JPH08184564A - Emission spectrochemical analytical method - Google Patents

Abstract

PURPOSE: To provide an emission spectrochemical analytical method of which analyzable range can be expanded and whose analytical accuracy can be enhanced easily and at a low cost by accumulating the intensity value of an intrinsic spectral line for every element only when a discharge current value in every discharge is in a predetermined constant region. CONSTITUTION: A discharge current value in every discharge is measured by an ampere meter 10, it is A/D-converted (14), it is integrated (15), it is sent to a central processing unit 17, and it is stored in a storage circuit 19 as a normal discharge-current region (a window width, i.e., the upper limit value and the lower limit value of a current value). Then, the intensity, of a spectral line from a detector 21, which is obtained in every discharge is A/D-converted (22), it is integrated by a pulse converter 23, it is sent to the unit 17 via a multiplexer 16, and it is adopted and stored as the intensity of a normal spectral line when it is situated in the region (the window width) which has been stored 19 previously. When the designated number of discharges is finished totally, the intensity, of a spectral line for every element, which has been stored 18 is analyzed totally or converted into a frequency distribution, its central value is then found, and the content of the element is computed by a working curve (a regression expression) which has been created in advance.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for analyzing elements contained in a metal sample, and more particularly to a method for improving analysis accuracy when quantifying elements in metals by emission spectroscopy.

[0002]

2. Description of the Related Art In an emission spectroscopic analysis method using spark discharge, first, spark discharge is carried out between a sample and a counter electrode, and each element contained in a metal sample is evaporated and vaporized by its discharge energy to make each element. The characteristic spectral line having an intensity corresponding to the concentration of is generated. At that time, the spectral lines at the source are mixed with the characteristic spectral lines and scattered light of each element,
Although it is in a so-called continuous spectrum line state, this continuous spectrum line is guided to a spectroscope and is dispersed by a diffraction grating installed inside, and the characteristic spectrum line of the element to be measured is selectively detected. Then, the intensities of the detected plural characteristic spectral lines are photometrically measured by a photomultiplier (detector) to be converted into numerical values, which are converted to the respective contents by comparing with the previously prepared calibration curves for each element. Therefore, the quantification is performed. The calibration curve for each element is obtained by performing regression calculation on the emission spectrum line intensities of a plurality of samples (20 to 40) each having a known content, and a regression equation (linear equation, quadratic equation or Cubic equation).

However, analytical samples, including those for preparing a calibration curve, cannot be obtained (a) samples having the same composition, or (b) samples having the same metallic structure cannot be obtained.
(C) Since the physical and chemical properties of each non-metallic inclusion are different in each sample due to the difference in concentration and distribution of non-metallic inclusions contained in the sample, the discharge form (discharge energy) is different during spark discharge. Different from sample to sample, the spectral line intensities of each element were not constant, which was the main cause of deterioration 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 sampling amount, and statistically reduce the error. (2) The spectral line intensity of the main component (iron for steel, aluminum for Al alloy, etc.) of the analysis sample was measured as an internal standard, and the “metal emission spectroscopy (September 20, 1972) Kyoritsu Shuppan Co., Ltd., pages 212-214 ”, for example, (target element spectral line intensity / main component spectral line intensity) is calculated and corrected as a corrected spectral line value. (3) If there are many inclusions in the sample, “Iron and Steel 198
2, vol68, No. 3, p523-528 ”, the main component element has a large variation in the spectral line intensity, and when the method (2) above is used, the spectral line intensity of the target element is a denominator even if it is normal. Since the components vary, the accuracy of analysis may decrease. for that reason,
For example, “Latest Steel Condition Analysis (August 10, 1979)
Jpn., Agne Co., Ltd., pp. 107-115 ”, the sample is discharged 1000 to 2000 times, and the characteristic spectral line intensity of the main component element is abnormally low (or abnormal). If it is very high), the content of each element is calculated by a photometric method (so-called Fe trigger method) that does not determine the characteristic spectral line intensity of the target element. In other words, it is an analysis method that cuts abnormal data and obtains a representative value rather than the true value of the sample.

[0005]

However, according to the research by the present inventor, the existence of the following problems has been clarified even if the above three treatments are performed. In the method of (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 discharges are continued for a long time. The conductivity and thermal conductivity are changed, the form of discharge is changed, and on the contrary, the emission spectrum line intensity of the element to be measured varies.

In the method (2), when the fluctuation of the characteristic spectrum line of the element to be measured and the fluctuation of the main component element are not synchronized or follow, a large error occurs. That is, the content of the main component element is naturally high, and it cannot be detected by emission spectroscopic analysis unless the detection sensitivity is slowed down.
Cannot detect small amount of change completely (less effective correction).

The method (3) has a problem that when the characteristic spectral line intensity of the main component is abnormal, the characteristic spectral line intensity of the target element is normal and is not used as data. In other words, the width of the main component spectral line intensity is set in advance to determine whether or not to use it as data (called the window width in the analytical field). There are some samples that increase or decrease and do not have an appropriate window width, causing an error. Therefore, it is necessary to prepare and analyze a calibration curve with samples having similar main component contents, which complicates the work and causes a work error.

