Showing papers on "Particle published in 1974"

Studies on the preparation and characterisation of monodisperse polystyrene laticee: III. Preparation without added surface active agents

Abstract: Preparative methods have been developed in order to obtain monodisperse polystyrene latices in the absence of added surface active agents. By suitable adjustment of the ionic strength of the aqueous phase the initiator concentration and the polymerisation temperature it was found possible to obtain a range of particle sizes, ca. 0.1 to 1.0 ,um, by single-stage reactions. The total initial ionic strength of the aqueous phase was found to play a critical function in determining particle size. A formula has been derived from the experimental data which enables the preparative conditions required to form a latex, containing particles of a particular size, to be predicted.

Particle-loaded microfiber sheet product and respirators made therefrom

Abstract: A self-supporting durable flexible conformable low-pressure-drop porous sheet product that contains a uniform three-dimensional arrangement of discrete solid particles. This sheet product comprises, in addition to the particles, a web of melt-blown microfibers in which the particles are uniformly dispersed. The particles are physically held in the web, even though there is only point contact between the microfibers and the particles, whereby the full surface of the particles is available for interaction with a medium to which the sheet product is exposed. The sheet product is especially useful in respirators in which, for example, the sheet product is shaped as a cup-like member adapted to fit over the mouth and nose of a person.

Hydrodynamic chromatography a technique for size analysis of colloidal particles

Abstract: When colloidal materials are carried in aqueous suspension through packed beds of spherical particles, it has been observed that the rate of transport of the colloidal particles depends on such factors as the size of the colloid, the size of the packing and the ionic composition of the aqueous phase. From such observations, a chromatographic technique has been developed, called hydrodynamic chromatography, which can yield size information on a variety of colloidal materials in the submicron range. Several examples are provided that illustrate how the technique is applied in the study of polymer latexes to determine particle size, assess particle size distribution, follow emulsion polymerization kinetics and provide evidence for particle agglomeration. The origin of the various transport and separation phenomena is also discussed.

Photoballistics of volcanic jet activity at Stromboli, Italy

Abstract: Two night eruptions of the volcano Stromboli were studied through 70-mm photography. Single-camera techniques were used. Particle sphericity, constant velocity in the frame, and radial symmetry were assumed. Properties of the particulate phase found through analysis include: particle size, velocity, total number of particles ejected, angular dispersion and distribution in the jet, time variation of particle size and apparent velocity distribution, averaged volume flux, and kinetic energy carried by the condensed phase. The frequency distributions of particle size and apparent velocities are found to be approximately log normal. The properties of the gas phase were inferred from the fact that it was the transporting medium for the condensed phase. Gas velocity and time variation, volume flux of gas, dynamic pressure, mass erupted, and density were estimated. A CO2-H2O mixture is possible for the observed eruptions. The flow was subsonic. Velocity variations may be explained by an organ pipe resonance. Particle collimation may be produced by a Magnus effect.

Diffusion experiments with numerically integrated isotropic turbulence.

Abstract: Results are presented of computer simulations of particle diffusion on a numerically integrated, decaying isotropic turbulent flow field. The diffusion of both fluid particles and “small” spherical particles is studied. Comparisons are made of the various temporal autocorrelation coefficients. It is found that for “short” times, the Lagrangian (fluid point) velocity correlation is larger than the Eulerian correlation, while for longer times the opposite is true. It is also found in the “small” spherical particle case that as the response time of the particle is increased, the velocity autocorrelation coefficient increases.

The dimensions and aggregation of ice crystals in natural clouds

Abstract: From ice particles collected in clouds and at ground stations in the Cascade Mountains during two winter seasons, measurements have been obtained of the lengths and widths of needles and columnar crystals and the thicknesses and diameters of hexagonal plates. Best-fit empirical relationships between these dimensions are presented. The particles have also been examined to obtain detailed information on the properties of aggregates of ice particles. The maximum dimensions of aggregates and the probability of the occurrence of aggregates decrease with decreasing temperature, but both exhibit a local maximum near the dendritic growth region. Below −15°C and for particle concentrations less than 0.1 cm−3, aggregates are unlikely to form; above −5°C and for particle concentrations in excess of 1 cm−3 there is more than a 50% chance of the formation of aggregates. The size spectra of aggregates depend mainly on the sizes of their component crystals. The number of component crystals in aggregates of various sizes is given.

The influence of carbon black on the extrusion characteristics and rheological properties of elastomers: Polybutadiene and butadiene–styrene copolymer

Abstract: An experimental study of the influence of carbon black loading, particle size, and structure on the extrusion characteristics of polybutadiene and butadiene–styrene copolymer synthetic rubber is described. The development of extrudate distortion and its mechanisms are considered. The viscosity and die swell have been related to black loading, particle size, and structure. Generally, it is found that black surface area and structure acts to increase viscosity and decrease elastic memory. This situation is analyzed in terms of the theory of nonlinear viscoelasticity. Two mechanistic theories are described which may explain this behavior. One theory is based on the continuum mechanics analysis of suspensions of particles in viscoelastic media. The rheological behavior of the black compounds is explained in terms of the increased severity of deformation in the polymer matrix surrounding the particle agglomerates. The second theory is based on the view of an entanglement network containing black particles. Polymer chains may be adsorbed onto the surface giving rise to increased entanglement densities.

