JP2007155529A - Ammonia gas sensor and its manufacturing method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an ammonia gas sensor having a sensitive layer formed easily in a short time, and to provide its manufacturing method. <P>SOLUTION: In manufacturing the ammonia gas sensor, the sensitive layer 40 is formed by separately producing YSZ powder and WO<SB>3</SB>powder in parallel, mixing the YSZ powder and WO<SB>3</SB>powder to form a mixture, and screen-printing paste made of the mixture on the electrode surface side of a substrate 10 via a pair of electrodes 20 and 30. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an ammonia gas sensor that detects an ammonia component contained in a gas to be detected in accordance with an electrical change in characteristics of a sensitive body, and a method for manufacturing the same.

  Conventionally, as this type of ammonia gas sensor, for example, an ammonia sensor described in Patent Document 1 below has been proposed. In this ammonia sensor, the sensitive layer is formed on the substrate via a pair of comb electrodes.

  Here, the above-mentioned sensitive layer is formed as follows. That is, after mixing yttrium hydroxide with a zirconium hydroxide solution prepared by adding aqueous ammonia to an aqueous solution of zirconium oxynitrate and yttrium nitrate, a YSZ powder in a pre-fired state is prepared through drying and firing processes.

Thereafter, the YSZ powder (ZrO ₂ powder) in the pre-fired state is impregnated and supported in an aqueous solution of ammonium tungstate adjusted to pH with aqueous ammonia, evaporated to dryness, and then dried and fired to obtain a solid. WO ₃ / YSZ (WO ₃ / ZrO ₂ ), which is a super strong acid substance, is prepared as a sensitive material.

Next, an organic solvent and a dispersing agent are added to the WO ₃ / YSZ to prepare a paste by slurrying, and this paste is screen printed on a substrate through a pair of electrodes and fired to form a sensitive layer. To do.
JP 2005-114355 A

However, in the ammonia sensor, WO ₃ / YSZ, which is a material for forming the sensitive layer, is prepared by impregnating and supporting a pre-fired YSZ powder prepared in advance in an aqueous solution of ammonium tungstate as described above. .

  For this reason, there is a problem that it takes time to form the sensitive layer and thus to manufacture the ammonia sensor.

Further, as described above, since it is essential to impregnate and support the YSZ powder in a pre-fired state in an aqueous solution of ammonium tungstate, there is a problem that the production of WO ₃ / YSZ is troublesome.

  Accordingly, an object of the present invention is to provide an ammonia gas sensor having a sensitive layer formed easily in a short time and a method for manufacturing the same in order to deal with the above-described problems.

In solving the above-mentioned problems, the ammonia gas sensor according to the present invention, according to the description of claim 1,
A pair of electrodes (20, 30) and a sensitive body (40) provided so as to be in contact with the pair of electrodes and having a characteristic that changes electrically according to the ammonia component in the gas to be detected are provided.

  In the ammonia gas sensor, the sensitive body is characterized by being formed by mixing at least two kinds of oxides having different coordination numbers so as to develop a charge-biased portion.

  As described above, the sensitive body is formed by mixing at least two kinds of oxides having different coordination numbers so as to develop a charge-biased portion. Therefore, it is possible to form a sensitive body by preparing at least two kinds of oxides separately from each other and mixing them. As a result, the sensitive body, and thus the ammonia gas sensor can be provided in a short time.

  Moreover, in forming the sensitive body, as described above, at least two kinds of oxides may be prepared separately and mixed together, so that the YSZ powder in the pre-fired state is made of ammonium tungstate as in the conventional case. There is no need to impregnate and support the aqueous solution, and the sensitive body, and thus the ammonia gas sensor, can be easily provided.

  As mentioned above, the ammonia gas sensor provided with the detection characteristic with respect to the ammonia component similar to the past at least can be simply provided in a short time.

According to a second aspect of the present invention, in the method for manufacturing an ammonia gas sensor, the sensitive body (40) is formed so as to be in contact with the pair of electrodes (20, 30).
The sensitive body is characterized in that it is formed by mixing at least two kinds of oxides having different coordination numbers so as to develop an uneven portion of charge.

