JPH0754292B2 - Particle size distribution measuring device - Google Patents

Description

TECHNICAL FIELD The present invention relates to a particle size distribution measuring apparatus utilizing a light scattering phenomenon by particles.

<Prior Art> A laser diffraction / scattering type particle size distribution measuring device has been put into practical use as a particle size distribution measuring device utilizing a light scattering phenomenon or a diffraction phenomenon.

This laser diffraction / scattering type particle size distribution measuring apparatus irradiates a group of particles in a dispersed flying state with laser light of a constant wavelength from a laser light source, and the spatial intensity distribution of the diffracted light or scattered light by the particles, that is, each diffraction / scattering angle. And the light intensity, the particle size distribution is obtained based on the Fraunhofer diffraction theory or the Mie scattering theory.

<Problems to be Solved by the Invention> In the laser diffraction / scattering type particle size distribution measuring apparatus as described above, first, a laser light source is used, and as a photometric sensor, the spatial intensity distribution of diffracting / scattering light is simultaneously measured. In order to measure, for example, a special one called a ring detector, which is a concentric array of multiple sensors with circular or semi-circular light receiving surfaces with different radii centered on one point on the optical axis of the irradiation light, is used. Since it is necessary to use it, there is a problem that it must be expensive.

Further, although it is possible to reduce the measurable particle diameter lower limit by shortening the wavelength of the irradiation light, since a short wavelength laser light source is extremely expensive, a He-Ne gas laser is generally used as a light source. Case wavelength 632.8n
In m, the lower limit of the measured particle size is about 0.1 μm, and it is impossible to measure the particle size smaller than that.

In addition, in the laser diffraction / scattering type particle size distribution measuring apparatus, in addition to the conventional laser light source, a light source including a halogen lamp, a wavelength filter and a polarization filter is separately provided, and the scattered light intensity of the light source is measured. By doing so, the lower limit of the measured particle size may be made smaller. In this conventional device, the wavelength of the irradiation light is changed to 3 by exchanging the wavelength filter that passes the light from the halogen lamp.
Measurement is performed about 6 times in total while changing the polarization direction of the light of each wavelength by 90 ° while changing the type of light.
Then, the particle size distribution is calculated using the relationship between the particle size and the difference (or ratio) in scattered light intensity at the time of 90 ° polarization and the reference wavefront at each wavelength. However, in the method of changing the wavelength of irradiation light using such a wavelength filter, there are functional problems such as poor wavelength purity (radius width) and the inability to use a large number of wavelengths. Since this optical system is separately added to the laser optical system of, there is a drawback that it is expensive.

In addition, as a method for measuring the particle size distribution in a relatively fine particle region by using a principle other than the laser diffraction / scattering method, a dynamic light scattering method for measuring the fluctuation of spot light based on Brownian motion of particles, or a flat column There is the FFF method, etc., in which a force is applied to particles that are flowing while being diffused, and the particle size is calculated from changes in the flow velocity of the particles. There are drawbacks such as the restriction on the distribution range and the distribution range, and the FFF method has a long measurement time.

As described above, conventionally, there is no inexpensive device that can accurately measure the particle size distribution in the submicron region or less, and an object of the present invention is to achieve this.

<Means for Solving the Problems> A structure for achieving the above object will be described with reference to FIG. 1 corresponding to an embodiment. The present invention accommodates sample particle groups dispersed in a medium. A measuring cell 1, a monochromator 2 which outputs a monochromatic light of an arbitrary wavelength according to a command signal and irradiates the measuring cell 1 and a scattered angle of 0 ° of scattered light by the sample particle group in the measuring cell 1 of the irradiated light. To a monochromator 2 and a storage means for storing an output signal from the photometric sensor 3 at a timing according to a command signal. On the other hand, a control means for supplying a command signal, respectively, and a computing means for converting the stored contents of the storage means into a particle size distribution of the sample particle group (storage means,
Each function of the control means and the arithmetic means is realized by, for example, the microcomputer 12, and the control means changes the output light wavelength λ _i (i = 1, 2, ... N) from the monochromator 2 with time. At the same time, the outputs I _i (i = 1, 2, ... N) of the photometric sensor 3 for each wavelength are sequentially stored in the storage means, and the calculation means stores the storage contents I _i of the storage means in the particle diameter D _j. (J =
1,2, ... m) using a preset coefficient a _ij corresponding to the scattered light intensity at the arrangement angle of the photometric sensor 3 when the light of wavelength λ _i is applied to the sample Characterized by converting to a particle size distribution of a particle group.

<Function> In the light scattering phenomenon by particles, when light having a constant intensity is irradiated, for particles having the same refractive index, if the wavelength of the irradiation light is constant, the scattering pattern (at each scattering angle Light intensity) is determined. A conventional laser diffraction / scattering type particle size distribution measuring apparatus utilizes this. That is, when a sample particle group, which is a group of particles having various particle diameters, is irradiated with laser light, scattered light having a spatial intensity distribution of a pattern corresponding to each particle diameter is generated from each particle, and as a whole, Scattered light having a spatial intensity distribution in which these are superimposed is observed. The spatial intensity distribution of this scattered light, that is, the light intensity I _i (i = 1, 2, ... N) for each scattering angle θ _i , is measured and converted into a particle size distribution using the conversion coefficient b _ij set in advance. . Here, the conversion coefficient b _ij is the scattering in the direction of the scattering angle θ _i when a unit amount of particles having a certain particle diameter D _j (j = 1, 2, ... M) is irradiated with laser light. It is a coefficient corresponding to the light intensity.

