US3098931A - Apparatus for use in determining particle size and distribution of particle size - Google Patents

Apparatus for use in determining particle size and distribution of particle size Download PDF

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Publication number
US3098931A
US3098931A US797125A US79712559A US3098931A US 3098931 A US3098931 A US 3098931A US 797125 A US797125 A US 797125A US 79712559 A US79712559 A US 79712559A US 3098931 A US3098931 A US 3098931A
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Prior art keywords
particle size
particles
distribution
specimen
sample
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Seymour Z Lewin
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Evans Res and Dev Corp
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Evans Res and Dev Corp
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Priority to LU38318D priority Critical patent/LU38318A1/xx
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Priority to US797125A priority patent/US3098931A/en
Priority to BE588172A priority patent/BE588172A/fr
Priority to FR820150A priority patent/FR1251558A/fr
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    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N23/00—Investigating or analysing materials by the use of wave or particle radiation, e.g. X-rays or neutrons, not covered by groups G01N3/00 – G01N17/00, G01N21/00 or G01N22/00
    • G01N23/02—Investigating or analysing materials by the use of wave or particle radiation, e.g. X-rays or neutrons, not covered by groups G01N3/00 – G01N17/00, G01N21/00 or G01N22/00 by transmitting the radiation through the material
    • G01N23/06—Investigating or analysing materials by the use of wave or particle radiation, e.g. X-rays or neutrons, not covered by groups G01N3/00 – G01N17/00, G01N21/00 or G01N22/00 by transmitting the radiation through the material and measuring the absorption
    • G01N23/12—Investigating or analysing materials by the use of wave or particle radiation, e.g. X-rays or neutrons, not covered by groups G01N3/00 – G01N17/00, G01N21/00 or G01N22/00 by transmitting the radiation through the material and measuring the absorption the material being a flowing fluid or a flowing granular solid
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N15/00—Investigating characteristics of particles; Investigating permeability, pore-volume or surface-area of porous materials
    • G01N15/02—Investigating particle size or size distribution

