bluuebunny/crossref_metadata_2025 huggingface dataset:
Electronic and Elastic Influences on the Energetics of Alloy Formation
Authors: Schaller H.‐J.
Published: July 2012

Palladium and platinum alloys have turned out to be a useful subject for relating thermodynamic properties with electronic and elastic quantities of the components. The mixing behavior of a number of interstitial and substitutional alloys exhibits analogous characteristics and may be interpreted by means of the same model. – Two effects are discussed to account for nonideal properties. An “electronic” effect is based on the observation that a number of alloy components behave as electron donors with respect to Pd and Pt. The charge transfer gives rise to a bonding contribution which is determined by the Fermi levels of the components and the valency of the solute. Extremely negative deviations from ideal mixing behavior have been predicted and observed upon adding unnoble components such as Al, Zr, Th or rare earth metals. For a number of Pd alloys the rise of the Fermi energy can be described as a function of the valence electron concentration only, irrespective of the particular donor. – An “elastic” effect is associated with the lattice distortion brought about by the dissolved particles. Models based on continuum elastic considerations are discussed in order to estimate the strain energy at infinite dilution. This quantity is correlated to the pair interaction energy in the quasichemical approach, which was used to calculate the concentration dependence of the elastic contribution. – Based on the underlying assumptions, the thermodynamic excess quantities can be separated in an electronic and an elastic part. These ideas are quite general and should be useful in a number of other metallic solutions.
Homogeneous Equilibria in Liquid Alloys and Glass Formation
Authors: Sommer F.
Published: July 2012

Using homogeneous equilibria reactions for the description of chemical short range order tendencies in liquid alloys with compound forming tendency it is possible, with the association model, to describe different kinds of asymmetrical concentration dependences, to calculate the temperature dependences of the thermodynamic mixing functions as well as to extrapolate for multicomponent systems. Some exemplary results are shown. The existence of a chemical short range order is an important factor of influence on the glass formation ability obtained by rapid quenching from the liquid phase. On the one hand, it causes small chemical driving forces for a crystallization and, hereby, a thermodynamic promotion of glass formation. On the other hand, glass formation is additionally kinetically favoured, if the stoichiometric compositions of the associates in the liquid alloys are not in accordance with those of the crystalline equilibrium phases in the glass formation range.
Experimental Aspects of Solid Galvanic Cell Methods for Thermodynamic Studies on Alloys
Authors: Kleykamp H.
Published: July 2012

The phase diagrams of the ZrO2–CaO, ZrO2–Y2O3, ThO2–Y2O3 and ThO2–La2O3 systems are discussed in view of the use of the electrolytes in emf measurements. It is shown that thermodynamic studies on metallic A‐B systems using solid galvanic cells with oxygen and fluorine ion conducting electrolytes require the knowledge of the phase diagrams of the corresponding ternary A‐B‐O and A‐B‐F systems for the cell arrangements. Examples for misleading emf measurements by use of incompatible electrodes are given. Asymmetric cells, side reactions between the electrodes and the electrical leads, and impurities in the cover gas as sources for erroneous emf measurements are demonstrated. The characteristics of reference electrodes for oxide electrolytes in environments with different oxygen partial pressures are outlined. The role of oxygen as an impurity in the electrodes for CaF2 electrolytes is investigated.
The Phase Boundaries of Wüstite
Authors: Knacke O.
Published: July 2012

According to Darken and Gurry and to Swaroop and Wagner, the iron/wüstite phase boundary shows a minimum in oxygen content. From general thermodynamic relations it follows that at this minimum, the enthalpy of solution and entropy of solution of metallic iron in wüstite must be zero. With this condition and the application of further thermochemical data for wüstite, an equation for the Gibbs energy has been derived which may be used to calculate iron/wüstite and wüstite/magnetite phase boundaries in agreement with those determined experimentally.
Vacancy‐Impurity Binding Energy and the Effective Vacancy Formation Energy as Determined from the Solidus Line for Binary Al‐Based Alloys
Authors: Górecki Tadeusz
Published: July 2012

The vacancy model of melting of metals has been used as a starting point for deriving the expressions permitting to determine the vacancy‐impurity binding energy, Ebv–i, and the effective vacancy formation energy from the knowledge of the solidus line for binary alloys. The calculated values of Ebv–i and E for binary Al‐based alloys show a fair agreement with the experimental data existing in the literature.
Thermodynamic Behavior of Impurity Atoms in α‐Range Alloys of the Noble Metals and Nickel
Authors: Hehenkamp Theodor
Published: July 2012

Thermodynamic data for dilute α‐range alloys are necessary to understand atomic migration. Such data, however, are very scarce in the literature and contradict each other in many cases. A comparison is presented between the results of different experimental techniques particularly designed to measure partial thermodynamic quantities at low impurity concentrations. The results for I‐B‐noble metals alloys are surprisingly uniform and indicate an electronic origin of the dependence of the excess potentials on concentration, if the impurity atom has the same ion core as the host metal. If the impurity atom exhibits a much different ion core, a minimum in the excess chemical potential becomes observable at low concentrations. The reason could be either a size misfit or a dependence of the excess functions on the atomic mass. The viewpoint of the mass dependence is corroborated by results in the Ag–As‐system, which is characterized by almost no size misfit but a different atomic mass, and some recent measurements in Nickel‐alloys.
Thermodynamic Properties of Pd‐X‐Alloys, with X = Gd, Y, Ce
Authors: Paasch S. , Schaller H.‐J.
Published: July 2012

