Showing papers in "Zeitschrift für Physikalische Chemie in 2009"
TL;DR: In this paper, the Solid Electrolyte Interphase (SEI) concept is introduced and the different requirements on the electrolyte and on the SEI formation process in the presence of various anode materials (metallic lithium, graphitic carbons, and lithium storage metals/alloys), in particular, similarities and differences, are highlighted.
Abstract: Abstract In this chapter, the Solid Electrolyte Interphase (SEI) concept is introduced and the different requirements on the electrolyte and on the SEI formation process in the presence of various anode materials (metallic lithium, graphitic carbons, and lithium storage metals/alloys), in particular, similarities and differences, are highlighted. The difficulties to understand and analyze the SEI characteristics and composition are discussed by examples.
667 citations
TL;DR: In this paper, the authors compared optical and molecular-beam mass spectrometry (MBMS) results obtained with several sampling configurations with the aim of comparing them to combustion modeling.
Abstract: New operating regimes for engines and combustors and the advocated use of non-conventional transportation fuels demand investigation of the combustion chemistry of different classes of chemicals, especially under premixed conditions. Detailed species compositions during combustion are needed to estimate hazardous emissions, and models for their prediction must be validated for the intended combustion conditions. Molecular-beam mass spectrometry (MBMS) is a common technique to measure quantitative species concentrations in flames. It is widely employed to characterize the flame chemistry of laminar premixed combustion, and it has been complemented with optical measurements for the detection of a number of molecular species and radicals. Significant progress has been made in recent studies through the introduction of synchrotron-based MBMS instruments. They have improved the identification process by using tunable vacuum-ultraviolet radiation for photoionization of the species to be detected, and isomer-specific measurements are now almost routinely possible. Along with quantitative species measurements, the temperature profile is needed as input parameter for chemical kinetic modeling. It is usually determined either using thermocouples or laser spectroscopic techniques. It is an ongoing discussion how sampling probes affect these measurements, and how MBMS results can be compared to combustion modeling. The present article is intended to contribute to this discussion by providing optical and MBMS results obtained with several sampling configurations.
152 citations
TL;DR: A recent overview of recent advances in the field of surface chemistry with tetrapyrroles can be found in this paper, where the authors discuss the following aspects: intramolecular conformation and supramolescular ordering, electronic interaction with the substrate, surface-confined synthesis, and ligand-related effects such as the surface trans effect.
Abstract: Abstract Recent years have seen rapid progress in the field of surface-confined coordination chemistry. Adsorbed metal complexes of tetrapyrroles (porphyrins, phthalocyanines, corroles) are especially interesting in this context, since they combine a planar structure-determining element with an active site. While earlier studies of adsorbed metallo-tetrapyrroles mainly addressed aspects of molecular self-assembly, the focus of interest has shifted gradually to electronic structure and chemical reactivity. This article gives an overview of recent advances in the field of surface chemistry with tetrapyrroles. In particular, the following aspects will be discussed: intramolecular conformation and supramolecular ordering, electronic interaction with the substrate, surface-confined synthesis, and ligand-related effects such as the surface trans effect.
85 citations
TL;DR: In this article, the authors investigated the extraction of micro amounts of calcium and strontium by a nitrobenzene solution of hydrogen dicarbollylcobaltate (H+B-) in the presence of octyl-phenyl-N,N-diisobutylcarbamoylmethyl phosphine oxide (classical CMPO, L) has been investigated.
Abstract: Abstract Extraction of microamounts of calcium and strontium by a nitrobenzene solution of hydrogen dicarbollylcobaltate (H+B-) in the presence of octyl-phenyl-N,N-diisobutylcarbamoylmethyl phosphine oxide (“classical” CMPO, L) has been investigated. The equilibrium data have been explained assuming that the complexes HL+, HL2+, CaL2+, CaL22+, CaL32+, SrL22+, SrL32+ and SrL42+ are extracted into the organic phase. The values of extraction and stability constants of the species in nitrobenzene saturated with water have been determined.
42 citations
TL;DR: In this article, rate constants for capture-controlled ion-molecule reactions and ion fragmentations are analyzed using phase space theory and rigidity factors accounting for the anisotropy of the potentials.
