JPS59126933A - Opto-acoustic analyzing device - Google Patents

Abstract

PURPOSE:To measure simultaneously the grain size distribution and concn. of suspended components by detecting and analyzing the intensity and phase of the opto-acoustic signal obtd. by projecting modulating light to a suspension. CONSTITUTION:A suspension of a sample is sealed in a measuring cell 8, and the pulsed light 7 obtd. by modulating laser light 5 from an argon laser 4 with an acousto-optic modulator 6 is irradiated thereto. The suspended particles emit a heat flow flux by absorbing the light 7 and generates a photo-acoustic signal 9 in a medium. The signal 9 is converted to an electrical signal by a piezoelectric element 14 and the signal is amplified with a lock-in amplifier 11. The intensity of said signal is inputted to a microcomputer 12 while the phase thereof is scanned with the reference signal 10 from an optical modulator 6 as a reference. The microcomputer 12 records the data on the phase and intensity in a two- dimensional arrangement and calculates the grain size from the data on the phase and the data in the intensity. The result thereof is outputted to a recorder 13.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Application of the Invention] The present invention relates to a photoacoustic analyzer, and in particular, to an improved device capable of automatically measuring the particle size distribution and concentration of suspended components in a suspension. This invention relates to a photoacoustic analysis device.

[Prior art]

Conventionally, photoacoustic analyzers are generally equipped with means for measuring the intensity of a photoacoustic signal obtained by projecting all modulated light onto a suspension, which is a sample, and based on the intensity of the measured photoacoustic signal, the concentration of suspended components can be determined. It is configured so that it can be detected completely.

However, since the above photoacoustic analyzer cannot measure the particle size distribution of suspended components, the particle size is measured by a light scattering method or the like. Particle size measurement using this light scattering method can only measure particles of about 0.2 to 1 μm depending on the wavelength of incident light.

However, when the concentration of a suspension is entirely measured by nephelometric analysis, an error occurs in the measured concentration due to differences in particle size, and this error can reach up to 10 cm, making accurate measurement difficult.

[Purpose of the invention]

In view of the above circumstances, the present invention seeks to provide a photoacoustic analyzer that can simultaneously measure the particle size distribution and concentration of suspended components in a suspension with high accuracy.

[Summary of the invention]

The present invention is configured so that the entire particle size distribution of suspended components can be measured by detecting and analyzing not only the intensity of the photoacoustic signal obtained by projecting all of the modulated light onto the suspension, but also the entire phase thereof.

Next, the principle of calculating the total particle size based on the phase of the photoacoustic signal will be explained with reference to FIG. This figure schematically depicts the entire state in which heat α1 [flux 3] emanates from suspended particles 1 when the light 2 is irradiated onto the suspended particles 1.

The suspended particles 1 absorb the light 2 and generate heat. Assuming that the amount of heat generated is 'kQ', Q is expressed as a function of the incident light intensity (2) and the radius r of the suspended particles as shown in the following equation.

Here, k is a proportionality constant. The heat generated is suspended particles 1
transfer from the surface to the liquid. Assuming that the heat flux from the suspended particles to the liquid is 3 total J, the relationship between J and Q is Q=J4 rc r2t −(2
), where t is the time required for heat to flow out.

According to equations (1) and (2), the relationship between t and r is i 3J "°° (3).If the optical modulation frequency is 1, the phase delay of the photoacoustic signal with respect to the modulation period of the incident light. From equation (3), φ = 2πf (10 -), which is a function of φbar.Jl, 11j et al., the phase spectrum of the acoustic signal is similar to the 8-diameter distribution of suspended particles. Here, R is the range of the detector, and V is the velocity in the medium.

What is the physical meaning of this measurement principle? It is described below. The heat generated within the particles due to light absorption passes through the entire surface of the particles and is released into the medium.

Equation (1) above assumes that the amount of light absorbed by suspended particles is proportional to the volume of the particles. Therefore, if the concentration of particles is constant, the amount of light absorbed is proportional to the mass of the particles. This relational expression applies very well to particles with a diameter of 501 Im or less.

