The stage of nonisothermal nucleation of supercritical particles of a new phase under nonstationary conditions of particle diffusion growth and heat transfer to a medium

An analytical theory has been formulated for the stage of nonisothermal nucleation of supercritical particles in a metastable medium with instantaneously generated initial supersaturation. The theory takes into account the nonuniformities of metastable substance concentration and temperature, which result from the nonstationary diffusion of the substance to growing particles and the nonstationary transfer of the heat of the phase transition from the particles to the medium. The formulated theory extends the approach based on the concept of excluded volume that has recently been used in the theory of the stage of nucleation under isothermal conditions. This approach implies that the nucleation intensity of new particles is suppressed in spherical diffusion regions with certain sizes that surround previously nucleated supercritical particles and remaining unchanged in the rest of the medium. It has been shown that, when self-similar solutions are used for nonstationary equations of substance diffusion to particles and heat transfer from the particles, the ratio between the excluded volume and the particle volume is independent of particle size, thereby enabling one to analytically solve the integral equation for the excluded volume throughout a system as a time function at the stage of nucleation. The main characteristics of the phase transition have been found for the end of the stage of nucleation. Comparison has been carried out with the characteristics obtained in terms of the isothermal and nonisothermal nucleation theory upon uniform vapor consumption and heat dissipation (the mean-field approximation of vapor supersaturation and temperature).     

Enrichment adsorption of a labile substance to the surface of particular mineral particles in river water as investigated by SEM-EDX and dilute-acid extraction/ICP-MS.

The selective enrichment behavior of a labile substance, such as hydroxides, to the surface of particular mineral particles in river water was clarified by scanning electron microscopy/energy dispersive X-ray microanalysis (SEM-EDX). Individual particles other than diatom collected on a 0.45 microm filter from the Fuji and Sagami rivers, central Japan, were analyzed by SEM-EDX and classified into seventeen groups according to the chemical composition and shape. Phosphorus, sulfur, chlorine, manganese and copper detected in each particle collected on the 0.45 microm filter could be successfully used as effective indicators of labile substance secondarily formed and adsorbed afresh in river water, because the detection frequencies of such elements are quite low, or negligible, in fresh mineral particles derived from igneous rocks. The labile substance adsorbed on mineral particles collected on the 0.45 microm filter was also evaluated by dilute-acid leaching, followed by inductively coupled plasma mass spectrometry (ICP-MS). Almost all parts of the manganese detected in individual particles were those adsorbed afresh as hydroxides together with iron and aluminum. Also, anionic elements, such as phosphorus, sulfur and chlorine, formed complexes with the hydroxides and/or were incorporated in them. Mg and/or Ca-rich aluminosilicate groups were the most effective adsorbers of such labile species. However, Si-rich and Na-, K- and Na-Ca rich aluminosilicates did not significantly adsorb the labile substance. Consequently, the remarkable selectivity was clarified in the adsorption process of labile substance to individual mineral particles in river water.     

Aggregation of primary nano and microparticles resulting in formation of hollow structures

It was demonstrated that the formation of preparations of hollow structures in oversaturated vapor or solution, varying from several micrometers to several tens millimeters in size, can be due to the following causes: (a) fast evaporation of the solvent from microdrops of the solution and crystallization of the dissolved substance in subsurface layer of a drop; (b) a chemical reaction between the substance in a drop and a substance in the environment surrounding the drop; (c) aggregation of primary nanoparticles in agitated aqueous suspension; (d) aggregation of particles produced in thermohydrolysis of the solid initial compound. Examples of hollow particle preparations matching the mechanisms indicated above are presented and their peculiarities are discussed.     

ON THE ORIGIN OF 628 nm FLUORESCENCE IN CERTAIN CHLOROPHYLL PREPARATIONS

Abstract— A fluorescence band at 628 nm seen in certain preparations of chlorophyll on polyethylene particles swollen with tetradecane comes not from an impurity of protochlorophyll in the original chlorophyll, but from a substance like protochlorophyll formed upon adsorption of chlorophyll to the particles. Much of the chlorophyll is grafted to polyethylene in the same particles by a process that does not affect the chromophore. These and other properties peculiar to the particles are tentatively ascribed to a prior free radical oxidation process in the swollen particles.     

New approach to the correlation problem: Electron interaction potential as a variable in solving the many-particle Schrödinger equation

The many-electron wave function is represented as the product of the wave function of the independent particles and the function that depends only on the value of the interelectron interaction potential. The function defines the electron correlation effects; a standard linear differential equation was derived to define the function. The equation depends on the functions of independent particles; a generalization of the Hartree-Fock equations including electron correlation was obtained for these functions. The total energy calculation of two-electron ions shows that even solving an ordinary differential equation for the function of independent particles represented by the functions of noninteracting electrons leads to higher accuracy than the one achieved in the Hartree-Fock theory.     

