Electroless preparation and electrochemical behavior of a platinum-doped nickel hexacyanoferrate film–zinc modified electrode: catalytic ability of the electrode for electrooxidation of methanol

The use of a zinc substrate as an electrode and the modification of its surface by means of a thin film of platinum-doped nickel hexacyanoferrate (Pt-NiHCF) were developed. The modification conditions of the zinc surface including the electroless deposition of metallic nickel on the electrode surface from NiCl₂ solution, chemical derivatization of the deposited nickel to the NiHCF film in 0.5 M K₃[Fe(CN)₆] solution, and electrochemical penetration of metallic platinum into the modified film are described. The modified zinc electrodes prepared under optimum conditions show a well-defined redox couple due to the [Ni^IIFe^III/II(CN)₆]^1–/2– system. The effects of pH, the alkali metal cation, and the anion of the supporting electrolyte on the electrochemical characteristics of the modified electrode were studied in detail. The diffusion coefficients of hydrated alkali metal cations in the film (D), the transfer coefficient (), and the transfer rate constant for the electron (k_s) were calculated in the presence of some alkali metal cations. The electrocatalytic activity of the modified electrode for methanol oxidation was demonstrated. The stability of the modified electrode under various experimental conditions was investigated.     

Synthetic diamond electrodes: Photoelectrochemical behavior of vacuum-annealed undoped polycrystalline diamond films

The photocurrent and photopotential for undoped polycrystalline diamond film electrodes prepared by chemical vapor deposition and annealed in vacuum at 1500–1640°C are measured. The metal-like samples (annealed at 1630°C) have a negligible photosensitivity. Judging from the positive sign of the photopotential and the cathodic direction of the photocurrent, the material under study formally behaves as a p-type semiconductor. The photoeffects are presumably caused by structure defects, in particular, the dislocations in diamond crystallites formed close to intercrystalline boundaries during the high-temperature annealing.Translated from Elektrokhimiya, Vol. 41, No. 3, 2005, pp. 343–349.Original Russian Text Copyright © 2005 by Pleskov, Krotova, Ralchenko, Khomich, Khmelnitskii.     

Preconcentration of gold on chelating polymer adsorbents and its determination in rocks and ores

A new class of chelating polymer adsorbents was synthesized on the basis of aminopolystyrene azo compounds and various para-substituted anilines. Physicochemical and analytical properties of adsorbents and their ionic associates with the [AuCl₄]^– anion were studied. Correlations between the ionization constants of amino group (pK _{NH 2}) and the Hammett electronic constant (_n) were found. A linear correlation between the charge on the amino group nitrogen atom and the (_n) value was revealed on the basis of the results of quantum-chemical calculations. A sorption-spectroscopic method was developed for determining gold in ores and rocks. The method was verified by analyzing certified reference samples of ores and rocks in the gold concentration range between n × 10^–3 and n × 10^–6% RSD = 5%.Translated from Zhurnal Analiticheskoi Khimii, Vol. 60, No. 3, 2005, pp. 264–270.Original Russian Text Copyright © 2005 by Basargin, Zueva, Rozovskii, Pashchenko.     

Hydrogen diffusion through a steel membrane in ethylene glycol solutions of hydrochloric acid containing sodium hydroarsenate: the effect of anodic polarization

The kinetics of the hydrogen evolution reaction on iron and the hydrogen diffusion rate (i _H) through a membrane of steel 3 are studied. The study is carried out in conditions of anodic polarization (E _a), in ethylene glycol and water–ethylene glycol solutions of HCl with a constant ionic strength, which contain As(V) predominantly in the form of H₃AsO₄. It is shown that the dependence of i _H on E _a passes through a maximum in media with different concentrations of water and HCl, different solvation form of the proton, and different nature of species that solvate the working surface of the membrane. The effect of E_a on i _H disappears in a certain range of anodic potentials. The presence of the maximum is shown to be due to the formation of two forms of adsorbed hydrogen (H^r,H^s). That i _H is independent of E _a is connected with chemical dissolution of the membranes working side.Translated from Elektrokhimiya, Vol. 41, No. 2, 2005, pp. 181–189.Original Russian Text Copyright © 2005 by Vigdorovich, Tsygankova, Kopylova.This revised version was published online in April 2005 with corrections to the article note and article title and cover date.     

Flow injection potentiometry for low level measurements in the presence of sensed ion in the carrier

Summary A theoretical treatment of the response of ion sensitive electrodes in flow-injection analysis is presented with emphasis on the influence of sample dispersion and the addition of sensed ion to the carrier solution. Guidelines are given for optimal conditions with respect to desired working range and sensitivity, i.e., the slope of the calibration plot. The comparison of predicted data and experimental results obtained with the fluoride and iodide sensitive electrodes showed significant deviations due to slow response. For low dispersion systems (D _max 1) a method for linearization of the calibration plot is proposed.

