阅读说明：本技术 气体检测装置 (Gas detection device ) 是由 高见晋 野中笃 大西久男 于 2018-09-05 设计创作，主要内容包括：本发明是关于在厨房或船舶厨房等湿度高的环境中使用的气体检测装置,提供耐湿性优异、同时在灵敏度方面也优异的气体检测装置。一种气体检测装置,具备薄膜型气体传感器,所述气体传感器是在基板上具有加热器部位、气体检测部位和催化剂部位而形成的,对加热器部位通电以将气体检测部位和催化剂部位加热的同时对检测对象气体进行检测,该气体检测装置采用气体传感器,其中的催化剂部位是在以过渡金属氧化物作为主要成分的载体上担载以铂作为主要成分的催化剂金属而构成的。(The present invention relates to a gas detection device used in a high humidity environment such as a kitchen or a ship kitchen, and provides a gas detection device having excellent moisture resistance and excellent sensitivity. A gas detection device provided with a thin-film gas sensor having a heater portion, a gas detection portion, and a catalyst portion formed on a substrate, wherein the heater portion is energized to heat the gas detection portion and the catalyst portion and simultaneously detect a gas to be detected, and the gas detection device employs the gas sensor in which the catalyst portion is formed by supporting a catalytic metal containing platinum as a main component on a carrier containing a transition metal oxide as a main component.)

1. A gas detection device comprising a gas sensor having a heater portion, a gas detection portion whose characteristic changes when the gas sensor is brought into contact with a gas to be detected, and a catalyst portion provided so as to cover at least a part of the gas detection portion,

the gas detection device detects the detection target gas while energizing the heater portion to heat the gas detection portion and the catalyst portion,

the catalyst site is formed by supporting a catalytic metal containing platinum as a main component on a carrier containing a transition metal oxide as a main component.

2. The gas detection device according to claim 1, wherein the transition metal oxide is one or both of zirconia and titania.

3. The gas detection apparatus according to claim 1 or 2, wherein the catalyst site is configured by supporting 0.3 mass% or more and 9 mass% or less of platinum as the catalytic metal on the carrier.

4. The gas detection apparatus according to claim 1 or 2, wherein one or both of palladium and iridium are contained as the catalyst metal in addition to the platinum as the main component.

5. The gas detection apparatus according to any one of claims 1 to 4, wherein the gas detection apparatus detects the detection target gas by repeating: a gas detection step of detecting the detection target gas while energizing the heater portion to heat the gas detection portion and the catalyst portion; and a non-detection step of bringing the temperatures of the gas detection site and the catalyst site to a lower level than the temperatures of both the sites in the gas detection step.

6. The gas detection apparatus according to any one of claims 1 to 5, wherein the gas detection apparatus detects the detection target gas by repeating: a gas detection step of detecting the detection target gas while energizing the heater portion to heat the gas detection portion and the catalyst portion; and a slight heating step of applying current to the gas detection portion and the catalyst portion at a temperature lower than the temperatures of the two portions in the gas detection step.

7. The gas detection apparatus according to any one of claims 1 to 5, wherein the gas detection apparatus detects the detection target gas by repeating: a gas detection step of detecting the detection target gas while energizing the heater portion to heat the gas detection portion and the catalyst portion; and a heating suspension step of stopping the energization of the heater portion.

8. The gas detection apparatus according to claim 7, wherein a heating time in the gas detection step is shorter than a heating stop time in the heating suspension step.

9. The gas detection apparatus according to claim 7 or 8, wherein at least the heating in the gas detection step is pulse heating in which a heating time is set to 0.05 to 0.5 seconds, and at least the following basic heating method is performed: that is, the pulse heating is repeated at a gas detection cycle of 20 to 60 seconds through the heating pause step.

10. The gas detection apparatus according to any one of claims 1 to 9, wherein a high-temperature heating step of heating the gas detection site and the catalyst site to a temperature for methane detection is included in the detection of the detection target gas.

11. A gas sensor used in the gas detection device according to any one of claims 1 to 10,

the gas sensor comprises a heater portion, a gas detection portion having a property that changes when the gas sensor contacts a gas to be detected, and a catalyst portion covering at least a part of the gas detection portion,

the catalyst site is formed by supporting a catalytic metal containing platinum as a main component on a carrier containing a transition metal oxide as a main component.

Technical Field

The present invention relates to a gas detection device including a gas sensor having a heater portion, a gas detection portion whose characteristic changes when the gas sensor comes into contact with a gas to be detected, and a catalyst portion covering at least a part of the gas detection portion,

the gas detection device detects the detection target gas while energizing the heater portion to heat the gas detection portion and the catalyst portion.

Background

Such gas detection devices are disclosed in patent documents 1 and 2.

Hereinafter, a gas detection device described in these documents will be described as an example.

The gas detection device is provided with a gas sensor, a heating control unit for heating and driving the gas sensor, and a gas detection unit for detecting a change in the characteristic of a gas detection site, and the gas detection device detects the gas by controlling the heating from a heater site by the heating control unit to heat the gas detection site and a catalyst site provided on the surface side thereof to an appropriate temperature according to the type of the gas to be detected.

The gas to be detected includes methane (CH)₄) Propane (C)₃H₈) Equal combustible gas, carbon monoxide (CO) or hydrogen (H)₂) And the like.

