Secondary electron emission from polymers and its application to the flexible channel electron multiplier

The basic characteristics of secondary electron emission (SEE) from various organic compounds have been investigated, and a channel electron multiplier with high gain and flexibility has been developed. The maximum SEE yield is higher for the aliphatic compound than for the aromatic, and is higher for the organic solid with high ionization potential. By studying the SEE yields from the electron-conductive polymeric compositions which consist of plasticized poly(vinyl chloride) and electroconductive particles (NaTCNQ or carbon black), it is shown that the SEE yield depends mainly on the characteristics of the matrix polymer and is almost independent of the addition of electroconductive particles which inherently have low SEE yields. Adding less than 5% stabilizers to these polymeric compositions has little effect on the SEE yields. A flexible channel electron multiplier (FCEM) made of the electron-conductive polymeric composition shows the following characteristics: gain ? 10⁸ (applied voltage of 3 kV); rise time ? a few nanoseconds; background count rate < 0.1 cps; and maximum output current ? 10^?6 A. As a photon detector in the vacuum UV region, the FCEM shows a threshold value of 8.4 eV for photoelectric emission.     

Secondary electron emission from CVD diamond films

Secondary electron emission from boron doped diamond polycrystalline membranes (hole concentration 5×10¹⁸ cm⁻³), prepared by microwave plasma assisted CVD, was investigated in both the reflection and transmission configurations. The model of secondary electrons behavior taking into account the distribution and diffusion mechanism of secondary electrons is proposed to explain the yield dependencies on primary electron energy in both configurations. The model predicts the SEE yield K=19 at the primary electron energy E₀ close to 1 keV for reflection configuration and K=3–7 at E₀=15–30 keV for transmission configuration for polycrystalline films used in the study. Experimental measurements of the SEE yield vs. primary electron energy (18 at E₀=950 eV for the reflection scheme and 3.5–4 at E₀=25 keV for the transmission one) are found to accord well with the theoretical results. Estimations, which were made using the model, show that SEE yield in transmission configuration can be increased up to 60 for the primary electron energy of about 10 keV. Since such high yields in transmission scheme may be obtained in monocrystalline membrane, another approach using porous polycrystalline diamond membranes is considered. Porous diamond membranes having SEE yield in transmission scheme of more than 10 at the primary electron energy E₀=1 keV were fabricated.     

A continuum constitutive model for cohesionless granular flows

A constitutive model is developed to represent shear granular flows of cohesionless solids. The model is based on the postulate that the friction coefficient and the solids fraction in a moving granular material are exclusive functions of the inertial number, which represents the ratio of inertial to normal stress forces. The constitutive equation obtained has the same form as a multidimensional Bingham fluid model, albeit with apparent viscosity and yield stress that depend on the vertical normal stress. The model is applied to previously published experimental results dealing with shear flows of granular beds made up of cohesionless spherical particles. The first case analyzed corresponds to a granular bed moving on top of a rotating disk. The model captures the main trends of the velocity profiles with a single adjustable parameter. The second case is a conventional Couette flow, for which the model is capable of representing the velocity and solids fraction profiles measured experimentally.     

π-ELECTRON CONTENTS OF RINGS IN THE DOUBLE-HEXAGONAL-CHAIN HOMOLOGOUS SERIES (PYRENE,ANTHANTHRENE AND OTHER ACENOACENES)

Abstract

Recently three methods for calculating the π-electron content of rings of benzenoid hydrocarbons were put forward: one based on the consideration of Kekuléstructural formulas, and the other two based on an analogous treatment of the Clar aromatic sextet formulas. These three methods are applied to the homologous series consisting of two condensed acene chains (whose first members are pyrene, anthanthrene, peri-naphthacenonaphthacene, …), leading to basically identical results. In contrast to acenes (in which the partition of π-electrons into rings is uniform), in the double-hexagonal-chain species the partition of π-electrons is highly non-uniform. The electron content monotonically decreases, in opposite directions, along the two acene chains, being maximal in the least annelated rings. Some other generally valid regularities in the π-electron properties of the double–hexagonal–chain benzenoids are also pointed out.     

