JPH0731180B2 - Method and apparatus for diffusible hydrogen fractionation in molten metal - Google Patents

Description

TECHNICAL FIELD The present invention relates to a method and an apparatus for analyzing hydrogen in a refining process of molten metal.

Analysis of hydrogen in molten metal during refining process is important for process control and quality control of refining process. For example, in the steel industry,
In the vacuum degassing process, which is the next step of decarburization in the converter, the process control and quality control of the dehydrogenation process are performed by analyzing the hydrogen in the molten steel.

(Prior Art) For the analysis of hydrogen in molten metal, a method of quantifying the hydrogen gas collected in a sampler in which the molten metal is collected is usually adopted by gas chromatography that detects thermal conductivity. In this method, hydrogen in molten metal sampled in a sampler is diffused into a vacuum chamber that has been depressurized in advance, and an inert gas such as helium, nitrogen, or argon is sent to this vacuum chamber as a carrier gas and collected in the vacuum chamber. The hydrogen contained in the molten metal was introduced into a separation column to separate the hydrogen from other components, and then introduced into a thermal conductivity detector to quantify the hydrogen (Reference: New Experimental Chemistry). Course 9, Analytical Chemistry (II) 3.1 Gas Chromatography p60-71).

The thermal conductivity detector used in conventional analysis is as follows. When a sensitive element and a compensating element made of tungsten or the like are heated by a constant current and only a carrier gas such as helium is flowing, heat is removed from the two elements at a constant rate into the carrier gas. The element maintains a constant temperature. Next, when gas components with different thermal conductivities are mixed in the carrier gas, this steady state is broken, the temperature of the sensitivity element changes, and the resistance change of the sensitivity element is measured by the Wheatstone bridge circuit. The amount of hydrogen is determined (references p68-69 above).

(Problems to be Solved by the Invention) When the conventional gas chromatography using a thermal conductivity detector is applied to the object of the present invention, there are the following problems. (1) Since the thermal conductivity detector does not have selectivity, the gas sample diffused and collected in the molten metal sampler needs to separate hydrogen from other gas components through a separation column in advance. (2) The time required for analysis is long because each component in the gas sample is separated. (3) Since the principle of the thermal conductivity detector is to transfer heat,
Strict temperature control of about 0.1 ° C is essential. (4) Since the thermal conductivity detector contains a metal filament such as normally heated tungsten, it is impossible to use an oxidizing gas such as air as a carrier gas for preventing wear due to combustion oxidation. (5) Quantitative sensitivity and accuracy are insufficient for controlling the degassing process of molten metal.

To summarize the above problems, applying a conventional thermal conductivity detector to the analysis of diffusible hydrogen in molten metal requires too much time for analysis, and it is necessary to improve quantitative sensitivity and accuracy. Means that there is an inconvenience that an oxidizing gas such as air cannot be used as a carrier gas.

The present invention, by solving the problems as described above,
(EN) A method and an apparatus for analyzing diffusible hydrogen in molten metal, which has an extremely simple structure, is small and inexpensive, and is practically convenient.

(Means for Solving Problems) The present invention is characterized in that a semiconductor-type hydrogen gas detector is adopted in place of the conventional thermal conductivity detector when analyzing hydrogen in molten metal. The main points are as follows.

(1) 10% in the analysis method for quantifying diffusible hydrogen in a molten metal by using a sampler that collects the molten metal by cooling the molten metal after cooling
To 21% of oxygen at a constant concentration and subjected to dehumidification treatment as a carrier gas, the diffusible hydrogen gas trapped in the sampler is provided with a gas sample introduction pipe and an outlet pipe inside the semiconductor. Diffusible hydrogen analysis in molten metal, characterized by installing a hydrogen gas detection element and sending it at a constant flow rate into a measuring cell housed in a temperature-controlled room to determine the concentration of diffusible hydrogen trapped in the sampler Method.

(2) Carrier gas supply unit consisting of a carrier gas supply source containing a fixed concentration of 10% to 21% oxygen, a gas dehumidifier, a gas flow controller, a standard hydrogen gas cylinder, and a standard gas supply unit consisting of a standard hydrogen gas meter. Is connected to a sampler storage part consisting of a sampler storage chamber having a carrier gas inlet and a carrier gas outlet with a thin tube, and next to the sampler storage part, a diffusible hydrogen gas inlet pipe and an outlet pipe are provided, and a semiconductor is provided inside. Installed hydrogen gas detection element,
An analyzer for diffusible hydrogen in molten metal, characterized in that the measuring cell section housed in a thermostatic chamber is connected with a thin tube, and the cell section is equipped with a power supply device and a data processing device.