When gas detection is performed, the heating control unit applies pulse current to the heater portion to heat the gas detection portion and the catalyst portion. In fig. 4(a), (b), and (c) of the present specification, the heating method is shown by a heating drive signal. Fig. 4(a) and (b) are diagrams showing the heating drive signal in the case where the gas to be detected is a combustible gas, and fig. 4(c) is a diagram showing the case where the gas to be detected is a combustible gas and a reducing gas.

As also shown in fig. 4 (a): the energization of the heater portion is composed of a gas detection step Ts for performing energization and a heating suspension step Tr performed immediately after the gas detection step Ts, and the gas detection is repeated at a predetermined gas detection cycle Rt.

The detection of the detection target gas is performed immediately before the stop of the energization as indicated by the black circle in these drawings.

In the detection of combustible gas, as shown in fig. 4(a) and (b), High-temperature heating (High) is employed, and the mixed gas which becomes the interfering gas is removed by combustion at the catalyst site in the detection.

A representative interfering gas is hydrogen (H)₂) Ethanol (C)₂H₅OH), and carbon monoxide (CO), and by such a function, the catalyst site is also called an oxidation catalyst layer. In the high-temperature heated state, a flame-retardant combustible gas (typically methane) that has passed through the catalyst site and reached the gas detection site can be detected.

The heating driving method shown in fig. 4(c) is a method of performing Low-temperature heating (Low) immediately after High-temperature heating (High), and detection of a reducing gas (typically, carbon monoxide) is performed immediately before the Low-temperature heating (Low) is stopped.

As shown in fig. 4 a, the gas detection step Ts is repeated at a predetermined gas detection period Rt, but the energization of the heater portion is stopped (off) in the heating suspension step Tr during the gas detection step Ts.

In the case where the gas sensor is a pulse-heatable gas sensor having a small heat capacity of the heated portion and high heating responsiveness, the energization in the gas detection step Ts is performed for a period of about 0.05 to 0.5 seconds, and the pulse energization is repeated in a gas detection period of about 20 to 60 seconds through the heating pause step Tr, thereby realizing power-saving driving.

That is, in this example, the heating in the gas detection step Ts is pulse heating, and the pulse heating is repeated at a predetermined gas detection period Rt with the heating pause step Tr interposed.

In this case, the time of the heating suspension step Tr is absolutely long, while the gas sensor is heated only for an extremely short time.

Such a gas sensor can be a power-saving gas detection device that uses a battery as a power source because the heating drive for gas detection is so-called pulse heating because of its low heat capacity, for example.

Patent document 1 describes a technique for preventing and maintaining a gas detection device, and patent document 2 describes a thin film gas sensor that suppresses moisture absorption by a gas sensing layer and maintains high sensitivity.

When the expression (the expression of patent document 1, the expression of patent document 2) corresponds to the expression used in the background art described above, the gas detection site becomes (the sensor layer 57, the gas sensor layer 5), and the catalyst site becomes (the selective combustion layer 58, the gas selective combustion layer 5 d).

The techniques disclosed in these patent documents also have found that: in the gas sensor provided in such a gas detection device, alumina (Al) is used₂O₃) A sintered material of palladium (Pd) or platinum (Pt) as a catalyst metal is supported on the carrier as a catalyst site.

Patent document 2 proposes to solve the problem of deterioration of the gas sensor with age due to humidity, and to use moisture absorption suppressing drive as shown in fig. 1 of the specification.

Documents of the prior art

Patent document

Patent document 1: japanese patent laid-open publication No. 2013-190232;

patent document 2: japanese patent laid-open No. 2007 and 24569.

Disclosure of Invention

Problems to be solved by the invention

The inventors of the present invention have also found a gas sensor with reduced methane sensitivity when studying a gas sensor of a gas detection device used in an environment with high humidity, such as a kitchen (kitchen) or a ship kitchen (valley).

The technique disclosed in patent document 2 proposes one measure that can be taken when the gas detection device is used in such an environment with high humidity, but moisture absorption suppressing drive is necessary in the heating suspension step, and the purpose of obtaining a power-saving gas detection device is not met.

Further, considering the sensitivity of the sensor to the gas to be detected, it is preferable that the sensitivity be as high as possible, but the present inventors have found that there is room for improvement in the conventional alumina carrier gas sensor through the study of the present inventors.

The present invention has been made in view of the above problems, and an object of the present invention is to provide: a gas detection device used in a high-humidity environment such as a kitchen or a ship kitchen is provided, which has excellent moisture resistance and excellent sensitivity.

The purpose is also that: a gas sensor usable for such a gas detection device is obtained.

Means for solving the problems

The 1 st feature of the present invention is: a gas detection device comprising a gas sensor having a heater portion, a gas detection portion whose characteristic changes when the gas sensor is brought into contact with a gas to be detected, and a catalyst portion covering at least a part of the gas detection portion,

the gas detection device detects the detection target gas while energizing the heater portion to heat the gas detection portion and the catalyst portion,

the catalyst site is formed by supporting a catalytic metal containing platinum as a main component on a carrier containing a transition metal oxide as a main component.

The inventors have found after intensive studies that: the reason why the sensitivity of the conventional gas detection device fluctuates with time is that moisture is adsorbed and accumulated in alumina, which is a main component of the carrier of the catalyst site. The alumina carrier has a strong interaction with water, and not only is the amount of water adsorbed by hydroxyl groups (OH groups) and chemically adsorbed increases in a short period of time, but also water molecules (physically adsorbed water) which are not completely dispersed during heating accumulate, and the physically adsorbed water gradually reacts with alumina to form a hydrate, which causes alumina to deteriorate.

