Influence of phytic acid concentration on performance of phytic acid conversion coatings on the AZ91D magnesium alloy

In this study, the phytic acid conversion coating, a new environmentally friendly chemical protective coating for magnesium alloys, was prepared. The influences of phytic acid concentration on the formation process, microstructure, chemical state and corrosion resistance of the conversion coatings on AZ91D magnesium alloy were investigated by means of weight gain measurement, field-emission scanning electron microscopy (FESEM), Fourier transform infrared (FTIR) spectroscopy, potentiodynamic polarization method and electrochemical impedance spectroscopy (EIS), respectively. And the depth profile of all elements in the optimal conversion coatings was analyzed by auger electron spectroscopy (AES).The results show that the growth, microstructure, chemical state and corrosion resistance of the conversion coatings are all obviously affected by the phytic acid concentration. The concentration of 5 g l⁻¹ corresponds to the maximum weight gain. The main elements of the coating are Mg, Al, O, P, and C, which are distributed gradually in depth. The functional groups of conversion coatings formed in higher concentration phytic acid solution are closer to the constituent of phytic acid than those formed in lower concentration phytic acid solution. The coatings formed in 1–5 g l⁻¹ are integrated and uniform. However, those formed in 20–50 g l⁻¹ have some micro-cracks on the α phase. The coating formed in 5 g l⁻¹ has the best corrosion resistance, whose open circuit current density decreases about six orders than that of the untreated sample, although the coatings deposited in 1–20 g l⁻¹ can all improve the corrosion resistance of AZ91D.     

The electrochemical synthesis of poly(pyrrole-co-o-anisidine) on 3102 aluminum alloy and its corrosion protection properties

The electrochemical syntheses of polypyrrole (PPy) and poly(pyrrole-co-o-anisidine) were achieved on 3102 aluminum alloy (Al) from 0.1 M monomer (pyrrole:o-anisidine, 8:2) containing 0.4 M oxalic acid solution using the cyclic voltammetry technique. The synthesized films were characterized by FT-IR spectroscopy. The thermal stability of films was determined by thermogravimetric analysis (TGA) technique. Surface morphologies were characterized by scanning electron microscope (SEM) images. The potential of zero charge (pzc) of Al was determined using electrochemical impedance spectroscopy (EIS). The corrosion behavior of samples was investigated with open circuit potential (E_ocp)–time, EIS, and anodic polarization techniques. It was found that copolymer coated Al provides better barrier property against of corrosion in 3.5% NaCl solution.     

Photovoltaic characteristics of TCNQ-incorporated CuPc-poly(p-phenylene) composite films

Composite films (CuPc–PPP–TCNQ) were produced by simultaneous deposition using copper phthalocyanine (CuPc) as a carrier generation material, poly(p-phenylene) (PPP) as a hole transport material, and tetracyanoquinodimethane (TCNQ) as a incorporation material. Schottky barrier photovoltaic cells, consisting of a semitransparent aluminum and the CuPc–PPP–TCNQ composite films, were fabricated. The junction properties and the photovoltaic properties on Al/CuPc–PPP–TCNQ/ITO sandwich cells were investigated. As well as a composite film of the CuPc and the PPP (CuPc–PPP), the conductivity of the CuPc–PPP–TCNQ composite film is improved as the TCNQ is simultaneously deposited in the CuPc–PPP composite film. Therefore, it is proven that the short circuit photocurrent density (J _sc) and the photovoltaic property increases significantly. The J _sc of the Al/CuPc–PPP–TCNQ/ITO cell is 2.60 A/cm², and it is found that the J _sc is about 20 times that of an Al/CuPc/ITO cell and double that of an Al/CuPc–PPP/ITO cell. Consequently, the power conversion efficiency of the Al/CuPc–PPP–TCNQ/ITO cell obtained was 3.68%.     

Corrosion behavior of AZ91 magnesium alloy in dilute NaCl solutions

The corrosion behavior of AZ91 magnesium alloy in dilute NaCl solutions was studied using electrochemical measurements, whereby a corrosion map in terms of electrode potential and chloride concentration [Cl⁻] was obtained. AZ91 alloy exhibited the corrosion and passivation zones in dilute NaCl solutions. The passivation zone became narrow with increasing [Cl⁻]. The values of open-circuit potential were in the passivation zone when the [Cl⁻] was less than 0.5 mol/L. XRD patterns showed the presence of the Mg(OH)₂, Mg₅(CO₃)₄(OH)₂·8H₂O and MgO phases in the corrosion product, whereas the latter two phases found in the passive film.     