Abstract: Abstract Rate constants for capture-controlled ion-molecule reactions and ion fragmentations are analyzed. It is shown that exothermic ion-molecule reactions governed by long-range potentials (class I reactions) and ion fragmentations and the reverse ion-molecule associations with large contributions from valence potentials (class II reactions) require different treatments. The results are expressed by phase space theory and rigidity factors accounting for the anisotropy of the potentials. Thermal and specific rigidity factors, frigid(T) and frigid(E,J)respectively, need to be internally consistent. Simplified two-parameter expressions for the two rigidity factors are designed with the hope that fitting of the parameters to limited experimental data allows one to extrapolate to unexplored ranges of conditions.
37 citations
TL;DR: In this paper, the adsorption of ethene (C2H4) has been studied on Pd(111) and ordered Sn/Pd(1) surface alloys using temperature programmed desorption (TPD), ultraviolet photoelectron spectroscopy (UPS), high-resolution electron energy loss spectroscopic (HREELS), and low energy electron diffraction (LEED).
Abstract: Abstract The adsorption of ethene (C2H4) has been studied on Pd(111) and ordered Sn/Pd(111) surface alloys using temperature programmed desorption (TPD), ultraviolet photoelectron spectroscopy (UPS), high-resolution electron energy loss spectroscopy (HREELS), and low energy electron diffraction (LEED). Two surface alloys were prepared by thermal treatment of Sn-films, which were vapor deposited on Pd(111) at room temperature. Depending on the preparation conditions, surface alloys giving a p(2×2) or a (√3×√3)R30° LEED pattern were produced. Below 250 K ethene adsorbs on pure Pd(111) in an undissociated – but substantially distorted – form relative to the molecular structure in the gas phase: HREELS suggests an adsorption in the di-σ bonded state. A π-bonded ethene species was, however, found to coexist with this strongly rehybridized form, probably as a result of hydrogen coadsorbed from the residual gas. TPD and annealing experiments followed by UPS and HREELS indicated that most of the adsorbed ethene desorbs reversibly in the temperature range between 150 K and 350 K, while a small amount dehydrogenates. After adsorption at room temperature, ethylidyne (≡CCH3) has been identified as the most important species. Alloying Pd(111) with Sn results in a decreasing ethene-substrate interaction with increasing Sn-content in the topmost layer of the substrate. Only π-bonded ethene was formed on both surface alloys and decomposition reactions were suppressed.
33 citations
Abstract: Abstract From extraction experiments and γ-activity measurements, the exchange extraction constants corresponding to the general equilibrium M+(aq)+CsL+(nb) ↔ ML+(nb)+Cs+(aq) taking place in the two-phase water-nitrobenzene system (M+ = K+, Rb+, Tl+; L = hexaethyl calix[6]arene hexaacetate; aq = aqueous phase, nb = nitrobenzene phase) were evaluated. Further, the stability constants of the ML+ complexes in water saturated nitrobenzene were calculated; they were found to increase in the cation order K+< Rb+< Tl+.
31 citations
TL;DR: In this paper, the reaction between diperiodatocuprate(III) and L-tryptophan in aqueous medium at a constant ionic strength of 0.20 mol dm-3 was studied spectrophotometrically at 298 K.
Abstract: Abstract The oxidation of L-tryptophan (L-TRP) by diperiodatocuprate(III) (DPC) in aqueous alkaline medium at a constant ionic strength of 0.20 mol dm-3 was studied spectrophotometrically at 298 K. The reaction between DPC and L-tryptophan in alkaline medium exhibits 1:4 stoichiometry (L-tryptophan: DPC). The reaction is of first order in [DPC] and has less than unit order in [L-TRP] and negative fractional order in [periodate] and [alkali]. Intervention of free radicals was observed in the reaction. The oxidation reaction in alkaline medium has been shown to proceed via a DPC- L-tryptophan complex, which decomposes slowly in a rate determining step followed by other fast steps to give the products. The main products were identified by spot test, IR, 1H NMR, 13CNMR and LC-MS spectral studies. The reaction constants involved in the different steps of the mechanism were calculated. The activation parameters with respect to slow step of the mechanism were computed and discussed and thermodynamic quantities were also determined.
31 citations
TL;DR: In this article, the interaction of hydrogen with bimetallic surfaces is assessed and discussed using structurally well defined PdAu and PtRu single crystal surfaces as model systems.
