JPH1010048A - New style hydrogen detecting element, its manufacture and gas sensor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reconcile high responsiveness and high sensitivity regardless of the presence or absence of oxygen content of a gas, and improve the detecting performance by discretely adhering a catalytic metal in dot form on a transparent base to form a thin layer. SOLUTION: A dotted catalytic metal thin layer 11 in which a catalytic metal is discretely adhered as a dotted pattern is formed on a transparent base 12 having transparency and optical homogeneity such as glass. As the catalytic metal forming the thin layer 11, a metal or metal, oxide called hydrogenated catalyst is used, and palladium as pure metal and a binary alloy of Pd with a IB group metal of the periodic table are more preferably used. For the formation of the thin layer 11, sputtering method of sputtering the catalytic metal as a target on the base 12, or evaporation method of adhering the catalytic metal vapor onto the base is used. The resulting hydrogen detecting element 10 is used, by which the responsiveness and sensitivity of a gas sensor can be improved, and the life of the detecting element 10 can be extended.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical hydrogen sensor which is installed in a city gas pipe, a combustion apparatus, a petrochemical plant, or the like, and detects the concentration of hydrogen gas with high reliability.

[0002]

2. Description of the Related Art In general, catalytic combustion type, semiconductor type, solid electrolyte type and optical sensors are known as combustible gas sensors. Of these, none of the three operate in anoxic conditions, and therefore cannot measure the hydrogen concentration in a normal city gas conduit containing no oxygen. Optical sensors, on the other hand, are useful for detecting hydrogen in gases that contain hydrogen and other flammable gases, such as city gas, regardless of the presence or absence of oxygen. Then, an optical sensor that operates even in the absence of oxygen is particularly suitable for explosion-proof measures for detecting a gas that easily generates an explosive mixed gas.

In general, a main part of an optical sensor detects a detector which generates a change in coloring or transmitted light or reflected light upon contact with a gas, a light source which projects a light beam on the detector, and detects a light beam passing through the detector. It comprises a photodetector, a measuring instrument for measuring a signal emitted from the photodetector and displaying it as a received light amount, a gas flow path for introducing gas to the detector, and the like.

[0004] Conventionally, as an optical detector used for an optical sensor for detecting hydrogen gas, for example, Japanese Patent Publication No. 3-15975 discloses a catalytic metal having an action of adsorbing hydrogen molecules and dissociating it into atomic hydrogen, for example, palladium. A detector is disclosed in which a thin film of (Pd) is used as a surface layer, and an oxide chemically reduced by the dissociated atomic hydrogen, for example, tungsten oxide (WO ₃ ) is used as a base layer and stacked on a substrate. Have been. WO ₃ reacts with the dissociated hydrogen to form a color, and the change in light transmittance due to the coloring is measured to detect hydrogen gas. However, WO ₃ has a practical problem since it has extremely poor water resistance.

As another optical hydrogen detector, an optical hydrogen detector formed by forming a thin film of the above-mentioned catalytic metal, for example, Pd on a substrate is disclosed in Japanese Patent Application Laid-Open No. 5-196569. This is to detect hydrogen gas by measuring the change in light transmittance or light reflectance of the Pd film caused by the action of dissociated hydrogen, and the response time is one order of magnitude faster than that of a detector using oxide. Good detection performance over time.

In the detector using the above-mentioned Pd film, the light reflectance of the thin film surface is reduced by the hydride generation of the thin film Pd in a hydrogen atmosphere, and the light transmittance of the Pd film itself is correspondingly reduced. Is to be increased. Therefore, the shorter the distance that hydrogen diffuses into the Pd film, the faster the reaction rate of the reversible hydrogenation reaction and the faster the response of detection. That is, the responsiveness improves as the thickness of the Pd film decreases.

However, when the Pd film is thinned by the conventional technique, when the hydrogen concentration is lower than a certain level, the increase in the light transmittance, which increases due to the presence of hydrogen in the gas to be detected, becomes very small, and the detection becomes difficult. That is, when the Pd film is made thin, the change in the light transmittance at which hydrogen can be detected gradually decreases, and in this sense, the detection sensitivity is significantly reduced, which is a practical problem.

Conversely, if the Pd film is thickened, the detection sensitivity is improved, but the so-called response time from when hydrogen reaches the detector surface to when the detector emits a detection signal becomes longer,
In this sense, the detection responsiveness deteriorates, which is a practical problem in the detector using the Pd film according to the related art.

[0009]

SUMMARY OF THE INVENTION Accordingly, the present invention provides an optical hydrogen detector using a catalytic metal, which quantitatively detects hydrogen in a mixed gas of hydrogen and other flammable gas such as city gas. In this case, it is an object of the present invention to achieve both high responsiveness and high sensitivity and to significantly improve detection performance regardless of the presence or absence of oxygen in the gas and in a range where the hydrogen content is low.

