JP2000329737A - Gas sensor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a gas sensor for selectively detecting a hydrogen gas without being affected by other gases. SOLUTION: The gas sensor is composed of a gas detection element 1 that is formed on a substrate 3 and a pair of measurement terminals 2, the gas detection element 1 is formed with CuO as a main constituent and Ag2O as a precious metal compound to be added. The gas detection element 1 has characteristics where an electrical resistance value changes selectively for a hydrogen gas contained in gas, thus selectively detecting the hydrogen gas by measuring the change in the resistance value via the measurement terminals 2.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

TECHNICAL FIELD The present invention relates to a gas sensor,
In particular, the present invention relates to a gas sensor capable of selectively detecting a trace amount of a specific gas contained in a gas.

[0002]

2. Description of the Related Art As an example of a conventional gas sensor of this type, Japanese Patent Application Laid-Open No. 06-258270 discloses that two comb-shaped electrodes are directly connected to a gas detecting section mainly composed of CuO.
A gas sensor formed so as to take out a change in the electrical characteristics of the gas detection unit by the comb-shaped electrode is shown. FIG. 14A shows a plan view of this conventional example, and FIG. 14B shows a cutting instruction line Q- in FIG.
As shown in the cross-sectional view of the Q ′ portion, a gas detection unit 22 containing CuO as a main component, and a pair of comb-shaped electrodes 23 and 24 for extracting a change in electrical characteristics of the gas detection unit 22 include: It is formed integrally with the upper surface of the substrate 25. In this conventional example, an alkali metal compound, particularly a Na compound or a K compound, or Al2 O3 is selected and added as an additive to the gas detection section 22 containing CuO as a main component. The point that the gas detection sensitivity to CO, that is, carbon monoxide gas can be selectively enhanced is described as a significant feature point. In the embodiment of the conventional example, Na2 CO3 is used as the Na compound among the alkali metal compounds, and K2 CO3 is used as the K compound.

[0003]

In the above-mentioned conventional gas sensor, as an additive to the gas detecting portion containing CuO as a main component, an alkali metal compound such as Na2 CO3 or K2 CO3, or Al2 O3 is added. By doing so, the gas detection sensitivity to carbon monoxide (CO) is selectively increased. However, in the technical field using a fuel cell, which has been attracting attention in recent years, the gas generated by the gas sensor is converted into methane or methanol or ethanol to extract H2 and CO. At the same time, H2 is required to have a function of selectively detecting its presence. In response to such a request, in the conventional gas detection function,
There is no problem in that the gas detection sensitivity to CO can be selectively increased. However, there is also a demand for selectively increasing the gas detection sensitivity for hydrogen gas. As described above, in order to perform selection detection other than CO using a sensor containing CuO as a main component, it is indispensable to search for an additive to CuO other than the above additive.

An object of the present invention is to provide a gas sensor capable of selectively increasing the gas detection sensitivity with respect to H2 of a test gas by improving the selection of an additive for the CuO.

[0005]

A gas sensor according to the present invention comprises:
A gas sensor comprising a semiconductor having CuO as a main component in a gas detection portion, wherein a gas-containing substance is added to the CuO in a gas sensor of a type that detects the presence of a gas by using a resistance change of the gas detection portion. I have. The Ag-containing substance may be an Ag compound, or the Ag compound may be silver oxide (Ag2O). Further, the Cu
The weight of the Ag element added to O may be 1% by weight or more and 30% by weight or less based on CuO as the main component.

Further, a heating means may be provided for heating the gas detecting section and maintaining the temperature of the gas detecting section at 200 ° C. or higher. The preferred temperature of the gas detector heated and held by the heating means may be specified to be 290 ° C. or higher, or the temperature of the gas detector heated and held by the heating means May be specified at 400 ° C. or lower.

[0007]

According to the above arrangement, the other carbon monoxide (C
Even in an environment where gases such as O), ethanol, carbon dioxide (CO2), and methane (CH4) coexist, the gas detection unit is not affected by the presence of these gases, but by the presence of the surrounding test gas H2. Significantly increases. Therefore, in the gas sensor of the present invention, the presence and concentration of H2 can be accurately detected by measuring the resistance value of the gas detection section.

[0008]

Next, an embodiment of the present invention will be described.