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Fließinjektions-Potentiometrie für Messungen niedriger Konzentrationen in Gegenwart des zu messenden Ions in der Trägerlösung

     

Synthesis and Crystal Structure of Rubidium Uranyltricarbonate

A procedure for the synthesis of uranyltricarbonatetetrarubidium Rb₄UO₂(CO₃)₃ was developed. Its crystal structure was determined by X-ray diffraction analysis: space group C2/c; a=10.778(5) , b=9.381(2) , c=12.509(3) . =94.42(3)°, Z=4; 1178 independent reflections, R=0.0662.__________Translated from Koordinatsionnaya Khimiya, Vol. 31, No. 5, 2005, pp. 387–390.Original Russian Text Copyright © 2005 by Chernorukov, Mikhailov, Knyazev, Kanishcheva, Zamkovaya.     

Studies of Nanocrystalline Phase and Residual Amorphous Phase of FeCuNbSib Alloy Using TG(M) Technique

The —T and d/dT—T curves of the FeCuNbSiB amorphous alloy, which are the relationship between the total saturated magnetic moment per unit mass and temperature, are investigated by magnetic thermogravimetry analysis (TG(M)) technique. It is found that the crystallization process of the samples can be divided into five stages. The studies of samples annealed in temperature range of 480–610°C for 1h show that when the annealing temperature (T_a) is less than 540°C, the quantity of nanocrystalline -Fe(Si) phase increases evidently with T_a, and the Curie temperature (T_C) of residual amorphous phase also increases linearly with T_a, i.e. T_C=0.52T_a+91.7°C, with correlation coefficient =0.98. The variation of volume fraction of -Fe(Si) nanocrystalline phase or residual amorphous phase with T_a is measured by TG(M) technique.This revised version was published online in November 2005 with corrections to the Cover Date.     

Phase equilibria in the Ag4SSe-SnTe system

The phase diagram of the system Ag₄SSe-SnTe is studied by means of X-ray diffraction, differential thermal and metallographic analyses and measurements of the microhardness and the density of the material. This diagram is divided into two eutectic-type subdiagrams by the composition Ag₄SSe·2SnTe. The unit-cell parameters of the intermediate phases 3Ag₄SSe·SnTe (phase A) and -Ag₄SSe·2SnTe (phase B) are determined as follows: for phase A: a=0.7851 nm, b=0.7196 nm, c=0.6296 nm, =101.32°, =85.90°, =111.36°; for phase B: a=0.3662 nm, b=0.3303 nm, c=0.3343 nm, =90.74°, =108.94°, =91.91°. The phase Ag4SSe·2SnTe melts congruently at 615°C and a polymorphic transition of the phase takes place at T _- =110°C.This revised version was published online in November 2005 with corrections to the Cover Date.     

Reaction between cis-diaquabisbiguanideruthenium(III) and hexathiocyanatochromium(III) ions in aqueous media. A mechanistic survey on the formation of a dinuclear bridged complex

The reaction between two complex species [Ru(BigH)₂(H₂O)₂]³⁺ and [Cr(SCN)₆]^3– has been investigated in aqueous medium in the pH range 4.00–6.10, and followed in the 21–40 °C range. Pseudo-first order rate constants were evaluated using the chromium complex in a ten-fold excess. The plot of k _obs versus pH has a bell shaped profile. From this and other evidence it was concluded that only the [Ru(BigH)₂(OH)(H₂O)]²⁺ form of the ruthenium complex is reactive under the experimental conditions, and forms the dinuclear complex [Ru(BigH)₂--(SCN)₂-Cr(NCS)₄]⁰. The rate constant for the dinuclear complex formation at 31 °C is (2.57 ± 0.05) × 10^–3 mol^–1 s^–1. H = 60 ± 2 kJ mol^–1 and S = 116 ± 10 J K^–1 mol^–1.     

Heat of Formation for LiMyMn2−yO4 (M=Co,Cr, Li,Mg, Ni) Spinel Solid Solution

The enthalpy of formation for LiM_yMn_2–yO₄ (M=Co, Cr, Li, Mg, Ni) was measured by a Tian-Calvet type high temperature isothermal microcalorimeter. The standard enthalpy of formation for LiMn₂O₄ at 876 K was evaluated to be H_f⁰=–1404.2±6.4 kJ mol^–1. The partial substitution of Co and Ni for Mn decreased the absolute H_f⁰ value, while that of Cr and Mg for Mn increased the absolute H_f⁰ value. In the case of the partial substitution of Li for Mn, no marked change in H_f⁰ could be observed.This revised version was published online in November 2005 with corrections to the Cover Date.     