Electromotive force measurements on cells with a CaF2 solid electrolyte were used to determine the activities of Gd, Y, and Ce in Pd‐rich alloys between 700°C and 800°C. The thermodynamic properties of these alloys are characterized by extreme negative deviations from ideal mixing behavior, up to −400 kJ/mol for the partial molar excess Gibbs energy of Ce and up to −320 kJ/mol for Gd and Y. The high thermodynamic stability of these alloys is attributed to a transfer of valence electrons to the electron gas of the alloy. At infinite dilution the resulting bonding contribution to the partial excess free energy is determined by the difference of the Fermi levels of the components and the valency of the solute. Including the size difference of the components as an additional effect, the mixing behavior of the alloys can be well described. – Within the homogeneity ranges of the intermetallic phases Pd3Y and Pd3Gd the activities of the unnoble components increase by more than ten orders or magnitude.
Thermodynamics of Liquid Na — Sn Alloys Using CaF2 Solid Electrolytes
Authors: Alqasmi R. , Egan J. J.
Published: July 2012

The thermodynamic properties of mixing for liquid Na – Sn alloys were determined between 750°C and 850°C by emf measurements using a CaF2 solid electrolyte. Concentrations were controlled by coulometric titration. Results are presented for partial and integral Gibbs energies, entropies, and heats of mixing across the entire composition range.
Self‐Consistent Solution of Sommer's Partial Associated Model. New Approach of the Configurational Entropy
Authors: Cunat Ch. , Hertz J.
Published: July 2012

We have worked with Sommer's partial associated model [1,2]. Considering that the adjustable parameters of this model are not real independant ones we have looked at iteration mathematical procedure to assure the self‐consistency with the formalism of the model. With respect to such a procedure, one isothermal enthalpy curve, for example, is mathematically sufficient to determine all the adjustable parameters. So we shall emphasize that all the results are strongly dependent on the choice of the configurational entropy model. Ours is coherent with the initial chemical assumption.
Photochemistry of Colloidal Metal Sulfides. 5. Fluorescence and Chemical Reactions of ZnS and ZnS/CdS Co‐Colloids
Authors: Henglein A. , Gutiérrez M.
Published: July 2012

Small colloidal particles of ZnS were obtained by precipitation of Zn2+ with SH− in the presence of colloidal silicon dioxide. Co‐colloids were prepared by simultaneously precipitating ZnS and CdS. Colloidal ZnS fluoresces at 425 nm. 90% of the fluorescence decays within 30 ns. The fluorescence is partly quenched by oxygen, chloroethanol and chloralhydrate. It can be completely quenched by methyl viologen and sulfide anions at low concentrations. The quenching actions are attributed to the scavenging of electrons or positive holes which are photo‐generated in ZnS. The onset of the absorption and the maximum of the fluorescence band are shifted towards shorter wavelengths with increasing Zn/Cd ratio of the co‐colloid. – ZnS in deaerated solution undergoes a slow photo‐anodic dissolution (quantum yield ø = 2 · 10−3 ZnS molecules/photon), the products being H2, Zn2+ (aq), sulfur and SO (aq). In the presence of air, a rapid decomposition with ø = 0.32 ZnS/photon takes place. In deaerated solutions, chloroorganic compounds promote the dissolution of ZnS. The chloroorganic compounds are decomposed, too. In the presence of sulfite, zinc metal is photo‐deposited onto the colloidal particles until hydrogen production takes over with ø = 0.18 H2/photon. In the presence of both sulfite and carbon dioxide, formic acid is produced with ø = 0.2 HCOOH/photon.
Absolute Measurements of the Thermal Conductivity of Aqueous NaCl Solutions at Pressures up to 40 MPa
Authors: Nagasaka Y. , Okada H. , Suzuki J. , Nagashima A.
Published: July 2012

The paper describes absolute measurements of the thermal conductivity of aqueous NaCl solutions in the concentration range 0 to 5 molality, the temperature range 0 to 80°C and the pressure range 0.1 to 40 MPa. An apparatus is based on the transient hot‐wire method using coated wire. The accuracy of the experimental results is estimated to be ± 0.5%. The results constitute the first measurements of the pressure effect on the thermal conductivity of NaCl solutions. The pressure coefficient of the thermal conductivity is compared with that of the viscosity. Three typical equations for predicting the thermal conductivity of aqueous electrolyte solutions are checked against the present experimental results. It is found that none of these equations can reproduce the present data within the experimental error.
Conformational Equilibrium and Calorimetric Behaviour of Systems Containing 1,2‐Dichloroethane
Authors: Baños Irene , Valero Jose , Gracia Mariano , Losa Celso Gutierrez
Published: July 2012

Excess molar enthalpies (HE) of 1,2‐Dichloroethane + n‐Hexane, + (n‐Hexadecane, + Cyclohexane, + Benzene, + Tetrachloromethane, and + 1,2‐Dibromoethane, at 288.15, 298.15, 308.15, and 318.15 K, and densities of the pure components at 298.15 K, were measured. The most relevant point about the results obtained is the sluggishness of HE to change with temperature. For explaining this effect, a correlation between interaction potential energy and intramolecular potential energy in the conformational equilibrium, should be taken into account.
Equilibrium Vapor Pressure Measurements for the n‐Alcohols in the Temperature Range from −30 °C to + 30 °C
Authors: Schmeling T. , Strey K.
Published: July 2012

