In situ characterization of N-methylpyrrole and (N-methylpyrrole-cyclodextrin) polymers on gold electrodes in aqueous and nonaqueous solution

Electrosynthesized polymers of N-methylpyrrole (NMPy) and N-methylpyrrole-2,6-dimethyl-β-cyclodextrin NMPy-β-DMCD were characterized with cyclic voltammetry and in situ conductivity measurements in aqueous and nonaqueous solutions. In situ UV–vis-spectra of PNMPy and poly(NMPy-β-DMCD) films show differences both in band absorbances and in energies of polaronic transitions. For the electrosynthesis of poly(NMPy-β-DMCD), a (1:1) (mole–mole) NMPy-β-DMCD supramolecular cyclodextrin complex of N-methylpyrrole was used as starting material, which was previously characterized with proton NMR spectroscopy. The PNMPy and poly(NMPy-β-DMCD) films were prepared from 0.05 M NMPy and 0.05 M NMPy-β-DMCD complex, respectively, in 0.1 M LiClO₄ aqueous solution and 0.1 M LiClO₄ nonaqueous solution (acetonitrile) by electropolymerization. A slight positive shift of the oxidation peak and further differences are observed for poly(NMPy-β-DMCD) electrosynthesized in comparison with PNMPy prepared in both aqueous and nonaqueous solutions. Different CVs and ΔE_p of films were observed at various scan rates. In situ conductivity values of PNMPy and poly(NMPy-β-DMCD) films prepared in nonaqueous solution (acetonitrile) show higher values than with films prepared in aqueous solutions.     

Studies on copper-semiconducting layer-electrolyte systems—I. Electrode potentials of copper and electrodeposited copper sulphide in S2− and Cu2+ media

Copper sulphide layers electrodeposited from a Na₂S bath consist chiefly of cuprous sulphide. Calculated values of the specific conductance of the deposited sulphide average around 3·8 × 10^?5 ohm^?1.cm^?1.Electrode potentials, E_H, of the Cu/Cu_2?δS in unbuffered Na₂S solutions and in solutions buffered at pH 9, correspond to the behaviour of a Cu/Cu_2?δS, overlayered with CuS/electrolyte. Steady reproducible potentials are obtained with the above electrodes in 0·5–10^?3M CuSO₄ solutions, closely comparable with those of the reversible Cu/Cu²⁺ couple.     

AlCl3-assisted formation of charge-transfer complexes between polyacetylene and tetracyanoethylene,TCNE

Polyacetylene, (CH)_x, the simplest conjugated polymer, can be converted into a conducting materials (8 Ω⁻¹ cm⁻¹) by treating it with TCNE/ AlCl₃/benzene solution. An electron transfer π-complex was obtained, as shown by EPR and XPS spectroscopies.     

Effect of sulphate ion on the electrochemical polymerization of pyrrole and N-methylpyrrole

Pyrrole and N-methylpyrrole were electrochemically polymerized in an identical manner in aqueous electrolytes containing (Et₄N)BF₄, LiClO₄ or Na₂SO₄ to give films of the corresponding p-doped polymers. The polymer obtained from the aqueous Na₂SO₄ electrolyte, [(poly N-methylpyrrole)^+y (SO₄)_y/2^2-]_x, differed from the other polymers in that it exhibited a very low conductivity (≈ 10^?7 S/cm), contained a high concentration of > C=O groups and had an EPR linewidth, ΔH_pp, more than an order of magnitude greater than that found in the corresponding polymers obtained from the (Et₄N)BF₄ and LiClO₄ electrolytes. A sample of [(polyN-methypyrrole)^+y(BF₄)_y^?]_x electrochemically synthesized in CH₃CN and subsequently converted electrochemically to the corresponding sulphate in the Na₂SO₄ aqueous electrolyte exhibited normal behaviour. A mechanism is proposed for the introduction of > C=O groups into the poly(N-methylpyrrole) polymer during its electrochemical polymerization in the Na₂SO₄ aqueous electrolyte.     