On the other hand, the heat released from a particle per unit time is proportional to the & area of the particle since the heat flux from the particle surface to the medium is one foot. Therefore, the amount of heat generated within the particle,
The ratio between the amount of heat to be released and the release time is expressed by the above equation (2). That is, three-dimensional spread 9? Is the heat source it has a two-dimensional heat passing surface? In order to release heat through
) yields a particle size-release time relationship expressed by the equation.

The emitted heat quickly causes a foreshadowing 111''zk of the medium and generates a photoacoustic signal, ie, a sound wave, within the medium.

The generated sound wave has a phase delay with respect to the incident light due to the previous process in equation (3) and a phase delay due to the propagation of the sound wave R/V (4)
Detected with expression. Collectively, the phase delay of the acoustic signal and the diameter of the particle are in a proportional relationship.

Based on the above-mentioned principle, in order to simultaneously detect the particle distribution and concentration of suspended components in a suspension with high precision, the photoacoustic analyzer of the present invention includes an optical modulator and a modulated light beam. In addition to providing a means for projecting onto the measurement cell, an amplifier having a function of measuring the phase difference between the photoacoustic signal inputted from the measurement cell and the optical signal inputted from the optical modulator is provided, and , an automatic calculation having a function of frequency-analyzing the output signal of the amplifier and calculating the phase spectrum while performing the photoacoustic signal gold scanning/ The diameter distribution can be measured completely automatically, reducing waiting time.

[Embodiments of the invention]

Next, an embodiment of the present invention will be described with reference to FIGS. 2 to 7.

FIG. 2 is a block diagram of the photoacoustic analyzer of the present invention.

In this embodiment, all 4 argon lasers are provided as light sources, and 51
Five laser beams of 4 nm iw are generated. The above laser beam 5 is input to an acousto-optic modulator 6 and modulated into a pulsed beam 7 of 10KH2.

This modulated light beam 7 is made to enter a measuring cell 8. As will be described in detail later, the measurement cell 8 has a structure in which it can be filled with a suspended sample to be measured, and is made of concavity-shaped pressure ceramics. A lock-in amplifier 11 is provided to input the photoacoustic signal 9 emitted from the 1IIIJ constant cell 8, and a part of the output of the acousto-optic modulator 6 is input to the lock-in amplifier 11 as the reference signal 10.

The lock-in amplifier 11 amplifies the photoacoustic signal 9, and inputs the phase difference with the reference signal and the intensity to the microcomputer 12. Microcomputer 12
performs data processing and outputs the results to all recorders 13.

FIG. 3 is a partial pi-plane view of the measurement cell 8 of this embodiment.

This measurement cell 8 is constructed by concentrically embedding a cylindrical piezoelectric element 14 having an inner diameter equal to that of the glass cylinder 15 in the center of a glass cylinder 15 having an inner diameter of 7 cm and a length of 100 mm. In this example, zirconium 7B i k was used as the sample, and cap 21. Teflon packing 19 and optical seal 1
6 is removed and the internal space 24 is filled with a sample suspension.

The optical window 16 is completely attached to prevent air bubbles from forming, the sample is sealed, and the Teflon gasket 19 and cap 21 are completely attached. 20 is a cover of the measurement cell.

In this example, the above cell cover 20 and cap 21
is made of stainless steel and serves as the outer shell of this measurement cell.

22 is a glass filter engraved with crosshairs, and 23 is the same holder, which is set so that the center line of this measurement cell coincides with the incident laser beam (7 shown in FIG. 2) using the crosshairs. This glass filter 22 is removably attached, and is removed after the optical axis support J mentioned above. With this preparation, a pulse-modulated laser beam (7 shown in FIG. 2) is projected onto all measurement cells. Reference numeral 25 denotes a signal output line connected to the piezoelectric element 14 in order to output the photoacoustic signal generated within this measurement cell.