Surface diffusion in liquid‐filled pores

Abstract: Surface diffusivities of benzaldehyde in liquid-filled pores of Amberlite particles (polystyrene) were measured at 25°C using water as a solvent. For particles of different surface areas but chemically similar pore surfaces, the intrinsic surface diffusivity Ds' was about the same, but the relative importance of surface to pore-volume diffusion increased with surface area. For a single type of particle, the adsorption capacity was decreased about twenty-fold by adding up to 19 mole % methanol to the solvent. This was accompanied by an increase in Ds' from 1.2 × 10−8 to 1.2 × 10−7 cm2/s. These results were interpreted in terms of a two-step theory for surface migration: (1) formation of a vacant site on the adsorbent surface followed by (2) movement of the adsorbate molecule into the site by breaking the surface-adsorbate bond. The theory predicts that surface transport will be large when the surface area is high and that the Ds' will be large when the heat of adsorption is low, and when the bond between solvent molecules and the surface is weak. In our studies the surface contribution to intraparticle transport was as much as 20 times the contribution due to pore-volume diffusion. This ratio increases as the concentration of adsorbate in the liquid decreases.

Trajectory calculation of particle deposition in deep bed filtration: Part I. Model formulation

Abstract: The packed bed model developed by Payatakes, Tien, and Turian (1973a, 1973b) is used as a basis for the study of particle deposition in deep bed filtration. The size of the particulate matters present in the suspension is assumed to be sufficiently large for Brownian motion to be negligible, but small enough for straining to be unimportant. The prediction of the rate of particle deposition is based on the one-step trajectory approach. The collector is represented by a unit bed element of the porous media model and the particle trajectory equation is formulated to include the gravitational force, the hydrodynamic force and torque (including the correction for the presence of the unit cell wall), the London force (including the retardation effect, which is shown to be of primary importance under conditions usually met in deep bed filtration systems), and the electrokinetic force. Sample capture trajectories, including the limiting capture trajectories, are given. Based on the limiting trajectories and the assumption of uniform particle distribution at the entrance of each unit cell, the number fractions (of suspended particles) impacted on each unit cell are determined and then used to calculate the fraction impacted on the entire unit collector and also the value of the filter coefficient for a clean bed. It is also shown how the capture trajectory calculation can be used to determine the local rate of deposition along the wall of a given unit cell.

Mechanism of alumina buildup in tundish nozzles during continuous casting of aluminum-killed steels

Abstract: During continuous casting of aluminum-killed steels, the pouring rate through the tundish nozzle often diminishes, posing serious operating problems. This happens because a buildup of microscopic alumina particles at the nozzle orifice effectively decreases the nozzle orifice diameter and causes constriction of the liquid-steel pouring stream. There are two major aspects of the constriction problem: (1) the source of the depositing particles, and (2) the mechanism by which the particles deposit at the nozzle orifice. Detailed microscopic examination of the buildup of alumina particles in nozzles from various casting trials and petrographic examination of the nozzle refractory indicated that the particles depositing at the nozzle orifice were already present in the melt because of deoxidation and reoxidation processes. A model proposed herein explains why and how the alumina particles deposit and stay at the nozzle orifice. The model considers a microscopically thin boundary layer at the nozzle bore where the velocity of the liquid steel approaches zero. Particles passing close to the refractory surface and in the slow-moving boundary layer attach to the wall and to each other. The presence of eddy currents in and close to the turbulent boundary layer increase the particle to particle collision. Such collisions of the particles thrown from outer region of boundary layers with the already attached particles keep on dumping the particles toward the refractory surface. The high interfacial energy of alumina inclusions in steel is a driving force for particles to attach to the refractory wall and to each other, and high-temperature sintering then occurs to form a network of alumina particles.

Association of the Membrane-Penetrating Polypeptide Segment of the Human Erythrocyte MN-Glycoprotein with Phospholipid Bilayers. I. Formation of Freeze-Etch Intramembranous Particles

Abstract: The membrane-penetrating segment of the surface MN-glycoprotein of the human erythrocyte is contained intact within the tryptic peptide T(is). We report here on the association of this peptide with hydrated phospholipid vesicles. Under these conditions 80 A intramembranous particles, as seen by freeze-etch electron microscopy, are produced that are similar in size to those seen in the native erythrocyte membrane. These particles increase in number as a linear function of T(is) concentration and a plot of particle number versus concentration is compatible with a micelle-like phenomenon; from this curve the critical concentration for the formation of particles is estimated to be approximately one mole of T(is) to 120 moles of lecithin. These data suggest that the membrane-penetrating peptide T(is) is being incorporated, monomerically and multimerically, within the hydrocarbon phase of lecithin bilayers. From these data it can be calculated that each intramembranous particle contains between 10 and 20 T(is) monomers. The peptide portion of each particle, therefore, has a molecular weight of 45,000-85,000. An exact analogy cannot be drawn at this time between the in vivo structure of erythrocyte intramembranous particles and the reconstituted particles described here, although an argument has been constructed to support this possibility. What is clear is that the reconstituted system promises to be useful for further examination of protein-lipid interactions in membranes.