Abstract: Abstract The interaction of hydrogen with bimetallic surfaces is assessed and discussed using structurally well defined PdAu and PtRu single crystal surfaces as model systems. The description is based on a correlation between the hydrogen adsorption behavior and the presence and abundance of specific bimetallic nanostructures. The latter are determined quantitatively by high resolution scanning tunneling microscopy. Following the changes in the hydrogen adsorption behavior on surfaces with systematically varied composition and thus varying concentrations of specific structural elements and adsorption ensembles allows a direct correlation between structural and chemical properties and thus to identify the adsorption characteristics of individual adsorption ensembles. This provides a structural basis for parallel theoretical studies, which are essential for a systematic understanding of the complex changes in the adsorption properties.Based on results from experimental studies and calculations, the role of electronic strain and ligand effects, including lateral and vertical ligands, as well the influence of geometric ensemble effects on the hydrogen adsorption characteristics are discussed. The distinct differences between surfaces modified by a monolayer or monolayer islands of a second metal and mixed surfaces such as surface alloys or alloy surfaces are discussed in these terms.
30 citations
TL;DR: In this article, the electronic structure properties of two pristine and defected models of zigzag and armchair boron nitride nanotubes (BNNTs) are computationally studied.
Abstract: Abstract The electronic structure properties of two pristine and defected models of zigzag and armchair boron nitride nanotubes (BNNTs) are computationally studied. Chemical shielding (CS) tensors at the sites of various boron-11 (B-11) and nitrogen-15 (N-15) nuclei in each of the optimized structures are calculated and converted to isotropic and anisotropic chemical shieldings (ICS and ACS, respectively). The ACS values revel that boron atoms at the end of nanotube play the major role in determining the characteristic properties of the BNNTs. Defects are considered by removing a B-N bond from the pristine models yielding B-B and N-N bonds in the zigzag but not in the armchair BNNT. The changes of the CS tensors at the sites of those B-11 and N-15 nuclei in the B-B and N-N bonds are the most significant among other nuclei. The calculations are performed employing BLYP method and 6–31G* standard basis set using GAUSSIAN 98.
30 citations
TL;DR: In this article, the topology of ternary phase diagrams of systems that are forming salts, cocrystals, solvates, or hydrates is discussed based on a simple mathematical model.
Abstract: Abstract The topology of ternary phase diagrams of systems that are forming salts, cocrystals, solvates, or hydrates is discussed based on a simple mathematical model. The considerations include the thermodynamic stability of the multi-component crystal relative to the individual components, the character of the interactions in solution, the effect of relative solubility of the components, the consequences of using liquid components, the formation of multi-component crystals with different stoichiometry, and the competition between cocrystals or salts and solvates. Based on the characteristics of the phase diagrams, recommendations are provided as to an efficient design of salt formation and cocrystallization experiments.
TL;DR: In this article, a low-pressure, lean, laminar, premixed hydrogen/oxygen/argon flames seeded with iron pentacarbonyl (35−170 ppm Fe(CO)5) were modeled with detailed chemistry and the results were compared to laser-induced fluorescence imaging measurements of iron atom concentration and gas phase temperature.
Abstract: Abstract Low-pressure, lean, laminar, premixed hydrogen/oxygen/argon flames seeded with iron pentacarbonyl (35−170 ppm Fe(CO)5) were modeled with detailed chemistry and the results were compared to laser-induced fluorescence imaging measurements of iron atom concentration and gas-phase temperature. The model includes recent rate coefficients for the decomposition of iron pentacarbonyl and thermodynamic data. The simulated iron concentrations correspond well with the measurements with only minor discrepancies in the rise of the iron profiles at low Fe(CO)5 concentrations. In addition, it was shown that the mechanism is able to predict the effect of Fe(CO)5 on the flame speed also for lean conditions, where the model was not established yet. The major iron species, aside from atomic iron, in this flame are predicted to be FeOH and Fe(OH)2 with some FeO2 early in the flame. The observed increased flame temperatures in the presence of Fe(CO)5 are attributed to catalytic hydrogen recombination.
TL;DR: The most probable structure of the 1 · H3O+ complex species was derived by using quantum mechanical DFT calculations in this paper, where the hydroxonium ion H 3O+ is bound partly to thiocarbonyl sulphur atoms and partly to phenoxy oxygens of 1 by strong hydrogen bonds and other electrostatic interactions.
