JP3733966B2 - Emission spectroscopic method - Google Patents

Description

  The present invention relates to a method for analyzing an element contained in a metal sample, and more particularly to a method for improving analysis accuracy when an element in a metal is quantified by an emission spectroscopic analysis method.

  In the emission spectroscopic analysis method using spark discharge, first, spark discharge is performed between the sample and the counter electrode, and each element contained in the metal sample is evaporated and vaporized by the discharge energy according to the concentration of each element. Intense characteristic spectral lines are generated. At that time, the spectral lines at the source are mixed with the intrinsic spectral lines and scattered light of each element and are in a so-called continuous spectral line state. These continuous spectral lines are guided to the spectrometer and installed inside. Spectroscopic analysis is performed using a diffraction grating, and the characteristic spectral lines of the element to be measured are selectively detected. Then, the intensity of a plurality of detected intrinsic spectral lines is photometrically measured with a photomultiplier (detector), converted into a numerical value, and converted into each content in comparison with a calibration curve prepared for each element. Quantification is performed. The calibration curve for each element is a regression formula (primary formula, quadratic formula or quadratic formula obtained by calculating the emission spectral line intensity with a plurality (20 to 40) of samples each having a known content and performing regression calculation. (Tertiary expression).

However, the analytical samples, including those for creating a calibration curve,
(A) A sample having the same component composition cannot be obtained.
(B) A sample of the same metal structure cannot be obtained.
(C) Since the physical and chemical properties of each sample are different for each sample because the concentration and distribution of the nonmetallic inclusions contained in the sample differ depending on the sample, the discharge mode (discharge energy) is different during spark discharge. Different from sample to sample, the spectral line intensity of each element was not constant, which was the main cause of a decrease in analysis accuracy.

Therefore, the current emission spectroscopic analysis method is intended to improve the analysis accuracy by taking the following measures.
(1) Increase the number of discharges, that is, increase the amount of sample collection, and statistically reduce the error.
(2) Measure the spectral line intensity of the main component of analysis sample (iron for steel, aluminum for Al alloy, etc.) as an internal standard, for example, (target element spectral line intensity / principal component spectral line intensity) Calculation and correction are performed as corrected spectral line values (see Non-Patent Document 1).
(3) When there are many inclusions in the sample, the fluctuation of the spectral line intensity of the main component element is large, and when the method of (2) is used, the main component which is the denominator is normal even if the spectral line intensity of the target element is normal. Since it fluctuates, the analysis accuracy may be reduced (see Non-Patent Document 2). Therefore, a photometric method in which 1000 to 2000 discharges per sample are performed, and when the intrinsic spectral line intensity of the main component element is abnormally low (or abnormally high), the intrinsic spectral line intensity of the target element is not obtained. The content of each element is calculated by a so-called Fe trigger method (see Non-Patent Document 3). In other words, this is an analysis method in which abnormal data is cut to obtain a representative value rather than a true value of the sample.
Metal emission spectrometry (September 20, 1967), published by Kyoritsu Shuppan Co., Ltd., pages 212-214 Iron and Steel 1982, vol 68, No. 3, p523-528 Latest steel state analysis (August 10, 1979) Agne, Inc., pages 107-115

However, according to the research of the present inventor, the following problems have been clarified even when the above three treatments are performed.
In the method (1), even if the population is increased, the contribution to the reduction of the standard deviation is small, and increasing the number of discharges means that the discharge is continued for a long time. The conductivity and thermal conductivity change, and the form of discharge changes, which in turn causes variations in the emission spectral line intensity of the element to be measured.

  In the method (2), if the variation of the characteristic spectrum line of the element to be measured and the variation of the main component do not synchronize or follow, a large error occurs. That is, the content of the main component element is naturally large, and it cannot be detected unless the detection sensitivity is lowered in the emission spectroscopic analysis. Therefore, a small amount of change cannot be completely detected (the effect of correction is small).

  In the method (3), there is a problem that when the intrinsic spectral line intensity of the main component is abnormal, the intrinsic spectral line intensity of the target element is normal and cannot be adopted as data. That is, in order to set the width (called the window width in the analysis field) for determining whether to adopt the principal component spectral line intensity as data in advance, if the content of the principal component differs depending on the sample, the principal component spectral line intensity is There are samples that increase or decrease and lose the proper window width and cause errors. Therefore, it is necessary to create and analyze a calibration curve with samples having similar content of the main component, which complicates work and causes work errors.

  As described above, at the current technical level, no further improvement in analytical accuracy can be expected, and the lower limit of quantification of carbon, sulfur, nitrogen, neighbors, etc. in steel by promoting higher cleanliness of steel materials. Cannot meet the needs of expansion. In view of such circumstances, an object of the present invention is to provide an emission spectroscopic analysis method that is simple, has high analysis accuracy, and can expand the lower limit of quantification of analytical elements.

  In order to achieve the above object, the inventor diligently reviewed the conventional emission spectroscopic analysis method and obtained the following knowledge.

