JP4734273B2 - Laser-induced fluorescence analyzer - Google Patents

Description

The present invention relates to a spectroscopic analyzer using a laser, and more particularly to a laser-induced fluorescence analyzer that remotely monitors the element concentration in molten metal in a metal refining furnace.

  In the refining process of a metal material, monitoring the concentration of component elements in the molten metal during the refining reaction in real time is very important for refining process optimization control. Hereinafter, steel will be described as an example of the metal material.

  In the manufacture of steel, after the converter refining that decarburizes by oxygen blowing, the concentration of carbon in the molten steel is further reduced by vacuum degassing in ladle refining, and the concentration range required to express the desired steel properties. Strict control is performed to enter.

  Many techniques have been reported so far in which a laser-based emission spectroscopic analysis method is applied for the purpose of measuring the concentration of such components in molten steel, particularly nonmetallic elements such as carbon and phosphorus. 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 for 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, which irradiates a vapor atom with a laser tuned to one of the resonance wavelengths of the target element and induces fluorescence of this atom, is known as an analytical method with high sensitivity and excellent selectivity. In view of this point, the present inventors have developed a monitoring technique for C and P in molten steel by a laser-induced fluorescence method. 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 Patent Laid-Open No. 60-231141 JP 2001-356096 A

  However, in the molten steel analysis by the laser induced fluorescence method described above, there is a problem that the stray light of the selective excitation laser interferes with the fluorescence signal, and the analysis accuracy and the lower limit of quantification are deteriorated. In particular, the selective excitation laser reflected by the surface of the window material of the probe enters the signal detection optical system and causes this problem. In order to reduce the reflection itself on the surface of the window material of this probe and reduce the detection of reflected light, an antireflection coating with a low reflectivity at the wavelength of the selective excitation laser is applied to the window material, or the light quantity is measured. As a countermeasure, an optical filter having a low transmittance at the selective excitation wavelength is arranged in front of the device. However, since the intensity of the selective excitation laser is several orders of magnitude larger than the fluorescence signal, it is difficult to completely prevent the light from reaching the detector even though it is a part of the scattered light.

Accordingly, an object of the present invention is to provide a laser-induced fluorescence analyzer that prevents deterioration of the signal / background ratio due to stray light of the selective excitation laser.

  The present invention has been made to solve the above-described problems, and the gist thereof is as follows.

(1) Evaporation / atomization by irradiating laser to molten metal, emission analysis, and measuring the amount of fluorescence generated by irradiating laser with wavelength that resonates with the element to be analyzed. A laser-induced fluorescence analyzer for quantifying the concentration of an element , comprising an ablation laser oscillator, an ablation laser reflection mirror for irradiating a sample with an ablation laser oscillated from the ablation laser oscillator, and a target element of the molten metal Tunable wavelength selective excitation laser oscillator that irradiates the resonance wavelength, selective excitation laser reflection mirror for irradiating the sample with the selective excitation laser oscillated from the selective excitation laser oscillator, and irradiation of the ablation laser The laser emission that reflects the light emitted from the plasma generated by the sample to the light-receiving optical system A reflection mirror, a laser light emitting / receiving terminal for receiving the light collected by the light emitting / receiving optical system, and a light amount for detecting the amount of laser-induced fluorescence generated in the sample by the irradiation of the selective excitation laser and converting it into an electrical signal A detector, a laser-induced fluorescence reflecting mirror that guides the laser-induced fluorescence to the light amount detector, a window material that is provided between the selective excitation laser reflecting mirror and the sample and transmits the selective excitation laser, and the light amount An optical filter disposed at the entrance of the detector for attenuating the reflected light of the selective excitation laser, the laser-induced fluorescence reflection mirror, the laser emission reflection mirror, the selective excitation laser reflection mirror, and the ablation laser reflection mirror; , Containing at least the optical filter and the light amount detector, and dust and splash from the molten metal, heat A protective case which protects the morphism, and spectrometer for measuring the spectrum with a laser emission wavelength dispersion, and laser-induced fluorescent signal processing device, the ablation laser oscillator, said selective excitation laser oscillator, the spectrometer and the laser-induced A pulse generator for controlling the operation of the fluorescence signal processing device; a means for transmitting an electrical signal from the light quantity detector to the laser-induced fluorescence signal processing device; and a light signal from a laser emission receiving / receiving transmission terminal to the spectrometer. and transmission means, at least equipped with the window material is a Rukoto reflection laser such installed with a slope of a predetermined angle which is not incident on the laser induced fluorescence reflecting mirror according to the window material selective excitation laser A laser-induced fluorescence analyzer.
(2) One end of the sample side is open, has a gas injection port, has a hollow tube through which the selective excitation laser and the laser-induced fluorescence pass, and the other end of the hollow tube is made of the window material The laser-induced fluorescence analyzer according to (1), which is hermetically sealed.
(3) The laser induction according to (1), wherein a direction of a normal line on the surface of the window material is set to a Brewster angle with respect to a propagation direction of a selective excitation laser incident on the window material. Fluorescence analyzer .

