Characterization of Hydrogen Permeation in Armco-Fe during Cathodic Polarization in Aqueous Electrolytic Media

The study of hydrogen permeation behavior in Armco-Fe showed that 0.1 M H₂SO₄ was a more effective medium for cathodic polarization compared to 0.1 M NaOH. When both electrolytes were “poisoned” with 1.00 g/L Na₂HAsO₄ · 7H₂O, as hydrogen recombination inhibitor, the corresponding hydrogen permeation levels were 3.5 × 10⁻⁵ A/cm² in 0.1 M H₂SO₄ while 0.75 × 10⁻⁵ A/cm² in 0.1 M NaOH. The breakthrough times were less than 30 s in 0.1 M H₂SO₄, while about 100 s in the NaOH. With varying amounts of “poisons”, peak permeation of hydrogen (1.75 × 10⁻⁵ A/cm²) was achieved with 10 g/L Na₂HAsO₄ · 7H₂O in 0.1 M H₂SO₄, while the least permeation resulted with 10 g/L (NH₂CSH₂) Thiourea addition for same level of 1.00 mA/cm² cathodic polarization.     

Structural Characterization and Corrosion Stability of a Si-Doped DLC Coating Applied on Cylinder Liner

The aim of this work was to characterize the structure and electrochemical behavior of a silicon-doped diamond-like carbon (DLC) film deposited by hollow cathode plasma immersion ion process (HCPIIP) on a cylinder liner for heavy duty diesel engine. The film structure was characterized by scanning electron microscopy, x-ray diffraction, and Raman spectroscopy. Nanoindentation tests were performed to evaluate the film hardness and Young’s modulus. Monitoring of the open circuit potential with time, electrochemical impedance spectroscopy (EIS), and potentiodynamic polarization measurements was performed in a solution consisting of 0.25 wt.% NaCl + 5.0 wt.% H₂SO₄ at room temperature. The results showed that the film has an amorphous nature consisting of a mixture of sp³ and sp²-like carbon bonds with an I _D/I _G ratio of 0.87. Nanoindentation tests showed that the H/E ratio of the DLC film was 0.102. EIS measurements indicated that the impedance values were higher for the DLC-coated material. Potentiodynamic polarization curves revealed that the corrosion current density was almost three times lower for the coated alloy. The HCPIIP process was considered successful to enhance the surface properties of the cylinder liner.     

φ–pH diagram of As–N–Na–H2O system for arsenic removal during alkaline pressure oxidation leaching of lead anode slime

In order to illustrate the thermodynamic characteristics of arsenic during alkaline pressure oxidation leaching process of lead anode slime (NaNO₃ as oxidant; NaOH as alkaline reagent), the φ–pH diagrams of As–Na–H₂O, N–H₂O, As–N–Na–H₂O systems at ionic mass concentration of 0.1 mol/kg and temperatures of 298, 373, 423 and 473 K were established according to thermodynamic calculation. The results show that the existence forms of arsenic are associated with pH value, which mainly exists in the forms of H₃AsO₄, H₂AsO₄^?, HAsO₄^2?, and As₂O₃ in lower pH region, while it mainly exists in the form of when pH>11.14. High alkali concentration and high temperature are advantageous to the arsenic leaching. The alkaline pressure oxidation leaching experiments display that the tendency of arsenic leaching rate confirms the thermodynamic analysis results obtained from the φ–pH diagrams of As–N–Na–H₂O system, and the highest leaching rate of arsenic reaches 95.85% at 453 K.     

A thermometric study of the dissolution of some CuZn alloys in acid solutions

The dissolution of Cu and Zn, and of three CuZn alloys in solutions of different concentrations of HNO₃ was studied by the thermometric technique. The variation of ΔT (i.e. T_m ? T_i) and the reaction number (R.N.) with the concentration of the attacking acid followed the relations:

$\Delta T=A_1(C?C_{\mathit{0}})$

and

$R.N.=A_2{\mathit{C}}_n,$

successively. Based on the values of the constants A₁, C_o, A₂ and n, the rate of dissolution of the different materials was found to increase in the order: Cu < Alloy I (70.5%Cu) < Alloy III (58.00%Cu) < Alloy II (62.00%Cu) < Zn.A break was noted in the thermometric curves of Alloy I. This was due to the primary attack on the Zn-component of the alloy, and was confirmed by studying the effect of the initial temperature, T_i, and the area/volume ratio on the shape of the curves, as well as by chemically analysing the corroding solution for both Cu²⁺ and Zn²⁺.The effect of the concentration of HCl, H₂SO₄, H₃PO₄ and of their salts on the reaction number of the alloys in 4N HNO₃ was examined in detail. The adsorption of the foreign acid anion on the metal surface retarded dissolution. Inhibition increased in the succession: Cl^? < HSO₄^? < H₃PO₄^?.The alloys were not affected by cold 4N HCl, H₂SO₄ or H₃PO₄. Attack could be initiated in the case of the first two acids through the addition of KNO₃. The thermometric curves were characterized by long incubation periods, by sharp temperature maxima and by the rapid decrease of temperature thereafter. This supported the conclusion that attack was of the pitting rather than of the general type. Because of stronger anion adsorption, attack in 4N H₂SO₄ was much lower than in 4N HCl. No attack was recorded in 4N H₃PO₄.Parallelism between corrosion assessment by the thermometric technique and by the weight loss method was established.     

Synthesis,characterization and electroluminescence properties of iridium complexes based on pyridazine and phthalazine derivatives with C^NN structure

We reported the synthesis and characterization of three novel tris-cyclometalated iridium(III) complexes with pyridazine and phthalazine derivatives as ligands bearing C^NN structure, namely, Ir(PYA)₃, Ir(PHB)₃, and Ir(PHC)₃. Reactions of the ligands with IrCl₃·3H₂O directly afforded tris-cyclometalated iridium(III) complexes in 31–39% yields. X-ray analysis revealed that the complexes exhibited the facial configuration, and the Ir–C bond lengths of the complexes are 2.009(3), 2.013(3), 2.019(3) Å for Ir(PYA)₃, and 1.993(4), 2.002(4), 2.004(4) Å for Ir(PHB)₃, respectively. The iridium complexes-based OLEDs fabricated by spin-coating technique exhibited promising performance. At 4 wt% doping level and a practical luminance of 100 cd m^?2, the external quantum efficiencies of the devices using Ir(PYA)₃, Ir(PHB)₃ and Ir(PHC)₃ as dopants reached 9.0, 6.9 and 9.3% photons/electron, respectively.     

Electrochemical Behavior of Nickel Hydride in Sodium Hydroxide Solutions

Electrochemical behavior of nickel hydride Ni₂H (-phase) is studied in 0.01–1 N NaOH by using common (VA) and cyclic (CVA) voltammetry, chronocoulometry, amperometry, and potentiometry. The limiting anodic and cathodic currents in VA and CVA curves are caused by the hydride decomposition via the following scheme Ni₂H -phase Ni + H_abs, where the intermediate -phase contains 0.003 at. % H, that is, one tenth that in the saturated -phase (0.03 at. %). At open circuit, the hydride maintains the equilibrium hydrogen potential. In the first 30 min, the hydrogen ionization from hydride is limited by solid-state diffusion and, later, the hydride decomposition. The anodic process involves ionization of sorbed hydrogen, while the cathodic process represents its electrochemical desorption: H₂O + H_ads + e H₂ + OH^–. The hysteresis observed in the cathodic CVA and open-circuit chronograms of the hydride potential in the beginning of anodic dissolution reflect the changes in the surface coverage of hydride with adsorbed hydrogen. The rate constant of hydride decomposition k, the rate Vitself, and the equilibrium constant K are as follows: k = k = 8 × 10^–5 s^–3, V = 3 × 10^–5 C/cm², and K = 10. The kinetic parameters of hydrogen electrochemical ionization from the hydride are b _a = 0.12 V and = 0.5.     

Growth and characterization of thin anodic oxide films on n-InSb(1 0 0) formed in aqueous solutions

Anodic oxide films were galvanostatically grown on n-InSb(1 0 0) surfaces at various pH in sodium hydroxide (0.1 M NaOH, pH=13), borate buffer (0.075 M Na₂B₄O₇ + 0.3 M H₃BO₃, pH=8.4) and phosphate buffer (0.3 M NH₄H₂PO₄, pH=4.4). Thickness, composition and morphology of the oxide films were determined by various surface analytical techniques such as Auger electron spectroscopy, X-ray photoelectron spectroscopy, scanning and transmission electron microscopy and atomic force microscopy. The oxides comprise mainly In₂O₃ and Sb₂O₃ and the oxide thickness increases with pH. Electrical properties of oxides indicate that the films may be useful as insulators in some device applications.     

