JP3492248B2 - Method for measuring trace helium in metals - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for measuring helium, and more particularly to a method for measuring a small amount of helium contained in a metal. Conventionally, in a trace helium measurement method for measuring a trace amount of helium (He) contained in a metal, helium is extracted from the solid side into the gas phase by raising the temperature of the sample metal, and a gas chromatograph is used. Gas phase (gas) helium has been measured using the principle of a heat conduction detector (or TCD cell). However, in such a conventional technique, it is difficult to accurately measure helium because there is an interference and dilution action by the carrier gas coexisting with helium. In recent years, the behavior of helium in metals has been analyzed, and at least a two-digit improvement in sensitivity to the conventional measurement accuracy is desired. However, it is difficult to improve the lower limit of quantification with the conventional technique. There is a problem of being. The present invention was devised in view of such problems, and avoids measurement interference and dilution action due to coexisting gases other than helium (He), and is intended to improve the lower limit of quantification. An object of the present invention is to provide a method for measuring trace amounts of helium. For this reason, the method for measuring a trace amount of helium in a metal according to the present invention generates a sample gas by heating the sample metal and collects the sample gas in a collection bag. the impurity was removed by cooling the sample gas through the sample gas to the adsorption tube, it is characterized by measuring the helium is introduced into helium detector. Thus, for example, in order to avoid measurement interference caused by a coexisting gas other than measurement helium, the residual gas in the measurement apparatus is eliminated by repeatedly performing supply and exhaust operations using the carrier gas. further,
Eliminates interference in the measurement gas by helium in the air that is present in the collection bottle and passes through the collection bag and enters the measurement gas, or by helium diffusing from the sample gas system into the collection bottle due to repeated measurement In addition to purging the collection bottle, the collection bag volume is changed during sample gas collection, or the volume of the collection bag is changed when introduced into the adsorption tube. In order to prevent outside air from being mixed while the collection bag volume is changing in the collection bottle, a small amount of carrier gas is allowed to flow through the switching valve to prevent backflow of air and prevent helium quantitative interference. . On the other hand, the carrier gas mixed in the measurement gas or the gas in the instrument system and piping dilutes helium in the measurement gas, increases the lower limit of measurement, and deteriorates the measurement sensitivity. It is necessary to separate and remove. For this reason, carrier gas, mainly oxygen and nitrogen air components, moisture generated by high-temperature heating of the sample, carbon dioxide gas, etc. are quantitatively removed through the cooled adsorbent.
In the present invention, components other than hydrogen and helium are removed with an efficiency of 99% or more, and apparently interference of the measurement component to the helium measurement is completely eliminated. Furthermore, the time change of helium extracted from the metal in the heating furnace is a delay controlled by the change in the heating temperature of the sample metal and the pipe length, so the extracted helium-containing gas reaching the collection bag is It is not constant. For this purpose, the collection timing of the sample gas in the collection bag is selected by monitoring with a heat conduction detector, avoiding unnecessary collection of the carrier gas as much as possible and reducing the concentration due to dilution of the coexisting gas (ie, A program is set up to prevent lowering of detection limit and sensitivity), and sample gas is collected under optimum conditions. DESCRIPTION OF THE PREFERRED EMBODIMENTS A method for measuring a trace amount of helium in a metal according to an embodiment of the present invention will be described below with reference to the drawings. FIG. 1 is a schematic diagram showing a flow sheet thereof. In FIG. 1, reference numeral 30 denotes a hydrogen analyzer (also referred to as a hydrogen meter), which includes a heating furnace 2, a column 4, a TCD cell 5, and the like. In the helium measurement method of the present application, a sample metal (sample) 1 is obtained using the hydrogen analyzer 30.
