RU2469309C1 - Ultrasonic method of determining grain-size composition of particulates - Google Patents

Abstract

FIELD: physics.

SUBSTANCE: sample prepared from the analysed particulate is exposed to elastic ultrasonic pulses which are incident at a normal to the surface of the sample which is placed in an immersion liquid; first and second pulses which have passed through the sample and a pulse which has passed through the layer of immersion liquid are received; the time interval between exposure pulses and the arrival of the pulses from the sounded region of the sample is measured, wherein the distance between pulses incident at a normal to the surface of the analysed sample is measured in the sounded region of the sample, after which the time for the onset of resonance of the heterogeneous residue at the onset of the first interference minimum of the standing wave is recorded; the time for the onset of the next interference minima is measured, after which the time for formation of each of the successively occurring resonance layers is measured; their total value is determined and a corresponding relationship is used to obtain a histogram from which the grain-size composition of the analysed particulate is determined.

EFFECT: easier and faster measurement, faster determination of grain-size composition of a particulate, high accuracy and reliability of determining grain-size composition of a particulate.

3 cl, 4 dwg

Description

The invention relates to an ultrasonic non-destructive method for determining the particle size distribution of dispersed materials and can be used in many industries: food, pharmaceutical, cosmetic, chemical, construction (when determining the quality of building materials), for controlling explosives, i.e. in all areas where heterogeneous dispersed material is used.

There are various methods for determining the particle size distribution of dispersed materials, the most commonly used in practice of which are the sedimentation method of analysis of dispersion, optical microscopy, laser diffraction, electron microscopy [1-3].

A known method for determining the grain size of an object (particles) using an acoustic microscope [4]. It consists in scanning the sample with an ultrasonic signal emitted by the transducer of the transceiver transducer relative to the object under study. The duration and frequency of the pulses is set by the master unit. The shape and amplitude response of the reflected pulses is displayed on the oscilloscope. By the amplitude and time characteristics of the signals, by comparison with the reference characteristics recorded in the memory unit, the structure of the material (its granularity) is judged. However, the known method is time-consuming, since it requires the preparation (or the availability of a finished) reference sample and a longer duration (hereinafter: time-consuming) of measurements.

, где ρ - плотность частицы, η - вязкость иммерсионной жидкости. Однако известный способ сопровождается явлениями, приводящими к агрегированию частиц, что оказывает влияние на его точность и достоверность.A known method for determining suspended particles in a liquid by exciting an ultrasonic resonance field in a multilayer composite resonator having a dispersion in the vessel (particles in the liquid), and also containing a transducer (piezoelectric transducer) and a mirror (reflector of ultrasonic waves) [5]. The establishment of a standing ultrasonic wave in a liquid leads to the formation of nodes and velocity anti-nodes to which the force created by the radiation forces the particles to move [6 and 7]. A standing wave arises from the interference of coherent waves. Coherent waves are waves of the same frequency, amplitude and constant phase difference. When reflected from a surface whose plane is parallel to the plane of the emitter, a coherent wave creates a standing wave upon interference (provided that the phase difference is equal to n / 2). The frequency of ultrasonic waves at resonance is related to the particle size

where ρ is the particle density, η is the viscosity of the immersion fluid. However, the known method is accompanied by phenomena leading to aggregation of particles, which affects its accuracy and reliability.

A known method of ultrasonic testing of the average grain size (particle) of a material [8], which is the closest in the set of essential features. To implement this method, the product (or test sample) is placed in an immersion fluid between the emitting and receiving piezoelectric transducers of the moving sheet metal and pulses are emitted normally to the surface of the product (sample). The first and second pulses passing through the sample are received and the pulse passed through the immersion fluid. The value of the third harmonic of the first transmitted pulse, the first and third harmonics of the pulse transmitted through the immersion liquid is measured. The arrival times of the first and second pulses passing through the sample are measured, as well as the pulse in the absence of the sample, and the average grain (particle) size is calculated.