As a result, the function of the catalyst portion as a combustion gas for other disturbance gases such as reducing gas and the gas detection function change. Further, the alumina is deteriorated by adsorption/accumulation of moisture, and the dispersion state of the catalytic metal such as palladium supported on the surface is deteriorated, the surface area of the catalytic metal is reduced, and similarly, the function as a catalytic site is deteriorated and cannot be restored (irreversibly changed).

Further, the temperature cannot be raised to a temperature necessary for detecting the detection target gas. It is estimated from these factors that the sensitivity to the detection target gas changes with time.

The finding that "the interaction between the carrier of the catalyst and water affects the temporal sensitivity variation of methane" is a completely new finding that is not found in the conventional findings.

Based on these new findings, the inventors studied the material of the carrier of the catalyst site and selected the transition metal oxide as the main component of the carrier.

In general, zirconia, which is a typical example of transition metal oxides, is not a material that has been actively used as a carrier for a catalyst site since it has a smaller specific surface area than alumina. The specific surface area of the alumina is about 120m²In contrast thereto, the zirconium oxide is about 30m²There is about a 4-fold difference per gram. Conventionally, the larger the surface area, the larger the area of interaction with the gas, and therefore, when used as a carrier for a catalyst site, it is considered that alumina has high performance as a catalyst site and zirconia has low performance.

However, the inventors have made a trial to use zirconia and titania as carriers for alumina to study the influence of moisture in the air (a high-humidity exposure experiment described later), contrary to the conventional findings, and have confirmed that: zirconia and titania are less susceptible to sensitivity variations even in high humidity than alumina. It was also confirmed that: zirconia and titania can suppress sensitivity reduction even under a high-humidity environment, compared with alumina. It is considered that these are caused by the fact that the interaction between the zirconia and the titania and water is small, and the effect is also similar to that of the transition metal oxide having the small interaction with water. Subsequently, the present invention using a transition metal oxide as a support for the catalyst site was completed.

If the sensitivity of the sensor is further explained, it is determined by the present study of the inventors that: even in the case of using the same catalyst metal, the sensitivity is improved by merely replacing the carrier of the catalyst site with alumina for the transition metal oxide, and the sensitivity is further improved by optimizing the catalyst composition. In addition, in the case of using zirconia as a carrier, platinum exhibits high sensitivity as a catalyst metal.

Therefore, according to the present configuration, as a gas detection device for detecting a gas using a gas sensor including a heater portion, a gas detection portion, and a catalyst portion, for example, a gas detection device used in a high humidity environment such as a kitchen or a ship kitchen, a gas detection device having excellent moisture resistance and high sensitivity can be obtained.

The gas sensor used in the gas detection device has the following configuration.

Comprising a heater portion, a gas detection portion whose characteristic changes by contact with a gas to be detected, and a catalyst portion covering at least a part of the gas detection portion,

the catalyst site is a carrier mainly composed of a transition metal oxide and a catalytic metal mainly composed of platinum supported on the carrier.

Therefore, as described in the configuration of the invention 2, the transition metal oxide as a main component of the carrier may be either zirconia or titania or both of them.

The 3 rd feature of the present invention is: the catalyst site is configured by supporting 0.3 mass% to 9 mass% of platinum as the catalyst metal on the transition metal oxide as the carrier.

According to the present configuration, moisture resistance can be obtained by using the transition metal oxide as the carrier, and a gas detection device having high sensitivity can be obtained by using platinum as the catalyst metal as compared with the case of using alumina as the carrier, as described later in the methane sensitivity test. Here, if the platinum supporting concentration is less than 0.3 mass%, sufficient selective oxidation ability cannot be obtained, and if it is more than 9 mass%, the oxidation ability becomes too high, and even methane passes through the catalyst and burns.

The 4 th feature of the present invention is that: the catalyst metal may contain one or both of palladium and iridium in addition to the platinum as the main component.

According to the present configuration, palladium or iridium is mixed with platinum to obtain a composite, which is selectively oxidized in the same manner, and a gas detection device having excellent sensitivity can be obtained.

A 5 th feature of the present invention is that the detection target gas is detected by repeating the following steps: a gas detection step of detecting the detection target gas while energizing the heater portion to heat the gas detection portion and the catalyst portion; and a non-detection step of bringing the temperatures of the gas detection site and the catalyst site to a lower level than the temperatures of both the sites in the gas detection step.

In this configuration, the gas detection device repeats the gas detection step and the non-detection step, but the gas detection site and the catalyst site are brought into a state in which the temperatures of the gas detection site and the catalyst site are lower than the temperatures of both sites in the gas detection step in the non-detection step, and thus the gas detection site and the catalyst site can be brought into a temperature at which the influence of water can be reduced even if the temperature does not reach a temperature at which gas detection can be performed, for example.

Such a non-detection step can be realized by, for example, suspending heating (stopping energization) and combining heating (energization) in an arbitrary manner. Here, if the temperatures of the two portions are controlled to be in a state of being less susceptible to the influence of water, which is the object of the present invention, the generation of the hydrate newly found by the present inventors can be effectively prevented. Therefore, high sensitivity can be maintained for a long life while suppressing power consumption.

