JPH05196569A - Hydrogen sensor - Google Patents

Abstract

PURPOSE:To obtain a sensor very quick in response speed and little in degrada tion due to repeated use by measuring the light intensity penetrating a catalytic metal layer or reflected from the catalytic metal surface. CONSTITUTION:A sensor has a catalytic metal layer 12 absorbing and separating hydrogen and gas including hydrogen compounds and a detector 10 constituted of, for example, platinum or paradium formed on the base 11. In the middle of a channel pipe 21 for the sensor gas, a light penetration chamber 22 is provided, openings 23 are provided on the penetration chamber 22 and the openings are sealed air-tight with glass windows 24. Inside of the one of the glass windows 24, a hydrogen detector 10 is fixed as to expose the catalytic metal layer 12 to the hydrogen gas side. On the outside of the hydrogen gas channel pipe 21, a light source 1 to cast a light beam 2 for penetrating the glass window 24 is arranged and on the opposit side, a light detector 3 to receive the light beam 2 is arranged. The received light intensity is measured with a meter 4 connected with the light detector 3. If hydrogen density increases, the penetration light intensity increases and the reflection light intensity decreases.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a sensor for detecting the presence of hydrogen gas in an oil refining plant or equipment or device handling hydrogen gas in a safe state by optical means.

[0002]

2. Description of the Related Art Conventionally, a catalytic combustion system or a semiconductor system has been widely used as a gas sensor. The catalytic combustion method is a method in which a thin wire of platinum or palladium is preheated as a heater, and the presence of hydrogen gas is detected by electrically detecting the change in conductivity caused by the contact and reaction of hydrogen gas. is there.

On the other hand, in the semiconductor system, a detector is used in which a layer of oxide semiconductor such as tin oxide or zinc oxide is formed on an insulating substrate, and a pair of electrodes opposed to each other with a constant interval are provided thereon. .. When hydrogen gas comes into contact with this detector, electrons are exchanged with the oxide, and as a result, the carriers in the semiconductor layer increase, the electric resistance decreases, and the current between the electrodes increases. That is, the presence of hydrogen gas can be known by detecting this change in current. However, in this method, it is necessary to preheat from the back surface of the insulating substrate when detecting hydrogen gas.

In any of the above-mentioned methods, it is necessary to heat the sensor in advance in order to detect hydrogen gas. Therefore, safety and explosion-proof measures are indispensable in an atmosphere of a flammable gas such as hydrogen gas. Since it is constantly heated, its deterioration is fast and there is a problem in reliability.

Recently, as a means for solving these problems,
A method of optically detecting hydrogen gas has been proposed. In this method, a thin film of a catalytic metal having a function of adsorbing and dissociating hydrogen gas, for example, palladium is used as a surface layer, and an oxide that is reduced by the dissociated hydrogen, for example, a thin film of tungsten oxide is used as a base layer on a substrate by vapor deposition or the like. To form a sensor.

When hydrogen gas comes into contact with this sensor, hydrogen is first adsorbed and dissociated in the palladium layer on the surface, and then the generated atomic hydrogen diffuses into the underlying tungsten oxide layer to cause coloring. Hydrogen gas is detected by measuring the change in light transmittance due to this coloring. Such an optical system is essentially safe because it does not require any means such as heating, has good selectivity for detecting hydrogen gas, and is an excellent method for detecting flammable gas called hydrogen gas.

[0007]

However, since tungsten oxide has extremely poor water resistance, it is difficult to prolong the life of the sensor, and the reaction characteristics with respect to hydrogen gas change remarkably over time, which poses a practical problem. It was

[0008]

Means for Solving the Problems In the process of studying the above-mentioned hydrogen sensor of the optical detection system, when the hydrogen comes into contact with the catalyst metal layer, the light transmittance of the catalyst metal layer itself is changed to the hydrogen concentration. In addition to the proportional increase, this change in transmittance occurs very rapidly, and the reproducibility of the phenomenon is extremely high. Therefore, hydrogen change can be detected by directly measuring the change in light transmittance or reflectance of the catalytic metal layer. High sensitivity,
I found that I can do it with fast responsiveness. The present invention is based on this finding.