As described above, at the current technical level, further improvement in analysis accuracy cannot be expected, and carbon, sulfur, and
We cannot meet the needs for expanding the lower limit of quantification for nitrogen, neighbors, etc.
Therefore, in view of such circumstances, an object of the present invention is to provide an emission spectroscopic analysis method which is simple, has high analysis accuracy, and can expand the lower limit of quantification of an analysis element.

[0009]

In order to achieve the above object, the inventor diligently reviewed the conventional emission spectroscopy analysis method and obtained the following findings. 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 200V to 400V), and triggers a higher voltage (1KV to 2KV) than the igniter circuit. Output is performed, and in synchronization with this, the discharge electrode discharges the sample. At that time, a so-called discharge gap (distance between the counter electrode and the sample: usually 3
The electric current flowing in (mm ~ 5 mm) is governed by the electrical conductivity and the thermal conductivity of the sample metal, and if the sample is homogeneous and always at the same temperature, these conductivities will remain constant and the analysis will start and end. There is no difference in the discharge current value in the vicinity. 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 differs depending on the concentration of the impurity component contained therein or the sampling method, and the crystal form also varies depending on the contents of carbon, manganese and the like. Moreover, in the sample, for example, MgO, S
There are also inclusions such as oxides, nitrides, and sulfides such as iO ₂ , Al ₂ O ₃ , TiN, and MnS, and the discharge form is
As described above, the shape of the sample inevitably varies, and the magnitude of the discharge current also varies. Furthermore, since the excitation energy of the sample is the time product (∫idt) of the discharge current i, the intensity of the emission spectrum line also changes depending on the current value.

Therefore, the present inventor has paid attention to this finding, measures the magnitude of the changed current for each discharge, and only when the current value falls within a preset current value width (window width), He has devised an analytical method that employs the characteristic spectral line intensity values of each photometric element as data. That is, in the present invention, spark discharge was performed a large number of times between a metal sample and a counter electrode in an inert gas atmosphere, and the emitted light from the metal sample excited for each discharge was dispersed, and each obtained In the emission spectroscopic analysis method for measuring the intensity of the characteristic spectral line of the element to quantify the value, accumulating the numerical value by a computer, and calculating the content of each element by arithmetic processing, measuring the discharge current value for each discharge, The emission spectroscopic analysis method is characterized in that the numerical values of the intensity values of the characteristic spectral lines of each element are accumulated and calculated by the computer only when the measured value is in a predetermined fixed region. Further, the present invention performs a spark emission spectroscopic analysis on a metal sample with few abnormal crystal structures and non-metallic inclusions, and processes all the current values for each discharge into a frequency distribution of the appearance frequency and the discharge current value. Also, the emission spectroscopic analysis method is characterized in that a region in which the upper and lower parts are cut off is defined and the region is defined as the constant region of claim 1.

[0011]

In the present invention, a spark discharge is generated a large number of times between a metal sample and a counter electrode in an inert gas atmosphere, and the emission from the metal sample excited at each discharge is spectrally obtained. Intensity of the characteristic spectral line of each element is measured and digitized, the numerical values are accumulated by a computer, in an emission spectroscopic analysis method for calculating the content of each element by arithmetic processing, the discharge current value for each discharge is measured, Only when the measured value is in a predetermined constant region, the numerical intensity values of the characteristic line of each element are accumulated and calculated by the computer, so that the characteristic line intensity of each element is almost the same. It becomes possible to evaluate under the same discharge current value (excitation energy). As a result, information from the abnormal part of the sample is excluded, and a correct representative value can be obtained.

Further, in the present invention, spark emission spectroscopic analysis is carried out on a metal sample having an abnormal crystal structure and a small amount of non-metal inclusions, and data processing of all current values for each discharge into frequency distribution of appearance frequency and discharge current value. In addition, the area cut off the bottom is defined, and the area is set as the constant area of claim 1. Therefore, it is possible to reduce the cost by adding some software without modifying the conventional optical emission spectrometer. Can easily improve the analysis accuracy and increase the lower limit of quantification of each element.

[0013]

EXAMPLE FIG. 1 schematically shows an example of an apparatus for carrying out the spark discharge optical emission spectroscopic analysis method according to the present invention. A discharge apparatus 1, an analysis sample (also an electrode) 2 and a counter electrode 3 are shown. And a light emitting portion, a diffraction grating 7, a slit 8,
Consists of a spectroscope including a detector (photomultiplier) 6 and the like, a photometric device 4 for digitally converting the analog amount of spectral lines to perform data processing, and a content calculator 5 for converting spectral line intensities into elemental contents. Has been done.

FIG. 2 shows an example of a part of the discharge circuit incorporated in the discharge device 1 and a part of a photometric device for photometrically measuring the spectral line intensity from a detector. Spark discharge is generated in the discharge gap 13 by controlling the inductance, capacitance and resistance. At that time, as a discharge trigger, the current boosted to 10000 V or more in the high voltage section 20 breaks the insulation by the igniter 11 and the electricity held in the capacitor 24 is passed. In order to carry out the present invention, an ammeter 10 (see FIG. 2) is provided in the above device, a frequency distribution processing and storage circuit 19 is provided in the photometric device of FIG. The calculation means for selecting the spectral line intensity data is newly incorporated.