Numerical simulation of a nonequilibrium plasma jet in an applied magnetic field using three-fluid model

A three fluid model is applied for the numerical simulation of the axisymmetric flow and temperature fields in a nonequilibrium argon plasma jet which can be controlled by applying art electromagnetic field. The effects of the magnetic field on the characteristics of each plasma species, i.e., electrons, positive ions, and neutral particles, should be accurately clamed. The three-fluid model applied here can clarify the behavior of each plasma species. Equations of conservation for each plasma species coupled witli the generalized Ohm's law, Maxwell's equations, and the equation of state are simultaneously solved taking variable transport properties into account. It is shown that the electron temperature is the highest and the electron velocity is strongly influenced by the magnetic field. Furthermore, the momentum and energy exchanges through electrons can be varied even by a small magnetic flux.Nomenclature B magnetic flux density (T) - c mathematical mean thermal velocity (m/s) - C _p specific heat at constant pressure (J/(kg · K)) d ₀ nozzle diameter (m) - e electron charge (C) - E electric field (V/m) - E effective electric field (V/m) - Ex ^* energy transfer by collision - g relative velocity (m/s) - G partition function - h enthalpy (J/kg) - h _Planck Planck's constant (J · s) - H diffusion enthalpy (J/kg) - j ^* current density (j/en ₀ u ₀ - k Boltzmann constant (J/K) - l mean free path length (m) - L ₀ length of calculation domain along stream (m) - m mass (kg) - M ^* momentum transfer by collision - n number density (m^–3) - production rate of species [/(m³ · 3)] - p pressure (Pa) - collision cross section (m²) - q heat flux (W/m²) - r radial coordinate (m) - r _in inner radius of round tube (m) - R gas constant (J/(kg · K)) - R _in magnetic Reynolds number (=u ₀ d ₀₀µ₀) - s ion slip coefficient [=( _n /gr ₂)² _{e i} ] - S ₁ cross section parameter (m²/J) - T temperature (K) - u axial component of velocity (m/s) - U axial component of diffusion velocity (m/s) - radial component of velocity (m/s) - V radial component of diffusion velocity (m/s) - w peripheral component of velocity (m/s) - W peripheral component of diffusion velocity (m/s) - z axial coordinate (m) - degree of ionization [=n _e /)n _e +n _i +n _n )] - Hall parameter (= ) - ₀ permittivity in vacuum (F/m) - ge ₁ first excitation energy (J) - _ion ionization energy (J) - viscosity (Pa · s) - peripheral coordinate - thermal conductivity [W/(m · K)] - µ₀ permeability in vacuum (H/m) - density (kg/m³) - electrical conductivity (S/m) - mean collision time (s) - cyclotron frequency (Hz) Suffix 0 nozzle exit - e electron - i ion - n neutral particle - r radial component - s plasma species ofs kinds - z axial component - gq peripheral component Originally published inTrans. of the Japan Society of Mechanical Engineers, Ser.B,60, No. 577, 3072–3079 (1994) (in Japanese).     

On-line glucose monitoring by using microdialysis sampling and amperometric detection based on ‘wired’ glucose oxidase in carbon paste

In-vitro on-line glucose monitoring is described, based on microdialysis sampling and amperometric detection operated in a flow-injection system. Samples were injected into a two-electrode microcell containing an Ag/AgCl quasi-reference electrode and a glucose enzyme electrode as the working electrode, operated at + 0.15 Vvs. Ag/AgCl. The enzyme electrode is constructed by mixing the wired glucose oxidase into carbon paste. {Poly[1-vinylimidazole osmium(4,4-dimethylbipyridine)₂Cl)]}^+/2+ was used to wire the enzyme. The non-coated electrodes, cross-linked with poly(ethylene glycol) diglycidyl ether, responded linearly to glucose concentrations up to 60 mM, and were characterized by a sensitivity of 0.23 A mM^–1 cm^–2, when operated in flow injection mode and of 5.4 AmM ^–1 cm^–2 in steady-state conditions. This sensitivity of the resulting enzyme electrode was 50% lower than that of similarly prepared but non-cross-linked electrodes. However, the cross-linked electrodes showed superior operational and storage stabilities, which were further improved by coating the electrodes with a negatively charged Eastman AQ film. An in-house designed microdialysis probe, equipped with a polysulphone cylindrical dialysis membrane, yielded a relative recovery of 50–60% at a perfusion rate of 2.5 l/min^–1 in a well stirred glucose solution. The on-line set up effectively rejected common interferences such as ascorbic acid and 4-acetaminophen when present at their physiological concentrations.     