Electrochemical behavior and multilayer films of the sandwich-type polyoxotungstate complex {K10Co4(H2O)2(PW9O34)2}

The electrochemical behavior of the sandwich-type polyoxotungstate complex of K₁₀Co₄(H₂O)₂(PW₉O₃₄)₂ (Co₄(PW₉)₂) was investigated by cyclic voltammetry in aqueous solutions. The polyoxoanion exhibits two successive redox peaks originating from the tungsten-oxo framework. The electrochemical behavior for the Co^II species was not detected. Moreover, the multilayer films consisting of PEI and Co₄(PW₉)₂ were prepared by the layer-by-layer self-assembly method. The films were characterized by UV–vis spectroscopy, cyclic voltammetry and atomic force image. The films exhibit the electrochemical behavior of Co₄(PW₉)₂ polyoxoanion. Moreover, the films can catalyze the electrochemical reduction of NO₂⁻. Electron transfer to Fe(CN)₆^3−/4− redox probe was also investigated.     

Electrochemical behaviour of Cu24Zn5Al alloy in alkaline medium in the presence of chloride ions and benzotriazole

This paper deals with electrochemical behaviour of Cu24Zn5Al alloy in a sodium tetraborate solution (borax), in the presence of chloride ions and benzotriazole. It was found that during anodic polarization of the investigated alloy, in a sodium tetraborate solution, at lower potentials, copper (I)-oxide formed on the alloy surface. The voltammograms show peak potential shifts corresponding to the formation of Cu₂O towards more positive values with longer immersion time. It was found that chloride ions had an activating effect in a sodium tetraborate solution containing various concentrations of chloride ions (0.001, 0.005, 0.010, 0.050 and 0.100 mol dm⁻³ Cl⁻). It was observed that Cu24Zn5Al alloy corroded more intensely in more concentrated solutions and with longer exposure to Cl⁻. Investigations of the effect of inhibitor concentrations (8.4 × 10⁻⁶, 8.4 × 10⁻⁵, 8.4 × 10⁻⁴ and 8.4 × 10⁻³ mol dm⁻³ BTA in 0.1 mol dm⁻³ borax solution) showed that BTA had a good protective effect. The inhibiting effect of BTA was also confirmed with various times of immersion of this alloy in a 1.7 × 10⁻² mol dm⁻³ solution of this inhibitor.     

Coupling extraction–flotation with surfactant and electrochemical degradation for the treatment of PAH contaminated hazardous wastes

The performance of a two-stage process combining extraction of polycyclic aromatic hydrocarbons (PAHs) with an amphoteric surfactant (CAS) followed by electro-oxidation of PAH-foam concentrate was studied for the decontamination of aluminum industry wastes (AIW) and polluted soils. The PAH suspensions extracted from AIW and soils were treated in a 2 L-parallelepipedic electrolytic cell containing Ti/RuO₂ anodes and stainless steel cathodes. Current densities varying from 4.6 to 18.5 mA cm⁻² have been tested with and without addition of a supporting electrolyte (6.25 to 50 kg Na₂SO₄ t⁻¹ of dry waste). The best performance for PAH degradation was obtained while the electrolytic cell was operated during 90 min at a current density of 9.2 mA cm⁻², with a total solids concentration of 2.0%, and in presence 12.5 kg Na₂SO₄ t⁻¹. The application of the process on AIW (initial PAH content: 3424 mg kg⁻¹) allowed extracting 42% of PAH, whereas 50% of PAH was electrochemically degraded in the resulting foam suspensions. By comparison, 44% to 60% of PAH was extracted from polluted soils (initial PAH content: 1758 to 4160 mg kg⁻¹) and 21% to 55% of PAH was oxidized in the foam suspensions. The electrochemical treatment cost (including only electrolyte and energy consumption) recorded in the best experimental conditions varied from 99 to 188 USD $ t⁻¹ of soils or AIW treated.     

Electrochemical corrosion behavior of 2A02 Al alloy under an accelerated simulation marine atmospheric environment

The corrosion behavior of 2A02 Al alloy under simulated marine atmospheric environment has been studied using mass-gain, scanning electron microscope/energy dispersive spectroscopy (SEM/EDS), laser scanning confocal microscopy, X-ray diffraction spectroscopy and localized electrochemical methods. The results demonstrate that the relationship between the corrosion induced mass-gain and the corrosion time is in accordance with the power rule. The mass-gain increases gradually during the corrosion time, while the corrosion rate decreases. With ongoing of the corrosion, corrosion products film changed from a porous to a compact structure. The various spectroscopic data show that the corrosion products films composed mainly of Al(OH)₃, Al₂O₃ and AlCl₃. The electrochemical corrosion behavior of the 2A02 Al alloy was studied by electrochemical impedance spectroscopy (EIS).     