Pitting corrosion of artificially aged T6 AA2024/SiCp composites in 3.5 wt.% NaCl aqueous solution

The pitting corrosion behavior of the underaged (UA), peakaged (PA) and overaged (OA) T6 AA2024/0, 8, 14, 19, 24 vol.% 40 μm SiC_p(particles) composites was studied. The processing route used for the materials was the compocasting technique. Corrosion potentials (E_cor), pitting potentials (E_pit) as well as protection potentials (E_prot) were extracted from Double Cycle Polarization (DCP) curves contacted in aerated 3.5 wt.% NaCl aqueous solution. In addition 40 days immersion tests carried out and weight loss curves as well as total pit depth measurements were acquired. Pitting initiation and propagation as the main corrosion mechanism was driven by the aging kinetics which is ruled by the reduction in the retained vacancy concentration and at the same time by the increase in dislocation density as SiC_p volume fraction increases. Thus, alteration in pitting behavior among composites of different SiC_p content took place, although their ageing status was exactly the same.     

Iodide substitution in lithium borohydride, LiBH4-LiI

The new concept, anion substitution, is explored for possible improvement of hydrogen storage properties in the system LiBH₄-LiI. The structural chemistry and the substitution mechanism are analyzed using Rietveld refinement of in situ synchrotron radiation powder X-ray diffraction (SR-PXD) data, attenuated total reflectance infrared spectroscopy (ATR-IR), differential scanning calorimetry (DSC) and Sieverts measurements. Anion substitution is observed as formation of two solid solutions of Li(BH₄)_1−xI_x, which merge into one upon heating. The solid solutions have hexagonal structures (space group P6₃mc) similar to the structures of h-LiBH₄ and β-LiI. The solid solutions have iodide contents in the range ∼0-62 mol% and are stable from below room temperature to the melting point at 330 °C. Thus the stability of the solid solutions is higher as compared to that of the orthorhombic and hexagonal polymorphs of LiBH₄ and α- and β-LiI. Furthermore, the rehydrogenation properties of the iodide substituted solid solution Li(BH₄)_1−xI_x, measured by the Sieverts method, are improved as compared to those of LiBH₄. After four cycles of hydrogen release and uptake the Li(BH₄)_1−xI_x solid solution maintains 68% of the calculated hydrogen storage capacity in contrast to LiBH₄, which maintains only 25% of the storage capacity after two cycles under identical conditions.     

Quantum chemical aided molecular design of ionic liquids as green electrolytes for electrodeposition of active metals

Quantum chemical calculation was used to estimate the reduction potentials of 25 organic cations and the oxidation potentials of 11 anions. This information was used to select promising cations and anions for the preparation of ionic liquids as green electrolytes for electrodeposition of active metals. The reasonable linear correlations between the lowest unoccupied molecular orbital (LUMO) energies and the reduction potentials of cations, and the linear relationships between the oxidation potentials and the highest occupied molecular orbital (HOMO) energies of anions were obtained. The orders of electrochemical stability for cations and anions being obtained agree well with the experimental measurements. The suitable ionic liquids with sufficiently wide electrochemical windows for electrodeposition of active metals are suggested to be [Emim]NTf₂, [Bmim]NTf₂, [Bmim]BF₄, [Bmim]PF₆, [Bmim]CTf₃, [Emim]BF₄, [Emim]PF₆, [Emim]CTf_3..     

Polyacetylene film: A new electrode material for photoenergy conversion

Polyacetylene films were characterized as an electrode material in aqueous solutions. The trans polyacetylene films behaved as electrodes under reducing conditions. Oxygen gas evolution was greatly retarded under oxidizing conditions, primarily due to the high reactivity with oxygen. Visible light illumination resulted in a positive shift in electrode potential. The electrode developed photopotential reversibly in accord with illumination. The polyacetylene electrode gave cathodic photocurrent when contacted with a deoxygenated acetate buffer. The cathodic photocurrent increased with decreasing pH, ranging from 0 to 5.5 × 10^?6 A/cm². The possible use of polyacetylene electrodes for photoenergy conversion is discussed.     

The effect of IR-drop on corrosion rates calculated from low polarization data

Corrosion rates calculated from low polarization data can have substantial errors due to uncompensated solution/surface film resistance, R, even in solutions of moderate conductivity. The resulting uncompensated IR-drop has the effect of increasing the calculated values of polarization resistance which by itself would be expected to make calculated corrosion rates too low. However, calculated corrosion rates can be too high due to an uncompensated IR-drop in cases where both polarization resistance, R_p and anodic Tafel slope for the metal, b_a,M, are calculated from low polarization data. This is true for metals corroding under conditions where the cathodic reaction(s) are limited by diffusion, because there is a greater positive error in calculated values of b_{a, M} than in R_p. These findings are confirmed experimentally, and techniques for measuring IR-drop are discussed. Electrochemically calculated corrosion rates corrected for both IR-drop and close approach between corrosion and metal equilibrium potentials are compared with those calculated from solution analysis.     