Abstract: Abstract From extraction experiments and γ-activity measurements, the extraction constant corresponding to the equilibrium H3O+(aq) + 1 · Na+(nb) ↔ 1 · H3O+ (nb) + Na+(aq) taking place in the two-phase water-nitrobenzene system (1 = p-tert-butylcalix[4]arene-tetrakis(N,N-dimethylthioacetamide); aq = aqueous phase, nb = nitrobenzene phase) was evaluated as log Kex (H3O+,1 · Na+) = –0.4±0.1. Moreover, the stability constant of the 1 · H3O+ complex in water saturated nitrobenzene was calculated for a temperature of 25 °C as log βnb (1 · H3O+) = 5.5±0.1. Finally, by using quantum mechanical DFT calculations, the most probable structure of the 1 · H3O+ complex species was derived. In this complex, the hydroxonium ion H3O+ is bound partly to thiocarbonyl sulphur atoms and partly to phenoxy oxygens of 1 by strong hydrogen bonds and other electrostatic interactions.
TL;DR: In this article, the diffusivity of two glass forming model systems, spodumene (LiAlSi2O6) and lithium metaborate (LiBO2), was examined using 7Li nuclear magnetic resonance (NMR) spin-lattice relaxometry and dc conductivity measurements.
Abstract: Abstract In the present study the Li diffusivity in nanostructured samples of two glass forming model systems, spodumene (LiAlSi2O6) and lithium metaborate (LiBO2), was examined using 7Li nuclear magnetic resonance (NMR) spin-lattice relaxometry and dc conductivity measurements. The nanostructured samples were prepared by high-energy ball milling of the respective crystalline starting material on the one hand and the corresponding glass on the other hand. The diffusivity of the glass exceeds that of the crystalline sample for both systems. However, when the crystalline samples are mechanically treated by ball milling the diffusivity is enhanced. Nevertheless, the diffusivity of these nanocrystalline samples remains lower than that of the corresponding glass. Surprisingly, when the glassy samples are treated in the same way the diffusivity decreases. After sufficiently long milling times the diffusivity of these nanoglassy samples approaches that of the nanocrystalline samples. This convergence effect seems to be due to structural relaxation processes as is suggested by supplementary infrared spectroscopy and 27Al, 12B magic angle spinning NMR measurements.
TL;DR: In this paper, the reactions of hydrogen atoms with phenyl radicals, H + C6H5 → products (1), and with benzene, H+C6H6 → products(2), have been studied behind reflected shock waves in the temperature range 1200-1350 K with argon as the bath gas.
Abstract: Abstract The reactions of hydrogen atoms with phenyl radicals, H + C6H5 → products (1), and with benzene, H + C6H6 → products (2), have been studied behind reflected shock waves in the temperature range 1200–1350 K with argon as the bath gas. H-atom resonance absorption spectrometry at 121.6 nm was used as detection technique. Hydrogen atoms and phenyl radicals were produced by thermal decomposition of C2H5I and C6H5I, respectively. Low initial concentrations (~1012–1015 cm-3) were employed to suppress consecutive bimolecular reactions as far as possible.The rate coefficients were determined from fits of the H atom concentration-time profiles in terms of a small mechanism. For reaction (1), a temperature-independent rate coefficient k1 = 1.3×10–10 cm3 s–1 was obtained at pressures around 1.3 bar. For the rate coefficient of reaction (2), the temperature dependence can be expressed as k2(T) = 5.8×10–10 exp(–8107 K/T) cm3 s–1, and a pressure dependence was not observed between 1.3 and 4.3 bar. The uncertainties of k1 and k2 were estimated to be ±40%.
TL;DR: In this article, the authors report recent efforts to understand the new MIT-Messina experimental discovery of a dynamic crossover at low temperatures in confined water, which they interpret in terms of a Widom line.
Abstract: Abstract We report recent efforts to understand the new MIT-Messina experimental discovery of a dynamic crossover at low temperatures in confined water. Preliminary calculations are not inconsistent with one tentative interpretation of this dynamic crossover as resulting from the system passing from the high-temperature high-pressure "HDL" side of the Widom line (where the liquid might display fragile behavior) to the low-temperature low-pressure "LDL" side of the Widom line (where the liquid might display strong behavior). The Widom line - defined to be the line in the pressure-temperature plane where the correlation length has its maximum - arises only if there is a critical point. Hence interpreting the MIT experiments in terms of a Widom line is of potential relevance to testing experimentally, for confined water, the liquid-liquid critical point hypothesis.