We measured the equilibrium vapor pressures pc ranging from 240 mmHg for methanol down to 5 · 10−3 mmHg for n‐hexanol, using capacitance pressure transducers. Good agreement is observed between literature data obtained by mercury manometers and our data in the ranges of overlap. Our data are found to be well described by the empirical Dupré‐Rankine formula. We analysed the thermodynamic basis of this relation and found its parameters to be interrelated. Once a reference temperature is chosen the number of adjustable parameters is reduced by one. The remaining parameters are physically relevant quantities, the molar vaporization enthalpy ΔHmv, and the difference of the molar specific heats of vapor and liquid phase ΔCmp. We evaluated these quantities from our measurements, and we give an overall fit of a combination of literature data and ours ranging from the boiling point to − 30 °C.
The Temperature Dependence of the Thermal Diffusion Factors of Binary Systems of Nitrogen with the Five Noble Gases and of Helium with Argon
Authors: Trengove R. D. , Dunlop Peter J.
Published: July 2012

Thermal diffusion factors, αT, are reported at several temperatures for binary systems of nitrogen with five noble gases. Similar data are reported for the system helium ‐ argon. Theoretical αT values are compared with the experimental data for two of the systems.
Solubility of Anthracene in Dense Gases and Liquids to 200°C and 2000 bar
Authors: Rößling G. L. , Franck E. U.
Published: July 2012

The solubility of anthracene to 200°C and 2000 bar, in some cases to 280°C and 3000 bar, was measured in 10 fluids: Ar, CH4, propane, n‐pentane, dimethylpropane, CO2, CHF3, CHClF2, NH3and H2O. Solution concentrations were derived from the absorption in the near UV‐band of anthracene near 370 nm. The high pressure optical cell, additional equipment and procedures are described. Results are given as anthracene concentrations and as “enhancement factors”. Enhancement factors up to 107were found. The factors increase with solvent density (except at very high density) and decrease with temperature at isochoric conditions. Virial coefficients B12are derived between 294 and 450 K. An improved sublimation pressure curve for pure anthracene was also determined.
Mechanistic Information from Temperature and Pressure Parameters for Some Substitution Reactions of dien and a Series of Ethyl Substituted dien Complexes of Palladium(II) in Aqueous Solution [1]
Authors: van Eldik R. , Breet E. L. J. , Kotowski M. , Palmer D. A. , Kelm H.
Published: July 2012

Substitution reactions of the type Pd(L)X+ + Y− → Pd(L)Y+ + X− with L = dien, 1,4,7‐Et3dien, 1,1,4‐Et3 dien, 1,1,7,7‐Et4 dien, 4‐Me‐1,1,7,7‐Et4 dien and 1,1,4,7,7‐Et5 dien, X = Cl, Br or I and Y = OH and I have been studied kinetically as a function of [Y−], temperature and pressure. The first‐order rate constant k1, for the solvolysis reaction path decreases along the series dien > 1,4,7‐Et3dien > 1,1,4‐Et3dien ≫ Et4 dien > MeEt4 dien ∼ Et5 dien, accompanied by an increase in ΔH* and almost constant values for ΔS# and ΔV#. The same applies to the second‐order rate constant k2 for the direct substitution reaction path in the case of Y = I, and the activation parameters for both k1 and k2 being indicative of an associative reaction mode for all complexes. For Y = OH, a significant [Y−] dependence was observed for the Et4 dien species only, and the value of Δ V# in this particular case favours a conjugate‐base mechanism. The results are discussed with reference to related studies reported in literature.
Stoßtwellenuntersuchungen zum Start der Reaktion CO + O2
Authors: Thielen K. , Roth P.
Published: July 2012

By use of the atomic resonance absorption spectrophotometry (ARAS) the rate coefficient of the reaction

k1 = 8.4 · 10−11 · exp (‐31800 K/T)cm3 s−1

has been determined by direct measurements of the time dependent concentrations of O atoms in the reaction zone behind reflected shock waves. With additional measurements of H atom concentrations the influence of catalysing impurity reactions can be determined. The experiments were done under very clean conditions in mixtures of argon with small relative concentrations of CO (500 to 10000 ppm) and of O2 (100 to 20000 ppm) in the temperature range 1700 K ≤ T ≤ 3500 K at total pressures of about 1.8 bar.
Moderne Entwicklungen bei der Untersuchung von Verbrennungsvorgängen
Authors: Just Th.
Published: July 2012

A survey is presented about newer results on the modeling of laminar as well as turbulent flames. Laser techniques for the local measurement of temperatures and concentrations in flames are discussed.
Reduction of Pollutant Formation in Combustion Processes
Authors: Sawyer Robert F.
Published: July 2012

Combustion sources account for approximately ninety percent of air pollutant emissions. Many of the effects of air pollutants upon human health and the environment are reasonably well understood. Some potential problems, however, such as the presence of carcinogens in urban atmospheres and the effect of carbon dioxide on climate, while not well understood, cause concern. — Modification of combustion processes to reduce pollutant emissions has proven successful. Better understanding of the fundamentals important to combustion often leads to pollutant reduction without compromise of efficiency or the quality of the combustion process. Treatment of combustion products to remove pollutants also has proven effective in cases where combustion modification fails to yield the required reduction. In other cases treatment of the fuel to remove pollutant percursors has been employed. A combination of these approaches has been chosen as an optimum strategy for some pollution control situations.
Ignition and Thermal Stability in Open Systems
Authors: Gray Peter
Published: July 2012

This paper is concerned with the resemblances and differences between the instabilities shown by exothermic gas reactions in closed and open systems. Even the simplest reaction (1st order, irreversible) in the simplest open system (uniform temperatures and concentrations, linear heat losses) can show very varied patterns of behaviour. The treatment highlights the roles of three essential time‐scales — residence time, Newtonian cooling time, and chemical reaction time — and the importance of the (dimensionless) adiabatic temperature in determining behaviour. Conditions for “ignitions” leading to oscillatory behaviour and for the extinction of oscillations are briefly discussed.
Ausbreitung von Flammen in Rohren mit einer Blende: Der Einfluß von Inertgas
Authors: Pangritz D. , Dörge K. J. , Wagner H. Gg.
Published: July 2012

