Molybdenum nitride for the direct decomposition of NO

The physico-chemical properties of passivated -Mo₂N have been investigated. The material showed high activities for NO direct decomposition: nearly 100% NO conversion and 95% N₂ selectivity were achieved at 450C. The amount of O₂ taken up by -Mo₂N increased with temperature rise and reached 3133.9 molg^–1 at 450C; we conclude that there formation of Mo₂O_xN_y occurred. This oxygen-saturated -Mo₂N material was catalytically active: NO conversion and N₂ selectivity were 89 and 92% at 450C. We found that by means of H₂ reduction at 450C, Mo₂O_xN_y could be reduced back to -Mo₂N and the oxidation/reduction cycle is repeatable; such a behaviour and the high oxygen capacity (3133.9 molg^–1) of -Mo₂N suggest that -Mo₂N is a promising catalytic material for automobile exhaust purification.     

Electrochemical behaviour of viologen-cyclodextrin inclusion complexes. The case of non-alkyl group substituted viologen

The electrochemical behavior of non-alkyl substituted viologen, 4,4-dibenzyl bipyridinium (BzV), 4,4-dicyanophenyl bipyridinium (CyV) and -,-,-cyclodextrin (, , -CD) was studied using cyclic voltammetry and a spectroelectrochemical method. It was found that BzV and Fe(CN) ₆ ^4– formed a charge-transfer (CT) complex with a ratio of 21 and the colour of the solution faded with the addition of an electrolyte. This behaviour is the same as in then-heptyl viologen and ferrocyanide system [1]. BzV, -CD and -CD formed an inclusion complex only in the reduced state, whilst BzV and -CD formed an inclusion complex in both the oxidized and the reduced state. An EC scheme in which a chemical reaction follows an electrochemical reaction was considered to predominate in the BzV and -, -CD systems, while a CE scheme in which a chemical reaction preceded an electrochemical reaction predominated in the BzV and -CD system. On the other hand, CyV was found to form an inclusion complex with -, -, -CD in both the oxidized and the reduced states. therefore a CE scheme was considered to predominate in the CyV--, -, -CD systems.     

Specific features of the phase transformations occurring during the sintering process of the beta-alumina based ceramics and their properties

Conclusions During the sintering process of beta-alumina obtained using the method of plasmochemical synthesis, the structural transformation occurs and it is accompanied by the separation of the excess Na₂O and the formation of an intergranular meltlike phase that is saturated with sodium and is characterized by high dielectric properties.The quantity of the meltlike phase and the magnitude of the /( + ) ratio determine the degree of stabilization (stability) and the final resistivity of the material and depend on the initial chemical composition and the heating rate maintained during the sintering process.It was shown that when the duration of residence of the material in the hot zone of the furnace is increased or when the specimens sintered maintaining high heating rates are subjected to additional heat treatment, one observes the occurrance of the reverse structural transformation that is characterized by an increase of the phase ratio /( + ) 1, a reduction in the quantity of the meltlike phase right up to its complete disappearance, and a decrease of the electrical resistivity of the material.In the materials having a large excess quantity of sodium oxide, the process of crystallization of the intergranular NaAlO₂ phase occurs simultaneously with the second phase transformation.The best ceramic and electrophysical parameters were obtained when sintering the material contained 7.9% Na₂O.Translated from Ogneupory, No. 3, pp. 13–18, March, 1990.     

Interrelation between the Glass Transition Temperature, Thermal Expansion Coefficient, and Poisson Ratio for Some Glasses in the AV–BVI–CVIISystems

In the framework of the free volume concept, the dependences of _g T _gand T _gon and are considered and the interrelation between the fraction of the fluctuation free volume f _g, Poisson ratio , and Grüneisen lattice parameter for chalcogenide, oxogenide, and oxohalide glasses is discussed. The fluctuation free volume model and the model of soft atomic configurations are compared in terms of anharmonicity of the glasses under investigation.     