[0009] One embodiment of the present invention provides a method in which C
It is formed by adding a substance containing Ag as a main component and containing uO,
A gas detection unit having a characteristic in which a resistance value changes depending on the type of gas present in the surroundings, and electrically connected to the gas detection unit, formed on the substrate for measuring the resistance value of the gas detection unit It comprises a pair of measurement terminals. The step of forming the gas detector on the substrate includes the step of
A paste-like substance containing uO and the substance containing Ag as main solid components is screen-printed on the substrate in contact with the pair of measurement terminals, and the paste-like substance is fired. In this case, when the paste-like substance is generated, a material such as silicon oxide (SiO2) is used as a binder material that does not adversely affect the gas detection sensitivity of the gas detection unit. Further, the shape of the pair of measurement terminals connected to the gas detection unit may be comb-shaped in order to obtain a stable resistance value, by using a generally used thin film forming method or thick film printing method or the like. It is formed on a substrate.

Further, it is desirable that the operating temperature of the gas sensor is maintained within a predetermined temperature range in order to maintain a good gas detection sensitivity of the gas detecting section. In addition, a heating means for heating the gas detection unit to maintain the operating temperature at a predetermined temperature is provided. As the heating means, a heater for maintaining the gas detection unit at a predetermined temperature may be built in the substrate, or the heater may be provided on the side of the substrate opposite to the gas detection unit mounting surface. In some cases, the entire gas sensor may be heated by a heater.

Next, a first example of this embodiment will be described with reference to the drawings.

FIG. 1 is a plan view and a side view showing the structure of this embodiment. FIG. 1A is a plan view thereof, and FIG.
FIG. 1B is a side view of the embodiment in FIG. As shown in FIG. 1, in the present embodiment, Ag2 O is selected and added as a substance containing Ag as a main component and containing CuO, and selectively with respect to H2 contained in the surrounding gas. And a pair of measuring terminals 2 for measuring a change in the resistance value and selectively detecting H2. And is configured integrally with the upper surface.

In this embodiment, the gas detector 1 adds a 10% by weight composition of Ag 2 O powder to a commercially available high-purity CuO powder (purity 99.99%).
As described above, as a binder material that does not affect the gas detection sensitivity, a weight composition ratio of 2
% Of silicon oxide (SiO2) powder. By forming the gas detection unit 1 and the pair of measurement terminals 2 on the substrate 3, a procedure for manufacturing a gas sensor was performed as follows. First, Ag2O powder and SiO2 powder are added to the high-purity CuO powder and kneaded with an appropriate amount of a vehicle to form a paste. The paste-like substance is previously formed with a pair of measurement terminals 2 formed on the upper surface. The printed substrate 3 was baked for 30 minutes in air at a maximum firing temperature of 530 ° C. In the gas sensor shown in FIG. 1, the description of the heating means for the gas detection unit 1 is omitted.

The measurement of the gas detection sensitivity of the gas detection section was performed using a detection sensitivity measuring device shown as a block diagram in FIG. As shown in FIG. 2, the detection sensitivity measuring device includes a selection switching solenoid valve 4 and flow meters 5 and 6.
, A permeator 7, a tubular furnace 8, a digital multimeter 10, a personal computer 11, an external storage device 12, a controller 13, and a temperature controller 1.
4, a heater 15, and a relay 16.