That is, in the hydrogen sensor of the present invention, a catalyst metal layer that adsorbs and dissociates hydrogen or a hydrogen-containing compound gas, for example, a detector formed by forming platinum or palladium on a substrate, and light is incident on this catalyst metal layer. And a received light amount detector for measuring the amount of light transmitted through the catalytic metal layer and / or the amount of light reflected from the surface of the catalytic metal layer.

The substrate used in the present invention is merely for holding the catalytic metal layer and is not particularly limited in material and shape as long as it is a material that does not substantially react with dissociated hydrogen, and a dielectric such as glass. General inexpensive materials such as organic substances and metals can be used.

However, if the sensor of the present invention is used to measure the amount of transmitted light, it is necessary to use a transparent body as the substrate. The substrate may be a transparent body or an opaque body as long as it is a method of measuring the amount of reflected light.

[0012]

The reason why the light transmittance of the catalytic metal layer is increased (the reflectance is decreased) by the contact with hydrogen in the present invention has not been fully clarified, but it is presumed as follows.

That is, the hydrogen gas contacted on the surface of the catalytic metal layer is adsorbed and dissociated, and the generated atomic hydrogen diffuses into the layer to form a hydride with the metal, thereby reducing the surface reflectance. However, the spectral transmittance increases. The hydride of the metal in this case depends extremely strongly on the hydrogen partial pressure, and the rate of decrease in reflectance is proportional to the concentration of hydrogen gas. When the contact with hydrogen gas is cut off, the hydride decomposes and returns to the original reflectance, which is detected as an increase in reflectance or a decrease in transmitted light.

In general, a catalytic metal such as palladium is also excellent in environmental resistance such as water resistance, and the detector of the sensor of the present invention can be constituted only by this catalytic metal layer and a substrate for holding the catalytic metal layer. Even below, it has extremely good weather resistance.

[0015]

EXAMPLE FIG. 1 shows an example of a hydrogen detector used in the hydrogen sensor of the present invention. The detector 10 includes a thin film layer 12 made of a catalytic metal that adsorbs and dissociates hydrogen or a hydrogen-containing compound gas, for example, a layer of palladium (Pd) is formed on the surface of a transparent substrate 11 such as glass by vapor deposition, sputtering, or other known thin film formation. It was formed in close contact using the method.

FIG. 2 shows an example in which the hydrogen sensor of the present invention is constructed by using the above detector 10. In the figure, 21
Is a hydrogen gas flow passage pipe, and a translucent chamber 22 is provided in the middle of this flow passage. The translucent chamber 22 is provided with openings 23 on opposite side walls sandwiching a hydrogen gas passage, and the openings 23 are hermetically sealed by a glass window 24.
Inside one of the glass windows 24, the hydrogen detector 10 described in FIG. 1 is attached by exposing the catalytic metal layer 12 to the hydrogen gas side.

A light source 1 for projecting the light flux 2 is arranged outside the hydrogen gas flow passage pipe so as to pass through the glass windows 24, 24, and on the opposite side of the transparent chamber 22. A photodetector 3 for receiving the light flux 2 is arranged, and a measuring device 4 connected to the photodetector 3 measures the amount of received light.

FIG. 3A shows the result of an experiment for hydrogen detection using the sensor of the present invention. The graph in FIG. 3 (A) is
100% hydrogen concentration in the room equipped with the detector of the present invention.
The operation of introducing the gas of (3), interrupting the introduction after a lapse of a certain time, and introducing again was repeated at a constant interval, and during that period, the light transmittance of the detector was continuously measured using light having a wavelength of 780 nm. In the figure, the portion marked with “H ₂ in” by the arrow is the time when hydrogen gas was introduced, and the portion marked “H ₂ disconnected” was the time when the introduction was stopped.

