Showing papers on "Particle-size distribution published in 1976"

A laser diagnostic technique for the measurement of droplet and particle size distribution

Abstract: : In order to verify the various theoretical models of practical combustion systems, experimental measurements are urgently required. A number of laser instrumentation systems which do not disturb the flow are being devised to satisfy this need. This study describes a technique which has been developed for the measurement of droplet or solid particle size distribution. These measurements are required, for example, as the input to mathematical models of combustion which include evaporation. The technique is based on the Fraunhofer diffraction of a parallel beam of mono-chromatic light by the moving droplets. A Fourier transform lens is used to focus a stationary light pattern onto a multielement photo-detector to measure the diffracted light energy distribution. A mini-computer program translates the light energy distribution into the corresponding, unique, droplet size distribution. The droplets or particles are classified into 31 size groups spanning two decades of diameter, (e.g. 5 micrometers to 500 micrometers using a 300 mm focal length Fourier transform lens).

Wear resistant alloy

Abstract: The alloy of the invention is of the type wherein 30-70% by volume of hard components are homogeneously dispersed in a matrix of binder metal (Fe, Co or Ni). The hard components are carbides or carbonitrides and/or borides of Ti, Zr, Hf, V, Nb, Ta, Cr, Mo and/or W. The mean grain size of the hard component particles is between 0.01 and 1.0 micron and their grain size distribution, represented by the standard deviation S, in which S 2 ≦(M/1+1.5 M z ) 2 μm 2 , not more than 15% of the grains are larger than 1.2 microns.

Dry deposition and resuspension of aerosol particles - a new look at some old problems

Abstract: Some problem areas in the study of dry deposition and resuspension of aerosol particles are viewed from a different perspective. First some inferences are made about possible aerosol particle log-area distributions that could be found in the atmosphere and qualitatively about the roles of dry deposition and resuspension. The dry deposition process in each of five layers a through e (aloft, boundary, canopy, deposition, and edaphic layers) is considered separately, and it appears that the overall process could be rate limited in any one (or more) of these layers. Two simple models for dry deposition to a smooth surface and to a canopy are presented. For the resuspension problem, suggestions are made that a kinetic equation for the soil particle size distribution should be explored further, that the critical u(*) required to move small particles may have an aerodynamic interpretation, that the soil particle size distribution dictates the saltation flux particle size distribution except for very large (approx 1 mm) particles, and that the convective diffusion equation is incapable of describing the suspended particle size distribution. A simple model is proposed for simultaneous deposition with some resuspension. The paper closes with an attempt to explain the physically meaningful variability ofmore » the resuspension factor.« less

Method of preparing micron size particles of solid polymers

Abstract: Micron size polymer particles with narrow particle size distribution are prepared by dissolving the polymer in a suitable liquid solvent, impinging an atomized spray of the dissolved polymer on a moving film of a liquid in which the polymer is insoluble and then recovering the polymer particles from the resultant mixture of liquids.

Liquid developer for use in electrostatic photography and preparation of same

Abstract: Liquid developers for use in electrostatic photography in which toner particles comprising pigment and specific polymer mixes having a particle size of from 0.2 to 0.8 μ, and a particle size distribution such that about 90% of the particles are in the particle size range of from 0.3 to 0.6 μ, are dispersed in a petroleum aliphatic hydrocarbon solvent having a solubility parameter of from 7.0 to 7.5, and method of preparation.

Comparative studies of grain size separates of 60009. [lunar soil samples]

Abstract: Five samples from 60009, the lower half of a double drive tube, were analyzed via grain-size methods, with particle types classified and counted in the coarser grain sizes. Studies were undertaken of particle types and distributions by petrographic methods, of magnetic fractions, of the size splits and magnetic splits as analyzed by ferromagnetic resonance (FMR) techniques, of maturity (based on agglutinate content, FMR index Is/FeO, mean size of sub-cm material, magnetic fraction), of possible reworking or mixing in situ, and of depositional history. Maturity indices are in substantial agreement for all of the five samples. Strong positive correlation of percent agglutinates and percent bedrock-derived lithic fragments, combined with negative correlation of those components with percent single crystal plagioclase, argue against in situ reworking of the same soil.

Particle Size Distribution of Coprecipitated Mn‐Zn Ferrite Powders

Abstract: The particle size distribution of 0.07- to 0.35-μm powders was measured by quantitative electron microscopy using an areal analysis. Measurements of at least 15 particles were required to characterize each size distribution. The specific surface area calculated from the size distributions satisfactorily agreed with that measured by the BET method. For the powders with surface area of 4.4 to 9.7 m2/g, the particle size distributions were generally narrow. In many cases the distributions were near log normal.