Flow-through and flow-by porous electrodes of nickel foam Part IV: experimental electrode potential distributions in the flow-through and in the flow-by configurations

Experimental distributions of the solution potential in flow-through and flow-by porous electrodes of nickel foam operating in limiting current conditions are presented. These are in good agreement with the corresponding theoretical distributions. In the case of a flow-by configuration used in a two-compartment cell, the experiments confirm the validity of the models, presented in Part III, which take into account the presence of a separator (ceramic porous diaphragm or ion exchange membrane).Nomenclature a _e specific surface area per unit volume of electrode - C ₀ entrance ferricyanide concentration (y=0) - D molecular diffusion coefficient of ferricyanide - E _e cathode potential - F Faraday number - mean (and local) mass transfer coefficient - L electrode thickness - L _s-L separator thickness - m number of sheets of foam in a stack - n number of terms in Fourier series - Q volumetric flow-rate - r _s ohmic specific resistance of the separator - mean flow velocity based on empty channel - V constant potential - X conversion - x coordinate for the electrode thickness - y coordinate for the electrode length - y ₀ length of the porous electrode - z number of electrons in the electrochemical reaction Greek symbols parameter - parameter - ionic electrolyte conductivity - _sc solution potential in the pores of the cathode - _M matrix potential ( _sc = constant) - parameter [=n/y ₀] - electrolyte density - mean porosity - kinematic viscosity - E _c potential drop in the porous cathode - potential drop defined in Fig. 5 Indices c cathodic - o electrolyte alone - s separator     

Living cationic polymerizations initiated by phosgene

Living cationic polymerization of isobutylene and styrene was performed by using phosgene as initiator and solvent, AlCl₃ as coinitiator in homogeneous phase. Polymerization of isobutylene by using phosgene and TiCl₄ also proved to be a living process, however, initiation in this case was performed by H₂O impurities, and the system was heterogeneous. In case of the COCl₂/AlCl₃ initiating system, ketonic carbonyl functionality was built-in into the polymer. The living character of the process, both in case of AlCl₃, and of TiCl₄ was demonstrated by the linear increase of ¯M_n with the cumulative amount of the monomer successively added, and by the conversion and temperature jump at every monomer additon. Observations on the permanence of the color (intensive yellow with IB and deep red with St) also support that the propagating cations are long living. An explanation of the observed phenomena is suggested on the base of Pearson's theory of hard and soft acids and bases.     

Electron pair donors in carbocationic polymerization

Preparatory to a detailed presentation of a large body of accumulated information, representative data have been selected to demonstrate that well-defined narrow molecular weight distribution (MWD) (¯M_w/¯M_n = 1.1) polyisobutylene (PIB) can be readily prepared in the M_n = 1000 – 100,000 range in the presence of certain types of electron pair donors (EDs) under a great variety of conditions. Specifically, many initiating systems, such as dicumyl chloride/BCl₃, dicumyl alcohol/BCl₃, 2-chloro-2,4,4-trimethylpentane/TiCl₄, that induce nonliving polymerizations and/or give relatively broad MWD PIBs, in the presence of suitable EDs, e.g., dimethyl sulfoxide (DMSO), dimethyl acetamide (DMA), give rise to living polymerizations and yield narrow MWD products. Evidently, by the use of select EDs various undesirable side reactions, i.e., uncontrolled initiation, chain transfer, irreversible termination, indanyl end-group formation, etc., that plague carbocationic polymerizations and which therefore yield ill-defined relatively broad MWD products, can be eliminated and well-defined narrow MWD products can be obtained. The addition of EDs to otherwise extremely rapid carbocationic polymerizations results in lower controlled rates. All these observations and beneficial effects can be explained by controlled carbocation stabilization by EDs, a subject that will be explored and discussed in detail in this series of publications.Paper XXV in the series living carbocationic polymerization     

Effect of crystallinity on the dynamic mechanical relaxations of poly(butylene isophthalate)

Summary The viscoelastic spectrum of poly(butylene isophthalate) annealed at 90 °C for different times has been examined by dynamic mechanical spectroscopy.Crystallinity affects both the main a absorption associated with the glass to rubber transition and the sub-ambient secondary relaxation region. The latter results from two overlapping processes, ₁ and ₂, that have been evidentiated by a resolution procedure. Values of 52 and 76 kJ/mol have been obtained for the activation energies of the low (₁) and high (₂) temperature component respectively. It is suggested that these values are not affected by the methylene chain length and by the isomerism of the phthaloyl residue.     