Prevention of passive film breakdown and corrosion of iron in 0.1 M KClO4 with and without Cl by covering with an ultrathin two-dimensional polymer coating and healing treatment in 0.1 M NaNO3

A two-dimensional polymer coating, the self-assembled monolayer of 16-hydroxy hexadecanoate ion HO(CH₂)₁₅ modified with 1,2-bis(triethoxysilyl)ethane (C₂H₅O)₃Si(CH₂)₂Si(OC₂H₅)₃ and octadecyltriethoxysilane C₁₈H₃₇Si(OC₂H₅)₃ was prepared on the passivated iron electrode and further, the passive film was healed by additional treatment in 0.1 M NaNO₃. This electrode was immersed in oxygenated 0.1 M KClO₄ solutions with and without 1 × 10⁻⁴ to 1 × 10⁻² M of Cl⁻. Protection of passive film against breakdown by covering the electrode with the polymer coating was examined by monitoring the open-circuit potential during immersion in the solutions for many hours to determine the time for passive film breakdown, t_bd. Repeated polarization measurements were carried out during immersion in these solutions for obtaining the protective efficiency, P. The t_bd value of the passivated, polymer-coated and healed electrode in 0.1 M KClO₄ solutions with and without Cl⁻ increased with a decrease in the concentration of Cl⁻. No breakdown occurred on the electrode during immersion in 0.1 M KClO₄ solutions with and without 1 × 10⁻⁴ of Cl⁻ for 360 h. The P values were extremely high, more than 99.9% before t_bd, indicating complete protection of iron from corrosion. The effect of healing treatment in 0.1 M NaNO₃ on passive film breakdown was investigated by electron-probe microanalysis.     

Studies on the anodic polarization of amalgams: The behaviour of nickel amalgams in alkaline solutions

Nickel amalgams of varying composition were oxidized in 0.1, 2, 4 and 6N NaOH solutions. Two different oxidation patterns were distinguished. The first describes the behaviour of concentrated nickel amalgams, and the second the behaviour of dilute nickel amalgams in NaOH solutions. The anodic curve for the concentrated amalgams showed regions for the charging of the anodic double layer, then oxidation of nickel and mercury, then oxygen evolution. NiO is first formed which is oxidized to Ni₃O₄, then to Ni₂O₃. For dilute amalgams the oxidation curves showed only one arrest corresponding to the system NiO/Ni₃O₄ before oxygen evolution. The relation between the polarizing current and the time of passivation was found to fit the equation

$\text{log}\text{τ = A ? n}\text{log}\text{i}$

, where A and n are constants. With cathodically pretreated electrodes the oxidation curves showed regions for the dissolution of the sodium amalgam formed during precathodization, the charging of the anode double layer and a prolonged indefinite arrest at the potential corresponding to the reaction

$\text{NiO + H}{}_2\text{O = Ni}{}_3\text{O}{}_4\text{+ 2H}{}^{\mathrm{+}}\text{+ 2e?}$

.     

Microwave Power Absorption in Materials for Ferrous Metallurgy

The characteristics of microwave power absorption in materials for ferrous metallurgy, including iron oxides (Fe₂O₃, Fe₃O₄ and Fe₀.₉₂₅O) and bitumite, were explored by evaluating their dielectric loss (Q _E) and/or magnetic loss (Q _H) distributions in the 0.05-m-thick slabs of the corresponding materials exposed to 1.2-kW and 2.45-GHz microwave radiation at temperatures below 1100°C. It is revealed that the dielectric loss contributes primarily to the power absorption in Fe₂O₃, Fe_0.925O and the bitumite at all of the examined temperatures. Their Q _E values at room temperature and slab surface are 9.1311 × 10³ W m^?3, 23.7025 × 10³ W m^?3, and 49.5999 × 10³ W m^?3, respectively, showing that the materials have the following heating rate initially under microwave irradiation: bitumite > Fe_0.925O > Fe₂O₃. Compared with the other materials, Fe₃O₄ has much stronger power absorption, primarily originated from its magnetic loss (e.g., Q _H = 1.0615 × 10⁶ W m^?3, Q _H/Q _E = 2.4185 at 24°C and slab surface), below its Curie point, above which the magnetic susceptibility approaches to zero, thereby causing a very small Q _H value at even the surface (Q _H = 1.0416 × 10⁵ W m^?3 at 880°C). It is also demonstrated that inhomogeneous power distributions occur in all the slabs and become more pronounced with increasing temperature mainly due to rapid increase in permittivity. Characterizing power absorption in the oxides and the coal is expected to offer a strategic guide for improving use of microwave energy in ferrous metallurgy.     