  According to the present invention, the stray light detection intensity of the selective excitation laser is reduced, the signal / background ratio of the laser-induced fluorescence signal is improved, and variation in the measurement value due to fluctuations in the stray light detection intensity is reduced. Analysis accuracy can be improved. Therefore, for example, it greatly contributes to improvement in controllability of steelmaking operations.

  Exemplary embodiments of the present invention will be described below in detail with reference to the accompanying drawings. In addition, in this specification and drawing, about the component which has the substantially same function structure, duplication description is abbreviate | omitted by attaching | subjecting the same code | symbol.

  An example of the configuration of the probe 19 for laser-induced fluorescence analysis according to the present invention is shown in FIG. The ablation laser a oscillated from the ablation laser oscillator 21 is reflected by the ablation laser reflecting mirror 5 while being converged by the ablation laser condensing lens 20 in the laser-induced fluorescence analysis probe 19, and is transmitted through the reflecting mirrors 2, 3 and 4. Further, the light passes through the window material 1, propagates through the hollow tube 16, and is irradiated on the measurement sample surface 17. The window material 1 is attached to the end of the wind box 14 that communicates with the hollow tube 16. The light emission d from the plasma generated by irradiation of the ablation laser a propagates in the hollow tube 16 in the direction opposite to that of the ablation laser a, is reflected by the laser emission reflecting mirror 3, and is received by the lens 6 at the light receiving end 7 of the optical fiber 8. And transmitted to the spectroscope 24 by the optical fiber 8 for spectroscopic measurement.

  The selective excitation laser b oscillated from the selective excitation laser 22 at an appropriate time interval from the irradiation of the ablation laser a is reflected by the selective excitation laser reflecting mirror 4 in the probe 19 for laser-induced fluorescence analysis, 2, further passing through the window material 1, propagating through the hollow tube 16, and irradiating the sample surface 17. The generated laser-induced fluorescence c propagates in the hollow tube 16 in the opposite direction to the selective excitation laser b, is reflected by the laser-induced fluorescence reflection mirror 2, and is condensed and collimated by the lenses 9 and 10. Thereafter, the light signal is converted into an electric signal by the light quantity detector 12 through the optical filter 11 and transmitted to the laser-induced fluorescence signal processing device 25 through the transmission line 13.

  The ablation laser oscillator 21 and the selective excitation laser oscillator 22 oscillate lasers a and b, respectively, according to the trigger pulse supplied from the pulse generator 23. The laser-induced fluorescence signal processing device 25 displays the laser-induced fluorescence signal that is converted into an electrical signal by the light quantity detector 12 and transmitted by the power transmission cable 13, converts it into digital data, and sends it to the data analysis computer 26. Forward. The spectroscope 24 measures the spectral spectrum by wavelength-dispersing the laser emission transmitted by the optical fiber 8 and transfers the result to the data analysis computer 26. Transmission of the lasers a and b to the probe 19 is performed by propagating the space using, for example, a mirror or a prism.

  As described above, according to the present embodiment, the element can be analyzed by the laser emission analysis method from the analysis result of the spectral spectrum detected by the spectroscope, and the laser-induced fluorescence detected by the light quantity detector 12 can be obtained. Analysis of elements by laser-induced fluorescence is possible from the signal analysis results. Carbon (C) and phosphorus (P) are analyzed by the laser-induced fluorescence method, and other elements are analyzed simultaneously with the laser-induced fluorescence method by the laser emission analysis method.

In order to protect the optical components such as mirrors 2, 3, 4, 5, lenses 6, 9, 10, optical filter 11, light quantity detector 12 from dust, splash, and heat radiation from the sample surface 17 of molten metal, Housed in the protective case 18. Further, for the purpose of eliminating dust, splash, fume and the like from the optical path of laser, light emission, and fluorescence, and preventing contamination of the inner wall of the hollow tube 16 and the window material 1, the gas inlet 15 enters the wind box 14. Gas is introduced and 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, N ₂ or the like that does not react with the sample is used.