Definitions

  • the invention consists in the novel steps, methods, combinations and improvements herein described.
  • a further object of this invention is to provide a novel method for determining particle size and/ or distribution of particle size in compositions having randomly distributed particles in a more simple, economical and eflicient manner than heretofore used methods.
  • Yet a still further object of this invention is to provide a novel particle size analyzer which is simple in construction for use in determining particle size and/ or distribution of particle size in compositions having randomly distributed particles.
  • a still further object of this invention is to provide a novel method for determining particle size and/ or distribution of particle size in a composition having randomly distributed particles without having to physically remove samples from said composi- 3,098,931 Patented July 23, 1963 tion.
  • Another object of this invention is to provide a novel apparatus (for use in determining particle size and/ or distribution of particle size in a composition having randomly distributed particles without having to physically remove samples from said composition.
  • This invention is based on the discovery that valuable information for use in determining particle size and/ or distribution of particle size in a composition having randomly distributed particles can be realized by obtaining data with respect to a number of different samples of said composition having the same predetermined volume, and subsequently observing the fluctuations in the data relating to said different samples of the same volume.
  • data is obtained with respect to different samples of the same volume of a composition having known particle size and/ or distribution of particle size.
  • This data serves as calibration data.
  • Data is also obtained on different samples of the same volume of the composition under consideration of unknown particle size and/ or distribution of particle size.
  • This data serves as specimen data.
  • the volumes of the aforementioned samples on which calibration data and specimen data are obtained are the same.
  • the data obtained is then compared and interpreted using calibration techniques whereby ultimately the particle size and/or particles size distribution of the composition under consideration may be determined.
  • the fluctuations in the calibration data are compared with the fluctuations in the specimen data as will be explained more in detail hereinbelow.
  • a fluctuation is defined as the difierence in magnitude of two independent measurements made on samples of precisely equal volumes.
  • the accuracy of the results obtained is dependent upon the sufficiency of the data with respect to sample volumes of both known and unknown particle sizes and/or particle sizes distribution. Also, for reasons that will be evident hereinlater, in order to obtain sufiicient data, it is important that data with respect to samples of different volumes be obtained.
  • the instant invention provides a novel method and apparatus whereby data of the aforementioned type may be obtained with respect to samples of compositions having known and unknown particle size and/or particle size distribution.
  • data is obtained without having to physically remove samples from such compositions.
  • data relating to particle size and/ or particle size distribution may be obtained with respect to a sample of predetermined volume in a compositon having randomly distributed particles, said sample being referred to hereinafter as the sampling, by:
  • a source of radiation is applied to the specimen.
  • the source of radiation it is essential that it possess the following characteristics with respect to the specimen:
  • the source of radiation must physically interact with specimen so as to pass a radiation beam through at least a portion of the specimen, which radiation beam is sensitive to the several phases of the specimen in the path of radiation.
  • the source of radiation should not be very weakly or very strongly absorbed by the specimen so that it would be impossible to measure with reasonable accuracy the attenuation produced by the specimen.
  • Radioisotopes which are beta emitters are preferred because in addition to fulfilling the aforementioned requirements, they also: (a) provide the desired radiations without requiring the use of expensive and bulky instrumentation, -(b) are sources of radiation of substantially constant intensity, subject only to the precisely calculable decay curve, and (c) are available at low cost in high specific activity and in a safe, easily shielded form.
  • Table I discloses a list of well known radioisotopes useful as the source of radiation in accordance with the present invention.
  • the data reported in Table I gives the maximum beta energy and the halfthickness for absorption in water for each of the radioisotopes listed in Table I.
  • the depth of penetration of the radiation beam is controlled by the characteristics of the specimen in the path of the radiation beam as well as the energy spectrum of the radiation emitted by the source of radiation.
  • the radiation beam is attenuated and the extent of attenuation measured using conventional techniques such, for example, as the technique of backscatter measurement or the technique of absorption (transmission) measurement.
  • the volume of the sampling involved in the measurement is determined by the area irradiated by the radiation beam, the depth of penetration of the radiation beam and the effective portion of the radiation beam that is attenuated.
  • FIG. 1 of the drawing illustrates schematically one embodiment of an analyzer of the present invention useful in determining particle size.
  • the means for measuring the extent of attenuation of the radiation beam is a back-scattering measuring instrument.
  • specimen 1 which may be of any composition having randomly distributed particles such, for example, as an emulsion, powder, gel, etc., is irradiated by a suitable source of radiation such, for example, as a tritium source 2.
  • the specimen is viewed in the backscattering position by detector means through aperture means.
