JPH0450981B2 - - Google Patents

Description

Detailed Description of the Invention (Field of Industrial Application) The present invention relates to a method for easily and quickly analyzing carbon contained in metal samples, and is useful for manufacturing process management in the steel industry or various non-ferrous metal manufacturing industries. It is used in the field of analysis and quality control analysis.

(Prior Art) In operational management of metal refining processes, etc., it is necessary to analyze as quickly as possible to understand the component content, and take appropriate measures based on the results. Highly accurate and rapid analysis is also required for product verification, and carbon in particular is an important component in determining quality in the steel manufacturing process.

There are various methods for analyzing carbon in metal samples, including combustion infrared absorption method (JIS G1211-1981 Method for determining carbon in iron and steel) and emission spectrometry method (JIS
G1253 (Emission spectroscopy analysis method using photoelectric photometry for iron and steel) is a typical analysis method.

The former is a method in which a cut metal sample is burned in an oxygen stream to convert carbon contained in the sample into carbon dioxide, and its absorption in the infrared region is measured to determine the carbon content. In the latter method, a high voltage is applied between the surface of a block-shaped metal sample and a counter electrode such as tungsten to cause a spark discharge, and the generated excitation light is separated using a spectrometer, and the intensity of the carbon emission spectrum line is determined. This is a method to determine the content in a sample.

Since the former is a combustion method, the sample to be analyzed must be in the form of cuttings. For this reason, in process control analysis in the metal refining process, cutting powder must be collected again from a block sample obtained by collecting molten metal and solidifying it, which is time consuming and has the disadvantage of being impractical. The latter is a practical method that targets block samples and allows simultaneous analysis of multiple elements including carbon in a short time. However, in order to prevent interference between the spectral lines of each element emitting light at the same time, it is necessary to analyze the emission spectrum with a high resolution of 1 angstrom or less. Therefore, spectrometers are large and the analysis equipment occupies a large amount of space, and since spectrometers are precision optical devices, they must be installed in a place where room temperature changes are small, vibrations do not occur, and there is little dust. . The price of analytical equipment also becomes very high.

Therefore, even though it is not possible to analyze multiple elements at the same time as with conventional emission spectroscopy, it is possible to analyze just carbon, which is important for refining metals, easily and quickly.Moreover, there are no strict installation restrictions, and it is an inexpensive analysis method. equipment is often desired.

(Problems to be Solved by the Invention) The present invention is provided for such purposes,
The method is completely new in principle. In other words, carbon, which is a major element that has an important effect on quality evaluation such as the mechanical strength of metals, can be analyzed easily, quickly, with high sensitivity, and with high performance, while also being able to analyze installation environment constraints such as temperature changes, vibrations, and dust. The cost of the equipment is low. In addition, it has features that are superior to conventional methods, especially in terms of high-sensitivity analysis, which is essential for the production of high-purity metals, which has become important in recent years.

(Means for solving the problem) The present invention excites carbon contained in a metal sample by spark discharge in an inert gas atmosphere containing oxygen gas, and converts carbon into gas components such as carbon monoxide. , the concentration of gas components is measured using a hydrogen flame ionization detector, and the carbon content in metal samples can be easily determined.
It is a quick analysis. This method and principle have already been filed by the present inventor in Japanese Patent Application No. 59-186563 (Japanese Unexamined Patent Publication No. 61-65154) titled ``Method and Apparatus for Rapid Analysis of Carbon and Sulfur Components in Metal Samples''.

The difference between the present invention and the prior invention is that when a spark discharge is applied to a metal sample, the atmospheric gas is first changed to a high-purity inert gas that does not contain impurities such as oxygen gas to preliminarily generate the spark discharge. The point is that the generation of carbon monoxide gas is stabilized by letting it fly, then switching the atmospheric gas to an inert gas containing oxygen and continuing to cause spark discharge. In an inert gas atmosphere containing oxygen, spark discharge is difficult to fly normally, and the amount of evaporation of each element becomes a diffusion discharge, which reduces the amount of carbon monoxide produced or becomes unstable, resulting in poor quantitative accuracy. However, this problem was solved by switching the atmospheric gas mentioned above.

