JP2996921B2 - Carbon monoxide detection sensor - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a carbon monoxide detection sensor for detecting the concentration of carbon monoxide present in a gas.

[0002]

2. Description of the Related Art As is well known, carbon monoxide is a gaseous substance at room temperature having flammability and strong toxicity to the human body, and is important as a raw material in the chemical industry. is there. Carbon monoxide is particularly often generated due to incomplete combustion, and means for detecting the concentration of carbon monoxide in exhaust gas is required as a direct means for detecting incomplete combustion. In detecting the concentration of carbon monoxide (CO) in such combustion exhaust gas, a sensor having the following characteristics is required. Have sensitivity to relatively high concentrations of CO. Operate continuously even under high humidity conditions. It is not affected by hydrogen (H ₂ ) concentration that occurs in incomplete combustion and fluctuates depending on the combustion mode. Conventionally, as a carbon monoxide sensor, a semiconductor sensor and a contact combustion type sensor are roughly classified, and a sensor based on tin oxide is known as a semiconductor sensor.

[0003]

However, the conventional carbon monoxide sensor has a drawback that carbon monoxide and hydrogen cannot be distinguished, and solving this problem is indispensable to obtain a sensor with high accuracy. As a technique for enhancing the selectivity to H ₂ of the semiconductor sensor CO which is based on tin oxide described above, the following two methods in view of the operating temperature has been studied. A method in which a precious metal is added to a semiconductor based on tin oxide, and the semiconductor is operated at a temperature of 100 ° C. or less as a detection unit. A method in which an alkaline earth metal or an alkali metal is added to a semiconductor based on tin oxide, and the semiconductor is operated at a temperature of about 300 ° C. as a detection unit. In the method (1), since the operating temperature is 100 ° C. or lower, water is adsorbed and the sensitivity gradually decreases. In order to maintain the sensitivity, it is necessary to periodically heat to remove water. Therefore, it is necessary to separately provide a heating means for volatilizing the moisture, which increases the cost and generates undetectable time. Also, according to the method, it is certain that H ₂ of CO
Selectivity increases for, but still sensitivity has for H _2, there is still room for improvement.

[0004] Further, even a contact-combustion sensor in which a noble metal catalyst is carried on a platinum coil or the like, a sensor having both durability and selectivity has not been obtained. An object of the present invention is to provide a sensor which is excellent in selective detection performance for carbon monoxide even in the presence of hydrogen and operates stably even in the presence of moisture.

[0005]

Means for Solving the Problems The present invention is a carbon monoxide detection sensor comprising a gas detection section and the electrode, the gas detection unit contains copper oxide and Periodic Table Group IIA metal compound
The present invention relates to a carbon monoxide detection sensor which is a mixture . Copper oxide semiconductors were known to have sensitivity to carbon monoxide, but their sensitivity was lower than tin oxide, and they also had sensitivity to hydrogen, so they have not been valued so far. Was. The inventor has found that by adding a Group IIA metal compound of the periodic table to the copper oxide semiconductor, the sensitivity to hydrogen can be suppressed to a level that does not affect the detection of carbon monoxide, and completed the present invention.

The Group IIA metal compound of the Periodic Table to be added to the copper oxide semiconductor used as the material for the gas detection section includes:
1 selected from barium, strontium and calcium
The compounds of the above alkaline earth metals are preferably used. These compounds have high performance of suppressing the sensitivity of the copper oxide semiconductor to hydrogen.

In a preferred embodiment, these Group IIA metal compounds are contained in the gas detector as at least one phase of an oxide, a hydroxide, a carbonate, or a composite oxide with copper. is there.

The composition of the Group IIA metal compound of the periodic table added to the copper oxide semiconductor used as the gas detector material is
When the equivalent of the metal in the group IIA metal compound in the periodic table is x, 0 <x /
It is preferable that Cu is contained in the range of Cu ≦ 2.0. If the Group IIA metal compound is not contained, the sensitivity of the gas detector to hydrogen increases, which is opposite to the sensitivity to carbon monoxide, and the compounding amount of the Group IIA metal compound is equivalent to copper. Although the sensitivity to hydrogen is maintained low even when the pressure is 2.0 or more, insulating carbonate and the like are precipitated, and the resistance value of the sensor increases. Furthermore, since carbonate absorbs moisture and embrittlement of a detection part progresses, addition of 2.0 or more is not preferable.