On the other hand, when the wavelength of the irradiation light is changed, the scattering pattern changes even with the same particle size. That is, when focusing on a certain scattering angle, the scattered light intensity at that angle changes by changing the wavelength of the irradiation light even with the same particle diameter. Then, how the scattered light intensity at the certain angle changes with the change of the irradiation light wavelength is determined by the particle diameter. Therefore,
A constant obtained when light of various wavelengths λ _i (i = 1,2, ... n) is radiated to particles of various amounts having various particle diameters D _j (j = 1,2, ... m). By _obtaining the conversion coefficient a _ij corresponding to the scattered light intensity at an angle in advance, the scattered light from the sample particle group for each wavelength λ _{i is} changed at a constant angle while sequentially changing the wavelength λ _i of the irradiation light. If only the measurement is performed, the particle size distribution of the sample particle group can be obtained without measuring the spatial intensity distribution of scattered light obtained when the monochromatic light having a constant wavelength is irradiated. The present invention utilizes this point.

That is, the particle size distribution can be calculated by measuring the scattered light intensity at a fixed angle at many wavelengths while changing the wavelength of the irradiation light by the monochromator 2 over a wide wavelength range.

<Example> FIG. 1 is a block diagram of an example of the present invention, and FIG. 2 is a block diagram of a sampling device for supplying a sample suspension S to the measurement cell 1.

The measuring cell 1 made of a transparent material such as glass has a liquid inlet.
This is a so-called flow cell provided with 1a and a liquid outlet 1b, and the sample suspension S is flown therein by the sampling device shown in FIG. That is, the sample suspension S in which the sample particles are dispersed in the liquid medium is placed in the ultrasonic bath 22 in the sample bath 21.
The particles are uniformly dispersed by the stirrer 23, and the particles are circulated between the sample tank 21 and the measurement cell 1 by the liquid feed pump 24.

The measuring cell 1 is irradiated with monochromatic output light from the monochromator 2. The monochromator 2 is a well-known one that is often used in spectrophotometers, and includes, for example, a light source lamp, a rotatable grating that receives light from the light source lamp, a motor that rotates the grating, and an entrance slit and an exit slit. Etc., the output light wavelength can be changed over a wide wavelength range based on the command signal.

The slit 4 is provided at a position of 90 ° with respect to the optical axis of the irradiation light L from the monochromator 2, and among the scattered light by the sample particles in the measurement cell 1, only the component in the 90 ° direction is the slit 4. Is configured to pass through.

The 90 ° scattered light that has passed through the slit 4 is guided to the light receiving surface of the photomultiplier 3 via the three prisms 5, 6 and 7.

In addition, the measuring cell 1 of the irradiation light L from the monochromator 2
The light passing through is blocked by the beam stopper 8 so that it does not enter the photomultiplier 3.

The point to be noted in the measuring optical system of the embodiment of the present invention described above is that the monochromator 2, the measuring cell 1 and the photomultiplier 3 are arranged in a straight line, and this configuration is similar to that of a normal spectrophotometer. The configuration is the same. That is, in this embodiment, the photometry system of the spectrophotometer is used as it is, the measurement cell 1 is changed to the flow cell type, and an optical system for guiding only 90 ° scattered light to the photomultiplier 3 is added. Therefore, it can be manufactured relatively inexpensively.

The output of the photomultiplier 3 is the amplifier 10, A-
It is taken into the microcomputer 12 via the D converter 11. In addition, the command signal to the above-mentioned monochromator 2 is also interfaced from this microcomputer 12.
Supplied via 13.

FIG. 3 is a flow chart showing the contents of the program written in the ROM of the microcomputer 12, and the operation will be described below with reference to this figure.

With the suspension S flowing in the measurement cell 1, first, the wavelength of the irradiation light L is set to a preset first wavelength λ ₁ , and the photometric data from the photomultiplier 3 in that state is set. Collect and store the data in RAM as Iλ _l .

Next, the wavelength of the irradiation light L is changed to the second wavelength λ ₂ which is also set in advance, and similarly, the photometric data from the photomultiplier 3 is sampled, and the data is Iλ.
Stored in RAM as ₂ .

By repeating this calculation, by changing the wavelength to lambda _l to [lambda] _n, after storing the photometric data Iλ _l ~Iλ _n at each wavelength in the RAM, and the particle size distribution of the sample by using the data Iλ _l ~Iλ _n To do.

This calculation method will be described below.

Scattered light intensity Iλ _i (i at each wavelength λ _i at a constant scattering angle
= 1 ... n) and the particle diameter D _j (j = 1 ... m) are as follows: W _j is the weight% of the particles of the particle diameter D _j in the sample particles, a _ij is the particle diameter D _j
Assuming that the scattered light intensity at the above-mentioned constant angle when the particles of the unit weight of is irradiated with the light of wavelength λ _i , It is represented by.