Method for applying coatings to solid particles

Abstract: The apparatus provides a homogeneous (with respect to particle size), dense, mass of sized particles in random motion so that highly uniform coatings of the same or of different solids can be applied to each particle by conventional spray-coating with the liquified coating material(s). The apparatus is a horizontal rotary drum containing lifting flights. A novel deflector pan is fixed in space inside the upper section of the drum which deflects particles falling from the lifting flights to the side of the drum where they form a narrow, dense falling cascade. The coating material is sprayed onto the cascading particles, preferably as they free-fall after leaving the lower edge of the pan. However, if desired, some or most of the coating material may be directed onto the top edge of the moving bed including the juncture of the cascade therewith.

The Compton-Getting Effect for low energy particles

Abstract: It was found that the traditional first-order Compton-Getting effect, which relates particle distributions as observed in two frames of reference moving with constant relative velocity, is inadequate for the description of low energy particles (less than a few hundred keV/nucleon) in the solar system. An exact procedure is given for recovering both isotropic and anisotropic distributions in the solar wind frame from observations made in a spacecraft frame. The method was illustrated by analyzing a particle event observed on IPM-7.

Aerosol‐particle sizes from light emission during excitation by TEA CO2 laser pulses

Abstract: Preliminary measurements of the time‐dependent light emission from aerosol particles (generated from submicron powders of carbon black and alumina) during excitation with pulses from a TEA CO2 laser show that this emission may be simply related to particle size

Stokes’ Settling and Chemical Reactivity of Suspended Particles in Natural Waters

Abstract: Equations are given for the Stokes settling velocities of the following particle shapes: the sphere, oblate spheroid, prolate spheroid, circular cylinder, elliptic cylinder, disc, and hemispherical cap. Dissolution of calcareous and silicate particles settling through ocean water, based on literature data, is analyzed in terms of a model for dissolution rate independent of the particle surface area, and a model for dissolution rate dependent on a surface reaction. The settling of dissolving particles in the presence of a countercurrent of upwelling water may lead to formation of thin nepheloid layers. Settling of calcite crystals through a stratified water column is treated as a case of variable nucleation (production) rates, dissolution and agglomeration of crystals en route to the bottom. A stochastic model presented in the paper gives a reasonably simple method for treating transient transport of particles in a physically heterogeneous water column.

Cosmic rays—astronomy with energetic particles

Abstract: All nuclei in the periodic table of the elements, as well as electrons and positrons, are present in the stream of cosmic-ray particles. The cosmic-ray particles constitute the only sample of matter from outside the solar system which reaches the earth. Some of the most accurate knowledge of the extrasolar-element abundance distribution is based on the study of these particles. Observational data concerning the cosmic rays are discussed along with cosmic-ray sources, questions of particle interactions and propagation, the electron spectrum, and the significance of the positron component. The directions of cosmic ray research in the immediate future are also considered, giving attention to some fundamental questions which have not yet been answered.

Some Physical Characteristics of Microcrystalline Cellulose 1. Powders for Pharmaceutical Use

Abstract: Four grades of coamercially available microcrystalline cellulose have been examined and the appearance, particle size distributions, specific surface areas, pore size distributions and surface energies determined. The median Stokes diamsters ahow general correlation with published data, but Coulter counter results are larger by a factor of approximately 1.4. Correlation is also seen with values obtained from air permeametry experiments.Scanning electron-microscopy demonstrated the presence of two general types of particle, one roughly rod-like and the other an irregular mass. At higher magnifications, fully hydrolysed samples show a microfibrillar structure, the individual fibrils possessing a transparent longitudinal axis. The possibility that the fibrils are hollow is confirmed by analysis of the adsorption isotherms using mathematical models which indicate that the materials are porous, With a modal radius value of about 2.0 nm.

Particle detecting system

Abstract: Submicron-sized particles are detected by a system which observes emission, as by scattering or by fluorescence from particles undergoing Brownian motion in a region of a fluid medium excited by an evanescent wave created adjacent an interface between the fluid medium and a multiple internal totally reflecting cell or light guide. The excited region can range in depth between several wavelengths and a fraction of the wavelength of the exciting beam, hence serves as an "aperture" having a dimension of about the same order of magnitude as the particles being detected. The particles can be classified according to size by examining the amplitude modulation arising out of the motion of the particles through the aperture.