Structural characterization of filter cake solids from a solvent-refined coal process (SRC-1)

A study has been undertaken to characterize the structural aspects of the solids that have been recovered from solvent refined coal (SRC-I). Both the mineral matter as well as the organic materials are characterized through the utilization of various analytical techniques: chemical analysis, X-ray techniques, optical microscopy and electron microscopy studies, surface area measurements, density gradient separation, electron spin resonance, magnetic susceptibility and ESCA studies. A comparison is being made of the solids from this particular process with solids derived from another SRC process. Some of the main findings of this study include the following. Major minerals are pyrrhotite and α-quartz. Organic inerts consist of fusinite, semifusinite, micrinite and macrinite. The least dense fraction is essentially organic, while the high density fraction contains much of the pyrrhotite. The e.s.r.-free-radical measurements show that the solids contain few reactive species.     

基于芴衍生物的D-A化合物及其共聚物的研究进展

芴衍生物具有吸电子性,作为电子受体在D-A共聚体的研究中备受关注。在D-A共聚体中,π-电子供体和π-电子受体通过π键或σ键交替连接,其共平面的共轭结构有利于降低体系的能隙;以芴、芴酮、9-二氰基亚甲基芴衍生物为电子受体单元的推拉型(D-A型)化合物和共聚物,具有优异的光电性能、电子传输性能、较好的电子和空穴迁移率及在空气中极好的稳定性等。主要对基于芴、芴酮、9-二氰基亚甲基芴的D-A化合物及其D-A共聚物的最新研究进展做简要综述。     

Prediction of fresh concrete flow behavior based on analytical model for mixture proportioning

Large number of experimental techniques and models has been developed recently in an attempt to link the parameters of Bingham equation to concrete composition. On the other hand, concrete mixture proportioning methods based on rheological approach usually do not provide direct input of a measurable rheological parameter(s) into the proportioning expression. In this study, series of concrete mixtures have been proportioned by the use of a theoretical model. The experimental results were compared with the predicted rheological quantity by the model. The evaluation of concrete flow parameters has been performed using a newly developed tube viscometer for concrete. The discussion presents a comparison between the model calculated apparent viscosity and the measured plastic viscosity of fresh mixes as function of volume fraction of solids, normalized with respect to their maximum packing values.     

Effect of particle size on the rheology of Athabasca clay suspensions

The success of the separation process conventionally used in Alberta for oil sands extraction is highly influenced by the rheology of the oil sands slurry. In the gravity separation vessel, high slurry viscosities can hinder the rise of aerated bitumen and reduce the efficiency of the recovery process. In this study, the effect of particle size on the viscosity of oil sands slurries is investigated. Solids from mature fine tails (MFT) obtained from tailings pond were fractionated into three fractions of different particle size distributions and their rheological properties were studied. The solids in each fraction were characterized by XRD analysis which showed the presence of different types of clays in each fraction. For the rheological measurements, dispersions of the three fractions were prepared in the supernatant water decanted from centrifuged MFT to maintain the solution chemistry of the solids. Suspensions of each fraction showed a non‐Newtonian shear thinning behaviour as well as yield stress that is characteristic of structure formation within the suspensions. For all solids fractions, increasing solids concentration led to higher viscosities and higher yield stress values. Viscoelastic properties of the suspensions showed stronger solid‐like behaviour at higher particle concentrations. Among the three fractions numbered from 1 to 3, solids in fraction 3 were coated with organic matters, exhibiting the highest suspension viscosities. Also for fraction 3, higher gelling potency was observed at much lower weight fractions of solids as compared to the other fractions.     

Applications of Phase Transfer Catalysis to Arenediazonium Cation Chemistry

Arenediazonium cations have been known for many years but the synthetic utility has been diminished by their lack of stability and by their proclivity for undergoing sundry side reactions. Arenediazonium BF₄ and PF₆ salts are generally stable solids, but are relatively insoluble in nonpolar organic media. Crown complexation and other forms of phase transfer catalysis increase solubility and allow numerous synthetic transformations to be conducted in good yield. The yield improvements result from a reduction in competing side reactions rather than any fundamental change in mechanism. The reactions to which the phase transfer technique is successfully applied are diazo coupling, reduction, halogenation, arylation and cyclization. In the latter case, the use of potassium superoxide is sometimes a more efficacious reagent than potassium acetate. The phase transfer approach can be used in the high yield synthesis of arenediazosulfones and arenediazocyanides. The latter undergo cycloaddition with many dienes to yield pyridazine derivatives.     

