JP7831107B2 - gas sensor - Google Patents

Description

This invention relates to a gas sensor. More particularly, it relates to a COe gas sensor that eliminates false detections due to sulfur dioxide and exhibits excellent COe sensitivity.

Conventionally, various gas sensors have been known for detecting gas components or determining gas concentrations in a gas mixture, including sensors based on solid electrolytes and operated by the hybrid potential principle, as well as catalytic combustion type gas sensors.

These gas sensors are required to accurately detect the target gas without being affected by impurities, even when impurities are mixed in with the target gas. For example, a known technique involves a catalytic combustion type gas sensor equipped with two sensor units that separately detect the concentration of the mixed target gas and impurities, and the concentration of the impurities alone. The concentration of the target gas is then determined by subtracting the impurities concentration from the mixed gas concentration (see, for example, Patent Document 1).

International Publication No. 2018/135100

The composition of impurities that may be present in the target gas varies greatly depending on the environment in which the gas sensor is placed, and the impurities that cause false detections are also diverse. For example, when the target gas is COe (CO equivalent) gas, sulfur dioxide ( _SO₂ ) gas may cause false detections as an impurity gas. In particular, when the target gas is exhaust gas from fuels such as coal, the exhaust gas may contain as much as 2000 ppm of _SO₂ gas. In such cases, the influence of _SO₂ gas as an impurity gas on the detection of COe gas is significant, and accurate measurement has sometimes been difficult.

When detecting COe gas using a mixed potential type gas sensor, it is necessary to eliminate the influence of _SO₂ gas, prevent false detections, and accurately obtain the COe gas concentration.

As a result of diligent research, the inventors focused on the fact that the characteristics of COe gas sensitivity and _SO₂ gas sensitivity differ in terms of film thickness dependence or temperature dependence. They then discovered that by using at least two sensors with different film thicknesses or temperatures of the detection electrodes, both COe concentration and _SO₂ concentration can be calculated, and false detection of COe gas due to _SO₂ gas can be reduced, thus completing the present invention.

According to one embodiment, the present invention is a COe gas sensor comprising a first sensor section including a first detection electrode and a counter electrode connected ionically via a solid electrolyte substrate, and a second sensor section including a second detection electrode and a counter electrode connected ionically via a solid electrolyte substrate,
a) The film thickness of the first detection electrode is smaller than the film thickness of the second detection electrode, or
b) The present invention relates to a COe gas sensor equipped with a mechanism capable of maintaining the temperature of the first detection electrode at a lower temperature than the temperature of the second detection electrode.

In the COe gas sensor described above, it is preferable that the first detection electrode and the second detection electrode are sintered bodies containing platinum-containing alloy particles and solid electrolyte particles, and that the counter electrode is a sintered body containing platinum-containing metal particles and solid electrolyte particles.

In the COe gas sensor described above, it is preferable that the film thickness of the first detection electrode is 10 μm or more thinner than the film thickness of the second detection electrode.

In the COe gas sensor described above, the film thickness of the first detection electrode is preferably 15 μm to 90 μm.

In the COe gas sensor described above, it is preferable that the mechanism is a heating unit capable of independently controlling the temperatures of the first detection electrode and the second detection electrode.

The present invention relates to a gas detector, according to another embodiment, which incorporates the previously described COe gas sensor in a tubular casing having an open end, wherein the first detection electrode, the second detection electrode, and the counter electrode are configured to be in contact with the target gas flowing in from the open end.

In the gas detector described above, an oxygen gas sensor is further provided within the tubular casing having the open end. The oxygen gas sensor includes a solid electrolyte substrate and at least a pair of electrodes ionically conductively connected via the solid electrolyte substrate. The pair of electrodes preferably includes an oxygen detection electrode made of a sintered body containing platinum-containing metal particles and solid electrolyte particles, and a counter electrode for oxygen detection made of a sintered body containing platinum-containing metal particles and solid electrolyte particles. The oxygen detection electrode is configured to contact the target gas flowing in from the open end, while the counter electrode for oxygen detection is shielded from the target gas atmosphere.

The present invention, according to another embodiment, is a method for detecting COe gas using the aforementioned gas sensor, comprising the steps of: obtaining the electromotive force Em ₁ of the first sensor unit and the electromotive force Em ₂ of the second sensor unit; and calculating the COe gas concentration _Xcoe and the SO2 gas concentration XSO2 based on the correlation between parameters a ₁₁ , a ₂₁ , b ₁₁ , b ₂₁ determined in advance for the first sensor unit, parameters a ₁₂ , a ₂₂ , b _{12 ,} b ₂₂ determined in advance for the second sensor unit, and Em ₁ , Em ₂ , wherein a ₁₁ , a ₁₂ are constants indicating the concentration dependence of the COe gas electromotive force, b ₁₁ , b ₁₂ are constants indicating the sensitivity limit concentration of the COe gas, a ₂₁ , a ₂₂ are constants indicating the concentration dependence of the _SO2 gas electromotive force, and b ₂₁ , b ₂₂ are constants indicating the sensitivity limit concentration of the _SO2 gas.

In the detection method described above, the constant is a constant determined by setting the first detection electrode to a first temperature and the second detection electrode to a second temperature. The step of obtaining the electromotive force is preferably performed with the first detection electrode at a first temperature and the second detection electrode at a second temperature, where the first temperature is 580 to 650°C and the second temperature is 30 to 100°C higher than the first temperature.