The influence of methylcellulose (MC) on solubility of calcium hydroxyapatite (HA) crystals in HA/MC nanocomposites

The influence of methylcellulose ([C₆H₇O₂(OH)_3–x(OCH₃)_x]_n, MC) on the morphology and solubility of calcium hydroxyapatite (Ca₁₀(PO₄)₆(OH)₂, GA) nanocrystals (NCs) in GA/MC organomineral nanocomposites (OMCs) is studied. GA/MC OMCs with the MC content of 0.5, 1, 2, 5, 10 and 20 wt % are synthesized in the Ca(OH)₂–H₃PO₄–[C₆H₇O₂(OH)_3–x(OCH₃)_x]_n–H₂O system under biomimetic conditions (37°C). The composition and structural features of OMCs, as well as crystallographic characteristics, size, and morphology of GA NC in OMCs, are determined via chemical analysis, X-ray diffraction (XRD), infrared spectroscopy (IRS), thermal analysis (DTA and DTG), scanning (SEM) and transmission (TEM) electron microscopy, and electron diffraction (ED). It is shown that the growth in the MC concentration in OMCs leads to the change in the GA NC morphology and the increase in their solubility (for Ca²⁺ and PO₄^3- ions).     

Effect of Cathodic Polarization on Hydrogen Diffusion across a Steel Membrane from HCl Ethylene Glycol Solutions

Hydrogen diffusion across a steel (C3) membrane from 0.01–1.0 M HCl in ethylene glycol containing water (0.1 and 5 wt %) was studied. The effect of the solvate form of the discharging proton (C₂H₄(OH)₂H⁺ and H₃O⁺), the concentration of H⁺ _solv, and the cathodic polarization on the process was revealed.     

Crack Propagation Resistance of α-Al2O3 Reinforced Pulsed Laser-Deposited Hydroxyapatite Coating on 316 Stainless Steel

Hydroxyapatite (HA) is a widely used bioceramic known for its chemical similarity with that of bone and teeth (Ca/P ratio of 1.67). But, owing to its extreme brittleness, α-Al₂O₃ is reinforced with HA and processed as a coating via pulsed laser deposition (PLD). Reinforcement of α-Al₂O₃ (50 wt.%) in HA via PLD on 316L steel substrate has shown modulus increase by 4% and hardness increase by 78%, and an improved adhesion strength of 14.2 N (improvement by 118%). Micro-scratching has shown an increase in the coefficient-of-friction from 0.05 (pure HA) to 0.17 (with 50 wt.% Al₂O₃) with enhancement in the crack propagation resistance (CPR) up to 4.5 times. Strong adherence of PLD HA–Al₂O₃ coatings (~4.5 times than that of HA coating) is attributed to efficient release of stored tensile strain energy (~17 × 10^?3 J/m²) in HA–Al₂O₃ composites, making it a potential damage-tolerant bone-replacement surface coating.     

Crystal structure, thermal expansion and electrical properties of the new Al0.32ErGe2 compound

A new ternary compound Al_0.32ErGe₂ has been synthesized and studied from 298 K to 773 K using X-ray powder diffraction technique. Its structure has been determined at room temperature by Rietveld refinement of X-ray powder diffraction data. The ternary compound Al_0.32ErGe₂ crystallizes in the orthorhombic with the defect CeNiSi₂ structure type (space group Cmcm, a = 0.40701(2) nm, b = 1.60401(9) nm, c = 0.39240(2) nm, Z = 4 and D_calc = 8.326 g/cm³). The average thermal expansion coefficients , and of Al_0.32ErGe₂ are 1.72 × 10⁻⁵ K⁻¹, 1.11 × 10⁻⁵ K⁻¹ and 1.52 × 10⁻⁵ K⁻¹, respectively. The bulk thermal expansion coefficient is 4.35 × 10⁻⁵ K⁻¹. Electrical resistivity of Al_0.32ErGe₂ was measured between 5 K and 300 K.     

Effects of Nitrogen Content on the Phase and Resistivity of TaN Thin Films Deposited by Electron Beam Evaporation

A series of amorphous electron beam evaporated Ta and TaN films with N/Ta ratio from 0 to 1.15 were deposited on Si/SiO₂ substrates at 200°C. As N/Ta ratio increases, the TaN films undergo phase changes from pure metallic Ta to a mixture of Ta, Ta₂N, and nitrogen-rich TaN films. The electrical resistivity of the Ta and TaN films increased from 242 µΩ-cm to 1126 µΩ-cm with increasing N/Ta ratio. X-ray diffraction patterns revealed the development of different phases of TaN that are in agreement with the TaN phase diagram. The presence of different phases on the film surface was also confirmed by x-ray photo-emission spectroscopy (XPS) analysis. Groups of Ta4f doublet related to different TaN phases were observed in the core-level spectra of TaN films. Field-emission scanning electron microscopy images revealed that surface morphology also varied with the phase change in TaN films. The N/Ta ratios from energy-dispersive x-ray generally agreed with those from the XPS analysis.     