In FIG. 2, when measuring the gas detection sensitivity, the gas sensor 9 is disposed inside the tubular furnace 8. The gas sensor 9 includes a gas detection unit 1, a pair of measurement terminals 2, and a substrate 3, as shown in FIG.
Although not shown in FIG. 1, a heater for heating and keeping heat is provided as a component. However, when the detection sensitivity is measured by being installed in the tubular furnace 8, the operation of the heating means is unnecessary. The inside temperature of the tubular furnace 8 is controlled by a heater 15 controlled to be heated by a temperature controller 13, and the temperature is maintained at an appropriate temperature for gas detection sensitivity measurement. Test gases such as N2, O2, CO and H2 supplied from the outside are controlled by a control signal output from the personal computer 11 at a predetermined timing in accordance with the detection sensitivity measuring procedure.
It is appropriately selected by the selection switching solenoid valve 4 via the controller 13 and the relay 16, and is introduced into the tubular furnace 8 via the flow meter 6. When the volatile component of the organic solvent such as ethanol is used as the test gas, the volatile component such as ethanol generated in the permeator 7 is supplied to the flow meter 6 by using N2 introduced through the flow meter 5 as a carrier. The gas is introduced into the tubular furnace 8 in a mixed state with the gas introduced via the air. In this manner, while the internal temperature of the tubular furnace 8 is maintained at a predetermined temperature, the resistance value of the gas detection unit 1 of the gas sensor 9 that changes according to the gas to be introduced is sequentially measured by the digital multimeter. Measured by 10.
The resistance measurement value is input to the personal computer 11 and processed, and the processing result is input to the external storage device 12 as the gas detection sensitivity for the corresponding test gas and stored. At the same time, the personal computer 1
From 1, after a lapse of a predetermined time after the resistance value processing, the control signal for switching the gas supplied from outside at a predetermined timing is output, and as described above, via the controller 13 and the relay 16, In the selection switching solenoid valve 4, selection switching of the test gas such as N 2, O 2, CO and H 2 is performed, and the next test gas is successively introduced into the tubular furnace 8.

In the present embodiment, the reference gas introduced into the tubular furnace 8 in which the gas sensor 9 is disposed is a base state by mixing 79% of N2 and 21% of O2 on a volume basis. The resistance value Rair of the gas detection unit 1 measured when the reference gas is introduced, and the gas detection unit 1 measured by separately adding each test gas to the tube furnace 8 and measuring the resistance value Rair.
The gas detection sensitivity of the gas sensor 9 for each test gas is obtained by calculating the ratio Rgas / Rair to the resistance value Rgas of the above (this is the same in the following embodiments). As the test gas, each test gas is added to a reference gas, and the concentration (volume basis) of each gas is H2: 2000 ppm, ethanol: 200 pp.
m, CO: 2000 ppm, CH4: 1000 ppm,
And CO2: a concentration such as 20,000 ppm.

FIGS. 3 and 4 show the measurement results of the gas detection sensitivity for each test gas performed as described above. FIG. 3 is a diagram showing the temperature dependence of the gas detection sensitivity when the amount of the substance containing Ag as an additive to the gas detection unit 1 containing CuO as a main component is zero. FIG. 4 is a diagram showing the temperature dependence of the gas detection sensitivity when Ag2O is added to the gas detection unit 1. In FIG. These FIGS. 3 and 4
,,, And are the detection characteristics for ethanol, CO, H2, CH4, and CO2, respectively, as shown below.

: Ethanol: CO: H2: CH4: CO2

As is apparent from a comparison between FIG. 3 and FIG.
When the temperature of the gas detection unit 1 exceeds 260 ° C., the gas detection sensitivity to ethanol tends to sharply decrease in any case. H2 relative to other test gases
The gas detection sensitivity has a high value. Then, in the case of the present invention in which Ag2 O is added to the gas detection unit 1 shown in FIG. 4, the gas detection sensitivity to H2 is much higher than other test gases. That is, in the gas sensor of the present invention, the effect of selectively improving the gas detection sensitivity to H2 is extremely remarkable, and the presence of H2 can be clearly detected with little influence from other gases. In addition, since the gas detection sensitivity to CO is also improved, if this embodiment is used in the absence of H2,
Can be detected with high sensitivity. Therefore, 29
At a temperature of 0 ° C. or higher, the detection sensitivity of ethanol decreases, and the effectiveness as a sensor for a fuel cell system of a type that reforms an alcohol system increases.

Next, a second example of this embodiment will be described.

The configuration of this embodiment is the same as that of the first embodiment shown in FIG. The weight composition ratio of Ag2O to CuO in the gas detector 1 is the same as that in the first embodiment. That is, in the weight composition ratio, 10% by weight of Ag2O is added to the weight of CuO to form the gas detecting section 1. Further, the reference gas is the same as in the first embodiment. However, in this embodiment, unlike the first embodiment, the measurement conditions of the gas detection sensitivity of the gas sensor are different as described below. That is, as the test gas, each test gas is added to the reference gas to reduce CO and H2 from 0 to 300.
The gas detection sensitivity was measured while changing the volume concentration to be 0 ppm. Further, the temperature of the gas detector 1 of the gas sensor 9 disposed inside the tubular furnace 8 was maintained at 320 ° C.
The gas detection sensitivity was measured in a dry (dry) atmosphere. FIG. 5 is a graph showing the measurement results of the relationship between the concentration of the test gas and the gas detection sensitivity in this case. From FIG. 5, it is clear that the gas detection sensitivity of H2 is higher than that of CO of the same concentration. FIG. 6 is a graph showing the measurement results of the concentration of the test gas and the gas detection sensitivity when the test gas was measured in a humidified state of 1.2% absolute humidity. Also in this case, the gas detection sensitivity for H2 is higher than the gas detection sensitivity for CO of the same concentration, and it can be seen that this embodiment is superior in the detection sensitivity for H2 selection.