  As described above, the sensitive body is formed by mixing at least two kinds of oxides having different coordination numbers so as to develop a charge-biased portion. Accordingly, the sensitive body can be formed by mixing at least two kinds of oxides prepared separately from each other. This means that the sensitive body can be formed in a short time. As a result, the ammonia gas sensor can be manufactured in a short time.

  Moreover, in forming the sensitive body, as described above, at least two kinds of oxides may be prepared separately and mixed together, so that the YSZ powder in the pre-fired state is made of ammonium tungstate as in the conventional case. There is no need to impregnate and support an aqueous solution, and the formation of the sensitive body and, consequently, the production of the ammonia gas sensor can be simplified.

  As mentioned above, the ammonia gas sensor provided with the detection characteristic with respect to the ammonia component similar to the past at least can be easily manufactured in a short time.

  According to a third aspect of the present invention, in the method for producing an ammonia gas sensor according to the second aspect, the at least two kinds of oxides are any of the groups IVA, IIIB and IVB. It is characterized by being an oxide containing an element belonging to the group V and an oxide containing an element belonging to the group VIA.

  Thus, the at least two kinds of oxides are an oxide containing an element belonging to any of the groups IVA, IIIB and IVB and an oxide containing an element belonging to the VIA group. As a matter of course, it is possible to form a sensitive body excellent in the detection characteristics of ammonia gas.

According to a fourth aspect of the present invention, in the method for producing an ammonia gas sensor according to the third aspect,
The oxide containing an element belonging to any of the groups IVA, IIIB and IVB is at least one oxide of ZrO ₂ , TiO ₂ , Al ₂ O ₃ and SiO ₂ ,
The oxide containing an element belonging to group VIA is at least one oxide of WO ₃ and MoO ₃ .

  Thereby, the effect of the invention of claim 3 can be further improved.

  According to the fifth aspect of the present invention, in the method for producing an ammonia gas sensor according to the third or fourth aspect, the oxide containing an element belonging to any of the groups IVA, IIIB and IVB The stabilizing material for is characterized in that it is an oxide containing an element belonging to either group IIA or group IIIA.

  As a result, an oxide containing an element belonging to any of the groups IVA, IIIB and IVB is stabilized with an oxide containing an element belonging to any of the group IIA and IIIA as a stabilizing material. The As a result, the effect of the invention according to claim 3 or 4 can be achieved, as well as the characteristics of the sensitive body, and thus the detection characteristics of the ammonia gas sensor without any change in heat resistance, etc. It can be kept stable.

According to a sixth aspect of the present invention, in the method for producing an ammonia gas sensor according to the fifth aspect,
The oxide containing an element belonging to any of Group IIA and Group IIIA is at least one of CaO, MgO, Y ₂ O ₃ , Yb ₂ O ₃ and Ga ₂ O ₃ .

  Thereby, the effect of the invention of claim 5 can be further improved.

  In addition, the code | symbol in the parenthesis of each said means shows a corresponding relationship with the specific means as described in the implementation shape mentioned later.

  Hereinafter, an embodiment of the present invention will be described with reference to the drawings.

  1 to 3 show an embodiment of an ammonia gas sensor according to the present invention. This ammonia gas sensor includes an alumina substrate 10, both comb-like electrodes 20 and 30, and a sensitive layer 40. Yes. The ammonia gas sensor is applied to, for example, a NOx selective reduction catalyst system that is disposed in an exhaust gas system of a diesel engine mounted on an automobile or the like.

  As can be seen from FIG. 2 or FIG. 3, the pair of electrodes 20 and 30 intersects on the right side surface portion (hereinafter also referred to as the electrode side surface portion) shown in FIG. Is formed.

  Further, the pair of electrodes 20 and 30 are electrically connected to each other at their connection terminals 21 and 31 (see FIG. 2 or FIG. 3) so as to be superimposed on the inner end portions of both leads 11 and 12. . Both leads 11 and 12 are formed in parallel with each other on the left surface portion (hereinafter also referred to as a lead-side surface portion) shown in FIG.