A kinetic model for formation of nanodisperse matter in the gas phase

Taking CsI aerosol as an example, it was shown that growth of primary aerosol particles can be described in terms of both discrete and continuum models. This conclusion is based on the results of experiments carried out using a method that makes it possible to distinguish primary particles against the background of their aggregates, to provide a complete transfer of the primary particles from aerosol bulk to a collector, and to determine the particle sizes by transmission electron microscopy. Under the conditions studied, the size distribution of the primary particles is described by a Fokker—Planck type equation.     

Precision Fitting of the Temperature Dependence of Density and Prediction of the Thermal Expansion Coefficient of Liqiuds

An equation for precision fitting of the temperature dependence of density of any substance in the entire temperature range of its liquid state and an equation for the prediction of the coefficient of thermal expansion, derived from this dependence, was considered. Constants of the equation for 50 liquids were tabulated.     

Adsorption of gases on adsorbents of various nature and porous structure at high pressures

The isotherms of excess adsorption of argon, nitrogen, and carbon dioxide on adsorbents with various porous structures (active carbon AU-71, polymeric sorbent MN-200, and synthetic zeolite NaA) were measured on the precision volumetric-gravimetric device in the pressure range of 0.1—150 MPa and at temperatures 300—400 K. The results of determination of the adsorption volumes of the studied adsorbents were compared using two methods. The first method is based on the Dubinin-Radushkevich equation, whereas the second one involves a conditional division of the weight of the substance in an ampule into the adsorbed portion and the part existing in the gas phase. The behavior of the adsorbed substance is described by the equation of adsorption of complete content corresponding to the physics of the adsorption process. The relation of the parameters of the empirical Dubinin—Radushkevich equation to the energy characteristics of the system was established.     

Kinetics of vinyl acetate emulsion polymerization

The emulsion polymerization of vinyl acetate has generally been considered a special type of reaction that is not covered by the Smith-Ewart theory. Although the number of particles depends on coalescence rates and can not be predicted by this theory, the polymerization rate data are consistent with the general concepts of Smith and Ewart, including reaction primarily inside swollen polymer particles, escape of radicals from particles, and termination of chains inside the particles. Allowing for rapid exchange of radicals following chain transfer leads to a simple equation which fits much of the published data for cases of both very low and very high values of n , the average number of radicals per particle.      

Photochemical degradation of an anionic surfactant by TiO<Subscript>2</Subscript> nanoparticle doped with C,N in aqueous solution

Novel C,N-doped TiO₂ nanoparticles were prepared by a solid phase reaction. The catalyst was characterized by X-ray powder diffraction (XRD), transmission electron microscopy (TEM) and energy dispersive X-ray spectroscopy (EDX). The results showed that crystallite size of synthesized C,N-doped TiO₂ particles were in nanoscale. UV light photocatalytic studies were carried out using sodium naphthalenesulfonate formaldehyde condensate (SNF) as a model pollutant. The effects of initial concentration of surfactant, catalyst amount, pH, addition of oxidant on the reaction rate were ascertained and optimum conditions for maximum degradation was determined. The results indicated that for a solution of 20 mg/L of SNF, almost 98.7% of the substance were removed at pH ~ 4.0 and 0.44 g/L photocatalyst load, with addition of 1 mM K₂S₂O₈ and irradiation time of 90 min. The kinetics of the process was studied, and the photodegradation rate of SNF was found to obey pseudo-first-order kinetics equation represented by the Langmuir–Hinshelwood model.     

Thermotropic behaviour of the complex liquid crystal system containing 8CB [4-cyano-4'-(<Emphasis Type="Italic">n</Emphasis>-octylbiphenyl)] and organic ferrofluid

Summary A ferronematic liquid crystal (FNLC) system containing 8CB (4-cyano-4'-[n-octylbiphenyl]) and magnetite particles was prepared by using the two steps method. The magnetite particles were dispersed in the organic (liquid crystalline) media by using toluene. However, the toluene affected the thermotropic and structural behaviour of the pure basic (8CB) substance, drastically. The product was stable as no any sedimentation and coagulation has been observed during several weeks after the preparation. However, the distribution of magnetite particles was found not to be homogeneous in the nm size range.     

Ash removal from viscous media by supercritical gas extraction

The separation of solid μ-sized particles from viscous media sometimes raises difficulties because sedimentation is too slow, so that use of a centrifuge is required. In the centrifuge, however, the particles may act as an abrasive material. Examples are finely dispersed solid ingredients in shale oil, in oils from tar sand, in hydrogenation process (slurries) suspensions etc.

