JP2012052822A - Emission spectral analysis method and apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method and an apparatus for improving linearity of a calibration curve in a high concentration range and improving quantitative analysis accuracy by suppressing influence of self-absorption under a stable discharge condition in quantitative analysis of a metal material by a spark discharge emission spectral analysis method.SOLUTION: In the emission spectral analysis method and apparatus for quantitatively analyzing components of a metal sample by applying pulse laser light to the metal sample and analyzing emission spectra generated by spark discharge between the metal sample and a counter electrode, the pulse laser light is applied to a position deviated from the center of an incident light axis of a spectroscope and the spark discharge is guided to measure the emission intensity of an emission line of an element to be analyzed.

Description

  The present invention relates to a spark discharge emission spectroscopic analysis method and apparatus for analyzing a component of a metal sample and its composition ratio, and more particularly to a quantitative emission spectroscopic analysis method and apparatus using discharge position control by a pulse laser.

  The emission spectroscopic analysis method by spark discharge is an excellent analysis method capable of quickly analyzing many elements in a metal sample simultaneously. However, when the component concentration in a metal material is quantified by the spark discharge emission spectroscopic analysis method, if the concentration of the element to be analyzed is a high concentration of several percent or more, the calibration curve is linear due to self-absorption of the emission intensity. The accuracy is lost and the curve becomes a curve. In such a case, quantitative analysis is performed using a calibration curve using an approximate curve.

  However, since the discharge state is not constant depending on the surface state of the analysis sample, the state of the counter electrode, etc., not only the emission intensity but also the atomic density in the plasma generated by the discharge changes in an unstable manner. As described above, since the influence amount of self-absorption on the emission intensity is not constant, there is a problem that the analysis accuracy is lowered in the quantitative analysis using the non-linear calibration curve.

  In response to this problem, in Patent Documents 1 and 2, by reducing the discharge energy of the spark discharge, the atomic density in the plasma is reduced, and the influence of self-absorption is reduced. The quantitative accuracy is improved by selecting a high emission line.

  On the other hand, Patent Document 3 discloses a technique for analyzing a component in a minute region of a metal sample by irradiating a sample with a laser prior to the spark discharge and generating a spark discharge between the laser irradiation unit and the discharge counter electrode. ing.

Japanese Patent Laid-Open No. 10-318926 JP 11-83744 A JP 2008-14649 A

  However, in the methods of Patent Documents 1 and 2, if the discharge energy is too small, the discharge becomes unstable and the analysis accuracy deteriorates, so there is a limit to the reduction of the discharge energy. Furthermore, in the spark discharge emission spectrometry, the discharge position on the sample is not constant, so only average information of the entire discharge region with a diameter of several mm can be obtained, and the emission intensity from a specific discharge position can be obtained. There is a problem that it cannot be done.

  Further, as disclosed in FIG. 2 of Patent Document 1 and FIGS. 1 and 2 of Patent Document 2, the nonlinearity of the calibration curve is not completely eliminated.

  On the other hand, although the method of Patent Document 3 can generate a spark discharge at the laser irradiation position, the distance between the sample and the counter electrode is adjusted in order to maintain a state in which no spark discharge occurs when there is no laser irradiation. There is a need to.

  However, the distance between the sample and the counter electrode that does not generate a spark discharge in the absence of laser irradiation is affected by the surface condition of the sample, the tip shape of the counter electrode, the atmosphere in the discharge chamber, etc. Adjustment to the interval is complicated and takes time. Moreover, there is no knowledge about the influence on the light emission intensity when the discharge is induced at the laser irradiation position.

  The present invention solves the above problems and suppresses the influence of self-absorption under stable discharge conditions in the quantitative analysis of metallic materials by the spark discharge emission spectroscopic analysis method, thereby improving the linearity of the calibration curve in a high concentration range. It is an object of the present invention to provide a method and apparatus for improving and improving quantitative analysis accuracy.

  Inventors etc. are irradiating the surface of a metal sample with a pulse laser and studying an analysis method for generating a spark discharge between the irradiation part and the counter electrode. When the pulse laser irradiation position changes, the emission intensity also changes. I found out. Therefore, the influence of the pulse laser irradiation position on the emission intensity and quantitative accuracy of each element was examined in more detail.

  The emission intensity of each element changes greatly when the pulse laser irradiation position is changed in a direction perpendicular to the incident optical axis of the spectrometer (FIG. 1 (b) x direction), and is above the center of the incident optical axis of the spectrometer. When the pulse laser is irradiated to induce discharge, the emission intensity is the highest, and the emission intensity decreases as the distance from the center of the incident optical axis of the spectrometer increases.

  In addition, by creating a calibration curve for typical analytical elements at the pulse laser irradiation position and comparing the quantitative accuracy, the calibration curve can be obtained when the pulse laser irradiation position deviates from the center of the incident optical axis of the spectrometer. It was further found that the linearity is improved and the quantitative accuracy is improved.