As shown in FIGS. 1 and 2, the sensitive layer 40 is made of a sensitive material for ammonia gas (for example, a mixture of powdered YSZ and powdered WO ₃ ). It is formed on the electrode-side surface portion of the substrate 10 via the pair of electrodes 20 and 30 so as to cover the electrodes 20 and 30. In the present embodiment, the pair of electrodes 20 and 30 and the sensitive layer 40 constitute a sensor element of the ammonia gas sensor.

  Further, as shown in FIG. 2, the ammonia gas sensor includes a resistance temperature detector 50 and a heater 60, and the resistance temperature detector 50 and the heater 60 are built in the substrate 10.

  The resistance temperature detector 50 is made of a platinum resistance, and the resistance temperature detector 50 is located in the substrate 10 immediately below the sensitive layer 40. In addition, the heater 60 is formed in a meandering pattern with a sintered body of platinum paste containing alumina, for example, and the heater 60 is lower than the resistance temperature detector 50 in FIG. Built in the substrate 10. Thus, the heater 60 controls the sensitive layer 40 to a constant temperature based on the resistance value (corresponding to the temperature) of the resistance temperature detector 50.

  In the ammonia gas sensor configured as described above, an AC voltage is applied between the pair of electrodes 20, 30 from the AC power source (not shown) via the leads 11, 12. The resulting impedance is measured. The impedance varies according to the concentration of the ammonia component in the gas to be detected (exhaust gas of the diesel engine) that contacts the outer surface of the sensitive layer 40.

Next, a method for manufacturing the ammonia gas sensor configured as described above will be described.
1. Preparation of Both Leads 11 and 12 and Both Comb-Shaped Electrodes 20 and 30 An alumina substrate including a resistance temperature detector 50 and a heater 60 is prepared as the substrate 10. Thus, both leads 11 and 12 are formed in parallel with each other on the surface of the substrate 10 on the lead side. Thereafter, an electrode pattern corresponding to the comb-like shape of the pair of electrodes 20 and 30 is screen-printed on the electrode-side surface portion of the substrate 10 using a paste made of an electrode material (for example, gold (Au)). To form.

The substrate 10 formed with the electrode pattern in this way is dried for 1 (hr) at 55 (° C.), and then baked for 1 (hr) at 1000 (° C.). A pair of electrodes 20 and 30 are formed on the electrode-side surface portion of the substrate 10.
2. Formation of Sensitive Layer 40 In the step 100 for dissolving zirconium oxynitrate and yttrium nitrate shown in FIG. 4, zirconium oxynitrate and yttrium nitrate are dissolved in water to prepare a mixed solution of zirconium oxynitrate and yttrium nitrate.

  Next, in the hydroxide mixture preparation step 110 of FIG. 4, ammonia water is added to the above-described mixed solution of zirconium oxynitrate and yttrium nitrate to adjust the hydrogen ion index of the mixed solution to pH 8, and the zirconium hydroxide and yttrium hydroxide are then added. A solution of a hydroxide mixture consisting of

  Thereafter, in the filtration washing step 120, the hydroxide mixture is sucked from the solution of the hydroxide mixture made of zirconium hydroxide and yttrium hydroxide thus prepared, and then washed.

  Next, in the drying step 130, the hydroxylated mixture filtered and washed as described above is dried at 110 (° C.) for 24 (hr) with a dryer.

Thereafter, in the next pre-baking step 140, the hydroxylated mixture dried as described above is pre-baked for 24 (hr) at 400 (° C.) in a baking furnace, and then the main baking step 150. Then, the calcined hydroxylated mixture is calcined at 800 (° C.) for 5 (hr). Thereby, powdery YSZ (hereinafter also referred to as YSZ powder) is produced. The YSZ powder has a shape with a high specific surface area of 50 (m ₂ / g).

  On the other hand, in addition to the YSZ manufacturing step, in the ammonium tungstate aqueous solution manufacturing step 200 (see FIG. 4), ammonium tungstate is dissolved in water to prepare an ammonium tungstate aqueous solution.

