Analysis of the kinetics for the H2 + - \frac{1}{2}O2 ⇌ H2O reaction on a hot Pt surface in the pressure range 0.10–10 Torr

The H₂ + O₂ ⇌ H₂O reaction on platinum at 700 and 1300 K has been studied. A stagnation flow geometry was used with a gas mixture of H₂ and O₂ at pressures between 0.10 and 10 Torr. Comparing SHG results with simulations using different reaction parameters, it was concluded that , and . LIF measurements showed an ambiguity in the choice of main water-producing channel. Both hydrogen addition with low sticking coefficients and hydroxyl disproportionation with high sticking coefficients are plausible. This revised version was published online in July 2006 with corrections to the Cover Date.     

Mass transfer at the electrodes of the ‘falling-film cell’

In the falling-film cell the electrolyte flows as a thin film in the channel between an inclined plane plate and a sheet of expanded metal which work as electrodes. The present work gives the mass transfer coefficients at both electrodes; the experimental variables are the electrolyte flow-rate, the angle of inclination of the channel and the interelectrode distance. The results allow three different flow regimes to be characterized. At low flow rates, there exists a particular regime where capillary effects are present; in this regime the mass transfer coefficient decreases with increasing flow rate, which is interesting from the point of view of possible industrial electrolytic applications.Nomenclature b width of the inclined channel - D diffusion coefficient - d interelectrode distance - e _m mean film thickness - Grashof number, based ond - Grashof number, based onL - ¯k overall mass transfer coefficient, defined by Equation 9 - L electrode length - Q _v volumetric flow rate - volumetric flow rate per unitQ _vl width of channel - Reynolds number - Schmidt number - Sherwood number, based ond - Sherwood number, based onL - mean velocity of the liquid film - inclination angle of the channel with respect to the horizontal - kinematic viscosity of them electrolyte     

Hydrogen half-cells in molten salts. A potentiometric investigation of the systems (Pt or Au) H2O/H2, OH− in fused alkali nitrates

The potentiometric behaviour of the hydrogen electrodes (Pt or Au) H₂O-H₂, OH_–has been investigated in molten (Na_0·5, K_0·5)NO₃ at 503 K. In both cases the potential of the indifferent electrode could be expressed by the general equation [H₂O]/[H₂] [OH^–] which is different from the one expected on the basis of a Nernstian behaviour of the theoretical overall system 2H₂O+2e=H₂+2OH^–.The experimental findings are discussed in terms of mechanistic models involving the actual electrode surface and the standard potential for the theoretical (reversible) hydrogen electrode is calculated: =–·0V(versus Ag/Ag⁺ 0·07 M).     

Effect of PVC on low-polar isobutylene polymerization in the presence of BCl3

Summary The isobutylene polymerizations in the presence of BCl₃ were carried out in dichloromethane ([M]=7 mol/l) at-20°C in the presence and absence of PVC. The products of polymerizations in the absence of PVC are oligoisobutylenes with a narrow molecular weight distribution ; their structure was analyzed by ¹H-NMR spectroscopy. In addition to the signals assigned to known unsaturated terminal structures [ 4.62 and 4.82-CH₂C(CH₃)=CH₂, 5.12-CH=C(CH₃)₂], a new intense signal was found at 5.09 ppm and assigned to the structure-CH=C(CH₃)CH₂CH₃. A mixture of isobutylene homopolymers and PVC grafted with isobutylene (approx. 9.5% wt. isobutylene grafted) is formed in the presence of PVC.     

Electrochemical redox reactions of chromium and iron ions in molten NaCl–2CsCl eutectic for pyro-reprocessing of nuclear fuels

Basic electrochemical and spectroscopic properties of Cr³⁺, Cr²⁺, Fe³⁺, and Fe²⁺ were studied to analyze the cyclic redox reactions of Cr and Fe, which may decrease the current efficiency of the electro-winning method using NaCl–2CsCl melts. The formal redox potentials of the and couples, and , in NaCl–2CsCl melts at 923 K were spectroelectrochemically determined to be −0.648 ± 0.005 V and , respectively. These values were determined by measuring electromotive force and UV–VIS absorption spectra at varying concentration ratios of trivalent and divalent ions. Cyclic voltammetry was also carried out to examine the characteristics of the voltammograms for the and couples in NaCl–2CsCl melts. The determined by the spectroelectrochemical method was close to that determined by cyclic voltammetry . The effect of temperature on the in NaCl–2CsCl melts was studied by cyclic voltammetry in the range from 823 to 1,023 K . Diffusion coefficients of Cr³⁺ and Cr²⁺, and , were determined between 823 and 1,023 K to be and , respectively. Molar absorptivities of Cr³⁺ and Cr²⁺ in NaCl–2CsCl melts at 923 K were determined to be 77.8 ± 2.4 M⁻¹ cm⁻¹ at 17,670 cm⁻¹ and 48.0 ± 1.4 M⁻¹ cm⁻¹ at 9,170 cm⁻¹, respectively. In addition, the effects of these ions on the cyclic redox reaction of the pyro-reprocessing process were discussed.     