Hereinafter, the present invention will be described in detail.

Semiconductor gas detector (Reference: "Intelligence of semiconductor sensors" editor / publisher, Mimatsu Data System, p165-18
6) takes advantage of the fact that oxygen adsorbed on the surface of a metal oxide semiconductor such as SnO ₂ reacts with the reducing gas such as supplied hydrogen and is desorbed to change its electrical conductivity. To detect the gas concentration. Therefore, as described above, the principle of the thermal conductivity detector that detects the gas concentration by utilizing the fact that the heat of the sensitive element heated by the supplied sample gas is taken away and the electrical resistance changes Are different. Usually, among semiconductor gas detectors, hydrogen gas detectors use hydrogen molecules such as ethanol and carbon monoxide by vapor-depositing a SiO ₂ film for the purpose of having a molecular sieving function on the semiconductor surface of metal oxides such as SnO _2. Block larger reducing gas molecules at the surface,
It uses a semiconductor-type hydrogen gas sensing element having selectivity (reference: the above-mentioned reference, p184). In addition, this semiconductor type hydrogen gas detection element needs to maintain a high temperature state of 300 to 400 ° C. and supply oxygen in order to accelerate adsorption / desorption of a target gas and obtain reproducibility.

Up to now, the gas detector has been used such as issuing an alarm when the preset border line of the target gas concentration is exceeded, and the purpose is to carry out a strict quantitative analysis of gas as in the present invention. I didn't. The present invention newly adopts the semiconductor type hydrogen gas detecting element as described above for strict hydrogen analysis, and introduces a gas sample by the flow of the carrier gas that is forcibly controlled. Alternatively, omission of a separation column, relaxation of temperature control conditions for the atmosphere in which the detection element is installed, simplification of the device structure by using air as a carrier gas, simplification of analytical operation, and significant improvement in practicality have been achieved. is there.

The configuration and operation of the present invention will be described based on the measurement results of the characteristics of the detector used in the apparatus of the present invention shown in FIG. 1 and the apparatus of the present invention shown in FIGS. The apparatus of the present invention shown in FIG. 1 mainly includes a carrier gas supply unit, a standard gas introduction unit, a sampler storage unit, a measurement cell unit, an analysis result display unit, and the like. The carrier gas supply unit includes an air pump 1, a dehumidifier 14, and a gas flow rate controller 3. As the carrier gas, a gas containing 10% or more by volume of oxygen is suitable. It is easiest and most convenient to supply air containing 20.9% oxygen by a pressure pump or cylinder, but of course, a gas in which 10% or more oxygen is mixed with argon or nitrogen may be used. The oxygen concentration characteristic of the detection element was investigated by supplying an argon-based gas containing oxygen up to several tens of percent and 500 ppm of hydrogen at a constant flow rate to the semiconductor-type hydrogen gas detection element used in the present invention. FIG. 2 shows a measurement chart by the recorder. Oxygen concentration is 15
When it is%, the response speed of hydrogen detection by the detection element is also fast, it shows a constant output in a short time, oxygen is 15% without hydrogen.
Even when the gas was switched to an argon gas containing, the output quickly returned to the original baseline. When the oxygen concentration was 7.5%, the response was slightly reduced, and the speed at which the output returned to the baseline was also reduced. Furthermore, when the oxygen concentration is lowered to 3.3%, only a part of hydrogen can participate in desorption at the sensing element due to lack of oxygen concentration, so the response becomes faster, but a low value is shown and quantification is impossible. It also took a very long time for the output to return to the original baseline. Third
In the figure, the time required for the output once hydrogen was detected to return to the original base output from the time when the oxygen-mixed argon gas containing no hydrogen was supplied was plotted. Third
As shown in the figure, when the oxygen concentration was below 10%, it took an extremely long time below that. From these examination results, the composition of the carrier gas for feeding the sample gas to the semiconductor hydrogen gas detector used in the present invention is nitrogen containing 10% or more of oxygen, helium,
Obviously, a gas such as argon is suitable. Of course, 100% oxygen gas does not cause any problems. But,
As can be seen from the experimental results shown in FIG. 3, when the oxygen concentration in the carrier gas is set to 10% or more, the time to return to the base output becomes almost constant. Therefore, in practice, prepare carrier gases with these compositions. Considering the labor and cost, it is most convenient to use air containing 20.9% oxygen by volume. Therefore, it is suitable that the oxygen concentration in the carrier gas is in the range of 10% to 21%. Further, when the oxygen concentration in the carrier gas changes, the resistance value of the detector changes even if hydrogen gas does not exist. This proves that the oxygen adsorption to this sensing element directly controls the resistance value, and the oxygen concentration in the carrier gas changes from 10% to 21% and the flow rate changes each time. However, since it becomes difficult to quantify hydrogen, the gas flow rate controller 3 always supplies a constant flow rate. Further, the semiconductor type hydrogen gas detecting element is sensitive to the humidity of the gas. It is considered that this is because the humidity adsorbs in such a manner as to reduce the resistance value of the semiconductor, and it is necessary to dehumidify and dry by passing through a dehumidifier 14 composed of a column packed with silica gel or molecular sieve.