The spark discharge device is composed of an electric circuit composed of a capacitor (capacitance), a coil (inductance), and a resistor with a constant voltage (usually about 200 V to 400 V), and triggers a higher voltage (1 KV to 2 KV) than the igniter circuit. Output is performed and the sample is discharged from the discharge electrode to the sample in synchronism with the output. At that time, the current flowing in the so-called discharge gap (distance between the counter electrode and the sample: usually 3 mm to 5 mm) is governed by the metal electrical conductivity and the thermal conductivity of the sample, so long as the sample is homogeneous and always at the same temperature. The conductivity does not change and is constant, and there is no difference in the current value of the discharge between the initial analysis and the end of the analysis. That is, the energy for exciting each element in the sample is constant, and the spectral line intensity of each element obtained does not change. However, the solidification process of the sample varies depending on the concentration of the impurity component contained therein or the sampling method, and the crystal form varies depending on the content of carbon, manganese, and the like. Further, in the sample, for example _{MgO, SiO 2, Al 2 O} 3, TiN, oxides such as MnS, nitrides also present inclusions such as sulfides, discharge form, as described above Depending on the form of the sample, the size of the discharge current is inevitably different. Furthermore, since the excitation energy of the sample is the time product (∫idt) of the discharge current i, the intensity of the emission spectral line also changes depending on the current value.

  Therefore, the inventor pays attention to this knowledge, measures the magnitude of the changed current for each discharge, and measures each photometric value only when the current value falls within a preset current value width (window width). He created an analysis method that uses the intrinsic spectral line intensity values of the elements as data.

  That is, in the present invention, in an inert gas atmosphere, spark discharge is performed a number of times between a metal sample and a counter electrode, and light emission from the metal sample excited for each discharge is spectroscopically analyzed. In an emission spectroscopic analysis method in which the intensity of the intrinsic spectral line of an element is measured and digitized, and the numerical value is accumulated and processed by a computer to obtain the content of each element, a metal with an abnormal crystal structure and non-metallic inclusions The spark emission spectroscopy was performed on the sample, the discharge current value for each discharge was measured, the current values were all processed into a frequency distribution of the frequency of occurrence and the discharge current value, and the area where the bottom was truncated The emission spectroscopic analysis method is characterized in that the current value in the upper and lower regions and the intensity value obtained by quantifying the intrinsic spectral line of each element corresponding to the current value are accumulated and calculated by the computer.

  According to the present invention, the analysis accuracy of the emission spectroscopic analysis method can be improved easily and at low cost. As a result, the analysis range of each element has been expanded, that is, the lower limit of quantification, development of high purity steel, improvement of yield in refining process and reduction of manufacturing cost, shortening of operation time, reduction of analysis cost, etc. A secondary effect can also be expected.

  Embodiments of the present invention will be described below with reference to the drawings.

  In the present invention, in an inert gas atmosphere, a spark discharge is performed a number of times between a metal sample and a counter electrode, and light emission from the metal sample excited for each discharge is spectroscopically analyzed. In the emission spectroscopic analysis method, in which the intensity of the intrinsic spectral line is measured and digitized, and the numerical value is accumulated and calculated by a computer to obtain the content of each element, a metal sample with few abnormal crystal structures and non-metallic inclusions is used. While performing the spark emission spectroscopy, measure the discharge current value for each discharge, data processing the current value to the frequency distribution of the appearance frequency and the discharge current value, and further, to determine the region that has been rounded down, Since the numerical values of the specific spectral lines of the respective elements corresponding to the current values in the upper and lower regions are accumulated and calculated by the above-mentioned calculator, the discharge current having almost the same specific spectral line intensity of each element. Value (encouragement Energy) will be able to evaluate under. As a result, information from the abnormal portion of the sample is excluded, and a correct representative value can be obtained. In addition, by adding a little software without modifying the conventional emission spectroscopic analyzer, the analysis accuracy can be easily improved at low cost, and the lower limit of quantification of each element can be achieved. Hereinafter, the present invention will be described in more detail with reference to examples.

  FIG. 1 schematically shows an example of an apparatus that implements the spark discharge emission spectroscopic analysis method according to the present invention. The light emission comprises a discharge apparatus 1, an analysis sample (also an electrode) 2, and a counter electrode 3. A spectroscope composed of a diffraction grating 7, a slit 8, a detector (photomultiplier) 6 and the like, a photometric device 4 for digitally converting an analog quantity of spectral lines and processing the data, and spectral line intensities containing elements It is comprised from the content calculator 5 converted into quantity.

  FIG. 2 shows an example of a part of a discharge circuit incorporated in the discharge device 1 and a part of a photometric device that measures spectral line intensity from a detector. Then, the discharge is controlled by the resistance and spark discharge is caused by the discharge gap 13. At that time, as a discharge trigger, the current boosted to 10000 V or higher by the high voltage unit 20 breaks the insulation by the igniter 11 and the electricity held in the capacitor 24 flows. In order to implement the present invention, the above device has an ammeter 10 (see FIG. 2) in the discharge circuit, a frequency distribution processing and storage circuit 19 in the photometric device in FIG. A calculation means for selecting spectral line intensity data is newly incorporated.