  • the detector means comprises detectors 3 and 3 which include electrodes 4 and 4*, respectively, surrounded by insulation 5 and 5 respectively.
  • the aperture means are provided by pinhole apertures 6 and 6 in blocks 7 and 7 respectively, made of radiation absorbing material.
  • the entire assembly of the radiation source, the detector means, and the aperture means are supported on rotatable shaft 8 on which are mounted collector rings 9 and 10.
  • Collector rings 9 and 1d are insulated from shaft 8 by insulation bushing 11. Alternatively, the entire assembly may be stationary and means provided for rotating the specimen.
  • the detectors 3 and 3 are allowed to count or integrate the back-scattered betas for a sufiicient time to reduce the counting random error to a suitably low value. If the tritium source is of high intensity (egg. of the order of a curie), this counting time may be as short as a few seconds.
  • the symbol BS means the fraction of the incident beam that is back-scattered.
  • the symbol d/ sec. means disintegration per second.
  • a change (erg. fluctuation due to sampling volume efiect) of 0.0001 (i.e., a change of one part in ten thousand) in the back-scattering corresponds to a change in activity of d/ sec. at the detector.
  • electrical means are provided to convert the beta rays to current which may be measured to provide the data required for comparison purposes.
  • the diiference in integrated detector currents is measured by meter 12, which responds to the voltage difierence between the two dropping resistors 13' and 14.
  • the meter 15 measures the total detector current.
  • Meters 12 and 15 are operated by voltage source 16. The difference in voltage on meter 12 is due to the randomness in the dis tribution of particles in the sampling volume together with the statistics of radioactive counting. However, the latter factor can be minimized by appropriate choice of the total integrated count so as to make the reading on meter 12 principally a measure of the sampling randomness.
  • the assembly In operation, the assembly is allowed to count for the necessary time at a given position, and the readings on meters 12 and 15 are recorded; then the assembly is rotated about its axis and new readings are taken. This may be repeated as many times as desired; the greater the number of readings, the better the accuracy of the results.
  • the average of the readings on meter 12, disregarding the sign of the deflection, is proportional to the half-width of the Gaussian distribution referred to hereinbelow.
  • the ratio of this to the reading on meter 15 is proportional to the relative fluctuation. This parameter is related to the concentration of particles in a certain size range, determined by the geometry of the apparatus. This range corresponds to the totality of particles from the largest down to a characteristic minimum size.
  • FIG. 1 may be simplified wherein only one detector is employed.
  • the meter 12 is eliminated and the only current measuring instrument employed would be meter 15 which would measure the detector current produced by the backscattening of beta beams scattered by one sample of predetermined volume.
  • the deteotor or detectors employed are preferably windowless proportional counters through which Q-gas is circulated (cf. Karraker, D. G., DP-34, December 1953), although other standard components, such as ionization chambers, scintillation counters, etc., may be used.
  • FIG. 1 illustrates an apparatus employing a back scattering measurement instrument
  • a particle analyzer may be used predicated on transmission measurements, rather than back-scattering measurements.
  • the detector means and the aperture means '5 are placed on the far side of the specimen, compared to the radiation source.
  • the apparatus of FIG. 1 provides a unit for obtaining data with respect to the cumulative particle sizes over a specific range of particle sizes. If it is desired to obtain information data about the distribution of particle size in a specimen, a number of units of the type illustrated by the unit of FIG. 1 may be employed, the various units differing only with respect to the energy spectrum of the source of radiation and the aperture diameter. Each unit yields information data about the concentration of a different range of particle size. Alternatively, a single unit may be used having a variable detector aperture that changes in diameter on a programmed basis, in accordance with the range of particle size under investigation. This variable aperture programming can be achieved by meachanical, electrical, or magnetic means.
  • the volume of the entire system is V and random samples are taken out of the system, the sampling volume being v then the number of particles found in each sample will vary statistically, showing an approximately Gaussian distribution about a mean determined by the individual particle size and the average concentration per unit volume.
  • the half-width :of this distribution depends upon the ratio of 1rr to v
  • V is much smaller than ,1rr Then, the number of particles per sample is always 0, but the frequency with which the sampling volume finds itself within a particle compared to outside a particle is. the same as in (a) above; with respect to the present application, cases a and b will yield the same physical result.
  • V is much larger than tirr
  • the number of particles per sample will be large, and the relative fluctuation from sample to sample will be small. It is a wellknown result of statistical theory that the relative fluctuation (half-Width of the Gaussian curve) decreases as the number of particles per sample, 11, increases (it is, in fact, proportional to 1/ /n).
  • the relative fluctuation in the sampling is small when the sample is large, and increases as the sample volume decreases, reaching a maximum when the sample volume is equal to or smaller than the particle size.
  • a beta ray passing through the specimen will encounter both phases in certain proportions, determined principally by the concentration of the mixture.
  • the relative fluctuation discussed above is a function of the ratio of the length of the beta path to the dimensions of the liquid or solid particles encountered by the betas.