According to the present invention, a mixed potential type COe gas sensor can be provided that can selectively detect COe gas with high sensitivity without being affected by _SO₂ gas.

Figure 1 is a conceptual diagram showing the cross-sectional structure of a COe gas sensor according to the first embodiment of the present invention. Figure 2 is a conceptual logarithmic graph illustrating the characteristic measurement of the first sensor unit in a COe gas detection method using a COe gas sensor according to the first embodiment of the present invention. Figure 3 is a conceptual logarithmic graph illustrating the characteristic measurement of the second sensor unit in a COe gas detection method using a COe gas sensor according to the first embodiment of the present invention. Figure 4 is a conceptual diagram showing an example of a gas detector according to a second embodiment of the present invention. Figure 5 is a conceptual cross-sectional view of the COe gas sensor located inside the casing of the gas detector shown in Figure 4. Figure 6 is a conceptual diagram showing another example of a gas detector according to a second embodiment of the present invention. Figure 7 is a conceptual cross-sectional view of the COe gas sensor located inside the casing of the gas detector shown in Figure 6. Figure 8 is a cross-sectional view taken along the line A-A in Figure 6. Figure 9 is a conceptual diagram showing yet another example of a gas detector according to a second embodiment of the present invention. Figure 10 is a conceptual diagram showing yet another example of a gas detector according to a second embodiment of the present invention.

Embodiments of the present invention will be described below with reference to the drawings. However, the present invention is not limited to the embodiments described below.

[First Embodiment: COe Gas Sensor]
The present invention relates to a COe gas sensor according to a first embodiment. The COe gas sensor according to this embodiment is a COe gas sensor that includes a first sensor part including a first detection electrode and a counter electrode connected ionically via a solid electrolyte substrate, and a second sensor part including a second detection electrode and a counter electrode connected ionically via a solid electrolyte substrate,
a) The film thickness of the first detection electrode is smaller than the film thickness of the second detection electrode, or
b) A COe gas sensor comprising a mechanism capable of maintaining the temperature of the first detection electrode lower than the temperature of the second detection electrode.

The COe gas sensor according to this embodiment measures a gas that includes COe gas, which is the gas to be detected, as well as non-detectable gases. Here, COe gas is a gas produced during the incomplete combustion of fuel, and contains carbon monoxide (CO) and hydrogen ( _H₂ ). Therefore, in this specification, COe gas concentration refers to the total concentration of CO gas and _H₂ gas. The COe gas sensor according to the present invention is a gas sensor that can detect the COe gas concentration and also detect the sulfur dioxide ( _SO₂ ) gas concentration separately from COe gas.

In the COe gas sensor according to this embodiment, there are two possible embodiments: one in which the COe gas concentration and _SO₂ gas concentration are obtained based on the electromotive force difference obtained from two or more sensor sections with different detection electrode thicknesses (embodiment a), and another in which the COe gas concentration and _SO₂ gas concentration are obtained based on the electromotive force difference obtained from two or more sensor sections with different detection electrode temperatures (embodiment b). Each embodiment will be described below.

[Aspect a: Sensor utilizing the difference in film thickness of the detection electrode]
Figure 1 is a schematic cross-sectional view of a COe gas sensor according to embodiment a of the first embodiment. The COe gas sensor 1 according to embodiment a consists of a first sensor section 13 and a second sensor section 17. The first sensor section 13 includes a solid electrolyte substrate 10, a first detection electrode 11, and a counter electrode 12. The second sensor section 17 includes a solid electrolyte substrate 14, a second detection electrode 15, and a counter electrode 16.

The first sensor unit 13 will now be described. The solid electrolyte substrate 10 is a component that forms a three-phase interface between the first detection electrode 11 or counter electrode 12 and the gas phase containing the gas to be detected, thereby enabling ion conduction. The shape of the solid electrolyte substrate 10 is not particularly limited; it is sufficient as long as it can connect the first detection electrode 11 and the counter electrode 12 in a way that enables ion conduction. Therefore, in addition to the flat solid electrolyte substrate 10 shown in Figure 1, for example, a cylindrical substrate or a cylindrical substrate with one end closed may also be used.

The solid electrolyte substrate 10 is preferably stabilized zirconia. Examples include, but are not limited to, zirconia stabilized with rare earth metal oxides such as yttria and ceria, calcia-stabilized zirconia, and magnesia-stabilized zirconia. From the viewpoint of ion conductivity, yttria-stabilized zirconia is particularly preferred.

The first detection electrode 11 functions as the working electrode and is configured to measure the difference in electromotive force between it and the counter electrode 12. In Figure 1, the first detection electrode 11 and the counter electrode 12 are each formed in contact with the solid electrolyte substrate 10, and are spaced apart from each other. However, it is sufficient that the first detection electrode 11 and the counter electrode 12 are ionically conductively coupled via the solid electrolyte substrate 10, and for example, another ionically conductive member may be interposed between the first detection electrode 11 and the solid electrolyte substrate 10. Also, in Figure 1, the first detection electrode 11 and the counter electrode 12 are spaced apart on one surface of the flat solid electrolyte substrate 10, but it is also possible to arrange the detection electrode on one surface of the flat solid electrolyte substrate 10 and the counter electrode on the other surface. However, it is necessary to configure the first detection electrode 11 and the counter electrode 12 to be in contact with the same gas-phase atmosphere, and the first detection electrode 11 and the counter electrode 12 are arranged in such a manner that the atmosphere between the first detection electrode 11 and the counter electrode 12 is not blocked by the solid electrolyte substrate.