  Next, in the ammonium tungstate aqueous solution pH adjustment step 210, ammonia water is added to the ammonium tungstate aqueous solution prepared as described above, and the hydrogen ion index of the ammonium tungstate aqueous solution is adjusted to pH 10 to pH 11.

Thereafter, in the drying step 220, the ammonium tungstate solution prepared as described above is dried at 110 (° C.) for 24 (hr) with a dryer, and then in the baking step 230, a baking furnace. Then, it is fired at 800 (° C.) for 5 (hr). Thereby, powdery tungsten oxide WO ₃ (hereinafter also referred to as WO ₃ powder) is produced.

As described above, when the YSZ powder and the WO ₃ powder are separately prepared, in the paste preparation process 300, the YSZ powder and the WO ₃ powder are put in a mortar together with an organic solvent and a dispersing agent, and 4 ( After dispersing and mixing for hr), a binder is added, and wet mixing is further performed for 4 (hr) to prepare a slurry-like paste composed of a mixture of YSZ powder and WO ₃ powder.

Thereafter, in the printing step 310, the paste made of the mixture of the YSZ powder and the WO ₃ powder produced as described above is applied to the electrode of the substrate 10 through the pair of electrodes 20 and 30 so as to cover the pair of electrodes 20 and 30. Screen printing is performed on the side surface portion, and baking is performed at 600 (° C.) for 1 (hr) in the next baking step 320. Thereby, the sensitive layer 40 is formed and the manufacture of the ammonia gas sensor is completed.

In the ammonia gas sensor manufactured in this way, as described above, after the YSZ powder and the WO ₃ powder were produced in parallel with each other, the YSZ powder and the WO ₃ powder were mixed to form a mixture. The sensitive layer 40 was formed with the paste.

Therefore, unlike the formation of the sensitive layer of the conventional ammonia gas sensor, the time required for the formation of the sensitive layer and thus the production of the ammonia gas sensor is greatly increased by the amount of the YSZ powder and the WO ₃ powder that are produced in parallel. It can be shortened.

Moreover, since the YSZ powder and the WO ₃ powder may be mixed as described above, it is not necessary to prepare a YSZ powder in a pre-fired state and impregnate it in an aqueous solution of ammonium tungstate as in the prior art. Formation can be simplified.

  Incidentally, using the model gas generator as an evaluation device, the characteristics of the ammonia gas sensor manufactured as described above and the comparative example were measured and evaluated under the following measurement conditions.

Above measurement conditions:
The temperature of the gas generated by the model gas generator is 280 (° C.). The temperature of the ammonia gas sensor and the comparative example is 400 (° C.).

The composition of the gas generated by the model gas generator is 10 (vol%) oxygen (O ₂ ), 5 (vol%) carbon dioxide (CO ₂ ), 5 (vol%) water (H ₂ ). O), ammonia (NH ₃ ) having a concentration within the range of 0 (ppm) to 1500 (ppm), each interfering gas (C ₃ H ₆ , CO, NO and NO ₂ ) having a concentration (100 ppm), and nitrogen.

  Moreover, in the said evaluation, the said comparative example is manufactured as follows. Among the manufacturing processes of the ammonia gas sensor described above, the manufacturing processes of the leads 11 and 12 and the comb-shaped electrodes 20 and 30 and the melting process 100 to the preliminary baking process 140 of zirconium oxynitrate and yttrium nitrate (FIGS. 4 and 5). The YSZ in a pre-fired state is produced by passing through (see).

  Thereafter, an ammonium tungstate aqueous solution preparation step 200 and an ammonium tungstate aqueous solution pH adjustment step 210 (see FIGS. 4 and 5) are performed to prepare an ammonium tungstate solution as described above.

  Next, in the YSZ impregnation step 400 of FIG. 5, the YSZ in the pre-fired state is impregnated and supported on the ammonium tungstate aqueous solution prepared as described above. Thereafter, the impregnated and supported YSZ in a pre-baked state is evaporated to dryness by an evaporator in a drying step 410 and then dried at 110 (° C.) for 12 (hr) by a dryer.

