PREDICTION OF LIQUID-PHASE MASS-TRANSFER COEFFICIENTS IN MULTICOMPONENT ION EXCHANGE: COMPARISON OF MATRIX, FILM-MODEL, AND EFFECTIVE-DIFFUSIVITY METHODS

Several methods are evaluated for predicting or correlating liquid-phase mass-transfer coefficients in multicomponent ion exchange. Comparisons are made of methods based on matrix generalizations of binary results, methods using the film-model relation between multicomponent fluxes and binary mass-transfer coefficients, and effective-diffusivity methods. It was determined that methods based on the film model give results in good agreement with matrix generalization methods and, where comparisons can be made, both of these methods give results in good agreement with exact calculations. Effective-diffusivity methods were found to be less reliable. The film-model methods developed in this study are analogous to methods commonly used in nonelectrolyte systems.     

A systematic method to create reaction constraints for stoichiometric matrices

Modeling rate-controlled chemically reactive systems in biocatalysis, fuel combustion, material science, and chemical process engineering involves the quantification and exploitation of interactions between many chemical species. These dynamic chemical systems, having relatively few limiting reactions, can be conceived as a series of snapshots where reactions have fixed extents but otherwise idle. Since the reactions affect the stoichiometric matrix of the internal constraints, such constrained equilibrium states cannot be defined in terms of conventional atomic mass balances.A systematic method for obtaining generalized equilibrium constraints for reaction mechanisms of arbitrary complexity is presented. Reaction matrices are converted into entity conservation matrices using row operations. The simultaneously introduced virtual components enable Gibbs energy calculations for complex reaction schemes including organic systems and enzyme-catalyzed biochemical transformations having multiple limiting reactions. Classical Gibbs energy minimization, which would otherwise readily model phase transformations and solvent interactions, is thereby made accessible to these emerging application fields.     

Electron spin resonance studies of some Canadian coals

Nine Canadian coals of different rank and composition were studied by electron spin resonance. For percentage of fixed carbon in the range of 43 to 78 wt%, the free radical g values were found to increase with decreasing carbon content, and did not level off for the low rank coals. The free radical linewidths are attributed to atomic species such as oxygen and not to protons of hydrogen.     

Guidance for Mutual Disposition of Chromophores for Singlet Fission

The choice of chromophores and of their mutual geometrical arrangement for optimized singlet fission (SF) rates are considered. The electronic matrix element that enters the Fermi golden rule for the rate of SF is worked out algebraically for a simple model, but the density of states factor is not analyzed here. The model treats only the highest occupied and lowest unoccupied orbitals of the partners. It provides an approximate formula that requires only the knowledge of the expansion coefficients of these orbitals and of overlap integrals between atomic orbitals on the partners to obtain an estimate of the electronic matrix element. An illustrative application to a pair of ethylene molecules suggests that favored geometries will be those in which one of the AOs on the first ethylene overlaps with both AOs on the second ethylene, while the other AO on the first ethylene overlaps with at least one, and preferably both, AOs of the second ethylene as little as possible.     

Morphology, thermal relaxations and mechanical properties of layered silicate nanocomposites based upon high-functionality epoxy resins

This paper investigates the possibility of improving the mechanical properties of high-functionality epoxy resins through dispersion of octadecyl ammonium ion-modified layered silicates within the polymer matrix. The different resins used are bifunctional diglycidyl ether of bisphenol-A (DGEBA), trifunctional triglycidyl p-amino phenol (TGAP) and tetrafunctional tetraglycidyldiamino diphenylmethane (TGDDM). All resins are cured with diethyltoluene diamine (DETDA). The morphology of the final, cured material was probed by wide-angle X-ray scattering, as well as optical and atomic force microscopy. The α- and β-relaxation temperatures of the cured systems were determined using dynamic mechanical thermal analysis. It was found that the presence of organoclay steadily decreased both transition temperatures with increasing filler concentration. Further, the effect of different concentrations of the alkyl ammonium-modified layered silicate on the toughness and stiffness of the different epoxy resins was analyzed. All resin systems have shown improvement in both toughness and stiffness of the materials through the incorporation of layered silicates, despite the fact that it is often found that these two properties cannot be simultaneously achieved.     