Differentiation of Competitive vs. Non-competitive Mechanisms Mediating Disruption of Moth Sexual Communication by Point Sources of Sex Pheromone (Part 2): Case Studies

Eleven out of 13 disruption profiles (plots of dispenser density vs. male catch) from moth sex pheromone literature were consistent with a competitive-attraction mechanism, in which dispensers attract males and thereby divert them from females. Mean dispenser activity (D _a) across all competitive-attraction cases was 0.04 ± 0.06 (SD); values ranged from 0.0005 for a tiny laminated flake dispenser of racemic disparlure targeting gypsy moth to 0.2 for polyethylene tube dispensers used against lightbrown apple moth. A dispenser application activity () can be calculated by multiplying D _a by the number of such dispensers applied per hectare of crop. The highest dispenser application activity () values approached 200 and corresponded to >99% inhibition of catches of male moths in monitoring traps. Relative to the scale, % inhibition of catches of male moths compressed and obscured large differences in when % disruption exceeded 90%. For cases of competitive attraction, these two efficacy scales can be interconverted by using the formula: . When disruptive point sources of pheromone were directly observed, male moths were seen approaching pheromone dispensers whose disruption profiles matched competitive attraction. Two cases fit non-competitive disruption mechanisms, which include camouflage, desensitization (adaptation and/or habituation), and sensory imbalance. In these cases, pheromone was released at rates higher than for cases of disruption by competitive attraction. Practical ramifications of the finding that competitive attraction appears to be the prevalent mechanism for moth mating disruption by pheromone point sources are listed. We believe that the congruence of diverse sets of mating disruption field data with explicit a priori predictions validates competitive-attraction theory. The analytical tools and principles governing competitive attraction that were uncovered during this study of mating disruption of moths should be generally applicable to competitive-attraction phenomena.     

Enhanced mass transfer in electrochemical cells using turbulence promoters

Many electrochemical processes suffer in varying degrees from mass transfer limitations. These limitations may require operation at considerably less than economic optimum current densities. Mass transfer to a surface may be considerably enhanced by insertion of turbulence promoters in the fluid flow path near the affected surface.An instrument was developed to measure local current densities in the hydrodynamically very difficult region near the turbulence promoter. A general method for the relative evaluation of hydrodynamic conditions has been developed. Generalization of the data permits optimization of hydrodynamic cell design using the promoter shapes investigated.

Notation

Symbols A Coefficient for cell power costs, $ m² (As)^–1 - A _c Cell area, m² - a Constant in Equation 4 - B Coefficient for area-proportional costs, $ A (m² s)^–1 - C Coefficient for pumping power costs, $ A (m² s)^–1 - C _b Bulk concentration, kg mol m^–3 - C _bi Inlet bulk concentration, kg mol m^–3 - C _e Energy cost, $ (Ws)^–1 - C _i Interfacial concentration, kg mol m^–3 - ¯C _s Amortized area cost, $ (m² s)^–1 - D Current—density-insensitive costs, $ s^–1 - D _e Equivalent diameter, m - D Diffusion constant, m² s^–1 - e Current efficiency - F _d Cell feed rate, m³ s^–1 - F 96.5×10⁶ A s kg eq^–1 - g Channel width, m - h Channel height, m - i Current density, A m^–2 - i _opt Economic optimum current density, A m^–2 - K Total costs of running cell, $ s^–1 - (K–D)_ideal Total sensitive costs under hydrodynamically ideal conditions, $ s^–1 - k _c Convective mass transfer coefficient, m s^–1 - L Total length of flow path, m - l Promoter spacing, m - N Mass flow rate to surface due to convection, kg mol m² s^–1 - n _e Number of electrons transferred in electrode reaction - P _c Power required by cell, W - P/L Average pressure gradient in channel, N m^–3 - R _av Effective cell resistance, m² - S Open channel cross-section, m² - S ₀ Minimum channel cross-section at promoter, m² - s _i Stoichiometric coefficient of species i - t _i Transport number of species i in solution - ¯t _i Effective tranport number of species at polarized surface - V Average fluid velocity, m s^–1 - x Distance from inception of concentration disturbance, m - ₁ Electrical power conversion efficiency - ₂ Pumping power conversion efficiency - Solution viscosity, kg (m s)^–1 - Solution density, kg m^–3 Dimemionless groups Fanning friction factor - Reynolds number - R h/g Channel aspect ratio - D _e/l Promoter frequency - S/S ₀ Contraction coefficient - Sherwood number - Degree of reaction - Dimensionless total sensitive - Dimensionless current density - Energy cost ratio     