Next, a third example of this embodiment will be described with reference to the drawings.

FIG. 7 is a diagram showing the configuration of this embodiment.
FIGS. 7A, 7B and 7C are a plan view (top view) and a cross-sectional view and a plan view (bottom view), respectively, taken along a section designating line QQ ′ of this embodiment. As shown in FIG. 7, in the present embodiment, a substrate 20, a gas detector 17 mounted on the upper surface of the substrate 20, a pair of comb-shaped electrodes 18 and 1
9 and a heater 21 provided on the lower surface of the substrate 20.

In this embodiment, the gas detector 17 shown in FIG. 7 is a sample in which the main component of the gas detector 17 is CuO, and a substance containing Ag is not added as an additive to CuO. (Referred to as sample A), as a substance containing Ag as an additive,
A sample in which 9.3% by weight of elemental Ag was added to O (referred to as sample B), and a fine Ag powder was used as a substance containing Ag as an additive.
Three types of samples were manufactured, including a sample (referred to as sample C) to which 5% by weight was added in terms of weight. Other manufacturing conditions were the same as in the first embodiment. The reference gas and the test gas were the same as in the first embodiment.

For each sample of the present embodiment, the gas detector 17 is heated by the heater 21 to an operating temperature of 160 ° C. to 380 ° C., and the gas detector in the atmosphere of each test gas and the reference gas is heated. 17 were measured.
The graphs shown in FIGS. 8, 9, 10, 11 and 12 are:
H2 (2000 ppm) and CO (2000 pp
m), CO2 (3%), CH4 (2000 ppm) and ethanol (200 ppm) as test gases, the temperature of the gas detector 17 and the gas detector 17 obtained in the atmosphere of the reference gas and the test gas. 3 shows the relationship with the gas detection sensitivity obtained from the resistance value (Rgas) of FIG. In each of these figures, the characteristics indicated by reference signs A, B, and C indicate the characteristics of samples A, B, and C of the gas detection unit, respectively. By referring to these graphs,
As for the gas detection unit 17, it can be seen that the gas detection characteristics of the sample B and the sample C are closer to those of the sample A. Further, according to FIG.
It can be seen that when the temperature of the liquid crystal becomes 250 ° C. or higher, the gas detection sensitivity to ethanol is substantially lost.
8, 9, and 10 show that Sample B and Sample C have high gas detection sensitivity to H2. 8 to 12 that maintaining the temperature of the gas detection unit 17 at 290 ° C. or higher is a temperature range in which the H 2 selectivity is good. Therefore, it is preferable that the temperature of the gas detector 17 be maintained at 290 ° C. or higher. On the other hand, FIG. 13 shows a temperature-resistance (Rgas) characteristic of the sample B of the gas detection unit 17. As is clear from FIG. 13, the gas detection unit 17 is provided separately from the gas detection sensitivity.
When the temperature is too high, the resistance value (Rgas) decreases. Therefore, when used as a gas sensor, the temperature of the gas detection unit 17 is preferably suppressed to 400 ° C. or less.

That is, in the present invention, even in an environment where other gases such as carbon monoxide, ethanol, carbon dioxide, and methane coexist, the presence of H2 makes the gas unaffected by the presence of these gases. There is a feature that the resistance value of the detection unit is significantly increased. Therefore, according to the gas sensor of the present invention, the presence and concentration of H2 can be selectively detected regardless of the presence of the other gas by measuring the resistance value of the gas detection unit.

[0027]

As described above, according to the present invention, the gas detecting portion is formed by a member formed by adding a substance containing Ag to CuO and containing CuO as a main component. By utilizing the characteristic that the resistance value changes remarkably due to the presence of H2, there is an effect that the presence of a small amount of H2 in the periphery can be accurately detected without being affected by other gases.