From to generate helium gas, after collecting the collection bag 7, and cooled through a helium gas suction pipes 12, after removing the impurities, so as to measure the helium is introduced into helium test can 15 It has become. The sample metal 1 is placed at a predetermined position in the heating furnace 2 after being ultrasonically cleaned, dried and weighed with a solvent such as acetone before being brought into the heating furnace 2. Is done. And in this state, the heating furnace 2 is 2000 °
Helium (He) in metal 1 heated to C or higher
Is extracted into the gas phase, and argon gas (Ar gas) is sent out from the carrier gas cylinder 3 to push out He from the heating furnace 2. Nitrogen may be used instead of argon gas. Then, the coexisting gas and He are separated in the column 4, and through a TCD cell (detector) 5, He is collected in a Tedra bag (flexible gas collection bag) 7 in a gas collection bottle. Reference numeral 19 is a bypass exhaust valve (three-way valve) for switching the gas flow path between the exhaust gas and the sample gas collection bag 7 system, the carrier gas flow rate set from the heating furnace conditions, a temporary change due to heating expansion, Furthermore, the switching of the bypass exhaust valve 19 is controlled by monitoring the optimum time zone between the distribution of the carrier gas and the extraction of the heated He with the TCD cell 5. Here, the bypass exhaust valve 19 is closed when energized, and is de-energized (normal time)
A normally open (NO) solenoid valve that is open at the same time, the hydrogen analyzer 30 and the exhaust path communicate with each other when the valve is opened. The sample gas collection bag 7 is flushed in advance. In addition, the needle valve 8, the three-way valve 9 and the suction pump (air pump) 10 are operated to completely remove the remaining He and the interference of He in the atmosphere, thereby completely replacing the remaining gas in the system with the carrier gas. Keep it. The measurement gas collected in the bag 7 is sent to a sorption pump 13 built in the adsorption pipe 12. The adsorption tube 12 is cooled by the refrigerant 11. Further, the adsorbent 1 is disposed in the adsorption tube 12.
4 or a filler is filled, and except for low-boiling point gases such as hydrogen and He are trapped (collected) and removed from the system. [0013] Then, He is reached amount of He by mass spectrometer detector for analyzing mass sent to H e biopsy can 15 corresponding to He mass 4 is measured and recorded in the recorder 16 . The measured value is compared with a calibration line (calibration curve) using a gas having a known He concentration sent from the standard cylinder 17 to obtain an accurate He amount, and the concentration of He in the metal is calculated from the amount of the sample metal 1. . In the setting and operation of the analysis operation step, the measurement operation is advanced step by step based on a command from the operation panel 18 equipped with a predetermined time program. Reference numerals 6, 20, 21, and 22 are an open valve, a shut-off valve, a fine flow needle valve (fine flow valve), and a three-way valve, respectively. The operations of 8, 9, and 19 are all controlled based on a control signal from the operation panel 18. [0015] Analysis Operation time program after mounting of the sample metal 1, the system in the purge, heating of the furnace, the sampling timing to the collecting bottle of the sample gas, helium test through a trap from the collection bottle on the basis of the set flow rate The operation or the like to be introduced into the container 15 is programmed so as to conform to (match) the operation conditions in a stepwise manner and in the microanalysis. Next, experimental examples will be described. The experimental apparatus has the same configuration as that described with reference to FIG. An important technical element of the present invention is how He in the open air
Or the influence of coexisting gases other than the measurement He. For this reason, as shown in FIG. 1, in this test apparatus, it is set as the double structure which provided the flexible gas collection bag 7 in the collection bottle which collects the gas which extracted He. From the heating furnace 2, setting conditions for suppressing the influence of gas diffusion and permeation between the outer layer and the bag layer to such an extent that they do not hinder the determination of a very small amount of He, the setting conditions for selective removal efficiency of interfering substances, and Detailed study on setting conditions of a series of time programs leading to the He measurement system,
