Application of the accelerated Tafel plot technique to corrosion kinetics: Role of double layer through simulation

Results on the simulated -t transient response of an actively corroding system under accelerated Tafel plot (ATP) conditions have revealed the influence of input parameters (i, ) and system parameters (C _dl,i _corr andb) and explained the observed dependence of kinetic parameters (arrived at on the basis of the intercept-slope method) on in certain time domains. New improved methods, which eliminate such dependence and give uniform corrosion rate data over all time domains, are described in the paper.Nomenclature ATP accelerated Tafel plot - transfer coefficient - b Tafel slope (V) - C _d double layer capacitance (F cm^–2) - i initial value of the exponentially decaying current (A) - E _c corrosion potential (V) - overpotential (V) - n overpotential corresponding to maximum in -t transient (V) - F Faraday constant (C mol^–1) - i _corr corrosion current density (A cm^–2) - n number of electrons involved in charge transfer step - p intercept of ATP (V) - R gas constant (JK^–1 mol^–1) - R _p polarization resistance ( cm²) - S slope of ATP, i.e. d/dt (V) - S _av average of theS values at > _el (V) - S _meas slope of the linear -t region, i.e. d/dt (Vs^–1) - T temperature (K) - t time (s) - t _m time corresponding ton _m in the -t transient (s) - time constant of the exponentially decaying current pulse (s) - _el electrode time constant given byR _p C _d (s)     

Effect of drag-reducing polymer on the rate of mass transfer in fixed-bed reactors

Rates of mass transfer were measured for the cementation of copper from dilute copper sulphate solutions containing polyethylene oxide drag-reducing polymer on a fixed bed of zinc pellets. Starting from a Reynolds number (Re) of 550, the rate of mass transfer was found to decrease by an amount ranging from 7.5 to 51% depending onRe and polymer concentration. The percentage decrease in the rate of mass transfer increased with increasingRe, passed through a maximum atRe=1400 and then decreased rapidly with further increase inRe. The possibility of using drag-reducing polymers to reduce power consumption in fixed-bed operation was discussed in the light of the present and previous results.Nomenclature A cross-section of reactor (m²) - a specific area of bed (m²) - C copper sulphate concentration at timet (moll^–1) - C ₀ initial copper sulphate concentration (moll^–1) - D diffusivity of copper sulphate (m₂s^–1) - d _p particle diameter (m) - J _d mass transfer J-factor (StSc ^2/3) - K mass transfer coefficient (m s^–1) - L bed height (m) - Q volumetric flow rate (m³s^–1) - Re Reynolds number (V _i d _p/) - Sc Schmidt number (/_D) - St Stanton number (K/V _i) - V volume of copper sulphate solution (m³) - V _i interstitial velocity (V _s/), (ms^–1) - V _s superficial velocity (ms^–1) - bed porosity - solution viscosity (kg m s^–1) - solution density (kg m^–3) - storage tank residence time (s)     

Characterization of phosphorus availability in selected New Zealand grassland soils

Appropriate evaluation of phosphorus (P) availability in soil is aprerequisite for ensuring the productivity and long-term sustainable managementof agroecosystems. Fifteen soils presently under grassland were collected fromdifferent areas of New Zealand and soil P availability was assessed by isotopicexchange kinetics (IEK) and related to P forms obtained by chemicalfractionation (sequential extraction). Concentrations of total P determined inthe 15 soils ranged from 375 to 2607 mg kg^–1(mean1104 mg kg^–1). Mean concentrations of inorganic P(Pi) extracted by sequential extraction with ammonium chloride, sodiumbicarbonate, sodium hydroxide (first), hydrochloric acid and sodium hydroxide(second) were 1.2, 41, 205, 113 and 23 mg kg^–1,respectively. Mean concentrations of organic P (Po) extracted by sodiumbicarbonate, sodium hydroxide (first) and sodium hydroxide (second) were 133,417 and 105 mg kg^–1, respectively. Similarly,results from IEK analysis showed that the intensity (water soluble Pi (Cp)),capacity (R/r₁ and n), and quantity (E value,isotopically exchangeable P pools (E_{1 min},E_{1 min–24 h},E_{24 h–3 m},E_{>3 m})) factors varied markedlyamongst soils. Thus Cp concentrations ranged from 0.02–1.90 mgL^–1, while concentrations of Pi determined in theE_{1 min}, E_{1 min–24},E_{24 h–3 m},E_{>3 m} pools were 2–29 (mean 10), 10–321(76), 11–745 (152), and 8–498 (177) mgkg^–1, respectively. The corresponding values forR/r₁ and n were 1.0–17.7 (mean 4.5) and0.10–0.50 (mean 0.37), respectively. Regression analysis revealed that Cpconcentrations were exponentially and inversely proportional toR/r₁,n and P sorption index (PSI)(R²=0.806(P<0.01), 0.852 (P<0.01) and 0.660(P<0.01), respectively). Cluster analysis identified twobroad groups of soils, namely those with low P availability (mean Cp0.11 mg L^–1, E_{1 min} Pi 5mg kg^–1, R/r₁ 3.9,n 0.44), and those with high P availability (mean Cp 1.33mg L^–1, E_{1 min} Pi 20mg kg^–1, R/r₁ 1.21,n 0.16). Correlation analysis indicated thatE_{1 min} P i was significantly correlated with bicarbonateextractable Pi (BPi, R²=0.37,P<0.05) and thesum of ammonium chloride extractable Pi (APi) and BPi(R²=0.38,P<0.05). However, the concentration of Pi in theE_{1 min} pool was generally lower than the sum of APi andBPi. Sodium hydroxide extractable Pi (N₁Pi) was significantlycorrelated with the sum of the E_{1 min},E_{1 min–24 h},E_{24 h–3 m} Pi pools(R₂=0.974, P<0.01),indicating that N₁Pi fractioncould be considered as representing potentially available soil P for pasturespecies over a growing season.     