  The sample side end surface of the hollow tube 16 may be immersed in the molten metal. Further, when the hollow tube 16 is provided by penetrating the refractory on the bottom surface or the side surface of the molten metal container, the gas flow rate required to prevent the molten metal from flowing out through the hollow tube 16 is set to the gas inlet 15. To blow from.

As the window material 1, an ablation laser, a selective excitation laser, and a material having high transmittance of light emission and fluorescence from the sample surface may be selected. Since atomic emission and fluorescence usually range from the visible region to the ultraviolet region, quartz glass, MgF ₂ , CaF ₂ or the like can be used.

When the selective excitation laser b passes through the window material 1, a part thereof is reflected by the surface of the window material 1. In the case of normal incidence, that is, when the angle formed between the incident laser and the normal of the window material 1 is 0 °, the reflectance R is generally R = (n−n ′) ² / (n + n ′) ² . Here, n is the refractive index of the window material 1 and n ′ is the refractive index of the gas with which the window material 1 is in contact. For example, when a laser propagating in the air enters the window material 1 made of quartz glass, n and n ′ are 1.5 and 1.0, respectively, and R = 0.04. That is, in this case, 4% of the incident laser is reflected.

  Here, FIG. 2 (A) shows a diagram in which the main part of the present invention is extracted from FIG. 1, and FIG. 2 (B) shows a comparative example that does not have the structural requirements defined in the present invention. ).

  As shown in FIG. 2B, when the selective excitation laser b is reflected on the surface of the window material 1 and the reflected light b ′ is incident on the laser-induced fluorescence reflecting mirror 2, a part of the reflected light b ′ is The light passes through the optical filter 11 and finally reaches the light amount detector 12. The reflected light b ′ is reduced by applying an anti-reflection coating that reduces the reflectance at the wavelength of the selective excitation laser b on the surface of the window material 1, and further attenuated by the optical filter 11. The effect does not reach the point where the intensity of the reflected light b ′ is completely suppressed. In particular, as the concentration of the target element to be detected decreases, the fluorescence intensity detected by the light quantity detector 12 and the stray light intensity due to the reflection of the window surface of the selective excitation laser b become approximately the same, greatly affecting the quantitative accuracy. The problem of making accurate quantification difficult arises.

  On the other hand, according to the present invention shown in FIG. 2A, the window material 1 is installed with an inclination of an angle at which the reflected light b ′ of the selective excitation laser b does not enter the laser-induced fluorescence reflecting mirror 2. In addition, the reflected light b ′ from the window material 1 does not reach the light amount detector 12 because it is deflected from the reflection region of the laser-induced fluorescence reflecting mirror 2. For this reason, the stray light (reflected light b ') resulting from the reflection of the window material 1 and the surface of the selective excitation laser b is effectively reduced, and accurate quantification is possible.

  In the present invention, the angle formed between the normal of the window material 1 and the incident direction of the selective excitation laser, that is, the incident angle may be an angle at which the reflected light b ′ deviates from the reflection region of the laser-induced fluorescence reflection mirror 2. However, unless the Brewster angle described later is present, the reflectance increases as the incident angle increases, so it is not preferable to make the incident angle larger than necessary.

A more preferred embodiment of the present invention is realized by making the angle formed by the propagation direction of the linearly polarized selective excitation laser b and the normal of the window material 1 be a Brewster angle. As shown in FIG. 3, the electric vector 103 of the selective excitation laser b is made parallel to the incident surface, the incident direction 104 of the selective excitation laser b into the window material 1 and the propagation direction 105 of the refracted light beam. Are realized by satisfying the relationship θ _i + θ _r = 90 ° between the angles θ _i and θ _r (see FIG. 3) formed with the normal line 102 of the window material. At this time, the reflectance is 0 from the Fresnel formula. From the law of refraction, sin (θ _i ) / sin (90 ° −θ _i ) = n ′ / n holds. If n and n ′ are 1 (air) and 1.5 (quartz glass), respectively, θ _i = 56.3 °, which is the Brewster angle. In the present invention, if a Brewster angle determined in this way is included and the reflectance in the vicinity thereof is set to an angle at which the reflectance is sufficiently low (for example, 1% or less), a higher effect than practical can be obtained. As described above, FIG. 4 shows the relationship between the incident angle and the reflectance when the window material 1 is quartz glass and the electric vector 103 of the selective excitation laser b is parallel to the incident surface. For example, when the reflectance should be 1% or less, the angle of the window material 1 may be set so that the incident angle is in the range θ _i1 ≦ θ _i ≦ θ _i2 shown in FIG.