When this drying is completed, in the next main baking step 420, the YSZ after impregnation support dried as described above is main-baked at 800 (° C.) for 5 (hr) in a baking furnace. Thereby, a powdery solid superacid material (10 (wt%) WO ₃ / YSZ) is produced.

In this way, when the powdered solid superacid material is produced, in the next paste production step 430, the powdered solid superacid material is placed in a mortar together with the organic solvent and the dispersing agent. After being dispersed and mixed for 4 (hr), a binder is added, and wet mixing is further performed for 4 (hr) to prepare a slurry paste made of WO ₃ / YSZ.

Next, in the printing step 440, the above-mentioned paste made of WO ₃ / YSZ is screen-printed on the electrode-side surface portion of the substrate 10 through the pair of electrodes so as to cover the pair of electrodes 20 and 30. In the baking step 450, baking is performed at 600 (° C.) for 1 (hr). Thereby, the said comparative example is manufactured.

Under the measurement conditions as described above, the ammonia gas sensor and the comparative example were arranged in the gas having the gas composition of the model gas generator. And by applying an alternating voltage of a predetermined frequency (400 (Hz)) between the pair of electrodes of the ammonia gas sensor and between the pair of electrodes of the comparative example, respectively, between the pair of electrodes of the ammonia gas sensor and the comparative example The impedance generated between each pair of electrodes was measured. Here, the impedance when the concentration of ammonia = 0 (ppm) is defined as the base impedance. This impedance was measured by changing the concentration of ammonia (NH ₃ ) within the range of 0 (ppm) to 150 (ppm) in the gas having the above gas composition.

According to such measurement results, the graphs 1 and 2 shown in FIG. 6 and the graphs 3 and 4 shown in FIG. 7 were obtained. In FIG. 6, graph 1 shows the relationship between the impedance of the ammonia gas sensor and the concentration of ammonia (NH ₃ ), and graph 2 shows the relationship between the impedance of the comparative example and the concentration of ammonia (NH ₃ ). Show the relationship. In addition, the graph 1 is shown on the coordinate plane which consists of a horizontal axis | shaft and the vertical axis | shaft which passes along ammonia concentration = 0 (ppm) on this horizontal axis in FIG. Moreover, the graph 2 is shown on the coordinate plane which consists of a horizontal axis | shaft in FIG. 6 and the vertical axis | shaft which passes along the ammonia concentration on this horizontal axis = 200 (ppm).

In FIG. 7, graph 3 shows the relationship between the ammonia sensitivity and ammonia (NH ₃ ) concentration of the ammonia gas sensor, and graph 4 shows the ammonia sensitivity and ammonia (NH ₃ ) concentration of the comparative example. The relationship between the two is substantially the same.

  The ammonia sensitivity, that is, the impedance change rate is defined by the following equation (1).

Ammonia sensitivity = {(Zb−Z) / Zb} × 100 (%) (1)
However, Zb is a base impedance and Z is an impedance when ammonia is added.

  According to the graphs of FIGS. 6 and 7, the base impedance of the ammonia gas sensor is slightly smaller than the base impedance of the comparative example as shown in FIG. Is almost the same as the ammonia sensitivity (see FIG. 7).

  Therefore, it can be seen that the detection characteristic of the ammonia gas sensor for the ammonia component is not substantially different from the detection characteristic of the comparative example for the ammonia component.

  Next, in order to evaluate the thermal durability of the ammonia gas sensor, a thermal durability test was performed on the ammonia gas sensor together with the comparative example. Specifically, by the above model gas generator, the ammonia gas sensor and each heater of the comparative example are heated to 500 (° C.) in the atmosphere under the measurement conditions, whereby the ammonia concentration = A thermal endurance test was conducted as to how the ammonia sensitivity at 100 ppm changed with the passage of the endurance time.

  As a result of this thermal endurance test, graphs 5 and 6 shown in FIG. 8 were obtained. Graph 5 shows the relationship between the endurance time of the ammonia sensitivity of the ammonia gas sensor, and graph 6 shows the relationship between the endurance time of the ammonia sensitivity of the comparative example. I'm doing it.