TL;DR: In this article, two newly synthesized Enaminone compounds were investigated at 20 to 50 ºC using weight loss and potentiostatic polarization techniques, and the results showed that the percentage inhibition efficiencies and surface coverage degrees increase with increasing additive concentration.
Abstract: Abstract Two newly synthesized Enaminone compounds ethyl-3-[(2-aminoethyl) amino]-2-butenoate (compound I) and ethyl-3-(2-aminoanilino)-2-butenoate (compound II)) in 0.5 M H2SO4 on AISI 316 have been investigated at 20 to 50 ºC using weight loss and potentiostatic polarization techniques. The percentage inhibition efficiencies and surface coverage degrees increase with increasing additive concentration. The inhibition is in both cases of a mixed anodic-cathodic nature. Differences in inhibition efficiency between compound I and II are correlated with their chemical structures. The inhibitors function through adsorption following Temkin isotherm in acid media. Activation energy (Ea) and Gibbs free energy (∆Gads) for adsorption of inhibitors are calculated. The values of ∆Gads decreased (attained more negative values) with increasing temperature.
TL;DR: In this paper, a method for global analysis of chemical kinetic models is discussed and applied to auto ignition of high hydrocarbons, mainly based on the concept of decomposition of motions and follows major steps of the ILDM method.
Abstract: In this paper a novel method for global analysis of chemical kinetic models is discussed and applied to auto ignition of high hydrocarbons. It is mainly based on the concept of decomposition of motions and follows major steps of the ILDM method. However, a very important difference of the suggested method is its ability of an explicit and global representation of the system decomposition as a standard singular perturbed system (SPS). The fact that the ILDM provides local information about the decomposition makes the ILDM quite accurate in description of the slow system dynamics, but for fast motions, which become very important in the context of ignition.extinction problems, there are up to now no reliable methods based on ILDM. Therefore, the current work is devoted to developing such a method which can be used efficiently for global analysis of the reaction mechanisms with subsequent formulation of explicit reduced models for unsteady combustion regimes like ignition processes. The suggested method is illustrated by a simple Lindemann kinetic model and then applied successfully to the auto ignition of a homogeneous n-heptane.air system.
TL;DR: In this paper, the authors investigated the self-diffusion coefficient, the shear viscosity and the thermal conductivity of a single component system interacting via a Gaussian core (GC) potential.
Abstract: Abstract In this study, we investigate the self-diffusion coefficient, the shear viscosity and the thermal conductivity of a single-component system interacting via a Gaussian core (GC) potential. The transport properties are studied by means of the Green-Kubo formulas calculated from molecular dynamics simulation. We show that, for certain state conditions, anomalous behaviour occurs for the diffusivity and the shear viscosity. Therefore, the Stokes-Einstein relation is violated for the GC fluid. We do not find anomalous behaviour for the thermal conductivity. We develop an equation of state for the deviation of the ideal gas pressure and we derive the excess entropy from this equation. Depending on the phase space region, the excess entropy also shows anomalous behaviour. We discuss recently developed scaling relationships between excess entropy and transport properties. Because the GC potential is bounded, these relationships do not work properly for the GC fluid. Using new empirical scaling relations we are able to fit the diffusion coefficient within one single master curve for the whole density and temperature range we have simulated. We were also able to find a single master curve for the viscosity, but only for state conditions where the classical Stokes-Einstein relation is valid.
TL;DR: Zusammenfassung et al. as discussed by the authors studied the origins of mixed-former effects in borophosphate glasses of general composition: Li0.5BO1.75 and 0.4 Na2O:0.6 [B2O3:(1−x)P2O5], and showed how these effects relate to changing ion-network interactions.
Abstract: Zusammenfassung We discuss the origins of mixed-former effects in borophosphate glasses of general composition: Li0.5BO1.75:(1−x)LiPO3 and 0.4 Na2O:0.6 [xB2O3:(1−x)P2O5], and show how these effects relate to changing ion-network interactions. In particular for the latter system, we analyse the permittivity spectra using the MIGRATION concept. The results show that the increase in the calculated “cage length” (spatial extent of localised ion motion) in the mixed former region correlates well with the increased abundance of the BO4 tetrahedra. We propose that more local cation sites are created and fast electronic bond-switching processes open up these sites to facilitate macroscopic transport. This picture of ion transport independent of network dynamics accounts for all favourable effects observed in mixed former glasses such as increase in ion mobility, rise in Tg and improvement in chemical durability.