The implementation contents of the emission spectroscopic analysis method according to the present invention will be described below. First, a comparatively uniform metal sample with a small amount of abnormal crystal structure and non-metallic inclusions, here carbon steel, is set in the sample holder of FIG. 1 and discharged by a commonly used method. The discharge current value of (200 to 400 times / second) is measured with an ammeter to determine the above-mentioned constant range region of the discharge current. Here, the pulse converter 15 is a circuit that holds the current value measured by the ammeter 10 after the current value is converted from analog to digital. Further, 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 integrating circuit is cleared before each subsequent discharge, but the current value is sent to the central processing unit 17. The discharge current value is shown in FIG.
It was arranged in the frequency distribution with the number of appearances. In the present invention, both ends of the horizontal axis (current value) of this frequency distribution are a
Only% and b% are deleted as abnormal values, and the value between a% and b% is set as a normal discharge current region (window width) and stored in the memory circuit 19. Of course, the values of a and b differ depending on the type of the 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, regarding the actual emission spectroscopic analysis procedure,
Set the metal sample to be analyzed in the sample holder as above,
Discharge and measure the current value with an ammeter. Further, the spectral lines of each element generated by the same discharge enter the spectroscope (12 in FIG. 2) of FIG. 1, are diffracted and separated, and a plurality of detectors 6 (FIG. Two
21). The output of the spectral line intensity from the detector is obtained for each discharge, is presented as a pulse by the pulse converter, is sent to the central processing unit 17 via the multiplexer, and is stored in the predetermined memory circuit 19 as described above. Window width of discharge current value (upper and lower limit value of current value: Fig. 3
Based on the above), only those which are determined to be normal discharge spectrum lines are selected and stored in the spectrum line intensity storage circuit 18 for each discharge. The state of the selection is shown in FIG. 4. In the upper diagram of FIG. 4, the spectrum line intensity corresponding to the case where the discharge current value falls between the upper limit value and the lower limit value is stored in the lower diagram as data in the storage circuit. 18 is shown.

Finally, the specified number of discharges (usually 1000
Discharge to about 2000 times), the discharge is terminated, and the spectral line intensity of each element in the memory circuit 18 is changed to
For example, after total integration or conversion into a frequency distribution, the median value thereof is calculated, the value is calculated, and the content is calculated by a calibration curve prepared in advance. Table 1 shows an example of the result of actually analyzing Al in carbon steel. In the case of this sample, the analysis accuracy (repetition accuracy: σ) of Al was 0.0011%, which is three times more than 0.0038% of the conventional method. The conventional method here is "conventional technology".
This is the so-called Fe trigger method described last in the section.

[0018]

[Table 1]

[0019]

As described above, 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, in addition to expanding the range of analysis of each element, that is, expanding the lower limit of quantification, development of high-purity steel, improvement of yield in the refining process and reduction of manufacturing cost, shortening of operating time, reduction of analysis cost, etc. Side effects can be expected.

[Brief description of drawings]

FIG. 1 is a schematic diagram showing the overall configuration of an emission spectroscopy analyzer.

FIG. 2 is a circuit diagram of spark discharge including an ammeter and a schematic configuration of a photometric device.

FIG. 3 is an explanatory diagram of a method of setting a constant region of a normal discharge current value.

FIG. 4 is a diagram illustrating a selection status of spectral lines of each element corresponding to a constant region of the discharge current value of FIG.

[Explanation of symbols]

 1 Discharge (light emission) device 2 Analytical sample 3 Counter electrode 4 Photometric device 5 Data processing device 6 Detector (photomultiplier) 7 Diffraction 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 storage circuit 20 High voltage section 21 Detector (photomultiplier) 22 A / D converter 23 Pulse conversion Container 24 discharging capacitor 25 terminal

Claims (2)

[Claims] 1. An element obtained by subjecting a metal sample and a counter electrode to a large number of spark discharges in an inert gas atmosphere and spectrally analyzing the light emitted from the metal sample excited at each discharge. In the optical emission spectroscopic analysis method, in which the intensity of the characteristic spectral line of is measured and digitized, and the numerical values are accumulated and arithmetically processed to obtain the content of each element, the discharge current value for each discharge is measured, and the measurement is performed. An emission spectroscopic analysis method, wherein the numerically calculated intensity values of the characteristic spectral lines of each element are accumulated and calculated by the computer only when the value is in a predetermined constant region. 2. A spark emission spectroscopic analysis is carried out on a metal sample having an abnormal crystal structure and a small amount of non-metal inclusions, and all the current values for each discharge are data-processed into a frequency distribution of appearance frequency and discharge current value. An emission spectroscopic analysis method, characterized in that a region of which the lower part is cut off is defined and the region is defined as the constant region of claim 1.