Further, since the gas detection sensitivity for selectively detecting H2 is extremely high, the gas sensor of the present invention can be used under environmental conditions that require detection of even a small amount of H2 for safety measures. In addition, it is possible to prevent an accident or a trouble caused by the presence of H2.

[Brief description of the drawings]

FIG. 1 is an external view showing a configuration of a first embodiment of the present invention.

FIG. 2 is a block diagram illustrating a configuration of a gas detection sensitivity measurement device that measures the gas detection sensitivity of a test gas.

FIG. 3 is a diagram showing the temperature dependency of gas detection sensitivity by a gas detection unit having no additive.

FIG. 4 is a diagram showing the temperature dependence of the gas detection sensitivity of the gas detector in the first embodiment.

FIG. 5 is a diagram showing measurement results of detection sensitivity corresponding to changes in the concentrations of H2 and CO in the second embodiment.

FIG. 6 is a diagram showing a measurement result of detection sensitivity corresponding to a change in the concentration of H2 and CO when the test gas is humidified in the second embodiment.

FIG. 7 is an external view showing the configuration of a third embodiment of the present invention.

FIG. 8 is a diagram showing measurement results of detection sensitivity corresponding to a change in H2 sensor temperature by using samples A, B, and C of the third embodiment.

FIG. 9 is a diagram showing measurement results of detection sensitivities of samples A, B and C according to the third embodiment, which correspond to changes in the CO sensor temperature.

FIG. 10 shows samples A, B and C of the third embodiment.
FIG. 7 is a diagram showing a measurement result of detection sensitivity corresponding to a change in sensor temperature of CO2 according to FIG.

FIG. 11 shows samples A, B and C of the third embodiment.
FIG. 7 is a diagram showing a measurement result of detection sensitivity corresponding to a change in sensor temperature of CH4.

FIG. 12 shows samples A, B and C of the third embodiment.
FIG. 7 is a diagram showing a measurement result of detection sensitivity corresponding to a change in the sensor temperature of ethanol according to the embodiment.

FIG. 13 is a diagram showing a measurement result of a resistance value change corresponding to a sensor temperature change in Sample B of the third embodiment.

FIG. 14 is an external view showing a configuration of a conventional example.

[Explanation of symbols]

 1, 17, 22 Gas detection unit 2 Measurement terminal 3, 20, 25 Substrate 4 Selection switching solenoid valve 5, 6 Flow meter 7 Permeator 8 Tubular furnace 9 Gas sensor 10 Digital multimeter 11 Personal computer 12 External storage device 13 Controller 14 Temperature controller 15 Heater 16 Relay 18, 19, 23, 24 Comb-shaped electrode 21 Heater

Continued on the front page (72) Inventor Kazuhisa Hasumi 2480 Kuno, Odawara-shi, Kanagawa F-term in Mikuni Odawara Works (reference) 2G046 AA05 AA11 BA01 BB02 BC04 BE03 CA09 DB05 DC16 DC17 EA04 EB06 FB02 FC01 FE02 FE11

Claims (7)

[Claims] 1. A gas sensor in which a semiconductor mainly composed of CuO is provided in a gas detecting section, and the presence of gas is detected by utilizing a change in the resistance value of the gas detecting section.
A gas sensor, wherein a substance containing Ag is added to the gas sensor. 2. The gas sensor according to claim 1, wherein the substance containing Ag is an Ag compound. 3. The gas sensor according to claim 2, wherein said Ag compound is silver oxide (Ag 2 O). 4. The weight of the Ag element added to the CuO is 1% by weight or more and 30% by weight based on the main component CuO.
The gas sensor according to claim 1, 2 or 3, wherein: 5. The apparatus according to claim 1, further comprising heating means for heating said gas detecting section and maintaining the temperature of said gas detecting section at 200 ° C. or higher. Gas sensor. 6. The gas sensor according to claim 5, wherein a preferable temperature of the gas detection unit heated and held by the heating unit is specified to be 290 ° C. or higher. 7. The gas sensor according to claim 5, wherein a temperature of the gas detection unit heated and held by the heating unit is specified to be 400 ° C. or less.