In a conventional detector using a Pd film,
Volume expansion occurs when Pd chemically absorbs hydrogen to generate hydrides, and volume contraction occurs when Pd desorbs hydrogen and returns to Pd again. That is, in the conventional detector, it is essentially unavoidable that the Pd film is damaged by the repeated stress of expansion and contraction. When the thickness of the Pd film is reduced in order to reduce the damage to the Pd film, as described above, the sensitivity for detecting hydrogen decreases, which is a practical problem.

Therefore, another object of the present invention is to dramatically increase the life of the optical hydrogen detector while maintaining the detection sensitivity of the optical hydrogen detector using a catalytic metal at a practical level. is there.

[0012]

Means for Solving the Problems The present inventors have studied on an optical hydrogen sensor using a Pd film based on a completely new idea, and have gradually reduced the thickness of a Pd film formed on a transparent substrate. In the case where a thin layer in which metal Pd is no longer in the form of a continuous thin film but is discretely applied like a spot pattern is formed, the Pd film of the prior art is formed in air and in hydrogen. It has been found that the light transmittance changes in the exact opposite direction.
In addition, since Pd is discretely deposited on the substrate in this manner, the repetitive stress generated by the adsorption and desorption of hydrogen can be reduced, so that the life of the detector is dramatically increased. The present invention has been completed using such a completely new principle.

In other words, when a thin layer in which metal Pd is discretely applied on a transparent substrate is exposed to a hydrogen atmosphere, the light transmittance becomes lower than the air transmittance in accordance with the hydrogen concentration. As a new finding, a hydrogen concentration can be detected with good responsiveness and high sensitivity by utilizing this phenomenon, and a detector having an extremely long life can be constructed.

That is, the present invention relates to a hydrogen detector comprising a thin layer (c) formed on a transparent substrate (a) by a catalytic metal (a) which adsorbs and dissociates hydrogen. An invention of an optical hydrogen detector, wherein a catalytic metal (A) is discretely deposited on the surface of the substrate (A) in a spot-like manner.

Further, the present invention is characterized in that a thin layer (c) formed by dispersing and applying the above-mentioned catalyst metal (a) in spots is formed on both the front and back surfaces of the transparent substrate (a). It is an invention of an optical hydrogen detector. By configuring the detector in this way, it was possible to achieve both high sensitivity and high responsiveness with respect to hydrogen detection and to achieve a longer life of the detector.

The structure of the detector according to the present invention will be described in detail. First, the transparent substrate (a) used in the present invention is a solid simply for holding a thin layer of the catalyst metal, but it is essential that the material does not substantially react with dissociated hydrogen. It is essential to have transparency and optical homogeneity in which the presence of hydrogen can be easily detected by a change in the amount of transmitted light. Specifically, synthetic resins such as glass and polycarbonate resin can be exemplified. The shape is preferably a flat plate shape or a condensing lens shape with a smooth surface in order to transmit light efficiently.

The catalyst metal (A) used in the present invention may be a metal or metal oxide commonly called a hydrogenation catalyst. As the metal, a pure metal or an alloy used for high-purity hydrogen purification can be used. Of the pure metals, platinum group metals are preferred. More preferably, palladium is used. Examples of the alloy include binary alloys of Pd and Group Ib metal of the periodic table (for example, Pd 70% by weight, Ag 30% by weight, etc.), and Pd and Id
A ternary alloy with a group b metal (for example, Pd 75% by weight, Ag2
0% by weight, 5% by weight of Au), Pd and Ib and XIII
(For example, 70% by weight of Pd, 25% by weight of Au, 5% by weight of Pt), and a quaternary alloy (for example, Pd6)
5% by weight, Ag 28% by weight, Au 5% by weight, Ru 2% by weight) and the like.

Next, a thin layer (c) which is a component of the present invention.
Is such that when the above-mentioned catalyst metal (A) is applied to the substrate (A), the catalyst metal (A) is discretely applied like a spot pattern and two-dimensionally applied. Such a spot-like deposition is empirically thinner than 2 nm when using Pd and a glass substrate when calculating the average thickness of the deposited metal as a thin layer. The upper limit of the deposition amount also depends on the metal used and the material of the substrate and the method of deposition,
It cannot be specified numerically.

Although it is difficult to express numerically the lower limit of the amount of catalyst metal (a) deposited, it is effective if the hydride expands when the thin layer is brought into contact with hydrogen to substantially fill the gaps between the spots. Since the light transmittance is reduced as a result of the gap filling, the lower limit of the amount of deposition that can detect a change in the intensity of the transmitted light passing through the detector is the lower limit of the amount of deposition as the gas sensor.

