Mass transfer in the gas phase during top-blowing with plasma jets

Deoxidation of copper melts by hydrogen has been investigated experimentally by top-blowing with argon-hydrogen plasma jets. The course of the deoxidation process has been described mathematically using kinetic laws. The overall divided course of the process can be examined in live partial steps, which are hydrogen transport within the gas phase, hydrogen transport within the melt, oxygen transport within the melt, reaction between hydrogen and oxygen, and H₂O transport within the gas phase. Based on these five elementary processes, an equation for the velocity of deoxidation has been derived. The values of the rate of deoxidation resulting from this equation, in combination with the mass-transter coefficients valid for this process, have been compared to the experimental data. The results of this study verify those of former investigations on vaporization of elements out of copper melts. The mass-transfer coefficients are the same, when the local activity differences are used as the driving force for mass transport in a system. This means that the surface-renewal theory is valid, when mass-transfer coefficients are defined in this way. This is the case, at least, when metallic melts are subjected to top-blowing by plasma jets.Nomenclature a activity (a _i =x _{i i} ) - A _c (m²) effective mass-transfer area - D(m) characteristic length, such as diameter - D _r(m²/s) diffusion coefficient - H(Cu) oxygen dissolved in copper - k _g (mol/m²s) mass-transfer coefficient in the gas phase [k _g (i) mass-transfer coefficient for speciesi] - k _N (mol/m²s) mass-transfer coefficient in the melt phase - K _i = (x _i /y _i )_eq equilibrium coefficient (distribution coefficient) - n _N (mol) mole number of the melt phase - n _G (mol) mole number of the gas phase - n _i (mol/s) mole flow of speciesi - O(Cu) oxygen dissolved in copper - p(N) momentum flow - t(s) time - T (°C or K) temperature;T _G : in the gas,T _s : in the melt,T ^f : at the phase interface - x _i (mol/mol) concentration in the melt - y _i , (mol/mol) concentration in the gas phase - activity coefficient     

Pulverized coal plasma gasification

A number of experiments on the plasma-vapor gasification of brown coals of three types have been carried out using an experimental plant with an electric-arc reactor of the combined type. On the basis of the material and heat balances, process parameters have been obtained: the degree of carbon gasification (_c), the level of sulfur conversion into the gas phase (_s), the synthesis gas concentration (CO+Hz) in the gaseous products, and the specific power consumption for the gasification process. The degree of gasification was 90.5-95.0%, the concentration of the synthesis gas amounted to 84.7–85.7%, and the level of sulfur conversion into the gas phase was 94.3–96.7%. Numerical study of the process of plasma gasification of coals was carried out using a mathematical model of motion, heating, and gasification of polydisperse coal particles in an electric-arc reactor of the combined type with an internal heat source (arc). The initial conditions for a conjugate system of nonlinear differential equations of the gas dynamics and kinetics of a pulverized coal stream interacting with the electric arc and oxidizer (water vapor) agree with the initial conditions of the experiments. The computation results satisfactorily correlate with the experimental data. The mathematical model can be used for the determination of reagent residence time and geometrical dimensions of the plasma reactor for the gasification of coals.Nomenclature c _i volume concentration of components (kmol m^–3) - x longitudinal coordinate (m) - f _i source members, determined by variation of the ith component due to chemical reactions in unit volume in unit time (kmol m^–3s^–1) - velocity (m s^–1) - M _s ash mass in one particle (kg) - C _D particle drag coefficient - 3.14 - r _s particle radius (m) - d particle diameter (m) - density (kg m^–3) - C _p heat capacity of components (J mol^t– K^–1) - Q _j thermal effect of reaction (J kmol^–1) - E_j activation energy of reaction - N _l volume concentration of particles of thelth fraction (m^–3) - T temperature (K) - emissivity factor of coal particles - 5.67 × 10^–8, blackbody emissivity coefficient (W m^–2 K^–4) - P pressure (Pa) - S reactor cross section (m²) - D reactor diameter (m) - V reactor volume (m³) - L _R reactor length (m) - F _W friction force on the wall (N) - f _g friction coefficient - residence time (s) - Nu Nusselt number - Re Reynolds number - Pr Prandtl number - thermal conductivity of gas (J m^– s^–1 K^–1) - R 8.3 × 10³, universal gas constant (J kmol K^–1) - µ _i molecular mass of component (kg kmol^–1) - dynamic viscosity coefficient of gas (kg m^–1 s^–1) - thermal efficiency of plasma reactor - q_arc specific heat flow from arc (W m^–3) - P ₁ heat supplied in vapor at T = 405 K (W) - P ₂ heat loss to wall (W) - P ₃ heat loss in the gas and slag separator chamber (W) - P ₄ heat loss in the synthesis gas oxidation chamber (W) - P ₅ heat loss in the slag catcher (W) - P ₆ heat carried away in the off-gas (W) - P heat input of arc (W) - P _arc electric power of arc (W) - Q_sp specific power consumption (kw Hr kg^–1) - d _w specific heat flow to wall (W m^–2) - _c degree of carbon gasification (%) - _s level of sulfur conversion into gas phase (%)     