The disadvantages of this method are the high time duration of the measurements (time), the complexity of these measurements, as well as the low accuracy and reliability of the measurement.

The claimed invention is devoid of these disadvantages.

The technical result of the claimed invention is the simplification and reduction of measurement time (reducing time), increasing the efficiency of determining the particle size distribution of dispersed material, as well as reducing the complexity and cost of measurements, improving the accuracy, reliability and cost-effectiveness of the method.

,The specified technical result is achieved by the fact that in the ultrasonic method for determining the particle size distribution of the dispersed material, which consists in irradiating the sample prepared from the studied dispersed material with elastic ultrasonic pulses incident normally to the surface of the sample placed in the immersion liquid, the first and second passes through the test sample pulses and a pulse passing through a layer of immersion liquid, measuring time intervals between irradiating a pulse According to the invention, in the audible region of the sample, the distance between pulses falling normally to the surface of the test sample is recorded, and then the time of the appearance of the resonance of the heterogeneous precipitate by the appearance of the first interference minimum of the standing wave is recorded, and the time of occurrence is measured subsequent interference minima, after which the formation time of each of the successive resonant layers, which judge the particle size distribution of each of these layers, determine their total value and the ratio:

,

where N _n is the number of granules in the resonant layer,

- сумма N_n каждого резонансного слоя,

- the sum N _{n of} each resonance layer,

get a histogram, which determines the particle size distribution of the investigated dispersed material

In addition, the specified technical result is achieved by the fact that the test sample is placed in a volume of at least 1% of the volume of immersion liquid.

In addition, this technical result is achieved in that the time of appearance of interference minima is fixed using an oscilloscope.

The specified technical result is achieved, therefore, by the fact that, as in the prototype method, elastic ultrasonic waves are excited using piezoelectric sensors, the test sample (particles) are introduced into the immersion liquid, ultrasonic pulses fall normally to the surface of the sample of the settled layer and measure the characteristic time intervals. But unlike the known method, the interferometer cuvette is filled with a liquid of volume V, after which the distance between the L sensors is fixed. After fixing the distance between the piezoelectric sensors, particles are introduced, the volume of which is at least 1% of the volume of the immersion liquid. Immediately after the particles are introduced into the immersion liquid, the time of the onset of sedimentation (sedimentation of particles) is recorded, then the time of the resonant heterogeneous precipitate is determined by the appearance of the first interference minimum of the standing wave t ₁ , the time of the appearance of subsequent interference minima on the oscilloscope screen t _n (n = 1, 2, 3 ...).

The obtained values of t _n determine the relationship between the number of the resonant layer and the time of its appearance, plotting (histogram) the dynamics of the appearance of the resonant layers. According to the obtained dependence, according to the Stokes law, the particle size distribution of the particles of the corresponding resonant layer of dispersed precipitate is calculated:

where η is the viscosity coefficient of the matrix,

H is the height with which the particles settle,

g is the acceleration of gravity,

t is the settling time of the particle,

ρ _h - particle density,

ρ _m is the density of the matrix,

V _n is the volume of a particle of radius r _n .

According to the wavelength of ultrasonic waves λ, the radius of the piezosensor R determine the volume of the resonant layer by the formula:

,

,

where V _p is the volume of the resonance layer,

R is the radius of the piezosensor,

λ is the ultrasonic wavelength.

резонансных слоев и по отношению

строится гистограмма частиц в осевших резонансных слоях дисперсного материала.By the ratio of the volume of the resonant heterogeneous layer to the volume of the particles forming the nth resonant layer, the number of particles N _n in the resonance layer is calculated, the total number of dispersion particles is determined, and the total number of particles is determined

resonant layers and in relation

a histogram of particles in the settled resonant layers of the dispersed material is constructed.

The essence of the invention is illustrated by the illustration presented in Fig.1-4.

Figure 1 presents a block diagram on which studies and testing of the claimed method; figure 2 presents the waveform; figure 3 presents a timing diagram and figure 4 presents a histogram.