The configuration of the present invention obtained from the above-described knowledge is as follows.
(1) In an emission spectroscopic analysis method for quantitatively analyzing a component of a metal sample by irradiating a metal sample with a pulse laser and spectroscopically analyzing the generated emission spectrum by spark discharge between the metal sample and a counter electrode, An emission spectroscopic analysis method characterized by irradiating a pulse laser at a position off the center of an incident optical axis of a spectrometer, inducing the spark discharge, and measuring the emission intensity of an emission line of an element to be analyzed.
(2) The position deviated from the center of the incident optical axis of the spectrometer is scanned while irradiating the pulse laser in a direction perpendicular to the center of the incident optical axis of the spectrometer, the emission intensity is measured, and the highest emission (1) The emission spectroscopic analysis method as described in (1) above, wherein the irradiation position shows an emission intensity of 1/20 or more and 1/2 or less of the intensity.
(3) In an emission spectroscopic analyzer provided with a pulse laser generator and a spark discharge generator, the pulse laser generator includes means for scanning and irradiating the surface of a metal sample;
An emission spectroscopic analysis apparatus for analyzing a component of a metal sample, characterized by comprising means for irradiating a pulse laser at a position off the center of the incident optical axis of the spectrometer.

  According to the method and apparatus of the present invention, it is possible to suppress the self-absorption of the emission line of the element to be analyzed by irradiating a metal sample with a pulse laser and controlling the discharge position. Therefore, the accuracy of quantitative analysis can be improved.

The schematic diagram of the measuring apparatus which is one Embodiment of the method of this invention Change in emission intensity when the laser irradiation position is changed from the center of the incident optical axis of the spectrometer in the vertical direction Calibration curve of Cr in stainless steel (Comparison of the presence or absence of laser irradiation) Calibration curve of Ni in stainless steel (Comparison of the presence or absence of laser irradiation)

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1A is a schematic diagram showing an example of an emission spectroscopic analyzer used in the embodiment of the present invention. 1 is a metal sample to be analyzed, 2 is a counter electrode for spark discharge, 3 is a discharge device for applying a voltage to the counter electrode 2, 4 is a spectroscopic analyzer (spectrometer), and 5 is the intensity of the light emission line after spectroscopy Is a data processing device, 6 is a pulse laser, 7 is a laser oscillator, 8 is a laser scanning device, 9 is a laser reflector, 10 is a laser condenser lens, 11 is a control device, and A is an optical axis incident on the spectrometer. Indicates.

The control device 11 is connected to the discharge device 3, the data processing device 5, and the laser oscillator 7, and controls the timing of irradiation with the pulse laser 6, application of voltage to the counter electrode 2, and counting of light intensity in the data processing device 5. Control.
FIG. 1B is a diagram in which the vicinity of the metal sample 1 in FIG. 1A is projected from the counter electrode 2 side.
The arrows in the figure indicate that the pulse laser 6 can be scanned in the x and y directions, respectively.

  Next, the analytical measurement procedure according to the present invention will be described below. The metal sample 1 is attached to the analysis position, and the pulse laser 6 is irradiated to the metal sample 1. Here, it is desirable that the laser oscillator 7 used in the present invention is capable of generating laser-induced plasma on the sample surface in order to effectively induce discharge at the laser irradiation position. For example, the energy per pulse is 1 mJ or more. It is desirable to use a solid pulse laser such as an Nd: YAG laser that can oscillate a laser pulse with a pulse width of 50 ns (nanoseconds) or less.

  Further, it is desirable that the repetition oscillation performance of the laser oscillator 7 is capable of high repetition oscillation of about 200 to 1000 Hz. If the repetition frequency used in spark discharge luminescence is 300 to 500 Hz and has the same repetitive performance, the analysis time is not extended as compared with the conventional spark discharge luminescence spectroscopy method. This is because the inventive method can be carried out. In addition, such oscillation performance has an advantage that the laser and the spark discharge can be easily synchronized.

  Next, after irradiating the surface of the metal sample 1 with the pulse laser 6, a voltage is applied to the counter electrode 2 by the discharge device 3 within a time of 5 μs or more to 500 μs or less to induce discharge at the pulse laser irradiation position. . It has been experimentally shown that a spark discharge can be generated at the position irradiated with the pulse laser 6 within this time.

  However, when this time is shorter than 5 μs, vapor and ions of the metal sample 1 generated by the irradiation of the pulse laser 6 are present at a high density on the surface of the metal sample 1, which acts as a barrier and the metal sample 1 and the counter electrode 2. And the occurrence of spark discharge to the desired analysis position becomes unstable.