Although this behavior is similar to the moisture absorption suppressing operation described above, in the present invention, the carrier constituting the catalyst site contains a transition metal oxide as a main component, and therefore, the degree of heating can be reduced or the heating frequency can be reduced as compared with the moisture absorption suppressing operation disclosed in the document. As a result, a gas detection device with high utility can be realized.

A 6 th feature of the present invention is that the detection target gas is detected by repeating the following steps: a gas detection step of detecting the detection target gas while energizing the heater portion to heat the gas detection portion and the catalyst portion; and a slight heating step of applying current to the gas detection portion and the catalyst portion at a temperature lower than the temperatures of the two portions in the gas detection step.

By interposing the slight heating step during the gas detection step, a heated state (for example, about 50 ℃) in which the gas detection site and the catalyst site are heated at room temperature can be achieved without heating the gas detection site and the catalyst site to a temperature at which gas detection can be performed, and the influence of water, which is an object of the present invention, on the catalyst site can be reduced.

In addition, by reducing the amount of heating, the power consumption can be suppressed to a low level.

A 7 th feature of the present invention is that the detection target gas is detected by repeating: a gas detection step of detecting the detection target gas while energizing the heater portion to heat the gas detection portion and the catalyst portion; and a heating suspension step of stopping the energization of the heater portion.

With this configuration, gas detection can be performed more economically without heating the gas sensor at an unnecessary timing.

Here, it is understood that the influence of water on the catalyst site hardly occurs in the gas detection step. This is due to the understanding that: in this step, the gas detection site and the catalyst site are sufficiently heated, and water is less likely to adhere to the catalyst site.

In contrast, in the heating suspension step, the energization of the heater portion is stopped, and the temperature of each portion is rapidly reduced to the normal temperature. Therefore, for example, in a gas detection device that performs pulse heating to periodically detect gas, the gas sensor can be placed in an environment (particularly, a temperature/humidity environment) that is generally greatly affected by water, as long as the gas sensor is instantaneously heated. As a result, the problems described above are likely to occur with time. This is also recognized in patent document 2 described above in that the step of performing the adsorption suppression driving is the heating pause step of the present invention.

However, in the present invention, by making the main component of the carrier of the catalyst site a transition metal oxide and making the main component of the catalyst metal platinum, highly sensitive gas detection can be performed without being affected by water.

The 8 th feature of the present invention is: the heating time in the gas detection step is shorter than the heating stop time in the heating suspension step.

With this configuration, the heating time is short, and gas detection with high sensitivity is performed while power consumption is suppressed.

The 9 th feature of the present invention is that: at least the heating in the gas detection step is pulse heating with a heating time of 0.05 to 0.5 seconds, and a basic heating method of repeating the pulse heating at a gas detection cycle of 20 to 60 seconds through at least the heating pause step is executed.

The basic heating method is a heating method at ordinary times except for the case where the heating conditions are periodically or aperiodically deviated for the purpose of measures for detecting delay, suppressing false alarms, diagnosing malfunctions, and improving performance.

With this configuration, gas detection can be performed with further reduced power consumption.

In the configuration of the present invention, even when methane detection is performed by battery driving, for example, gas detection can be performed satisfactorily for a predetermined period required by a gas detection device.

The 10 th feature of the present invention is: the detection of the detection target gas includes a high-temperature heating step of heating the gas detection site and the catalyst site to a temperature for methane detection.

According to this configuration, methane can be detected with high moisture resistance and high sensitivity, and this detection is very important for detecting town gas (natural gas) leakage, which is one of the gases to be detected.

Drawings

FIG. 1 is a view showing an outline of a gas detection device;

FIG. 2 is a graph showing the change with time of methane sensitivity in a high-humidity exposure experiment;

FIG. 3 is a comparative graph showing the sensitivity of a gas detection device using various catalyst metals;

FIG. 4 is an explanatory view showing a manner of heating driving;

FIG. 5 is an explanatory view showing another embodiment of the heating drive;

FIG. 6 is a view showing another embodiment of the gas sensor;

FIG. 7 is a diagram showing another embodiment of the gas sensor.

Detailed Description

A gas detection device 100 according to the present embodiment will be described with reference to fig. 1.

The gas detection device 100 includes a sensor element 20 (an example of a gas sensor), a heating control unit 12, and a gas detection unit 13.

The gas detection device 100 receives power from the battery 15 in a state where the battery 15 is attached, and detects a detection target gas.

The sensor element 20 is a so-called electricity-saving gas sensor having a diaphragm structure. It can also be seen from fig. 1 that: the sensor element 20 is configured to include a heater layer 6 (an example of a heater portion), a gas detection layer 10 (an example of a gas detection portion), and a catalyst layer 11 (an example of a catalyst portion) on a support layer 5 of a diaphragm structure. Therefore, the catalyst layer 11 is exposed to the ambient environment, and the detection target gas reaches the gas detection layer 10 through the catalyst layer 11. The gas to be detected that has reached comes into contact with the layer 10, and changes its characteristics. Here, the characteristic may specifically be a resistance value or a voltage value.

The gas detection device 100 heats the gas detection layer 10 to an appropriate temperature according to the type of the gas to be detected by energizing the heater layer 6 with the heating control unit 12, and detects the gas to be detected based on a change in the characteristics of the gas detection layer 10 while maintaining the temperature.