Oxidation of polyacetylene in aqueous solutions containing sulphuric acid and selected supporting oxidants

It has been found that the addition of strong oxidants such as HNO₃, NaNO₂, KMnO₄, K₂Cr₂O₇ and NaIO₃ to an aqueous solution of sulphuric acid greatly facilitates the insertion of HSO₄^? ions into (CH)_x. [CH-(HSO₄)_y]_x formation occyrs even in less concentrated solutions in which sulphuric acid alone does not oxidize polyacetylene. Based on the above observation, a new analytical method for NO₃^? determination has been proposed. The method consists of acidification of any neutral, aqueous solution of a nitrate salt with sulphuric acid to 5.7 M. Although H₂SO₄ of such concentration does not oxideze polyacetylene, in the presence of NO₃^?, doping occurs due to the formation of free HNO₃ upon acidification. The doping reaction results in a significant increase of the electronic conductivity of the polyacetylene, σ. Log σ vs NO₃^? concentration plots are linear over a nitrate concentration range of 2 - 40 mM and can be utilized in chemical analysis. The selectivity of the proposed method is limited. Although the majority of common ions (HSO₄^?, Cl^?, PO₄^3?, etc. …) do not influence the measurements, the presence of other (than HNO₃) oxidants in the solution must be avoided.     

Corrosion behavior of alumina ceramics in aqueous HCl and H2SO4 solutions

The corrosion behavior of cold isostatically pressed (CIP) high purity alumina ceramics in aqueous HCl and H₂SO₄ solutions with various concentrations has been studied simultaneously at room temperature (25 °C). Corrosion tests were also performed with 0.65 mol/l HCl and 0.37 mol/l H₂SO₄ solutions at 40, 55 and 70 °C for 48 h. Chemical stability was monitored by determining the amount of Al³⁺, Mg²⁺, Ca²⁺, Na⁺ Si⁴⁺ and Fe³⁺ ions eluted in different concentrations of HCl and H₂SO₄ solutions by means of atomic absorption spectrometry (AAS). By increasing the concentration from 0.37 to 6.5 mol/l, it was notified that the corrosion susceptibility in HCl and H₂SO₄ solutions for the CIP alumina specimens at room temperature decreases.     

Limits determination of toleration of aggressive anions by a certain passivator on zinc surface

The open circuit potentials of Zn electrode were followed as a function of time in different concentrations Na₂B₄O₇ solutions until steady-state, E_st., values were attained. The potential shifts immediately towards positive values, indicating film thickening and repair. The effect of addition of NaCl, NaBr and NaI as aggressive agent on the steady-state potential of a Zn electrode previously equilibrated in a passivating borate solution was also established. For each Na₂B₄O₇ concentration, the variation in the potential with the quantity of aggressive anions follows an S-shaped relationship. The new potentials are established after an induction period which decreases with the increase in the concentration of the aggressive anion, C_agg., and/or decreases in that of the passivator anion, C_pass.. The concentration, C_agg., that can be tolerated by a certain concentration of the passivator anion, C_pass., is given by the relation: log C_pass. = k + n log C_agg., where k and n are constants. This is derived on the basis of competitive adsorption of both types of anion and the structure of the double layer at the metal/solution interface. The implications of the equations are briefly discussed.     

The first-class reciprocal quaternary system H3PO4-K2SO4-K3PO4-H2SO4-H2O application to fertilizer fabrication problems

The first-class reciprocal quaternary system H₃PO₄-K₂SO₄-K_3PO₄-H₂SO₄-H₂O has been carefully investigated at 25 and 75°C. Representations have been given using the J?necke coordinates. Using the established diagrams as a base, a procedure is proposed for preparing specific fertilizers containing potassium and phosphate ions by reacting phosphate rock with aqueous solutions of KHSO₄, addition of calculated amounts of water to the reaction mixture, elimination of an insoluble products, and programmed water evaporation.     