Kinetics and mechanism of electroreduction of ethylenediamine and hydroxyethylenediamine complexes of zinc(II) on a dropping-mercury electrode

The kinetics of electroreduction of ethylenediamine and hydroxyethylenediamine complexes of zinc(II) on a dropping-mercury electrode (DME) in 1 M NaClO₄ solutions of pH 9–11.5 is studied at different ethylenediamine concentrations at 25, 35, and 50°C. One wave with a diffusion limiting current is observed at an overall concentration of zinc(II) complexes of 2 × 10^–5 M and current recording times t ₁ = 0.3–4 s. The polarographic peak that distorts the wave at t ₁ 0.5 s, pH 11.5, and 25°C is due to the accumulation of insoluble reduction products on the electrode surface. The slow electrochemical step on DME involves complexes Znen²⁺, which form in preceding reversible chemical steps from complexes present in solution.__________Translated from Elektrokhimiya, Vol. 41, No. 4, 2005, pp. 397–405.Original Russian Text Copyright © 2005 by Kurtova, Kravtsov, Tsventarnyi.     

Conductance and transport numbers of acidified sodium aluminate solutions and the zero point of charge of aluminium hydroxide

Summary Conductance measurements of acidified sodium aluminate solutions showed a gradual drop as the alumina content of the solution increases. This behaviour was explained by adsorption of H⁺ ions, as visualised from linear plots of ( ₀–) per mole of alumina against (where ₀ is the specific conductance of the corresponding (NaOH + HCl), is the specific conductance of (sodium aluminate + HCl) and is the amount of H⁺ ions adsorbed per mole of alumina). Transport number experiments showed that alumina behaves as a non-electrolyte and that the transport number of the Cl– ion increases with increase in alumina content. This behaviour was explained on the basis of aggregation of water molecules around alumina.The zero point of charge of colloidally dispersed aluminium hydroxide was determined from potentiometric and conductance measurements.

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Zusammenfassung Leitfähigkeitsmessung von angesäuerten Natrium-Aluminat-Lösungen zeigen einen Abfall, wenn der Aluminat-Gehalt der Lösungen wächst. Dieses Verhalten wird durch Adsorption von Wasserstoff-Ionen erklärt, erkennbar aus der linearen Auftragung von ( ₀–) pro Mol/Aluminat gegen Dabei ist ₀ die spezifische Leitfähigkeit der entsprechenden (NaOH + HCl)-Lösung, die spezifische Leitfähigkeit vom Gemisch Natriumaluminat + HCl und der Betrag an Wasserstoffionen, adsorbiert pro Mol/Aluminat. überführungszahl-Experimente zeigen, daß Alumina sich nicht als Elektrolyt verhält und daß die überführungszahl für Cl^–-Ionen mit dem Alumina-Anteil wächst. Dieses Verhalten wird erklärt auf Grund einer Aggregation von Wassermolekülen um das Alumina.Der Neutralpunkt für Ladung von kolloidal dispergiertem Alumiumhydroxid wurde aus potentiometrischen und Leitfähigkeitsmessungen bestimmt.

     

The crystal structure of the syn-proximal-5,11,17,23-tetra-tert-butyl-25,26-bis[(2-pyridylmethyl)oxy]-27,28-dihydroxy-calix[4]arene ethanol 1 : 1 Inclusion Complex

The crystal structure of the title compound (1 · C₂H₅OH) has been determined by single-crystal X-ray analysis and refined to anR-value of 0.074 for 2732 observed reflections [I > 2.0(I)]. Crystals are triclinic, space group P , witha = 13.6150(18),b = 13.7195(11),c = 16.5497(16) Å, = 73.132(7), = 66.165(9), = 65.580(8)° andZ = 2. Calix[4]arene (1) adopts a relatively open distorted cone conformation in the solid state, with two pendantsyn-proximal O-CH₂-Py groups. The major conformation determining features in (1 · C₂H₅OH) are the presence of (a) an intramolecular O-H...O hydrogen bond between adjacent proximal phenolic oxygens, O...O 2.719(7) Å and (b) an intramolecular O-H...N hydrogen bond between a phenolic oxygen and a proximal pyridinyl nitrogen, O...N 2.810(8) Å. The intramolecular hydrogen bonding and the interplanar angles of 65.1(3) and 50.7(3)° between opposite aromatic rings facilitate the inclusion of an ethanol molecule within the calixarene cup.Supplementary Data relating to this article are deposited with the British Library as Supplementary Publication No. SUP 82141 (26 pages).     