(Configuration, operation, and embodiments of the invention) The configuration and operation of the present invention will be explained based on an example of an apparatus for implementing the present invention shown in FIG. The apparatus of the present invention mainly includes a carbon monoxide gas generation section 1, a spark discharge power supply section 2, an inert gas control section 3 such as argon gas, a gas sampling section 4, and a detection section 5. The carbon monoxide gas generation section 1 has a counter electrode 7 made of tungsten or the like, facing the analysis sample 6.
is provided, forming a small volume discharge chamber 8 provided with an inert gas supply port and a discharge port. The counter electrode 7 is held by a heat-resistant insulating material and is insulated from the analysis sample 6. A cathode and an anode of the spark discharge power supply device 2 are connected to the analysis sample 6 and the counter electrode 7, respectively. A high voltage is applied to these two electrodes to generate a spark discharge between the surface of the analysis sample 6 and the tip of the counter electrode 7, thereby exciting and vaporizing each element in the analysis sample. Appropriate conditions for spark discharge are those that provide good reproducibility of excitation of each element. For example, the spark discharge circuit constant is self-induction 10μH, capacitance 3μF, resistance
When common low-pressure spark discharge conditions were used, such as 0Ω, voltage of 1000V, frequency of 100 to 400Hz, and electrode gap of approximately 4 to 6mm, the sensitivity and accuracy of the quantitative results were excellent.

The gas control unit 3 includes a high-purity argon gas cylinder 9,
High-purity argon gas cylinder 10 mixed with oxygen gas at about 0.001 to 0.1%, flow meter with needle valve 11
a, 11b, electromagnetic valves 12a, 12b, etc., and performs flow path switching and flow rate control of argon gas and oxygen-mixed argon gas. First, after setting the analysis sample 6 in the carbon monoxide gas generation section 1, follow the path of the arrow in FIG.
a, gas supply pipe 13, discharge chamber 8, gas transport pipe 15
and argon gas in the path to the solenoid valve 12c.
It flows at a flow rate of 20/min to exhaust and remove the atmosphere remaining in the discharge chamber 8 and to preliminarily cause a spark discharge. This preliminary discharge is performed in order to prevent this from occurring, since if discharge is started from the beginning with oxygen-mixed argon gas, it will become a diffusion discharge, making it impossible to obtain a normal spark discharge and deteriorating the accuracy of carbon analysis. That is, the purpose is to make the discharge easier to fly, to stabilize the discharge state, and to remove any slight carbon component stains on the sample surface.

Next, the atmospheric gas is switched to oxygen-mixed argon gas without stopping this preliminary discharge. That is, an oxygen mixed argon gas cylinder 10, a flow meter 11b, a solenoid valve 12b, a supply pipe 13, a discharge chamber 8, a conveyance pipe 14,
0.5% of oxygen mixed argon gas is introduced into the path of the solenoid valve 12c, particulate filter 15, and gas metering tube 16.
Flow at a flow rate of ~3/min to generate spark discharge. Switching the atmospheric gas for this spark discharge is a feature of the present invention, but Japanese Patent Application Laid-Open No. 59-1991 does not switch the gas.
-186563 and a steel sample containing 0.20% carbon, the analysis accuracy (coefficient of variation) was compared when repeated 10 times. As a result, the coefficient of variation of the present invention was 0.85%, which was a significant improvement in analysis accuracy compared to 3.7% of Japanese Patent Application No. 59-186563.

The sampling section 4 includes a solenoid valve 12c, a particulate filter 15, a gas measuring tube 16, and the like. When spark discharge is performed under argon gas flow, iron, carbon, manganese, silicon and
Each element, such as sulfur and phosphorus, is excited, but they form particles together within a very short time. This particle is
They are extremely fine particles of about 0.01 μm in size, and their composition is close to that of the original steel sample, although it depends on the circuit constants of the spark discharge. However, they are made by mixing oxygen gas with high-purity argon gas. When a spark discharge is performed in the same manner as above, iron, manganese, silicon, etc. in the steel sample form ultrafine particles, but the moment carbon is excited, it reacts with oxygen and forms carbon monoxide and carbon dioxide gas. It was discovered that the oxide gas of The main component of the produced gas was carbon monoxide gas. The carbon monoxide gas generated in the discharge chamber 8 is filtered through a particulate filter 15 to remove fine particles 2 such as iron, which are sent along with the carbon monoxide gas, and a gas metering device consisting of a thin tube with a switching valve has a constant capacity of about 1 to 5 c.c. It fills the pipe 16 and is discharged outside the system. The carbon monoxide gas filled in the metering tube 16 is sent to the detection section 5 using argon gas supplied from another cylinder as a carrier gas by operating the switching valve.