Spherical particle populations: approximate analytic relationship between size distribution parameters and integral optical properties

Abstract: The absorption and scattering efficiencies of spherical particles in a certain size range can be approximated by a three-parameter formula. With this formula, an analytic relationship is developed between the extinction, scattering, or adsorption coefficient and the parameters of a log-normal size distribution. The technique permits approximate calculation of these coefficients from the mean radius, its standard deviation, and the total number concentration. By an inversion the size distribution parameters can be estimated from measurements of any of the coefficients at three wavelengths. The calculations require only hand calculators or slide rules. It is shown that use of the technique is justified for many cases of atmospheric aerosol particles and visible radiation.

Magellan: A balloon-borne collection technique for large cosmic dust particles

Abstract: The paper describes a balloon-borne system for collecting large (50 to a few hundred micrometers in the major dimension) solid particles falling through the atmosphere at an altitude of about 30 km which are postulated to be fragments of larger cosmic particles or bodies which disintegrate on entering the atmosphere. The major component of the system is the collection surface - a funnel, 7.2 m in diameter, fabricated from mylar, 12 microns thick, and lightly coated with aluminum. Also described is the sample collector, which collects the particles gathered in the apex of the cone. Two successful flights of short duration using zero-pressure balloons have been achieved. Some examples of particles collected are shown. Mg, Al, Si, S, K, Ca, Ti, and Fe have been detected in these particles by energy dispersive X-ray analysis.

Particle size analysis techniques for suspension concentrates

Abstract: Suspension concentrates are dispersions of sparingly soluble active ingredients in water or in organic solvents and generally contain particles with diameters in the range 0.4–12 μm. Four particle size analysis techniques were tested for their suitability for these formulations. Experimental details which are of particular significance for these formulations and methods of presenting the results are discussed for the different techniques. It was found that: the electron microscope was suitable but time-consuming when used without counting devices; the optical microscope was reliable only for the coarse samples, i.e. samples with a median of the volume distribution greater than 2 μm; the Coulter counter model TA was quick and reliable; the centrifugal disc photosedimentometer was also quick and reliable but its suitability decreased with increasing particle size.

Application of ferrofluid density separation to particles in the micrometer-size range

Abstract: A device designed and described by AVCO* as a ''Ferrofluid Density Separator''/sup (1)/ develops an apparent fluid density from nominally 2 to 20 g/cm/sup 3/ dependent on the magnitude of an imposed magnetic field gradient The ferrofluid retains other normal properties of a liquid One of these devices and a concentration series of ferrofluids were obtained in order to determine the practicality of separating groups of micrometer-size particles into density fractions Such separations would be of enormous value in the study of various particle burdens because particles of interest are almost always diluted with overwhelming amounts of other particles The results of a study of separations of micrometer-size particles with the ferrofluid density separator are presented

Determination of structure parameters and size distribution of colloidal particles by means of small-angle X-ray scattering

Abstract: A dilute silica suspension was used for examining the possibilities of using the small-angle X-ray scattering in the investigation of objects of colloid dimensions The average radius of gyration, weight, volume and specific surface of the SiO2 particles were determined The particle size distribution curve was determined by integral transformation of the scattering curve and by adjusting the parameters of empirical functions

Comparison of the particle size distribution curves determined manually and automatically in an accurately calibrated Coulter Counter.

Abstract: An accurately calibrated Coulter Counter, Model ZB Industrial, was used to compare the size distribution curves of seven different standard particles obtained by calculation and after the attachment of a Channelyser, Model C-1000 coupled to an X Y recorder. Comparisons were made at the modes of the curves and it was found that the automatic method consistently reported the particles to be slightly larger.