TL;DR: In this article, a mini-review focusing on recently discovered nanomeshes and nanotemplates made from carbon, boron nitride and their mixtures with a thickness of just a single atomic layer is presented.
Abstract: Abstract This mini-review focuses on the recently discovered nanomeshes and nanotemplates made from carbon, boron nitride and their mixtures with a thickness of just a single atomic layer. Typically they exist on some transition metal or semiconductor substrate, the interaction with it playing a crucial role in nanopattern formation. We review systems such as graphene/SiC(0001), graphene/Ru(0001), h-BN/Ru(0001), and h-BN/Rh(111), their atomistic models, synthesis routes, as well as possible applications as templates for nanoperiodic arrays of clusters and molecules. Scanning tunneling microscopy (STM), a technique with ultimate resolution in real space, is stressed as an indispensable tool for a comprehensive characterization of the given systems.
TL;DR: In this paper, the oxidation of carbon monoxide over polycrystalline ruthenium dioxide (RuO2) powder was studied in a packed bed reactor and by bulk and surface analytical methods.
Abstract: The oxidation of carbon monoxide over polycrystalline ruthenium dioxide (RuO2) powder was studied in a packed-bed reactor and by bulk and surface analytical methods. Activity data were correlated with bulk phases in an in-situ X-ray diffraction (XRD) setup at atmospheric pressure. Ruthenium dioxide was pre-calcined in pure oxygen at 1073 K. At this stage RuO2 is completely inactive in the oxidation of CO. After a long induction period in the feed at 503 K RuO2 becomes active with 100% conversion, while in-situ XRD reveals no changes in the RuO2 diffraction pattern. At this stage selective roughening of apical RuO2 facets was observed by scanning electron microscopy (SEM). Seldom also single lateral facets are roughened. EDX indicated higher oxygen content in the following order: flat lateral facets > rough lateral facets > rough apical facets. Further, experiments in the packed bed reactor indicated oscillations in the CO2 formation rate. At even higher temperatures in reducing feed (533-543 K) the sample reduces to ruthenium metal according to XRD. The reduced particles exhibiting lower ignition temperature are very rough with cracks and deep star-shaped holes. An Arrhenius plot of the CO2 formation rate below the ignition temperature reveals the reduced samples to be significantly more active based on mass unit and shows lower apparent activation energy than the activated oxidized sample. Micro-spot X-ray photoelectron spectroscopy (XPS) and XPS microscopy experiments were carried out on a Ru(0001) single crystal exposed to oxygen at different temperature. Although low energy electron diffraction (LEED) images show a strong 1x1 pattern, the XPS data indicated a wide lateral inhomogeneity with different degree of oxygen dissolved in the subsurface layers. All these and the literature data are discussed in the context of different active states and transport issues, and the metastable nature of a phase mixture under conditions of high catalytic activity.
TL;DR: In this article, the relation of the primitive relaxation time to the conductivity relaxation time predicted by the Coupling Model is shown to hold in all cases considered, and the existence of primitive relaxation is demonstrated by experiments and molecular dynamics simulations.
Abstract: Abstract For solution of the problem of conductivity relaxation and diffusion of ions in ionic conductors with high density of ions, it is essential not to neglect treatment of the effects of many-ion dynamics. This view is shared by the Coupling Model (CM) and the MIGRATION CONCEPT (MC), although the treatment, emphasis and some predictions of the two models are different. Notwithstanding, a basic element is common to both models, namely the primitive relaxation, which performs two important functions. It terminates the caged ion dynamics at short times and initiates the many-ion dynamics at longer times. We demonstrate by experiments and molecular dynamics simulations the existence of the primitive relaxation, and the two functions it performs. The relation of the primitive relaxation time to the conductivity relaxation time predicted by the CM is shown to hold in all cases considered.
TL;DR: The primary products of the bimolecular reactions of ortho-benzyne, o-C6H4 (1,2-dchydrobenzene), with ethene, propene, and acetylene have been detected by molecular beam mass spectrometry at it combustion relevant temperature of T = 1475 K as mentioned in this paper.