Thermodynamic and kinetic aspects of the electron transfer reaction of bovine cytochrome c immobilized on 4-mercaptopyridine and 11-mercapto-1-undecanoic acid films

Bovine cytochrome c (cyt c) was adsorbed on a polycrystalline gold electrode coated with 4-mercaptopyridine and 11-mercapto-1-undecanoic acid self-assembled monolayers (SAMs) and the thermodynamics and kinetics of the heterogeneous protein-electrode electron transfer (ET) reaction were determined by cyclic voltammetry. The E°′ values for the immobilized protein were found to be lower than those for the corresponding diffusing species. The thermodynamic parameters for protein reduction ( and ) indicate that the stabilization of the ferric state due to protein–SAM interaction is enthalpic in origin. The kinetic data suggest that a tunneling mechanism is involved in the ET reaction: the distance between the redox center of the protein and the electrode surface can be efficiently evaluated using the Marcus equation.     

Influence of temperature on the electro-dissolution of tin in NaCl aqueous solution at pH4

The influence of temperature in the range 25 to 80°C on the dissolution of tin was investigated in an acidic solution at pH4 containing 0.1 to 1m NaCl. The corrosion current is slightly dependent on both the temperature and the Cl^– ion concentration. The main dissolution characteristics of tin are

Electrical conductivity of low melting baths for aluminium electrolysis: the system Na3AlF6-Li3AlF6- AlF3 and the influence of additions of Al2O3, CaF2, and MgF2

The electrical conductivity was investigated for a section of the molten ternary mixture Na₃AlF₆-Li₃AlF₆-AlF₃ with molar ratio n(Li₃AlF₆):n(AlF₃) = 1 : 2. The conductivity of this system can be described by the following equation: where (i) represent the mole fractions of the additions. The influence of additions of CaF₂, MgF₂ and/or Al₂O₃ on the electrical conductivity of the binary system Na₃AlF₆-Li₃AlF₆ and the ternary system Na₃AlF₆-Li₃AlF₆-AlF₃ was also studied.     

Study of mass transfer in a vertically moving particle bed electrode

A study was made of the influence of process parameters on the mass-transfer coefficient in a flow-through cell with a cascade of rotating drums partially filled with conductive particles (called the vertically moving particle bed). Copper deposition from an acidic sodium sulphate solution was used as the model reaction. To evaluate the experimental data a macrohomogeneous mathematical model of potential and current density distribution inside the cell was developed. The electrolyte flow distribution between the empty space above the particle bed and through the bed was evaluated. On the basis of these results the following correlation is proposed:

Electrochemical behaviour of a new triiron-substituted polyoxomolybdate

A new complex of the Keggin trilacunary polyoxomolybdate (PMo₉) with Fe³⁺ ions, having the formula (PFe₃Mo₉), has been synthesized and characterized by chemical analysis, FT-IR, Raman, UV-VIS-NIR and EPR spectroscopy, as well as by magnetic susceptibility measurements. Cyclic voltammetry performed at different scan rates, pH and supporting electrolyte composition, was used to investigate the electrochemical behaviour of the PFe₃Mo₉ complex in acidic medium and its electrocatalytic effect on H₂O₂ reduction. The voltammetric waves were assigned, and the enhanced electrocatalytic efficiency of PFe₃Mo₉ relative to PMo₉ was attributed to the presence of Fe atoms.     