The media containing the finely dispersed particles are processed with a compressed gas at high density using an entrainer. The conditions are chosen so that the ternary (or pseudoternary) system composed of supercritical gas, entrainer and viscous substance (or mixture) is supercritical. In this way, high concentration of the viscous medium are obtained in the gas phase. As the viscosity of the supercritical gas phase is relatively low, the density of the gas phase can be adjusted by variation of pressure and temperature so that the difference between the solid and the gas phase is sufficiently high for rapid separation of the solid particles. The velocity of sedimentation at constant temperature and pressure depends on the concentration of the viscous substance in the gaseous phase. Even at concentrations of the viscous medium in the gaseous phase, of 30 to 35 % in weight the velocity of sedimentation is sufficiently rapid for the process to be of economical interest.     

Calculating Density of Molecular Liquids Using Agrawal-Thodos Equation

The correlation between the parameters of the Agrawal-Thodos equation, the fundamentalconstants of a substance are established. A modified equation is proposed, in which the minimum set of easily measurable properties of the substance is used as input data.     

Study of Recrystallization Kinetics of AgBr Microcrystals in Water–Gelatin Gel

Recrystallization kinetics (Ostwald ripening) of silver bromide microcrystals in gelatin gel was studied. The study was made on model mixtures containing small silver bromide particles (about 60 nm) and larger microcrystals of different sizes (100–400 nm) and habits (cubic and octahedral). Variations in the average size of large crystals in the system were controlled by spectral turbidimetry. The growth rate of the large crystals was found to be directly proportional to the total solubility of a substance constituting the dispersed phase, as well as to difference in sizes of large and small particles. The kinetics of large crystal growth was also shown significantly to depend on the average distance between particles of the system. The theoretical model describing mass transfer during the Ostwald ripening in the closed disperse system was proposed, providing that interacting particles are immovable.     

Simulation of the motion of solid particles in the carrier liquid flow in a rotating coiled column

Particle fractionation is necessary to solve problems related to the determination of impurity speciation of natural waters, soils, and bottom sediments. It was shown earlier that rotating coiled columns are suitable for field-flow fractionation of particles in a transverse centrifugal field. However, the wide use of rotating coiled columns for separating particles in the substance analysis of natural materials is hampered by the progress of theoretical aspects of the method. In this work, a mathematical model is proposed to describe the behavior of solid particles in the carrier liquid flow in rotating coiled columns. The motion of particles in the flow of a carrier liquid and their migration along the column walls are considered. Equations relating the velocity, radius, and density of a particle; the density and viscosity of the carrier liquid; and the operational and construction parameters of the rotating column are derived. Some practical recommendations are made for the selection and optimization of fractionation conditions.__________Translated from Zhurnal Analiticheskoi Khimii, Vol. 60, No. 4, 2005, pp. 349–356.Original Russian Text Copyright © 2005 by Fedotov, Kronrod, Kasatonova.     

On the fracture of composites based on ultrahigh-molecular-weight polyethylene and fine aluminum particles

Mechanical characteristics of polymerization filled composite materials based on ultrahigh-molecular-weight polyethylene and fine aluminum particles are studied. The prepared composites preserve their ability for high plastic deformations even when the volume filler content is φ = 0.57. For the tensile drawing of the composite material with randomly distributed particles, an equation describing the dependence of breaking stress on the volume filler content is derived. For the model of the composite with regularly ordered particles, the Nielsen equation is the approximation of the equation proposed in this work for a material with randomly distributed particles.     

Violation of the linearity principle of additivity of sorption energy in chromatography. A universal equation describing retention behavior

Deviations from the additivity of energy contributions to substance sorption energies, determined on the basis of thermodynamic studies of GC behavior of homologous series of organic compounds fall into two categories: one for n-alkanes, the other for homologous series containing a functional group. A previously derived equation is proposed for homologous series, describing the deviation from the linear dependence of retention parameters with a propagating homolog n-alkyl chain. The equation permits calculation of retention parameters of homologs starting from the first member in gas-liquid, gas-solid, and liquid-liquid systems. The results prove its universal applicability.     

Influence of Intramolecular Interactions on Some Parameters in Adsorption Thin-Layer Chromatography

Abstract

Using the equation connecting the R_M values with the appropriate data of the adsorption process from solutions the values of the parameters characterizing substance ? mobile phase interactions have been calculated for the systems: silica gel-benzene+acetone and silica gel-acetone+methanol.Quinoline, aniline, nitrobenzene, phenol and their derivatives were the chromatographed substances. An influence of the structure of the substance on the parameter values has been examined, special attention being paid to intramolecular effects, mainly those of hydrogen bonds.