The influence of nitrogen on the flame acceleration by an orifice in a tube of 40 mm diameter in C2H4–O2 mixtures has been investigated by measuring pressure profiles and flame‐speeds. For mixtures with nitrogen contents down to 60% the maximum overpressures are proportional to the laminar flame speed. Detonations develop close to the orifice when the nitrogen content is further reduced.
Hydrocarbon Oxidation at High Temperatures
Authors: Warnatz Jürgen
Published: July 2012

The detailed knowledge of combustion mechanisms is important, for example for the control of (kinetically determined) pollutant formation (e.g. NO, hydrocarbons, soot), for ignition problems, or for the extrapolation to technologically important but experimentally inaccessible condition. – In this review it is described how by suitable separation and elimination of unimportant reactions a mechanism is developed with the aid of the present kinetic data for the elementary reactions involved. This mechanism explains, without fitting, the currently available experimental results for laminar premixed flames of alkanes, alkenes and acetylene (flame velocity and structure of free flames, concentration and temperature profiles in burner‐stabilized flames). These experimental results are simulated by the solution of the corresponding conservation equations with suitable models describing diffusion and heat conduction in the multicomponent mixture considered. – In lean and moderately rich flames the hydrocarbon is attacked by O, H, and OH in the first step. These radicals are produced by the chain‐branching steps of the oxyhydrogen reaction. The alkyl radicals formed in this way always decompose to smaller alkyl radicals by fast thermal elimination of alkenes. Only the relatively slow thermal decomposition of the smallest alkyl radicals (CH3 and C2H5) competes with recombination and with oxidation reactions by O atoms and O2. This part of the mechanism is rate‐controlling in the combustion of alkanes and alkenes, and is therefore the reason for the similarity of all alkane and alkene flames. – In rich flames of aliphatic fuels, acetylene becomes a very important intermediate leading to soot precursors and to Non‐Zeldovich‐NO. Details of the reaction mechanisms are not yet known.
Rate Constants and CH3O Product Yield of the Reaction OH + CH3OH → Products
Authors: Hägele J. , Lorenz K. , Rhäsa D. , Zellner R.
Published: July 2012

Absolute rate constants and CH3O product yield for the reaction of OH radicals with methanol have been determined using a combined laser photolysis/resonance fluorescence (laser induced fluorescence) technique. The rate coefficient for total OH (kg = k1 + k2) is found to be kg = (1.2 ± 0.3) · 10−11 exp[–(810 ± 50) K/T] cm3/molecule · s over the temperature range 295–420 K. – The branching ratio of CH3O formation, ϕ = k1/k1 + k2, where (1) OH + CH3OH → CH3O + H2O and (2) OH + CH3OH → CH2OH + H2O, is found to be 0.11 ± 0.03 and 0.22 ± 0.07 at 298 and 393 K, respectively. From the temperature dependence of ϕ it is predicted that channel (1) is dominant in the combustion temperature region.
Temperaturmessung in sich ausbreitenden Flammenfronten (Methan/Luft, p0 = 1 bar, λL = 1,2) mit Hilfe funkenangeregter Fluoreszenz (SIF)
Authors: Saggau B.
Published: July 2012

A premixed combustible mixture of methane/air of an air/fuel equivalence ratio λL = 1.2 and different pressures 0.5 ≤ p0 ≤ 1 bar is ignited in a cylindrical combustion chamber. The temperature profile of the generated flame front, which is travelling laminarly through the chamber, is measured by spark induced fluorescence (SIF), at which the gas at the right position is excited perpendicularly through the flame front to fluorescence by a short electrical spark. Each temperature is measured as a rotational temperature, delivered from the O – O rotational band of the 2. positive system of nitrogen, the main component in the chamber. Using a vidicon camera and an optical multichannel analyzer, a whole temperature profile can be measured by one single shot. At p0 = 1 bar the measured flame front thickness is LT = 0.5 mm and the maximum temperature of the s‐shaped flame front is measured to T ≈ 2100 K.
Structural Description of Water‐in‐Oil Microemulsions Using Electrical Resistance
Authors: Singh H. N. , Swarup Shanti , Singh R. P. , Saleem S. M.
Published: July 2012

The present article presents data on the formation and characterization of water in oil (W/O) microemulsion systems composed of ionic surfactants‐water‐benzene‐n‐alcohols (C4 – C8). The influence of the alcohol chain length and surfactant concentration, on the formation of microemulsion systems, has been investigated. When the amount of benzene or water was increased, the microemulsion system's appearance changed from clear to bluish to turbid. The transitions were identified on the basis of both visual appearance and specific resistance measurements. A dramatic change in the specific resistance was observed for the transitions. This was rationalized by assuming a change in the water structure from spherical to cylindrical to lamellae type. The critical nwater/noil ratio (Vc), for stable microemulsion system was calculated with the help of viscosity measurements.
Orientation and Spectral Characteristics of the Azobenzene Chromophore in the Ammonium Bilayer Assembly
Authors: Shimomura M. , Ando R. , Kunitake T.
Published: July 2012