PARTITIONING OF π-ELECTRONS IN RINGS OF POLYCYCLIC conjugated HYDROCARBONS. PART 1: CATACONDENSED BENZENOIDS

Recently a novel view on Kekulé valence structures (or resonance structures) was reported in which their standard geometrical representation was replaced by a numerical representation obtained by assigning π-electrons associated with CC double bonds to individual benzenoid rings. In the present article, we examine in more detail the partitioning of π-electrons to benzenoid rings for cata-condensed benzenoid hydrocarbons. For special families of cata-condensed benzenoids, we offer formulas which allow one to obtain the average π-electron ring content for individual benzenoid rings of polycyclic conjugated hydrocarbons. We also show that the average π-electron ring content for individual benzenoid rings can be calculated from Pauling bond orders without a need to examine all Kekulé resonance structures of a molecule.     

Kinetic studies on dehydrogenation of butanol to butyraldehyde using zinc oxide as catalyst

Butyraldehyde is an important chemical for many industrial applications, especially in the production of polyvinylbutyral. A systematic study of its synthesis by catalytic dehydrogenation of butanol, using zinc oxide as catalyst has been carried out. The effect of the method of preparation of zinc oxide on its catalytic activity for the title reaction has also been studied. The optimum conditions for maximum yield have been worked out and on the basis of secondary electron micrograms the reasons for higher activity/selectivity in the case of zinc oxide calcined from zinc hydroxide is attributed to the presence of hexagonal morphology. A kinetic study for the best zinc oxide catalyst has been carried out and the rate equation has been determined.     

MO-LCAO-Berechnungen an Polymethinen. IV. Zum DÄHNEschen Konzept der gekoppelten Polymethine

MO-LCAO Calculations on Polymethines. IV Contribution towards DÄHNE'S Conception of Coupled Polymethines Starting from a quantumchemical characterization of the polymethine π-electron system covered in the previous papers the significance of streptopolymethine sub-structures in more complicated molecular entities has been investigated. In order to relate the electronic structure of a composite system to those of its constituent parts the electronic wave functions are subjected to the configuration analysis. Indices have been employed to evaluate the localizability of the atomic or molecular sub-systems. According to these indices many structures may be considered as being composed from polymethinic, polyenic and aromatic fragments. In the case of the several carbo-and heterocyclic π-systems serious shortcomings of the composite system approach are clearly indicated. Scope and limitation of this model can, however, easily be recognized by application of the simple second order perturbation theory.     

Catalytic gasification of char from hydrocracked pitch

Gasification of hydrocracked pitch (vacuum residuum) was performed non-catalytically and with K₂CO₃ and V₂O₅ catalysts. In agreement with studies of many other workers, K₂CO₃ was found to enhance the gasification rate. In contrast, V₂O₅ was found to inhibit gasification when compared to the non-catalytic rate. X-ray photoelectron spectra were obtained on both catalysts and on catalyst-pitch residues. They indicated that K₂CO₃ does not exist under reaction conditions. This experimental finding suggests that some of the catalytic gasification mechanisms recently reported in the literatúre may be incorrect. In this work, both catalysis and inhibition during gasification have been explained in terms of three effects, reaction at carbon edge planes, intercalation of the catalyst or inhibitor, and electron transfer. Potassium donates its outer electron to the π-electron clouds associated with the carbon layers. Extra electrons facilitate the formation of an unstable reaction intermediate which leads to the evolution of carbon monoxide. The vacant d-orbitals in vanadium stabilize π-electrons in the carbon layers, thereby making carbon monoxide evolution less likely. Thus, opposite extremes of a single effect account for both catalysis and inhibition.     

Alternierende und nichtalternierende Polymethine – eine Verallgemeinerung bisheriger Farbregeln

Alternant and Nonalternant Polymethines – a Generalisation of the Hitherto Existing Colour Rules In alternant polymethines the characteristic π-electron density alternation is maintained on branching or other modification of the structure. Alternant polymethines commonly absorb at shorter wavelengths than the parent non-branched polymethine units. Nonalternant polymethines are characterised by a perturbation of the uniform π-electron density alternation. They absorb at considerably longer wavelengths than the constituent non-branched polymethine units. If the polymethine structure of alternant and nonalternant polymethines is changed in favour of aromatic or polyenic systems the light absorption is shifted generally to shorter wavelengths.     