Study on Li-ion diffusion in nano-crystalline LiMn2O4 thin film cathode grown by pulsed laser deposition using CV, EIS and PITT techniques

In the present work, LiMn₂O₄ thin films have been prepared by pulsed laser deposition on stainless steel substrates. The films deposited at 400 °C and 200 mTorr of oxygen were mainly composed of nano-crystals less than 100 nm and their agglomerates. Three different electrochemical methods including CV, EIS and PITT were applied to measure the overall Li⁺-ion diffusion coefficients and charge-transfer resistances at various potentials from 3.85 to 4.5 V. The Li⁺ diffusion coefficients were in the range of 10⁻¹² to 10⁻¹⁰ cm² s⁻¹, depending on the potentials. It was found that the charge-transfer resistances decreased with the increase of potentials. Especially, relatively high diffusion coefficients and low charge-transfer resistances were observed above 4.2 V.     

Voltammetric determination of ethamsylate in bulk solution and pharmaceutical tablet by nano-material composite-film coated electrode

A sensitive electrochemical method was described for voltammetric determination of ethamsylate at a glassy carbon electrode (GCE) coated with a nano-material thin film. In this work, a nanometer material, namely, multi-wall carbon nanotubes (MWCNT) was dispersed successfully into water in the presence of dihexadecyl hydrogen phosphate (DHP) and a MWCNT–DHP composite film was conveniently obtained on the GCE surface. The electrochemical behavior of ethamsylate at this modified electrode was investigated and a pair of reversible redox peak was observed. Compared with the electrochemical response of ethamsylate at the bare GCE, the separation of peak potential (ΔE_p) of ethamsylate decreased obviously from 438 to 40 mV and the current density of redox peaks increased greatly. Based on this, differential pulse voltammetry (DPV) was employed to determine ethamsylate. Various experimental parameters such as pH value of the supporting electrolyte, the amount of modifier and so on were optimized. Under optimal conditions, a linear response of ethamsylate was obtained in the range from 1.0 × 10^− 6 to 2.0 × 10^− 5 mol/L, and the detection limit was 6.0 × 10^− 7 mol/L. The proposed method was successfully applied to detect ethamsylate in pharmaceutical samples.     

Oxidation behavior of (Ti1 − xAlx)N films perpared by r.f. reactive sputtering

(Ti, Al)N films have drawn much attention as alternatives for TiN coatings, which are oxidized easily in air above 500 °C. We have investigated the effect of Al content on the oxidation resistance of (Ti_{1 − x}Al_x)N films prepared by r.f. reactive sputtering.(Ti_{1 − x}Al_xN films (O ≤ x ≤ 0.55) were deposited onto fused quartz substrates by r.f. reactive sputtering. Composite targets with five kinds of Al-to-Ti area ratio were used. The sputtering gas was Ar (purity, 5 N) and N₂ (5 N). The flow rate of Ar and N₂ gas was kept constant at 0.8 and 1.2 sccm, respectively, resulting in a sputtering pressure of 0.4 Pa. The r.f. power was 300 W for all experiments. Substrates were not intentionally heated during deposition. The deposited films (thickness, 300 nm) were annealed in air at 600 900 °C and then subjected to X-ray diffractometer and Auger depth profiling.The as-deposited (Ti_{1 − x}Al_x)N films had the same crystal structure as TiN (NaCl type). Al atoms seemed to substitute for Ti in lattice sites. The preferential orientation of the films changed with the Al content of the film, x. Oxide layers of the films grew during annealing and became thicker as the annealing temperature increased. The thickness of the oxide layer grown on the film surface decreased with increasing Al content in the film. For high Al content films an Al-rich oxide layer was grown on the surface, which seemed to prevent further oxidation. All of the films, however, were oxidized by 900 °C annealing, even if the Al content was increased up to 0.55.     