Separation of a binary gas mixture by pressure swing adsorption: Comparison of different PSA cycles

Gas separation of a binary gas mixture by various pressure swing adsorption (PSA) cycles was studied by a numerical simulation in order to provide a guidance in selecting PSA cycles. PSA cycles considered in this study are 3, 4-step cycles for production of only one component and a cycle with pressure equalization for production of a light component. 4 and 5-step cycles for simultaneous production of both components of a binary gas mixture are also considered. Separation of a CH₄/CO₂ gas mixture with zeolite 5A was chosen as a case study. Performances of cycles were examined and compared in view of purity, recovery and productivity. Their relative advantages were discussed. Inclusion of a purging step to a 3-step cycle for production of only one component improves a cycle performance. Further performance improvement of a cycle for production of a light component can be achieved by employing pressure equalization. Sircar's 4-step cycle with a recycle of effluent shows the best performance in view of purity and recovery among cycles for simultaneous production of both components.Nomenclature B Langmuir adsorption constant, bar^–1 - C concentration of sorbate in gas phase, mol/m³ - D defined by Eq. (7) - n amount of sorbate in solid phase, mol/kg - n _s monolayer amount adsorbed, mol/kg - P pressure, bar - R gas constant, J/mol K - T temperature, K - t time, s - U effluent gas velocity, m/s - z height of one cell, m - bulk density of a bed, kg/m³ - bed void fraction - A CH₄ - B CO₂ - H high pressure feed step - P purge step - R heavy-component rinse step - i cell number (i=1 toN)     

Study of a hollow cathode arc discharge in the presence of chromium oxide

A hollow cathode arc discharge in hydrogen has been used for the purpose of chromium oxide reduction, the solid oxide being placed inside the anode. Mass transport from the oxide to the gas phase and excitation conditions in the plasma have been investigated. The results show that a substantial amount of oxide is transferred to the gas phase with subsequent reduction and deposition inside the cathode cavity, in the form of a pure metal. The residual part condenses on the discharge chamber wall as an amorphous substance, containing 50–60% of Cr metal, and on the anode surface under the form of a mixture of chromium oxide and metal crystals (10%). From spectroscopic investigations it follows that, inside the anode zone, total Cr concentration in the gas phase is of the order of 10¹⁴ cm^–3, the excitation temperature of the atoms and ions being 4500 and 5500 K, respectively, and the ionization temperature being about 6000 K.Notation I absolute spectral line intensity (W cm^–2 sr^–1) - emission coefficient (W cm^–3 sr^–1) - A relative absorption - absorption coefficient (cm^–1) - L plasma diameter (mm) - f _tk oscillator strength - _D full Doppler width (cm^–1) - S( ₀ L) Ladenburg-Levy function - wave number (cm^–1) - k _pl mass transport rate (mol cm^–2 s^–1) - k _th thermal reduction rate (mol cm^–2 s^–1) - u ion mobility (mm V^–1 s^–1 ) - E electric field strength (V mm^–1) - drift velocity (cm s^–1)     