The first detection electrode 11 may be a sintered body comprising metal particles made of a metal containing platinum (Pt) or a metal alloy containing Pt, and solid electrolyte particles. The metal alloy containing Pt may include alloys of Pt and rhodium (Rh), or alloys of Pt and gold (Au), etc. The mass ratio of Pt to other metals in the Pt-containing alloy may be, for example, about 98:2 to 85:15, but is not particularly limited. The average particle size of the metal particles may be about 0.5 to 2.5 μm, but is not particularly limited. The solid electrolyte particles may be stabilized zirconia particles, and may be one or more selected from any stabilized zirconia listed as materials for the solid electrolyte substrate 10. Furthermore, the stabilized zirconia may have the same composition as the stabilized zirconia that forms the main component of the solid electrolyte substrate 10, or it may have a different composition. Yttria-stabilized zirconia particles are particularly preferred for the solid electrolyte particles. The average particle size of the solid electrolyte particles may be approximately 0.1 to 1 μm, but is not particularly limited.

Such a sintered body can be obtained by dispersing a mixture containing metal particles made of Pt or a Pt alloy and solid electrolyte particles in a suitable solvent, such as an organic solvent dissolved in a binder, and then applying and shaping the resulting paste onto a solid electrolyte substrate 10, for example, in a thin layer, and firing it in air at 1200 to 1400°C.

The material of the counter electrode 12 may be a sintered body containing a metal containing platinum (Pt) or metal particles composed of platinum and Pt, and solid electrolyte particles. The particle size and preferred composition range of the metal particles and solid electrolyte particles may be the same as those of the first detection electrode 11, and the manufacturing method of the sintered body may also be the same as that of the first detection electrode 11.

The first sensor unit includes detection units (not shown) connected to the first detection electrode 11 and the counter electrode 12, respectively. The detection units include a detection circuit and wiring. The wiring includes a wire with one end connected to the first detection electrode 11 and the other end connected to the detection circuit, and a wire with one end connected to the counter electrode 12 and the other end connected to the detection circuit. The detection circuit may be a device capable of measuring the electromotive force (potential difference) between the first detection electrode 11 and the counter electrode 12, and may be a general-purpose electrometer. The wiring may also be made of a conductive material, and may be made of Pt wire or a sintered body with the same composition as the electrode material to which the wiring is connected.

The second sensor unit 17 will now be described. The configuration of the second sensor unit 17 may be substantially identical to that of the first sensor unit 13. Therefore, the material and shape of the solid electrolyte substrate 14, the material and shape of the second detection electrode 15 and the counter electrode 16, and their positional relationship may also be substantially identical to those of the first sensor unit 13. The configuration of the detection unit (not shown) may also be identical, and only requires the inclusion of a detection circuit consisting of equipment capable of measuring the electromotive force between the second detection electrode 15 and the counter electrode 16 wiring, and the wiring connecting them.

In embodiment a, the film thickness _t1 of the first detection electrode 11 is smaller than the film thickness _t2 of the second detection electrode 15. The difference between the film thickness _t1 of the first detection electrode 11 and the film thickness _t2 of the second detection electrode is preferably 10 μm or more, and more preferably 30 μm or more. Furthermore, the film thickness _t1 of the first detection electrode is preferably 15 μm to 90 μm. This is because a clear difference in the electromotive force characteristics of COe and _SO₂ occurs within this film thickness range.

The relationship between the film thickness _t1 of the first detection electrode 11 and the film thickness of the counter electrode 12 is not particularly limited. Similarly, the relationship between the film thickness _t2 of the second detection electrode 15 and the film thickness of the counter electrode 16 is not particularly limited. The relationship between the film thicknesses of the two counter electrodes 12 and 16 is also not limited, but it is preferable that their film thicknesses be the same, for example, they can be about 20 to 50 μm.

In the illustrated embodiment, the first sensor unit 13 and the second sensor unit 17 each independently comprise separate solid electrolyte substrates and counter electrodes. However, in this invention, the first sensor unit 13 and the second sensor unit 17 can share a solid electrolyte substrate. In this case, the counter electrodes can also be optionally shared. That is, the first detection electrode, the second detection electrode, and the counter electrodes paired with each detection electrode may be located on a single continuous solid electrolyte substrate, or the first detection electrode, the second detection electrode, and a single counter electrode may be located on the same substrate.

The COe gas sensor according to this embodiment may also include a heater (not shown) as a further optional element. The heater may be a device capable of raising the solid electrolyte substrate 10 to a predetermined temperature as needed, and may be a thin-layer heater made of a tungsten (W) thin film or a platinum (Pt) thin film, a ceramic heater, or any other heater. If the first sensor unit 13 shown in Figure 1 further includes a heater, the heater can be formed, for example, by providing an insulating film on one surface of the solid electrolyte substrate 10, on the surface opposite to where the first detection electrode 11 and counter electrode 12 are provided, so that the first detection electrode 11 and counter electrode 12 and the heater face each other via the solid electrolyte substrate 10 and the insulating film. Alternatively, the heater may be provided near the solid electrolyte substrate, for example around the solid electrolyte substrate, without contact with the solid electrolyte substrate, but is not limited to any particular embodiment. The second sensor unit 17 can also be provided with a heater in a similar configuration. The first sensor unit 13 and the second sensor unit 17 may be equipped with separate heaters, or they may be equipped with a single heater that heats both sensor units.