Octa- and tetra-(benzo-15-crown-5)phthalocyanines in surfactant-containing solutions

The behavior of octa-(benzo-15-crown-5)phthalocyanine (H₂cr₈Pc), as well as cobalt octa- and tetra-(benzo-15-crown-5)phthalocyaninates (Cocr₈Pc and Cocr₄Pc), in aqueous solutions containing cationic or anionic surfactants, such as cetyl trimethylammonium bromide (CTAB), sodium carboxymethyl cellulose (Na-CMC), and sodium dodecyl sulfate (SDS), is studied using electronic spectroscopy. The presence of eight benzo-15-crown-5 ether fragments on the periphery of the phthalocyanine ring is shown to facilitate the dissolution of Pc in an aqueous environment. The interactions between CTAB and crown-containing Pc promotes the dissolution of H₂cr₈Pc; Cocr₈Pc; and, to a lesser degree, Cocr₄Pc, which is accompanied by the appearance of molecular aggregates, including heteronuclear cofacial dimers. The presence of a metal in the ring is not the necessary condition of the process. In microscopically heterogeneous medium, such as an aqueous SDS-containing solution, H₂cr₈Pc is present in monomeric form at SDS concentrations close to C _cr and in dimeric form at SDS content below C _cr. Under similar conditions (environment, surfactant), Cocr₄Pc can exist in monomeric form at SDS concentrations much high than C _cr. The effect of the size of cation on the form of the crown-containing Pc in an aqueous solution is illustrated by an example of H₂cr₈Pc. Na-CMC promotes the dissolution of Pc and enables one to produce K⁺/Mcr₈Pc-modified films from aqueous solutions.     

Reactive polymer films: Polypyrrole oxidation kinetics in aqueous solution

The oxidation kinetics of electrogenerated polypyrrole films was studied in aqueous solution. The influence of reactant concentrations (LiClO₄ in solution and active centres in the polymer film) and temperature on the kinetics has been studied. The usual procedure for any kinetic study was now repeated for different initial states, attained by electrochemical reduction at the same cathodic potential for different reduction times. For rising reduction times, lower kinetic coefficient (k) and higher activation energies (E_a) were obtained. The activation energy is assumed to include rising conformational energy for more packed conformations of the initial states. Both kinetic magnitudes become a way to quantify the initial packing conformational degree. So, kinetic magnitudes can include structural information opening a new window for the chemical kinetics of reactive macromolecules that could be extended to reactive biopolymers. When compared the evolutions of k and E_a experimental changes from aqueous and acetonitrile solutions of the same salt, important differences were found. Evolutions of k and E_a from different solvents could be used as tools to quantify the polymer–solvent interaction evolution along the reaction.     

The effect of molybdenum on the corrosion behaviour of the high-entropy alloys Co1.5CrFeNi1.5Ti0.5Mox in aqueous environments

The purpose of this study is to investigate the electrochemical properties of the Co_1.5CrFeNi_1.5Ti_0.5Mo_x high-entropy alloys in three aqueous environments which simulate acidic, marine, and basic environments at ambient temperature (∼25 °C). The potentiodynamic polarisation curves of the Co_1.5CrFeNi_1.5Ti_0.5Mo_x alloys, obtained in aqueous solutions of H₂SO₄ and NaOH, clearly revealed that the corrosion resistance of the Mo-free alloy was superior to that of the Mo-containing alloys. On the other hand, the lack of hysteresis in cyclic polarisation tests and SEM micrographs confirmed that the Mo-containing alloys are not susceptible to pitting corrosion in NaCl solution.     

Mechanical properties and corrosion resistance of nanocrystalline ZrNxOy coatings on AISI 304 stainless steel by ion plating

Transition metal oxynitrides have become emerging decorative coating materials due to their adjustable coloration and high hardness and corrosion resistance. This research studied the effect of oxygen content on the coloration, mechanical properties and corrosion resistance of ZrN_xO_y thin films deposited on AISI 304 stainless steel using hollow cathode discharge ion plating (HCD-IP). The Zr/N/O ratios of the ZrN_xO_y films were determined using X-ray photoelectron spectroscopy (XPS). The color of the ZrN_xO_y thin film changed from golden yellow to blue and then slate blue with increasing oxygen content. X-ray diffraction (XRD) patterns revealed that phase separation of ZrN and m-ZrO₂ occurred as the oxygen content reached 31.2 at.%. ZrN(O) (ZrN with dissolving oxygen) is dominant at oxygen content less than 18.1 at.%, while m-ZrO₂ phase was prevailed at oxygen content above 40.3 at.%. Phase separation lowered the hardness of the ZrN_xO_y films as the fraction of ZrO₂ was less than 40%. The residual stresses in ZrN phase was higher than that in ZrO₂, and the residual stress decreased for the specimen containing 30 to 37% ZrO₂. For the samples containing more than 44% ZrO₂, the average residual stress was close to that in ZrO₂ phase. The corrosion resistance was evaluated by salt spray test and potentiodynamic scan in two solutions: 0.5MH₂SO₄ + 0.05 M KSCN and 5% NaCl solutions. The results showed consistent trend in the two solutions. From the results of potentiodynamic scan, corrosion resistance increased as the packing density of the film increased, whereas the film thickness was not a crucial factor on corrosion current; moreover, the electrical conductivity of the film may be one of the significant factors in corrosion resistance. Results of salt spray tests suggested that the corrosion of ZrN_xO_y in NaCl may play an important role in corrosion resistance.     