Mechanism of copper-nickel alloy electrodeposition

The codeposition kinetics of copper and nickel alloys in complexing citrate ammonia electrolytes has been investigated by means of polarization and electrochemical impedance techniques. It is confirmed that the two-step discharge of the complexed cupric species Cu(II)Cit is diffusion-controlled during the alloy deposition, resulting in an increase in the nickel content of the alloy with electrode polarization. Impedance spectra are also consistent with a two-step discharge of Ni(II) cations involving an intermediate adsorbate, Ni(I)_ads, originating from the reversible first step. A reaction model is developed for the parallel discharge of Cu(II)Cit and Ni(II) in which the reactions for nickel deposition are catalysed by active sites permanently renewed at the surface of the growing alloy. The surface density of these sites, slowly nucleated from Ni(I)_ads and included in the deposit, varies with the electrode polarization, thus generating a low-frequency feature specific of Cu–Ni codeposition. This reaction model reproduces to a reasonable extent the potential dependence of the partial current densities for nickel and copper discharge, the current dependence of the alloy nickel content and also most of the experimental relaxation processes observed on impedance spectra.Nomenclature b ₁,b ₂,b ₃,b ₃ b ₄,b ₅,b ₇ Tafel coefficients (V^–1) - C concentration of Cu(II)Cit at distancex (mol cm^–3) - [Cu(II)] bulk concentration of Cu(II)Cit (mol cm^–3) - C ₀ concentration of Cu(II)Cit atx=0 (mol cm^–3) - C* concentration of Cu(I)Cit atx=0 (mol cm^–3) - C ₀, C* variations inC ₀,C* due to E - (Cu), (Ni) molecular weights (g) - C _dl double layer capacitance (F cm^–2) - D diffusion coefficient of Cu(II)Cit (cm² s^–1) - E electrode potential (V) - f frequency (s^–1) - F Faraday (constant 96 487 A s mol^–1) - g interaction factor between adsorbates - i,i _Cu,i _Ni current densities (A cm^–2) - Im(Z) imaginary part ofZ - j (–1)^1/2 - k mass transfer coefficients (cm s^–1) - K ₁,K ₃ rate constants (cm s^–1) - K ₂ rate constants (s^–1) - K ₃,K ₄,K ₅,K ₆,K ₇ rate constants (cm^–2 s^–1) - [Ni(II)] bulk concentration of NiSO₄ (mol cm^–3) - R _t charge transfer resistance ( cm²) - Re(Z) real part ofZ - t time (s) - x distance from the electrode (cm) - Z _F faradaic impedance ( cm²) - Z electrode impedance - maximal surface concentration of Ni(I)_ads intermediates (mol cm^–1) - nickel content in the deposited alloy (wt %) - thickness of Nernst diffusion layer (cm) - ₁ electrode coverage by adsorbed Ni(I)_ads intermediate - ₂ electrode coverage by active sites - ₁, ₂ variations in ₁, ₂ die to E - * =K ₂ ^–1 (s) - _d diffusion time constant (s) - ₁ time constant relative to ₁ (s) - ₂ time constant relative to ₂ (s) - angular frequency (rad s^–1) - electrode rotation speed (rev min^–1)     

A wall-jet electrode reactor and its application to the study of electrode reaction mechanisms Part I: Design and construction