Studies on nonisothermal solid state galvanic cells — effect of gradients on EMF

An expression for the EMF of a nonisothermal galvanic cell, with gradients in both temperature and chemical potential across a solid electrolyte, is derived based on the phenomenological equations of irreversible thermodynamics. The EMF of the nonisothermal cell can be written as a sum of the contributions from the chemical potential gradient and the EMF of a thermocell operating in the same temperature gradient but at unit activity of the neutral form of the migrating species. The validity of the derived equation is confirmed experimentally by imposing nonlinear gradients of temperature and chemical potential across galvanic cells constructed using fully stabilized zirconia as the electrolyte. The nature of the gradient has no effect on the EMF.Nomenclature J _i flux of speciesi - X _i generalized forces - L _ij Onsagar coefficient - ₁ electrochemical potential of ions - ₂ electrochemical potential of electrons - T absolute temperature - U ₁ ^* total energy of transfer of the ion - partial molar enthalpy of the ion - Q ₁ ^* heat of transport of the ion - Z ₁ charge on the ion - F Faraday constant - electrostatic potential - ₂ chemical potential of the electron - ₁ chemical potential of the ion - partial entropy of the ion - E _SE EMF developed across the solid electrolyte - E _Pt EMF developed across the platinum lead - ( ₂)_Pt chemical potential of electrons in platinum - partial entropy of electrons in platinum - (Q ₂ ^* )_Pt heat of transport of electrons in platinum - E _cell EMF developed across the whole cell - chemical potential of oxygen - chemical potential of oxygen in its standard state - R universal gas constant - partial pressure of oxygen - relative chemical potential of oxygen - _M relative chemical potential of metal M - a _M activity of metal M     

Combustion and the transition to detonation in a gas mixture in a closed space

The possibility of going from deflagration to detonation in mixtures of CH₄+2(O₂+N₂) and 2H₂+O₂ ±N₂ (03.76) was investigated experimentally in a space enclosed by various combinations of three thin-walled metal concentric turbulator-sphere (diameters in a ratio 124) with large numbers of openings (permeability 0.1–0.4). Transition from deflagration to detonation was observed for 1 in the first mixture and for 3.2 in the second.Balashikha. Translated from Fizika Goreniya i Vzryva, Vol. 29, No. 3, pp. 171–174, May–June, 1993.     

Carbocationic polymerizations in supercritical carbon dioxide

The first carbocationic polymerization of isobutylene (IB) in supercritical carbon dioxide (SC·CO₂) has been accomplished. It was demonstrated that in CO₂ at 32.5°C and 120 bar the 2-chloro-2,4,4-trimethyl-pentane (TMPCl)/SnCl₄ and TMPCl/TiCl₄ initiating systems lead to 30% IB conversion, and gave polyisobutylenes (PIB) with M_n2000 and M_w/M_n2.0. This is the highest temperature IB was ever polymerized to reasonably high molecular weight products. Polymerizations at 32.5 °C under similar but conventional (non-living) conditions in the absence of SC·CO₂ would yield only very low molecular weight oligomers (tetramers). The structure of the PIBs obtained in SC·CO₂ is virtually identical to those obtained at much lower temperatures in conventional liquid-phase systems indicating the presence of chain transfer to monomer in both systems. In contrast to TMPCl initiated polymerizations, the 1,3-bis-(2-hydroxy-2-propyl)-5-tert-butylbenzene (HPBB) initiator in conjunction with BCl₃ and SnCl₄ yields only oligomers (M_n500) in SC·CO₂.     