The block diagram of the experimental setup shown in Fig. 1 contains an acoustic cell 1 made in the form of a transparent cylinder, in particular, from a plexiglass, piezoelectric sensors 2 and 3, an ultrasonic wave generator 4, an ultrasonic wave receiver 5, an oscilloscope 6.

In the process of testing the inventive method, the emitting piezosensor 2 was mounted on a rod, which, using a special device mounted on the lid of the cuvette, was fixed relative to the lower receiving piezosensor 3 mounted on the bottom of the cuvette (acoustic cell). When mounting the acoustic cell, the alignment and parallelism of the planes of the emitting and receiving quartz were necessarily checked. The readiness of the installation for operation was checked by measuring on it the speed of ultrasonic waves in distilled water, for which a speed of 1490 m / s was obtained under normal conditions, which coincided with the test table data.

, возникает резонанс и появляется интерференционный минимум. Фиксируется время появления интерференционного минимума, время появления последующих интерференционных минимумов по мере осаждения частиц дисперсии и возникновения резонансов осевших слоев. Скорость оседания частиц определяется по формуле:The essence of the invention is as follows. An acoustic cuvette (cell) with two piezoelectric sensors is filled with a liquid whose volume is V. The upper sensor is fixed relative to the lower sensor at a distance L. Particles of dispersed material in a volume of at least 1% of the volume of immersion liquid are introduced into the cuvette at level H. The time of the beginning of sedimentation is recorded particles. Upon reaching the thickness of the resonance layer equal to

, resonance occurs and an interference minimum appears. The time of the appearance of the interference minimum, the time of the appearance of subsequent interference minima as the dispersion particles are deposited and the resonances of the deposited layers are recorded, are recorded. The sedimentation rate of particles is determined by the formula:

,

,

where H is the height at which the particles of the test sample settle; t is the particle settling time.

Particle sedimentation rate according to Stokes law, taking into account the buoyancy correction according to Archimedes law:

,

,

where m is the mass of the particle,

r is the radius

η is the viscosity coefficient of the matrix,

H is the height from which the particles of the test sample settle,

g is the acceleration of gravity,

ρ _h - particle density,

ρ _m is the density of the matrix.

и по соотношению

получают гистограмму, по которой судят о гранулометрическом составе исследуемого дисперсного материала.From the obtained formulas (1) and (2), information is obtained on the particle size and volume of the particles of the corresponding resonance layer, the volume of the resonance layer V _p and the number of particles N _n in the resonance layer are determined. Determine the total value

and in relation

get a histogram, which is used to judge the particle size distribution of the investigated dispersed material.

The claimed invention was tested at the laboratory base of St. Petersburg State University (SPbSU) in real time on the basis of numerous experimental studies conducted on samples, in particular the particle size distribution of the suspension of starch particles.

Examples of specific implementations of the claimed method are presented in the table, which is based on the results of experimental studies of the particle size distribution of a suspension of starch particles.

Table The results of the experimental determination of the particle size distribution of a suspension of starch particles n is the number of the resonance layer t, sec r, μm N _n

one 1200 4,5 19910 ⁶ 35.5 2 820 5.5 113 · 10 ⁶ 20.1 3 630 6.2 75.5810 ⁶ 13.5 four 494 7.1 52.6610 ⁶ 9.3 5 460 7.4 46.25 · 10 ⁶ 8.2 6 344 8.5 30,60 · 10 ⁶ 5,4 7 245 10 18.3910 ⁶ 3.2 8 186 11.5 12.16 · 10 ⁶ 2.1 9 139 13,4 7.8610 ⁶ 1.4 10 85 17.1 3.7510 ⁶ 0.6 eleven 38 25.5 1.12 · 10 ⁶ 0.2

Example.