The operation program and steps as shown in FIG. 2 were determined through examination of the optimum operation conditions of the apparatus and equipment and the function of the system. The extracted operation conditions are shown below. Heating furnace: induction heating method, heating temperature 2200 ° C, heating time 3-10 min Sample metal amount: 0.1-5 g Sampling time exhaust: 0.6 min from furnace heating Bag collection: 1.4-5. 1 min (sampling time is governed by device characteristics. See FIG. 7) Carrier: High purity nitrogen gas (He <0.01 ppm),
Flow rate: 10 to 400 ml / min Column: MS-5A packed, length 200 mm Gas collection bottle: Internal volume 3000 ml Flexible bag: Tedora bag, Volume: Up to 3000 ml when inflated Purge times: Carrier gas supply / exhaust 3 times or more during bag operation Collection bottle carrier gas purge amount: 130% excess adsorption tube of gas movement maximum amount: Quartz powder filling / liquid air cooling Next, the time program shown in FIG. 2 will be described. It is set to achieve. 1. Collection of analysis sample gas: Carrier gas is present in the measuring apparatus tube, furnace, and the like. When the carrier gas coexists in the target sample gas when heating the sample metal 1 or when extracting He, the signal to be measured by the TCD detector 5 is monitored because the measurement He is diluted to reduce the measurement sensitivity. Then, the three-way valve 19 is operated so as to collect only the gas in the time zone containing He in the Tedora bag 7. 2. Purging in the sample collection bag (Tedora bag) 7: Tedla bag 7 as a flexible bag
The interior is purged with a carrier gas in advance, and the three-way valve 9 and the suction pump 10 are used for intake and exhaust. 3. In-pipe exhaust: The three-way valve 22 and the suction pump (air pump) 10 are operated to replace and purify the residual gas in the pipe. 4. Desorption / exhaust of impurities: The heater of the sorption pump 13 is operated to desorb / exhaust the impurities collected in the adsorption pipe 12. 5. Sa sampling / analysis: The fine flow valve 21 and the shutoff valve 20 are operated to perform sampling. Next, each operation will be described in detail with reference to FIG. 2. For example, purging, sampling of sample gas, and analysis are performed as follows. Flow path and tedlar bag 7 in preparation for purge sample gas collection
Purge inside. (1) The three-way valve 19 is switched from the exhaust side (NO side) (NC side), and the flow path is purged with the carrier gas in the hydrogen analyzer 30. Note that a bypass passage for bypassing the three-way valve 19 may be provided between the hydrogen analyzer 30 and the exhaust passage, and a two-way valve may be provided in this bypass passage. After switching the three-way valve 19 to the NC side, the two-way valve of the bypass passage is closed after a predetermined time (for example, 3 seconds) to purge the flow path. (2) And a predetermined time (for example, 2 minutes)
Thereafter, the three-way valve 19 is switched to the exhaust side. At the same time, in order to exhaust the gas accumulated in the tedra bag 7, the three-way valve 22 is opened (ON), the air pump 10 is turned on, and the gas accumulated in the tedra bag 7 is passed through the three-way valves 9 and 22 by the suction action of the air pump 10. And exhaust. As described above, when a bypass passage that bypasses the three-way valves 19 and 22 and a two-way valve that opens and closes the bypass passage are provided, the two-way valve is placed on the exhaust side immediately before the three-way valve 19 is switched to the exhaust side. To reduce the flow path switching shock. (3) When the exhaust in the tedora bag 7 is finished, the three-way valve 22 is switched to the closed (off) state and the air pump 10 is turned off. At the same time, the needle valve (two-way valve) 8 is opened to supply Ar gas (also referred to as zero gas because it does not contain helium to be detected) from the carrier gas cylinder (Ar gas cylinder) 3 to the tedra bag 7. (4) After about 1 minute, the needle valve (two-way valve) 8
Is closed and the supply of Ar gas is stopped. At the same time as this, the three-way valve 22 is opened and the air pump 10 is switched on to exhaust. (5) Thereafter, the operations in (3) and (4) are repeated, and the purge in the tedlar bag 7 is executed. Sample Gas Sampling (1) The sample metal 1 is introduced into the heating furnace 2 of the hydrogen analyzer 30 and heated and melted to develop hydrogen and helium in the gas phase.