As a comparative example, a conventional optical hydrogen gas sensor, that is, a sensor having a two-layer film structure in which a tungsten oxide (WO ₃ ) film is provided on a substrate and a palladium film is provided on the film, is used. The change in transmittance due to the coloring of WO ₃ due to the hydrogen dissociation of was measured and the result is shown in FIG. 3 (B).

As shown in FIG. 3A, in the hydrogen detector of the present invention, a reaction occurs instantaneously with the contact of hydrogen gas, which is detected as an increase in the transmittance of output light. Also, when the contact with hydrogen gas is cut off, the original state is quickly restored.

As is clear from the comparison between FIGS. 3A and 3B, the response response of the present invention is one digit or more faster than that of the conventional colored photosensor.

FIG. 4 shows a numerical example of the relationship between the light transmittance and hydrogen concentration of the detector of the present invention. In the figure, the vertical axis represents the optical density of the light transmittance, that is, the absolute value of the logarithmic value of the value obtained by dividing the amount of emitted light by the amount of incident light, and the horizontal axis represents the hydrogen gas concentration in logarithm.

As shown in the figure, the absolute sensitivity is proportional to the film thickness of palladium. When the palladium film thickness is 80 nm, 1
Even at a hydrogen gas concentration of about 000 ppm, the light transmittance changes by 2%.

FIG. 5 and FIG. 6 show the results of repeated reproducibility comparison experiments for the detector of the present invention and the conventional colored sensor. As you can see from Figure 5,
Although the detector of the present invention does not show deterioration even when the number of times of introducing hydrogen gas exceeds 100 times, the conventional colored sensor shows remarkable deterioration as shown in FIG.

Further, FIGS. 7A and 7B show FIGS.
The same evaluation as is shown by the change in transmittance with time. As is clear from the figure, the detector of the present invention is 1
The responsiveness does not change even after 000 hours, whereas the conventional colored sensor deteriorates the responsiveness.

8 to 11 show various examples in which a hydrogen sensor is constructed by using the detector of the present invention.

Of these, FIGS. 8 and 9 are examples of the transmission type. In FIG. 8, the light of the light source 1 located at a distant place is guided to the hydrogen gas flow path by the optical fiber 30A, and the light emitted from the fiber is emitted. After being converted into a parallel light flux by an optical lens 31A such as a gradient index lens, the parallel light flux is projected onto the hydrogen detector 10 of the present invention arranged in the hydrogen gas flow path, and the transmitted light is condensed by the other lens 31B. It is configured such that it is incident on the fiber 30B and is guided to the photodetector 3 located at a remote place.

Further, in the example of FIG. 9, for example, the glass substrate 11
A waveguide 32 composed of a region having a refractive index larger than that of the surroundings is formed by ion exchange or the like, and a palladium layer 12 is formed on the upper surface of the waveguide, so that the light from the light source 1 is transmitted through the optical fiber 3
The light emitted from the waveguide 32 is guided to the photodetector 3 by the optical fiber 30B. In the case of this structure, the evanescent wave of the light passing through the waveguide 32 comes into contact with the palladium layer 12 and is affected by the change in the transmittance of the palladium layer 12, and the amount of light emitted from the waveguide changes.

FIG. 10 and FIG. 11 show an example in which a reflection type sensor is constructed. In FIG. 10, the detector 10 of the present invention is arranged on one side wall surface in the hydrogen gas flow path, and the incident optical fiber 30A and the lens 31A are arranged on the other side wall opposite thereto.
A pair of the output optical fiber 30B and the lens 31B is arranged so that the light source light is projected onto the surface palladium layer 12 of the detector 10 and the light reflected by the surface is received.

Further, in the example of FIG. 11, the substrate 1 of the detector 10 is
A 1/4 pitch length gradient index lens is used as 1, and a palladium layer 12 is provided on one surface of the lens,
This surface is exposed in a hydrogen gas flow path (not shown), and the other side of the lens has an optical fiber for incidence 30A symmetrical about the central axis.
And the ends of the output optical fiber 30B are connected to each other. In this structure, the light diffused and emitted from the incidence fiber 30A is incident on the inner surface of the palladium layer 12 as a parallel light flux, is condensed after being reflected, and enters the emission fiber 30B.

