JP2004191099A - Laser emission spectroscopic analyzer - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a compact laser emission spectroscopic analyzer capable of measuring the concentration of a composition element, in particular, in an iron steel material with high accuracy by combining high wavelength resolution and wide measurement wavelength area, with respect to the laser emission spectroscopic analyzer capable of analyzing the composition of solid sample and liquid sample with high sensitivity. <P>SOLUTION: In this laser emission spectroscopic analyzer for spectroscopically analyzing the excited light from plasma produced on a sample by the irradiation of laser beam, a spectrograph is an echelle spectrograph, and the detector is a CCD detector. <P>COPYRIGHT: (C)2004,JPO&NCIPI

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a laser emission spectrometer used for analyzing solid and molten metal materials, and more particularly to a small laser spectrometer capable of rapidly, sensitively and accurately analyzing the composition of these samples.
[0002]
[Prior art]
As a method for quickly analyzing the composition of a solid or liquid sample, there is a laser emission spectroscopy method in which a sample surface is irradiated with laser pulsed light and the resulting plasma is spectrally analyzed. Since this method can be analyzed in a non-contact and atmospheric pressure atmosphere with a sample, sampling, such as fluorescent X-ray analysis and spark discharge emission spectroscopy conventionally used for composition analysis of metal materials, can be performed. There is a feature that processing such as cutting and polishing is unnecessary, and analysis can be performed quickly. Further, since not only a solid sample but also a liquid sample can be analyzed, there is a feature that a metal in a molten state can be directly analyzed in a refining process of a metal material or the like.
[0003]
In laser emission spectroscopy, emission lines of constituent elements in a sample are measured over a wide wavelength range from 150 nm to 400 nm or more. The concentration of the element to be analyzed can be determined from one or more emission line intensities of the element using a calibration curve or the like prepared in advance using a standard sample or the like having a known concentration.
[0004]
As a method for simultaneously analyzing emission lines from a plurality of elements, a method of measuring excitation light dispersed by a spectroscope using a CCD detector as disclosed in Patent Document 1 is known. However, as shown in FIG. 1, the emission spectrum of a steel material has a very large number of Fe emission lines in a wide range of 200 to 400 nm, and these Fe emission lines interfere with the emission line of the target element. There is a problem that the emission line intensity of the target element cannot be measured accurately, and the composition cannot be quantified accurately.
[0005]
On the other hand, by increasing the focal length of the spectroscope or increasing the number of grooves in the diffraction grating of the spectrometer, the wavelength resolution per CCD detector element is increased to increase the wavelength resolution of the spectrum. It is possible to separate the emission line of the target element from the emission line of Fe in the vicinity of the emission line. However, in this case, since the wavelength range that can be detected by the CCD detector is narrowed, there is a problem that a plurality of light-emitting lines cannot be detected simultaneously. Further, when the focal length of the spectroscope is increased, there is a disadvantage that the size of the apparatus is increased.
[0006]
On the other hand, there is an echelle spectrometer as a spectrometer capable of measuring a wide wavelength range with high wavelength resolution. The echelle spectrometer achieves high wavelength resolution using high-order diffracted light.However, since light of a plurality of wavelengths having different orders is diffracted at the same diffraction angle, the dispersion direction of the echelle diffraction grating and In general, orders are separated in the vertical direction, and detection is performed using a two-dimensional detector such as a CCD detector. As the order separating means in the echelle spectroscope, a prism is used as shown in Patent Document 2 and the like.
[0007]
However, when the order separation by the prism is adopted, the transmittance of vacuum ultraviolet light having a wavelength of 200 nm or less is low. Therefore, for example, among the constituent components of the steel material, C (wavelength: 193.09 nm) which greatly affects the product characteristics is used. ), S (wavelength: 180.73 nm) and P (wavelength: 178.29 nm) have a problem in that the measurement sensitivity of emission lines is low.
[0008]
[Patent Document 1]
JP-A-10-185817 [Patent Document 2]
JP-A-8-75550
[Problems to be solved by the invention]
The present invention has been made in order to solve the above-mentioned problem, and has a high wavelength resolution and a wide measurement wavelength in a laser emission spectrometer capable of analyzing the composition of a solid sample or a liquid sample quickly and with high sensitivity. It is an object of the present invention to provide a small-sized laser emission spectrometer capable of accurately measuring the concentration of a composition element in a steel material, in particular, by balancing the ranges.
[0010]
[Means for Solving the Problems]
The gist configuration of the present invention is as follows.