Ostwald ripening in ionic crystals

Abstract: The Lifshitz-Slezov-Wagner (LSW) theory of Ostwald ripening, limited by bulk diffusion or surface reaction rates, is extended to the case of dislocation or grain-boundary diffusion. The theory predicts a universal particle size distribution, F(R/Re), where RC is the critical radius i.e. the radius of a particle which is instantaneously in equilibrium with the solute concentration in the matrix. Some of the approximations used in the theory are critically examined. The approximation eulR 1 + m/R, used in applying Thomson's equation to the theory, is not always valid and can cause a significant error in the shape of the size distribution function for small values of R. Inhomogeneities in the distribution of interparticle separation can cause different groups of particles in the same solid to ripen independently, thus giving an observed size distribution which does not agree with the simple theory. A comparison of the theory with recent experiments on alkali halides and glass supports the above findings and explains a variety of observations satisfactorily. The observed size distribution of Ag particles in glass is described by two overlapping distributions for the bulk diffusion case. Ag particles in KC1 are described by the narrow distribution obtained for the dislocation diffusion case and the distribution of MnC12.6 NaCl (Suzuki phase) in NaCl by the surface reaction case when allowance is made for the errors due to the approximations discussed above. l. Introduction. The kinetics of precipitation from a supersaturation of solute atoms or defects in a crystal matrix have been extensively discussed by numerous authors e. g. [l-71, and recently applied to the aggregation of F centres into metallic colloids [g]. The precipitation process proceeds until the supersaturation of solute has become small, and most of the excess solute has been incorporated into precipitated particles. The particle size distribution during this process remains fairly narrow. However, this distribution does not persist, because the larger interfacial energy of a large number of small particles drives the system towards a situation where the mean particle size is increased. This process is known as Ostwald ripening, and in principle extends until the particles (*) Permanent address : Defence Research and Development Organization, South Block, New Delhi 11001 1, India. have grown into a single large precipitate or the solute has migrated to the surface of the crystal [9]. The mechanism of Ostwald ripening relies on the transport of solute from small precipitates to larger precipitates, so that the small ones shrink and the large ones grow. These solute currents arise because the solute concentration C, in equilibrium with a particle of radius R is given by Thomson's equation [9]. C , is the solute concentration in equilibrium with a plane surface and a = 2 SZalkT, where S2 is the atomic volume and a the interfacial energy of the particle in the matrix. Since CR is larger for small values of R a concentration gradient will exist so that solute flows from the region near a small particle towards a large particle. During Ostwald ripening a range of particle sizes will be present. Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:19767103 C7-464 S. C. JAIN AND A. E. HUGHES The theory of Ostwald ripening was formulated by Greenwood [l01 and considerably extended by Lifshitz and Slezov [ll-121 and Wagner [13]. These theories predict that the ripening system evolves into a quasi steady state in which the size distribution F(u) expressed in terms of the reduced variable U = R!R does not change with time and in which the mean radius R grows as t"where n < 1. The exponent n is + when the ripening process is controlled by the rate at which solute evaporates and condenses at the particles (case l), and 4 when the rate-limiting process is bulk diffusion of solute atoms (case 2). Extensive experimental work has been done to test these theories in the case of metal alloys 191, with reasonable success. However, the observed size distributions are usually rather wider than predicted. Very little work has been done on ionic crystals and glasses, although size distributions of colloids and precipitates have been reported [14-181, and some attempt has been made to interpret the ripening results theoretically [19-211. In this paper we report a more extensive analysis of the experimental results, and extend the Lifshitz-SlezovWagner (LSW) theory in two important respects. The first of these is to cover the case where transport of solute between particles takes place by dislocation or grain boundary diffusion (case 3) rather than through the bulk crystal. We also show that it is possible under some conditions for different groups of precipitate particles to ripen almost independently in the same crystal. This leads to an interpretation of features of the observed size distributions which are not explained by the conventional LSW theory. Since the detailed arguments have been presented in another report [22] we shall concentrate only on the main results. 2. Ripening theory and its extension to dislocation and grain boundary diffusion. Suppose that the concentration of solute at a point distant from a precipitate particle is C,, i. e. C, represents the average value of the solute concentration in the bulk of the crystal. The rate of change of the radius of a particle is then given in the steady state approximation (see

Particle size analysis for fine-grained soils

Abstract: British standard BS1377 is concerned with methods of test for soils for engineering purposes. The author refers to two items in the 1975 revision which require careful attention by all who use hydrometers for particle size tests on soils. The first, and more significant, follows from the use of a new type of hydrometer which is now specified. This new hydrometer has to be calibrated to read 1.000 at 20 degrees C whereas the previous hydrometer was simply required to be calibrated in g/ml at 20 degrees C. This difference could lead to inconsistencies in the reporting of the clay fraction of soils based on the hydrometer sedimentation tests, because the new procedure will give results different from those obtained by following the 1967 standard. The second relates to the use of consistent units in the calibration of hydrometers. This note describes the new hydrometer and the old, and indicates how the old hydrometers can be used to comply with the 1975 revision if the new hydrometers are not available. A simplified procedure is also suggested. /TRRL/