JP5000379B2 - Laser-induced fluorescence analysis method and laser-induced fluorescence analysis probe - Google Patents

Description

  The present invention relates to a remote, non-contact element concentration determination technique using a laser, and particularly to a laser-induced fluorescence analysis technique.

  Analytes that are difficult to access due to high temperatures, toxic gases, harmful radiation, etc. need to be analyzed directly. An example of such an analysis object is a molten metal being refined.

  For example, in converter refining, where decarburization is performed by oxygen blowing during the steel manufacturing process, the total Fe concentration in the slag is increased by excessive blowing, the free oxygen concentration is excessive in the molten steel, and the yield of Fe and Mn is reduced. In order to suppress such factors that increase the cost of steelmaking, it is not sufficient to perform point measurement with current sublances, and continuous monitoring of the carbon concentration in molten steel is strongly required.

  The technology that has applied laser-based emission spectroscopy for the purpose of directly measuring the concentration of non-metallic elements such as carbon and phosphorus, such as carbon and phosphorus, without taking a sample. Have been reported a lot. Most of these measure the concentration of elements in molten steel by generating a plasma state by condensing a pulse laser with high peak power and irradiating the molten steel, and analyzing the emission from this plasma. Generally, it is called a laser emission analysis method or the like. For example, Patent Document 1 discloses a method of performing spectroscopic analysis by irradiating a molten steel with laser through a tuyere penetrating a refractory of a converter and transmitting light emission to a spectroscope through an optical fiber.

On the other hand, the laser-induced fluorescence method, in which a vapor atom is irradiated with a laser whose wavelength is tuned to one of the resonance wavelengths of the target element to induce fluorescence of this atom, is a highly sensitive and highly selective analytical method. The present inventors have known this point and have developed a monitoring technique for C and P in molten steel by laser-induced fluorescence. Details of these techniques are disclosed in Patent Document 2. In analysis using laser-induced fluorescence, an ablation laser is first irradiated to evaporate and atomize a part of the sample. Then, after an appropriate delay time has elapsed from the ablation laser pulse, the selective excitation laser is irradiated. At this time, since only the fluorescence of the target element is selectively emitted, there is no need to use a large spectroscope, and the amount of signal emitted directly from the target element by a light quantity measuring device such as a photomultiplier tube or a photodiode is calculated. Can be measured.
Japanese Unexamined Patent Publication No. 60-231141 JP 2001-356096

  However, in the analysis of molten steel by the laser-induced fluorescence method described above, the analysis point is finally irradiated due to the output fluctuation of the selective excitation laser oscillator and the fluctuation of the output (energy) transmission efficiency up to the analysis point of the selective excitation laser. There is a problem that the amount of laser-induced fluorescence fluctuates due to fluctuations in the output of the selective excitation laser. These fluctuations are unavoidable problems in continuous analysis in daily operations, and are factors that deteriorate daily analysis accuracy.

  The laser-induced fluorescence analysis method is a relative analysis method in which the concentration is quantified using a calibration curve, as in other instrumental analysis methods such as emission spectrometry and absorption spectrometry. In these relative analysis methods, generally, a standard sample with a known concentration is analyzed to prepare a calibration curve, and based on this, a sample with an unknown concentration is quantified. On the other hand, for example, in the case of direct analysis of molten metal, a calibration curve is obtained from the correlation between the result of collecting and analyzing a molten metal sample in a refining furnace and the amount of laser-induced fluorescence measured by directly analyzing the molten metal. Is required. However, in order to reduce the time, labor, and cost required for sampling, it is required to minimize the sampling frequency. Therefore, in order to quantify the concentration based on the calibration curve created in the initial stage, a means for correcting the energy fluctuation of the selective excitation laser irradiated to the sample is necessary.

  Therefore, an object of the present invention is to provide a laser-induced fluorescence analysis method and a laser-induced fluorescence analysis probe that can correct fluctuations in energy of a selective excitation laser by a simple method in order to solve the above-described problems.