(1) In a laser emission spectrometer for spectrally analyzing and exciting excitation light from plasma generated on a sample by laser light irradiation, it is assumed that the spectroscope is an echelle spectroscope and the detector is a CCD detector. A laser emission spectrometer with high wavelength resolution.
[0011]
(2) In the above (1), in the laser emission spectrometer, the order separation means is a diffraction grating having a blaze wavelength of 250 nm or less, so that excitation light having a wavelength of 200 nm or less can be analyzed with high sensitivity. Laser emission spectrometer.
[0012]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, the laser emission spectrometer of the present invention will be specifically described.
FIG. 2 shows an example of a laser emission spectrometer according to the present invention.
In the figure, number 1 is a laser oscillator, 2 is a reflection mirror, 3 is a condenser lens, 4 is a sample, 5 is an ultraviolet light reflection mirror, 6 is an order separation spectrometer, 7 is an echelle spectrometer, 8 is a CCD detector, 9 is a control computer.
[0013]
The laser pulse light emitted from the laser oscillator 1 is condensed and irradiated on the surface of the sample 4 via a condensing optical system, that is, a reflection mirror 2 and a condensing lens 3, and generates laser-excited plasma. The excitation light from the laser plasma is condensed by an optical means, for example, an ultraviolet light reflection mirror 5 and guided to the spectroscope. The excitation light that has entered the spectroscope side is first dispersed in the order separation spectrometer 6 in the direction perpendicular to the dispersion direction of the echelle spectrometer 7 and guided to the echelle spectrometer 7. Then, the light is dispersed by the echelle spectroscope 7 to be two-dimensionally dispersed on the detection surface of the CCD detector 8. The control computer 9 controls the gate of the CCD detector 8 in synchronization with the oscillation of the laser oscillator 1 and also processes the excitation light intensity measured by the CCD detector 8 to calculate the composition of the sample. It is.
[0014]
Here, the spectrum of the excitation light dispersed from the echelle spectrometer 7 to the CCD detector 8 via the order separation spectrometer 6 has a high wavelength resolution in the dispersion direction of the echelle spectrometer 7 and has a vertical It is measured as a plurality of spectra having different wavelength ranges. The function of the order separation spectroscope 6 will be described below.
In general, a linear dispersion dλ / dx [nm / mm] (corresponding to an order resolution described later), which is a ratio of a distance difference dx of two lights having a wavelength difference dλ on a focal plane of a spectroscope, is represented by the following equation. It is.
dλ / dx = d · cos θ / (m · f)
Here, d is the groove interval (nm) of the diffraction grating, θ is the diffraction angle, m is the order, and f is the focal length (mm) of the lens for imaging the diffracted light. When a CCD detector is used, assuming that the element size is x (mm / pixel), the wavelength width per element, that is, the resolution [nm / pixel] is obtained from the product of the inverse linear dispersion and the element size. .
x · dλ / dx = x · d · cos θ / (m · f)
In the echelle spectroscope, since the light is separated under a diffraction condition having a large order, the inverse dispersion on the detection surface is very small and the wavelength resolution is high. However, in the Echelle spectrometer, since light of a plurality of wavelengths having different orders satisfy the diffraction condition and is diffracted at the same angle as in the following equation, a means for separating the light is required.
m × λ = (m + 1) × λ ′ = (m + 2) λ ″ = --- = 2d sin θ
Therefore, by installing a low-resolution spectroscope in the direction perpendicular to the dispersion direction of the echelle spectrometer, the order is separated in the direction perpendicular to the echelle spectrometer, and a spectral image that has been spectrally separated in the dispersion direction of the echelle spectrometer with high resolution is obtained. can get.
As a result, the emission spectrum of the sample can be measured while achieving both high wavelength resolution and a wide measurement wavelength range.
[0015]
In particular, a monochromator using a diffraction grating having a blaze wavelength of 250 nm or less is preferably used for the order separation spectroscope 6. That is, the blaze wavelength is a wavelength at which the reflection efficiency of the diffraction grating having the blaze wavelength is maximized. Therefore, by using such an order-separating spectrometer 6, it is possible to perform high-sensitivity measurement even in an ultraviolet region of 200 nm or less, where sufficient sensitivity was not obtained with a conventional prism.
[0016]
Further, in order to obtain a sufficient transmittance of vacuum ultraviolet light, the spectrometer is preferably placed in an atmosphere of an inert gas such as nitrogen or argon or under vacuum (under extremely reduced pressure). Further, it is more preferable that the periphery of the sample be in an inert gas atmosphere.
[0017]
Here, as the ultraviolet light reflecting mirror 5, it is preferable to use a mirror having a reflectance of 70% or more for ultraviolet light having a wavelength of 250 nm or less in order to obtain sufficient sensitivity.