Evaluation of the interelemental effect in X-ray fluorescence analysis by the total addition method

Summary An algorithm for quantifying interelemental effects in X-ray fluorescence techniques is developed. By applying an addition process, the ratio between the mass absorption coefficients of the analyte and the unknown sample ( _i ^* / _s ^* ) is calculated to correct the fluorescence intensity of the element to be determined and linearize the I-c calibration plot. This coefficient can be calculated graphically and numerically. The method is applied to the determination of tin in lead alloys with good results over wide concentration ranges.Notation used Q Constant of proportionality in Eq. (4) X-ray fluorescence intensity of the I _i ^o standard - I _i ^s unknown sample - I _i ^ns dilute unknown sample - I _i ^ms unknown sample after addition of i analyte Corrected fluorescence intensity of the I _i ^cs unknown sample - I _i ^msc unknown sample after addition of i analyte Relationship of fluorescence intensity between R_i sample and standard - R _i dilute sample and standard Factor of f_m addition - f_x addition equivalent to the mass fraction of the i analyte in the unknown sample Mass absorption coefficient of _i ^* analyte - _s ^* unknown sample - _ms ^* unknown sample after addition Mass fraction of c _i ^s analyte - c _i ^ms unknown sample after addition     

Kinetics of the competitive chlorinations of some perfluoroalkyl iodides determination of the bond dissociation energies D(CD3-I), D,(C2F5-I), and D,(i,-C3F7-I)

The reactions (R = CF₃, C₂F₅, and i,-C₃F₇) have been studied competitively in the gas phase over the range of 27–231°C. The following Arrhenius parameters were obtained:

Gas phase reaction of heptafluoroisopropyl radicals with carbon tetrachloride

The reaction was investigated in the gas phase over the range 80–225°C using the photolysis of heptafluoroisopropyl iodide as the source of radicals. The rate constant, based on the value of 10^13.36 cm³ mol^?1 s^?1 for the recombination of i-C₃F₇ radicals, is given by where θ = 2.303 RT/cal mol^?1. Arrhenius parameters for chlorine abstraction from CCl₄ by CF₃, C₂F₅, n-C₃F₇, and some hydrogenated radicals are compared.     

Linear dependency in the refinement of force constants with the Jacobian method

The Jacobian method in the refinement of force constants is studied. Theoretical and experimental frequencies and other observables, ν_s, are matched by minimizing Σ_sW_s(ν – ν)², where s = 1, 2, 3,…, proceeds over all normal modes and isotopes, and W_s are weighting factors. Modification of the theoretical frequencies is accomplished with the Jacobian matrix, J , with elements J_si = ?ν_s/?k_i involving each force constant or associated parameter, k_i, i = 1, 2, 3,…, by Δν = J Δ k . The parameters are adjusted directly with Δ k = ( J ^T WJ )^?1( JW ) Δν, where W is a diagonal matrix which weights the frequencies. The linear dependence problem must be addressed prior to inversion of J ^T WJ . The approach entails diagonalization of J ^T WJ , analysis of the components of the eigenvectors associated with zero and small eigenvalues, identification of the linearly dependent parameters, successive elimination of selective parameters, and a repeat of this procedure until linear dependency is removed. The Jacobian matrices are obtained by differencing the frequencies when the parameters are varied and by numerical and analytical evaluation of the derivative of the potential. The unitary transformation, U , used to calculate J = U ^T (? F /? k ) U or J = U ^T (Δ F /Δ k ) U , is obtained from the diagonalization of the Hessian, F_mn = ?²ν/?p_m?q_n, where p, q = x, y, z are the Cartesian coordinates for atoms m, n = 1, 2, 3,…, at the initial value of k_i, i = 1, 2, 3, ? The accuracy of and the ability to evaluate the Jacobian matrix by these methods are discussed. Applications to CH₄, H₂CO, C₂H₄, and C₂H₆ are presented. Linearly dependent and ill-conditioned parameters are identified and removed. The procedure is general for any observable quantity. © 1994 by John Wiley & Sons, Inc.     