The thin layer (c) may be applied to only one surface of the transparent substrate (a), or may be applied to both front and back surfaces. By applying the coating on both sides, uneven coating can be averaged, so that the deviation of the detection performance is reduced and the quality of the detector is stabilized. Further, since the amount of change in the intensity of the transmitted light is also amplified, the sensitivity is also improved.

As a method of forming the thin layer, a sputtering method in which a catalyst metal is sputtered on a substrate using a target as a target, or a vapor deposition method in which a catalyst metal is melted in a vacuum and vapor generated is attached to the substrate, is used in the art. Can be used under well-known raw materials and conditions commonly used.

The effect of using the thin layer (c) in which the catalytic metal (a) is discretely applied in spots in the present invention is considered as follows. That is, the catalyst metal (A) discretely deposited on the surface of the transparent substrate (A) in the form of spots does not cause any physical or chemical change when hydrogen does not exist in the gas to be detected. Is directly passed through the gap between the speckled metals and detected by the photodetector. The light transmittance at this time is T.

However, when hydrogen is mixed in the gas to be detected, the catalytic metal (A) chemically reacts with hydrogen to generate hydride, and thus the spotted catalytic metal (A) is converted to hydrogen. The concentration causes volume expansion corresponding to the concentration, which leads to a reduction in the gap between the metal spots and the closing of the gap. In this state, the light transmitted through the spot-like metal is detected by the photodetector, so that the light transmittance decreases monotonically with increasing hydrogen concentration. Assuming that this light transmittance decrease is ΔT, the light transmittance T− △ when hydrogen is present.
T is measured. In a specific thin metal layer (c), the decrease ΔT in light transmittance due to the expansion action of the spot-like metal corresponds to the hydrogen concentration on a one-to-one basis, and therefore, T in the absence of hydrogen. By measuring the difference from T−ΔT in the presence of hydrogen, a detector that detects the hydrogen concentration using a new principle completely different from the prior art could be constructed.

[0024]

FIG. 1 shows an example of a detector according to the present invention. The detector 10 is formed by forming metal Pd on the surface of a transparent substrate 12 in the form of a spot-like thin layer 11 and attaching it. FIG. 2
Shows an embodiment of the detector according to claim 2, in which a spot-like thin layer 11 of metal Pd is applied to both front and back surfaces of a transparent substrate 12, and the thin layers on both sides are the flow of the gas 8 to be detected. And the light flux is transmitted through the thin layers on both sides.

The detector according to the first and second aspects of the present invention based on the configuration described above includes the following embodiments. [Embodiment 1] The optical hydrogen detector according to claim 1 or 2, wherein the catalyst metal (A) is a platinum group metal.

[Embodiment 2] The optical hydrogen detector according to claim 1 or 2, wherein the catalytic metal (a) is palladium.

FIG. 3 shows an example of a gas sensor using the detector of the present invention. A gas 8 to be detected is introduced into a light-transmitting chamber 22 containing an optical hydrogen detector 10 fixed so as to face an opening 23 provided with a glass window 24, and a light beam 2 emitted from a light source 1 using a semiconductor laser is split by a beam splitter. The one split by 3 is irradiated on the detector 10, and the transmitted light 5 and the other light split by the beam splitter 3, changed the course by the mirror 9, and transmitted through the transparent substrate 12 are captured by the scanner 6. The difference between the two intensities is displayed on the multimeter 7. The gas sensor includes, for example, a change in emission intensity of the light source 1 due to a change in environmental temperature, or a detector 1 due to fine dust in the gas flow pipe 21.
Noise is generated due to 0 or a decrease in the light transmittance of the glass window 24. Therefore, in the optical gas sensor of the present invention, the transparent substrate 12 having no thin layer adhered is disposed near the detector 10 for reference to remove noise,
The configuration is such that the change in transmitted light can be measured with higher accuracy.

The manufacturing method of the optical hydrogen detector 10 of the present invention and the result of a hydrogen detection performance test by the gas sensor of the present invention using the same will be described as examples.

【Example】

Example 1 Method for Manufacturing Detector 10 of the Present Invention Pd was produced using a high-frequency magnetron sputtering apparatus.
Using a metal as a target, sputtering was performed on the glass substrate surface in an argon gas atmosphere at 1 mTorr. High frequency output: 20 W, sputter rate: 0.12 nm / s
ec, the thin layer generation time was 10 seconds. Under this condition, a thin layer of metal Pd was formed on one side of the glass substrate. The average thickness of the Pd thin layer was 1.2 nm.