[0018]
In the example of FIG. 2, an optical means using a reflection mirror is shown as a means for introducing the excitation light into the spectroscope, but an optical fiber for ultraviolet light or the like may be used in combination. Also in this case, it is preferable that the transmittance of the entire light-collecting system to ultraviolet light of 250 nm or less is 70% or more.
[0019]
Further, as the CCD detector, it is preferable to use a CCD detector capable of high-speed gating in less than 2.0 μs in order to separate continuous light emitted from plasma immediately after laser irradiation from elemental light emission.
On the other hand, a pulsed laser such as an Nd: YAG laser used in the conventional laser emission spectroscopy may be used as the laser.
[0020]
【Example】
FIG. 3 shows an image obtained by measuring the emission spectrum of stainless steel with a CCD detector using the laser emission spectrometer shown in FIG. The size of this image is 1024 × 228 pixels. In the figure, the Y-axis direction is the dispersion direction of the order separation spectroscope (monochromator), and the larger this Y is, the higher the order of the spectrum is. On the other hand, the X-axis direction is the dispersion direction of the echelle spectroscope, and the larger this X is, the longer the wavelength is.
[0021]
In FIG. 3, the ranges of the Y-axis values of 1 to 7 pixels and 213 to 216 pixels correspond to the 87th-order and 125th-order spectra, respectively, and the spectrum when the respective ranges are integrated in the Y direction is shown in FIG. (A) and (b). 4A correspond to Fe: 276.75 nm, Cr: 276.26 nm, and Cr: 276.65 nm, and the respective peaks in FIG. 4B correspond to Fe: 192.63 nm and C: 193.09 nm. The peak values of each spectrum in the X-axis direction on the CCD are 303, 456, 417, and 650 for Cr: 276.26 nm, Fe: 276.75 nm, Fe: 192.63 nm, and C: 193.09 nm. Pixel. From this, the wavelength resolution in each spectrum is about (276.75-276.26) / (456-303) = 0.0032 nm / pixel in the 87th order, and (193.09-192.63) / in the 125th order. It can be seen that (650-417) = 0.022 nm / pixel, which is extremely high.
Also, it can be seen that spectrum measurement over a wide range from 190 nm to 280 nm can be simultaneously performed.
[0022]
FIG. 5 shows the correlation between the emission line intensity and the concentration of each element obtained using stainless steels having different Mn and Cr concentrations in the sample. The analysis conditions are a laser pulse energy of about 100 mJ / pulse and an analysis time of 20 seconds (repetition frequency 15 Hz, 300 pulse = 15 Hz × 20 sec). In FIG. 5, the errors in the analysis of Cr and Mn are 0.20 mass% and 0.04 mass%, respectively, and it can be confirmed that the analysis can be performed accurately with a short analysis time.
[0023]
【The invention's effect】
According to the present invention, it is possible to provide a small-sized laser emission spectrometer capable of achieving both high wavelength resolution and a wide measurement wavelength range, and particularly capable of quickly and accurately measuring the concentration of a constituent element in a steel material.
[Brief description of the drawings]
FIG. 1 is a diagram showing a laser emission spectrum (wavelength range: 180 to 390 nm) of a steel sample.
FIG. 2 is a diagram showing a main configuration example of a laser emission spectrometer according to the present invention.
FIG. 3 is a view showing a CCD image of an emission spectrum of stainless steel measured by a laser emission spectrometer according to the present invention.
4A is a diagram showing a Y-direction integrated spectrum of Y range 1 to 7 pixels in FIG. 3, and FIG. 4B is a diagram showing a Y-direction integrated spectrum of Y range 213 to 216 pixels in FIG. .
FIG. 5 is a diagram showing a correlation between Cr and Mn emission line intensities and concentrations of stainless steel having different Cr and Mn concentrations.
[Explanation of symbols]
REFERENCE SIGNS LIST 1 laser oscillator 2 reflection mirror 3 condenser lens 4 sample 5 ultraviolet reflection mirror 6 order separation spectrometer 7 echelle spectrometer 8 CCD detector 9 control computer

Claims (2)

A laser emission spectrometer for spectrally analyzing and exciting excitation light from plasma generated on a sample by laser light irradiation, wherein the spectrometer is an echelle spectrometer and the detector is a CCD detector. , A laser emission spectrometer with high wavelength resolution. 2. The laser emission spectrometer according to claim 1, wherein the order separation means is a diffraction grating having a blaze wavelength of 250 nm or less, so that excitation light having a wavelength of 200 nm or less can be analyzed with high sensitivity. Spectroscopic analyzer.

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