  • Andreasen has shown that the percentage of void space is approximately independent of the particle size for any given degree of shaking or packing (A. H. M. Andreasen, Ingenigzirvidensradeige Skrifter, No. 3, The Fineness of Solids, Copenhagen, 1939).
  • the percentage of void space may be as small as 15%, due to small particles filling in the voids between large ones, but the randomness is still as great or greater than in the case of mono-sized dispersions.
  • T he fluctuations in the number of particles per sampling are due to both (1) the existence of an appreciable void space, and (2) the presence of randomness (disorder) in the packing.
  • the relative fluctuation observed in replicate samplings is composed of the summation of the fluctuations associated with each of the diiferent sizes of particles present.
  • the volume ot the specimen that is involved in the measurement in accordance with the present invention is determined by the area irradiated by the beta beam, the depth of penetration of the betas into the specimen (determined by the energy of the particles and the density of the medium), and the effective viewing aperture of the detector.
  • the effective viewing aperture of the detector there are a number of factors that can be independently adjusted in order to achieve any desired sampling volume.
  • these factors are adjusted to give a sampling volume that is of the same order of magnitude as the effective volume of a small number of the particles of the size range of interest in the dispersion under study.
  • the relative fluctuation in replicate samplings obtained by making slight changes in the position of the detectors relative to the specimen between measurements or by stirring or disturbing the specimen between measurements, will be large.
  • the relative fluctuation in replicate measurements due to these particular particles diminishes.
  • the relative fluctuation is proportional to the cumulative oversize particle concentration, i.e., the total concentration of particles in the size range, from the largest ones present down to a lower limit that is a function of the magnitude of the sampling volume.
  • the radioisotope of choice is tritium, H This is a pure beta emitter, of maximum energy, 18.9 kev.
  • H tritium
  • the half-thickness of water for these betas is approximately 0.5 micron.
  • the infinite thickness for back-scattering is proportional to this number, and may be taken as approximately four times the half thickness.
  • the infinite thickness would be slightly different, but this numb er can be adopted to give a reliable order of magnitude for the following calculations, which are presented solely for illustrative purposes. If these betas are back-scattered by a specimen, the average beta that reaches the detector would have passed through about 1 micron of the specimen.
  • the cifective volume of the specimen that is being sampled is small enough that only a few thousand particles of 1 micron diameter could be included, and only about a hundred 3 micron particles, assuming conditions of very close packing of the particles, such as in dry, packed powders; these numbers would be correspondingly smaller for more dilute dispersions.
  • the sample could include several hundred thousands of 1 micron particles, but only several dozen 20 micron particles.
  • Certain drugs such as penicillin and streptomycin, are used in the form of suspensions of the solid in oily or aqueous media which are injected into the body.
  • the ability of these preparations to withstand prolonged storage and to be re-suspended after settling and the rate of absorption of the crystals in the lymphatic fluids are determined by the particle size and size distribution of the crystals.
  • getters of zirconium and tantalum are applied to vacuum tube anodes in the form of a suspension by means of a spraying or dipping process. Good adhesion of this suspension to the metal surface is critically dependent upon the particle size distribution.
  • abrasives such as in milling and storage facilities
  • dyes such as in milling and storage facilities
  • cosmetic emulsions such as in milling and storage facilities
  • photographic emulsions such as in milling and storage facilities
  • salves and ointments such as in milling and storage facilities
  • fertilizers such as in milling and storage facilities
  • fuels such as in milling and storage facilities
  • metal powders such as in powder metallurgy
  • muds such as in powder metallurgy
  • ores such as in powder metallurgy
  • pigments for paints
  • plastics such as in milling and storage facilities
  • soils such as in milling and storage facilities
  • explosives such as in milling and storage facilities
  • a particle size analyzer for use in obtaining data relating to particle size and particle size distribution with respect to a composition having an imperfectly ordered arrangement of particles, comprising means for applying to said composition radiant energy which reacts substantially simultaneously with 'a plurality of said particles and which is sensitive to the several phases of the composition; means for controlling the degree of irradiation by said radiant energy, means for adjusting the dimension of a sample region of said composition to a magnitude which is of the same order of magnitude as the dimension of a small number of certain of said particles, and means for measuring the reaction of said sample region to said radiant energy to provide data with respect to said sample.
  • a particle size analyzer according to claim 1, wherein the means for providing said radiant energy is a radioisotope.
  • reaction measuring means include detector means for measuring rays of said radiant energy affected by said composition and said adjusting means com-prise aperture means for controlling the eflective dimensions of said sample, the reaction of which is measured by said detector.
  • reaction measuring means comprise means for measuring back-scattering by the sample under consideration.
  • Apparatus according to claim 5 including means responsive to the absolute output of at least one of said detecting means whereby in conjunction with said differential measuring means, the percentage value of said fluctuations may be determined.