Non-metal catalytic synthesis of graphene from a polythiophene monolayer on silicon dioxide

Direct synthesis of graphene without metal catalysts on a dielectric substrate is a major goal in graphene-based electronics and is an increasingly popular nanotechnology alternative to metal oxide semiconductor technology. However, current methods for the synthesis of these graphenes have many limitations, including the use of metal catalyst. Herein, we report a facile approach to the direct synthesis of graphene sheets based on the self-assembled monolayers (SAMs) technique. The new method for metal catalyst-free direct synthesis of a graphene sheet is through a solution-processable, inexpensive, easy, and reproducible cross-linked polythiophene self-assembled monolayer (SAM) that is formed via the [4 + 2] π cycloaddition reaction of π-electron conjugated thiophene layer self-assembled on the dielectric silicon dioxide substrate. The bifunctional molecules were carefully designed to create an SAM via silanization of alkoxy silane groups on the SiO₂ substrate, and at the other end, a thin cross-linked polythiophene layer via a [4 + 2] π-electron cycloaddition reaction of π-electron conjugated thiophene SAM. By heating the cross-linked polythiophene SAM up to 1000 °C under a high vacuum, single-layered or few-layered graphene sheets were successfully prepared on the dielectric silicon oxide substrate.     

Combustion characteristics of crude oils

Small‐scale free‐burning pool fire tests were conducted in a cone calorimeter to obtain the combustion characteristics of 14 different crude oils. Measurements included the heat release rate based on oxygen consumption calorimetry, mass loss rate, radiative heat flux from the flame to a nearby target, liquid fuel temperature, extinction coefficient and CO₂ and CO concentrations in the exhaust duct. The effective heat of combustion, radiative heat loss fraction and smoke yield were calculated on the basis of the measured data. It was found that the heat release rate, mass loss rate, flame radiation and smoke yield were a function of the type of crude oil. The effective heat of combustion, extinction coefficient and radiative heat loss fraction were nearly constant for the range of crude oils evaluated in this programme. The heat release rate, mass loss rate, flame radiation and smoke yield appeared to correlate well with the crude oil density. Copyright © 2001 John Wiley & Sons, Ltd.     

Solids volume fraction measurements on riser flow using a temporal‐histogram based DIA method

In this article we introduce a temporal histogram‐based method for digital image analysis (DIA) of pseudo‐2D fluidized bed risers. This method enables an accurate whole field measurement of the solids volume fraction in lab‐scale pseudo‐2D riser flows by successfully removing image imperfections and merely accounting for the particles’ intensity. Moreover, the new correlation between normalized intensity and solids volume fraction that is proposed in this work enables a quantitative approach for solids concentration measurements by DIA techniques. This technique can be easily adjusted with experimental settings and shows a great stability against adverse imaging conditions. The combination of this parameter‐free method with particle image velocimetry under riser flow conditions has been successfully applied, enabling the experimental acquisition of full field hydrodynamic data. © 2016 American Institute of Chemical Engineers AIChE J, 62: 2681–2698, 2016     

The Thermal Reaction of Substituted Vinylcyclopropanes with Iron Pentacarbonyl

The thermal reactions of 1-aryl-1-cyclopropylethylenes and 1,1-dicyclopropylethylene with pentacarbonyliron are investigated. Reactions of the former substrates yield 2-aryl-1,3-pentadiene-tricarbonyliron complexes via cyclopropane ring opening, hydrogen migration and coordination to iron. Reaction with the latter substrate gives 2-cyclopropyl-1,3-pentadienetricarbonyliron in similar fashion, and, in addition, 3-(1′-propenyl)-cyclohex-2-enone tricarbonyliron derived from the opening of the second ring coupled with carbon monoxide insertion. The cyclopropane ring serves as a two π-electron donor in these reactions, and the vinylcyclopropane system emerges as a novel source of four π-electrons which are available to coordination in direct analogy to reactions of formal diene systems with iron carbonyls.