A PROCESS FOR DISPOSAL OF HALON 1301 (CBrF3)

We report the results of an experimental and kinetic modeling study of gas-phase reaction between methane and halon 1301 (CBrF³). At 1000 K, with an equimolar feed of CH⁴ and CBrF³ and at a residence time of 1 second, CHF³ and CH³Br are produced at selectivities in excess of 90%. Other reaction products detected include C²H²F², C²H², C²H², and CHBrF². Very good agreement between kinetic modeling and experimental results was obtained.     

Influence of Drying Conditions on the Hazelnut Quality. III. Browning

The influence of drying conditions on browning in hazelnut (Corylus avellana L.) has been studied by means of color measurement. Samples of unshelled and shelled hazelnuts were dried under six air temperatures (30. 40, 50, 60, 70 and 80°C). The drying experiments were done with forced air circulation, and two varieties of hazelnut were investigated, Negret and Pauetet. CiELab system was used to evaluate changes in total color (δE^*), lightness (L^*), chroma (C^*) and hue angle (H^*) on dried hazelnuts. Browning of hazelnut was observed to occur a1 all temperatures studied. The rate of pigment formation was determined from the δE' values with zero-order kinetic model, and temperature dependence was described by the Arrhenius equation with an activation energy (E_a) varying from 28 to 39 kJlmol. Negret variety showed the highest rate of browning.     

EVALUATION OF SOME TRANSPORT AND THERMODYNAMIC PROPERTIES OF SUPERHEATED STEAM: EFFECTS OF STEAM TEMPERATURE AND PRESSURE

For machine computation of drying, humidification and dehumidification processes it is necessary to have reliable correlations to predict transport and thermodynamic properties of the drying medium as functions of temperature and pressure. In this paper empirical correlations for specific volume, dynamic viscosity, thermal conductivity as well as specific isobaric heat capacity of superheated steam over the temperature range of 160-500^° C and the pressure range of 100-500 kPa are presented. The Prandtl numbers at various temperatures and pressures are also presented. Comments on the properties and the use of these correlations are given.     

GENERALIZED EQUATION OF PRESSURE LOSSES IN DISPERSED POWDER FLOW THROUGH VERTICAL PIPES

The results of the experimental investigation of pressure losses in a vertical co-current flow of a two phase solid particles-air system are given for the transient character of flow of the continuous phase. The dispersed phase was formed by 6 fractions of polypropylene particles and 5 fractions of glass ballotini of 90 · 10^-6-370 · 10^-6 m and 60 · 10^-6-200 · 10^-6 m equivalent diameter, respectively. The relative mass fraction of solid particles varied over the interval 0-1 dilute. On the basis of experimental data the generalized equation for the computation of pressure losses for the vertical transport was derived. The pressure losses calculated on the basis of this equation were compared with data published by 9 authors.     

Mobility of Cation Vacancies in the Solid Solution KCl-RbCl

Of theoretical interest is the way in which the jump frequencies of cations A⁺ and B⁺ vary in the solid solution (A⁺ B⁺)X^- as a function of composition. To provide experimental data for analysis, the electrical conductivity of various compositions of pure and doped KCI-RbCI was measured, and from these measurements the cation vacancy mobility μv(c⁺) was calculated. In this system μv(c⁺) was constant. The relation of this finding to mass transport properties is discussed.     

THERMODYNAMICS OF CONCENTRATED ELECTROLYTE SOLUTIONS

A new equation is derived for the activity coefficient of an electrolyte in a liquid solvent (such as water) as a function of electrolyte concentration. This equation contains contributions from long-range electrostatic forces and from short-range attractive forces; it holds from high dilution to the solubility limit. The new equation is based upon extended Debye-Huckel theory for long-range effects and upon the local-composition concept for short-range effects. For a single-electrolyte solution, the new equation contains only one adjustable energy parameter and three other parameters that are ion-specific, not electrolyte-specific. Therefore, extension to multicomponent electrolyte solutions follows without additional assumptions. Ion-specific parameters are reported for H⁺, K⁺, Li^-, Br^- and Cl^- ions. Calculated and experimental activity coefficients are in excellent agreement for aqueous solutions of HBr, HC1, KBr, KCl, LiBr and LiCl.     