A wall jet electrode reactor possessing a laminar flow regime, suitable for mechanistic studies, is reported. This reactor is different from those described in the literature in the size of its working electrode surface area. The reactor is evaluated by means of mass transport-limited current measurements using as a model reaction the reduction of ferricyanide ions at a platinum electrode surface from a 0.01 m K₃Fe(CN)₆-0.01 m K₄Fe(CN)₆ solution containing 1 m KCl as supporting electrolyte. The dependence of the mass transport-limited current on the crucial reactor parameters — the volume flow rate V _f (m³ s^–1), the nozzle diameter a (m) and the radius of the working electrode R (m) — is established and verified by theoretical predictions. The reactor is shown to have the desired wall jet hydrodynamics for: 1.6 × 10^–6 V _f 4.3 × 10^–6 m³ s^–1, 1.5 × 10^–3 a 3 × 10^–3 m and 1.5 × 10^–2 R 2 × 10^–2 m.List of symbols a nozzle diameter (m) - C _A concentration of A in the bulk (mol m^–3) - D _A diffusion coefficient of A (m² s^–1) - F Faraday's constant (C mol^–1) - dynamic viscosity (gm^–1 s^–1) - H distance between the working electrode and the tip of the nozzle (m) - I _lim mass-transport-limited current (A) - k _r constant linking the typical velocity of the wall-jet to the mean velocity in the nozzle - v kinematic viscosity (m² s^–1) - n number of electrons exchanged - density (g m^–3) - R radius of the working electrode (m) - t time (s) - V _f volume flow rate (m^–3 s^–1)     

Choked two-phase flow during electrochemical machining

A one-dimensional, two-phase fluid flow theory is formulated for the electrolyte-gas mixture behaviour in the interelectrode gap during electrochemical machining. The condition for generating the choked two-phase flow is described by an analytical formula. The initiation of choked two-phase flow in a flat, axially symmetric cavity is discussed.Nomenclature A(s) total area (cross-section of interelectrode gap (m²) - A _g,A _f cross-section of interelectrode gap filled with gas and electrolyte, respectively (m²) - c _p specific heat of electrolyte (J kg^–1 K^–1) - d diameter of inlet tube for flat radial cathode (tool (m) - d _g,d _f,d _m densities of gas, electrolyte and anode metal, respectively (kg m^–3) - d _R density ratio (see Equation 28) - D outer diameter of flat tool (m) - E voltage drop in interelectrode gap (V) - E _A,E _C potentials of anode and cathode (V) - Eu Euler number (see Equation 29) - f multiplier of dp/ds (see Equation 27) - f _r tool feed rate (m s^–1) - F Faraday constant, 96487 (A s mol^–1) - g(s) thickness of interelectrode gap (m) - g ₀,g _e inlet and outlet (exit) values ofg(s) (m) - h _a,h _f enthalpies of anode metal and electrolyte, respectively (J kg^–1) - L length of gap (m) - m _a mass flux rate for anode dissolution (kg m^–2 s^–1) - M _g,c molar mass of hydrogen or inert gas present in electrolyte (kg mol^–1) - i current density (A cm^–2) - I total current (A) - p(s) static pressure in interelectrode gap (Pa) - p ₀,p _e static pressures at inlet and outlet of the gap, respectively (Pa) - P(s) perimeter of the tool at distances (m) - R _g gas constant, 8.31471 J mol^–1 K^–1 - Re _M Reynolds number (see Equation 23) - s coordinate along gap (m) - T(s) electrolyte temperature in interelectrode gap (K) - T ₀,T _e temperatures at inlet and outlet parts of gap (K) - _g, _f linear velocities of gas and electrolyte, respectively (m s^–1) - V _a velocity of anode dissolution (m s^–1) - V _c velocity of tool (cathode) (m s^–1) - volume flow rates of gas and electrolyte, respectively (m³ s^–1) - y _g,y _f part of the interelectrode gap filled with gas or electrolyte, respectively (m) - _M limiting volume fraction of gas in electrolyte, calculated as right-hand side of Equation 30c - (s) volume fraction of gas in electrolyte - ₀, _e volume fractions of gas at inlet and outlet, respectively - _R temperature coefficient of specific resistivity, see Equation 12 (K^–1) - _a, _c electrochemical equivalents for dissolution of anode material and for gas evolution on cathode (kg C^–1) - angle (see Fig. 1) - _f kinematic viscosity of electrolyte (m² s^–1) - _M specific resistivity of gas-electrolyte mixture (m) - _f,0 specific resistivity of electrolyte at inlet (m) - slip ratio (for bubbles in the electrolyte)     