The present invention has been made in order to solve the above-described problems in laser-induced fluorescence analysis at low cost and simply, and the gist thereof is as follows.
(1) Laser-induced fluorescence light intensity (F) generated by irradiating the sample with an ablation laser for evaporating and atomizing the sample and a selective excitation laser having a wavelength that resonates with the target element, and irradiating the sample This is a laser-induced fluorescence analysis method that quantifies the target element concentration by detecting the fluctuation amount (L ′) of the selected excitation laser light amount and correcting the target element concentration with the obtained ratio F / L ′. And
The wavelength of the selective excitation laser (λ _ex ) and the wavelength of the laser induced fluorescence (λ _fl ) do not match, λ _ex > 200 nm, λ _fl <200 nm, and the laser induced fluorescence light amount (F) is changed to λ _ex And a laser-induced fluorescence analysis method, characterized in that the detection is performed by a light amount detector having substantially no sensitivity .
(2 ) The laser-induced fluorescence analysis method according to (1), wherein the light amount detector uses Cs-I as a photocathode material .
(3 ) To detect the amount of laser-induced fluorescence (F) generated by irradiating the sample with an ablation laser for evaporating and atomizing the sample and a selective excitation laser having a wavelength that resonates with the target element. A laser-induced fluorescence analysis probe comprising at least a light amount detector, a light amount detector for detecting a fluctuation amount (L ′) of a selective excitation laser light amount irradiated on a sample, and a concentration correction means for a target element concentration The wavelength (λ _ex ) of the selective excitation laser and the wavelength (λ _fl ) of the laser-induced fluorescence do not match, λ _ex > 200 nm, λ _fl <200 nm, and the laser-induced fluorescence light amount (F) is detected A laser-induced fluorescence analysis probe characterized in that the light quantity detector for the sensor is substantially insensitive at the wavelength of the selective excitation laser .
(4 ) The laser-induced fluorescence analysis probe according to (3) , wherein the light amount detector uses Cs-I as a photocathode material .

  According to the present invention, in a remote, non-contact analysis of an analysis object that is difficult to access due to high temperature, harmful gas, harmful radiation, etc., it is stable daily without being affected by the energy fluctuation of the selective excitation laser irradiated to the sample. Since it is possible to carry out component concentration determination continuously, for example, when this is used in the steel manufacturing process, the decarburization end point determination in the converter and secondary refining process is optimally performed, etc. It greatly contributes to improving controllability.

The present invention will be described in detail below.
The main point of the present invention is to correct the variation in the amount of laser-induced fluorescence caused by the variation in the energy of the selective excitation laser irradiated to the sample. By the way, in the present invention, molten metal is analyzed by a laser-induced fluorescence method. In this embodiment, however, a selective excitation laser oscillator is generally used for heat, dust, etc. from an apparatus such as a refining furnace containing molten metal to be analyzed. It is required to be installed at a position sufficiently separated so as not to be affected by. Therefore, the energy of the selective excitation laser irradiated to the sample as a result is influenced not only by the fluctuation of the energy of the laser oscillated from the laser oscillator but also by the fluctuation of the laser transmission efficiency from the laser oscillator to the sample. The latter is caused by, for example, deterioration of transmittance of an optical fiber that transmits a laser, loss due to contamination of an optical element such as a mirror or a lens, and the like.

  Therefore, the present inventors detect the fluctuation light quantity (L ′) of the selective excitation laser in a probe in which a light quantity detector for measuring the fluorescence light quantity (F) is irradiated by irradiating the molten metal with a laser. By quantifying the target element concentration by correcting the target element concentration c with the light intensity ratio F / L ′, the quantitative value due to the energy fluctuation of the selective excitation laser as described above can be obtained. As a result of experiments, it was found that variation can be reduced, and the present invention has been achieved.

In the present invention, it is preferable to select each transition (non-resonant fluorescence) so that the wavelength of the selective excitation laser (λ _ex ) and the wavelength of the laser-induced fluorescence (λ _fl ) are different. By doing so, it is possible to separate from the other light by using an optical element such as a mirror or an optical filter that selectively reflects or transmits light of either wavelength. Then, as the spectral sensitivity curve of the laser-induced fluorescence light quantity detector, by selecting one having sensitivity to λ _fl and little sensitivity to λ _ex , the stray light of the selective excitation laser is separated. The net laser-induced fluorescence amount can be measured.

For example, a photomultiplier tube is suitable as the light quantity detector having the above characteristics. Photomultiplier tubes have different spectral sensitivity curves depending on the material of the photocathode. Those having sensitivity only in the ultraviolet or vacuum ultraviolet region are generally called solar blind tubes. As an example, since the photocathode material with Cs-I has almost no sensitivity on the long wavelength side from 200 nm, select an excitation wavelength of λ _ex > 200 nm and a laser-induced fluorescence wavelength of λ _fl <200 nm. Thus, the amount of laser-induced fluorescence can be measured without being affected by the stray light of the selective excitation laser. Similarly, when a material using Cs-Te as the photocathode material is used, it is appropriate to select an excitation wavelength of λ _ex > 350 nm and a laser-induced fluorescence wavelength of λ _fl <350 nm.