  According to this, it can be seen that the ammonia sensitivity of the ammonia gas sensor hardly decreases even after the endurance time of 1000 (hr), like the ammonia sensitivity of the comparative example. Therefore, it can be seen that the thermal durability of the ammonia gas sensor is substantially the same as that of the comparative example.

  Next, when Raman measurement (Raman measurement) was performed on the sensitive layer of the ammonia gas sensor and the sensitive layer of the comparative example, graphs 7 and 8 as shown in FIG. 9 were obtained. Here, the graph 7 shows the relationship between the spectral intensity and the Raman shift in the sensitive layer of the ammonia gas sensor, and the graph 8 shows the relationship between the spectral intensity and the Raman shift in the sensitive layer of the comparative example.

According to these graphs, in the Raman measurement, the sensitive layer of the ammonia gas sensor is active with respect to crystallized WO ₃ , and in each vicinity of wave numbers 723 (cm ⁻¹ ) and 819 (cm ⁻¹ ), WO 3 It can be seen that ₃ peaks (see the vicinity of each line 7-1 and 7-2 in FIG. 9) are expressed. On the other hand, when WO ₃ and ZrO ₂ are chemically bonded as in the sensitive layer of the comparative example, WO ₃ is not precipitated and the WO ₃ peak does not appear.

Thus, unlike the sensitive layer of the comparative example, the sensitive layer of the ammonia gas sensor can confirm the WO ₃ peak by Raman measurement, as described above. Therefore, it can be seen that the ammonia gas sensor includes different chemical bonds even in the sensitive layer made of the same material as the sensitive layer of the comparative example.

Moreover, it investigated about the influence of each interference gas with respect to the said ammonia gas sensor and the said comparative example. Here, the respective interference gas, C ₃ H _6, CO described above, and NO and NO _2.

According to this, bar graphs 9-1 and 9-2 as shown in FIG. 10 were obtained. Here, the graph 9-1 shows the relationship between the ammonia sensitivity at the concentration (100 ppm) of the ammonia gas sensor, ammonia (NH ₃ ), and each of the interference gases. Graph 9-2 shows the relationship between ammonia sensitivity at the concentration of 100 (ppm) in the above comparative example, ammonia (NH ₃ ), and each of the interference gases.

  According to each of the graphs 9-1 and 9-2, in both the ammonia gas sensor and the comparative example, the ammonia sensitivity is about 76% for ammonia. Is zero. Therefore, it can be seen that the dependence of the ammonia gas sensor on the interfering gas is shown by the same result as the dependence on the interfering gas of the comparative example. Thereby, it turns out that the detection selectivity with respect to ammonia of the said ammonia gas sensor is ensured satisfactorily without being influenced by each said interference gas similarly to the detection selectivity with respect to the ammonia of the said comparative example.

As can be seen from the above description, the sensitive layer of the ammonia gas sensor is different from the sensitive layer of the comparative example, and as described above, by mixing the YSZ powder of the main firing and the WO ₃ powder, An ammonia gas sensor having the same long-term stability as in the comparative example and good ammonia detection characteristics can be easily manufactured in a short time.

In carrying out the present invention, the following various modifications are possible without being limited to the above embodiments.
(1) The main component zirconia (YSZ) and the accessory component tungsten oxide (WO ₃ ) are synthesized from nitrate and ammonium salt, respectively, but even if commercially available oxides are used as these zirconia and tungsten oxide, Similar to the above embodiment, an ammonia gas sensor can be manufactured. However, the specific surface area of the main component is preferably 10 (m ² / g) or more.
(2) YSZ which is one of the forming materials of the sensitive layer 40 is not limited to this, and is at least one of YSZ (that is, ZrO ₂ ), TiO ₂ , Al ₂ O ₃ and SiO _2. Also good.
(3) The sensitive layer 40 may be formed by mixing at least two kinds of oxides having different coordination numbers so as to develop a charge bias portion.