A Highly Sensitive and Selective Enzymatic Biosensor Based on Direct Electrochemistry of Hemoglobin at Zinc Oxide Nanoparticles Modified Activated Screen Printed Carbon Electrode

A sensitive enzymatic biosensor has been developed for the detection of hydrogen peroxide (H₂O₂), nitrite ( ) and trichloroacetic acid (TCA) by using hemoglobin (Hb) immobilized on activated screen printed carbon electrode (ASPCE) and zinc oxide (ZnO) composite. A pair of well defined redox peaks is observed with a heterogeneous electron transfer rate constant (K_s) of 5.27 s^?1 for Hb at ASPCE/ZnO. The biosensor exhibits the detection of H₂O₂, TCA and in the concentration range of 0.5–129.5 µmol L^?1, 2.5–72.5 mmol L^?1 and 0.2–674 µmol L^?1 with the detection limit of 0.083 µmol L^?1, 0.12 mmol L^?1 and 0.069 µmol L^?1, respectively.     

Kinetic study of the bromine-catalyzed alcoholysis of butoxytriethylsilane: n-Butoxy group–s-butoxy group exchange reaction

In order to compare the catalytic activity of bromine with those of iodine and iodine monohalides, kinetic studies on the reaction, Et₃SiOBuⁿ + Bu^sOH ? Et₃SiOBu^s + BuⁿOH, were undertaken. Pseudo first-order rate constants were determined at 0°, 10°, 15°, 20°, and 30°C by means of gas chromatography on the reaction mixtures containing both butanols in excess. From the observed rate constants, the catalytic coefficients of bromine were evaluated as follows: The enthalpies and entropies of activation were estimated to be (42.0 – 42.2) kJ/mol, ?(103 – 104) J/K (forward reaction), and (40.4 ? 40.7) kJ/mol, ? (101 ? 102) J/K (reverse reactions). These data suggest that bromine is much more active than iodine and iodine monohalides, and its high activity was interpreted on the basis of the structure of the reaction intermediate.     

Fractional factorial design study of a pressure swing adsorption-solvent vapor recovery process

A two-level fractional factorial study was performed by computer simulation on the periodic state process performance of a pressure swing adsorption-solvent vapor recovery process (PSA-SVR). The goal was to investigate factor (parameter) interaction effects on the process performance, i.e., interaction effects that cannot be ascertained from the conventional one-at-a-time approach. Effects of seven factors, i.e., the purge to feed ratio, pressure level, pressure ratio, heat transfer coefficient, feed concentration, feed volumetric flow rate and bed length to diameter ratio, on the process performance were investigated. The results were judged in terms of the light product purity, heavy product enrichment (and relative enrichment) and recovery, and bed capacity factor. Only the purge to feed ratio, pressure ratio, and feed concentration had significant effects on the benzene vapor enrichment (and relative enrichment); and no two-factor and higher interactions were observed. The light product purity was affected by all seven factors; and the relative importance of the effect of each factor depended on the levels of the other factors, i.e., significant two-factor interaction effects existed. Two-factor interaction effects also existed on the benzene vapor recovery, although the effects of all seven factors and their interactions were relatively small. The bed capacity factor was affected mainly by the purge to feed ratio, the heat transfer coefficient and the feed concentration; two factor and higher order interaction effects were insignificant. Overall, this study demonstrated the utility of fractional factorial design for revealing factor interactions and their effects on the performance of a PSA-SVR process.Nomenclature BCF bed capacity factor, % - b, b ₀ isotherm parameters, m³/(mol K^0.5) - C _pg gas phase heat capacity, kJ/(kg K) - C _ps solid phase heat capacity, kJ/(kg K) - E enrichment - E _I ideal enrichment - E _R relative enrichment - H heat transfer coefficient, kJ/m² s K) - H heat of adsorption, kJ/mol - k number of factors, or mass transfer coefficient, l/s - l number of levels - L bed length, m - LD bed length to diameter ratio - PF purge to feed ratio - P _H adsorption high pressure, kPa - P _L desorption pressure, kPA - PL pressure level, represented byP _I - PR pressure ratio - q amount adsorbed, mol/kg - q ^xx equilibrium amount adsorbed, mol/kg - q ^xx _j equilibrium amount adsorbed at the feed conditions, mol/kg - r _b bed radius, m - R solvent vapor recovery, % or gas constant, m³ (mole K) - T temperature, K - T ₀ ambient temperature, K - t time, s - u interstitial velocity, m/s - VF volumetric feed flow rate, m³ STP/s - YF feed mole fraction - Y _p light product mole fraction - z axial coordinate, m Greek Symbols _g gas phase density, kg/m³ - _s solid phase density, kg/m³ - bed void fraction     