  By setting the inclination of the window material 1 so that the above condition is satisfied, the reflected light b ′ is not only prevented from being reflected by the laser-induced fluorescence reflecting mirror 2 and entering the light amount detector 12, but also the reflected light b. It is also possible to minimize stray light that enters the light amount detector 12 by being reflected or scattered by the wall surface of the protective case 18, the optical element inside the protective case 18, a holder, or the like.

  The laser-induced fluorescence analysis probe 19 shown in FIG. 1 was brought close to the molten steel surface melted in the induction melting furnace, and the fluorescence signal intensities of carbon and phosphorus in the molten steel were measured by a laser-induced fluorescence method. At the same time, the laser emission transmitted by the optical fiber 8 was spectrally analyzed by the spectroscope 24. A Q switch pulse Nd: YAG laser was used as the ablation laser oscillator 21, and a titanium sapphire laser was used as the selective excitation laser oscillator 22. The delay time between the ablation laser and the selective excitation laser was set to 100 μs, Ar gas was introduced from the gas inlet 15, and analysis was performed while spraying from the lower end of the hollow tube 16 onto the Ar gas molten steel surface (sample surface 17).

  In (Example 1) in FIG. 5, the window material 1 is formed at an angle at which the reflected light b ′ of the selective excitation laser b is not incident on the laser-induced fluorescence reflection mirror 2 as shown in FIG. 5 (Comparative Example) in FIG. 5 is a result of measurement using a tilted probe. As shown in FIG. 2B, the angle at which the window material 1 is tilted is smaller, and the reflected light b ′ is laser-induced fluorescence. It is the result measured using the probe which injects into the reflective mirror 2. FIG. Further, FIG. 6 shows the probe according to the present embodiment in which the angle θi formed by the normal line of the window material 1 and the incident direction of the selective excitation laser b is inclined to be a Brewster angle of 56 ° in the present test conditions. It is the result of (Example 2) measured using this. All are average values of signal intensities obtained by measuring five times at one concentration level, and error bars indicate standard deviation. Further, the carbon concentration [C] on the horizontal axis of the graph is a value obtained by quantitatively analyzing the sample collected at each concentration level by the combustion infrared absorption method.

  Referring to (Comparative Example) in FIG. 5, the position of the intercept on the vertical axis when the correlation line is extrapolated to a concentration of 0 ppm is higher than that of (Example 1). This cause indicates that the stray light of the selective excitation laser b is detected relatively strongly. Further, in (Example 2) shown in FIG. 6, the position of the section is further lower than (Example 1) in FIG. 5.

  The position of the section corresponds to the background. In general, the higher the background, the larger the background noise, and the quantitative accuracy deteriorates. One of the indicators of the background height is the background equivalent concentration. This represents the background height as a concentration equivalent amount of the measurement element. Generally, the lower the background equivalent concentration, the lower the lower limit of quantification.

  Therefore, according to the said Example, it turns out that background noise becomes small in order of a comparative example, Example 1, and Example 2, and a fixed_quantity | quantitative_assay improves.

  The above is a description of the laser-induced fluorescence intensity of carbon. Similar results were obtained for the laser-induced fluorescence intensity of phosphorus in the concentration range of 50 ppm to 500 ppm.

Table 1 shows the background equivalent concentration and the correlation coefficient (R ² ) of the correlation line in each of carbon and phosphorus obtained in each of the cases of (Example 1), (Example 2) and (Comparative Example). showed that.

  From Table 1, it can be seen that the background concentration can be greatly reduced according to the present invention. The correlation coefficient has also improved, thus indicating that a lower lower limit of quantification is achieved.

  In (Example 1) and (Example 2), carbon and phosphorus were measured alternately using a single wavelength-variable selective excitation laser oscillator 22, but these were measured by means such as using two laser oscillators. It is also possible to measure laser-induced fluorescence of two elements simultaneously.

  In (Example 1) and (Example 2), the laser emission spectrum was also measured in parallel with the laser-induced fluorescence measurement. FIG. 7 shows an analysis result of Al as an example. In addition, it goes without saying that elements having an analytical line wavelength of approximately 250 nm or more, such as Mn and Ti, can be analyzed simultaneously with elements such as carbon and phosphorus by laser-induced fluorescence measurement.

  As mentioned above, although preferred embodiment of this invention was described referring an accompanying drawing, it cannot be overemphasized that this invention is not limited to the example which concerns. It will be apparent to those skilled in the art that various changes and modifications can be made within the scope of the claims, and these are naturally within the technical scope of the present invention. Understood.