Mass diffusion-controlled bubble behaviour in boiling and electrolysis and effect of bubbles on ohmic resistance

A survey is given of theoretical asymptotic bubble behaviour which is governed by heat or/and mass diffusion towards the bubble boundary. A model has been developed to describe the effect of turbulent forced flow on both bubble behaviour and ohmic resistance. A comparison with experimental results is also made.Nomenclature ga liquid thermal diffusivity (m² s^–1) - B width of electrode (m) - c liquid specific heat at constant pressure (J kg^–1 K^–1) - C ₀ initial supersaturation of dissolved gas at the bubble wall (kg m^–3) - d bubble density at electrode surface (m^–2) - D diffusion coefficient of dissolved gas (m² s^–1) - D _h –4S/Z, hydraulic diameter, withS being the cross-sectional area of the flow andZ being the wetted perimeter (m) - e base of natural logarithms, 2.718... - f local gas fraction - F Faraday constant (C kmol^–1) - G evaporated mass diffusion fraction - h height from bottom of the electrode (m) - h _w total heat transfer coefficient for electrode surface (J s^–1 m^–2 K^–1) - h _w,conv convective heat transfer coefficient for electrode surface (J s^–1 m^–2K^–1) - H total height of electrode (m) - i electric current density (A m^–2) - j, j ^* number - J modified Jakob number,C ₀/ ₂ - enthalpy of evaportion (J kg^–1) - m density of activated nuclei generating bubbles at electrode surface (m^–2) - n product of valency and number of equal ions forming one molecule; for hydrogenn=2, for oxygenn=4 - p pressure (N m^–2) - p excess pressure (N m^–2) - R gas constant (J kmol^–1 K^–1) - R ₁ bubble departure radius (m) - R ₀ equilibrium bubble radius (m) - R/R relative increase of ohmic resistance due to bubbles, R, in comparison to corresponding value,R, for pure electrolyte - Re Reynolds number,D _h/ - Sc Schmidt number,/D - Sh Sherwood number - t time (s) - T absolute temperature (K) - T increase in temperature of liquid at bubble boundary with respect to original liquid in binary mixture (K) - gu solution flow velocity (m s^–1) - x mass fraction of more volatile component in liquid at bubble boundary in binary mixture - x ₀ mass fraction of more volatile component in original liquid in binary mixture - y mass fraction of more volatile component in vapour of binary mixture - contact angle - local thickness of one phase velocity boundary layer (m) - _m local thickness of corresponding mass diffusion layer (m) - ^* local thickness of two-phase velocity boundary layer (m) - _o initial liquid superheating (K) - constant in Henry's law (m² s^–2) - liquid kinematic viscosity (m² s^–1) - ^* bubble frequency at nucleus (s^–1) - ₁ liquid mass density (kg m^–3) - ₂ gas/vapour mass density (kg m^–3) - surface tension (N m^–1) Paper presented at the International Meeting on Electrolytic Bubbles organized by the Electrochemical Technology Group of the Society of Chemical Industry, and held at Imperial College, London, 13–14 September 1984.     

Study of the Supported K2MoO4 Catalyst for Methanethiol Synthesis by One Step from High H2S-Containing Syngas

ESR and XPS are used to study the Mo-based catalysts MoO₃/K₂CO₃/SiO₂ and K₂MoO₄/SiO₂ prepared with two kinds of precursors, (NH₄)₆Mo₇O₂₄4H₂O and K₂MoO₄. The catalytic properties of the catalysts for methanethiol synthesis from high H₂S-containing syngas are explored. The activity assay shows that the two catalysts have much the same activity for the reaction. By the ESR characterization of both functioning catalysts, the resonant signals of oxo-Mo(V) (g=1.93), thio-Mo(V) (g=1.98) and S (g=2.01 or 2.04) can be detected. In the catalyst MoO₃/SiO₂ modified with K₂CO₃, as increasing amounts of K₂CO₃ are added, the content of oxo-Mo(V) increases, but thio-Mo(V) decreases. The XPS characterization indicates that Mo has mixed valence states of Mo⁴⁺, Mo⁵⁺ and Mo⁶⁺, and that S includes three kinds of species: S^2– (161.5 eV), [S–S]^2– (162.5 eV) and S⁶⁺ (168.5 eV). Adding K₂CO₃ promoter to the catalysts, the Mo species of high valence state is easily sulphided and reduced to Mo₂S and oxo-M(V), and the derivation of [S–S]^2– and S^2– species from S is promoted simultaneously. The methanethiol synthesis is favored if the mole ratio of (Mo⁶⁺ + Mo⁵⁺)/Mo⁴⁺ 0.8 and S^2–/[S–S]^2– is kept at a value of about 1.     