Azobenzene‐containing, single‐chain ammonium amphiphiles in which the alkyl chain length in the tail and spacer portions was systematically varied were prepared, and their aggregation behavior in water was studied by electron microscopy, differential scanning calorimetry and absorption spectroscopy. These amphiphiles exist as molecular dispersions, hydrated microcrystals, micelles, or bilayers. The formation of stable bilayers was deduced on the basis of three criteria which include the spectral agreement between aqueous dispersions and the corresponding cast films. Stable bilayers were obtainable when the sum of tail and spacer is not smaller than C14 to C16, and the tail is at least C8. Double‐chain ammonium amphiphiles which possess an octadecyl chain in addition to the azobenzene‐containing chain were prepared and shown to form stable bilayers. The absorption spectrum reflected the aggregate structure. In particular, the bilayer spectra were classified into four types: type A (λmax ca. 300 nm) for the parallel chromophore orientation (H aggregate), type B (330 – 340 nm) for the dimeric chromophore, type C (ca. 355 nm) for the isolated chromophore, and type D (360–390 nm) for the head‐to‐tail chromophore orientation (J‐like aggregate). Liquid‐crystalline bilayers gave type B spectra, while crystalline bilayers gave either of types A, B, and D, depending on the alkyl chain length. Finally, various examples of spectral control were discussed in relation to the present results.
The Photochemistry of 1,3‐Diphenyltriazene in Various Media. I: Photolysis in Liquid Solutions
Authors: Baro J. , Dudek D. , Luther K. , Troe J.
Published: July 2012

1,3‐Diphenyltriazene has been irradiated at 360 nm in various liquid solutions. Reversible trans‐cis photoisomerization has been detected in solvents which do not form hydrogen bonds. Irreversible photolysis is observed with an appreciable amount of cage recombination products in all solvents. This reaction is well suited for a study in solid environments.
Thermodynamics of Polydimethylsiloxane Solutions. II. Application of an Extended Flory‐Theory
Authors: Heintz A. , Neff B. , Lichtenthaler R. N.
Published: July 2012

Extensive experimental data of thermodynamic excess properties of Polydimethylsiloxane (PDMS)/solvent systems have been used for testing the consistency of Flory's theory of polymer solutions. The weakness of this theory in predicting chemical potentials and heat of dilutions consistently has been removed by introduction of an improved formula of the combinatorial entropy and a variable concentration dependent surface to volume ratio of the PDMS molecule. – A method has been developed which allows the determination of the parameters needed for the extended theory from calorimetric data only.
A Generalized van der Waals Equation of State II. Excess Heat Capacities of Mixtures Containing Cycloalkanes (C5, C6) Methylcycloalkanes (C5, C6) and n‐Decane
Authors: Siddiqi M. A. , Svejda P. , Kohler F.
Published: July 2012

The excess heat capacities, C of methylcyclohexane + cyclopentane, methylcyclopentane + cyclopentane, cyclohexane + methylcyclopentane, methylcyclohexane + methylcyclopentane and n‐decane + methylcyclopentane were measured by a Picker flow microcalorimeter at 293.15 K and atmospheric pressure. Also C‐values were calculated for these systems using a generalized van der Waals model augmented by the Boublik‐Nezbeda equation for hard convex bodies in a manner outlined in a previous publication. The measurements pointed to packing effects caused by the different molecular shapes. The calculations reproduced the experimental results rather well and supported the interpretation of the experimental results. The van der Waals model underlying these calculations is further substantiated by the measurements.
Experiments and Theoretical Considerations on the Solution of Oxygen in Binary Metal Alloys
Authors: Anik S. , Frohberg M. G. , Kapoor M. L.
Published: July 2012

By means of EMF measurements the activities of oxygen in the system copper‐oxygen‐bismuth were determined at 1473 K. From the results the unknown phase boundaries could be fixed. The miscibility gaps of the binary systems copper‐oxygen and bismuth‐oxygen extend far into the ternary system. The solubility of oxygen in homogeneous copper‐bismuth melts first shows an increasing tendency; later it decreases and arrives at a minimum at NCu/NBi = 4/6. In order to explain the solubility of oxygen in binary molten alloys a statistical model was derived. It was supposed that the oxygen atoms occupy a part of the interstitial lattice sites whereas the metal atoms occupy the substitutional sites. The model permits the determination of thermodynamic data of oxygen in the melt. Moreover it is possible to calculate the self‐interaction parameter of the interstitially solved component. The theoretical approach is checked by the own experimental results.
The Effect of Oxidation of Cu0.35V2O5 on its Activity in the Catalytic Oxidation of Carbon Monoxide
Authors: van den Berg J. , Brans‐Brabant J. H. L. M. , van Dillen A. J. , Geus J. W. , Lammers M. J. J.
Published: July 2012

The effect of oxidation of a copper‐vanadium bronze (β‐Cu0.35V2O5) catalyst was examined by studying the kinetics of the oxidation of CO between 200°C and 525°C in a continuous flow reactor. At 500°C the catalyst appeared to be slowly oxidised in an excess of oxygen to a mixture of CuV2O6 and highly disordered V2O5. – The solid‐state transformation could be inferred from the results concerning the catalytic activity, thermal analysis (TG, DTG, DTA), X‐ray powder diffraction, electron spin resonance, BET and scanning electron microscopy. – The kinetics can be described by an associative mechanism at temperatures up to about 400°C, whereas the reaction proceeds via the reduction‐oxidation mechanism at higher temperatures. This holds irrespective of the degree of oxidation of the catalyst. An anomalous order of the reaction‐rate with respect to oxygen was ascribed to a substantial amount of lattice defects present in the V2O5 matrix. These defects appear in a stabilising configuration.
Besteht ein Zusammenhang zwischen der Zahl primärer Rußpartikel und der Ionen‐dichte bei der Kohlenwasserstoffpyrolyse im thermischen Plasma?
Authors: Spangenberg H.‐J. , Börger I. , Lachmann J.
Published: July 2012

