JP3446410B2 - Laser diffraction particle size distribution analyzer - Google Patents

Description

Description: BACKGROUND OF THE INVENTION [0001] 1. Field of the Invention [0002] The present invention relates to a laser diffraction type particle size distribution measuring apparatus, and more particularly, to a method in which an open type cell is used to measure a cell horizontally. The present invention relates to a vertical laser diffraction type particle size distribution measuring device used for measuring the particle size of a sample having a small amount and a relatively high concentration. 2. Description of the Related Art For example, in a vertical laser diffraction type particle size distribution measuring apparatus, an open cell 31 is used as shown in FIG. The sample is irradiated with laser light at right angles to the cell from above in the vertical direction, and diffracted / scattered light output below is detected by an array sensor such as a ring detector to measure the particle size distribution of the sample. In a general-purpose particle size distribution measuring apparatus, it is necessary to measure even small-diameter particles such as submicron particles. In this case, not only forward scattered light but also about 90 If the side scattered light in the degree direction and the back scattered light output to the rear of the cell are measured and the entire change is not detected, the distribution state of the particle diameter cannot be analyzed. Therefore, side scattered light and back scattered light are detected as shown in the figure. However, when the amount of the sample introduced into the cell is large as shown in FIG. 2, there is no problem because the side scattered light by the laser beam is strong. In the case where the depth of the cell 32 is shallow as described above, or when the thickness of the sample layer in the cell 32 is small due to the small amount of the sample, the side scattered light is particularly weak and cannot be detected, and the particle size distribution May not be measured. On the other hand, in order to obtain a large amount of side scattered light, FIG.
If the cell depth is increased and the amount of sample is increased, a large cell and a large amount of sample are required, which is not only economical, but also increases the possibility of multiple scattering. There is a problem that the measurement of the sample becomes very difficult. The present invention has been made in order to solve the above-mentioned problems. Even when the thickness of a sample layer in a cell is small, side scattered light can be obtained and even fine particles can be measured. An object of the present invention is to provide a vertical laser diffraction type particle size distribution measuring device. In order to achieve the above object, a laser diffraction type particle size distribution measuring apparatus according to the present invention comprises: means for irradiating a sample layer having a predetermined thickness with a laser beam; Means for measuring the intensity distribution of diffracted / scattered light in front of the irradiation by the sample particle group obtained by the irradiation of the laser beam, and means for measuring the intensity distribution of the side scattered light outputted in a direction substantially perpendicular to the laser optical axis. The sample layer is a sample in which the sample is placed in an open cell, a sample in which a sample is dropped on a transparent plate, or a plate-shaped sample, and a laser optical axis is predetermined with respect to a thickness direction of the sample layer. The laser light irradiating means is configured to have an angle of?, And the distance that side scattered light passes through the sample layer is reduced. With this configuration, when the sample layer is irradiated with laser light, light scattered in a direction at about 90 degrees with respect to the laser optical axis, as in the conventional case, has a depth (thickness) of the sample layer from above. When the laser beam is irradiated along the direction, the distance that the light passes through the sample is shorter than that of the light scattered sideways, so that it is less susceptible to multiple scattering by the sample particles, and the intensity distribution of the scattered light Since the measuring means can be brought close to the point where the side scattered light is generated, the side scattered light having a high intensity can be measured. An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 shows the configuration of a vertical laser diffraction type particle size distribution measuring apparatus according to the present invention. 1 is a laser light source, 2
Is a collimator that converts output light from the laser light source 1 into a parallel light beam having a predetermined cross-sectional area; 3 is an open-type cell having an open upper surface and containing a suspension in which sample (sample) particles are dispersed;
4 is a condensing lens, 5 is a forward diffraction / scattered light sensor comprising a ring sensor or an array sensor, 6 is a side scattered light sensor, 7 is a back scattered light sensor, and 8 is a signal detected by each light sensor. Computer for calculating the particle size distribution of the sample. The open cell 3 is placed horizontally, and a condensing lens 4 is arranged above the open cell 3 in the traveling direction of the irradiation laser beam, and a diffraction / scattered light sensor 5 is arranged behind the condenser lens 4. I have. Around the open cell 3, a side scattered light sensor 6 is formed in a direction making an angle of about 90 degrees with the optical axis of the irradiation laser light.
However, a backscattered light sensor 7 is arranged behind the cell 3. The laser light emitted from the laser light source 1 is converted into a parallel light beam having a predetermined cross-sectional area by the collimator 2 and is applied to the open cell 3. Since the cell 3 contains a suspension in which the sample particles are dispersed, the irradiated laser light is scattered or diffracted by the sample particles. The diffracted / scattered light passes through the condenser lens 4 and forms a diffracted / scattered image on the light receiving surface of the forward diffracted / scattered light sensor 5. The intensity of the scattered light having a large scattering angle is measured by the side scattered light sensor 6 or the back scattered light sensor 7. The output of the forward diffraction / scattered light sensor 5, the output of the side scattered light sensor 6, and the output of the back scattered light sensor 7 are sent to a computer 8 via an amplifier, an A / D converter, etc. (neither is shown). The computer 8 calculates the particle size distribution of the sample particles by using the respective light intensity data, that is, the diffraction / scattered light intensity distribution data, by the following algorithm. The light intensity distribution pattern changes depending on the size of the particles. Since particles having different sizes are mixed in an actual sample, the light intensity distribution pattern generated from the particle group is a superposition of diffraction / scattered light from each particle. When this is expressed by a matrix, s = Aq (1) Where: [Equation 2] s is a light intensity distribution vector. The element s _i (i =
1, 2,... M) are incident light amounts detected by the respective elements of the ring detector and the side scattered light sensor.
q is a particle size distribution (frequency distribution%) vector. The particle size distribution range is finite, and the range is divided into n, and the maximum value is d.
₁ and the minimum value is dn _{+ 1} . Each divided section [d _j , d _{j + 1} ] is represented by one particle diameter X _j . q
The element q _j (j = 1, 2,... N) is the particle amount corresponding to the particle diameter X _j . Usually, Is normalized (normalized) so that A is a coefficient matrix for converting a particle size distribution (vector) q into a light intensity distribution (vector) s. A _ij of elements of A (i = 1, 2,... M, j = 1, 2,.
Physical meaning of · · n) is the incident light amount for the i-th element of the light diffracted / scattered by particles in the unit particles of particle size x _j. The numerical values of a _{i, j} can be calculated theoretically. For this, the Fraunhofer diffraction theory is used when the particle diameter is sufficiently large compared to the wavelength of the laser beam serving as the light source. However, whether the particle size is about the same as the wavelength of the laser light,
For smaller submicron regions, Mie scattering theory must be used. The Fraunhofer diffraction theory can be considered to be a good approximation of the Mie scattering theory that is effective in forward small angle scattering when the particle size is sufficiently large compared to the wavelength. In order to calculate the elements of the coefficient matrix A using the Mie scattering theory, it is necessary to set the refractive index of the particles and the medium in which the particles are dispersed. By deriving an equation for obtaining the least squares solution of the particle size distribution (vector), the following equation is obtained: q = (A ^T A) ^-1 A ^T s (5) Where A ^T is the transposed matrix of A, and () ⁻¹ indicates the inverse matrix. In the right side of the equation (5), each element of the light intensity distribution (vector) s is a numerical value detected by the forward diffraction / scattered light sensor, the side scattered light sensor, and the back scattered light sensor. Further, the coefficient matrix A can be calculated in advance using the Fraunhofer diffraction theory or the Mie scattering theory. Therefore, using those known data, (5)
It is obvious that the particle size distribution (vector) q is obtained by executing the calculation of the expression. In order to measure the particle size distribution of the submicron particles, it is necessary to set the refractive index of the particles to be measured and the medium in which the particles are dispersed. As described above, a wide particle size distribution including a submicron region of the suspension in the cell can be obtained. Even when the sample layer is very thin, the laser beam is emitted from an oblique direction that forms a predetermined angle with the vertical direction, so that the amount of side scattered light increases, and this scattered light is increased. Can be detected. The thin sample layer reduces the risk of multiple scattering, and enables measurement of a sample with a relatively high concentration. Therefore, not only when the suspension in which the sample (sample) particles are dispersed is placed in the open cell as described above, but also when the sample is rare, the sample is placed on a transparent plate such as a slide glass. Is dropped, and the particle size distribution can be measured in a state of being spread over a certain area without attaching a cover glass or the like. Also, for a plate-shaped sample, a similar measurement can be performed by simply providing a table with a hole that can be disposed so as to pass through the optical axis and placing it on the sample, without requiring any special fixing means. In the above-described embodiment, the laser beam is irradiated from below at a predetermined angle with respect to the vertical direction (the thickness direction of the sample layer). However, the laser light source and the collimator are arranged above the cell. The same effect can be obtained by disposing the condenser lens and the forward diffraction / scattered light sensor below the cell and irradiating the laser beam from above at a predetermined angle with respect to the vertical direction (the thickness direction of the sample layer). Can be As described above, according to the laser diffraction type particle size distribution measuring apparatus of the present invention, the direction of the laser optical axis is inclined at a predetermined angle with respect to the thickness direction of a predetermined sample layer. Thus, even if the sample layer is thin, side scattered light can be detected, and a wide range of particle size distribution measurement including a submicron region of the sample can be performed. Further, since the sample layer may be thin, multiple scattering can be suppressed even for a sample having a relatively high concentration, so that accurate measurement can be performed.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a diagram showing a vertical laser diffraction type particle size distribution measuring device according to an embodiment of the present invention. FIG. 2 is a view showing a conventional vertical laser diffraction type particle size distribution measurement. FIG. 3 is a diagram illustrating a conventional vertical laser diffraction type particle size distribution measurement.

Claims (1)

(57) [Claims] 1. A means for irradiating a laser beam to a sample layer having a predetermined thickness, and the intensity of diffraction / scattered light in front of irradiation by a group of sample particles obtained by the irradiation of the laser light. In a particle size distribution measuring device comprising a means for measuring the distribution and a means for measuring the intensity distribution of side scattered light output in a direction substantially perpendicular to the laser optical axis, the sample layer is an open cell Laser light irradiation means is a sample in which a sample is placed, a sample in which a sample is dropped on a transparent plate, or a plate-shaped sample, and a laser beam axis is arranged at a predetermined angle with respect to a thickness direction of the sample layer. A laser diffraction type particle size distribution measuring device, wherein the distance that side scattered light passes through the sample layer is shortened.