The standard gas introduction section is a section that supplies standard hydrogen gas from the cylinder 2 filled with standard hydrogen gas to the meter 5 and measures a fixed amount. When a fixed amount of standard hydrogen gas is measured by a sampling coil or the like, the flow path switch 4 is actuated so that the carrier gas sends the standard hydrogen gas to the measuring cell 7. Obtain the correlation between the output signal amount of the sensing element obtained at this time and the standard hydrogen amount introduced, and substitute the output signal amount of the gas sample collected by the actual molten metal sampler to determine the hydrogen concentration in the sample. Ask.

The sampler storage unit 6 is arranged in the middle of the carrier gas supply unit and the standard gas introduction unit and the measurement cell unit, and has a carrier gas introduction port for feeding the gas sample collected in the sampler to the measurement cell 7 by the carrier gas. A discharge port is provided. There are several types of molten metal hydrogen samplers, but an example of molten steel hydrogen sampler is
Shown in the figure. This is a thin steel pipe 15 made of thin steel plate, and a conduit 16 for solidifying the molten steel into a certain rod shape is housed in the molten steel, and a sealed tip 17 is immersed in the molten steel. Is sucked and then slowly cooled to completely release hydrogen in the molten steel and collect it in the vacuum chamber 18.
The thin steel tube 15 made of thin steel plate 15 and the portion corresponding to the vacuum chamber 18 made of crushable quartz glass are also used. The storage part 6 of the former steel sampler is shown in FIG.
The storage part 6 of the latter quartz glass sampler is shown in FIG. In the case of the steel sampler shown in FIG. 5, the sampler is inserted into the storage chamber 22, and the outer wall of the thin steel pipe 15 is tightened with the O-ring 20 to form a closed state, and the hydrogen released from the molten steel 19 collected is collected. A metal needle connected to the carrier gas introduction pipe and the discharge pipe is inserted into the vacuum chamber 18 to introduce the carrier gas, and hydrogen is sent to the measurement cell 7. In the case of the glass sampler 21 shown in FIG. 6, the sampler 21 is put in the storage chamber 22 and the lid 23 is covered, and the carrier gas is introduced from the direction of the arrow in FIG.
Flow it at a constant flow rate to discharge it toward the bellows 24 and the metal blade 25 by rotating the drive screw 26.
Is pressed down to crush the sampler 21, and the hydrogen collected is sent to the measuring cell 7.