In the present invention, it is preferable that the gas detecting section is formed on a substrate as a thin film. Further, the gas detection section may be made by a powder sintering method, and when manufactured by the powder sintering method, in order to increase the physical strength of the gas detection section, as a constituent material, It is also preferred to use a binder material which does not influence. The selectivity in detecting CO with respect to hydrogen remains the same regardless of whether a thin film is formed or a powder is formed by the powder sintering method.

Furthermore, the surface of the gas detecting portion of the carbon monoxide detection sensor of the present invention may further include a platinum group catalyst layer, by providing such catalyst layers, other than H _2, for example, unburned As a result, miscellaneous gases such as hydrocarbons as fuel components can be removed, and as a result, the selectivity of the sensor for CO can be further improved.

In the structure of the sensor of the present invention, it is preferable that the substrate on which the gas detecting portion is formed can be heated by a heater. With this configuration, the temperature of the gas detection unit can be kept constant in order to stabilize the sensitivity, and the condition with the highest sensitivity can be set by selecting the heating temperature. Can be removed by heating even if it is contaminated with tar or the like.

[0012]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The structure of a sensor according to the present invention will be described based on an example shown in FIG. In the sensor shown in FIG. 1, the gas detecting section is formed by a thin film forming method.

The gas detector 1 is formed on a substrate 4, and the substrate 4 has a built-in heater. The electrodes 2 and 3 are provided in the gas detection unit.

Known methods such as a thin film forming method and a powder sintering method can be used as a method of forming the gas detecting portion on the substrate, and a chemical vapor deposition method (CVD) can be used as the thin film forming method.
Method) is preferable, and examples thereof include thermal CVD, plasma CVD, and laser CVD.

The gas detector of the present invention can also be manufactured by a powder sintering method. In the powder sintering method, commercially available high-purity copper oxide (CuO) powder is used, and a metal compound of Group IIA of the periodic table, preferably an alkaline earth metal compound, particularly preferably CaCO ₃ , SrCO ₃ , BaC is used.
O ₃ powder is added at a predetermined ratio and heat-treated at 600 to 1000 ° C. to obtain a sintered body as a gas detection unit. Sintering is preferably performed on a substrate. Electrode materials are formed at regular intervals on the gas detector thus manufactured. As the electrode material, use of a noble metal such as gold (Au), silver (Ag), and platinum (Pt) is preferable. When only the gas detection unit is formed, it is necessary to fix the gas detection unit to the substrate, and a heating substrate is provided on the surface of the gas detection unit opposite to the electrode forming surface. The gas detector may be heated by burying a heater inside the powder detector when sintering the powder, providing the heater inside the gas detector, and supplying power to the heater.

When the gas detecting section is manufactured by the powder sintering method, a binder material which does not affect the sensitivity can be used. Examples of such a binder material include magnesium oxide (MgO) and silica (SiO ₂ ). And strontium titanate (SrTiO ₃ ).

Further, as the above-mentioned catalyst used in the gas detecting section, a noble metal catalyst such as Pt, Pd, Rh, Au or the like can be used, and may be attached to the surface of the gas detecting section.
When the gas detection unit is manufactured by the powder sintering method, the gas detection unit may be attached by mixing and sintering with the raw material powder.
By using such a catalyst, sensitivity to CO can be improved.

Regarding the operating temperature of the sensor, the sensitivity to CO decreases as the temperature of any of the gas detectors of the present invention increases, whereas the response speed decreases at a temperature of 250 ° C. or less, which is not preferable. The optimal temperature range is 300 ~
350 ° C.