Synthesis, thermal, photoluminescent, and electroluminescent properties of a novel quaternary Eu(III) complex containing a carbazole hole-transporting functional group

A novel quaternary Eu(III) complex containing a carbazole fragment as hole-transporting functional group was synthesized, and its thermal stability, photoluminescent (PL), electroluminescent (EL) properties were studied. Its glass transition temperature (T _g) was 131 °C and 5% weight loss temperature was 325 °C. In studies of its EL properties, two devices with the Eu(III) complex as red light-emitting materials were fabricated and measured. Device 1: ITO/NPB (40 nm)/Eu(III) complex (30 nm)/Alq₃ (30 nm)/LiF (0.7 nm)/Al (100 nm), NPB was N,N′-di(naphthalene-1-yl)-N,N′-diphenyl-benzidine as the hole-transporting layer, Alq₃ was tris(8-hydroxyquinoline) aluminum as the electron-transporting layer. Device 1 gave two emission bands of the Eu(III) complex and Alq₃ with the maximum luminance of 437 cd/m² at 17.34 V, and its turn-on voltage was 10 V. In device 2, an electron-transporting/hole-locking layer of BCP (2,9-dimethyl-4,7-diphenyl-1,10-phenanthroline, 30 nm) was added between the Eu(III) complex and Alq₃ layers, only a sharp red emission band of the Eu(III) complex was given with the maximum luminance of 186 cd/m² at 20.08 V, and its turn-on voltage was 12 V.     

Redox Behavior of Am(IV) and Methods of Its Preparation in Alkaline Media

A scheme was suggested for Am(OH)₄ isolation by treatment of Am(OH)₃ suspension in 0.1–1.0 M NaOH with ozone (3.5–5 vol %)-oxygen mixture (4–5 l h⁻¹ flow rate) at 20°C for 40 min, followed by ultrasonic treatment of the resulting Am(VI) (44 kHz, 1 W cm⁻³) for 45 min. The separated precipitate of Am(III) hydroxy peroxide was treated with 1–2 mlof 7–10 M NaOH to form Am(OH)₄. Mixing suspensions of equivalent amounts of Am(III) and Am(V) hydroxides in NaOH also gives Am(IV) hydroxide in a >98% yield. The reproportionation Am(III) + Am(V) = 2Am(IV) in 1 M NaOH starts on heating above 70°C, whereas at NaOH concentration higher than 7 M it is completed even at room temperature. The reaction of Am(III) with Am(VI) in alkaline solutions, Am(VI) + 2Am(III) → 3Am(IV), occurs during mixing the reactants. The equilibrium reaction of Am(OH)3 with [Fe(CN)₆]³⁻ in alkaline solutions was studied. It was shown that increasing the alkali concentration to 2 M NaOH promotes formation of Am(OH)₄. At further increase in the alkali concentration, Am(V) is formed.__________Translated from Radiokhimiya, Vol. 47, No. 3, 2005, pp. 234–238.Original Russian Text Copyright © 2005 by Nikonov, Gogolev, Tananaev, Myasoedov, Clark.     

Spectrophotometric determination of Sb(III) and Sb(V) in biological samples after micelle-mediated extraction

This work presents a micelle-mediated extraction method for simultaneous preconcentration and determination of Sb(III) and Sb(V) species in biological samples as a prior preconcentration step to their spectrophotometric determination. The analytical system is based on the selective reaction between Sb(III) and bromopyrogallol red (BPR) in the presence of cetyltrimethylammonium bromide (CTAB) and potassium iodide at pH 6.4. Total Sb concentration was determined after reduction of Sb(V) to Sb(III) in the presence of potassium iodide and ascorbic acid. The optimal extraction and reaction conditions were studied and the analytical characteristics of the method (e.g., limit of detection, linear range, preconcentration factor, and improvement factors) were obtained. Linearity for Sb(III) and Sb(V) were obeyed in the range of 0.2–20.0 ng mL⁻¹ and 0.4–25.0 ng mL⁻¹, respectively. The detection limit for the determination of Sb(III) and Sb(V) were 0.05 ng mL⁻¹ and 0.08 ng mL⁻¹, respectively. The interference effect of some anions and cations was also studied. The method was applied to the determination of Sb(III) in the presence of Sb(V) and total antimony in blood plasma and urine samples.     

Synthesis of LiV3O8 by an improved citric acid assisted sol–gel method at low temperature

LiV₃O₈ was synthesized by the normal citric acid assisted sol–gel method and an improved citric acid assisted sol–gel method. The improved method compares with the normal method in detail by thermogravimetry (TG), FTIR, X-ray diffraction (XRD), scanning electron microscopy (SEM), charge–discharge test, cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). Results show that the improved method can synthesize LiV₃O₈ successfully at much lower temperature than normal method.     