The active dissolution of tin in acidic chloride electrolyte solutions — a rotating disc study

The anodic dissolution of tin in acidic chloride electrolyte has been investigated using the rotating disc technique. The dissolution reaction has a Tafel slope of 64 ±5 mV dec^–1 after the effects of diffusion are eliminated. The order of reaction with respect to Cl^– ion has been found to be unity. The measured currents were also found to depend onC _H+. The suggested mechanism involves quasi-reversible charge transfer.A possible explanation is given for the observed current-time behaviour at low anodic current densities.Notation i Current density - i ₍₎ Current density at infinite rotation speed - i _d ,Cl^– Limiting current density due to Cl^– diffusion - C _cl ^– Concentration of chloride ion - C _H+ Concentration of hydrogen ion - d ₀ Diffusion coefficient of oxidised species - k _b Rate constant for reduction of oxidised species - Kinematic viscosity - Angular velocity - Anodic transfer coefficient - Rate constant at standard equilibrium potential - Direction of reaction     

Impedance spectroscopy of the Ti(IV)/Ti(III) redox couple in the molten LiCl-KCl eutectic melt at 470°C

The electrochemical oxidation of Ti³⁺ ions in LiCl-KCl eutectic melt at 470°C occurs in two different ways according to the current densities. In our experimental conditions (concentration of Ti³⁺ ions 0.11 mol kg^–1) for potentials lower than –0.48 V (vs chlorine electrode) and current densities lower than 10 mA cm^–2 soluble Ti⁴⁺ ions are formed, whereas, for higher potentials solid K₂ TiCl₆ precipitates at the electrode resulting in a partial passivation of the electrode. Both reactions have been studied by means of impedance measurements which have shown the reversibility of the electrochemical reaction (k ₀=0.25 cm s^–1; =0.3) and the porosity of the K₂ TiCl₆ layer electrochemically formed. The thickness of this layer has been estimated from the amount of electricity involved in the reaction and from the resistance and the capacitance characterising the deposit, measured at high frequencies. This comparison shows that the deposit is composed of a very thin (0.1 m) barrier layer covered by a very thick (70 m) porous external layer.Paper presented at the EUCHEM Conference on Molten Salts 1988, St Andrews, Scotland, 6 July 1988.     

Flow-through and flow-by porous electrodes of nickel foam. I. Material characterization

This paper deals with the characterization of three nickel foams for use as materials for flow-through or flow-by porous electrodes. Optical and scanning electron microscope observations were used to examine the pore size distribution. The overall, apparent electrical resistivity of the reticulated skeleton was measured. The BET method and the liquid permeametry method were used to determine the specific surface area, the values of which are compared with those known for other materials.Nomenclature a _e specific surface area (per unit of total volume) (m^–1) - a _s specific surface area (per unit of solid volume) (m^–1) - (a _e)_BET specific surface area determined by the BET method (m^–1) - (a _e)_Ergun specific surface area determined by pressure drop measurements (m^–1) - mean pore diameter (m) - mean pore diameter determined by optical microscopy (m) - mean pore diameter using Ergun equation (m) - e thickness of the skeleton element of the foam (m) - G grade of the foam (number of pores per inch) - P/H pressure drop per unit height of the foam (Pa m^–1) - r electrical resistivity ( m) - R _h hydraulic pore radius (m) - T tortuosity - mean liquid velocity (m s^–1) Greek symbols mean porosity - circularity factor - dynamic viscosity (kg m^–1 s^–1) - liquid density (kg m^–3) - pore diameter size dispersion     

Critical solution point and chain dimension of branched-polystyrene solutions

Summary Critical solution point and chain dimension were measured for branched polystyrene(BPS) in solution as a function of molecular weight(M) and compared with those for linear polystyrene(LPS). The critical concentration _c of BPS was quite different from that of LPS at a fixed M, but the same at a fixed overlap-concentration ^*, i.e., plots of _c vs. ^* fall on a single straight line for both BPS and LPS (gf_c ^*). Reduced critical temperature _c defined by gt_c=(–T_c)/ [T_c: critical temperature, : the -temperature] was related to _c as _{c c} ² for BPS, whereas _{c c} for LPS.     