Next, a method for manufacturing a gas sensor having this configuration will be described. The manufacturing method for the gas sensor according to this embodiment includes the step of forming detection electrodes 11 and 15 and counter electrodes 12 and 16 on solid electrolyte substrates 10 and 14 for both the first sensor section 13 and the second sensor section 17.

In the electrode formation process of the first sensor unit 13, a first detection electrode 11 and a counter electrode 12 are formed on the solid electrolyte substrate 10. The method for forming each electrode is as described above. It is preferable to form both a paste made of the material for the first detection electrode 11 and a paste made of the material for the counter electrode 12 on the solid electrolyte substrate 10, and then arrange wiring connecting the first detection electrode 11 and the counter electrode 12 to the detection circuit on the solid electrolyte substrate 10 before firing them. The solid electrolyte substrate 10 can be a commercially available product, or it can be manufactured by molding the solid electrolyte material into a desired shape prior to the electrode formation process. Furthermore, in a gas sensor that includes a heater, which is an optional component, on the solid electrolyte substrate, the heater can be formed on the solid electrolyte substrate 10 by forming an electrically insulating layer such as alumina in advance, and then forming a heater electrode pattern made of Pt paste or the like by printing and firing it. Through the electrode formation process, a gas sensor including the solid electrolyte substrate 10, the first detection electrode 11, the counter electrode 12, and the wiring can be obtained. The same applies to the second sensor unit 17. When forming the first detection electrode, the second detection electrode, and the counter electrode on a single solid electrolyte substrate, these can be deposited and fired simultaneously.

Figure 1 illustrates a COe gas sensor 1 consisting of a first sensor unit and a second sensor unit, but the COe gas sensor may also include additional sensor units. The additional sensor units may include additional detection electrodes, and the film thickness of the additional detection electrodes may be within the preferred film thickness range of the first or second detection electrode, and may have the predetermined preferred film thickness difference in relation to either the first or second detection electrode. The number of additional sensor units is not particularly limited in principle. Providing additional sensor units may offer the advantage of obtaining more accurate calculation results.

Next, a COe gas detection method using a COe gas sensor according to embodiment a will be described. The COe gas detection method can also be called a method for operating the COe gas sensor. The COe gas detection method using a COe gas sensor according to embodiment a includes the following steps.
(1) A step of obtaining the electromotive force Em ₁ of the first sensor unit and the electromotive force Em ₂ of the second sensor unit. (2) A step of calculating the COe gas concentration Xcoe and the SO2 gas concentration XSO2 based on the correlation between the parameters a ₁₁ , a ₂₁ , b ₁₁ , b ₂₁ determined in advance for the first sensor unit, the parameters a _{12 , a 22} , b ₁₂ , b ₂₂ determined in advance for the second sensor unit, and Em ₁ , Em _2.

The gas to be measured may generally be a gas that may contain COe gas. Typically, it may be a gas generated in equipment such as waste incinerators or boilers, but is not limited to these. The temperature of the gas generated in the equipment is not particularly limited, but may be, for example, -10°C to 600°C. The temperature of these gases can be controlled to reach a predetermined temperature of 600°C or higher when they come into contact with the first and second sensor units. For gas detection, the sensor according to embodiment a of the first embodiment can be installed in a flue or the like through which such the gas to be measured flows. In this case, the gas sensor is installed such that both the first detection electrode 11 and the counter electrode 12 of the first sensor unit 13, and both the second detection electrode 15 and the counter electrode 16 of the second sensor unit 17, are in contact with the gas to be measured.

Preliminary Step: Determination of Sensor Characteristics In the method according to this embodiment, a step to determine the sensor characteristics is performed before the COe gas sensor is put into operation. Taking into account individual differences in COe gas sensors, this step must be performed individually for all COe gas sensors before they are put into operation. Generally, for one COe gas sensor, it is sufficient to determine the characteristics once before putting it into use. In some cases, it is also possible to perform characteristic determination periodically and calibrate the sensor characteristics. The determination of sensor characteristics can be performed by the following steps.
1) For the first sensor unit, the step of experimentally obtaining the dependence of the electromotive force difference between the first detection electrode and the counter electrode (hereinafter referred to as sensitivity; unit: -Ewc/mV) on the COe gas concentration (ppm) and the dependence of the sensitivity on the _SO₂ gas concentration (ppm). 2) For the second sensor unit, the step of experimentally obtaining the dependence of the sensitivity (-Ewc/mV) on the COe gas concentration (ppm) and the dependence of the sensitivity (-Ewc/mV) on the _SO₂ gas concentration (ppm). 3) The step of plotting the experimental results on a graph where the X-axis is gas concentration, the Y-axis is sensitivity, and the X-axis is displayed on a semi-logarithmic scale, obtaining an approximate straight line on the high-concentration side, and obtaining the slope and X-axis intercept of the approximate straight line.

