 10-3 Ω· cm, highest carrier mobility of 43. 7 cm2. W-1. s-1 and carrier concentration of 1. 4× 1020 cm-3 was obtained at the content of 2. 8 wt. ％. The average optical transmittance from 300 nm to 900 nm reached 87. 6％.     

Electron Temperature and Density of the Plasma Measured by Optical Emission Spectroscopy in VLPPS Conditions

Measurements of electron temperature and electron density have been carried out on a plasma plume under very low pressure conditions (P = 1 mbar) using optical emission spectroscopy. The plasma torch was operated at a power level of 20-55 kW corresponding to an Ar/H₂ flow rate of 40/0 to 40/8 L/min and current intensity variation from 500 to 700 A. The electron temperature (T _e) was determined based on the calculation of the relative intensity of two spectral lines, H_α and H_β. It was found that T _e decreased from 0.2 to 0.9 eV with increasing detection distance from the nozzle exit from 40 to 60 cm. Changes in the current and the flow rate of H₂ also had a significant impact on it. There are significant fluctuations in the hydrogen emission intensity when using current intensity of 700 A or with increasing hydrogen fraction in the mixture. However, it seemed that there was no evident change in T _e when different powder sizes were injected. Correspondingly, electron densities ranged from 0.76 × 10¹⁴ to 1.41 × 10¹⁵ cm⁻³ and were obtained using Stark-effect broadening of the H_β (486 nm) line under the assumption of local thermodynamic equilibrium (LTE).     

Sensing behavior of silica-coated Au nanoparticles towards nitrobenzene

In the present work, we report silica-stabilized gold nanoparticles (SiO₂/Au NPs) as a wide-range sensitive sensing material towards nitrobenzene (NB). Surface hydroxyl groups of silica selectively form Meisenheimer complex with electron-deficient aromatic ring of NB and facilitate its immobilization and subsequent catalytic reduction by Au cores. Silica-coated Au NPs were synthesized and characterized for their chemical, morphological, structural, and optical properties. SiO₂/Au NPs-modified electrodes were characterized with impedometric and cyclic voltammetric electrochemical techniques. SiO₂/Au NPs are found to have a higher optical detection window of range, 0.1 M to 1 μM and a lower electrochemical detection window of range, 10⁻⁴ to 2.5 × 10⁻² mM with a detection limit of 12.3 ppb. A significant enhancement in cathodic peak current, C ₁, and sensitivity (102 μA/mM) was observed with modified electrode relative to bare and silica-modified electrodes. The I _P was found to be linearly co-related to NB concentration (R ² = 0.985). The interference of cationic and anionic species on sensor sensitivity was also studied. Selectivity in the present sensing system may be further improved by modifying silica with specific functional moieties.