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US797125A 1959-03-04 1959-03-04 Apparatus for use in determining particle size and distribution of particle size Expired - Lifetime US3098931A (en)

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LU38318D LU38318A1 (en)) 1959-03-04
US797125A US3098931A (en) 1959-03-04 1959-03-04 Apparatus for use in determining particle size and distribution of particle size
BE588172A BE588172A (fr) 1959-03-04 1960-03-01 Procédé et appareil pour déterminer la dimension de grains de matière et la répartition des dimensions de grains.
FR820150A FR1251558A (fr) 1959-03-04 1960-03-02 Procédé et appareil pour déterminer la dimension de grains de matière et la répartition des dimensions de grains

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Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3177760A (en) * 1963-02-07 1965-04-13 Ex Cell O Corp Apparatus embodying plural light paths for measuring the turbidity of a fluid
US3609043A (en) * 1968-11-19 1971-09-28 Parker Hannifin Corp Spray droplet analyzer

Citations (8)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US1974522A (en) * 1934-09-25 Counting op microscopic bodies-
US2304910A (en) * 1940-05-29 1942-12-15 Texas Co Determination of specific gravity of fluids
US2494441A (en) * 1948-07-28 1950-01-10 Rca Corp Method and apparatus for electronically determining particle size distribution
US2498506A (en) * 1947-06-11 1950-02-21 Atlantic Refining Co Optical metering means for gas using a sliding tube
US2586303A (en) * 1951-01-04 1952-02-19 Tracerlab Inc Radiation type thickness gauge
US2675482A (en) * 1952-03-25 1954-04-13 Isotope Products Ltd Method and apparatus for measuring material thickness
US2731202A (en) * 1951-04-03 1956-01-17 Rca Corp Electronic particle counting apparatus
US2763790A (en) * 1952-04-05 1956-09-18 Ohmart Corp Comparator

Patent Citations (8)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US1974522A (en) * 1934-09-25 Counting op microscopic bodies-
US2304910A (en) * 1940-05-29 1942-12-15 Texas Co Determination of specific gravity of fluids
US2498506A (en) * 1947-06-11 1950-02-21 Atlantic Refining Co Optical metering means for gas using a sliding tube
US2494441A (en) * 1948-07-28 1950-01-10 Rca Corp Method and apparatus for electronically determining particle size distribution
US2586303A (en) * 1951-01-04 1952-02-19 Tracerlab Inc Radiation type thickness gauge
US2731202A (en) * 1951-04-03 1956-01-17 Rca Corp Electronic particle counting apparatus
US2675482A (en) * 1952-03-25 1954-04-13 Isotope Products Ltd Method and apparatus for measuring material thickness
US2763790A (en) * 1952-04-05 1956-09-18 Ohmart Corp Comparator

Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3177760A (en) * 1963-02-07 1965-04-13 Ex Cell O Corp Apparatus embodying plural light paths for measuring the turbidity of a fluid
US3609043A (en) * 1968-11-19 1971-09-28 Parker Hannifin Corp Spray droplet analyzer

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LU38318A1 (en))
FR1251558A (fr) 1961-01-20
BE588172A (fr) 1960-09-01

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