Local Symmetry of Cu2+ Ions in Sodium Silicate Glasses from Data of EPR Spectroscopy

Sodium silicate glasses with a constant ratio of oxide concentrations (mol %) SiO₂/Na₂O = 2.4 and with copper ions introduced in the form of CuO (from 1 to 10 mol %) are studied by the EPR method. The shape and width of the EPR line of copper ions are analyzed, and the spin-Hamiltonian parameters g _||, g , A _||, and A are determined by simulating the EPR spectrum and comparing the simulated and experimental spectra. The EPR spectrum of copper ions (1 mol %) is characterized by the parameters g _|| = 2.35, g = 2.065, A _|| = 135 × 10^–4 cm^–1, A = 7 × 10^–4 cm^–1, and H = 25 G. An analysis of this spectrum shows that the nearest environment of the Cu²⁺ ion has the shape of an elongated octahedron. The EPR spectrum of the sodium silicate glass containing 10 mol % Cu is a superposition of the spectrum of an octahedral complex (g _|| = 2.35, g = 2.075, A _|| = 135 × 10^–4 cm^–1, H = 40 G) and the spectrum of a cluster (g _|| = 2.35, g = 2.15, A _|| = 135 × 10^–4 cm^–1, H = 50 G).     

Effect of gas evolution on mass transfer in an electrochemical reactor

Experiments were conducted to study the effect of gas bubbles generated at platinum microelectrodes, on mass transfer at a series of copper strip segmented electrodes strategically located on both sides of microelectrodes in a vertical parallel-plate reactor. Mass transfer was measured in the absence and presence of gas bubbles, without and with superimposed liquid flow. Mass transfer results were compared, wherever possible, with available correlations for similar conditions, and found to be in good agreement. Mass transfer was observed to depend on whether one or all copper strip electrodes were switched on, due to dissipation of the concentration boundary layer in the interelectrode gaps. Experimental data show that mass transfer was significantly enhanced in the vicinity of gas generating microelectrodes, when there was forced flow of electrolyte. The increase in mass transfer coefficient was as much as fivefold. Since similar enhancement did not occur with quiescent liquid, the enhanced mass transfer was probably caused by a complex interplay of gas bubbles and forced flow.List of symbols A electrode area (cm²) - a constant in the correlation (k = aRe ^m , cm s^–1) - C _{R, bulk} concentration of the reactant in the bulk (mol^–1 dm^–3) - D diffusion coefficient (cm² s^–1) - d _h hydraulic diameter of the reactor (cm) - F Faraday constant - Gr Grashof number =gL ³/² (dimensionless) - g gravitational acceleration (cm s^–2) - i _g gas current density (A cm^–2) - i _L mass transfer limiting current density (A cm^–2) - k mass transfer coefficient (cm s^–1) - L characteristic length (cm) - m exponent in correlations - n number of electrons involved in overall electrode reaction, dimensionless - Re Reynolds number =Ud _h^–1 (dimensionless) - Sc Schmidt number = D ^–1 (dimensionless) - Sh Sherwood number =kLD ^–1 (dimensionless) - U mean bulk velocity (cm s^–1) - x distance (cm) - _N equivalent Nernst diffusion layer thickness (cm) - kinematic viscosity (cm² s^–1) - density difference = (_L – ), (g cm^–3) - _L density of the liquid (g cm^–3) - average density of the two-phase mixture (g cm^–3) - void fraction (volumetric gas flow/gas and liquid flow)     

Rates and controls on denitrification in an agricultural soil fertilized with liquid lagoonal swine waste

Under laboratory conditions, we studied rates and controls on denitrification and denitrification potential (denitrifying enzyme activity, DEA) in agricultural soils in the southeastern United States that had been repeatedly fertilized with liquid lagoonal swine effluent. This is a waste management practice commonly employed by large-scale swine production facilities that have proliferated regionally in the past 10 years. The microbial community was rapidly responsive to the added waste, as denitrification N flux (N₂ + N₂O) from intact soil cores increased from about 200 to as high as 2850 g N m^–2 h^–1, usually within 1 day of application. Elevated rates of denitrification were short-lived (3 days), as the combination of coarse soil texture (rapid drainage) and low mineralization potential (low organic content) of the waste rapidly restored aerobic conditions. Although <2% of the fertilizer-N was lost to denitrification by the time rates had returned to pre-fertilization values after 8–12 days, soil NO₃^––N levels increased from 5 g N g_dw soil^–1 to as high as 43 g N g_dw soil^–1, providing not only substrate for additional denitrification following rainfall, but also a mobile N source for both offsite transport by surface and groundwater and assimilation by plants. Both N₂O and N₂ production from denitrification were unresponsive to changes in soil moisture until field capacity was approached or exceeded. Temperature coefficients (Q₁₀) for DEA varied from 1.6 to 2.8 between 7 and 30 °C, depending on the temperature interval, while high DEA between 20 and 40 °C pointed to a denitrifying community well-adapted to regional summer soil temperatures. Glucose-C or NO₃^––N amendments proved equally stimulatory to DEA in homogenized soils relative to water-only controls. However, addition of the combined substrates gave the best response, indicating that these chemical factors were equally important controls on potential denitrification in these soils once anaerobic conditions had become established.     