Measurement of Light Transmittance and Response Time Using the gas sensor shown in FIG. 3, a 100% nitrogen gas (N ₂ ) is first flowed through the gas flow pipe 21 and a wavelength of 780 nm using a semiconductor laser as a light source. Detector 1 using light
The light transmittance T of 0 was measured by the multimeter 7. Then while flowing about 5 minutes gas is switched to a mixed gas of H ₂ 5 vol% and N ₂ 95 vol%, the light transmittance T-△ T and measuring the response speed, the light is switched back to 100% N ₂ The transmittance T and the response course were measured. The measurement results are shown in FIG. It can be seen that both the response to the introduction of H _{2 and} the recovery of T due to the suspension of the introduction are completed within 3 seconds.

Repetition Characteristics of Light Transmittance and Response Time As described above, the effect on performance caused by repeating the switching cycle of 100% N ₂ gas and H ₂ 5% by volume mixed gas every 5 minutes was examined by the detector. Initial start of use and 100
About the light transmittance and response time after repeated use 0 times,
These are shown in FIGS. 5A and 5B. Comparing the two, it can be seen that the detector of the present invention does not substantially deteriorate in its performance even after repeated use, and has a long life.

[Comparative Example 1] Film forming time 4
At 0 seconds, a detector having a Pd metal continuous thin film having an average film thickness of about 4.8 nm was manufactured, and the response characteristics T + ΔT at the initial stage of use and the characteristics after repeated use 1000 times were measured.
And FIG. From these results, the conventional hydrogen detector composed of a continuous thin film responded instantaneously to the introduction of H _{2 in the} initial stage of use, and the response time was as short as that of Example 1. Response time after use is 1
It can be seen that the performance of the detector of the present invention is much better than that of the detector according to the present invention in terms of the life.

[0032]

FIG. 4 and FIG. 4 show that the hydrogen detector of the present invention having a novel configuration is not inferior to the conventional detector in sensitivity (change in light transmittance ΔT) and responsiveness (response time). 6 can be seen from the comparison. In addition, the conventional hydrogen detector composed of a continuous thin film responded instantaneously to the introduction of H _{2 in the} early stage of use and had extremely good response, but as shown in FIG. After use, the response time is remarkably increased and the performance is clearly deteriorated. On the other hand, as shown in FIGS. It can be seen that the service life was maintained at a level and the life was significantly prolonged.

[0033]

[Brief description of the drawings]

FIG. 1 is a schematic diagram for explaining a configuration of a hydrogen detector according to the present invention.

[0034]

FIG. 2 is a schematic view showing another configuration of the hydrogen detector of the present invention.

[0035]

FIG. 3 is a schematic diagram for explaining a configuration of a gas sensor of the present invention.

[0036]

FIG. 4 is a diagram showing sensitivity (change in light transmittance due to gas switching) and response characteristics (time from the moment of gas switching to reaching a new level of light transmittance) of the hydrogen detector of the present invention.

[0037]

FIG. 5 is a diagram showing values (a) of sensitivity and response characteristics at the initial stage of use of the hydrogen detector of the present invention and values (b) after repeated use 1000 times.

[0038]

FIG. 6 is a diagram showing initial values of sensitivity and response characteristics of a conventional hydrogen detector.

[0039]

FIG. 7 is a diagram showing the deterioration of sensitivity and response characteristics after repeated use of a conventional hydrogen detector 1000 times.

[0040]

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Light source 2 ... Light beam 3 ... Beam splitter 4 ... Photodiode 5 ... Transmitted light 6 ... Scanner 7 ... Multimeter 8 ... Detection target gas 9. ··· Reference light mirror 10 ··· Hydrogen detector 11 ··· Spotted catalyst metal thin layer 12 ··· Transparent substrate 21 ··· Gas flow pipe 22 ··· Translucent chamber 23 ··· Opening 24 ··· Glass window

Claims (4)

[Claims] 1. A hydrogen detector formed by forming a thin layer (c) on a transparent substrate (b) with a catalytic metal (a) that adsorbs and dissociates hydrogen, wherein the thin layer (c) is formed of the catalyst Metal (A)
Wherein the optical hydrogen detector is applied in a spot-like manner on the surface of the substrate (a). 2. The optical device according to claim 1, wherein a thin layer (c) formed by dispersing and depositing the catalyst metal (a) in spots is formed on both surfaces of the substrate (a). Hydrogen detector. 3. The method according to claim 1, wherein the thin layer is formed by a sputtering method or an evaporation method.
A method for producing the optical hydrogen detector according to the above. 4. A gas sensor using the optical hydrogen detector according to claim 1 or 2.