Electrodeposition Process and Performance of CuIn(Se<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>S<Subscript>1−<Emphasis Type="Italic">x</Emphasis></Subscript>)<Subscript>2</Subscript> Film for Absorption Layer of Thin-Film Solar Cells

CuIn(Se _x S_1?x )₂ thin film is prepared by the electrodeposition method for the absorption layer of the solar cell. The CuIn(Se _x S_1?x )₂ films are characterized by cyclic voltammetry measurement for the reduction of copper, indium, selenium and sulfur in selenium and sulfur in aqueous solutions with sodium citrate and without sodium citrate. In the four cases, the defined reduction process for every single element is obtained and it is observed that sodium citrate changes the reduction potentials. A linear relationship between the current density of the reduction peak and (scan rate v)^1/2 for copper and indium is achieved, indicating that the process is diffusion controlled. The diffusion coefficients of copper and indium ions are calculated. The diffusional coefficient D value of copper is higher than that of indium, and this is the reason why the deposition rate of copper is higher. When four elements are co-deposited in the aqueous solution with sodium citrate, the quaternary compound of CuIn(Se _x S_1?x )₂ is deposited together with Cu₃Se₂ impure phases after annealing, as found by XRD spectra. Morphology is observed by SEM and AFM. The chemical state of the films components is analyzed by XPS. The UV-Visible spectrophotometer and electrochemistry workstation are employed to measure the photoelectric properties. The results show that the smooth, uniform and compact CuIn(Se _x S_1?x )₂ film is a semiconductor with a band gap of 1.49 eV and a photovoltaic conversion efficiency of 0.45%.     

Spectroelectrochemical studies of polyaniline

The structural change and electrode reaction mechanism of polyaniline with counter anion NO⁻₃ were investigated on the basis of vis-n.i.r. absorption spectra at different potentials in 1 M NaNO₃ aqueous solution at pH 1.5, with and without alkali treatment of the polyaniline film. Three redox stages were found in the spectra and the cyclic voltammogram in the potential range −0.4 V to 0.8 V (versus SCE). The equilibrium electrode potential of as-prepared polyaniline film is ≈0.3 V (versus SCE) in 1 M NaNO₃ aqueous solution at pH 1.5. The spectral changes with time after removing the polarization potential show that the stable state in the solution is in the potential range 0.2 –0.4 V; the over-oxidized state at higher than 0.5 V and the reduction state at lower than 0.1 V are both unstable.     

Microstructure,Phase Occurrence,and Corrosion Behavior of As-Solidified and As-Annealed Al-Pd Alloys

In the present work, we studied the microstructure, phase constitution, and corrosion performance of Al₈₈Pd₁₂, Al₇₇Pd₂₃, Al₇₂Pd₂₈, and Al₆₇Pd₃₃ alloys (metal concentrations are given in at.%). The alloys were prepared by repeated arc melting of Al and Pd granules in argon atmosphere. The as-solidified samples were further annealed at 700 °C for 500 h. The microstructure and phase constitution of the as-solidified and as-annealed alloys were studied by scanning electron microscopy, energy-dispersive x-ray spectroscopy, and x-ray diffraction. The alloys were found to consist of (Al), ε _n (~ Al₃Pd), and δ (Al₃Pd₂) in various fractions. The corrosion testing of the alloys was performed in aqueous NaCl (0.6 M) using a standard 3-electrode cell monitored by potentiostat. The corrosion current densities and corrosion potentials were determined by Tafel extrapolation. The corrosion potentials of the alloys were found between ? 763 and ? 841 mV versus Ag/AgCl. An active alloy dissolution has been observed, and it has been found that (Al) was excavated, whereas Al in ε _n was de-alloyed. The effects of bulk chemical composition, phase occurrence and microstructure on the corrosion behavior are evaluated. The local nobilities of ε _n and δ are discussed. Finally, the conclusions about the alloy’s corrosion resistance in saline solutions are provided.