JPS63269042A - Method for measuring particle size distribution of high density specimen utilizing diffraction of laser beam - Google Patents

Abstract

PURPOSE:To accurately measure particle size distribution without diluting a high conc. specimen suspension, by arranging the thickness direction of a gap having a minute thickness along the optical axis of laser beam to be allowed to irradiate and receiving the specimen suspension in said gap to perform measurement. CONSTITUTION:A specimen suspension prepared by dispersing a particle group tested in a liquid medium is irradiated with laser beam and the laser beam diffracted in accordance with the size of a particle is condensed to the detector 5, which is arranged to the focus surface of the lens 4 arranged behind the specimen suspension, by the lens 4 and the particle size distribution of the particle group tested is calculated from the intensity distribution of the receiving light of the detector 5 in the radius direction thereof. In this case, a gap G having a predetermined minute thickness is formed between beam pervious plate materials 31, 32 parallel to each other so that the thickness direction thereof is arranged along the optical axis A of the laser beam allowed to irradiate and the specimen suspension is received in the gap G to perform the measurement.

Description

DETAILED DESCRIPTION OF THE INVENTION <Industrial Application Field> The present invention relates to a particle size distribution measuring method using laser light diffraction, and particularly to a measuring method suitable for measuring high-density samples.

<Prior art> In a method of measuring the particle size distribution of a particle group using Fraunhofer diffraction, a particle group dispersed in a medium is generally irradiated with a parallel laser beam, and the particle size distribution is determined according to the size of each particle. The diffracted light is received by a lens, and a concentric diffraction image is formed on the focal plane of this lens. Then, the particle size distribution of the particle group is calculated from the measured value of the light intensity distribution of this diffraction image.

In such measurement methods, when the particle concentration in the medium is high, multiple scattering, in which light scattered by one particle is further scattered by other particles, increases, as shown in Figure 6, and the scattering Its intensity increases for light with large angles. A larger scattering angle means that there are apparently more small particles, and the obtained particle size distribution measurement result deviates to a smaller particle size than the true particle size distribution, making accurate measurement impossible.

Therefore, in this type of measurement method, measurement has conventionally been carried out using a suspension diluted to a concentration that does not cause multiple scattering.

<Problems to be solved by the invention> By the way, some powders and granules are stable only in a suspension state within a certain concentration range, and their properties such as particle size change when dried or diluted. There is something. When the above concentration range is high, even if we try to accurately measure the particle size distribution, it is impossible not only by the laser light diffraction method described above, but also by other sedimentation methods, pore passing methods, etc., and it is difficult to obtain expensive and complicated images. The only option was to use an analytical device (microscope).

An object of the present invention is to provide a method that can accurately measure particle size distribution without causing multiple scattering by using laser light diffraction without diluting a highly concentrated sample suspension.

Means for Solving the Problems> As shown in FIGS. 1 to 3 corresponding to Examples, the present invention involves applying a laser beam to a sample suspension in which sample particles are dispersed in a medium. A laser beam that is irradiated with light and diffracted according to the size of the particles is focused by a lens 4 placed behind the sample suspension onto a detector 5 placed at the focal plane of the lens 4. In the method of determining the particle size distribution of the sample particle group from the radial light intensity distribution of the detector 5, a gap G of a predetermined minute thickness is formed between two mutually parallel translucent flat plate materials 31 and 32, This gap G is characterized by arranging the thickness t direction along the optical axis A of the irradiated laser beam, storing the sample suspension in the gap G, and performing the measurement.

Effect> Even in a highly concentrated sample suspension, if the number of particles present in the direction of the optical axis A of the irradiated laser beam is small, the probability of multiple scattering occurring will decrease. A small gap G with a thickness t is
By arranging the laser beam so that its direction is along the laser optical axis A and accommodating the sample suspension therein, the particles spread out on a plane.
The number of particles existing in the optical axis A direction is reduced, and the intended purpose is achieved.

<Example> Embodiments of the present invention will be described below based on the drawings.

FIG. 1 is a schematic diagram of an apparatus for carrying out the invention.

Laser light from a laser light source 1 is expanded by a beam expander 2, becomes parallel laser light, and is irradiated onto a flat cell 3, which will be described later. A sample suspension in which test particles are dispersed in a medium is contained in the flat cell 3.
The irradiated laser beam is diffracted by the dispersed sample particles at an angle corresponding to each particle diameter. The diffracted light forms a diffraction image on a detector 5 placed on the focal plane of the condensing lens 4 at the next stage.

The detector 5 is, for example, a ring detector having a plurality of concentric ring-shaped light-receiving surfaces, and among the light diffracted by the dispersed particles in the flat cell 3, light with a small diffraction angle is sent to the inner ring, and the light with a small diffraction angle is The larger light is focused on each outer ring.

The amount of light incident on each ring-shaped light-receiving surface is converted into an electrical signal, quantized by a multiplexer, an amplifier, and an A-D converter (all not shown), and then input into a microcomputer. In the microcomputer, the particle size distribution of the sample particle group can be calculated by a known calculation method using the light amount data on each ring-shaped light-receiving surface.

FIG. 2 is a front view of the flat cell 3, and FIG. 3 is a sectional view taken along the line mm.

The flat cell 3 includes two transparent flat plates 3 made of Pyrex or the like.
1,32. Spacers 33, 34. It is constructed so that it can be assembled and disassembled freely by a holder 35 and a plurality of holding elastic members 36 such as springs.
A gap G having a uniform minute thickness t can be formed therebetween. That is, the transparent flat plate 31.32 is the spacer 33.3.
4 are placed parallel to each other, inserted into the holder 35, and pressed against each other at both left and right ends by the presser elastic members 36...36. In this state, the spacers 33 and 34 allow the transparent flat plates 31 and 32 to
A gap G with a uniform minute thickness t is formed in between.Next, the operation will be described along with the measurement procedure.

First, a sample suspension is accommodated in the gap G of the flat cell 3. To do this, for example, the flat cell 3 is disassembled, and an appropriate amount of the sample suspension is dropped onto one of the transparent flat plates 31. The other light-transmitting flat plate 32 is placed on top of it with spacers 33 and 34 interposed therebetween, and is incorporated into the holder 35. As a result, the sample suspension spreads within the gap G on a plane.

Next, in this state, the flat cell 3 is placed at a predetermined position behind the beam expander 2 so that the thickness t direction of the gap G is along the optical axis A of the laser beam, and the laser beam is irradiated.

At this time, since the sample suspension is spreading in a plane within the gap G, multiple scattering does not occur.

The critical concentration of the sample suspension at which an accurate particle size distribution can be obtained without causing multiple scattering has a predetermined relationship with the optical path length (thickness t of the gap G) within the sample suspension. Moreover, it was revealed through experiments that there is a correlation with the average particle size of the sample particle group.

That is, when the optical path length in the sample suspension is longer than a certain distance, accurate measurements cannot be made unless the density is about 105 particles/cc or less, regardless of the optical path length. This is already known. However, as the optical path length was decreased, the critical concentration increased below a certain optical path length. It has been found that the optical path length at the point where the critical concentration becomes high enough to be useful compared to conventional measurement methods is less than five times the average particle size of the sample particle population. That is, by setting the thickness t of the void G to 5 times or less the average particle diameter of the sample particle group, it is possible to use a suspension with a concentration several times to several tens of times higher than the conventionally known limit concentration. We were also able to obtain accurate measurement results.

FIG. 4 shows an example of the results of an experiment conducted using the method of the present invention. In this experimental example, the average particle size was 3 as the sample particle group.
Using stone powder of 0 μm, the thickness t of the gap G of the flat cell 3 was set to 100 μm, and measurements were performed on suspensions of various concentrations. As a result, the critical concentration for obtaining accurate measurement results without causing multiple scattering was found to be a concentration in which 2 g of particles were dispersed in 320 cc of medium.

Figure 5 shows the average particle diameter of 30 mm using the conventional measurement method.
These are the results when stone particles of μm were measured.

In this example, the optical path length in the suspension is 5 dragons, i.e. the thickness is 5
A normal measuring cell of fl was used. As a result, 2g of particles
Accurate measurement results could not be obtained unless it was dispersed in 20.000cc of medium.

Note that the present invention is not limited in any way to the structure of the flat cell 3, and in addition to the above-mentioned embodiments, the transparent flat plate 31.
32, a suspension introduction path can be formed above the gap G, and the suspension can be injected into the gap G through this introduction path without disassembling the flat cell 3. In this case, the two light-transmitting flat plates 31 and 32 can be substantially integrated. Alternatively, a so-called flow cell type may be used in which the suspension flows through the gap G.

<Effects of the Invention> As explained above, according to the present invention, in a particle size distribution measuring method using laser light diffraction, a gap with a predetermined minute thickness is formed between two parallel transparent flat plates. This void is arranged so that its thickness direction is along the optical axis of the irradiated laser beam, and the sample suspension is contained in the void for measurement, so the sample particles are contained within this void. spreads out on a flat surface, making it difficult to cause multiple scattering. As a result, the critical concentration of the sample suspension is high, making it possible to measure sample suspensions with high concentration (high density).According to experiments, the critical concentration is 60 times higher than with conventional methods. We obtained results ranging from

In addition, according to the present invention, only a very small amount of sample is required, so it can be used not only for measuring highly concentrated suspensions, but also when the sample amount is small or when the sample is expensive and you do not want to consume a large amount. , can be a useful measurement method.

[Brief explanation of the drawing]

Fig. 1 is a schematic diagram of an apparatus for implementing the present invention, Fig. 2 is a front view of the flat cell 3, Fig. 3 is a cross-sectional view taken along line mm, and Fig. 4 is an experimental result using the present invention. FIG. 5 is a graph showing an example of measurement results using the conventional measurement method. FIG. 6 is an explanatory diagram of multiple scattering. 1... Laser light source 2... Beam expander 3... Flat cell 31.32... Translucent flat plate 33.34... Spacer 35... Holder 36--36... Holder Elasticity for use, member 4...Condensing lens 5...Dedekta Patent applicant Shimadzu Corporation Agent Agent
Patent Attorney Nishi 1) Fragment 1 Figure 2 Figure 31! 1 10 J JJ
-1m) Figure 6

Claims (2)

[Claims] (1) A sample suspension consisting of a group of test particles dispersed in a medium is irradiated with a laser beam, and the laser beam, which is diffracted according to the size of the particles, is placed behind the sample suspension. In this method, the particle size distribution of the sample particle group is determined from the radial received light intensity distribution of the detector by focusing the light onto a detector disposed on the focal plane of the lens using a lens that is parallel to each other. A gap with a predetermined minute thickness is formed between the flat plate materials, and this gap is arranged so that the thickness direction thereof is along the optical axis of the irradiated laser beam, and a sample suspension is accommodated in the gap. A method for measuring the particle size distribution of a high-density sample using laser light diffraction. (2) A high-density sample using laser light diffraction according to claim 1, characterized in that the thickness of the voids is 5 times or less the average particle diameter of the particle group to be measured. Particle size distribution measurement method.