1) In this step, the sensitivity is measured by bringing an experimental gas containing COe at a known concentration and free from impurities into contact with the first sensor unit. Measurements can be taken at approximately 4 to 10 points within the COe concentration range expected during gas sensor operation, preferably within the range of 10 ppm to 3000 ppm. Here, COe can be, for example, an equimolar mixture of CO and _H₂ . Similarly, the sensitivity is measured by bringing an experimental gas containing _SO₂ gas at a known concentration and free from impurities into contact with the first sensor unit. The concentration range of the _SO₂ gas to be measured may be the same as that of the COe gas, for example, 10 ppm to 3000 ppm. Furthermore, the sensor temperature conditions and experimental gas flow rate conditions in this step are preferably those expected for the sensor temperature and the flow rate of the gas to be measured during gas sensor operation. When using the sensor according to embodiment a, the sensor temperature can generally be around 600 to 700°C, but is not limited to this condition. Furthermore, the measured gas flow velocity refers to the flow velocity of the gas being measured when it comes into contact with the sensor.

2) In this step, the second sensor unit is measured in the same manner as in step 1). Measurements in steps 1) and 2) can be performed simultaneously.

3) Plots are created for both the first sensor unit and the second sensor unit. Figure 2 shows an example of a plot created for the first sensor unit. In the three-phase interface gas sensor according to the first embodiment, as shown in Figure 2, when the gas concentration dependence of sensitivity is plotted on a semi-logarithmic graph of the x-axis, a linear relationship with a constant slope is generally observed on the high-concentration side. The term "high concentration" here varies depending on the characteristics of the sensor and is not limited to a specific numerical range. Those skilled in the art can extract the high-concentration region showing a linear relationship with a constant slope based on the plot results. In Figure 2, the concentration dependence of COe gas is shown in black, and the concentration dependence of _SO₂ gas is shown in white circles. In addition, the line extrapolated to the high-concentration plot is shown as a dashed line, and the x-intercept of the extrapolated line is also shown in black or white circles. Here, the parameter representing the slope is a _ij , and the parameter representing the x-intercept where the sensitivity is 0 is b _ij . i=1 is a parameter related to COe, i=2 is a parameter related to _SO₂ , and i=m is a parameter related to the mixed gas. j=1 is a parameter related to the first sensor unit, and j=2 is a parameter related to the second sensor unit.

From Figure 2, the slope a ₁₁ and intercept b ₁₁ of the COe graph, and the slope a ₂₁ and intercept b ₂₁ of the _SO₂ graph are obtained. All of these are values specific to the first sensor unit and are constants. Similarly, from Figure 3, the slope a ₁₂ and intercept b ₁₂ of the COe graph, and the slope a ₂₂ and intercept b ₂₂ of the _SO₂ graph are obtained. All of these are values specific to the second sensor unit and are constants. The inventors have found that by configuring the first and second sensor units to have different film thicknesses of the detection electrodes, the X-axis intercept and graph slopes, which represent the gas concentration dependence characteristics of sensitivity, differ for both COe gas and _SO₂ gas. Then, using eight parameters _a11 , _b11 , _a21 , _{b21, a12} , _b12 , _a22 , and _b22 , we conceived of deriving a relationship between the COe gas concentration, _SO2 gas concentration, and the electromotive force of each sensor. An example of the method for deriving the relationship will be explained below.

From Figures 2 and 3, if we let the COe gas concentration be the variable X _COe , the _SO₂ gas concentration be the variable X _SO₂ , and the sensitivity be the variable E _ij , then in the region where a linear relationship holds, the relationship between gas concentration and sensitivity can be expressed by the following equation using each parameter.

When calculating the sensitivity (electromotive force E _m ) in the case of a mixed gas, assuming a parallel circuit of internal resistance _R and electromotive force E, E _m1 and E _m2 can be expressed by the following formulas when the gas sensitivity of the first sensor unit is E ₁₁ , E ₂₁ and internal resistance R 1, and the gas sensitivity of the second sensor unit is E ₁₂ , E ₂₂ and internal resistance R ₂ .
E _m1 = 1/(1+A) E ₁₁ + 1/(1+A ^-1 ) E ₂₁
E _m2 = 1/(1+A) E ₁₂ + 1/(1+A ^-1 ) E ₂₂

Here, A is the internal resistance ratio of the electrodes A = _R1 / _R2 . However, since this is the gas sensitivity at the same electrode, assuming A = 1, the sensitivity (electromotive force) of the first sensor unit and the second sensor unit to the mixed gas can be expressed by the following equation.
2E _m1 =E ₁₁ +E ₂₁
2E _m2 =E ₁₂ +E ₂₂

2E _m1 =E ₁₁ +E ₂₁ =a ₁₁ (log(X _COe )-log(b ₁₁ ))+a ₂₁ (log(X _SO2 )-log(b ₂₁ ))
2E _m2 = E ₁₂ + E ₂₂ = a ₁₂ (log(X _COe )-log(b ₁₂ ))+a ₂₂ (log(X _SO2 )-log(b ₂₂ ))

The data is compiled into log(X _COe ) and log(X _SO2 ).
Multiplying both sides by the inverse matrix from the left and removing the logarithm, X _COe and X _SO2 can be expressed by the following equations (1) and (2).

The COe gas detection method is carried out using the main formula obtained in the preliminary step. Note that the calculation method for deriving the formula is not limited to the method described herein. If the COe gas concentration and SO₂ gas concentration can be derived from the relational formulas shown in Figures 2 and ₃ , it is also possible to use calculation methods such as artificial intelligence.

Step 1: Step to obtain electromotive forces _Em1 and _Em2 In Step 1, the electromotive force _Em1 of the first sensor unit and the electromotive force _Em2 of the second sensor unit are obtained. When obtaining the electromotive forces, a COe gas sensor according to embodiment a is used, and the temperature of the gas in contact with the first detection electrode 11 and the second detection electrode 15, and the gas flow rate are the same as in the characteristic determination experiment in the preliminary step.