In the methane detection, the catalyst layer 11 is heated to a High temperature of 300 ℃ or higher (High shown in fig. 4(a), (b), and (c)) by the heater layer 6, and burns another interfering gas such as a reducing gas such as carbon monoxide or hydrogen, and transmits and diffuses methane having a low activity to reach the gas detection layer 10. This improves the detection accuracy of methane.

Incidentally, when detecting carbon monoxide, the catalyst layer 11 is heated to 50 to 250 ℃ (Low in fig. 4 (c)) at a Low temperature by the heater layer 6, and burns other mixed gas such as reducing gas such as hydrogen. A part of the carbon monoxide is burned, but most of the carbon monoxide permeates and diffuses to reach the gas detection layer 10. Methane or the like having low activity in this low temperature region is not detected in the gas detection layer 10.

In other words, the catalyst layer 11 has a function of making the gas detection device 100 have gas selectivity by heating an interfering gas (non-detection target gas) such as hydrogen gas or alcohol (ethanol) gas other than the detection target gas to an appropriate temperature and burning the interfering gas without reaching the gas detection layer 10. Further, supplying oxygen to the surface of the gas detection layer 10 also serves to improve sensitivity.

(sensor element)

The sensor element 20 has a diaphragm structure in which an end portion of the support layer 5 is supported on the silicon substrate 1. The support layer 5 is formed by thermally oxidizing the film 2 and silicon nitride (Si)₃N₄) Film 3, silicon oxide (SiO)₂) The films 4 are sequentially laminated. Further, a heater layer 6 is formed on the support layer 5, an insulating layer 7 is formed to cover the entire heater layer 6, a pair of bonding layers 8 are formed on the insulating layer 7, and an electrode layer (an example of an electrode) 9 is formed on the bonding layers 8. The heater layer 6 generates heat by energization to form the gas detection layer 10 and the catalyst layer 11And (4) heating. The sensor element 20 may have a block structure in which each layer is relatively thick, and the heater layer 6 may also serve as an electrode layer. In addition, a so-called bridge structure may be employed as the support structure.

A gas detection layer 10 is formed between the pair of electrode layers 9 on the insulating layer 7. The gas detection layer 10 is a layer of a semiconductor containing a metal oxide as a main component. In this embodiment, tin oxide (SnO)₂) The mixture as the main component serves as the gas detection layer 10. The gas detection layer 10 changes its resistance value when it comes into contact with a detection target gas. The gas detection layer 10 may have a thickness of 0.2 to 1.6μA film having a thickness of about 1.6 or moreμm (thick film).

A catalyst layer 11 is formed on the gas detection layer 10 so as to cover the gas detection layer 10. The catalyst layer 11 is configured by supporting a catalytic metal on a carrier containing a metal oxide as a main component. The catalyst layer 11 is formed by bonding metal oxides carrying a catalyst metal to each other with a binder.

As the catalyst metal, a metal that can be used as a catalyst capable of removing an interfering gas (a reducing gas such as ethanol or hydrogen) that can cause erroneous detection at the time of detection of the detection target gas is used. As the catalyst metal, palladium, platinum, and iridium (Ir) may be used, but in the present embodiment, at least one of palladium, platinum, and iridium is contained.

Alumina has been mainly used as a carrier for supporting a catalytic metal. In the present embodiment, zirconia is used as a material whose surface is less likely to generate hydroxyl groups than alumina and which can suppress adsorption/accumulation of moisture in the air in the catalyst layer 11.

As the binder for binding the carrier, fine powders of metal oxides, for example, zirconia, fine silica powder, silica sol, magnesia, and the like can be used. If a small amount of the binder is used, fine alumina powder or alumina sol may be used as long as the function of the catalyst layer 11 is not impaired.

The catalyst layer 11 is formed by supporting zirconia as a metal oxidation catalystPowder (particle size 1-10)μm or so), a binder and an organic solvent, and firing the mixture at 500 ℃ for 1 hour after drying the mixture at room temperature. The catalyst layer 11 is set to a size sufficient to cover the gas detection layer 10. The thickness is thus reduced by screen printing. The zirconia sintered body thus formed had a specific surface area of about 30m²And about/g.

The catalyst metal, the metal oxide as a carrier, and the binder may be used alone in 1 kind, or 2 or more kinds may be used in combination.

The amount of the catalyst metal contained in the catalyst layer 11 is preferably 0.3 to 9 mass% based on the total mass of the catalyst metal and the carrier. When 2 or more kinds of metals are used as the catalyst metal, the total mass of the catalyst metal is preferably 0.3 to 9 mass% based on the total mass of the catalyst metal and the carrier.

When only methane detection is performed, the mass of platinum is preferably 0.3 mass% or more and 6 mass% or less.

(heating control section)

The gas detection apparatus 100 for detecting methane will be described as an example, and as described above, the heating drive signals for the detection are shown in fig. 4(a) and (b).

The heating control unit 12 is configured to perform an energization behavior in which the heater layer 6 is energized (the timing of performing the energization behavior is referred to as a gas detection step Ts in the present invention) and a non-energization behavior in which the heater layer 6 is not energized (the timing of performing the non-energization behavior is referred to as a heating suspension step Tr in the present invention). This energization action (gas detection step Ts) is repeated with a gas detection period Rt. That is, the pulse heating is repeated at the gas detection period Rt.

The heating control unit 12 is configured to vary the temperature of the heater layer 6, and is configured to be able to heat the heater layer 6 to an arbitrary set temperature.