H2, CO, N2, O2和CH4在碳膜中的扩散

Diffusion of pure H2, CO, N2,O2 and CH4 gases through nanoporous carbon membrane is investigated by carrying out non-equilibrium molecular dynamics （NEMD） simulations. The flux, transport diffusivity and activation energy for the pure gases diffusing through carbon membranes with various pore widths were investigated. The simulation results reveal that transport diffusivity increases with temperature and pore width, and its values have a magnitude of 10^-7 m^2·s^-1 for pore widths of about 0.80 to 1.21 nm at 273 to 300 K. The activation energies for the gases diffusion through the membrane with various pore widths are about 1-5 kJ·mol^-1, The results of transport diffusivities are comparable with that of Rao and Sircar （J. Membr. Sci., 1996）, indicating the NEMD simulation method is a good tool for predicting the transport diffusivities for gases in porous materials, which is always difficult to be accurately measured by experiments.     

Mechanism of Oxygen Diffusion in Glassmelts Containing Variable-Valence Ions

A mechanism is proposed to describe the influence of redox reactions, which involve variable-valence ions, on the diffusional mass transport of molecular dissolved oxygen in glassmelts. The concentration profile for molecular dissolved oxygen in a melt with diffusional transport in one direction in a Cartesian coordinate system is described by a differential equation: ∂(O₂/∂ t = D_c (∂²[O₂]/∂ x ²), where D_c depends on the actual value of the diffusivity D of physically dissolved oxygen, the local molecular oxygen concentration, the concentration of variable-valence ions, and the equilibrium constant for the relevant redox reaction. This equation is applicable for diffusion into or outwards from the melt from or into the furnace atmosphere. It is shown here that the value of D_c is always less than D . Concentration profiles for diffusing oxygen in glassmelts with refining agents (containing variable-valence ions) are thus steeper than profiles in melts without refining agents. A decrease in temperature of a glassmelt with variable-valence ions generally leads to diffusion of oxygen into the melt. The flux of oxygen gas into (oxidation) or out (reduction) of the melt is proportional to ( D/D_c )^1/2 and is enhanced by the effect of variable-valence ions dissolved in the melt.     

Exchange and oxidation of CO on O-predosed Rh---Al2O3 and Rh---CeO2 catalysts

Exchange and oxidation of C¹⁶O were investigated at 450°C on ¹⁸O-predosed Rh and Pt catalysts supported on A1₂O₃, CeO₂ and CeO₂-Al₂O₃. In all cases, a rapid exchange of C¹⁶O with the surface can be observed. CO oxidation leads to C¹⁶O₂, C¹⁶O¹⁸O and C¹⁸O₂. Significant formation of C¹⁶O₂ is due to the relatively high ¹⁶O coverage in reaction resulting from the C¹⁶O exchange and from an exchange between O surface species and ¹⁶O internal atoms. Hydrogen is also formed via a water-gas shift reaction (CO + surface OH) in higher proportion on CeO₂-containing catalysts than on A1₂O₃. Chlorine inhibits all the reactions (exchange, oxidation and WGS) and particularly the internal exchange.     

Practical applications of modified poly(ethylene oxide) networks

Modified poly(ethylene oxide) (PEO) networks have been studied as phase transfer catalysts, flocculates and solvent-free polymer electrolytes. The activity of the hydrogels has been investigated with respect to the structure and crosslinking density of the networks, their degree of quaternization and amphiphilic properties (hydrophilicity coefficients). It has been found that the microenvironment of the active sites (EO segments and ammonium ions) affects the catalytic activity and sorption ability of the modified networks. Hydrophobic organic compounds such as sodium picrate and bromophenolblue are bound predominantly to the lipophilic quaternary ammonium ions. A stable level of electrical conductivity of 5.0×10⁻⁵ S cm⁻¹ was achieved without using of additives. A probable mechanism of ion transport within the networks has been proposed. Potential applications of PEO-based materials as solvent-free solid polymer electrolytes are also discussed.     

Experimental Evaluation of the Acceptor-States Compensation in Positive-Temperature-Coefficient-Type Barium Titanate

Experimental evidence shows that the acceptor-state levels in Sb-doped positive-temperature-coefficient-type BaTiO₃ are compensated up to a critical acceptor-state density. Using the slope of the natural logarithm of the resistivity with respect to 1/ T , instead of maximum resistivity as a measure for the acceptor-state density, it is possible to estimate this critical value. The value obtained (4.2 × 10¹⁷ m⁻²) is believed to be the first reported estimate based on experimental data. It is in good agreement with the estimate of 6 × 10¹⁷ m⁻² (first reported by Jonker) obtained from the spontaneous polarization of BaTiO₃. This shows that the ferroelectric behavior of BaTiO₃ is indeed a feasible explanation for the low resistivity below the Curie point, as proposed by Jonker.     