Gas induced bath circulation in aluminium reduction cells

Gas induced bath circulation in the interpolar gap of aluminium cells was studied in a room temperature physical model and by computer simulation. The circulation velocity increased with increasing gas formation rate, increasing angle of inclination and decreasing bath viscosity, while it was less affected by anode immersion depth, interpolar distance (in the normal range), and convection in the metal. A typical bath velocity near the cathode was 0.05 m s^–1. The flow velocity decreased with decreasing bubble size. The results were fitted to a simple semi-empirical expression, and the velocities measured in the model experiments were in good agreement with the findings of the computer simulation.Nomenclature A Surface area (m²) - c _D Drag coefficient (l) - c _pr Concentration of 1-propanol (ml/1000 ml) - d _e Equivalent diameter of gas bubble (m) - F Faraday constant (96 487 C mol^–1) - g Acceleration due to gravity (9.82 m s^–2) - g Gravity component along anode surface (m s^–2) - h Vertical dimension of gas-filled layer (m) - H Anode immersion depth (m) - i Current density (A m^–2) - k Turbulent energy (m² s^–2) - P Pressure (N m^–2) - q Gas formation rate (m³ s^–1 m^–2) - R Universal gas constant (8.314 J mol^–1 K^–1) - t Time (s) - U Liquid velocity parallel to anode surface (m s^–1) - U _b Bubble velocity parallel to anode surface (m s^–1) - U _rel Relative velocity between bubble and liquid (m s^–1) - V Liquid velocity perpendicular to anode surface (m s^–1) - x Distance from centre of anode (m) - y Vertical distance from cathode (m) - Y Interpolar distance (m) - Angle of inclination referred to the horizontal (deg.) - Dissipation rate of turbulent energy (m² s^–3) - Volume fraction of liquid (1) - v Kinematic viscosity / (m² s^–1) - Dynamic viscosity (kg m^–1 s^–1) - _t Turbulent viscosity (kg m^–1 s^–1) - Density of liquid (kg m^–3) - /g9 Kinematic surface tension (m³ s^–2) - Bubble void fraction (1) Paper presented at the 2nd International Symposium on Electrolytic Bubbles organized jointly by the Electrochemical Technology Group of the Society of Chemical Industry and the Electrochemistry Group of the Royal Society of Chemistry and held at Imperial College, London, 31st May and 1st June 1988.     

The impedance of the alkaline zinc-manganese dioxide cell. II. An interpretation of the data

The impedance of small alkaline zinc-manganese dioxide cells has been interpreted in terms of a controlling charge-transfer and diffusion process at the zinc electrode throughout the early stages of discharge. After about 20% of the available charge has been removed, it becomes necessary to include the manganese dioxide electrode circuit components. This network has the circuit elements for charge transfer and a proceeding chemical reaction. The Warburg component for the manganese dioxide electrode need not be considered since the effective area considerably exceeds that of the zinc. The relative areas are confirmed by the magnitudes of the circuit element components. The decomposition of the impedance data has been successfully accomplished as far as 80% discharge; after this point cells show considerable differences from cell to cell, especially in the low-frequency range, which makes a confident interpretation difficult. It is considered that this is due to the loss of the physical definition of the system.Nomenclature C _m,C _z double-layer capacitances of MnO₂ and Zn electrodes, respectively - C _X,R _X parallel branch accounting for current density varying with fractional electrode coverage - R resistance of electrolyte - V open-circuit voltage of cell - Z, Z, Z impedance of cell,resistive component ofZ and reactive component ofZ, respectively - _m, _z transfer resistance of MnO₂ and Zn electrodes, respectively - , _R, _C in Warburg equation:Z _W = ^–1/2(1–i) orZ _W = _R^–1/2– i_Cco^–1/2     