[0019]

[Creation of gas detector]

(Example 1) A commercially available high-purity CuO powder was used as a Cu source as a raw material for producing a gas detector, BaCO ₃ was used as a raw material for forming a Ba compound, and the Ba / Cu ratio was set to a predetermined ratio. These raw materials are mixed, and 600 to 96
By a heat treatment at 0 ° C., a sintered body gas detector was formed. The equivalent ratio of Ba / Cu was varied in the range of 0 to 2. The equivalent ratio of Ba / Cu used specifically is 0.0
005, 0.001, 0.005, 0.01, 0.0
3, 0.05, 0.11, 0.67, 1.0, and 2.0. For comparison, a system without the Ba compound was also examined. As a result of measuring the gas detector thus obtained by X-ray diffraction, the crystal phase of the sintered body was Cu
For those containing O and BaCuO ₂ as the main components and having a large amount of added Ba and low heat treatment temperature, a BaCO ₃ phase was also observed. An electrode was formed using platinum as an electrode material on one surface of the above-described gas detection unit, and a heating substrate was fixed on the other surface to form a sensor element for gas detection.

(Example 2) As a raw material of a Ca compound,
Except that CO ₃ was used, Ca /
A Cu-based gas detector was prepared. However, the firing temperature was 600 to 960 ° C. The equivalent ratio of Ca / Cu specifically used is 0.0005, 0.00
1, 0.005, 0.01, 0.03, 0.05, 0.
1, 0.2, 0.5 and 2.0. For comparison, C
The system to which the compound a was not added was also examined. As a result of measuring the gas detection unit thus obtained by X-ray diffraction, the crystal phase of the sintered body was mainly composed of CuO and Ca ₂ CuO ₃ , and the amount of Ca added was large and the heat treatment temperature was low. As for those, a CaCO ₃ phase was also observed. Also in the gas detection unit obtained in this example, the electrodes and the substrate were provided as in Example 1, and the gas detection element was used.

Example 3 Sr compound as a raw material
Except that CO ₃ was used, Sr /
A Cu-based gas detector was prepared. The equivalent ratio of Sr / Cu used specifically was 0.0005, 0.001,
0.005, 0.01, 0.03, 0.05, 0.1
1, 0.5, 1.0 and 2.0. For comparison, S
A system without the addition of the r compound was also studied. As a result of measuring the gas detector thus obtained by X-ray diffraction, the crystal phase of the sintered body was CuO, CuSrO ₂ , Cu
_An SrCO ₃ phase was also found in those containing ₂ SrO ₃ as a main component and having a large amount of Sr added or a low heat treatment temperature. Also in the gas detection unit obtained in this example, the electrodes and the substrate were provided as in Example 1, and the gas detection element was used.

[Measurement of Sensitivity] As a test gas, a gas obtained by mixing carbon monoxide (CO) and hydrogen (H ₂ ) at a predetermined concentration in air and further adding a certain amount of water vapor was used. The oxygen concentration of this test gas was about 20%, and the volume ratio of humidity was about 10% (about 80 g / m ³ in terms of absolute humidity). The measurement is performed by applying a predetermined voltage to the substrate of the gas sensor element illustrated in FIG.
The sample was heated so as to be maintained at a predetermined temperature in the range of ° C., was brought into contact with a test gas in this state, the electric resistance between both electrodes was measured, and the relationship between the change and the CO gas concentration was measured. The gas sensitivity S was determined by the following equation. S = Rg / Rb Rg: CO , resistance when contacted with a test gas containing H _2. Rb: resistance value when contacted with a gas having a concentration of 0. As is apparent from this equation, when S becomes 1, there is no sensitivity to the gas. When a plurality of types of gases are present, the target gas can be sufficiently detected if the S value of the target gas (CO) is low and the S value of the other gas (H ₂ ) is even closer to 1. .

Table 1 and FIGS. 2 to 7 show the results of measuring the sensitivity of the test gas containing CO or H ₂ using the gas sensor elements obtained in Examples 1 to 3.