Determination of concentration dependent diffusion coefficient matrix inside porous sorbent particles

An efficient method is proposed for determining the matrix of diffusion coefficients inside various types of porous sorbents representing the so-called type P (‘pore’) and type S (‘solid’) models of the mass transfer of sorbed molecular species. The method is based upon the application of the analytical solutions of the diffusion equation in the asymptotics of small (t → O) and large (t → ∞) times to the experimental sorption uptake curves obtained for different components and different combinations of a binary mixture from the set of multicomponent mixtures under study. The approach to the problem is shown to be useful in finding relationships between diffusion coefficients and the concentration of the mixture components.     

Reaction and nucleation mechanisms of copper electrodeposition from ammoniacal solutions on vitreous carbon

The reaction and nucleation mechanisms of the electrodeposition of copper from ammoniacal solutions were investigated by cyclic voltammetric (cv) and chronoamperometric (ca) techniques, respectively. Each experiment with both electrochemical techniques was followed by morphological studies by atomic force microscopy (AFM). With respect to pH, the studies were performed on ammoniacal solutions at pH 4, pH 6, and pH 8, each representing a characteristic predominance region in E-pH diagrams. The experimental parameters were copper concentration, scanning rate, deposition potential, and electrode conditioning. It was found that at pH 4 copper electrodeposition occurs via reduction of cupric species to cuprous, which in turn can be either reduced, or disproportionated to metallic copper. At pH 6, deposition occurs from free and complexed cupric species, while at pH 8, only cupric amine complexes are involved. Copper nucleates according to instantaneous mechanisms at pH 4, and progressive nucleation mechanisms at pH 6 and pH 8. The diffusion coefficients of the copper species involved were also determined and are reported in this study.     

Prediction of pyrolysis of pistachio shells based on its components hemicellulose, cellulose and lignin

The objective of this contribution is to describe thermal degradation of pistachio shells by a detailed reaction mechanism. Pistachio shells are assumed to be composed of hemicellulose, cellulose and lignin of which degradation is described by relevant kinetics based on experimental data. The mechanism yields a detailed composition of product gases, and therefore, is well-suited to predict evolution of both thermal decomposition and products. Thermal degradation is described by a system of coupled differential conservation equations for mass, momentum, species, and energy for a pistachio shell particle. The relevant conservation equations are discretised by the Finite Volume Method (FVM) and solved within the conversion module of the Discrete Particle Method (DPM). A comparison between experimental data and predicted results yielded good agreement.     

An analytical approach to evaluate the coefficients of thermal expansion of textile composite materials

An analytical approach is developed to evaluate the coefficients of thermal expansion (CTE) of textile reinforced composites. At the micro level, a cylindrical composite model is employed to model the fiber/matrix thermal and mechanical interactions. The effects of voids and fiber coating on the thermal expansion coefficients of composites are considered at this level. The cylindrical model was then embedded in a macro hybrid finite element solutio structure to calculate the value of the CTE for textile composites. AS‐4/epoxy balanced plain weave textile composites were manufactured. Five different fiber volume fractions were tested for CTE. Evaluatio of the thermal expansion coefficients using the current model was compared to experimental data for in‐plane and out‐of‐plane directions.     

Effect of crystallization on morphology-conductivity relationship in polypyrrole/poly(?-caprolactone) blends

Electrically conducting blends, based on polypyrrole (PPy) as the conductive polymer and poly(?-caprolactone) (PCL) as an insulating polymeric matrix, were prepared by polymerizing pyrrole (Py) in its vapor state inside the PCL matrix. The roles of specific interactions between blend components as well as the crystallization of PCL matrix in the resulting morphology have been analyzed by Fourier-transform infrared spectroscopy (FTIR), thermo-optical analysis (TOA) and atomic force microscopy (AFM). The results indicate that PPy is located within both the intra and interspherulitic regions of the PCL matrix achieving a well-developed connected network. Compared with amorphous matrices, considerable conductivity (around 1 S/cm) was raised with the crystalline PCL matrix with only a relatively low level of the conductive polymer (∼5%) in the blend.     

Morphological and Mechanical Properties Dependence of PLA Amount in PET Matrix Processed by Single-Screw Extrusion

In this study, the dependence on the morphology and mechanical properties was analyzed when different amounts of polylactic acid are added to the polyethylene terephthalate polymer matrix using single-screw extrusion. Thermograms of the polymer blends obtained by differential scanning calorimetry couple to thermal gravimetric analysis show a displacement in the glass transition temperature with the amount of polylactic acid (1, 2.5, 5, and 7.5 wt%) added to the polymer matrix. Scanning electron microscopy and atomic force microscopy images showed two different kinds of morphology, both characteristics of miscible and partially miscible polymer blends. Fourier transform infrared spectroscopy measurements confirmed a physical interaction by hydrogen bond in the polymer blends. The impact resistance and tensile strength are reduced with the polylactic acid addition and are influenced by the fraction of segments of hydrogen bonded in the polyethylene terephthalate/polylactic acid blends as well as their miscibility.     