Electrodeposition of cesium at mercury electrodes in the tri-1-butylmethylammonium bis((trifluoromethyl)sulfonyl)imide room-temperature ionic liquid

The electrochemistry of cesium was investigated at mercury electrodes in the tri-1-butylmethylammonium bis((trifluoromethyl)sulfonyl)imide (Bu₃MeN⁺Tf₂N⁻) room-temperature ionic liquid (RTIL) by using cyclic staircase voltammetry, rotating disk electrode voltammetry, and chronoamperometry. The reduction of cesium ions at mercury exhibits quasireversible behavior with k⁰ = 9.8 × 10⁻⁵ cm s⁻¹ and = 0.36. The diffusion coefficient of Cs⁺ in this RTIL was 1.04 × 10⁻⁸ cm² s⁻¹ at 303 K. Bulk deposition/stripping experiments conducted at a rotating mercury film electrode gave an average recovery of 97% of the electrodeposited Cs. The density, absolute viscosity, and equivalent conductance of Bu₃MeN⁺Tf₂N⁻ were measured over the range of temperatures from 298 to 353 K. A polynomial equation describing the temperature dependence of the density is presented. Both the viscosity and conductance exhibited the non-Arrhenius temperature dependence typical of glass-forming liquids. The ideal glass transition temperature and the activation energies for viscosity and conductance were obtained by fitting the Vogel–Tammann–Fulcher (VTF) equation to the experimental data for these transport properties.     

EFFECTIVE DIFFUSIVITY ASSOCIATED WITH AXIAL TRANSPORT IN INSULATED OPEN-ENDED GORTER-MELLINK DUCTS

Steady, single-phase transport characterized by high eddy diffusivity in axial direction is a special case of vessel transport phenomena which has not been studied systematically so far. In the present paper, experiments are reported for a Gorter-Mellink duct, at zero net mass flow, covering turbulent eddy transport in cold He⁴ pressurized beyond its thermodynamic critical pressure above 4 K. Axial transport in vertical direction is induced by gravitational buoyancy. A new phenomenological equation is proposed on the basis of quantum fluid convection postulated originally for He II below the lambda point (Goner and Mellink, 1949). Our data agree reasonably with the equation.     

Initial Sintering of Submicrometer Titania Anatase Powder

Measurements of surface area reduction of TiO₂ anatase powder (of initially 100 m²· g⁻¹) were carried out for various partial pressures of water and oxygen at 823 K. The kinetic equation obtained for the experimental rates has the formulation r = k[P _H2O]^1/α [ P _O2]^1/β where α and β are equal to 2 and -12, respectively. A mechanistic model involving six consecutive elementary steps was developed, in which hydroxyl species play a dominant role. No geometrical assumption is required. The general expression of the deduced theoretical rates has the same form as previously given. The comparison between the experimental and the predicted rates points out that the rate-limiting step is the surface diffusion of hydroxyl species. This model can easily be used for any other compounds, for particle growth, and for porosity elimination.     

ON THE FLEXIBILITY AND LIMITATIONS OF CUBIC EQUATIONS OF STATE

Cubic equations of state have received much attention during the last decade^1-10 due to their simplicity and practical success. In particular, Abbott² has discussed a general form of the cubic equation of state and shown that cubic equations of state commonly used for chemical engineering calculations^11,12 are specializations of the generic form. The purpose of this work is to further study the flexibility and limitations of the generic form so as to enhance the understanding of recent developments and to provide a guide for future search of better specializations.     