Contribution to the thermodynamics of emulsions

Summary In this paper there are derived equations for thermodynamically stable emulsions of phase II in phase I in the presence of surfactants.

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Zusammenfassung In dieser Arbeit werden Gleichungen für thermodynamisch stabile Emulsionen einer Phase II in Phase I in Gegenwart oberflächenaktiver Stoffe abgeleitet.

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Notation A interfacial area between phase I and phase II - interfacial tension between phase I and phase II - ⁰ interfacial tension without presence of a surfactant - n _i number of moles = amount of componenti - C ₃ concentration of the surfactant = component 3 in phase I in mol/cm³ With 1 figure and 2 tables     

Tantalum(v) oxoalkoxides. Synthesis and structure

Anodic oxidation of tantalum in isopropyl alcohol or prolonged reflux of an alcohol solution of Ta(OPrⁱ)₅ afford crystalline oxoisopropoxide Ta₂O(OPrⁱ)₈ · PrⁱOH (1). In its molecule, two octahedra about Ta atoms are linkedvia the shared edge [(OPrⁱ)O]. Compound1 is the first example of oxoalkoxide containing such a small number of metal atoms. Unlike the known polynuclear molecules M _n O _m (OR) _p , oxoalkoxide1 is stable in solutions; on transition to the gas phase, this compound is desolvated to form a very stable molecule Ta₂O(OPrⁱ)₈ (apparently, consisting of two octahedra with a shared edge). According to the data of mass spectrometry, analogous molecules exist in the gas phase over Ta(OAlk)₅ (Alk = Me, Et, Prⁱ, or Bu¹¹). When compound1 is heated invacuo (10^–2–10^–3 Torr), Ta(OPrⁱ)₅ is sublimated. Crystals of Ta₇O₉(OPrⁱ)₁₇ (2) were formed upon prolonged storage of solutions of1 in PrⁱOH. Heptanuclear molecule2 consists of two [Ta₄] tetrahedra with a shared vertex. These tetrahedra are additionally linked togethervia one ₃-oxo and two ₂-OPrⁱ groups. Complex2 is a representative of heptameric oxoalkoxides of a new structural type.Deceased in I995.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 1, pp. 125–131, January, 1996.     