Weak Gel Behaviour of Poly(vinyl alcohol)-Borax Aqueous Solutions

Thermal transition of PVA-borax aqueous gels with a PVA concentration of 60 g/L and a borax concentration of 0.28 M was investigated at temperatures ranging from 15 to 60C using static light scattering (SLS), dynamic light scattering (DLS), and dynamic viscoelasticity measurements. Three relaxation modes, i.e. two fast and one slow relaxation modes, were observed from DLS measurements. Two fast relaxation modes located around 10^–310¹ sec, with one fast mode (_f1) being scattering vector q-dependent and the other fast mode (_f2, with _f2>_f1) being q-independent. The _f1 mode was attributed to the gel mode whilst the _f2 mode could be due to the hydrodynamics of intra-molecular hydrophobic domains formed by uncharged segments of polymer backbones. The slow relaxation mode with relaxation time located around 10¹10³ sec in DLS data was due to the motion of aggregated clusters and was observed only at temperatures above 40C. The amplitude and relaxation time of slow mode decrease as temperature is increased from 40 to 60C. At temperatures below 40C, no slow relaxation mode was observed. The SLS measurements showed PVA-borax-water system had fractal dimensions D _f2.4 and D _f2.0 as temperature was below and above 40C, respectively. The simple tilting test indicated gel behaviour for the PVA-borax aqueous system at temperatures below 40C with a creep flow after a long time exposure in the gravity field. But the dynamic viscoelasticity measurements demonstrated a solution behaviour for PVA/borax/water at temperatures below 40C, the critical gel point behaviour for G() and G() was not observed in this system as those reported for chemical crosslinked gels. These results suggest that the PVA-borax aqueous system is a thermoreversible weak gel.     

Mass transport in a weakly stratified electrochemical cell

A study of natural convection in an electrochemical system with a Rayleigh number of the order 10¹⁰ is presented. Theoretical and experimental results for the unsteady behaviour of the concentration and velocity fields during electrolysis of an aqueous solution of a metal salt are given. The cell geometry is a vertical slot and the reaction kinetics is governed by a Butler-Volmer law. To reduce the effects of stratification, the flush mounted electrodes are located (symmetrically) in the middle parts of the vertical walls. It is demonstrated, both theoretically and experimentally, that a weak stratification develops after a short time, regardless of cell geometry, even in the central part of the cell. This stratification has a strong effect on the velocity field, which rapidly attains boundary layer character. Measured profiles of concentration and vertical velocity at and above the cathode are in good agreement with numerical predictions. For a constant cell voltage, numerical computations show that between the initial transient and the time when stronger stratification reaches the electrode area, the distribution of electric current is approximately steady.List of symbols a _i left hand side of equation system - b _i right hand side of equation system - c concentration (mol m^–3) - c dimensionless concentration - c _i concentration of species i' (mol m^–3) - c₀ initial cell concentration (300 mol m^–3) - c ₀ dimensionless initial cell concentration - c_wall concentration at electrode surface (mol m^–3) - dx increment solution vector in Newton's method - D _i diffusion coefficient of species i (m² s^–1) - D ₁ 0.38 × 10^–9 m² s^–1 - D ₂ 0.82 × 10^–9 m² s^–1 - D effective diffusion coefficient of the electrolyte (0.52 × 10^–9 m² s^–1) - _x unit vector in the vertical direction - _y unit vector in the horizontal direction - F Faraday's constant (96 487 A s mol^–1) - g acceleration of gravity (9.81 m s^–2) - i dummy referring to positive (i = 1) or negative (i = 2) ion - f current density (A m^–2) - f dimensionless current density - i₀ exchange current density (0.01 A m^–2) - J _ij Jacobian of system matrix - L length of electrode (0.03 m) - N _i transport flux density of ion i (mol m^–2 s^–1) - n unit normal vector - p pressure (Nm^–2) - p dimensionless pressure - R gas constant molar (8.31 J K^–1 mol^–1) - R _i residual of equation system - Ra Rayleigh number gL ³ c ₀/D (2.54 × 101¹⁰) - S _c Schmidt number /D (1730) - t time (s) - t dimensionless time - T temperature (293 K) - velocity vector (m s^–1) - dimensionless velocity vector - U characteristic velocity in the vertical direction - V _± potential of anode and cathode, respectively - x spatial coordinate in vertical direction (m) - x dimensionless spatial coordinate in vertical direction - x solution vector for c, and - y spatial coordinate in horizontal direction (m) - y dimensionless spatial coordinate in horizontal direction - z _i charge number of ion i Greek symbols symmetry factor of the electrode kinetics, 0.5 - volume expansion coefficient (1.24 × 10^–4 m³ mol^–1) - _s surface overpotential - constant in equation for the electric potential (–5.46) - _s diffusion layer thickness - scale of diffusion layer thickness - constant relating c/y to the Butler-Volmer law (0.00733) - kinematic viscosity (0.9 × 10^–6 m2 s^–1)     