  Here, the at least two kinds of oxides may be an oxide containing an element belonging to any of the groups IVA, IIIB and IVB and an oxide containing an element belonging to the VIA group.

The oxide containing an element belonging to any one of the groups IVA, IIIB, and IVB described above is at least one oxide of ZrO ₂ , TiO ₂ , Al ₂ O _3, and SiO ₂ . The oxide containing an element belonging to Group VIA may be at least one oxide of WO ₃ and MoO ₃ .

  Further, if an oxide containing an element belonging to any of Group IIA or IIIA is used as a stabilizing material for an oxide containing an element belonging to any of the above-mentioned groups IVA, IIIB and IVB, Oxides containing elements belonging to any of the groups IVA, IIIB, and IVB are stabilized, and the characteristics of the sensitive layer, and thus the detection characteristics of the ammonia gas sensor, are not changed in heat resistance, etc. , Can be kept stable.

Here, the oxide containing an element belonging to any of the IIA group and the IIIA group described above may be at least one of CaO, MgO, Y ₂ O ₃ , Yb ₂ O _3, and Ga ₂ O _3. Good.

It is a perspective view which shows one Embodiment of the ammonia gas sensor to which this invention is applied. It is sectional drawing which follows the 2-2 line in FIG. It is a disassembled perspective view of the ammonia gas sensor of FIG. It is a figure which shows the main manufacturing processes of the ammonia gas sensor of FIG. It is a figure which shows the main manufacturing processes of the comparative example in the said embodiment. It is a graph which shows the relationship between each impedance of the ammonia gas sensor and comparative example in the said embodiment, and the density | concentration of ammonia, respectively. It is a graph which shows the relationship between each ammonia sensitivity and ammonia density | concentration of the ammonia gas sensor and comparative example in the said embodiment, respectively. It is a graph which shows the relationship between each ammonia sensitivity and durable time of the ammonia gas sensor in the said embodiment, and a comparative example, respectively. It is a graph which shows the relationship between the spectrum intensity | strength and Raman shift in the Raman measurement of each sensitive layer of the ammonia gas sensor and comparative example in the said embodiment, respectively. It is a graph which shows the relationship between each ammonia sensitivity (it has a density | concentration of 100 ppm), ammonia, and each interfering gas of the ammonia gas sensor and comparative example in the said embodiment, respectively.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 ... Board | substrate, 20, 30 ... Electrode, 40 ... Sensitive layer.

Claims (6)

In an ammonia gas sensor comprising a pair of electrodes and a sensitive body that is provided so as to be in contact with the pair of electrodes and has a characteristic that changes electrically according to the ammonia component in the gas to be detected.
The ammonia gas sensor is characterized in that the sensitive body is formed by mixing at least two kinds of oxides having different coordination numbers so as to develop a charge bias portion. In the method of manufacturing an ammonia gas sensor formed by forming a sensitive body so as to be in contact with a pair of electrodes,
The method for producing an ammonia gas sensor, wherein the sensitizer is formed by mixing at least two kinds of oxides having different coordination numbers so as to develop a charge-biased portion.   The at least two kinds of oxides are an oxide containing an element belonging to any of the groups IVA, IIIB and IVB and an oxide containing an element belonging to the VIA group. The manufacturing method of the ammonia gas sensor of description. The oxide containing an element belonging to any of the groups IVA, IIIB and IVB is at least one oxide of ZrO ₂ , TiO ₂ , Al ₂ O ₃ and SiO ₂ ,
Oxide containing an element belonging to the group VIA The manufacturing method of the ammonia gas sensor according to claim 3, characterized in that at least one oxide of WO ₃ and MoO _3.   The stabilizer for an oxide containing an element belonging to any one of the groups IVA, IIIB and IVB is an oxide containing an element belonging to any of the groups IIA and IIIA The method for manufacturing an ammonia gas sensor according to claim 3 or 4. The oxide containing an element belonging to any of the IIA group and the IIIA group is at least one of CaO, MgO, Y ₂ O ₃ , Yb ₂ O _3, and Ga ₂ O _3. Item 6. A method for producing an ammonia gas sensor according to Item 5.

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