Influence of the dopant concentration on the morphology of hole-transporting alignment layers based on a polyimide matrix

Investigations on hole-transporting alignment layers (HTALs) consisting of a polyimide matrix doped with hole-transporting materials (HTMs) at different concentrations by means of low-voltage scanning electron microscopy and atomic force microscopy are reported. These layers were recently used as HTALs for liquid crystalline polyfluorenes in polarized light-emitting diodes. For HTM concentrations below 15 wt%, phase-separation was found to be not significant, and the layer characteristics were dominated by the stiff polyimide matrix. These layers aligned polyfluorene very well, resulting in polarization ratios in electroluminescence of more than 20. On the contrary, the morphology was substantially altered at higher dopant concentrations. Moreover, microgrooves became visible after rubbing, indicating that the degree of imidization of the polyimide matrix was reduced. As a result, increasing the concentration of the HTMs above a certain level resulted in a dramatic decrease of the aligning ability of the HTAL.     

Study on relationship between oil,protein, and gossypol in cottonseed kernels

Study on interrelationship between oil, protein, and free gossypol in cottonseed kernels of 97 varieties is reported. Relationship between these properties was studied for each botanical species separately, as well as for all the varieties together. Protein and oil were negatively correlated. The correlation coefficients (γ) were significant at the 1% level in the case ofGossypium arboreum, Gossypium hirsutum, andGossypium barbandense, as well as for all the varieties combined. In the case ofGossypium herbaceum varieties, γ was significant at 5% level. No correlation was found between oil and free gossypol. Protein and free gossypol were negatively correlated. The correlation coefficients were significant at the 1% level in the case ofG. hirsutum, G. barbadense, and all the varieties combined, while it was significant at 5% in the case ofG. herbaceum varieties.     

原子吸收光谱法测定废酸液中铅、锌、钙、钠、钾的含量

研究了火焰原子吸收光谱法测定工厂废酸液中的金属元素铅、锌、钙、钠、钾的含量。对最佳仪器条件进行研究,使被测元素的浓度与吸光度值呈线性关系,相关系数R不小于0.998 5,样品测定结果令人满意。     

Spectroscopic and radiation shielding features of Nemrut,Pasinler, Sarıkamıs and Ikizdere obsidians in Turkey: Experimental and theoretical study

Naturally occurring volcanic glassy rocks, obsidians, are widely used for medical tools and have great interests in alternative medicine, auxiliary therapy, spa, cosmetics and jewellery fields. In this paper, we studied the spectroscopic and radiation shielding properties of obsidian samples collected from four main volcanic regions, named as Nemrut Mountain, Erzurum-Pasinler, Kars-Sarıkamış and Rize-Ikizdere, eastern Turkey. In this regard, important and effective spectroscopic techniques; Electron paramagnetic resonance, X-ray diffraction, Fourier transform infrared spectrometry, Raman spectroscopy, Energy dispersive spectroscopy and Scanning electron microscopy were used to give information about structural, magnetic and morphological features of the obsidians. Additionaly, radiation shielding potentials of the obsidians were evaluated by determination of mass attenuation coefficients, effective atomic numbers, and buildup factors. Recently developed EpiXS code was used for obtaining radiation shielding parameters. It is concluded that the studied obsidians can be considered as radiation shielding materials. By this comprehensive study, both spectroscopic and shielding properties of obsidian samples from different volcanic regions in Turkey are presented and compared.     

Coarsening Kinetics in Mg(Ca,Ti,Y)-Partially-Stabilized Zirconias

The coarsening kinetics of a magnesia-partially-stabilized zirconia with and without ternary additions of calcia, titania, or yttria at the 2 mol% level have been studied as a function of aging time at 1420°C. Addition of titania was found to markedly increase the coarsening rate and it is thought that this is due to a higher precipitate volume fraction in this system. Both calcia and yttria decreased the coarsening kinetics by a similar amount, probably due to both lower precipitate volume fractions and lower interdiffusion coefficients. The precipitate "transformability" was found to vary among the four systems examined, with calcia and yttria acting to stabilize tetragonal precipitates to larger sizes; titania was found to act as a destabilizer. Coherency stresses are important in determining the precipitate morphology and distribution in these alloys but we were unable to ascertain what effect these stresses had on the coarsening rates of the different alloys.     