During the pyrolysis of hydrocarbons in the plasma jet black carbon is formed, possessing special conditions. The primary particles of black carbon have diameters in the range of 3…7 nm. The measured ion density alongside the axis of the plasma jet increases in the region of the formation of the soot. Finally the problem is discussed whether a connection exists between the number of the formed primary particles of black carbon and the ion density in this region.
The Adsorption of CO on a Porous Pt‐Electrode in Sulfuric Acid Studied by DEMS
Authors: Wolter O. , Heitbaum J.
Published: July 2012

The adsorption and oxidation of CO on porous Pt‐electrodes was studied with Differential Electrochemical Mass Spectroscopy (DEMS). The following results were obtained:

1. When CO is removed from the solution after adsorption has taken place, the adsorbed species mainly occupies two Pt‐sites. It is oxidized within two peaks at 0.52 and 0.73 V giving CO2 thereby consuming 2 electrons. No evidence of “reduced CO” was found independent of the adsorption potential.

2. When CO is present in the solution, a physisorbed species reversibly bound to one Pt‐site covers about 60% of the electrode surface. It is oxidatively desorbed at 0.85 V.
Oxygen and Chlorine Evolution on Ruthenium‐Iron‐Disulphide Mediated by Low Energy Photons
Authors: Kühne H.‐M. , Tributsch H.
Published: July 2012

Incorporation of iron (a few percent) into RuS2 (ΔEG = 1.85 eV) changes the energy gap to ΔEG = 1.1 eV. The resulting n‐type compound, which can approximately be described by “Ru1‐xFexS2”, is able to evolve oxygen and chlorine from aqueous electrolytes utilizing visible and near infrared light under energy gain with high quantum efficiency (23% to 60%). — Oxygen and chlorine evolution, mediated by infrared light, is found clearly below the respective redox potentials. Under such conditions of energy conversion the electrode does not indicate signs of photocorrosion. At more extreme electrode potentials traces of a ruthenium tetroxide species are observed — Attempts are made to correlate the (inhomogeneous) distribution of iron in Ru1‐xFexS2 electrodes with photocurrent spectra and scanning laser spot current patterns. — Experiments show that the electrode surface is subject to chemical changes during the photoreaction with water. They are investigated by means of capacity measurements, dynamic current voltage sweeps, and systematical variations of redox potentials in the electrolyte. — A model is presented which accounts for the role of iron in this compound and which explains its photoelectrochemical advantages compared to pure RuS2.
Untersuchung der Spektralsensibilisierung durch Verwendung einer chemischen Modifizierungstechnik
Authors: Nakao Masashi , Watanabe Tadashi , Itoh Kiminori , Fujishima Akira , Honda Kenichi
Published: July 2012

Spectral sensitization process was examined by measuring the fluorescence intensities and the photocurrents caused by rhodamine B esterically bound with the surface species of SnO2. It was found that about 20% of its fluorescence intensity were reduced by the Sn02 substrate, and this value was well coincident with the maximum quantum efficiency of the sensitized photocurrent. From the results the charge transfer mechanism of supersensitization is discussed.
Study of the Vaporization of Amalgams with a New Knudsen Cell — Mass Spectrometer System. Part II: The Compounds Mg5Hg3, Mg2Hg, Mg5Hg2, and Mg3Hg and the Formation Enthalpies of All Compounds of the Mg — Hg System
Authors: Hilpert K.
Published: July 2012

Evaporation of the compounds Mg5Hg3(s), Mg2Hg(s), Mg5Hg2(s), and Mg3Hg(s) was studied using a Knudsen cell‐mass spectrometer system. They evaporate according to the equations

2 Mg5Hg3(s) ⇄ Hg(g) + 5 Mg2Hg(s), (1)

5 Mg5Hg(s) ⇄ Hg(g) + 2 Mg5Hg2(s), (2)

3 Mg5Hg2(s) ⇄ Hg(g) + 5 Mg3Hg(s), and (3)

Mg3Hg(s) ⇄ Hg(g) + 3 MgHg(s) (4)

The Hg partial pressures of Eqs. (1) to (4) are

log(pPa) = (4973.1 ± 60.3) K/T + (9.886 ± 0.12) (440 ‐ 540 K),

log(pPa) = (6605.6 ± 69.1) K/T + (10.91 ± 0.11) (499 ‐ 7110 K),

log(pPa) = (7118.3 ± 116.5) K/T + (10.91 ± 0.19) (548 ‐ 9890 K), and

log(pPa) = (7502.3 ± 58.8) K/T + (11.29 ± 0.10) (525 ‐ 695 K).

The enthalpy changes of reactions Eqs. (1) to (4) were determined by the second and third law method. Formation enthalpies in kJ mol−1 at 298 K were obtained as –60.5 ± 4.3 (MgHg2), –56.4 ± 1.7 (MgHg), –217.1 ± 7.3 (Mg5Hg3), –79.8 ± 2.8 (Mg2Hg), –166.0 ± 6.8 (Mg5Hg2), and –84.2 ± 4.0 (Mg3Hg) for the compounds given in parentheses. Gibbs energies of formation of these compounds are also given. Formation entropies are discussed.
Diffusion in Liquid Mixtures of Light and Heavy Water
Authors: Weingärtner Hermann
Published: July 2012

With the aid of the diaphragm cell technique tracer diffusion of tritium‐labelled water in H2O—D2O mixtures has been measured at 8, 25 and 45°C. In addition, self‐diffusion coefficients in H2O—D2O mixtures have been determined by the proton n.m.r. spin‐echo technique. Paralleling the behaviour of the mutual diffusion coefficient, the tracer diffusion coefficients exhibit small negative departures from a linear concentration dependence which usually is predicted for diffusion in ideal systems.
Core and Valence Electron Binding Energies of FeI2 and Stabilities of Gas Phase Species
Authors: Grade M. , Rosinger W. , Dowben P. A.
Published: July 2012