Principal vectors of crystallographic groups and applications

For a crystallographic group acting on ann-dimensional Euclidean space we consider the -invariant linear elliptic differential operatorP with constant coefficients and to it the -automorphic eigenvalue problemP [] + = 0. N() is the number of all eigenvalues smaller than or equal to the frequency bound ^q (q: order ofP). Earlier we found the asymptotic estimationN() c₀ · ⁿ + c₁ · ^n–1 (c ₀,c ₁: certain volumina). Furthermore,N() was interpreted as the number of so-called principal classes of principal lattice vectors within a convex domain. In this paper we demonstrate these results for the casen = 2 for two representative crystallographic groups and the assigned lattices. Above all we demonstrate a counting method for an exact estimation ofN() if a is not too big. In an analogous way we can treat all the 230 space groups of crystallography. It will be seen that these applications are brought about by the so-called principal vectors of these lattices.     

Pressure and temperature effects on the excess deuteron and proton conductance

The limiting molar conductances ° of deuterium chloride DCl in D₂O were determined as a function of pressure and temperature in order to examine the proton-jump mechanism in detail. The excess deuteron conductances °_E(D ⁺), as estimated by the equation [°_E(D ⁺) = °(DCl/D ₂ O) – °(KCl/D ₂ O)], increases with an increase in the pressure and temperature as well as the excess proton conductance [°_E(H ⁺) = °(HCl/H ₂ O) – °(KCl/H ₂ O)]. The isotope effect on the excess conductances, however, depends on the pressure and temperature contrary to the model proposed by Conway et al.: °_E(H ⁺)/°_E(D ⁺) decreases with increasing pressure and temperature. The magnitude of the decrease with pressure becomes more prominent at lower temperature. These results are discussed in terms of the pre-rotation of adjacent water molecules, the bending of hydrogen bonds with pressure, and the difference in strength of hydrogen bonds between D₂O and H₂O.     

Inclusion of water by a crown amide. First crystal structure of a respective host-guest combination

Crown amide (1) forms a stoicheiometric 1:1 inclusion complex with water, the X-ray crystal structure of which is reported. Crystals of1 · H₂O are triclinic, space groupP1, witha=7.503(1),b=11.394(3),c=13.443(2) Å, =107.066(18), =96.627(10), =106.377(14)°, andZ=2.R _F =0.039 for 1697 MoK reflections [I>3(I)] measured at 24°C. The structure features a hydrogen bonded hostguest relationship with concrete1 · H₂O units. Hydrogen bonds are between the water oxygen and O(4), N(4), respectively. The crystal packing shows a cavity arrangement of four ligands around each water molecule. Supplementary Data relating to this article are deposited with the British Library as Supplementary Publication No. SUP 82055 (16 pages).     

Electrodeposition of lead on to a graphite probe for electrothermal atomic absorption spectrometry

A simple system for controlled potential electrodeposition on to a graphite probe electrode is described. Totally pyrolytic graphite was found to be better for electrodeposition than microporous glassy carbon or electrographite coated with pyrolytic graphite. Lead can be deposited by anodic and cathodic processes as PbO₂ and Pb, respectively. Potentials of + 1.2 to + 2.0 V were best for anodic deposition and – 0.8 to– 2.0 V were best for cathodic deposition. With an electrodeposition time of 120 s, AAS sensitivity gains of × 9 and × 3.5 were achieved for anodic and cathodic deposition, respectively, in comparison with the results obtained by direct injection of 20 1 sample volumes on to the probe. The lead cathodic process was unaffected by NaCl concentrations up to 10^–2 M, but only 10^–3 M NaCl could be tolerated by anodic deposition.     

Analysis of the Impedance Frequency Spectrum of a Passive Iron Electrode by Combined Impedance and Photoadmittance Measurements

The frequency spectra of electrochemical impedance Z, photocurrent i, and photopotential E are obtained for a passive Fe electrode in 0.2 M KOH in a frequency range 1.3 to 8300 Hz. The validity of relationship E/i = –Z is proved experimentally. The oxide film impedance Z _F is calculated from the frequency spectrum of E with expression Z _F = –E/g. The generation current g is found from the photocurrent frequency spectrum. The frequency impedance spectrum Z _F/S of the oxide/solution interface is determined with equation Z _F/S = Z – Z _F – R _el, where R _el is the solution resistance.