Fundamental studies on a new concept of flue gas desulphurization

A new process for removal of sulphur dioxide from waste gases is proposed consisting of both electrochemical and catalytic sulphur dioxide oxidation. In the catalytic step a part of the sulphur dioxide is oxidized by oxygen on copper producing sulphuric acid and copper sulphate. The other part is oxidized electrochemically on graphite. The cathodic reaction of this electrolysis is used for recovering the copper dissolved in the catalytic step. The basic reactions of this process have been studied experimentally in detail. It has been shown that sulphur dioxide can be electrochemically oxidized on carbon electrodes to sulphuric acid with high current efficiency. The reaction rate of the electrochemical copper deposition is increased by dissolved sulphur dioxide in the electrolyte. The catalytic oxidation of sulphur dioxide on copper has been investigated for different sulphur dioxide concentrations and temperatures. The ratio of the reaction products, sulphuric acid and copper sulphate, varies over a wide range depending on the experimental conditions.Nomenclature SO₂ concentration (gas phase) (vol % SO₂) - SO₂ concentration (electrolyte) (g l^–1) - E potential vs saturated calomel electrode (V) - E _s specific energy consumption (W g^–1 SO₂) - F Faraday constant (A s^–1 mol^–1) - i current density (mA cm^–2) - molecular weight (g mol^–1) - T temperature (° C) - U _c cell voltage (V) - v _e number of electrons being transferred - space-time yield of SO₂-oxidation (g SO₂ h^–1 dm^–3) - _cu space-time yield of Cu-corrosion (g Cu h^–1 dm^–3) - ratio - fractional conversion of SO₂ - current efficiency for SO₂ oxidation     

[CuL(H2O)2]{[CuL][Fe(CN)6]}2·2H2O (L=3,10-Bis(2-hydroxyethyl)-1,3,5,8,10,12-hexaazacyclotetradecane): A Novel Three-Dimensional Coordination Polymer via H-Bonded Linkages of One-Dimensional Zigzag Chain

A complex with the formula [CuL(H₂O)₂]{[CuL][Fe(CN)₆]}₂·2H₂O, where L=3,10-bis(2-hydroxyethyl)-1,3,5,8,10,12-hexaazacyclotetradecane, has been synthesized and crystallographically characterized. The structure is composed of a one-dimensional zigzag chain of units, and [CuL(H₂O)₂]²⁺ units. The one-dimensional zigzag chain extents through linkages. The adjacent two polymer chains are linked by the hydrogen bonding between [CuL(H₂O)₂]²⁺ and [Fe(CN)₆]^3–, forming a 3D supramolecular structure with inner hydrophilic channels. Magnetic susceptibility measurements show no exchange interaction between the Cu(II) and Fe(III) ions due to the longer (axial) bond length.     

Electrical Properties and the Structure of Halogen-Containing Lead Borate Glasses: I. The PbF2–2PbO · B2O3 System

The concentration and temperature dependences of the dc electrical conductivity of glasses in the PbF₂–2PbO · B₂O₃ system is investigated. It is found that, at 20–25 mol % PbF₂, the dependences log = f([F]) and E = f([F]) exhibit kinks. The concentration dependence of the true transport number of fluorine ions _F – is studied using the Tubandt method. It is shown that the introduction of 20–25 mol % PbF₂ leads to a crossover from the protonic conductivity to the unipolar fluorine ionic conductivity ( ). The results obtained are discussed in terms of the Myuller theory of the microinhomogeneous glass structure associated with the selective interaction of the components during the synthesis.     

Tailoring the Degree of Polymerization of Low Molecular Weight Cellulose

The degradation of cellulose to lmw samples with $\overline {DP} _{{\rm w}} $ varying from 15 to 130 is investigated. Cellulose samples prepared from the hydrolysis of regenerated cellulose fibers in dilute HCl possess $\overline {DP} _{{\rm w}} $ = 50. Applying homogenous degradation of microcrystalline cellulose in H₃PO₄ at RT for 3 weeks, samples with $\overline {DP} _{{\rm w}} $ = 35 and a PDI of 1.58 are obtained. Decreasing the hydrolysis temperature to 8 °C results in lmw cellulose with $\overline {DP} _{{\rm w}} $ > 70. Fractionation in DMA/LiCl provides samples with $\overline {DP} _{{\rm w}} $ = 12 to 130, together with a narrow molecular weight distribution. Detailed structural analysis by 2D NMR spectroscopy reveals that the prepared lmw celluloses are suitable as mimics for cellulose.