Abstract: The primary products of the bimolecular reactions of ortho-benzyne, o-C6H4 (1,2-dchydrobenzene), with ethene, propene, and acetylene have been detected by molecular beam mass spectrometry at it Combustion relevant temperature of T = 1475 K, o-Benzyne was produced by flash pyrolysis of phthalic anhydride in the absence and presence of the respective reactant. Potential reaction pathways of the addition reactions were investigated by quantum chemical calculations. Channels with biradical intermediates were found to be energetically more favorable than alternative quasi-concerted [2+1] cycloaddition and concerted H-transfer pathways. Bicyclic benzocyclobutene and benzocyclobutadiene were identified as the main products of the reactions with C2H4 and C2H2, respectively. At combustion temperatures, however, these cyclic products are likely to undergo sequential ring opening. In the case of propene, the presence of an allylic H atom initiates it favorable ene-type reaction sequence yielding the open-chain product allylbenzene. Overall, hydrocarbon reactivity was found to increase in the order C2H2, C2H4 to C3H8. The range of the estimated bimolecular rate constants is comparable to the rate constants of the corresponding phenyl radical reactions and hence point out it potentially important role of o-C6H4 reactions in flame and soot formation chemistry.
TL;DR: In this paper, various distribution functions of hydrogen bond lifetimes, used to describe the dynamics of breakage and formation of these bonds are calculated for a molecular dynamics model of water of 3456 molecules at 310 K.
Abstract: Various distribution functions of hydrogen bond lifetimes, used to describe the dynamics ofbreakage and formation of these bonds are calculated for a molecular dynamics model of waterof 3456 molecules at 310 K. Quenched (inherent) structures are derived from instantaneousMD structures. Comparing the distribution functions from I and Q structures allows interpretingtheir characteristic features. The sharp peak at ~15 fs, which prevails in the most frequentlyused distributions, is ascribed to short-lived “false” H bonds which results from violations ofhydrogen bonding criteria induced by dynamic intermolecular vibrations of molecules. A specialtype of distribution, proposed earlier [34], contains information not only on dynamics, but on
TL;DR: In this paper, the authors measured the mechanical properties of single alginate beads by means of squeezing experiments between two parallel plates and found that capsules formed with pure ferrous ions were less stable than particles which were cross-linked with calcium or ferric ions.
Abstract: Abstract In a series of experiments we measured the mechanical properties of single alginate beads by means of squeezing experiments between two parallel plates. We used multivalent counter-ions as cross-linking molecules for the formation of three dimensional alginate gels. In this article we examined pure Fe(II) (ferric), Fe(III) (ferrous) and Ca(II) (calcium) ions as cross-linking agents and different mixtures between these charged compounds. The results of squeezing experiments showed that capsules formed with pure ferrous ions were less stable than particles which were cross-linked with calcium or ferric ions. It turned out that at equal molar concentrations calcium and ferrous ions formed stronger gels than ferric ions. In addition to squeezing capsule experiments we also investigated different particles by optical microscopy and scanning electron microscopy. Experiments of Energy-dispersive X-ray spectroscopy (EDAX) show different compositions of these beads.
TL;DR: In this article, a mean-field method based on low frequency a.c. impedance measurements of the limiting low frequency space charge polarization capacitance that develops as a result of the mobile carrier population diffusing to blocking electrodes is proposed.
Abstract: A method is proposed using mean-field theories to help solve a long standing problem in the study of ionically solid electrolytes. While it has been long known that the ionic conductivity in solid electrolytes is comprised of two terms, the mobility and number of mobile charge carriers, there has been no accurate method developed to determine these two quantities independently. In this paper, we apply a mean-field method based upon low frequency a.c. impedance measurements of the limiting low frequency space charge polarization capacitance that develops as a result of the mobile carrier population diffusing to blocking electrodes. The space charge capacitance that develops is shown to be a simple function of the number of charge carriers and is found to be independent of the d.c. conductivity, but strongly dependent upon temperature. Measurements on two simple but well studied ion conducting glasses, LiPO3 and NaPO3, suggest that the carrier population is thermally activated where only a small fraction of the cations are mobile in the glass. The activation energy for carrier creation in LiPO3 is larger (49 kJ.mol) than that for NaPO3 glass (44 kJ.mol) and is in agreement with models of activation energies in ion conducting glasses that associate the creation energy with the cation charge density.
TL;DR: In this article, the authors describe the compilation and validation of a compact reaction mechanism for the oxidation of n-heptane, toluene and its mixtures using the Chemistry Guided Reduction approach.