It is a diagram illustrating a configuration of analysis apparatus of the present invention. It is a schematic diagram which shows the principal part of a probe, Comprising: It is a figure which compares and shows the window material of (A) this invention and the window material which is not (B) this invention. It is a schematic diagram which shows the entrance plane and electric vector which consist of the incident direction of a selective excitation laser, and a refraction direction. It is a figure which shows the relationship between the incident angle to the window material of a selective excitation laser, and a reflectance. It is a figure which shows the laser-induced fluorescence measurement result (Example 1) of carbon in molten steel using the analyzer of this invention, and the laser-induced fluorescence measurement result (comparative example) of carbon in molten steel using the probe not based on this invention. . It is a figure which shows the measurement result (Example 2) of carbon in molten steel using the probe inclined so that the incident angle of the selective excitation laser might become a Brewster angle especially in the analyzer of this invention. It is a figure which shows the laser emission intensity | strength measurement result of Al measured simultaneously with the laser induced fluorescence intensity measurement using the analyzer of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Window material 2 Laser-induced fluorescence reflection mirror 3 Laser emission reflection mirror 4 Selective excitation laser reflection mirror 5 Ablation laser reflection mirror 6, 9, 10 Lens 7 Optical fiber receiving end 8 Optical fiber cable 11 Optical filter 12 Light quantity detector 13 Signal transmission cable 14 Wind box 15 Gas inlet 16 Hollow tube 17 Sample 18 Protective case 19 Probe for laser induced fluorescence analysis 20 Ablation laser condenser lens 21 Ablation laser oscillator 22 Selective excitation laser oscillator 23 Pulse generator 24 Spectrometer 25 Laser induced fluorescence signal processing Equipment 26 Computer for data analysis a Ablation laser b Selective excitation laser b ′ Reflected light of selective excitation laser by window material 1 c Laser induced fluorescence d Laser emission

Claims (3)

The concentration of the element to be analyzed in the sample is measured by irradiating the molten metal with a laser to evaporate and atomize, analyze the emission, and measure the amount of fluorescence generated by irradiating the laser with a wavelength that resonates with the element to be analyzed. A laser-induced fluorescence analyzer for quantifying
An ablation laser oscillator,
An ablation laser reflecting mirror for irradiating the sample with an ablation laser oscillated from the ablation laser oscillator;
A tunable selective excitation laser oscillator that tunes and irradiates the resonance wavelength of the target element of the molten metal ; and
A selective excitation laser reflecting mirror for irradiating the sample with a selective excitation laser oscillated from the selective excitation laser oscillator;
A laser emission reflection mirror that reflects the emission of plasma generated in the sample by irradiation of the ablation laser and guides it to an emission light receiving optical system;
A laser light emitting / receiving transmission terminal for receiving the light collected by the light emitting / receiving optical system;
A light amount detector that detects the amount of laser-induced fluorescence generated in the sample by irradiation of the selective excitation laser and converts it into an electrical signal;
A laser-induced fluorescence reflecting mirror that guides the laser-induced fluorescence to the light quantity detector;
A window material provided between the selective excitation laser reflecting mirror and the sample, through which the selective excitation laser passes;
An optical filter disposed at the entrance of the light amount detector to attenuate the reflected light of the selective excitation laser;
Containing at least the laser-induced fluorescence reflection mirror, the laser emission reflection mirror, the selective excitation laser reflection mirror, the ablation laser reflection mirror, the optical filter, and the light amount detector; Protective case that protects against dust, splash, and heat radiation,
A spectroscope for measuring the spectral spectrum by wavelength dispersion of the laser emission ;
A laser-induced fluorescence signal processing device;
A pulse generator for controlling operations of the ablation laser oscillator, the selective excitation laser oscillator, the spectrometer and the laser-induced fluorescence signal processing device;
Means for transmitting an electrical signal from the light quantity detector to the laser-induced fluorescence signal processing device;
Means for transmitting an optical signal from a laser light emitting / receiving terminal to the spectrometer;
Comprising at least
The window material is laser-induced fluorescence analysis device according to claim Rukoto reflected laser such installed with a slope of a predetermined angle which is not incident on the laser induced fluorescence reflecting mirror according to the window material selective excitation laser. One end of the sample side is opened, has a gas injection port, and has a hollow tube through which the selective excitation laser and the laser-induced fluorescence pass,
The laser-induced fluorescence analyzer according to claim 1, wherein the other end of the hollow tube is hermetically sealed with the window material. The laser-induced fluorescence analyzer according to claim 1, wherein the normal direction of the surface of the window material is set to a Brewster angle with respect to a propagation direction of a selective excitation laser incident on the window material. .

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