The development status is observed with a monitor, and the sampling timing is determined. (2) When sampling of the sample gas is started, first, the three-way valve 19 is moved from the exhaust side (NO side) to the communication side (N
Switch to C side). As described in the purge, when a bypass path and a two-way valve for opening and closing the bypass path are provided between the hydrogen analyzer 30 and the exhaust path,
After switching the three-way valve 19 to the NC side, the two-way valve is closed after a predetermined time (about 3 seconds) to reduce the flow path switching shock. (3) Thereafter, after a predetermined time has elapsed (hydrogen +
When the sampling is finished, the three-way valve 19 is switched to the NO side. Further, when the above-described bypass path and the two-way valve for opening and closing the bypass path are provided, the two-way valve is switched to a closed state immediately before the three-way valve 19 is switched to the NO side to reduce the flow path switching shock. At the same time when the three-way valve 19 is switched to the NO side, the shutoff valve 20 is closed. 3. Analysis (1) First, by switching the three-way valve 9 to the sorption pump 13 side (NC side), as an open regulation of micro-flow needle valve 21, for introducing a sample gas Tedorabaggu within 7 to H e test can 15 . At this time, the shutoff valve 20 is manually opened.
Incidentally, as shown in FIG. 2, before the three-way valve 9 is switched to the NC side, remains NO side (the air pump 10 side), by being switched to the NC side, the sample gas Tedorabaggu within 7 H e It flows into the conduit inspection can 15 side. (2) When the analysis is completed, set the three-way valve 9 to NO.
In addition, the three-way valve 22 is opened and the air pump 10 is turned on to exhaust the sample gas remaining in the tedla bag 7. (3) When exhaust is completed, the three-way valve 22 is closed and the air pump 10 is switched off. If the exhaust performance of the sorption pump 13 is lowered after the sorption pump 13 is stopped for a long time, the regeneration is performed according to the following procedure. (1) The shutoff valve 20 is closed and the sorption pump 13 is separated from the hydrogen analyzer 30. (2) The release valve 6 is opened, and a vacuum pump (not shown) on the exhaust side of the release valve 6 is turned on substantially simultaneously. At the same time, a sorption pump heater (not shown) is turned on. (3) The adsorbent 14 is activated for about 3 hours. (4) The release valve 6 is closed and both the vacuum pump and the sorption pump heater (not shown) are both turned off. (5) Cool naturally until the sorption pump 13 reaches room temperature. Fig. 3 shows the ratio of the number of purges of the equipment / piping system to the atmospheric components remaining in the system in order to know how much the impurities remaining in the system affect the determination of He. It is. From the test results, it was confirmed that if the system was purged three times, the interference rate would be 1% or less and would not interfere with the He measurement. FIG. 4 shows the operating conditions of the adsorption tube held at a low temperature for concentrating the He in the measurement sample gas (that is, removing the coexisting impurity gas (atmospheric component)). Adsorbent 14 packed bed height 35mm, 100mm
In other words, the relationship between the pipe flow velocity and the removal rate of atmospheric components was obtained. For a removal rate of 99% or higher, a flow rate of 30
It was grasped that it should be made cm / sec or less. FIG. 5 shows a calibration curve obtained with a standard gas using this apparatus. The concentration of He is about 0.01 to 10.
It shows that linearity (linear) is established in the ppm range. FIG. 6 is an example of a chart during actual gas measurement.
The horizontal axis indicates time, and the vertical axis indicates the signal intensity of He. In the graph, the peak height is correlated with the concentration of He. FIG.
Is the heating and melting time of the sample metal 1 for measuring He,
This shows the relationship between the carrier gas flow rate and the He arrival time in the detector, and shows the proper time to collect He in the furnace gas accurately and with less impurities.
For example, at a carrier of 200 ml / min, if the sample is collected between 1.5 and 5.2 min from the start of heating of the furnace, the collection rate can be 99% or more and the measurement can be performed with an impurity minimum. Table 1 shows the He measurement results (results of the above experimental examples) of the standard sample carried out based on the above conditions. In addition, the result measured by the conventional measuring method is also shown. [Table 1] (Note) The measurement results in the table are the sample metal 0.370.
