JPS6324139A - Measuring method for particle size - Google Patents

Abstract

PURPOSE:To easily measure the particle size of corpuscles by projecting radiation on a sample which contains the corpuscles, detecting light scattered by the corpuscles, and measuring the particle size of the corpuscles based on the white level of the power spectrum density of the detection output. CONSTITUTION:Luminous flux 2 emitted by a light source 1 is split by a half- mirror 3 into luminous flux 4 and luminous flux 5. The luminous flux 4 is converged by a convergence lens 6 and projected on a transparent cell 7. The luminous flux 5 is incident on a photodetector 8. The light scattered by the corpuscles 9 in the cell 7 is passed through a collimator 10 with a couple of pinholes and incident on a photodetector 11. The signal of the detector 8 is supplied to a data processor 14. The signal of the detector 11 is supplied to the processor 14 through a low-noise amplifier 15 and a low-pass filter 15. The processor 14 finds the white level of the power spectrum density of intensity fluctuations of the scattered light and outputs of the measurement result of the particle size of the corpuscles. Consequently, the particle size of the corpuscles is easily measured.

Description

[Detailed description of the invention] [Industrial application field] The present invention relates to a method for measuring the particle size of microparticles.

[Conventional technology]

A conventional technique for measuring particle size using the power spectrum density of scattered light intensity fluctuation is disclosed in Japanese Patent Application Laid-Open No. 61-28866.
There is a public issue. In this method, the relaxation frequency of the power spectral density of the intensity fluctuation of scattered light obtained by projecting radiation onto a fine particle is inversely proportional to the particle size, and the relaxation frequency is inversely proportional to the particle size. It has been described that the particle size can be measured from the relaxation frequency.

[Problem that the invention seeks to solve]

In the conventional particle size measurement method, the particle size was determined from the relaxation frequency of the power spectrum density, so it was necessary to accurately determine the relaxation frequency. Furthermore, it is difficult to accurately determine the relaxation frequency at one point from a wide frequency range.

The present invention provides a new particle size measurement method that solves these problems.

[Means for solving problems]

The present invention projects radiation into a sample containing particulates,
This method of measuring particle size is characterized by detecting light scattered by particles and measuring the particle size of the particles based on the white level of the power spectrum density of the detection output.

[Effect]

The white level of the power spectrum density of the intensity of scattered light by the fine particles is proportional to the particle size of the fine particles.

Therefore, the particle size of the fine particles can be determined from the white level of the power spectrum density of the intensity of scattered light due to the fine particles whose particle size is unknown.

〔Example〕

FIG. 1 is a diagram showing an embodiment of a particle size measuring apparatus for carrying out the method of the present invention. As the radiation, coherent light or incoherent light can be used. In this example, the light source 1 is He-Ne which emits coherent light.
A gas laser (wavelength: 632.8 nm) is provided. light source 1
A light beam 2 emitted from the light beam 2 is separated into a light beam 4 and a light beam 5 by a half mirror 3. One of the light beams 4 is condensed by a condensing lens 6 and projected onto a transparent self. The other light beam 5 is made incident on a photodetector 8 and converted into a monitor signal representing fluctuations in the output light intensity of the light source 1.

A sample containing fine particles is contained within the cell.

Scattered light scattered by the fine particles 9 in the self is made to enter a photodetector 11 consisting of a photomultiplier tube through a collimator 10 having a pair of pinholes. The output monitor signal of the photodetector 8 is supplied to a data processing device 14 via a low noise amplifier 13. Furthermore, the output signal of the photodetector 1 is supplied to a data processing device 14 via a low-noise amplifier 15 and a low-pass filter 16. The data processing device 14 includes A/
A D conversion section 17, a fast Fourier transform section 18, and an arithmetic processing section 19 are provided to perform signal processing as described later and output measurement results of particle diameters. This measurement result is supplied to the display device 20 and displayed.

The intensity of the scattered light from the self is normalized by the short-time average output of the light source intensity monitor signal from the photodetector 8, and after removing fluctuations in the light intensity emitted from the light source, the power of the intensity fluctuation of the scattered light is The spectral density is determined, and based on this, the particle size of the fine particles 9 in the self is measured.

FIG. 2 is a diagram showing a detailed configuration of the collimator 10 shown in FIG. 1. The collimator 10 of this example has a hollow structure, and the hollow mLOa has a dark box structure to eliminate the influence of external light, and its inner surface has an antireflection structure.

Pinholes 10b and 10c are formed before and after the cavity 10a. Now, let the radius of these pinholes 10b and 10c be al and az, respectively, the distance between the pinholes be n, the refractive index of the internal medium of the sky 1110a be n, and the wavelength be λ.
When, the following formula (1) is satisfied.