The measurement cell unit is composed of a measurement cell 7 having a semiconductor hydrogen gas detection element 8 built-in and a temperature-controlled room 9 accommodating the measurement cell. As described above, the semiconductor hydrogen gas detection element 8 has a SiO ₂ film deposited on the surface of a metal oxide semiconductor, and a conductor such as an electrode and an iridium-palladium alloy for a heater is embedded therein. Although a sintered body of SnO ₂ is mainly used as a semiconductor, ZnO, TiO ₂ or the like may be used. This sensing element is originally intended to detect inorganic compounds such as hydrogen and CO, saturated chain hydrocarbons such as methane and ethane, unsaturated hydrocarbons such as ethylene and propylene, cyclic hydrocarbons such as benzene and toluene, and alcohols. Detects and has little selectivity.
However, the hydrogen gas detection element 8 manufactured by subjecting the SiO ₂ film to vapor deposition has excellent selectivity in hydrogen measurement. In the case of a molten steel hydrogen sampler, a slight amount of CO gas and the like coexist in the gas collected in the vacuum chamber 18 in addition to hydrogen. In the hydrogen gas detecting element 8, for example, CO needs to have a concentration of 500 times that of hydrogen in order to obtain the same output signal as hydrogen. If the amount of other components coexisting in the gas sample is large and the amount of hydrogen is affected, it is advisable to install a separation column in front of the measurement cell 7. Does not need The structure of the measurement cell 7 is such that the gas sample carried by the carrier gas can pass through the hydrogen gas detection element 8 quickly without being overwhelmed and the internal volume is as small as possible. A cylindrical tube shape with 28 at both ends is suitable. As described above, the hydrogen gas detection element 8 is constantly heated to 300 to 400 ° C., and the carrier gas having a constant flow rate of, for example, several hundred ml / min is constantly detected under a constant condition in the closed measurement cell 7. Element 8
The temperature of the sensing element 8 is constant because it only passes through the contact. Normally, the thermal conductivity detector used as a detector of hydrogen gas in gas chromatography is ± 0.1
In contrast to having to be installed under a strict temperature control condition such as ° C, the semiconductor hydrogen gas detecting element 8 used in the present invention
In this case, the temperature control of the measuring cell 7 to be installed may be remarkably gentle. However, since the object of the present invention is accurate quantitative analysis of hydrogen, the measuring cell 7 is installed in a thermostatic chamber controlled with an accuracy of ± 2 to 3 ° C.

(Example) An example in which molten steel (5 g) was sampled with a molten metal sampler and hydrogen in the molten steel was quantified using the apparatus of the present invention shown in FIG. 1 will be described. First, from the air pump 1 through the dehumidifier 14 filled with silica gel and molecular sieve,
Air adjusted to a flow rate of 3.5 l / min by the flow rate controller 3 is circulated as a carrier gas to the measurement cell 7 via the sampler housing section 6. Metering device 5 consisting of a standard hydrogen gas cylinder 2 and a flow controller 3 ', and a sampling coil etc.
A fixed amount of standard hydrogen gas measured by the above is supplied to the sampler storage part 6 by the air of the carrier gas by the operation of the flow path switching device 4.
It is sent to the measuring cell 7 via. The relationship between the hydrogen concentration and the output signal of the detection element 8 is obtained by the operation using this standard gas. Next, the molten metal sampler is stored in the sampler storage chamber 22, the drive screw 26 is operated while the air of the carrier gas is flowing to crush the sampler, and the hydrogen gas collected in the sampler is adjusted to about 50 ° C. The gas is introduced from the gas sample introduction pipe 27 into the measuring cell 7 inside. The gas sample comes into contact with and passes through the detection element 8 connected to the power source 10, and the exhaust pipe 28
Is discharged to the outside of the system. Semiconductor hydrogen detector 8 after a few seconds
The output signal of is passed through the amplifier 13 or attenuator, and the integrated intensity or peak height of the detected peak is displayed and recorded in the data processor 14. The hydrogen concentration in the molten steel sample is calculated and recorded from the relational expression between the standard hydrogen gas stored in advance and the output signal of the detection element 8.

Table 1 shows an example of the results obtained by collecting and analyzing molten steel having a composition equivalent to JIS SS41 in a ladle of a vacuum degassing apparatus that is an iron making facility. Table 1 also shows the quantitative accuracy when the molten steel at each hydrogen concentration level was repeatedly quantified 5 times. The quantification accuracy was good, and it was in good agreement with the analysis value by conventional thermal conductivity detection-gas chromatography.

Further, the present invention has extremely high quantitative sensitivity, and as described above, the carrier gas flow rate is set to a large flow rate of 3.5 l / min to dilute the gas sample and supply it to the detection element 8. Therefore, the sensitivity can be improved by reducing the carrier gas flow rate, and the sensitivity is 10 times or more higher than that of the conventional thermal conductivity detector.
An example of a calibration curve is shown in FIG.