Among the examples shown above, the configurations of FIGS. 9 and 11 have an advantage that the detection light does not pass through hydrogen gas or air as in the other examples, so that it is not adversely affected by dust or the like. There is.

<Example> Using a high-frequency magnetron sputtering device, palladium metal as a target of 1 mT
Sputtering was performed on the glass substrate surface in an argon gas atmosphere of orr to form a palladium thin film with a thickness of 10 to 20 nm. The high frequency power at this time is 100W
The sputter rate was 4 nm / sec.

Using the hydrogen detector thus obtained, FIG.
A hydrogen gas to be detected having a predetermined hydrogen concentration was produced by diluting 100% hydrogen gas with dry air and introduced into an airtight cell. When the change in light transmittance of the detector was measured, it was shown in FIG.
The response characteristics shown in (A) and FIG. 5 were obtained.

Next, a plastic (polycarbonate) substrate was used as a substrate and the same sputtering method was applied to form a detector having a thin film layer structure. In this case, since the temperature of the substrate must be 100 ° C. or lower, the vapor deposition temperature was lowered to form the film.

In all cases, the contact rate with hydrogen gas increased the transmittance, and when the hydrogen gas was cut off, the original state was restored.

[0036]

The sensor according to the present invention can detect all hydrogen gas as a light signal such as a change in reflectance and a change in transmittance, and has a small size, high reliability, electromagnetic induction resistance, fire resistance, explosion proof, and the like. The characteristics can be fully utilized.

Further, unlike the conventional colored type optical hydrogen detection sensor, rather than utilizing the multi-step reaction of hydrogen dissociation in the catalytic metal layer and the resulting color change of the oxide below, the catalytic metal is not used. Since the surface phenomenon of reducing the light reflectance (increasing the transmittance) due to hydride generation on the surface of the layer is utilized, the response speed is extremely fast, reversible and extremely stable.

Further, it can be said to be an epoch-making sensor in that the structure is simple and the mass productivity is high, and the conventional optical sensor is expensive, and the preconceived idea is not taken into consideration.

[Brief description of drawings]

FIG. 1 is a sectional view showing an example of a detector used in a sensor of the present invention.

FIG. 2 is a sectional view showing a first embodiment of the present invention.

FIG. 3 is a graph showing a comparison of response characteristics between the detector of the present invention (A) and a conventional optical hydrogen sensor (B).

FIG. 4 is a graph showing characteristics of the detector of the present invention with respect to hydrogen concentration.

FIG. 5 is a graph showing the results of the number of times the reproducibility of the detector of the present invention is repeatedly used.

FIG. 6 is a graph showing the results of the number of times the reproducibility of a conventional optical hydrogen detection sensor is repeatedly used.

FIG. 7 is a graph showing the results of reproducibility of the detector of the present invention (A) and the conventional optical hydrogen detection sensor (B) repeatedly used over time.

FIG. 8 is a sectional view showing a second embodiment of the present invention.

FIG. 9 is a sectional view showing a third embodiment of the present invention.

FIG. 10 is a sectional view showing a fourth embodiment of the present invention.

FIG. 11 is a sectional view showing a fifth embodiment of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 light source 2 light flux 3 photodetector 4 light receiving amount measuring instrument 10 detector 11 substrate 12 palladium (catalyst metal) layer 21 hydrogen gas flow path 22 translucent chamber 23 opening 24 glass window 30A, 30B optical fiber 31A, 31B lens 32 guide Waveguide

Claims (2)

[Claims] 1. A detector formed by forming a catalyst metal layer for adsorbing and dissociating hydrogen or a hydrogen-containing compound gas on a substrate, a light source for making light incident on the catalyst metal layer, and transmitting through the catalyst metal layer. A hydrogen sensor comprising: a light receiving amount detector for measuring a light amount or / and a light amount reflected from the surface of the catalytic metal layer. 2. The hydrogen sensor according to claim 1, wherein the catalytic metal is palladium (Pd).