The detection unit 5 includes a gas reduction device 17, a flame ionization detector (FID) 18, and a data processing device 19.
Consists of etc. The FID detector 18 is a detector commonly used in gas chromatographs, and uses a hydrogen flame as an excitation source to ionize an analytical component and measure the ion current. Since carbon monoxide and carbon dioxide gas cannot be directly measured with an FID detector, a gas reduction device 17 in which a nickel catalyst is heated is installed in front of the FID detector.
Carbon monoxide and carbon dioxide are reduced to methane
Introduced into FID and detected with high sensitivity. The detection signal is sent to the data processing unit 19, the detected peak height or peak area is determined, and the carbon content in the steel sample is calculated based on a calibration curve determined in advance using a steel standard sample. . If a gas component separation column is attached between the gas metering pipe 16 and the gas reduction device 17 and the measurement is performed, carbon monoxide and carbon dioxide will be separated and detected in about 3 minutes. Since no interfering gas components were detected, the installation of a separation column was not absolutely necessary. Therefore, if a separation column is not used, both carbon monoxide and carbon dioxide produced in small amounts are reduced to methane by the reduction device 17, so in FID, the total amount of both gas components can be reduced in a short period of about 40 seconds. Measured in hours. The flow rate of oxygen (40ppm) mixed argon gas during spark discharge is 2/
min, the sampling amount of carbon monoxide gas is 1
Fig. 2 shows an example of a calibration curve created by analyzing carbon in a steel standard sample. As can be seen from FIG. 2, according to the present invention, trace amounts of carbon in a steel sample can be easily and accurately quantified in a short time of less than one minute.

(Effects of the Invention) As explained above, the present invention has the advantage that the element to be analyzed is limited to carbon, compared to the conventional optical emission spectrometry method that rapidly analyzes carbon in metals using block-shaped samples. However, the constraints on the measurement environment for the analyzer such as vibrations, temperature changes, and dust are loose, and the equipment price is about 1/5th of the low price. It is useful as a non-destructive rapid analysis with short laboratory time and excellent quantitative sensitivity, and it targets carbon, which is the most important element for quality evaluation of metals such as steel, titanium, aluminum, and copper. It is extremely effective for operational management of refining and manufacturing processes.

[Brief explanation of the drawing]

FIG. 1 is an explanatory diagram showing the configuration of an apparatus for implementing the present invention. FIG. 2 is an example of a calibration curve prepared by analyzing carbon in a steel standard sample using the method of the present invention. Note that the numbers in FIG. 1 indicate the following. DESCRIPTION OF SYMBOLS 1... Carbon monoxide gas generation part, 2... Spark discharge power supply part, 3... Atmosphere gas control part, 4...
Gas sampling section, 5...Detection section, 6...Analysis sample, 7...Counter electrode, 8...Spark discharge chamber, 9...
...Argon gas cylinder, 10...Oxygen mixed argon gas cylinder, 15...Particle filter, 16
...Gas measuring tube, 17...Gas reduction device, 18...
...Hydrogen flame ionization detector.

Claims (1)

[Claims] 1. In an analysis method for determining the carbon component content in a sample using gas components generated by spark discharge on the surface of a metal sample, the spark discharge is first performed preliminary in an inert gas atmosphere. After stabilizing the sample surface condition and discharge condition, spark discharge is performed in an inert gas atmosphere containing a trace amount of oxygen, reducing carbon gas components such as carbon monoxide generated and producing methane. A method for rapid analysis of carbon in a metal sample, characterized by introducing the carbon into a hydrogen flame and measuring the ionic current of the carbon component to determine the carbon content.