Mass transfer at rough gas-sparged electrodes

Rates of mass transfer were measured by the limiting current technique at a smooth and rough inner surface of an annular gas sparged cell in the bubbly regime. Roughness was created by cutting 55°V-threads in the electrode normal to the flow. Mass transfer data at the smooth surface were correlated according to the expression j = 0.126(Fr Re)^–0.226 Surface roughness of peak to valley height ranging from 0.25 to 1.5 mm was found to have a negligible effect on the mass transfer coefficient calculated using the true electrode area. The presence of surface active agent (triton) in the solution was found to decrease the mass transfer coefficient by an amount ranging from 5% to 30% depending on triton concentration and superficial air velocity. The reduction in the mass transfer coefficient increased with surfactant concentration and decreased with increasing superficial gas velocity.Nomenclature a constant - A electrode area (cm²) - C _p specific heat capacity Jg^–1 (K^–1) - C ferricyanide concentration (m) - d _c annulus equivalent diameter, (d _o – d _i) (cm) - d _o outer annulus diameter (cm) - d _i inner annulus diameter (cm) - D diffusivity of ferricyanide (cm²s^–1) - e peak-to-valley height of the roughness elements (cm) - e ⁺ dimensionless roughness height (eu ^*/) - f friction coefficient - F Faraday constant (96 500 Cmol^–1) - g acceleration due to gravity (cm s^–2) - h heat transfer coefficient (J cm^–2 s K) - I _L limiting current (A) - K mass transfer coefficient (cm s^–1) - K thermal conductivity (W cm^–1 K^–1) - V _g superficial air velocity (cm s^–1) - Z number of electrons involved in the reaction - Re Reynolds number (_L V _g d _e/) - J mass or heat transfer J factor (St Sc ^0.66) or (St Pr ^0.66), respectively - St Stanton number (K/V _g for mass transfer and h/C _p V _g for heat transfer) - Fr Froude number (V _g ² /d _e g) - Sc Schmidt number (/D) - Pr Prandtl number (C _p/K) - PL solution density (g cm^–3) - kinematic viscosity (cm²s^–1) - gas holdup - u ^* friction velocity = V _L(f/2) - diffusion layer thickness (cm) - solution viscosity (gcm^–1 s^–1)     

Synthesis, Characterization and Anti-microbial Activity of Oligo-N-2-aminopyridinylsalicylaldimine and Some Oligomer-metal Complexes

The oxidative polycondensation and optimum reaction conditions of N-2-aminopyridinylsalicylaldimine using air oxygen, H₂O₂ and NaOCl were determined in an aqueous alkaline solution between 40–90°C. Oligo-N-2-aminopyridinylsalicylaldimine (OAPSA) was characterized by using ¹H-NMR, FT-IR, UV-vis and elemental analysis. N-2-aminopyridinylsalicylaldimine was converted to oligomer by oxidizing in an aqueous alkaline medium. The number average molecular weight (M _n), weight average molecular weight (M _w) and polydispersity index (PDI) values were found to be 7487 gmol^–1, 7901 gmol^–1 and 1.06, respectively. According to these values, 70% of N-2-aminopyridinylsalicylaldimine turned into oligo-N-2-aminopyridinylsalicylaldimine. During the polycondensation reaction, a part of the azomethine (–CH=N–) groups oxidized to carboxylic (–COOH) group. Besides, the structure and properties of oligomer-metal complexes of oligo-N-2-aminopyridinyl salicylaldimine (OAPSA) with Cu (II), Ni (II), and Co (II) were studied by FT-IR, UV-vis DTA, TG and elemental analysis. Anti-microbial activities of the oligomer and its oligomer-metal complexes have been tested against C. albicans, L. monocytogenes, B. megaterium, E. coli, M. smegmatis, E. aeroginesa, P. fluorescen and B. jeoreseens. Also, according to the TG and DTA analyses, oligo-N-2-aminopyridinylsalicylaldimine and its oligomer-metal complexes were found to be stable thermo-oxidative decomposition. The weight loss of OAPSA found to be 20%, 50% and 98% at 350°C, 535°C and 1000°C, respectively.     

Synthesis of ternary Li–Mn–O phase at a temperature of 260 ∘C and electrochemical lithium insertion into the oxide

A lithium–manganese oxide, Li _x MnO₂ (x=0.30.6), has been synthesized by heating a mixture (Li/Mn ratio=0.30.8) of electrolytic manganese dioxide (EMD) and LiNO₃ in air at moderate temperature, 260 C. The formation of the Li–Mn–O phase was confirmed by X-ray diffraction, atomic absorption and electrochemical measurements. Electrochemical properties of the Li–Mn–O were examined in LiClO₄-propylene carbonate electrolyte solution. About 0.3 Li in Li _x MnO₂ (x=0.30.6) was removed on initial charging, resulting in characteristic two discharge plateaus around 3.5V and 2.8V vs Li/Li⁺. The Li _x MnO₂ synthesized by heating at Li/Mn ratio=0.5 demonstrated higher discharge capacity, about 250mAh (g of oxide)^–1 initially, and better cyclability as a positive electrode for lithium secondary battery use as compared to EMD.