[0024]

[Table 1]

For the Ba-based copper oxide semiconductor sensor element of Example 1, the sensitivity S was measured for a test gas containing CO at a concentration of 1000 ppm and a test gas containing H ₂ at a concentration of 1000 ppm, and Ba was added. The dependence of the sensitivity on the amount is shown in the column of Table 1 "Ba". From this result,
Even with the addition of a small amount of Ba having a Ba / Cu ratio of about 0.0005, the sensitivity to hydrogen greatly decreases, the sensitivity to carbon monoxide exceeds the sensitivity to hydrogen, and Ba / C
When u = 0.03 or more, the ratio of the resistance value to 1000 ppm of H ₂ and the resistance value to 0 ppm becomes almost 1 and the sensitivity to hydrogen is lost, and it can be seen that CO can be selectively detected with particularly high sensitivity.

FIG. 2 shows that Ba / Cu = 0.11 and 0.67.
The dependence of the sensitivity on the concentration of CO and H ₂ was shown for the _two elements using the gas detection part having the composition ratios of The measurement was performed at a gas detector temperature of 300 ° C and a volume ratio of humidity of the test gas of about 10
%. From this result, it can be seen that CO in a gas containing hydrogen, such as exhaust gas, and whose concentration fluctuates can be selectively detected with almost no fluctuation in hydrogen concentration.

Further, FIG. 3 shows the sensitivity to the test gas containing CO at a concentration of 1000 ppm and the test gas containing H ₂ at a concentration of 1000 ppm with respect to the element using the gas detection unit of Ba / Cu = 1.0. The relationship between the temperature and the temperature of the gas detector was shown. Even when the gas detection unit temperature is 400 ° C.,
Shows selective sensitivity to hydrogen, but C
It can be seen that the O detection sensitivity is also high, which is preferable.

For the Ca-based copper oxide semiconductor sensor element of Example 2, the sensitivity S was measured for a test gas containing CO at a concentration of 1000 ppm and a test gas containing H ₂ at a concentration of 1000 ppm, and Ca was added. The dependence on the amount is shown in the column of "Ca" in Table 1. From these results, Ca /
Even with the addition of a small amount of Ca having a Cu ratio of about 0.0005, the sensitivity to carbon monoxide exceeds the sensitivity to hydrogen, and from around Ca / Cu = 0.01, the sensitivity to hydrogen almost disappears, as in Example 1. It can be seen that carbon monoxide can be selectively detected with particularly high sensitivity.

FIG. 4 shows that Ca / Cu = 0.1, 0.5,
The dependence of the sensitivity on the concentration of CO and H ₂ was shown for the element using the gas detection unit having a composition ratio of 2.0. The measurement was performed at a gas detector temperature of 300 ° C and a volume ratio of humidity of the test gas of about 10
%. From this result, the aforementioned Ba / C
Similarly, in the case of the u-system, even under conditions where hydrogen is present and its concentration fluctuates, particularly as occurs in exhaust gas, it is hardly affected by fluctuations in hydrogen concentration, and CO is selectively produced. It can be seen that it can be detected.

FIG. 5 shows the sensitivity of the element using Ca / Cu = 1.0 to the test gas containing CO at a concentration of 1000 ppm and the test gas containing H ₂ at a concentration of 1000 ppm. The relationship between the temperature and the temperature of the gas detector was shown. Even when the gas detection unit temperature is 400 ° C.,
Shows selective sensitivity to hydrogen, but C
It can be seen that O detection sensitivity is high and preferable.

For the Sr-based copper oxide semiconductor sensor element of Example 3, the sensitivity S was measured for a test gas containing CO at a concentration of 1000 ppm and a test gas containing H ₂ at a concentration of 1000 ppm, and Sr was added. The dependence on the amount is shown in the column of Table 1 “Sr”. From this result, Sr /
Even with a slight addition of Sr having a Cu ratio of about 0.0005, the sensitivity to carbon monoxide exceeds the sensitivity to hydrogen, and from around Sr / Cu = 0.03, the sensitivity to hydrogen almost disappears, as in Example 1. It can be seen that carbon monoxide can be selectively detected with particularly high sensitivity.