λ In the present invention, as described above, the power spectral density of the intensity fluctuation of the scattered light is detected, but this power spectral density includes a term due to the fluctuation of the interference component due to the diffusion of the fine particles over a distance of about the wavelength, It consists of a term due to fluctuations in the number of particles caused by the movement of particles into and out of the scattering volume.

Of these, fluctuations in scattered light due to interference are observed as spatial fluctuations in the speckle pattern, but if this is directly incident on the photodetector 11, which has a wide light-receiving surface, the light will be scattered spatially over the area of the light-receiving surface. Since smoothing is performed,
The detected fluctuation becomes small. Therefore, by limiting the field of view of the photodetector 11 using the collimator 0 having a pinhole as described above, fluctuations can be detected with high sensitivity. In this embodiment, in order to satisfy the above formula (1), it is practical enough to use air with a refractive index n=1 as the medium in the cavity 10a. That is, diameter 0
, 31 pinholes 10b and 10c are 30c+++Jt
If the collimator 10 with tf is used, the above formula (1) will be satisfied.

In the embodiment described above, the direction of the light beam 4 incident on the self and the optical axis direction of the collimator 10 are set to 906, and the homodyne method is adopted in which the incident light beam does not directly enter the photodetector 11. It is also possible to adopt a heterogain method in which the light beam is incident on the photodetector 11. That is,
As shown in FIG. 3, the angle θ formed between the light beam 4 incident on the self and the optical axis of the collimator 10 can be set arbitrarily.

When detecting the scattered light in a homodyne manner, the output signal of the photodetector 11 consisting of a photomultiplier tube is proportional to the average value of the square of the electric field strength of the scattered light (Es). In the case of heterodyne detection in which scattered light and incident light are detected together, assuming that the electric field strength of the directly incident light is 107, the output signal of the photodetector 11 is: ]]14−+ = old - s ) 2 = 1007 + 200e
, Es-107. Here I ``ha yuragi gana ((
If there were, the remaining two terms would fluctuate even at L7 (it would be slower than the fluctuation of the scattered light). Also, since the intensity of the scattered light is extremely weak compared to the incident light, 2Ee ・
Since "Es >>Es", an output signal approximately proportional to the amplitude of the electric field of the scattered light can be obtained.

Further, the collimator 10 is not limited to the above-mentioned configuration, but may have any configuration as long as it can limit the field of view of the photodetector 11 to one speckle pattern or less.

Using the above-mentioned device, the output signal of the photodetector 11 is supplied to the data processing device 14 through the low-pass filter 16, and processed together with the monitor signal from the photodetector 8 to obtain the power spectrum of the intensity fluctuation of the scattered light. The results of determining the density will be explained next. Here, the power spectral density S (f) of the stationary stochastic process x(t) can be expressed as follows.

Based on this equation (2), the power spectral density is calculated using advanced Fourier transform. That is, photodetector 1
The output signal from 1 is amplified by a low noise amplifier 15 so that the quantization level of A/D conversion in the data processing device 14 is covered as wide as possible, and this quantized data is processed by a microprocessor. The power spectral density was determined.

FIG. 4 shows the power spectrum density of intensity fluctuations of scattered light by spherical latex particles with a diameter of 0.212 μm. The latex concentration is 0.23 wt%.

The power spectral density becomes white in the low frequency range, and tends to decrease as the frequency increases in the high frequency range.

Next to the white level, a method for determining the white level of the power spectral density thus determined will be explained.

The first method is to first set the frequency fanf at a predetermined interval Δ,
,f,,...+L..., (f,-
The power spectral density 5(
fo), 5(fl), 5(ft).

5(r3), ..., S(f,), ... are compared sequentially, and when a predetermined number of data decreases continuously, the data that first starts to decrease is calculated. The previous data is used as the first-order average value, which is the frequency fp of the bending point.

FIG. 5 is a flowchart showing the sequential steps of determining the white level by the second method.

The second method is to A/D convert the measurement data and then supply it to the fast Fourier transform section to power spectral density S (f
). This includes many small fluctuations as shown in FIG. 6A. Next, this is Fourier-transformed to obtain a signal as shown in FIG. 6B.

Furthermore, when this is passed through a low-pass filter consisting of a digital filter that passes signals below frequency fc, and then subjected to inverse Fourier transform, a smooth power spectrum density is obtained as shown in FIG. 6C.