Ethynylene-disilanylene copolymers

Polymers of structure (SiR₂SiR₂-C C-SiR₂SiR₂-C C) _n , in which ethynylene units alternate with disilylene units, have been prepared by two routes: (a) condensation of dichlorodisilanes with dilithium derivatives of 1,2-diethynyldisilanes and (b) ring-opening polymerization of strained cyclic disilanylene-acetylnes, (SiR₂SiR₂C C)₂. The polymers display UV absorption near 240 nm indicative of – conjugation between the Si₂ and the C C moieties. Polymers with R=R=n-Bu or R=n-Bu, R=Ph, undergo solid-state transitions to form liquid crystalline mesophases resembling those observed for many poly(silylenes). Single crystals were obtained for the polymer with R=R=CH₃, by precipitation from dilute cyclohexane solution. The solid-state properties and structures of this family of polymers are discussed.This paper was presented at the Second International Topical Workshop, Advances in Silicon-Based Polymer Science.     

Spontaneous Ignition of Methane–Air Mixtures in a Wide Range of Pressures

The ignition delay in methane–air mixtures = 0.5) within the range of temperatures of 1200–1700 K and pressures of 3–450 atm behind reflected shock waves in a shock tube is measured on the basis of emission of the electronexcited OH radical (transition A²⁺ – X²) at the wavelength of 306.4 nm and on the basis of absorption corresponding to the component F₁ ⁽²⁾ (₃ = 1) F₂ ⁽²⁾ (₃ = 0) of the P(7) line of the ₃ mode of the CH₄ molecule at the wavelength of 3.3922 m. The measured ignition delays are compared with those calculated by the GRIMech 3.0 mechanism; good qualitative agreement of results is obtained in a wide range of pressures.     

Heterogeneous asymmetric reactions. 23. Enantioselective hydrogenation of ethyl pyruvate over cinchonine- and α-isocinchonine-modified platinum catalysts

The enantioselective hydrogenation of ethyl pyruvate to (S)-ethyl lactate over cinchonine- and -isocinchonine-modified Pt/Al₂O₃ catalysts was studied as a function of modifier concentration and reaction temperature. The maximum enantioselectivities obtained under the applied mild conditions were 89% ee using cinchonine (0.014 mmoldm^–3, 1 bar H₂, 23°C, 6% AcOH in toluene), and 76% ee in the case of -isocinchonine (0.14 mmoldm^–3, 1 bar H₂, –10°C, 6% AcOH in toluene). Since -isocinchonine of rigid structure exists only in anti-open conformation these data provide additional experimental evidence to support the former suggestion concerning the dominating role of anti-open conformation in these cinchona-modified enantioselective hydrogenations.     

Apple ermine moth,Yponomeuta malinellus Zeller Two components of female sex pheromone gland highly effective in field trapping tests

When electroantennographic responses of maleYponomeuta malinellus Zeller to model compounds were determined at dosages of 0.3–30 ng, the strongest responses were obtained from (Z)-9-dodecen-1-ol acetate (Z9–12Ac). Also, strong responses were obtained from (Z)-11-tetradecenal (Z11–14A1) and (Z)-11-tetradecen-1-ol (Zl1–14OH). At a dosage of 0.3 ng,Z11–14A1 produced a stronger response thanZ11–14OH, while at a dosage of 30 ng,Z11–14OH andZ11–14A1 produced equal responses. Gas chromatographic and mass spectral analysis of extracts of female sex pheromone glands showed the presence ofZ9–12Ac, tetradecan-1-ol (14OH), (E)-11-tetradecen-1-ol (E11–14OH),Z11–14OH, hexadecan-1-ol, and hexadecan-1-ol acetate in a ratio of 0.62003710014035. In field tests,Z9–12Ac andZ11–14OH together were required for trap catch, and addition ofZ11–14A1,E11–14OH, 14OH, or (Z)-11-tetradecen-1-ol acetate did not increase catch. Ratios in rubber septa of 0.599.5 to 1.598.5 (Z9–12 Ac/Z11–14OH) captured the most males and captures were statistically equivalent for dosages of 10–1000 g/rubber septum. Traps baited with the synthetic lure produced better catches than those baited with females.Lepidoptera: Yponomeutidae.     