Electrochromic features of hybrid films composed of polyaniline and metal hexacyanoferrate

Hybrid organic/inorganic films, composed of polyaniline (PANI) matrix and Prussian blue-like nickel hexacyanoferrate redox centers, showed reversible electrochromic behavior in acidic potassium salt electrolytes. The system's coloration properties were assessed from various spectroelectrochemical measurements including voltabsorptometry that involved monitoring of the time-derivative signal of absorbance at 700 and 410 nm as a function of linearly scanned potential. Gold-covered foil was used as a conductive, optically transparent, substrate onto which the composite film was electrodeposited by potential cycling in the mixture for modification consisting of aniline monomer, Ni²⁺, Fe(CN)₆³⁻ and electrolyte containing K⁺ and H⁺ ions. An important feature of hybrid (composite) material was that its electrochromic properties were dominated by color changes occurring in the PANI component. Coloration originating from nickel hexacyanoferrate barely affected the system's electrochromic characteristics. But the cyanometallate redox centers distributed in the PANI matrix behaved reversibly as expected for a system capable of fast charge transport.     

Crown ether-thiourea conjugates as ion transporters

Na⁺,Cl^?and K⁺are the most abundant electrolytes present in biological fluids that are essential to the regulation of pH homeostasis,membrane potential and cell volume in living organisms.Herein,we report synthetic crown ether-thiourea conjugates as a cation/anion symporter,which can transport both Na+and Cl^–across lipid bilayers with relatively high transport activity.Surprisingly,the ion transport activities were diminished when high concentrations of K+ions were present outside the vesicles.This unusual behavior resulted from the strong affinity of the transporters for K⁺ions,which led to predominant partitioning of the transporters as the K⁺complexes in the aqueous phase preventing the transporter incorporation into the membrane.Synthetic membrane transporters with Na⁺,Cl^?and K⁺transport capabilities may have potential biological and medicinal applications.     

两相更新支撑液膜中金属二价镍的迁移行为研究(英文)

A novel disphase supplying supported liquid membrane(DSSLM),containing supplying feed phase and supplying stripping phase for transport behavior of Ni(II),have been studied.The supplying supported feed phase included feed solution and di(2-ethyhexyl) phosphoric acid(HDEHP) as the carrier in kerosene,and supplying stripping phase included HDEHP as the carrier in kerosene and HCl as the stripping agent.The effects of volume ratio of membrane solution to feed solution(O/F),pH,initial concentration of Ni(II) and ionic strength in the feed solution,volume ratio of membrane solution to stripping solution(O/S),concentration of H2SO4 solution,HDEHP concentration in the supplying stripping phase on transport of Ni(II),the advantages of DSSLM compared to the traditional supported liquid membrane(SLM),the system stability,the reuse of membrane solution and the reten-tion of membrane phase were studied.Experimental results indicated that the optimum transport of Ni(II) was ob-tained when H2SO4 concentration was 2.00 mol·L-1,HDEHP concentration was 0.120 mol·L-1,and O/S was 4:1 in the supplying stripping phase,O/F was 1︰10 and pH was 5.20 in the supplying feed phase.The ionic strength in supplying feed phase had no obvious effect on transport of Ni(II).When initial Ni(II) concentration was 2.00×10?4 mol/L,the transport percentage of Ni(II) was up to 93.1 % in 250 min.The kinetic equation was deduced in terms of the law of mass diffusion and the interface chemistry.     

THE GROWTH OF ICE DENDRITES UNDER MIXED CONVECTION CONDITIONS

Dendritic solidification of ice from a supercooled melt is studied under conditions which include thermal convection, forced convection, and the effect of the moving solid-liquid interface, which manifests itself as apparent convection. A theory based on Oseen rectilinear flow suggests that heat transfer from the tip of a growing dendrite can be described by a linear superposition of Peclet numbers due to the individual mechanisms of convection by forced bulk motion of the fluid and by the moving boundary which creates the apparent convection effect

This simple result was tested by plotting the experimental data over the full range available of rates of dendritic growth, in terms of the Nusselt number, as a function of the Peclet number, Pe^*, which is based on the tip radius and the sum of the forced velocity of the fluid and the velocity of the tip of the dendrite. This procedure clearly reveals three regions in which different mechanisms control the process: 1) Dendritic growth is dominated by apparent and natural convection when the Peclet number, Pe^*, is below about 2 10^-3 2) When Pe^* is equal to or greater than 10^-1, dendritic growth is dominated by forced convection. 3) Between these limits, the combined effects of apparent and natural convection compete for dominance with forced convection. The equation which correlates the data over the full range of operating conditions, including the mixed convection region is obtained by non linear superposition of the Nusselt number correlations for Pe^* less than 2 10^-3 and greater than 10^minus;1. The resulting Nusselt number represents the experimental data well over the full range studied.