Step 2: Gas Concentration Calculation Step In Step 2, the COe gas concentration and _SO₂ gas concentration are calculated from the equation derived in the preliminary step and the electromotive forces _Em1 and _Em2 obtained in Step 1. This calculation step allows for the separate acquisition of COe gas concentration and _SO₂ gas concentration without misdetecting _SO₂ gas as COe gas, enabling accurate measurement of COe gas.

Furthermore, if an additional sensor unit is provided, and this additional sensor unit is designated as the nth sensor unit, then further parameters _a1n , _{b1n, a2n} , and _b2n for the nth sensor are determined in a preliminary step. Then, the relationship between gas concentration and sensitivity, and the relationship between the sensitivity (electromotive force) of the nth sensor to the mixed gas are sequentially derived, and, similar to equations (1) and (2), a relationship can be obtained in which X _COe and X _SO2 are expressed using the electromotive force and parameters of each sensor.

[Aspect b: Sensor utilizing the temperature difference of the sensing electrodes]
The COe gas sensor according to embodiment b also consists of a first sensor section and a second sensor section, and each sensor section is common in that it comprises a solid electrolyte substrate, a detection electrode, and a counter electrode. The materials and manufacturing methods of the solid electrolyte substrate, detection electrode, and counter electrode are also common, and the solid electrolyte substrate and counter electrode may be one each.

In embodiment b, the film thickness of the first detection electrode and the second detection electrode may be the same, and there is no need for them to be different, which is a difference from embodiment a. Furthermore, embodiment b differs in that it includes a mechanism (hereinafter referred to as the temperature holding mechanism) capable of holding the first detection electrode and the second detection electrode at different temperatures. The temperature holding mechanism is not particularly limited and may be a device capable of holding the first detection electrode at a first temperature and the second detection electrode at a second temperature when detection is performed, or a relative positional relationship with the target gas that can be held at these temperatures. Here, the temperature of the first detection electrode refers to the temperature at the intersection of the diagonals if the part of the electrode pattern of the first detection electrode excluding the lead portion is rectangular, and is the temperature measured by an electrically insulated thermocouple or resistance thermometer type sensor. The first temperature may be 580 to 650°C, and is preferably 600 to 620°C. It is also preferable that the second temperature is 30 to 100°C higher than the first temperature.

An example of a temperature-maintaining mechanism is a heater that allows for separate temperature control of the first detection electrode and the second detection electrode. The mechanism may also include a heater as exemplified in embodiment a, a temperature sensor, and a device that enables temperature control.

One example of a temperature maintenance mechanism is the positional relationship between the first and second detection electrodes on the solid electrolyte substrate. The COe gas sensor according to this embodiment is typically used in piping or other systems through which the target gas flows, such as in plant equipment. In this case, the gas sensor can be configured such that the second detection electrode is positioned closer to the target gas than the first detection electrode on the solid electrolyte substrate. In this case, a temperature sensor for detecting the temperature of each detection electrode can be provided.

In a typical embodiment, in embodiment b, the first detection electrode and the second detection electrode may have the same film thickness, surface area, material, and structure. However, one or more of these characteristics may differ.

The COe gas detection method using a COe gas sensor according to embodiment b, like embodiment a, includes a preliminary step of determining the sensor characteristics, a first step of obtaining electromotive forces _Em1 and _Em2 , and a second step of calculating the gas concentration.

In the preliminary step, the dependence of sensitivity (-Ewc/mV) on COe gas concentration (ppm) and the dependence of sensitivity (-Ewc/mV) on _SO₂ gas concentration (ppm) are experimentally obtained for the first sensor unit and the second sensor unit, respectively. In embodiment b, the first sensor unit obtains the gas concentration dependence of sensitivity by maintaining the temperature of the first detection electrode at a first temperature, and the second sensor unit obtains the gas concentration dependence of sensitivity by maintaining the temperature of the second detection electrode at a second temperature. The inventors found that by operating the first sensor unit and the second sensor unit under conditions where the detection electrode temperatures are different, the X-axis intercept and the slope of the graph representing the gas concentration dependence characteristics of sensitivity differ for both COe gas and _SO₂ gas. Therefore, in embodiment b as well, the plot shown in Figure 2 can be obtained from the first sensor unit, and the plot shown in Figure 3 can be obtained from the second sensor unit. Similar to embodiment a, the parameter representing the slope is denoted as a _ij , and the parameter representing the X-axis intercept where the sensitivity is 0 is denoted as b _ij , with both i and j defined in the same way as in embodiment a. As a result, for the operation of each sensor part at the first and second temperatures, a relationship _equation between the COe _gas concentration, _SO₂ gas concentration, and the electromotive force of each sensor part can be derived using the eight parameters a ₁₁ , b 11, a _21, b ₂₁ , a ₁₂ , b ₁₂ , a 22, and b _22. The specific relationship equations are the same as equations (1) and (2) in embodiment a.

In embodiment b, the parameters derived in the preliminary step are specific to the COe gas sensor, taking into account individual differences in the sensor, and are specific to the first and second temperatures. Therefore, even when using a COe gas sensor, if the first and second temperatures, which are the measurement conditions when the gas sensor is operating, are changed, it is necessary to determine the numerical values of eight parameters specific to the first and second temperatures in the preliminary step and derive relational equations (1) and (2). Furthermore, by determining the numerical values of the parameters for even more temperatures in the preliminary step, detection becomes possible using the temperature difference between two temperatures selected from those values.