Improvement of healing treatment with NaNO3 for a passivated iron electrode covered with an ultrathin polymer coating to prevent iron corrosion in some solutions containing aggressive anions

An ultrathin and ordered polymer coating was prepared on a passivated iron electrode by modification of a 16-hydroxyhexadecanoate ion self-assembled monolayer with 1,2-bis(triethoxysilyl)ethane (C₂H₅O)₃Si(CH₂)₂Si(OC₂H₅)₃ and octyltriethoxysilane C₈H₁₇Si(OC₂H₅)₃. Further, the passivated and polymer-coated electrode was healed by treatment in 1.0 M NaNO₃ for 4 h. Prevention of passive film breakdown and iron corrosion for the passivated, polymer-coated and healed electrode was examined by monitoring of the open-circuit potential and repeated polarization measurements in oxygenated 0.1 M KClO₄, 0.1 M Na₂SO₄ and 0.1 M NaCl for many hours. The values of the time for passive film breakdown, t_bd were >240, 22.2 and 9.5 h in these solutions, respectively. The protective efficiencies for the electrode were extremely high, more than 99.9% before t_bd, indicating complete protection of substrate iron against corrosion in these solutions, unless passive film breakdown occurred. The presence of on the passive surface by treatment in 1.0 M NaNO₃ was detected by X-ray photoelectron and FTIR reflection spectroscopies. The self-healing activity of adsorbed to suppress passive film breakdown was discussed.     

Kinetics of Scheelite Conversion in Sulfuric Acid

Complete conversion of scheelite in H₂SO₄ solution plays a key role in exploration of cleaner technology for producing ammonium paratungstate. In this work, the factors influencing scheelite conversion were investigated experimentally to model its kinetics. The results indicated that the conversion rate increases with increasing temperature and reducing particle size, but is almost independent of stirring speed. Moreover, although the conversion rate increases with increasing initial H₂SO₄ concentration (≤ 1.25 mol/L), it decreases rapidly at 1.5 mol/L H₂SO₄ after 10 min due to formation of a H₂WO₄ layer. The experimental data agree quite well with the shrinking core model under chemical reaction control in ≤ 1.25 mol/L H₂SO₄ solution, and the kinetic equation was established as: \( 1- ( 1- \alpha )^{ 1 / 3} = 2 2 2 5 4 6. 6\cdot C_{{{\text{H}}_{ 2} {\text{SO}}_{ 4} }}^{ 1. 2 2 6} \cdot r_{ 0}^{ - 1} \cdot e^{{\frac{ - 3 9 2 6 0}{RT}}} \cdot t \) (t, min). This work could contribute to better understanding of scheelite conversion in H₂SO₄ solution and development of a new route for ammonium paratungstate production.     

Preparation and Dielectric Properties of CaCu3Ti4O12 Ceramics with Different Additives

Li₂CO₃, MgCO₃, BaCO₃, and Bi₂O₃ dopants were introduced into CaCu₃Ti₄O₁₂ (CCTO) ceramics in order to improve the dielectric properties. The CCTO ceramics were prepared by conventional solid-state reaction method. The phase structure, microstructure, and dielectric behavior were carefully investigated. The pure structure without any impurity phases can be confirmed by the x-ray diffraction patterns. Scanning Electron Microscopy (SEM) analysis illuminated that the grains of Ca_0.90Li_0.20Cu₃Ti₄O₁₂ ceramics were greater than that of pure CCTO. It was important for the properties of the CCTO ceramics to study the additives in complex impedance spectroscopy. It was found that the Ca_0.90Li_0.20Cu₃Ti₄O₁₂ ceramics had the higher permittivity (>45000), the lower dielectric loss (<0.025) than those of CCTO at 1 kHz at room temperature and good temperature stability from ?30 to 75 °C.     

Anodic Behavior of Hydrogenated Nickel in Sodium Hydroxide Solutions

The anodic behavior of hydrogenated nickel in sodium hydroxide solutions (0.01 to 1 N) is studied with the use of cyclic voltammetry, chronocoulometry, and chronoammetry. At the anodic dissolution of an -phase (Ni–0.03 at. % H), the ionization of hydrogen is limited by its diffusion in the solid phase. The diffusion coefficient of hydrogen D _H and the apparent thickness _H of the nickel layer depleted of hydrogen are calculated to be D _H = 1 × 10^–8 ± 2 × 10^–9 cm²/s and _H = 1.9 × 10^–4 cm. The D _H value is independent of the alkali concentration, while _H is independent of the duration and potential of hydrogenation. The cyclic voltammetry experiments have shown that the diffusion is unaffected by the possible formation of nickel oxides.