Anisotropy in the strength of cellulosic fibres

Conclusions It is proposed to use the equation of a lemniscate, or the Cassini curve, to determine the destructive stress at break for cellulose films in any direction. Thereupon, to determine , it is necessary to know the destructive stress along two basic directions (₀ and ₉₀).To obtain cellulosic films which are isotropic in plane, a necessary and sufficient condition is ₀=₉₀.Translated from Khimicheskie Volokna, No. 6, pp. 34–35, November–December, 1987.     

Methane partial oxidation by silica‐supported iron phosphate catalysts. Influence of iron phosphate content on selectivity and catalyst structure

Selective oxidation of methane to methanol and formaldehyde at atmospheric pressure was studied over a series of silicasupported FePO₄ catalysts, with iron phosphate content ranging from 2 to 16 wt%. Performance was evaluated over the range T=773–963 K, GHSV=25,000–65,000 h^–1, and CH₄ : O₂=1. The main products were formaldehyde, carbon monoxide and carbon dioxide. Small, but quantifiable amounts of methanol were also observed. Catalytic activity exhibited a clear dependence on the iron phosphate content. The highest selectivity and space time yield (STY) to formaldehyde and methanol were observed for 2 wt% FePO₄ on silica (STY of 622 and 25 g/kg_cat h, respectively). The selectivity–conversion pattern suggests that methane is oxidized directly to methanol and formaldehyde, and sequentially to carbon oxides. Characterization was performed by Xray powder diffraction, Xray photoelectron spectroscopy, and Mössbauer spectroscopy. Crystalline FePO₄ is observed at all loading levels, however, a significant fraction of the iron (58% at 2 wt% FePO₄) is present in an Xray amorphous phase. Mössbauer spectra suggest that this phase contains iron in fivefold coordination, and with a higher electron density relative to bulk FePO₄. The amount of this fivecoordinate phase present is roughly 1 wt% Fe, independent of total iron loading. XPS confirms the lower effective oxidation state of iron, and indicates that at low loading the surface is enriched in phosphorus relative to bulk FePO₄. It is proposed that iron in fivefold coordinate sites, isolated by phosphate groups, more selectively activates methane than crystalline FePO₄. As loading increases, so does the amount of crystalline FePO₄, which is proposed to more rapidly catalyze sequential oxidation of the selective products.     

The rotating cylinder electrode

The transfer of mass onto a rotating cylindrical nickel electrode was investigated at relatively low rates. The simple electrochemical reaction of ferricyanide ion in an alkali medium was applied for this purpose. In the investigations particular attention was paid to the phenomenon of the penetration of eddies into the laminar sublayer. A modification and broadening of the basic Taylor expression, namely Taylor's linear theory, was proposed for the systems with a greater interelectrode distance. The experimental results can be better interpreted with a thus modified expression.Symbols A surface area - b constant - c _b,c _s bulk and surface concentrations - d _c diameter of rotating inner cylinder - D diffusion coefficient - zF Faradaic equivalence - h height - k _f friction factor - i ₁ limiting current density - I ₁ limiting current - dimensionless number - k _L mass transfer coefficient - N rotation per minute - r _i,r _o radii of inner and outer cylinders - = r _i peripheral velocity - x distance along the electrode - y distance normal to the electrode - _N, _Pr thickness of Nernst diffusion and Prandtl hydrodynamic boundary layers - _o thickness of laminar or viscous sublayer - coefficient of viscosity - density - kinematic viscosity - angular velocity - (Re) Reynolds number,d _c/ - (Sc) Schmidt number,/D - (Sh) Sherwood number,k _L d _c/D - (St) Stanton number,k _L/