The core and valence levels for FeI2 have been determined using XPS, UPS and electron impact techniques. The gaseous fragmentation products of FeI2 have also been studied. By combining the present data with available published data, thermodynamic cycles are constructed for gaseous neutral species, ionic gas‐phase species and molecular iodine adsorption on iron in an attempt to systematically characterize iodine interaction with iron. Comparisons with the other ferrous halides are also drawn.
Vaporization of Sodium Iodide and Thermochemistry of (NaI)2(g) and (NaI)3(g): An Experimental and Theoretical Study
Authors: Hilpert K.
Published: July 2012

The evaporation of NaI(s) has been investigated by high temperature mass spectrometry and mass‐loss Knudsen effusion experiments with a micro recording vacuum balance. The gaseous phase in equilibrium with NaI(s) consists of NaI(g), (NaI)2(g), and (NaI)3(g). Partial pressures given by the equations

log(pPa) = –(9.479±0.13) 103/T + 11.49±0.17 for (NaI)(g),

log(pPa) = –(10.953±0.06) 103/T + 12.72±0.06 for (NaI)2(g), and

log(pPa) = –(13.543±0.11) 103/T + 13.58±0.15 for (NaI)3(g)

were determined in the temperature range of the measurements 674 to 843 K. Sublimation enthalpies were obtained in kJ mol−1 for the reactions

i NaI(s) ⇄ (NaI)i(g) (i = 1,2,3) (1)

as ΔH00 = 196.3±4.4 (i = 1), ΔH00 = 226.8±1.3 (i = 2), and ΔH00 = 284.8±6.6 (i = 3). The enthalpy changes of the dimerization and trimerization reactions

i NaI(g) ⇄ (NaI)i(g) (i = 2,3) (2)

are ΔH00 = –165.8±8.9 (i = 2) and ΔH00 = –304.1±14.8 kJ mol−1 (i = 3). The given enthalpy values are averages of the values determined with the second and third law method for each of the reactions Eqs. (1) and (2). Molecular parameters were estimated for (NaI)3(g) and enthalpy increments as well as Gibbs energy functions computed with these data are given. The enthalpy change of the trimerization reaction, Eq. (2) (i = 3), was predicted with Pauling's model for alkali halides as ΔH00 = –293.4 kJ mol−1 which agrees well with our experimental value. Entropies of sublimation to monomer, dimer, and trimer as well as dimerization and trimerization entropies were obtained at 750 K as 130.1, 148.0, 173.9, –112.2, and –216.4 J mol−1 K−1, respectively. Appearance potentials of 8.7±0.1 (Na+), 14.4±0.2 (I+), 8.2±0.1 (NaI+), 8.6±0.1 (Na2I+), 7.5±0.1 (Na2I2+), 8.3±0.1 (Na3I2+), and 8.4±0.1 (Na3I3+) were determined in V for the ions given in parentheses. The data obtained are discussed in the context of literature data.
Titanium/Chromium Oxide Composite Electrodes – Basic Characteristics
Authors: Beck F. , Schulz H.
Published: July 2012

Ti sheet has been activated by the ceramic method, starting from solutions of Cr‐III‐chloride and Ti‐IV‐butanolate in isopropanole:

A) via firing in air, TA = 350 – 750°C.

B) As (A), but subsequent annealing in vacuum at TV = 450 – 850°C.

Coulometric, chemical and X ray analysis led to the following results: Electrode A has a layer of α‐Cr2O3 at TA ≥ 450°C, which is anodically oxidized in 1 M H2SO4. With slow cyclic voltammetry, half peak potential is Up/2 (SHE) = 1.77 V. CrO3, which is formed, dissolves. The charge involved in this process is proportional to layer thickness. Electrodes fabricated by mode B carry predominantly a chromium layer at TV ≥ 700°C. These electrodes exhibited a dissolution peak at Up/2 (SHE) = 1.32 V (CrO3). It relates to the transpassive dissolution of chromium. – Steady state and nonsteady anodic and cathodic processes have been investigated with these new electrodes. Their application for electroorganic oxidations via redox catalysis is proposed.
Production and Properties of Atomic and Molecular Microclusters
Authors: Recknagel E.
Published: July 2012

This review reports on the microcluster research at Konstanz University. Metallic and ionic microclusters are produced by an inert gas condensation technique, while clusters from different gases are obtained by adiabatic expansion. An electronic time of flight‐mass‐spectrometer is used for cluster detection. Fragmentation processes, pronounced intensity distributions and the disintegration of multiple charged microclusters are discussed. An example of intramolecular reaction in organic clusters is given.
Comparison between Electron Diffraction Patterns of Ar, CH4 and N2 Clusters and Related Structures
Authors: Farges J. , De Feraudy M. F. , Raoult B. , Torchet G.
Published: July 2012

Clusters of Ar, CH4 and N2 are produced in a free jet expansion and studied by electron diffraction. Large clusters comprising several thousand molecules have a crystalline structure. Simple models have been constructed on the basis of the same fcc structure, with a particular attention paid to molecular motions in the case of N2. Small clusters with a few ten molecules have an amorphous structure, namely the polyicosahedral structure which has been established previously for small Ar clusters.
A Chemical Reaction and Charge Transfer in Heteroclusters of Fluorobenzene
Authors: Dimopoulou‐Rademann U. , Rademann K. , Bisling P. , Brutschy B. , Baumgärtel H.
Published: July 2012