FIG. 6 shows that Sr / Cu = 0.1, 0.5,
The dependence of the sensitivity on the concentration of CO and H ₂ was shown for the element using the gas detection unit having a composition ratio of 2.0. The measurement was performed at a gas detector temperature of 300 ° C and a volume ratio of humidity of the test gas of about 10
%. From these results, as in Examples 1 and 2, the Sr / Cu-based sensor also selects CO in a gas containing hydrogen whose concentration fluctuates, such as exhaust gas, with almost no influence of fluctuation in hydrogen concentration. It can be seen that it is possible to detect it.

FIG. 7 shows the sensitivity of the element using the gas detector of Sr / Cu = 1.0 to the test gas containing CO at a concentration of 1000 ppm and the test gas containing H ₂ at a concentration of 1000 ppm. The relationship between the temperature and the temperature of the gas detector was shown. Even when the gas detection unit temperature is 400 ° C.,
Shows selective sensitivity to hydrogen, but C
It can be seen that O detection sensitivity is high and preferable.

[0034]

According to the present invention, even in the presence of hydrogen gas, it has excellent selective detection performance for carbon monoxide,
A sensor that can operate continuously even under humid conditions can be obtained. Such a sensor can also be suitably used for detecting carbon monoxide in exhaust gas.

[Brief description of the drawings]

FIG. 1 is a schematic diagram showing a configuration of a carbon monoxide sensor of the present invention.

FIG. 2 is a graph showing the dependence of the sensitivity of a sensor using a Ba / Cu-based gas detector on the concentration of CO and H _2.

FIG. 3 is a graph showing the temperature dependence of the sensitivity of a sensor using a Ba / Cu-based gas detection unit to the gas detection unit;

FIG. 4 is a graph showing the CO and H ₂ concentration dependence of the sensitivity of a sensor using a Ca / Cu-based gas detector.

FIG. 5 is a graph showing the temperature dependence of the sensitivity of a sensor using a Ca / Cu-based gas detection unit, and the temperature of the gas detection unit.

FIG. 6 is a graph showing the dependence of the sensitivity of a sensor using an Sr / Cu-based gas detector on CO and H ₂ concentrations.

FIG. 7 is a graph showing the temperature dependence of the sensitivity of a sensor using an Sr / Cu-based gas detection unit on the gas detection unit.

[Explanation of symbols]

 1 gas detector 2, 3 electrode 4 substrate

──────────────────────────────────────────────────続 き Continuation of the front page (72) Inventor Souichi Tabata 4-1-2, Hirano-cho, Chuo-ku, Osaka-shi, Osaka Inside Osaka Gas Co., Ltd. No. 1-2, Osaka Gas Co., Ltd. (56) References JP-A-6-102225 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) G01N 27/12 JICST file (JOIS )

Claims (8)

(57) [Claims] 1. A carbon monoxide detection sensor comprising a gas detector and an electrode, wherein the gas detector comprises copper oxide and a periodic table II.
A carbon monoxide detection sensor , which is a mixture containing a group A metal compound and has a reduced sensitivity to hydrogen. 2. The carbon monoxide detection sensor according to claim 1, wherein the Group IIA metal compound of the periodic table is a compound of one or more alkaline earth metals selected from barium, strontium, and calcium. 3. The method according to claim 1, wherein the group IIA metal compound is contained as at least one phase of an oxide, a hydroxide, a carbonate, or a composite oxide with copper. Carbon monoxide detection sensor. 4. The Group IIA metal compound of the Periodic Table whose metal-based equivalent number x is based on the copper-based equivalent weight of copper
0 <x / Cu ≦ 2.0.
4. The carbon monoxide detection sensor according to any one of 3. 5. The carbon monoxide detection sensor according to claim 1, wherein the gas detection section is formed on a substrate as a thin film. 6. The gas detecting section according to claim 1, wherein the gas detecting section is formed by a powder sintering method, and includes a binder material that does not affect sensitivity as a constituent material thereof.
Item 12. The carbon monoxide detection sensor according to Item 1. 7. The carbon monoxide detection sensor according to claim 1, wherein a catalyst layer is further provided on the surface of the gas detection unit. 8. The carbon monoxide detection sensor according to claim 1, wherein the substrate on which the gas detection section is formed can be heated by a heater.