In the photoacoustic analyzer configured as above, when a suspension (of the sample) is sealed in the analysis cell and the entire pulse-modulated laser beam is irradiated, the modulated beam is captured by the suspended particles according to the principle described earlier. The photoacoustic signal generated by thermal expansion accompanying this heat generation is converted into a stain signal by the piezoelectric element 14 and amplified by the lock-in amplifier 11. This photoacoustic signal is input to the microcomputer 12 with its intensity P=i while scanning the phase φ with reference to the reference signal 10 from the optical modulator 6. In microcomputer 12,
Phase and intensity data are recorded in a two-dimensional array. Of this input data, all phase data is linearly converted into particle size using equation (4) using a microcomputer, and intensity P'tC=AP
...(6) and linearly transform into concentration. Here, A is the slope of the calibration number measured in advance and is a proportionality constant.

By the above operation, the (d11) constant data of (phase 2 intensity) is rearranged into (particle size, density), and this result is outputted to the recorder 13.

FIG. 4 shows the particle size distribution of the zirconium suspension, which was measured in advance using a micrograph. This suspension sample was 5μ
It has a particle size distribution gold with m=i center particle size. The entire phase spectrum of the photoacoustic signal obtained as a result of measurement with this sample analyzer is shown in FIG.

In addition, the calibration curve of this sample measured with this analyzer was
As shown in the figure. From Figure 6, it can be seen that the value of the proportionality constant A in equation (6) is A = 0.5 (p (n / μv). Also, from the physical property constant table, 2πf- = 140.0
(mrad). Therefore, using these values, the data is processed by a microcomputer according to equation (4). Figure 7 shows the result of the measurement. In the measurement results of this example, the central grain size was 5.08 m1.
The concentration relative to the central particle size was 0.98 llIn, which could be measured with an accuracy of within 2 circles.

〔Effect of the invention〕

As described in detail above, the photoacoustic analyzer of the present invention has an optical modulator and a means for projecting modulated light onto a measurement cell, as well as a y-color acoustic signal input from the measurement cell. , the function to measure the total phase difference with the reference signal input from the above optical modulator? The suspended components in the suspended atomizer are provided with an automatic calculator having a function of scanning the photoacoustic signal, frequency-analyzing the output signal of the amplifier, and calculating the entire phase spectrum. particle size distribution and one time can be measured simultaneously with high precision.

[Brief explanation of the drawing]

Fig. 1 is an explanatory diagram schematically depicting the entire state of light absorption and heat generation by suspended particles, Fig. 2 is a block diagram of an embodiment of the photoacoustic analyzer of the present invention, and Fig. 3 is a measurement cell as well. Fig. 4 is a diagram showing the particle size distribution of the zirconium suspension, Fig. 5 is a chart showing the phase spectrum of the photoacoustic signal, and Fig. 6 is the chart showing the detection line amount of the zirconium suspension. FIG. 7 is a chart showing grain size distribution calculation and polishing of a zirconium suspension using a photoacoustic analyzer. 1...Suspended particles, 2...Light, 3...Heat flux, 4.
... Argon laser, 5... Laser light, 6... Acousto-optic modulator, 7... Pulse light, 8... Measurement cell, 9
... Optical prayer signal, 10 ... $ black signal, 11 ... Lock-in amplifier, 12 ... Microcomputer, 1
3...Recorder, 14...Piezoelectric transducer, 15...Glass cylinder, 16...Optical window, 17...Backing, 1
8...backing, 19...banking, 20...
・Cell cover, 21...Cap, 22...Glass filter, 23...Glass filter holder, 24...
- Space for placing the sample, 25...Signal output line. Agent 9th Burial Masami Akimoto / Diagram / Built 20 Funeral 3 Diagram '2nd Rise Figure 1 Grain size (, am) Iga Kiguchi (771 light a) Figure 6 θ / 234-5 Temperature CPPyn Figure 171 #L stopper θ Yura-16゛

Claims (1)

[Claims] 1. In the photoacoustic analysis device, an optical modulator and a means for projecting the modulated photoacoustic sound onto the measurement cell are provided, and
An amplifier having a function of measuring the total phase difference between the photoacoustic signal input from the measurement cell and the reference signal input from the optical modulator is provided, and while scanning the photoacoustic signal, An automatic computing machine with the function of analyzing all frequencies of the output signal of the amplifier and calculating the entire phase spectrum is installed to automatically measure the concentration and particle size distribution of fine particles in the sample in the measurement cell. Photoacoustic analyzer that measures the percentage.