Heterodimers of fluorobenzene (FB) with 1,4‐dioxane and methanol were synthesized in a seeded supersonic beam and studied by resonant two‐photon ionization combined with TOF mass spectrometry. The electronic spectra near the origin of the S1(π π*)← S0 transition of FB revealed solvent induced shifts and spectral features due to the excitation of van der Waals modes. In addition, strong dynamic behaviour of the photo‐ionized dimers could be observed.
Metal‐Clusters: Preparation, Properties, Theory
Authors: Schumacher E. , Kappes M. , Marti K. , Radi P. , Schär M. , Schmidhalter B.
Published: July 2012

Methods for the production of small molecules Mn with 2 < n < 100 are critically discussed and explained. The characterization must take into account the existence of a size‐distribution as a consequence of the generation process. Several new spectroscopic methods have been developed for the observation of single particle properties in these mixtures. They all make use of the mass spectrometer as detector. Discussed are the ionization‐potentials as function of size which do not reveal an abrupt change in electronic properties during the transition from a discrete molecular to a metallic behaviour. Certain aspects of the optical spectra of a few diatomic and triatomic clusters are then presented. Quantumchemical elucidations in the small cluster‐range are necessary and very helpful. However, more realistic computations are needed to understand spectra.
Theoretical Aspects of the Electronic Structure and the Stability of Small Clusters
Authors: Koutecký Jaroslav , Pacchioni Gianfranco
Published: July 2012

The investigation of the small clusters of metallic and nonmetallic elements shows that some clusters have some features common with the crystals (cluster bond lengths and cluster bond angles) and simultaneously other stable cluster forms exhibit very specific properties (for example, the planarity of Ia, IIIa, IVa‐tetramers, and Li6, Li7 clusters with pentagonal symmetries). The cluster stability and geometry can be generally well explained from the electronic properties of constituent atoms. Studies of the interactions of clusters with atoms and small molecules yield results which are interesting for the theory of chemisorption (for example, the donation, back‐donation picture of the CO‐metal interaction) and for the understanding of the electronic structure of organometallic compounds.
Calculation of Cluster Geometries with the Help of Hellmann‐Feynman Forces
Authors: Martins José Luís , Buttet Jean , Car Roberto
Published: July 2012

The equilibrium geometries of Nan clusters (n ⩽ 7) are calculated by letting randomly generated clusters relax under the action of the Hellmann‐Feynman forces. We find that clusters with five atoms or less have a planar structure whereas larger clusters have closely packed three‐dimensional geometries. The calculated adiabatic ionization potentials are in good agreement with the experimental appearance potentials.
Cluster Size Separation by Crossjet Deflection
Authors: Gspann J.
Published: July 2012

Intersection of a beam of clusters with an uncondensed free jet leads to a size dependent cluster deflection. For large clusters the size distribution function may be obtained from the spatial distributions of mass flow and cluster sizes. Focusing of the average cluster trajectories results from the passage of regions of differing integral crossjet flow or of differing crossjet flow inclination. The limit of the resolution depends upon the prevailing type of collision, elastic reflection leading to a minimum beam spread proportional to the square root of the ratio of the beam and jet particle masses.
Optical Properties of Small Metallic Particles
Authors: Bennemann K. H. , Reindl S.
Published: July 2012

A brief review of the electrodynamical properties of small metallic clusters is presented. Experimental results for absorption, photo‐yield and van der Waals interaction are given. Also, recent progress of the theory for the interaction between light and small metallic clusters is discussed. Comparison between experiment and theory shows that presently theory is not able to calculate correctly most of the electrodynamical properties of small clusters.
Gas Phase Chemical Reactions of Transition Metal Clusters
Authors: Riley S. J. , Parks E. K. , Pobo L. G. , Wexler S.
Published: July 2012

Transition metal clusters are generated by pulsed laser vaporization and nucleation in a continuous gas‐flow reactor. Gaseous reactants are added downstream, and the resulting products expanded into vacuum, collimated into a molecular beam, and analyzed by pulsed laser nonresonant multiphoton ionization and time‐of‐flight mass spectrometry. Oxidation of iron clusters is found to yield iron‐deficient species with the approximate composition Fe0.9O. Nickel cluster oxidation gives oxygen‐deficient products having the formula NiO0.75. The relation of these results to bulk metal oxidation is discussed. Hydrogenation/deuteration of iron clusters is described, and evidence for H‐D exchange on iron clusters is presented. Reaction of iron clusters with CO is also reported.
Excitonic Clusters and the Phase Transitions in Fluid Mercury
Authors: Turkevich L. A. , Cohen M. H.
Published: July 2012

We review the metal‐nonmetal transition in expanded liquid mercury and the dielectric transition in dense mercury vapor. Previous explanations for these transitions are found to be deficient. We propose that the high‐temperature, high‐pressure fluid is an excitonic insulator phase. The condensation instability of the Frenkel excitons is shown to result from improved coordination within the fluid. The phase diagram for the excitonic insulator naturally explains both the metal‐nonmetal and the dielectric transitions.
Magnetic Measurements on Stable Fe(0) Microclusters. Part I
Authors: Schmidt F. , Stapel U. , Walther H.
Published: July 2012

Fe(0) microclusters have been isolated in a zeolite matrix. The magnetization isotherm at 4.2 K has been analyzed in terms of a sum of Brillouin functions corresponding to a distribution of cluster sizes. Each function represented a fraction of individual clusters with total cluster spin quantum number (N · S). The (N · S)‐value of clusters with an average of 7 atoms per cluster was found to be 4.