The first step using the COe gas sensor of embodiment b can be carried out in the same manner as in embodiment a, except that the first detection electrode is kept at a first temperature and the second detection electrode is kept at a second temperature to obtain electromotive forces _Em1 and _Em2 , and the second step can be carried out in the same manner as in embodiment a.

In embodiment b, an additional sensor unit can be provided, and parameters can be obtained under additional temperature conditions, a relational expression can be derived, and X _COe and X _SO2 can be calculated.

It is also possible to use the sensors of embodiment a and embodiment b in combination to create a single COe gas sensor.

According to the COe gas sensor of the first embodiment of the present invention, both embodiment a and embodiment b include at least two sensor units, making it possible to accurately obtain the COe gas concentration without being affected by _SO₂ gas. Embodiment a is particularly excellent in that it is easy to achieve the same sensor temperature by making the positional relationship between the heater and the electrode the same. Embodiment b is particularly excellent in that it is possible to make the film thickness conditions the same when coating and molding in a thin layer shape during electrode formation, and it is excellent in that it simplifies the manufacturing conditions.

[Second Embodiment: Gas Detector]
The present invention relates to a gas detector according to a second embodiment. The gas detector according to this embodiment is a gas detector in which the COe gas sensor of the first embodiment is built into a tubular casing having an open end, wherein the first detection electrode, the second detection electrode, and the counter electrode are configured to be in contact with the gas to be measured flowing in from the open end.

The gas detector is equipped with a COe gas sensor and may optionally be equipped with an oxygen gas sensor. The gas detector can have multiple configurations with different solid electrolyte substrate structures and arrangements of multiple electrodes. Each configuration will be described below with reference to the illustrative drawings.

[Aspect 1]
Figures 4 and 5 are conceptual diagrams showing an example of a gas detector according to the second embodiment. Figure 4 is a side view of a test tube-shaped solid electrolyte substrate, and Figure 5 is a cross-sectional view of the solid electrolyte substrate passing through its central axis. The gas detector 2 according to embodiment 1 is a direct insertion type gas detector that incorporates a structure in which a COe gas sensor and an oxygen gas sensor, according to embodiment a of the first embodiment, are integrated. Referring to Figures 4 and 5, the casing 28 contains a test tube-shaped solid electrolyte substrate 21, a first detection electrode 22, a second detection electrode 24, a counter electrode/oxygen detection electrode 23, and an oxygen detection counter electrode 25. It further includes COe detection units 26 and 29 connected to the first detection electrode 22, the second detection electrode 24 and the counter electrode/oxygen detection electrode 23, and an oxygen detection unit connected to the counter electrode/oxygen detection electrode 23 and the oxygen detection counter electrode 25.

The solid electrolyte substrate 21 is a tubular structure with one end closed. More specifically, the solid electrolyte substrate 21 is formed in an elongated cylindrical shape with a constant diameter and a predetermined length, having an open base end in the longitudinal direction and a closed tip end in the longitudinal direction, thus forming a test tube shape. The first detection electrode 22, the second detection electrode 24, and the counter electrode/oxygen detection electrode 23 are provided on the outer wall of the solid electrolyte substrate 21.

The first detection electrode 22 and the second detection electrode 24 are positioned substantially equidistant from the leading edge of the solid electrolyte substrate 21. This allows the first detection electrode 22 and the second detection electrode 24 to be maintained at substantially the same temperature, regardless of the presence or absence of a temperature control device.

The counter electrode/oxygen detection electrode 23 is provided on the outer wall of the solid electrolyte substrate 21, which is located at the tip of the test tube shape, spaced apart from the first detection electrode 22 and the second detection electrode 24. The first detection electrode 22, the second detection electrode 24, and the counter electrode/oxygen detection electrode 23 are ionically conductively connected via the solid electrolyte substrate 21. The counter electrode/oxygen detection electrode 23 functions as a common counter electrode for COe detection, shared with the first detection electrode 22 and the second detection electrode 24, and also functions as a working electrode that comes into contact with the target gas for oxygen detection.

Detection circuit 26 measures the electromotive force _Em1 between the first detection electrode 22 and the counter electrode/oxygen detection electrode 23, and detection circuit 29 measures the electromotive force _Em2 between the second detection electrode 24 and the counter electrode/oxygen detection electrode 23.

The materials and forming methods of the first detection electrode 22, the second detection electrode 24, and the counter electrode/oxygen detection electrode 23 may be as described in the first embodiment. In the gas detector according to embodiment 1, by arranging the first detection electrode 22, the second detection electrode 24, and the counter electrode/oxygen detection electrode 23 as shown in the figure, the COe concentration and _SO2 concentration can be measured separately and accurately due to the sensor characteristics resulting from the difference in film thickness between the first detection electrode 22 and the second detection electrode 24.