The time required for the analysis according to the present invention is as short as 30 seconds or less, but it takes about 3 minutes in the conventional thermal conductivity detection-gas chromatography.

(Effects of the Invention) As described above, in the present invention, the quantification of diffusible hydrogen in molten metal has become extremely simple as compared with the gas chromatography with thermal conductivity detection that has been generally used conventionally. That is, compared to the conventional method, a separation column is not required, and the control conditions of the ambient temperature of the sensing element can be relaxed, so the device becomes cheaper, more compact and simple, and the handling of the device including maintenance is extremely difficult. It became easy. In addition, quantitative sensitivity and accuracy have been improved, reliability has been improved, and analysis has become possible in a short time. Furthermore, it became possible to include oxygen in the carrier gas, and the use of air that was cheap and easy to handle was realized. This eliminates the need for an inert gas cylinder, makes it possible to carry the device, and eliminates restrictions on the installation location, which is a great advantage in reducing analysis costs.

[Brief description of drawings]

FIG. 1 is an explanatory view of the overall configuration of the apparatus of the embodiment of the present invention, FIGS. 2 and 3 are the results of measuring the characteristics of the detector of the apparatus of the present invention, and FIG. 4 is the hydrogen in molten steel targeted by the present invention. FIGS. 5 (a) and 5 (b) and 6 (a) and 6 (b) are explanatory views of the sampler housing of the apparatus of the present invention, and FIGS. 7 (a) and 7 (b) are examples of calibration curves obtained in the present invention. 1 ... Air pump, 2 ... Standard gas cylinder, 3, 3 '... Gas flow rate controller, 4 ... Flow path switching device, 5 ... Standard gas meter, 6
... Sampler housing, 7 ... Measurement cell, 8 ... Semiconductor hydrogen gas detection element, 9 ... Constant temperature room, 10 ... Power supply device, 11 ... Magnifier,
12 ... Data processing device, 13 ... Analysis result display, 14 ... Dehumidifier, 15 ... Thin steel pipe, 16 ... Conduit, 17 ... Tip, 18 ... Vacuum chamber, 19
… Molten steel, 20… O-ring, 21… Glass sampler, 22
… Sampler storage chamber, 23… Stopper, 24… Bellows,
25 ... Metal blade, 26 ... Drive screw, 27 ... Gas sample introduction tube, 28 ...
Gas sample discharge pipe.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Yuuo Tozawa 1-6-6 Taito, Taito-ku, Tokyo Riken Kogyo Co., Ltd. (56) Reference JP 59-138956 (JP, A) JP 56 -31642 (JP, A) JP-A-58-158551 (JP, A) JP-A-49-29187 (JP, A) Actual development Sho-59-113743 (JP, U)

Claims (3)

[Claims] 1. An analytical method for quantifying diffusible hydrogen in a molten metal by using a sampler for collecting and cooling the molten metal after diffusing and collecting hydrogen contained in the molten metal. A dehumidified gas containing a constant concentration of 21% oxygen was used as a carrier gas, and a diffusible hydrogen gas collected in the sampler was equipped with a gas sample introduction pipe and an outlet pipe, and a semiconductor type was used inside. A method for analyzing diffusible hydrogen in molten metal, which comprises installing a hydrogen gas detection element and sending it at a constant flow rate into a measuring cell housed in a temperature-controlled room to determine the concentration of diffusible hydrogen trapped in the sampler. . 2. A carrier gas supply unit comprising a carrier gas supply source containing a constant concentration of 10% to 21% oxygen, a gas dehumidifier, a gas flow controller, a standard hydrogen gas cylinder, and a standard gas comprising a standard hydrogen gas meter. The supply part is connected with a thin tube to a sampler storage part consisting of a sampler storage chamber with a carrier gas inlet and a carrier gas outlet, and next to the sampler storage part, a diffusible hydrogen gas inlet pipe and an outlet pipe are provided. A semiconductor-type hydrogen gas detection element was installed in the measurement cell, and the measurement cell section housed in a temperature-controlled room was connected with a thin tube, and the cell section was equipped with a power supply device and a data processing device. Hydrogen analyzer. 3. A carrier gas supply unit pressurizes and supplies air, a pump or a cylinder filled with air, an air dehumidifier,
An analyzer for diffusible hydrogen in molten metal according to claim 2, comprising an air flow controller.