After performing such pre-treatment, the frequency fp of the bending point is determined in the same manner as in the first method described above. 2 is a graph showing the relationship between the white level of the power spectral density S (f) of a standard sample suspended in the sample and the particle size. The white level T of the power spectral density changes in proportion to the particle size. This shows that the particle size of fine particles whose particle size is unknown can be measured from the white level of the power spectrum density.

1. To measure the particle size of fine particles contained in the sample, a calibration line is created to determine the particle size from the white level. FIG. 8 shows a flowchart for creating a calibration line.

First, a plurality of standard samples with different particle sizes adjusted to a constant weight concentration are prepared. Next, the scattered light intensity is measured for each of the standard samples having different particle sizes to obtain measurement data. After the measurement data is A/D converted, it is subjected to FFT to obtain the power spectrum density and the white level is calculated using the first or second method described above. Next, from the obtained multiple white levels, the relationship between particle size and white level, φ
(x, s) = a s + b ・−・−
−−・(31 is determined. Here, φ (x, s) is
The size of the particle size at a certain weight concentration x w t %, where is the white level, a is the slope, and b is the initial value.

This equation (3) is prepared in advance for a plurality of weight concentrations in order to facilitate sample measurement.

Measurement of particle size A flowchart of particle size measurement is shown in FIG.

First, the weight concentration of fine particles contained in the sample is measured, and the weight concentration is adjusted by diluting with a suspending medium so that it matches the weight concentration for which a calibration line has been created. The sample adjusted to a predetermined weight concentration is stored in a self-contained cell, and the first
It is set in the device shown in the figure, measures the scattered light intensity of the particles in the sample, calculates the white level capacity of the power spectrum density, calculates the particle size of the particles in the sample from equation (3), and displays it on the display device 20. indicate.

In the above embodiment, the power spectrum density of fine particles contained in the standard sample and the sample whose particle size is to be measured is measured using the apparatus shown in FIG.
In the present invention, any device that can measure the power spectrum density from the intensity of light scattered by fine particles can be used. - An example is shown in FIG.

FIG. 1O shows an apparatus for measuring particle size from the power spectrum density of multiple scattered light by fine particles. The same parts as in FIG. 1 are given the same reference numerals, and details are omitted. The difference from FIG. 1 is that the polarized light Fi, 21, 22 is placed on the optical path of the light beam 4 so as to sandwich the self. The polarizing plate 22 is provided so that only the polarized light component at 90 degrees to the polarization direction of the polarizing plate 21 passes through. Therefore, the photodetector 11 detects only the cross polarization of the linearly polarized light incident on the self. Since the 180° scattered light of the spherical fine particles has the same polarization component as the incident light, it is cut by the polarizing plate 22, and only the multiple scattered light having a different polarization component from the incident light passes through the polarizing plate. Therefore, the power spectral density is determined from the multiple scattered light by the fine particles, and the particle size can be measured from the white level of this power spectral density.

The present invention is applicable not only to isotropic fine particles but also to anisotropic fine particles. Even highly anisotropic particles behave in the same way as isotropic particles if they are on the order of one-tenth or less of the wavelength of incident light.

As described above, the present invention can be used to measure the particle size in the latex manufacturing process, and to measure the particle size of various fine particles in the atmosphere and factory wastewater.

〔Effect of the invention〕

According to the present invention, the particle size can be measured from the white level of the power spectrum density of light scattered by the particles.

[Brief explanation of drawings]

1 is a diagram showing an embodiment of a particle size measuring device implementing the present invention, FIG. 2 is an enlarged view of the collimator 10 in FIG. 1, FIG. 3 is a diagram showing a modification of FIG. 1, Figure 4 is a graph showing the power spectrum density of scattered light by latex particles with a particle size of 0.212 μm. Figure 5 is a flowchart showing the process of determining the white level. Figure 6 A, B, and C are smooth power spectrum density curves. A graph to explain how to
A graph showing the relationship between white level and particle size using a t% latex suspension. Figure 8 is a flowchart showing the process of creating a calibration line. Figure 9 is the particle size of fine particles contained in the sample. FIG. 10 is a flowchart showing the process of measuring the particle size measuring device shown in FIG. 1. FIG. 1... Light source 2, 4.5... Luminous flux 3...
Half mirror 6...Condensing lens 7...Cell
8, 11...light) moxibustion device 9...fine particles
10...Collimator 13, 15...Low noise amplifier 14...Data processing device 16...Low pass filter 20...Display device 21.22...Polarizing plate

Claims (1)

[Claims] Particle size measurement characterized by projecting radiation into a sample containing fine particles, detecting light scattered by the fine particles, and measuring the particle size of the fine particles based on the white level of the power spectrum density of this detection output. Method.