  On the other hand, when this time is longer than 500 μsec, the laser-induced plasma generated by the irradiation of the pulse laser 6 is diffused, and similarly, the occurrence of spark discharge at the desired analysis position becomes unstable. The emission intensity of each element emission generated by the discharge is counted and accumulated by the spectroscopic analyzer 4 and the data processor 5. In addition, the control device 11 can perform timing control with a time resolution of 1 μs or less in order to accurately control the timing of irradiation with the pulse laser 6, application of voltage to the counter electrode 2, and counting of light intensity in the data processing device 5. It is desirable that

  Prior to this measurement, the laser scanning device 8 is used to change the irradiation position of the pulse laser 6 on the sample surface in a direction perpendicular to the incident optical axis A of the spectrometer (the x-axis direction in FIG. 1B). However, the emission intensity of each element at each pulse laser irradiation position is measured, and a position deviating from the highest emission intensity is determined as the laser irradiation position. At this time, it is preferable to determine the position where the emission intensity is 1/20 or more and 1/2 or less of the highest emission intensity as the laser irradiation position. If it is less than 1/20 of the highest emission intensity, the S / B ratio (signal / background ratio) is lowered, and the accuracy is lowered, which is not preferable. In addition, if it exceeds 1/2 of the highest emission intensity, the influence of self-absorption in the high concentration region cannot be sufficiently reduced, which is not preferable. In this way, the spark discharge emission spectroscopic analysis is performed while irradiating the determined irradiation position with the pulse laser.

  The laser scanning device 8 is preferably a galvano scanner capable of two-dimensionally changing the irradiation position of the pulse laser 6 on the surface of the metal sample 1, but is not limited thereto.

  According to the present invention, a laser scanning device is used to change the pulse laser irradiation position on the sample surface in a direction perpendicular to the incident optical axis A of the spectrometer, and the calibration curve of each element at each pulse laser irradiation position is obtained. Created and determined the pulse laser irradiation position with less influence of self-absorption, and then performed the spark discharge emission spectroscopic analysis while inducing the discharge by irradiating the pulse laser to the specified irradiation position. It becomes possible to perform quantitative analysis while suppressing self-absorption of the emission line.

  Cr and Ni in stainless steel were analyzed by the emission spectral analysis method according to the present invention. Samples to be analyzed have Cr and Ni concentration ranges of wt% (hereinafter, unless otherwise specified,% indicates wt%), and 10.34 to 27.02% and 4.03, respectively. Stainless steel of ~ 29.62% was used. As the emission spectroscopic analyzer, PDA-5017 (product number) manufactured by Shimadzu Corporation was used, and a light emission stand provided with an incident window for irradiating a metal sample with a pulse laser was used. As a discharge condition, a normal spark mode having the smallest discharge energy among discharge conditions preset in the apparatus was used. The wavelengths of the intrinsic spectral lines of Fe, Cr, and Ni used for measurement were 287.2 nm, 298.9 nm, and 227.7 nm, respectively. As the laser, an Nd: YAG pulse laser having a wavelength of 1064 nm and a pulse width of 12 ns was used, and laser focusing and scanning were performed by a galvano scanner equipped with an fθ lens having a focal length of 100 mm.

  FIG. 2 shows a change in emission intensity when the laser irradiation position is changed in the vertical direction from the center of the incident optical axis of the spectrometer. The horizontal axis is the distance from the center of the incident optical axis of the spectrometer, and the vertical axis is the emission intensity of each element.

  When a discharge is induced by irradiating a laser at a position shifted by 2 mm in the vertical direction from the center of the incident optical axis of the spectrometer (as shown in FIG. 2, a position that is 1/20 of the highest emission intensity), The calibration curves for Cr and Ni are shown in FIGS. 3 and 4 in comparison with the case without laser irradiation. As shown in the figure, when there is no laser irradiation, the emission intensity tends to be saturated in the Cr and Ni high concentration region, and the calibration curve becomes a curve. On the other hand, in the method according to the present invention in which the discharge position is removed from the central axis of the spectrometer by laser irradiation, it can be confirmed that the calibration curve is improved linearly. Thus, by controlling the discharge position by laser irradiation, the linearity of the calibration curve particularly in the high concentration region is improved.

DESCRIPTION OF SYMBOLS 1 Analytical sample 2 Discharge counter electrode 3 Discharge device 4 Spectroscopic analysis device 5 Data processing device 6 Pulse laser 7 Laser oscillator 8 Laser scanning device 9 Laser reflecting mirror 10 Laser condensing lens 11 Control device A Center of incident optical axis of spectroscope

Claims (3)

  In the emission spectroscopic analysis method for quantitatively analyzing the components of the metal sample by irradiating the metal sample with a pulse laser and spectrally analyzing the generated emission spectrum by spark discharge between the metal sample and the counter electrode, the pulse laser is An emission spectroscopic analysis method characterized by irradiating a position off the center of an incident optical axis of a spectroscope, inducing the spark discharge, and measuring an emission intensity of an emission line of an element to be analyzed.   The position off the center of the incident optical axis of the spectrometer is scanned while irradiating the pulse laser in a direction perpendicular to the center of the incident optical axis of the spectrometer, and the emission intensity is measured. The emission spectroscopic analysis method according to claim 1, wherein the emission position is an irradiation position exhibiting an emission intensity of / 20 or more and ½ or less. In an emission spectroscopic analyzer equipped with a pulse laser generator and a spark discharge generator,
The pulse laser generator is
Means for scanning and illuminating the surface of the metal sample;
An emission spectroscopic analysis apparatus for analyzing a component of a metal sample, characterized by comprising means for irradiating a pulse laser at a position off the center of the incident optical axis of the spectrometer.

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