Abstract: Abstract The present study describes the compilation and validation of a compact reaction mechanism for the oxidation of n-heptane, toluene and its mixtures using the Chemistry Guided Reduction (CGR) approach. By the module-wise composition of validated reaction schemes and the successive application of chemical lumping and redundant species removal for the n-heptane oxidation model, a compact mechanism is generated for reference fuel blends of n-heptane and toluene. The new mechanism is validated for recently published OH-concentrations histories and ignition times from shock tube studies, HCCI engine experiments and flame speed measurements. The good agreement between experiment and prediction demonstrates the general applicability of the CGR method.
TL;DR: Renard, P.J. Van Tiggelen and J.Vandooren as discussed by the authors showed that the replacement of 5.7% C2H4 by 4.3% C3H8O2, keeping the equivalence ratio equal to 2.50, is responsible for it decrease of the maximum mole fractions of Most of the detected intermediate species.
Abstract: Two rich premixed ethylene/oxygen/argon and ethylene/dimethoxymethane/oxygen/argon flat flames burning at 50 mbar were investigated experimentally by using molecular heart mass spectrometry to study the effect of methylal (dimethoxymethane) addition on species concentration profiles (C. Renard, P.J. Van Tiggelen and J. Vandooren, Proc. Combust. Inst.. 29 (2002) 1277-1284). The replacement of 5.7% C2H4 by 4.3% C3H8O2, keeping the equivalence ratio equal to 2.50, is responsible for it decrease of the maximum mole fractions of Most of the detected intermediate species. If this phenomenon is barely noticeable for C-2 to C-4 intermediates, it becomes more efficient for C-5 to C-10 species. Previously, a reaction mechanism has been validated against a premixed rich C2H4/O-2/Ar flame (phi = 2.50) which describes in detail the formation of soot precursors and more precisely the main pathways involving,, benzene (V. Dias, C. Renard, P.J. Van Tiggelen and J. Vandooren. European Combustion Meeting. Orleans, France. p.221, 2003). The aim of this work is to extend this original model by building a sub-mechanism taking into account the formation and the consumption of oxygenated species' involved in dimethoxymethane combustion. The new mechanism contain,, 474 elementary reactions and involves 90 chemical species in order to simulate both ethylene flames with and without methylal addition. The model leads to a good simulation for all species detected in these flames, and Underlines the effect of methylal addition on species concentration profiles. According to this mechanism, the two train degradation pathways of methylal (CH3OCH2OCH3) in C2H4/methyl/oxygen/argon flame are: 1) CH3OCH2OCH3 -> CH3OCH2OCH2 -> CH3OCH2 -> CH2O 2) CH3OCH2OCH3 -> CH3OCHOCH3 -> CH3OCHO -> CH3OCO -> CH3O -> CH3OH -> CH2OH -> CH2O with the first one being the fastest.
TL;DR: In this paper, a detailed chemical kinetic reaction mechanism consisting of 33 elementary reactions and 26 species was used to model the experimentally obtained H-atom profiles, with help of sensitivity and reaction flux analysis, it was concluded that reaction R 1 2 -C4H6 4 2-C 4H5 + H is crucial for the observed formation of H-atoms during the thermal decomposition of both investigated species and within the investigated range of temperatures and pressures.
Abstract: For investigating the pyrolysis of 1,3-butadiene (1,3-C4H6) and 2-butyne (2-C4H6), reactive gas mixtures highly diluted with argon as bath gas were prepared. The experiments were carried out in a high purity shock tube device over a temperature range of about 1500–1800 K at total pressures between 1.2 and 1.9 bar. The time-dependent formation of H-atoms was measured behind reflected shock waves by using the very sensitive method of atomic resonance absorption spectrometry (ARAS). A detailed chemical kinetic reaction mechanism consisting of 33 elementary reactions and 26 species was used to model the experimentally obtained H-atom profiles. From kinetic modelling, with help of sensitivity and reaction flux analysis, it was concluded that reaction R 1 2-C4H6 4 2-C4H5 + H is crucial for the observed formation of H-atoms during the thermal decomposition of both investigated species and within the investigated range of temperatures and pressures. Moreover, at temperatures above about 1650 K, the decay of propargyl radicals (C3H3) turns out to contribute significantly to the amount of produced Hatoms. The following rate expressions were obtained for three reactions (R 1– R3 )– among them the isomerisation from 2-butyne to 1,3-butadiene – important with respect to the formation of H-atoms within the investigated parameter range. The uncertainties are estimated to be ±30%: