JP2803296B2 - Particle size distribution analyzer - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a particle size distribution measuring apparatus utilizing a diffraction / scattering phenomenon that occurs when a particle group dispersed and flying in a medium is irradiated with light.

<Prior Art> In measurement of the particle size distribution of submicron particles using a laser diffraction / scattering method, Mie's scattering theory is used particularly in a small particle region. This Mie scattering theory requires that the relative refractive index between the medium and the particles be known. Therefore, in this type of apparatus, conventionally, it is necessary for a human (measurer) to select the refractive index of particles and a medium (medium liquid) and to instruct the apparatus by key input or the like.

In other words, in order to convert the intensity distribution of scattered light or the like into a particle size distribution, it is generally necessary to perform an operation using a conversion matrix, but in a submicron region where the particle diameter is approximately equal to or smaller than the wavelength of the laser light Mie scattering theory is used. When Mie's scattering theory is used, the refractive index of the particle to be measured and the refractive index of the medium are required to calculate the elements of the transformation matrix.

<Problems to be Solved by the Invention> By the way, among particles, the refractive index is not known, and even if the refractive index of the material is known, a different value may be adopted in the state of the particles. And there is no reliable method for directly measuring the refractive index of particles.

In such a case, in the conventional apparatus, it is necessary to perform the measurement while changing the refractive index many times, and based on a large number of obtained results, it is necessary for a human to select an appropriate refractive index. There is no quantitative standard for this selection, and there is also a problem that there is a high possibility that an artificial error is present in the particle size distribution measurement result.

The present invention has been made in order to solve such a problem, and it is an object of the present invention to provide an apparatus that can quickly and accurately obtain a particle size distribution without intervention of an artificial element even for particles having an unknown refractive index. .

<Means for Solving the Problems> In order to achieve the above object, in the present invention, the refractive index of the same sample is changed to a plurality of values, and the diffraction / scattered light intensity distribution measurement results are each converted to a particle size distribution. A first calculating means for converting, and a second calculating means for selecting a smoothest curve from the obtained particle size distribution curves based on a quantitative judgment, and a particle size related to the selected curve. It is configured to output the distribution as the particle size distribution of the particle group.

<Function> For example, when the diffraction / scattered light intensity distribution of a particle group having a particle size distribution as shown in FIG. Thus, the smoothness of the particle size distribution curve is impaired.

The present invention takes advantage of this point and converts the diffraction / scattered light intensity distribution of one sample into a plurality of particle size distributions by changing the condition relating to the refractive index to a plurality of conditions. It is determined quantitatively, and the smoothest one is adopted as the final particle size distribution measurement result.

<Embodiment> FIG. 1 is a block diagram of an embodiment of the present invention.

The laser light emitted from the laser light source 1 is applied to the flow cell 2. In the flow cell 2, a suspension 3 in which particles to be measured are dispersed in a medium is flowing in a direction perpendicular to the sheet of the drawing, and the irradiated laser light is scattered or diffracted by the particles and spatially. A diffraction / scattered light intensity distribution pattern results.

A lens 4 is disposed in the traveling direction of the irradiation laser light, in front of the flow cell 2, and a ring detector 5 is disposed further in front of the lens 4 at a focal position thereof. The ring detector 5 is formed by concentrically arranging a plurality of optical sensors having ring-shaped or semi-ring shaped light-receiving surfaces having different radii from each other about the optical axis of the lens 4. The forward light is condensed by the lens 4 and forms a diffraction / scattered image on the ring detector 5.

An optical sensor 6 is provided on the side of the flow cell 2, and scattered light to the side is detected by the optical sensor 6.

Each element of the ring detector 5 and the output signal of the optical sensor 6 pass through an amplifier 12 and then a multiplexer 7
The digital signal is guided to the A / D converter 8 via the input / output interface 9a and sequentially converted into digital data.

In the computer 9, for one sample, A-
From the light intensity distribution data taken in through the D converter 8,
A plurality of particle size distributions are calculated by changing the condition relating to the refractive index to a plurality by an operation described later, and the one having the smoothest curve is quantitatively selected from among them, and the particle size distribution is used as the final particle size distribution. , Connected printer 10 and CR
Output to T11.

Next, a calculation method by the computer 9 will be described.

Although the intensity distribution pattern of the diffraction / scattered light by the particle group changes depending on the size of the particle, since the actual sample contains particles having different sizes, the light intensity distribution pattern generated from the particle group is Diffraction from particles of
The scattered light is superimposed.

Expressing this as a matrix, Becomes However, Are as shown below.

here Is a light intensity distribution vector. The element r _i (i = 1,2, ‥
‥ m) is the incident light amount detected by each element of the ring detector 5 and the optical sensor 6 for side scattered light.

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 ,
Let the minimum value be dn _{+ 1} . Each divided section [d _j , d _{j + 1} ]
Is represented by one particle diameter D _j (j = 1, 2, Δn). f
Element f (j = 1,2, ‥‥ n ) is the amount of particles corresponding to the particle diameter D _j.

Here, Σf _j = 100 (%).

Light intensity distribution (vector) Is a coefficient matrix to be converted to.

Element a _{i, j} of the (i = 1,2, ‥‥ m, j = 1,2, ‥‥ n) physical meaning of the diffracted by the particles of unit particles of particle size D _j /
This is the amount of incident light on the i-th element of the scattered light.

The value of a _{i, j} can be calculated theoretically. For this purpose, if the particle diameter is sufficiently larger than the wavelength of the laser beam serving as a light source, the Fraunhofer diffraction theory is used. However, when the particle diameter is in the submicron range that is about the same as or smaller than the wavelength of the laser beam, it is necessary to use the Mie scattering theory. The Fraunhofer diffraction theory can be considered to be an excellent approximation of the Mie scattering theory that is effective when the particle diameter is sufficiently large compared to the wavelength in forward small angle scattering.

Using Mie scattering theory, In order to calculate the element (1), it is necessary to set the refractive index of the above-described particles and the medium in which the particles are dispersed.

Now, based on the equation (1), the particle size distribution Deriving the equation for the least squares solution of Is obtained. However, And () ^-1 represents an inverse matrix.

On the right side of the equation (4), the light intensity distribution Are elements detected by the ring detector 5 and the optical sensor 6 for side scattered light, and a coefficient matrix Can be calculated in advance using the Fraunhofer diffraction theory or the Mie scattering theory, and if the calculation of (4) is performed using the known data, the particle size distribution can be calculated. Obviously,

The above is the basic measurement principle of the laser diffraction / scattering method. However, what is shown here is an example of the calculation method of the particle size distribution, and there are various other variations. Further, there are various variations in types and arrangements of sensors and detectors. Regardless of the calculation method, the type of various measurement elements, and the like, in order to measure the particle size distribution of submicron particles, it is necessary to set the refractive index of the particles to be measured and the medium liquid.

Here, it takes a very long time to calculate the coefficient matrix shown in the equation (3). Therefore, in actual measurement,
A plurality of coefficient matrices are calculated in advance corresponding to a plurality of refractive indexes, and registered in a memory or an auxiliary storage device of the measuring device. Then, the most suitable coefficient matrix is selected from the selected matrix and used for the calculation of the particle size distribution, which has been conventionally performed. At this time, the criterion for selecting the coefficient matrix becomes a problem. If the coefficient matrix is selected incorrectly, an accurate particle size distribution cannot be obtained. As described above, this point becomes a problem when the refractive index of the particles is not clear.

In the embodiment of the present invention, the optimum one is automatically selected based on the following characteristics based on the quantitative determination of the relative refractive index of the particles and the medium.

First, using a plurality of coefficient matrices having different refractive index conditions, a plurality of particle size distributions are obtained from the light intensity distribution obtained from one sample.

If the particle size distribution calculated using the coefficient matrix of an appropriate refractive index is shown as an integrated distribution% under a screen (volume basis), a smooth curve is obtained as shown in FIG. 2 (a), for example. However, if an erroneous coefficient matrix of the refractive index is used, a discontinuous curve as shown in FIG.

If the degree of smoothness of the particle size distribution curve can be quantitatively expressed, it can be a practical reference for selecting a coefficient matrix (selecting a refractive index).

Now, the frequency distribution% calculated by equation (4) And the cumulative distribution% The following relationship holds between.

However, Here, a smooth curve is applied to the cumulative distribution%, and the result is And For example, if a third-order polynomial is used, G _j ′ (j = 1,2,2n, n + 1) is given by g _j ′ = c ₃ · (log d _j ) ³ + c ₂ · (log d _j ) ² + c ₁ (log d _j ) + C ₀ ‥‥ (8). Here, c ₀ , c ₁ , c ₂ , and c ₃ are coefficients determined by the least square method or the like.

First obtained cumulative distribution% And the cumulative distribution% obtained by fitting the curve The sum of squares e of the error of each element of Can be calculated by Then, this e is integrated distribution% Is used as a criterion for judging the smoothness of.

As a specific procedure, first, for the same light intensity distribution data, a plurality of coefficient matrices are considered within a range considered to be appropriate. Is used to determine the particle size distribution (integrated distribution%) in each case.

Next, in each case, a smooth curve is applied, and e shown in Expression (9) is calculated.

And a coefficient matrix when e is minimized Is selected, and the calculated particle size distribution (frequency distribution% and integrated distribution%, or one of them) is output to the printer 10 and / or the CRT 11 as a measurement result.

As described above, the refractive index that is considered to be closest to the true refractive index (relative refractive index) is converted into the light intensity distribution.

Note that there are various variations as described above regarding the specific calculation method of the particle size distribution and the arrangement of each sensor and the like, and the present invention is not limited to the above-described embodiment. It can be widely applied to a particle size distribution measuring device using the method.

<Effects of the Invention> As described above, according to the present invention, the diffraction / scattered light intensity distribution data of the same sample is changed to a plurality of conditions for the refractive index and changed to a plurality of particle size distributions. Converted, the one with the smoothest particle size distribution curve is selected by quantitative judgment, and it is output as the particle size distribution measurement result. Quick and accurate particle size distribution measurement of unknown samples can be performed.

[Brief description of the drawings]

FIG. 1 is a configuration diagram of an embodiment of the present invention, and FIG. 2 is an explanatory diagram of a difference in a particle size distribution conversion result due to a difference in a selected refractive index. DESCRIPTION OF SYMBOLS 1 ... Laser light source 2 ... Flow cell 3 ... Suspension 4 ... Lens 5 ... Ring detector 6 ... Optical sensor 8 ... A / D converter 9 ... Computer

Claims (1)

(57) [Claims] An intensity distribution of diffracted / scattered light obtained by irradiating a parallel light beam to a group of particles in a dispersed and flying state in a medium is measured, and the measurement result is calculated by calculation using the refractive index of the particles. An apparatus for converting a particle group into a particle size distribution, a first calculating means for changing the refractive index to a plurality for the same sample and converting each of the intensity distributions into a particle size distribution, A second calculating means for selecting the smoothest curve from the
A particle size distribution measuring device configured to output a particle size distribution related to the selected curve as a particle size distribution of the particle size group.