The retention equation in reversed-phase ion-pair chromatography

In this paper, by combination of the statistical thermodynamic method with the Freundlich isotherm, the retention equations to describe the effects of the mobile phase composition, concentration of the ion-pair reagent and the ionic strength on the amount of adsorbed ion-pair reagent and the retention value of the ionic solute have been reported by simultaneously considering the electrostatic and molecular interaction between solutes, ion-pair reagent and molecule or ion in each phase in the reversed-phase ion-pair chromatography. The validity of these retention equations has been confirmed by calculation of capacity factor of the different phenylamine and naphthylamine sulphonic acids during systematic change of concentration of the strong solvent, the ion-pair reagent and the ionic strength in the mobile phase.Symbols a, b, c, d, d ₁,e, f, h, g anda, b, c, d, e, f', g, h parameters related to chromatographic system - A solute - B constant - B _i solventi - C _b andC _p concentration of strong solvent and ion-pair reagent - C _P ^a amount of adsorbed ion-pair reagent - D dielectric constant - E _AP , andE _pp molecular interaction of adjacent pair of solute-ion-pair reagent, solute-solventB _i , ion-pair reagent-solventB _i and ion-pair reagent-ion-pair reagent - E _p ^a andE _e ^a non-electrostatic and electrostatic adsorption energy of ion-pair reagent - F Faraday constant - h Planck constant - I ionic strength - j _A , andj _p internal partition function of solute, solventB _i and ion-pair reagent - k Boltzmann constant - k capacity factor - k _p ,n _p andk ₁,n ₁ parameters of Freundlich isotherm of ion-pair reagent and solventB ₁ - K _AP , and constants related with the molecular size of solute, ion-pair reagent and solventB _i - m _A ,m _P and molecular weight of solute, ion-pair reagent and solventB _i - N _A ,N _P and numbers of solute, ion-pair reagent and solventB _i in solution - N _A ^a ,N _P ^a and numbers of solute, ion-pair reagent and solventB _i adsorbed on the surface - N _s number of adsorbed sites on the surface - P ion-pair reagent - R gas constant - T absolute temperature - V ₀ volume of solution - V _p and volume of ion-pair reagent and solventB - X potential function - X _P ¹ andX _P ^l potential function of ion-pair reagent on the surface and in the solution - X _A ^a andX _A ^l potential function of solute on the surface and in the solution - Z _A ,Z _P andZ _i charge numbers of soluteA, ion-pair reagent and inorganic ioni - Z _AP and numbers of ion-pair reagentP and solventB _i surrounding the soluteA - ₀ permittivity in a vacuum - electrostatic potential of the surface Dedicated to Professor J. F. K. Huber on the occasion of his 65th birthday     

Background elimination in three-dimensional spectroscopy using the intensian method

The method to eliminate background in the case of quantitative multidimensional spectroscopy, chromatography or any analytical 3-dimensional technique is shown. The 3-dimensional signal is required to be proportional to the concentration of determined substance and the additivity of signals should be obeyed. Eliminated background is assumed to be a low-order polynomial of two variables. The intensian method [1] is a generalization of the Beer-Lambert law, where a certain determinant called intensian replaces absorption and absorptivity. In practice there will be no need to use determinants, since usually they are replaced by expressions of few terms. Some details on the practical use of the method are given.Index of used symbols x, y UV, IR, GC, NMR or other scale. - A (x, y) intensity (absorption) of the 3-dimensional band of interest. - a (x, y) standard intensity (absorption) of the 3-dimensional band of interest. - B(x, y) intensity (absorption) of 3-dimensional background. - S(tx, y) intensity (absorption) of 3-dimensional multicomponent spectrum. - f (x, y) auxiliary function:f (x, y) =A (x, y), B(x, y), a(x, y), S(x, y). - (x _i, Yi) selected point,i positive integer number. - f(xi, yi) value off (x, y) in point (xi, yi). - S _i value ofS(x, y) in point (x _i, y_i). - b pathlength, measurement coefficient,c concentration. - , , , real numbers. - ij, _ij real coefficients of power expansions. - x ⁱy^j monomial of degree (i +j). - F(·) linear functional acting on 3-dimensional spectral functions. - J^3-dim(·) 3-dimensional intensian acting on 3-dimensional spectral functions. - J _n ^3-dim (·) 3-dimensionaln-points intensian. - d _i ith intensian coefficient, cofactor of expansion of J _n ^3-dim (f(x, y)) according to its first row (eq. (10)). - (.) absolute error. - r _i,, R random variables: eqs. (13) and (14). - G(.) (normal) distribution function. - z ordinate axis. - a - f , h abreviations for some arguments. - d _ijk,D _mnp abreviations defined in eq. (22).     