The electrochemical behaviour of naturally passivated hafnium in aqueous solutions of different pH

Naturally passivated hafnium was investigated in solutions of different pH. The effect of prevailing gas on the electrochemical behaviour of the metal was studied. The steady state potential of the metal was found to be a linear function of the solution pH in the range 4–10. The slope of E_SS vs. pH relation is equal to 18 mV/pH indicating the exchange of three electrons in the electrochemical equilibrium. In oxygen saturated solutions, the potential gets more positive which reflects the increased passivity of the metal surface in naturally aerated and oxygen saturated aqueous solutions. The passive film is highly stable in neutral solutions due to the presence of the stable HfO(OH)₂. The activation energy of the passive film dissolution is relatively lower in acid solution due to the formation of the hafnyl ions HfO²⁺. EIS and polarization experiments are consistent and the naturally occurring passive film can be fitted to a simple electronic equivalent circuit. Naturally passivated hafnium deviate slightly from ideal capacitor behaviour. Anodic oxide films on hafnium deviate greatly from the ideal capacitor behaviour and complicated electronic circuits should be proposed to fit their impedance characteristics.     

Surface and interface characterization of nanoporous alumina templates produced in oxalic acid and submitted to etching procedures

High purity aluminum (Al) sheets were used to produce ordered nanoporous alumina templates by two step anodization technique using oxalic acid as electrolyte. Electrochemical polishing of Al sheets was performed in order to study the surface roughness influence on the pore roundness of the alumina templates. The templates were submitted to progressive reduction of anodizing voltage (electrochemical etching) to thin the Al₂O₃ barrier layer on the bottom of the pores, and to chemical etching to widen the diameter of the pores. The pore diameter and porosity increase linearly with the chemical etching time, while interpore distance, circularity, pore density and pore distribution do not change. Electropolished Al substrates produce nanoporous Al₂O₃ templates with more circular pores, and the Al₂O₃ barrier layer at the Al₂O₃/Al interfaces is completely removed after the electrochemical and chemical etching processes.     

Organic light-emitting devices based on solution-processible quinolato-complex supramolecules

This paper discusses a new type of supramolecular material tris{5-N-[3-(9H-carbazol-9-yl)propyl]-N-(4-methylphenyl)aminesulfonyl-8-hydroxyquinolato} aluminum(III), Al(SCarq)₃, which we synthesized using three 5-N-[3-(9H-carbazol-9-yl)propyl]-N-(4-methylphenyl)aminesulfonyl-8-hydroxyquinoline as bidentate ligands. The peak photoluminescence in the solid phase appears at 488 nm. In cyclic voltammetric measurement, two oxidation peaks, which were obtained at ?5.6 and ?5.9 eV, correspond to HOMO sites of carbazoyl and aluminum quinolates, respectively. In the investigation of solid morphological thin film, the flat surface was investigated using an atomic force microscope. The root mean square (rms) and mean roughness (R_a) were respectively measured to be 0.427 and 0.343 nm. For the fabrication of organic light-emitting devices (OLEDs) using spin-coating techniques, the turn-on voltage and maximum luminescence of the optimized electroluminescence device, glass/ITO (20 nm)/PEDOT:PSS (75 nm)/Al(SCarq)₃ (85 nm)/BCP (8 nm)/LiF (1 nm)/Al (200 nm), were respectively 9.6 V and 35.0 cd m^?2. Due to the electroplex formation between the carbazole (electron-donor) and the aluminum quinolates (electron-acceptor) moieties under an applied DC bias, the chromaticity of electroluminescence shifted to green-yellow with 1931 CIE_x,y (0.40, 0.47).     

Synthesis,characterization and temperature studies on the conductivity of AlCl<Superscript>−</Superscript><Subscript>4</Subscript> ion doped polypyrrole

Synthesis of free standing conducting polypyrrole film using room temperature melt as the electrolyte is reported. We also report variation in the contribution of ionic conductance with temperature of the polymer film by four probe method and electrochemical properties like diffusion coefficient and ionic mobility of AlCl⁻₄ doped polypyrrole film. An attempt has been made to arrive at the stability of charge carrier concentration over a temperature range of 295 to 350 K under vacuum. The film was characterized by optical techniques and scanning electron micrography.     

Synthesis of Ti3Al and TiAl based surface alloys by pulsed electron-beam melting of Al(film)/Ti(substrate) system

Phase formation and surface hardening in the 100-nm-thick Al(film)/Ti(substrate) system under conditions of pulsed electron-beam melting (～15 keV, ～3 μs, 3–4 J/cm²) have been studied depending on the number of film deposition-melting cycles. Using this method, submicrocrystalline and nanocrystalline surface alloys with thicknesses ≥3 μm based on Ti₃Al and TiAl intermetallics have been obtained on the titanium substrate.