  A laser-induced fluorescence analysis probe of the present invention for analyzing molten steel is shown in FIG. This laser-induced fluorescence analysis probe includes a hollow tube 16 for irradiating a molten steel (sample 17) with a laser, a light amount detector 1 for laser-induced fluorescence, and a light amount detector for detecting a variable light amount of a selective excitation laser. 2 is mainly composed of a built-in protective case 18.

  The ablation laser a oscillated by the ablation laser oscillator 19 is reflected by the mirror 4, passes through the reflection mirrors 5 and 6, further passes through the window material 3, propagates through the hollow tube 16, and measures the sample 17. The surface is irradiated.

  The selective excitation laser b oscillated by the selective excitation oscillator 20 at an appropriate time interval from the irradiation of the ablation laser a is reflected by the mirror 5, passes through the mirror 6, and further passes through the window material 3 to be hollow. It propagates through the tube 16 and is irradiated onto the measurement surface of the sample 17. Then, the fluorescence generated by the irradiation of the ablation laser a and the selective excitation laser b propagates in the hollow tube 16 in the direction opposite to the lasers a and b, is reflected by the mirror 6, and is condensed by the lenses 9 and 10. After being collimated, the light is reflected by the mirrors 7 and 8 and detected by the light quantity detector 1. The laser-induced fluorescence light amount (F) detected by the light amount detector 1 is converted into an electric signal and transmitted to the data processing device 21 through the transmission line 12. Further, the light quantity detector 2 detects the fluctuation light quantity (L ′) of the selective excitation laser. For example, the selective excitation laser reflected by the surface of the optical window 3 is reflected by the mirror 6, passes through the mirror 7, and is detected by the light quantity detector 2 as a variable light quantity.

Optical components such as the mirrors 4 to 8, the lenses 9 and 10, and the light quantity detectors 1 and 2 are housed in a protective case 18 in order to protect them from dust, splash, and heat radiation from the molten metal (sample 17). Yes. In addition, for the purpose of eliminating dust, splash, fume, etc. from the laser, light emission, and fluorescent light paths, and preventing contamination of the inner wall of the hollow tube 16 and the window material 1, the inside of the hollow tube 16 is introduced from the gas inlet 15. Then, gas is blown toward the sample surface 17 from the sample side end surface of the hollow tube 16. Here, as the type of gas, an inert gas such as Ar, He, or N ₂ that does not react with the sample is usually preferable.

  The sample side end surface of the hollow tube 16 may be immersed in the molten metal. Needless to say, in the case of a hollow tube penetrating the refractory on the bottom surface or side surface of the molten metal container, a gas flow rate necessary for preventing the molten metal from flowing out through the hollow tube is blown.

  The data processing device 21 records the laser-induced fluorescence light amount (F) detected by the light amount detectors 1 and 2 and the fluctuation light amount (L ′) of the selective excitation laser, and calculates the light amount ratio F / L ′. From the corrected calibration curve obtained in advance, the concentration is displayed and recorded every moment.

Ablation laser oscillator 19 is a pulse laser oscillator, the energy density and peak power density on the analysis plane, respectively, approximately 5~125J / cm ^2, so that 0.3~7.5GW / cm ^2, the condenser It is preferable to irradiate. The most commonly used laser for this purpose is a Q-switched pulse Nd: YAG laser, with a pulse time half width of 5 to 15 ns, a pulse energy of 100 to 1000 mJ, and a pulse repetition of 10 to 50 Hz being generally marketed. Yes.

  As the selective excitation laser b, a titanium sapphire laser, a dye laser, an optical parameter oscillator (OPO), or the like can be used.

(Example 1)
The probe shown in FIG. 1 was brought close to the surface of the molten steel melted in the induction melting furnace, and the carbon (C) concentration in the molten steel was measured by laser-induced fluorescence analysis. A Q-switched pulse Nd: YAG laser was used as the ablation laser a, and a titanium sapphire laser was used as the selective excitation laser b. The ablation laser a and the selective excitation laser b were operated in synchronization with each other at a delay time of 50 to 100 μs at a repetition rate of 10 pulses per second by a trigger pulse from a pulse generator (not shown).

  Ar gas was introduced from the gas inlet 15 and analyzed while spraying the molten steel surface from the lower end of the hollow tube 16.

  The wavelength of the selective excitation laser b was 247.85 nm, and the laser-induced fluorescence light amount (F) having a wavelength of 193.09 nm was measured by the light amount detector 1. The selective excitation laser b reflected on the surface of the optical window is partially reflected by the laser-induced fluorescence reflection mirror 6 and then transmitted through the second laser-induced fluorescence reflection mirror 7, and then the light quantity detector 2 (L ') as a variable light quantity. As the light quantity detector 1 and the light quantity detector 2, photomultiplier tubes having Cs-I and Cs-Te as photocathodes were used.