Mass,size and shape of micelles formed in aqueous solutions of ethoxylated nonyl-phenols

The study was extended to analysis of mass, size and conformation of micelles formed in aqueous solutions of ethoxylated nonyl phenols. The results obtained by ultracentrifugal technique between 293 and 323 K have proved that the slightly ethoxylated nonyl phenols form micelles with high molecular mass and larger size at constant temperature, while the increasing length of the ethylene oxide chain favours formation of micelles of smaller molecular mass and size. The transformation of conformation from oblate to spherical shapes ensues with increasing temperature at constant ethoxy number or with ethoxylation at constant temperature. The second virial coefficient decreases with increasing temperature and decreasing ethoxy number. In accordance with the earlier conclucions, the change of the second virial coefficient relates to enhanced variation of monomer solubility, stabilization of micelle structure and increased deviation from ideal behaviour of a given micellar system.Symbols a major axis of micelle, Å - a _m attractivity factor, cm³ erg molecule² - b minor axis of micelle, Å - c concentration, g dm^–3 - c _b equilibrium concentration at the bottom of the cell, g dm^–3 - c _m equilibrium concentration at the meniscus of the cell, g dm^–3 - c _o initial concentration in the cell, g dm^–3 - c _M critical micellization concentration, mol dm^–3 - e eccentricity - f _IS Isihara-constant - f/f _o frictional ratio of micelle - amount of water in micelle per ethoxy group, mol H₂O/mol EO - n aggregation number, monomer micelle^–1 - n _EO number of ethoxy groups - r distance of Schlieren peak from the axis, cm - r _b distance of cell bottom from the axis, cm - r _m distance of cell meniscus from the axis, cm - R _h equivalent hydrodynamic radius of micelle, Å - s _t sedimentation coefficient, s - reduced sedimentation coefficient, s - reduced limiting sedimentation coefficient, s - ¯v _t volume of micelle, cm³ micelle^–1 - partial specific volume of solute, cm³g^–1 - partial specific volume of solute reduced to 293 K, cm³ g^–1 - B _a, B_e constants, cm³ mol g^–2 - B ₂ second virial coefficient, cm³ mol g^–2 - M _m ^a mass average apparent molecular mass of micelle, g mol^–1 - M _m mass average molecular mass of micelle corrected withB ₂, g mol^–1 - M _m ^cM mass average molecular mass of micelle belonging toc _M, g mol^–1 - M ¹ mass average molecular mass of monomer, gmol^–1 - N _A the Avogadro's number, molecule mol^–1 - R universal gas constant, erg mol^–1 K^–1 - T temperature, K - _t ^o dynamic viscosity of solvent atT temperature, g cm^–1 s^–1 - dynamic viscosity of solvent at 293 K, g cm^–1 s^–1 - _t density of solution atT temperature, g cm^–3 - _t ^o density of solvent atT temperature, g cm^–3 - density of solvent at 293 K, g cm^–3 - angular velocity, rad s^–1 - time, s     

Kinetics of the alizarine red S surface redox reaction

Kinetics of the surface redox reaction of alizarine red S adsorbed on mercury is measured by square-wave voltammetry. In 1 mol/l KNO₃ buffered to pH 9.22, the standard reaction rate constant of the redox couple anthraquinone/anthrahydroquinone in the adsorbed alizarine red S molecule is k_s=100 ±10 s^-1 and the cathodic transfer coefficient is =0.4. At pH 2 in this medium k_s is greater than 500 s^-1.     