Specifically, the heating control unit 12 receives power supply from the battery 15 power supply, and energizes the heater layer 6 of the sensor element 20 to heat the sensor element 20. The temperature at which heating is performed, that is, the arrival temperature of the gas detection layer 10 and the catalyst layer 11, is controlled by changing the voltage applied to the heater layer 6, for example.

(gas detecting section)

The gas detection unit 13 measures changes in the characteristics of the gas detection layer 10 at an appropriate timing in the gas detection step Ts, and detects the detection target gas. In the present embodiment, the gas detection unit 13 measures the resistance value (an example of characteristics) between the pair of electrode layers 9, thereby measuring the resistance value of the gas detection layer 10, and detects the concentration of the detection target gas based on the change in the resistance value.

(detection of gas to be detected)

A case will be described where a combustible gas (gas to be detected) such as methane or propane is detected using the gas detection apparatus 100 configured as described above.

The heater layer 6 is energized by the heating control unit 12, and the gas detection layer 10 and the catalyst layer 11 are heated to 300 to 500 ℃ for methane detection for 0.05 to 0.5 seconds. During this period (specifically, immediately before the stop of the energization shown by black circles in fig. 4(a) and (b)), the gas detection section 13 measures the resistance value of the gas detection layer 10, and detects the concentration of a combustible gas such as methane or propane based on the value.

After that, the energization to the heater layer 6 is stopped. Therefore, the gas detection step Ts described above becomes a high-temperature heating step.

During this period, in the catalyst layer 11 having reached a high temperature, other mixed gas such as reducing gas such as carbon monoxide or hydrogen is burned by the combustion catalytic action of the catalytic metal. Then, the combustible gas such as inert methane or propane permeates through the catalyst layer 11 and diffuses, reaches the gas detection layer 10, and reacts with the metal oxide (tin oxide) of the gas detection layer 10 to change the resistance value.

In the above operation, the combustible gas is detected by the gas detection device 100.

The gas detection step Ts is repeated at a gas detection period Rt of 20 to 60 seconds, but after the gas detection step Ts, the energization is stopped (off) as described above (heating pause step Tr).

[ high humidity Exposure experiment ]

In order to examine the influence of the type of carrier material on the secular change in sensor sensitivity, a sample in which only the type of carrier was changed was prepared, and the secular change in sensor sensitivity (methane sensitivity) was measured.

The measurement objects were the following 3 samples.

(high temperature Exposure Experimental example 1)

In the presence of zirconium oxide (ZrO) as a carrier₂) A sample obtained by supporting 5 mass% of platinum (Pt) and 2 mass% of iridium (Ir) thereon.

(high temperature Exposure Experimental example 2)

In titanium oxide (TiO) as a carrier₂) A sample obtained by supporting 5 mass% of platinum (Pt) and 2 mass% of iridium (Ir) thereon.

(high temperature Exposure Experimental example 3)

In alumina (Al) as carrier₂O₃) A sample obtained by supporting 5 mass% of platinum (Pt) and 2 mass% of iridium (Ir) thereon.

FIG. 2 shows the change with time of methane sensitivity (RCh 4/Rair obtained by dividing the resistance value RCh4 in methane gas of 3000ppm at 400 ℃ heating by the resistance value Rair in air at 400 ℃ heating) of a sample subjected to the 50 ℃ 60% RH exposure test. The methane sensitivity was measured in a clean atmosphere at 20 ℃ and 65% RH.

The gas detection is performed by repeating the pulse heating described above at the gas detection period Rt (the same applies to the methane sensitivity test described later).

As shown in fig. 2, in the high-humidity exposure experimental examples 1 and 2 in which the carrier was zirconia or titania, the methane sensitivity did not change with time. In contrast, in experimental example 3 (in which the support was alumina) in which the high-humidity exposure was performed, the methane sensitivity was decreased with time.

The inventors speculate that the main reason is as follows.

The interaction with water in the catalyst layer 11 includes the following 3 stages.

Stage (1): OH groups are adsorbed in a short period, and the chemical adsorption water is increased;

stage (2): water molecules (physically adsorbed water) that are not completely dispersed during heating accumulate; and

stage (3): the adsorbed water reacts with the cake (carrier) to form a hydrate.

The heating process is performed according to the steps (1) → (3) when the heating pause step is not included, and according to the steps (2) → (3) when the heating pause step is included. Therefore, in SiO which has strong interaction with water₂、Al₂O₃When the carrier is a carrier, the carrier is likely to be generated (1) in high humidity without including the heating suspension step, and when the carrier is a carrier including the heating suspension step as the object of the present embodiment, the carrier is likely to be generated (2) in high humidity, and the carrier is likely to be shifted to (3) with time, thereby changing the sensitivity of the gas to be detected.

This is because in the case of using zirconia or titania as a support, which hardly has interaction with water, (1) is less likely to occur even in high humidity without including the heating pause step, and (2) is less likely to occur even in high humidity with including the heating pause step. Therefore, hydrates are not formed over time, and sensitivity does not change. In addition, gas sensitivity is also independent of humidity.

[ methane sensitivity test ]

In order to compare methane sensitivity in the case where the type of the carrier and the type/amount of the catalyst metal are different, 19 samples in which the type/amount of the catalyst metal is mainly changed were prepared, and methane sensitivity in a normal environment was measured.