Acoustical,thermal, and morphological properties of zein reinforced oil palm empty fruit bunch fiber bio‐composites

In this research, biodegradable composites were prepared with zein as a polymer matrix and oil palm empty fruit bunch (OPEFB) as fiber reinforcement. The fibers were treated with sodium hydroxide (NaOH). The effects of sodium hydroxide treatment on sound absorption, thermal stability, and fiber‐polymer matrix interaction in composites were examined. The acoustical sound absorption coefficients of the composites were evaluated using two‐microphone transfer function impedance tube method. The spectral, thermal, and morphological studies of the composites were analyzed and characterized using scanning electron microscope (SEM), thermogravimetric analysis (TGA), and Fourier transform infrared (FTIR) spectroscopy. It was found that in all the biodegradable composites, the sound absorption coefficients increased as the frequency increased. Increases in fiber loading caused sound absorption coefficients of the composites to increase. The sodium hydroxide treatment showed a better interface adhesion on fiber and zein matrix. It was also found that this treatment increased the sound absorption coefficients. This was supported by qualitative analysis on the SEM micrographs and FTIR spectrum. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 44164.     

A two-dimensional, transient, compressible isothermal and two-phase model for the air-side electrode of PEM fuel cells

A two-dimensional, transient, compressible, isothermal and two-phase flow of reactant-product mixture in the air-side electrode of proton exchange membrane fuel cells (PEMFC) are numerically studied in the present paper. The mixture is composed of four species: oxygen, nitrogen, liquid water and water vapor. The governing PDE’s are conservation of the water vapor and oxygen species, momentum equation of the mixture (gas+liquid), mass conservation of the liquid phase, and mass conservation of the mixture. In this study, a separate PDE for the mass conservation of the liquid water is solved to calculate the saturation levels. The capillary pressure was used to determine the slip velocity between the phases. A full compressible form of the momentum equation was used, with the ∇⋅V preserved in the equation. The Maxwell-Stefan equation was used to model the diffusive fluxes of the multi-component gas mixture. The strongly coupled equations are solved based on a recently developed finite volume SIMPLER scheme of S.V. Patankar, Numerical Heat Transfer and Fluid Flow, Hemisphere Publishing Corp., McGraw-Hill Book Company, 1984. The computational domain consists of two regions; an open area (gas delivery channel) linked to a porous gas diffusion layer (GDL). A single (unified) set of the PDE’s are used for the whole domain with the corresponding properties of each sub-domain. A polarization curve for the whole spectrum of the dry and wet regions were obtained. The results were compared with the experiments of E.A. Ticianelli, C.R. Derouin, A. Redondo, S. Srinivasan, J. Electrochem. Soc. 135 (1988) 2209, and good agreements were achieved.     

不同方法测定生物制品中硫柳汞含量的比较

目的比较原子吸收分光光度法(简称仪器法)与滴定法测定生物制品中硫柳汞含量的精密性和准确性,为仪器法列入《中国药典》(2010版)提供依据。方法由不同实验室分别采用仪器法与滴定法测定不同硫柳汞含量的样品,并进行精密性和准确性比较。结果不同实验室在测定硫柳汞含量为65.8、25.0及1.5μg/ml的样品时,仪器法的变异系数均小于滴定法,回收率较滴定法更接近100%;在测定硫柳汞含量为100μg/ml的样品时,两种方法回收率均不理想,但仪器法优于滴定法。结论仪器法测定生物制品中硫柳汞含量的精密性和准确性均优于滴定法,但仍需进一步完善。     

Effects of relative gas flow direction in the anode and cathode on the performance characteristics of a Molten Carbonate Fuel Cell

In this work, three-dimensional numerical simulation of conservation equations for mass, momentum, energy, species and electrochemical reaction has been carried out to compare the performance characteristics of a Molten Carbonate Fuel Cell (MCFC) with three different flow types, co-flow, counter-flow and cross-flow. Depending on the flow types, distributions of pressure difference, temperature and current density in the electrolyte matrix were examined and the fractions of various losses were scrutinized. The simulation results show that the co-flow type has the lowest pressure difference across the matrix and the distributions of temperature and current density are more uniform than other types. However, it was found that since irreversible losses due to ohmic resistance, anode activation and cathode activation are smallest in the counter-flow type, best performance can be expected by the MCFC with the counter-flow type.