  Below, the implementation content of the emission-spectral-analysis method based on this invention is demonstrated. First, a relatively uniform metal sample with few abnormal crystal structures and non-metallic inclusions, here carbon steel, is set in the sample holder of FIG. A discharge current value of 200 to 400 times / second) is measured with an ammeter, and a certain range region of the discharge current is determined. Here, the pulse converter 15 is a circuit that holds the current value measured by the ammeter 10 after analog / digital conversion. The pulse converter 15 may be an integrating circuit that integrates and holds the current measured by the ammeter 10. The hold circuit or the integration circuit is cleared before the next discharge is performed for each discharge, but the current value is sent to the central processing unit 17. The discharge current values were arranged in a frequency distribution with the number of appearances as shown in FIG. In the present invention, both ends of the horizontal axis (current value) of the frequency distribution are deleted as abnormal values by a% and b%, respectively, and a value between a% and b% is a normal discharge current region (window width). And stored in the storage circuit 19. Of course, the values of a and b vary depending on the type of metal sample to be analyzed, but in the case of ordinary steel, a is in the range of 0 to 20%, b is in the range of 0 to 10%, and preferably a is 10%. , B is 5%.

  Next, as an actual emission spectroscopic analysis procedure, the metal sample to be analyzed is set in the sample holder in the same manner as described above, discharged, and the current value is measured with an ammeter. Further, the spectral lines of each element generated by the same discharge enter the spectroscope of FIG. 1 (12 of FIG. 2), are diffracted and spectrally separated, and a plurality of detectors 6 (FIG. 6) are arranged at the wavelength positions of the specific spectral lines of each element. 2) 21). The output of the spectral line intensity from the detector is obtained for each discharge, presented as a pulse by the pulse converter, sent to the central processing unit 17 through the multiplexer, and stored in the storage circuit 19 in advance. Based on the window width of the discharge current value (upper limit value and lower limit value of the current value: the contents are shown in FIG. 3), only those determined to be normal discharge spectrum lines are selected, and the spectrum line intensity storage circuit 18 is selected. Is stored for each discharge. FIG. 4 shows the state of the selection. In the upper diagram of FIG. 4, the spectral line intensity corresponding to the case where the discharge current value is between the upper limit value and the lower limit value is stored as data in the lower diagram. 18 is stored.

  Finally, after discharging the specified number of discharges (usually about 1000 to 2000 times), the discharge is terminated, and the spectral line intensity of each element in the memory circuit 18 is fully integrated, for example, or converted into a frequency distribution. After that, the median value is obtained, the value is obtained, and the content is calculated using a calibration curve prepared in advance. Table 1 shows an example of the results of actual analysis of Al in carbon steel. In the case of this sample, the Al analysis accuracy (repetition accuracy: σ) improved by 0.0011% to 3 times or more compared to 0.0038% of the conventional method. The conventional method here is the so-called “Fe trigger method” described last in the section “Background Art”.

It is a schematic diagram which shows the whole structure of an emission-spectral-analysis apparatus. It is the figure which showed the schematic diagram of the circuit diagram of a spark discharge containing an ammeter, and a photometry apparatus. It is explanatory drawing of the method of setting the fixed area | region of a normal discharge current value. It is a figure explaining the selection condition of the spectral line of each element corresponding to the fixed area | region of the discharge current value of FIG.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Discharge (light emission) apparatus 2 Analytical sample 3 Counter electrode 4 Photometry apparatus 5 Data processing apparatus 6 Detector (photomultiplier)
7 Grating 8 Slit 9 Power supply unit 10 Ammeter 11 Igniter discharge unit 12 Spectrometer 13 Spark discharge unit 14 A / D converter 15 Pulse converter 16 Multiplexer 17 Central processing unit 18 Spectral line intensity storage circuit 19 Frequency distribution processing and Memory circuit 20 High voltage section 21 Detector (Photomultiplier)
22 A / D converter 23 Pulse converter 24 Discharge capacitor 25 Terminal

Claims (1)

In an inert gas atmosphere, a spark discharge was performed many times between the metal sample and the counter electrode, and the emission from the metal sample excited for each discharge was dispersed, and the characteristic spectral lines of each element obtained were In an emission spectroscopic analysis method for calculating the intensity of light by measuring the intensity, accumulating the numerical value with a computer, and calculating the content of each element by calculation processing,
Spark emission spectroscopy is performed on a metal sample with an abnormal crystal structure and few non-metallic inclusions, and the discharge current value for each discharge is measured, and all the current values are processed into a frequency distribution of appearance frequency and discharge current value. In addition, a region in which the lower part is cut off is defined, and the current values in the upper and lower regions and the corresponding intensity values of the characteristic spectrum lines of the respective elements are accumulated and calculated by the computer. Emission spectroscopic analysis method.

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