The methane sensitivity was the same as described in [ high humidity exposure experiment ] above except for the ambient conditions. That is, the methane sensitivity is RCh4/Rair obtained by dividing the resistance value RCh4 in methane gas at 3000ppm when heated at 400 ℃ by the resistance value Rair in air when heated at 400 ℃.

Examples 1, 2 of high temperature exposure previously used in the high humidity exposure experiment are sample 16, sample 18.

The samples to be measured were arranged as follows.

1. Kind of the vector

Samples 1-17 zirconia;

18 titanium oxide;

19 of alumina.

2. Catalyst metal

The catalyst metals to be investigated were 3 kinds of palladium (Pd), iridium (Ir), and platinum (Pt).

Tables 1, 2, 3 and 4 shown below show the amount (mass%) of the catalyst metal supported in samples 1 to 19. The column not described shows that the catalyst metal is not supported.

[ Table 1]

[ Table 2]

[ Table 3]

[ Table 4]

The methane sensitivity of each sample is further shown in fig. 3.

The upper part of the figure shows the sample number, and the lower part of the figure shows the kind and concentration (% by mass) of the metal oxidation catalyst.

As a result, the methane sensitivity of sample 17 obtained by changing only the carrier to zirconia, as compared with sample 19 (alumina carrier/7 mass% palladium) equivalent to the conventional art, was improved.

Of the two samples, sample 17 was also the preferred result with no sensitivity change in the high humidity exposure experiment performed separately.

In the samples (1 to 17) on which zirconia was used as a carrier as a comparative sample, all samples showed higher sensitivity to methane than the sample 19.

In addition, sample 18, which was the comparative sample and which had titanium oxide as a carrier, showed a higher sensitivity to methane than sample 19.

Samples 1 to 18 exhibited methane sensitivity higher than that of the high-temperature exposure experimental example 3 (alumina carrier/5 mass% platinum, 2 mass% iridium) than that of the high-temperature exposure experimental example 3 described above.

Among the samples to be investigated, those having zirconia as a carrier and a catalyst metal composed of only platinum (8 and 13) exhibited particularly high methane sensitivity.

The results show that: the use of a combination of platinum alone as a catalyst metal and zirconia as a carrier is particularly preferable as a gas sensor.

Further, when comparing the sample 8 with the sample 13, the methane sensitivity of the sample 13 having a high platinum concentration is improved, and the methane sensitivity is improved as the platinum concentration is higher. On the other hand, when comparing sample 15 and sample 16, the methane sensitivity decreases as the platinum concentration increases with respect to the same iridium concentration. From the above results, it is clear that: the methane sensitivity increases as the platinum concentration increases until a certain platinum concentration is reached, but the methane sensitivity decreases conversely when a certain concentration is exceeded, and there is an appropriate concentration range for obtaining a high methane sensitivity. The reason why the sensitivity of methane decreases beyond a certain concentration is considered to be: the oxidation activity of platinum is increased, and even methane is burned and oxidized in the catalyst layer. From the above results, it is considered that: the concentration of platinum is preferably 0.3 mass% or more and 9 mass% or less, more preferably 0.3 mass% or more and 6 mass% or less.

[ other embodiments ]

(1) In the above experiment, the significance of the present invention has been explained by the experimental example relating to methane as an example of combustible gas, and as described above, the detection of low carbon number hydrocarbon gas such as propane can be detected by using the gas detection device according to the present invention.

(2) In the above experiment, an example of the catalyst metal-supporting carrier composed of zirconia and titania was shown, but as described in paragraph [0034] above, since the interaction between the transition metal oxide and water is small, the transition metal oxide can be used as the catalyst metal-supporting carrier.

(3) In the case where the carrier is composed of a transition metal oxide, in the above experiment, an example in which the carrier is composed of only zirconia or titania is shown, but the carrier of the catalyst site may be composed mainly of a transition metal oxide. The main component is 50 mass% or more (in the case of being composed of a plurality of transition metal oxides, the total mass thereof is 50 mass% or more).

In the present invention, it is preferable that the catalyst metal contains platinum as a main component and has a catalyst concentration of 0.3 to 9 mass% based on the total mass of the catalyst metal and the carrier.

Here, the term "platinum as a main component" means that the amount of platinum is smaller than the amount of platinum when platinum is supported in the above range and another metal oxidation catalyst (one or more selected from palladium and iridium) is contained.

(4) In the above description, the case of detecting methane has been mainly described using the heating drive signals shown in fig. 4(a) and (b), but as shown in fig. 4(c), methane and carbon monoxide may be alternately detected together with carbon monoxide detection after methane detection. In the detection of carbon monoxide, the gas detection layer 10 and the catalyst layer 11 are heated to 50 to 250 ℃. During this period (specifically, immediately before the stop of the energization shown by the black circle in fig. 4 (c)), the gas detection section 13 measures the resistance value of the gas detection layer 10, and can detect the concentration of carbon monoxide from the value.

In fig. 4(c), the detection of carbon monoxide is continuously performed immediately after the detection of methane, but a heating suspension step of stopping energization to the heater portion may be interposed between the two detections.

(5) In the above-described embodiment, the case where the heater portion is energized in the gas detection step Ts by a pulse having an energization time of 0.05 to 0.5 seconds, and the pulse energization is repeated at the gas detection period Rt of 20 to 60 seconds through the heating pause step Tr has been described.