This equation (1) is the scattered light intensity I _i (i = 1) at each θ _i of each scattering of the usual laser diffraction / scattering type particle size distribution measuring apparatus.
... n) and the particle diameter D _j (j = 1 ... m), And the form of the formula are the same, and b _{ij in} formula (2) is the particle size D
_While the unit weight of _j is the intensity of light scattered in the direction of the scattering angle θ _i , this coefficient b _ij only changes to a _ij described above.

Therefore, the data Iλ ₁ ... Iλ _n can be converted into the particle size distribution by changing the coefficient b _ij to a _ij by the same calculation method as the particle size distribution calculation method based on the conventional scattered light intensity distribution.

When only 90 ° scattered light is measured using the above-described example using a normal spectrophotometer, the measurement range of the particle size distribution is about 1 μm to about 0.02 μm.

The upper limit of this measurement range can be extended to 10 μm or more by measuring scattered light at smaller angles. FIG. 4 is a diagram showing a main part of an optical system in the case of measuring scattered light of a small angle. Scattered light of a desired angle is taken out through a slit 41, and two mirrors 42 and 43 are used for the photomultiplier 3
Leading to. If this optical system and the optical system of FIG. 1 can be selected, or if the measurement scattering angle can be arbitrarily changed, it is possible to measure the particle size range of 10 μm or more to 0.02 μm as a whole. .

In each of the above examples, when the wavelength of the irradiation light L from the monochromator 2 is changed, its intensity is also changed in general, but when a single-beam monochromator is used, the measurement is performed prior to the actual measurement. in a state where in the cell 1 was flowed only Nakadachieki keep sampling the photometric data I _o lambda _i at each wavelength lambda _i, may be added to correct the actual photometric data Airamuda _i this as the reference light data.

When a double-beam monochromator is used, a cell for reference light photometry is provided as in the spectrophotometer, and only the liquid medium is allowed to flow through the cell to measure the actual photometric data Iλ _i.
At the same time, the photometric data I _o λ _i of the reference light may be collected and corrected.

Further, the flow cell type of the measurement cell 1 prevents the particle size distribution of the particles existing in the irradiation beam from changing during the wavelength scanning when the sedimentation speed of the sample particles in the medium is high. This is because the usual batch cell type can be used when the sedimentation speed of the particles is low.

Furthermore, in the configuration of FIG. 1, the prisms 5, 6, and 7 may be replaced with mirrors, respectively, and when the photometric system of the spectrophotometer is not used in the photometric system of the present invention, the photomultiplier 3 The disposition position may be, for example, immediately after the slit 4 in the example of FIG. 1, and this point is not limited at all.

<Effects of the Invention> As described above, according to the present invention, the wavelength of monochromatic light with which the sample particles in the dispersed state are irradiated is changed in a wide wavelength range using a monochromator, and scattered light at each wavelength is changed. Since the particle size distribution of the sample is calculated by measuring the light at a constant scattering angle, use an expensive short-wavelength laser light source or a special photometric sensor such as a ring detector to measure the spatial intensity distribution of scattered light. Instead, it is possible to measure the particle size distribution of fine particles with high accuracy simply by adding simple parts and software to an ordinary inexpensive spectrophotometer.

[Brief description of drawings]

1 is a block diagram of an embodiment of the present invention, FIG. 2 is a block diagram of a sampling device for supplying the sample suspension S to the measuring cell 1, and FIG. 3 is a microcomputer 12 of the embodiment of the present invention. ROM
FIG. 4 is a flowchart showing the contents of the program written in FIG. 4, and FIG. 4 is a main part configuration diagram of an optical system of another embodiment of the present invention. 1 ... Measuring cell 2 ... Monochromator 3 ... Photomultiplier 4 ... Slit 5,6,7 ... Prism 8 ... Beam stopper 11 ... AD converter 12 ... Microcomputer

Claims (1)

[Claims] 1. A measuring cell containing a sample particle group dispersed in a medium, a monochromator for outputting monochromatic light of an arbitrary wavelength to irradiate the measuring cell in accordance with a command signal, and the irradiation light in the measuring cell. Of the light scattered by the sample particle group of
A photometric sensor for injecting scattered light at a constant angle other than the scattering angle of 0 °, a storage means for storing the output signal from the photometric sensor at a timing according to a command signal, and the monochromator and the storage means respectively. It has a control means for supplying a command signal and a computing means for converting the stored contents of the storage means into the particle size distribution of the sample particle group, and the control means has an output light wavelength λ _i (i
= 1,2, ... n) is changed over time, and the output I _i (i = 1,2, ... n) of the photometric sensor for each wavelength is sequentially stored in the storage means, and the arithmetic means is used. At the arrangement angle of the photometric sensor when the storage content I _i of the storage means is irradiated with light of wavelength λ _i for a particle unit amount of particle diameter D _j (j = 1, 2, ..., M). A particle size distribution measuring device characterized by converting into a particle size distribution of a sample particle group using a preset coefficient a _ij corresponding to scattered light intensity.