Kinetics and mechanism in the decomposition of NH3 in a radio-frequency pulse discharge

Studies of time-resolved absorption spectra of transient species in the decomposition of NH₃ by an r.f. pulse discharge together with product analysis showed that the major radical formed was NH at concentrations of the order of 10^–6 mol dm^–3 (10⁵ molec. cm^–3). Possible mechanisms for the formation of the radical during the discharge and its decay following pulse cut-off were tested by computer simulation of the kinetic data. Following zero-order formation with rate coefficient 0.19±0.03 mol dm^–3 s^–1, the decay was second order in NH with rate coefficient 2.1±0.5×10⁹ mol^–1 dm³ s^–1 both for pure NH₃ and where NH₃/rare gas mixtures were investigated. The kinetic data are consistent with NH removal in a nonassociative radical-radical reaction proceeding via a short-lived collision complex, probably 2NH N₂H₂ N₂ + H₂.     

Farbe und Konstitution bei anorganischen Feststoffen, 15. Mitt.: Die Lichtabsorption des zweiwertigen Kobalts in Silikaten vom Olivintypus

Zusammenfassung Mischkristalle Co _x Mg_1-x CaSiO₄ (I) und Co _x Mg_2-x SiO₄ (II), in denen sich das Mg²⁺ vollständig durch Co²⁺ ersetzen läßt, wurden röntgenographisch und spektralphotometrisch untersucht, desgleichen Mischkristalle {CoCaSiO₄+y Co₂SiO₄} (III), <y0,1>. In I befindet sich das Co²⁺ in den triklin verzerrten OktaederpositionenM _i , in II und III außerdem in den monoklin verzerrten OktaederlückenM _s des Olivingitters (M _i M _s SiO₄).Beim Einbau von Co²⁺ in Mg₂SiO₄ werden die kleinerenM _i O₆-Polyeder bevorzugt besetzt und aufgeweitet. Die Absorptionsspektren des Co _s ²⁺ von II und III konnten ermittelt werden, indem man die überlagerte Lichtabsorption des Co _i ²⁺ durch ein Näherungsverfahren eliminierte. Beim Übergang Co _s ²⁺(II) Co _s ²⁺(III) wird eine beträchtliche IR-Verschiebung beobachtet; sie ist die Folge der Aufweitung derM _s O₆-Polyeder bei der Substitution von Mg²⁺ (bzw. Co²⁺ durch Ca²⁺.Folge der starken Verzerrung der Koordinationsoktaeder im Olivingitter, deren Konstitution ausführlich beschrieben wird, ist eine Verbreiterung und Aufspaltung der Absorptionsbanden. Während der Feldstärkenparameter für Co _i ²⁺ in den Co-haltigen Olivinphasen mit (Co²⁺) von Co _x Mg_1-x O vergleichbar ist. resultieren für Co _s ²⁺ auffallend niedrige -Werte.

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Mixed crystals Co _x Mg_1–x CaSiO₄ (I)<0,1x1,0>, Co _x Mg_2–x SiO₄ (II) <0,05x2,0>, and {CoCaSiO₄+yCo₂SiO₄} (III) –1). These phases crystallize in the olivine structure (M _i MM _s SiO₄) containing two differently distorted octahedral sites (M _i of triclinic andM _s of monoclinic symmetry).In I the Co²⁺ are incorporated in the intersticesM _i , in II and III in the intersticesM _s in addition. In II—for small values ofx—the smallerM _i O₆-polyhedra are occupied preferably by Co²⁺ and also widened. The spectra for Co _s ²⁺ of II and III could be obtained by eliminating the superimposed absorption of the Co _i ²⁺ using an approximative substraction method. Going from Co _s ²⁺(II) to Co _s ²⁺(III) produces a considerable shift of the absorption bands towards IR as a consequence of the expansion of theM _s O₆-polyhedra caused by the large Ca²⁺ in III.The considerable distortion of the coordination octahedra in the olivine lattice causes a broadening and splitting of the absorption bands. Whereas the ligand-field-parameter of Co²⁺ in theM _i -sites ofM _i M _s SiO₄ may be compared to (Co²⁺) of Co _x Mg_1–x O, remarkably low -values are observed for Co _s ²⁺.

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Mit 8 Abbildungen

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14. Mitt.:O. Schmitz-DuMont, H. Fendel, M. Hassanein undHelga Weissenfeld; Mh. Chem.97, 1660 (1966).