This energization system is a system in which so-called pulse heating is repeated for a predetermined gas detection period Rt, and is an example of a normal basic energization system as described above.

Therefore, when there is a possibility that methane, for example, is detected while the basic energization system is being executed, the gas detection period, which is the period of pulse energization (pulse heating), may be set to an arbitrary short period such as a period of 5 seconds to 10 seconds, for example.

On the other hand, as described above, the relationship between the heating time in the gas detection step and the heating stop time in the heating suspension step is preferably shorter in the former than the latter in terms of power saving.

(6) In the above-described embodiment, the example in which the energization of the heater portion in the gas detection step Ts is pulse energization for a period of 0.05 to 0.5 seconds has been shown, but the pulse energization period may be set to 5 seconds or less in a case where the gas detection period Rt is 20 to 60 seconds.

(7) Further, in the embodiment shown heretofore, an example is shown in which the heating suspension step Tr for suspending heating is executed after the gas detection step Ts.

However, according to the gist of the present invention, the heater portion is energized for a period of time corresponding to the above-described heating pause step Tr to heat the gas detection portion and the catalyst portion, which is preferable in terms of moisture resistance.

Therefore, during the gas detection step of detecting the detection target gas while the heater portion is energized to heat the gas detection portion and the catalyst portion, the slight heating step Trh may be performed by heating to a temperature lower than the temperatures reached by the gas detection portion and the catalyst portion in the gas detection step (for example, a temperature lower than 100 ℃ and higher than the normal temperature in the case of performing only methane detection, a temperature lower than the detection temperature of carbon monoxide thereof in the case of performing carbon monoxide detection, and a temperature lower than 100 ℃ and higher than the normal temperature (a temperature of about 50 ℃ in the case of performing carbon monoxide detection at 100 ℃). Fig. 5 shows an example of performing such a slight heating step. Fig. 5(a) is an explanatory view corresponding to fig. 4(a), and a slight heating step Trh is performed immediately after the gas detection step Ts. In this slight heating step Trh, some degree of heating is performed by making some degree of energization. The example shown in this figure is a combination of a slight heating step Trh immediately after the gas sensing step Ts, and a gas sensing period Rt holds. Fig. 5(b) and (c) each show an example of methane detection, and (b) shows an example of a constant heating state shown in (a) with slight heating. (c) The heating is performed slightly by suspending heating (stopping energization) and heating (energization).

That is, in the configuration in which the non-detection step in which the gas detection is not performed is performed after the gas detection step Ts in which the gas detection is performed, the non-detection step may be the heating suspension step Tr or the slight heating step Trh, but in the non-detection step, the heating suspension (stopping of the energization) and the heating (energization) may be arbitrarily combined, and in the non-detection step, the temperatures of the gas detection site and the catalyst site may be set to be lower than the temperatures of both sites in the gas detection step. In this case, if the temperatures of the two portions are maintained at temperatures that are less susceptible to water, the generation of hydrate can be inhibited. The combination of heating suspension (stop of energization) and heating (energization) here includes, of course, any one or more of selection of timing of the combination and selection of magnitude of energization amount. The temperature may change over time.

Further, the temperature management in the non-detection step may employ any means, for example, means other than energizing the heater portion may be employed.

(8) In the above-described embodiment, the gas sensor (gas detection element 20) constituting a part of the gas detection device 100 has a so-called substrate type as shown in fig. 1, but may have another configuration. For example, the insulating layer 7 covering the heater layer 6 may not be provided, and the heater layer 6 may also have the electrode layer 9.

As shown in fig. 6, for example, the gas sensor 20a may have the following structure: a gas detection site 23 made of an oxide semiconductor is formed around the coil 22 of the electrode wire 21 having both an electrode and a heater site, and catalyst layers (catalyst sites) 24 and 25 are formed around the gas detection site. Here, the catalyst layer is 2 layers, but may be a single layer. When the number of layers is 2, the ratio of the catalyst metal can be changed between layers. In this case, the term "platinum as a main component" means that the amount of platinum in at least 1 layer is within the above range and is larger than the amount of the other catalyst metal.

As shown in fig. 7, the gas sensor 20b may be configured as follows: the other electrode 33 is disposed at the center of the coil 32 of the electrode wire 31 having both an electrode and a heater portion, a gas detection portion 34 made of an oxide semiconductor is formed around the coil 32, and a catalyst layer 35 is formed around the gas detection portion.

The gas detection device 100 may be any gas detection device as long as it includes: the present invention is not limited to the embodiments described above, and is not limited to a gas sensor including a heater portion, a gas detection portion whose characteristics change by contact with a detection target gas, and a catalyst portion covering at least a part of the gas detection portion, and configured to detect the detection target gas while energizing the heater portion to heat the gas detection portion and the catalyst portion.

(9) The catalyst portion in which the catalytic metal mainly composed of platinum is supported on the carrier mainly composed of the transition metal oxide may be provided so as to cover at least a part of the gas detection site. This is due to: it is considered that by providing such a catalyst site, selective combustion of the interfering gas can be performed.

Description of the symbols

5: a support layer (substrate);

6: a heater layer (heater portion);

9: an electrode layer (electrode);

10: a gas detection layer (gas detection site);

11: a catalyst layer (catalyst site);

12: a heating control unit;

13: a gas detection unit;

15: a battery (power supply);

20: a sensor element (gas sensor);

100: a gas detection device.