˜1.628 g of the particles are weighed, and is an average value or a calculated value of the analysis results of 7 times each. As described above, according to the method for measuring a trace amount of helium in a metal according to an embodiment of the present invention, it is possible to avoid measurement interference and dilution action of a coexisting gas other than helium (He) present in the internal conduit, and In addition to being able to prevent interference from, there is an advantage that it is possible to greatly improve the lower limit of measurement and improve the data fluctuation range. In addition, there is an advantage that it is possible to save and simplify the measurement. The present invention is not limited to the above-described embodiment, and various modifications can be made without departing from the spirit of the present invention. In particular, the present invention separates He and atmospheric components in the test gas by the adsorption method, concentrates He to increase the measurement sensitivity, and lowers the lower limit of quantification, and these techniques are set by special program settings. The point to deal with is not limited. As described in detail above, according to the method for measuring a trace amount of helium in a metal of the present invention, the sample metal is heated to generate the sample gas, and the sample gas is collected in the collection bag. after, to remove impurities by the sample gas is cooled through the sample gas to the adsorption tube, helium the sample gas
Since measuring the helium is introduced into detector has the following advantages. 1. Measurement interference and dilution effect due to coexisting gas other than helium existing in the internal pipe can be avoided and interference from outside the system can be prevented. 2. It is possible to greatly improve the lower limit of measurement and improve the data fluctuation range. 3. Labor saving and simplification of measurement can be achieved.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic diagram showing a flow sheet of a method for measuring a trace amount of helium in a metal according to an embodiment of the present invention. FIG. 2 is an example of a time chart showing a procedure of a method for measuring a trace amount of helium in a metal according to an embodiment of the present invention. FIG. 3 is a diagram showing the relationship between the number of purges and the atmospheric component interference rate in the method for measuring trace helium in metals according to an embodiment of the present invention. FIG. 4 is a diagram showing the relationship between the flow velocity in the adsorption tube and the removal rate of atmospheric components in the method for measuring trace helium in metals according to an embodiment of the present invention. FIG. 5 is a diagram showing an example of a calibration curve of helium gas obtained using the method for measuring a trace amount of helium in a metal according to an embodiment of the present invention. FIG. 6 is an example of a chart for measuring and analyzing helium gas in the method for measuring a trace amount of helium in a metal according to an embodiment of the present invention. FIG. 7 is a diagram showing the relationship between the furnace heating time and the helium extraction concentration in the method for measuring a trace amount of helium in a metal according to an embodiment of the present invention. [Explanation of Symbols] 1 Sample metal 2 Heating furnace 3 Carrier gas cylinder 4 Column 5 TCD cell (detector) 6 Opening valve 7 Sampling bag (flexible gas sampling bag or Tedra bag) 8 Needle valve 9 Three-way valve 13 Soap pump 15 Helium detection vessel 19 bypass exhaust valve (three-way valve) 20 shutoff valve 21 fine flow valve 22 three-way valve 30 hydrogen analyzer

Front page continuation (51) Int.Cl. ⁷ Identification symbol FI G01N 30/00 G01N 30/00 E (72) Inventor Yoichiro Yamaguchi 622, Funaishikawa, Tokai-mura, Naka-gun, Ibaraki Prefecture In-house ( 72) Inventor Yasuhiro Takeda 622, Funishikawa, Tokai-mura, Naka-gun, Ibaraki Prefecture 12 Nuclear Development Co., Ltd. In-house (56) Reference Japanese Patent Laid-Open No. 2001-162369 (JP, A) Japanese Patent Laid-Open No. 5-180822 (JP, A) JP-A-3-21867 (JP, A) JP-A-56-31642 (JP, A) Practical application 2-101269 (JP, U) (58) Fields investigated (Int. Cl. ⁷ , DB name) G01N 33/20 G01N 1/22 G01N 1/34 G01N 27/62 G01N 30/00

Claims (1)

(57) [Claims] [Claim 1] A sample gas is heated to generate a sample gas, and the sample gas is collected in a collection bag, and then the sample gas is passed through an adsorption tube to form the sample gas. the impurity was removed by cooling the, and measuring the helium is introduced into helium detector, trace helium measuring method in the metal.