  Outputs from the light quantity detectors 1 and 2 were transmitted by a transmission line and recorded by an oscilloscope 21.

For each pulse, the ratio <F> _av / <L '> _av of the average value over 100 pulses of F and L ′ measured simultaneously was determined.

FIG. 2 shows three sets of data obtained on different measurement dates, and shows the correlation between <F> _av and C concentration [C] without applying the correction according to the present invention. The three sets of data each show a linear correlation, but the correlation lines do not match each other. Therefore, since there is no one-to-one correspondence between the measured value <F> _av and [C], the concentration cannot be quantified.

On the other hand, according to the present invention, the correlation between the light amount ratio <F> _av / <L ′> _av and [C] is illustrated as shown in FIG. 3, and a single correlation line was obtained. Therefore, once the correlation between the light intensity ratio <F> _av / <L '> _av and [C] is obtained, the concentration can be quantified using this as a corrected calibration curve. It was shown to be applicable to monitoring.

(Example 2)
The carbon (C) concentration of the molten steel in the ladle during RH vacuum degassing was analyzed using the laser-induced fluorescence analysis probe shown in FIG. In the same manner as in Example 1, the C concentration [C] in the molten steel was measured at 30 second intervals. The solid line in FIG. 4 shows the transition with respect to the refining time of the C concentration [C] obtained from the measured value <F> _av / <L '> _av based on the corrected calibration curve measured in advance. A circle indicates a result obtained by collecting a molten steel sample and quantifying it by a combustion infrared absorption method. The continuous [C] value according to the present invention is in good agreement with the conventional collected sample analysis results, indicating that continuous analysis can be performed with high accuracy.

  The present invention can be applied to the field of element concentration determination using a laser.

It is a figure showing the structure of the probe concerning embodiment of this invention. It is a figure which shows the relationship of 3 sets of C density | concentrations-laser induced fluorescence light quantity obtained on a different measurement day. It is a figure which shows the relationship of three sets C density | concentration-light quantity ratio <F> _av / <L '> _av obtained on a different measurement day. It is a figure which shows the result ((circle): result which analyzed the molten steel extract | collected sample by the conventional method) which measured continuously the C density | concentration in the molten steel in a ladle at the time of RH vacuum degassing by the method of this invention.

Explanation of symbols

1: Laser-induced fluorescence light intensity detector
2: Light intensity detector
3: Window material
4: Ablation laser reflection mirror
5: Selective excitation laser reflection mirror
6, 7, 8: Laser-induced fluorescence reflection mirror
9, 10: Lens
12, 13: Signal transmission cable
15: Gas inlet
16: Hollow tube
17: Sample
19: Ablation laser oscillator
20: Selective pump laser oscillator
21: Data processing device
a: Ablation laser
b: Selective pump laser

Claims (4)

Laser-induced fluorescence light amount (F) generated by irradiating the sample with an ablation laser for evaporating and atomizing the sample and a selective excitation laser having a wavelength that resonates with the target element, and the sample irradiated A laser-induced fluorescence analysis method that quantifies the target element concentration by detecting the fluctuation light amount (L ′) of the selective excitation laser light amount and correcting the target element concentration with the obtained ratio F / L ′.
The wavelength of the selective excitation laser (λ _ex ) and the wavelength of the laser induced fluorescence (λ _fl ) do not match, λ _ex > 200 nm, λ _fl <200 nm, and the laser induced fluorescence light amount (F) is changed to λ _ex And a laser-induced fluorescence analysis method, characterized in that the detection is performed by a light amount detector having substantially no sensitivity . The laser-induced fluorescence analysis method according to claim 1, wherein the light amount detector uses Cs-I as a photocathode material . Light intensity detector for detecting the amount of laser-induced fluorescence (F) generated by irradiating the sample with an ablation laser for evaporating and atomizing the sample and a selective excitation laser with a wavelength that resonates with the target element And a laser-induced fluorescence analysis probe comprising at least a light amount detector for detecting a fluctuation amount (L ′) of the selective excitation laser light amount irradiated to the sample and a concentration correction means for the target element concentration, the selection The wavelength of the excitation laser (λ _ex ) does not match the wavelength of the laser-induced fluorescence (λ _fl ), and λ _ex > 200 nm, λ _fl <200 nm, and the light amount for detecting the laser-induced fluorescence light amount (F) A laser-induced fluorescence analysis probe characterized in that the detector is substantially insensitive at the wavelength of the selective excitation laser . The laser-induced fluorescence analysis probe according to claim 3 , wherein the light amount detector uses Cs-I as a photocathode material .

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