     

Determination of electrode kinetics by corrosion potential measurements: Zinc corrosion by bromine

An attractive way of determining the electrode kinetics of very fast dissolution reactions is that of measuring the corrosion potential in flowing solutions. This study analyses a critical aspect of the corrosion potential method, i.e., the effect of nonuniform corrosion distribution, which is very common in flow systems. The analysis is then applied to experimental data for zinc dissolution by dissolved bromine, obtained at a rotating hemispherical electrode (RHE). It is shown that in this case the current distribution effect is minor. However, the results also indicate that the kinetics of this corrosion system are not of the classical Butler-Volmer type. This is explained by the presence of a chemical reaction path in parallel with the electrochemical path. This unconventional corrosion mechanism is verified by a set of experiments in which zones of zinc deposition and dissolution at a RHE are identified in quantitative agreement with model predictions. The practical implications for the design of zinc/bromine batteries are discussed.Notation C _i concentration of species i (mol cm^–3) - D _` diffusivity of species i (cm² s^–1) - F Faraday constant - i _j current density of species j (A cm^–2) - i ₀ ^b exchange current density referenced at bulk concentration (A cm^–2) - J , inverseWa number - N - n number of electrons transferred for every dissolved metal atom - P _m Legendre polynomial of orderm - r ₀ radius of dise, sphere, or hemisphere - s stoichiometric constant - t ₊ transference number of metal ion - V _corr corrosion overpotential (V) Greek letters anodic transfer coefficient of Reaction 21b - _a anodic transfer coefficient of metal dissolution - _c cathodic transfer coefficient of metal dissolution - anodic transfer coefficient of zinc dissolution - velocity derivative at the electrode surface - (x) incomplete Gamma function - , exchange reaction order ofM ⁺ⁿ - , inverseWa number - _a activation overpotential (V) - _c concentration overpotential (V) - polar angle (measured from the pole) (rad) - k solution conductivity (^–1 cm^–1) - kinematic viscosity (cm² s^–1) - ₀ solution potential at the electrode surface (V) - rotation rate (s^–1) - * indicates dimensionless quantities     

A simplified theory for generalizing results from a radiant panel rate of flame spread apparatus

Experimental results on the rate of lateral flame spread and time for piloted ignition under an externally imposed radiant flux were analyzed with a simple theroretical model. The data were developed from a radiant panel apparatus that considers a wall mounted sample with a flux distribution \documentclass{article}\pagestyle{empty}\begin{document}$ (\dot q_{\rm e} ^{\prime \prime } ) $\end{document} of 5 W cm^?2 at the ignited end to 0.2 W cm^?2 at the other end. It is shown that after an appropriate preheating time (flux exposure time before sample is ignited) the rate of flame spread (V_f) results can be correlated by \documentclass{article}\pagestyle{empty}\begin{document}$ V_{\rm f} - {\textstyle{1 \over 2}} = C\left( {\dot q''_{{\rm o,ig}} - \dot q_{\rm e} ^{\prime \prime } } \right) $\end{document} where C is a material ‘constant’ and \documentclass{article}\pagestyle{empty}\begin{document}$ \dot q''{\rm }_{{\rm o,ig}} $\end{document} is minimum flux for piloted ignition—also a material (and configuration) constant. An extension of this model demonstrates that V_f can also be expressed in terms of an ‘ignition temperature’ and the surface temperature of the material. Both correlations are derivable from a single flame spread experiment. Results are presented for a number of typical wood and plastic materials.     

Bifunctional N-Oxides of Alkyldiamidoamines

A homologous series of new surface-active 1,1-bis{[3-(N,N-dimethylamino)ethyl]-amido}alkane-di-N-oxides were synthesized in the reaction of an appropriate diethyl 2-alkylmalonate with N,N-dimethylethylenediamine followed by oxidation with an aqueous solution of hydrogen peroxide. The adsorption isotherms of their aqueous solutions were measured and evaluated to obtain adsorption parameters: critical micelle concentration (CMC), surface excess concentration (Γ_CMC), equilibrium surface tension at the CMC (γ _CMC), cross-sectional area of the adsorbed surfactant molecule (A _CMC), standard free energies of adsorption and micellization

Measurement and regulation of oxygen content in selected gases using solid electrolyte cells. IV. Accurate preparation of CO2-CO and H2O-H2 mixtures

Mixtures of CO₂-CO, H₂O-H₂ and Ar-H₂O-H₂ of precise composition were prepared using a zirconia pump and analysed with a zirconia gauge. The ratio was varied from 5×10^–2 to 10⁴ and the ratio from 3×10^–4 to 10^–2. A Faraday's Law test proved to be a simple and reliable procedure for checking the conditions of utilization of these gaseous mixtures and for verifying that no significant disproportionation of CO or leakage along the gas circuit altered the prepared composition. From a practical point of view the best methods of preparing mixtures with low oxygen activity are reduction of carbon dioxide in the range 5×10^–11 to 10^–17 atm and oxidation of inert gas-H₂ in the range 10^–19 to 10^–27 atm at 800°C.