и по соотношению

строилась гистограмма, по которой судят о гранулометрическом составе исследуемого дисперсного материала. Полученная гистограмма представлена на Фиг.4.After fixing the distance between the piezoelectric sensors, starch particles, the volume of which is 1.2% of the volume of the immersion liquid, were introduced into the immersion liquid (water). Immediately after the particles were introduced into the immersion liquid, the time of the onset of sedimentation (sedimentation of particles) was recorded, then the time of formation of a resonant heterogeneous precipitate was determined by the appearance of the first interference minimum of the standing wave t ₁ , the time of appearance of subsequent interference minima on the oscilloscope screen t _n (n = 1, 2, 3 ...). The dependence of the settling time of particles on the number of the resonant layer is shown in the time diagram, Fig.3. Using known formulas, the size r and the volume of starch particles of the corresponding resonance layer were calculated, the volume of the resonance layer V _p and the number of particles N _n in the resonance layer were determined. The total value was determined

and in relation

a histogram was constructed, according to which the particle size distribution of the dispersed material under study was judged. The resulting histogram is presented in Figure 4.

The proposed method, as shown by the results of numerous studies, can improve the accuracy and reliability of measuring the average granule size of the test material in the particle range from 1 μm to 200 μm. The advantages of the method also lies in its cost-effectiveness, versatility, efficiency, reducing the complexity and reducing the measurement time.

Information sources

1. Kurkov A.V. “Development of methods and means of increasing the information content of ultrasonic measurements with the help of general-purpose flaw detectors” // Abstract of dissertation for the degree of candidate of technical sciences, St. Petersburg, 2010.

2. Kvesko N.G. “Regularities of the process of layer sedimentation of particles in a liquid medium as applied to practical granulometry” // Abstract of dissertation for the degree of Doctor of Technical Sciences, Tomsk, 2002.

3. Pershina S.V., Katalymov A.V., VG Only, Pershin V.F. "Weighting of granular materials" // "Engineering", Moscow, 2009.

4. RF patent No. 20111194, IPC G01N 29/04.

5. Felix Trampler, Ewald Benes. "Method and device for the separation of suspended particles", 06/10/1996

6. Koltsova I.S. "The propagation of ultrasonic waves in heterogeneous environments" // Ed. SPbSU, 2007.

7. Shutilov V.A. "Fundamentals of Physics of Ultrasound" // Ed. LU, Leningrad, 1980.

8. RF patent No. 2187102, IPC G01N 29/04 (prototype).

9. RF patent №2334224, IPC G01N 29/04.

10. RF patent No. 2350944, IPC G01N 29/04.

11. RF patent No. 2262694, IPC G01N 29/04.

12. RF patent No. 2346261, IPC G01N 15/02.

13. RF patent No. 2330705, IPC B01D 21/00, C02F 1/34, C02F 1/74.

14. RF patent №2325208, IPC B01D 11/00.

15. RF patent No. 2261147, IPC B03B 5/02, B01D 21/00.

16. RF patent No. 2084887, IPC G01N 27/72, 15/06.

Claims (3)

1. Ultrasonic method for determining the particle size distribution of a dispersed material, which consists in irradiating a sample prepared from the studied dispersed material with elastic ultrasonic pulses incident normally to the surface of a sample placed in an immersion liquid, receiving the first and second pulses passing through the sample and the pulse passing through the layer immersion liquid, measuring the time intervals between irradiating pulses and the arrival times of pulses from the voiced region of the sample characterized in that in the voiced region of the sample, the distance between pulses falling normally to the surface of the test sample is fixed, then the time of the appearance of the resonance of the heterogeneous precipitate is recorded by the appearance of the first interference minimum of the standing wave, the time of appearance of subsequent interference minima is measured, and then the formation time of each from successively arising resonant layers, determine their total value and the ratio:

,
where N _n is the number of granules in the resonant layer,
∑N _n is the sum N _{n of} each resonance layer,
get a histogram, which determine the particle size distribution of the investigated dispersed material. 2. The ultrasonic method according to claim 1, characterized in that the test sample is placed in a volume of at least 1% of the volume of the immersion liquid. 3. The ultrasonic method according to claim 1, characterized in that the time of appearance of interference minima is fixed using an oscilloscope.

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