Next, an oxygen gas sensor, which is an optional component of the gas detector according to this embodiment, will be described. The oxygen gas sensor includes a detection unit comprising a solid electrolyte substrate 21, a counter electrode/oxygen detection electrode 23, an oxygen detection counter electrode 25, and a detection circuit 27. The material and structure of the counter electrode/oxygen detection electrode 23 may be the same as that of the counter electrode in the first embodiment. The material and structure of the oxygen detection counter electrode 25 may also be the same as that of the counter electrode in the first embodiment. The detection circuit 27 measures the electromotive force between the counter electrode/oxygen detection electrode 23 and the oxygen detection counter electrode 25. The oxygen detection counter electrode 25 is provided on the inner wall of the solid electrolyte substrate 21, which corresponds to the tip of the test tube shape, and is positioned approximately opposite to the counter electrode/oxygen detection electrode 23. That is, the oxygen detection counter electrode 25 is ionically conductively connected to the counter electrode/oxygen detection electrode 23 via the solid electrolyte substrate 21 and functions as an electrode that comes into contact with a calibration gas for oxygen detection. The oxygen detection counter electrode 25 is configured to be isolated from the atmosphere to which the counter electrode/oxygen detection electrode 23 is in contact, i.e., the atmosphere of the gas being measured, by a solid electrolyte substrate 21. The oxygen detection unit can detect oxygen by measuring the electromotive force resulting from the difference between the oxygen concentration in the atmosphere to which the counter electrode/oxygen detection electrode 23 is in contact and the oxygen concentration to which the oxygen detection counter electrode 25 is in contact. The oxygen gas sensor is located within the same casing as the COe gas sensor and can function independently. Therefore, the gas detector according to this embodiment may or may not include an oxygen gas sensor.

The inner wall of the casing 28 may optionally be equipped with a heater (not shown). The heater can be positioned around the solid electrolyte substrate 21 in a manner capable of heating the substrate 21, and can be connected to an external power source.

A gas detection method using a gas detector according to this embodiment will be described. The gas detector according to this embodiment can be directly inserted into a flue or the like through which a high-temperature target gas flows to measure COe, SO₂ _, and optionally oxygen concentration. In this case, generally, the tip of the solid electrolyte substrate 21, i.e., the position where the counter electrode/oxygen detection electrode 23 is provided, is the hottest, and the temperature decreases as you approach the base end, and the temperature distribution generally depends on the distance from the tip. The target gas is introduced to the outer circumference of the solid electrolyte substrate 21 inside the casing 28, and a calibration gas, such as air, is introduced to the inner circumference of the solid electrolyte substrate 21. These introduction paths are hermetically sealed to prevent the atmospheres of the two from mixing. Then, by heating the first detection electrode 22 and the second detection electrode 24 to a predetermined temperature with a heater, the electromotive force between the first detection electrode 22 and the second detection electrode 24, as described in the first embodiment above, and the counter electrode can be measured, and the COe and _SO₂ concentrations in the target gas can be obtained. Furthermore, the difference in oxygen partial pressure between the gas to be measured in contact with the counter electrode/oxygen detection electrode 23 and the calibration gas in contact with the oxygen detection counter electrode 25 generates an electromotive force in the solid electrolyte substrate 21. By measuring this electromotive force, the oxygen concentration in the gas to be measured can be obtained. According to this gas detector, the counter electrodes for COe and _SO2 detection can also be used as oxygen detection electrodes, which has the advantage of enabling accurate and simple measurements with a small number of electrodes.

This embodiment is primarily used in a gas detector equipped with a COe gas sensor according to embodiment a of the first embodiment. However, by providing heaters that allow for individual temperature control of the first detection electrode 22 and the second electrode 24, it can also be applied to a gas detector equipped with a COe gas sensor according to embodiment b of the first embodiment.

[Aspect 2]
Figures 6 to 8 are conceptual diagrams showing another example of a gas detector according to the second embodiment. Figure 6 is a side view of a test tube-shaped solid electrolyte substrate, Figure 7 is a cross-sectional view of the solid electrolyte substrate passing through its central axis, and Figure 8 is a cross-sectional view taken along line A-A in Figure 6. The gas detector 3 according to embodiment 2 is also a direct insertion type gas detector that incorporates a COe gas sensor and an oxygen gas sensor according to embodiment a of the first embodiment. Referring to Figures 6 to 8, the casing 37 contains a test tube-shaped solid electrolyte substrate 31, a first detection electrode 32, a counter electrode 38 for the first detection electrode, a second detection electrode 39, and a counter electrode 40 for the second detection electrode. It also includes an oxygen detection electrode 33 and an oxygen detection counter electrode 34. The system further includes a COe detection circuit 35 connected to the first detection electrode 32 and its counter electrode 38, a COe detection circuit (not shown) connected to the second detection electrode 39 and its counter electrode 40, and an oxygen detection circuit 36 connected to the oxygen detection electrode 33 and its oxygen detection counter electrode 34.

In embodiment 2, the following points differ from embodiment 1: The counter electrode 38 of the first detection electrode and the counter electrode 40 of the second detection electrode are provided separately. Furthermore, the first detection electrode 32, the counter electrode 38 of the first detection electrode, the second detection electrode 39, and the counter electrode 40 of the second detection electrode are all provided on the outer wall surface of the solid electrolyte substrate 31, at substantially equidistant positions from the leading edge of the solid electrolyte substrate 31. Referring to Figure 8, the four electrodes are also arranged equidistant along the outer circumference of the solid electrolyte substrate 31, and a pair of detection electrodes and counter electrodes connected ionically are positioned adjacent to each other. The optional components, the oxygen detection electrode 33 and the oxygen detection counter electrode 34, are provided separately from the electrodes for COe detection, and the electrodes are not shared between different detection circuits.

In Embodiment 2, the gas detection method is substantially the same as in Embodiment 1, and the same effects can be obtained. Furthermore, Embodiment 2, like Embodiment 1, can also be applied to a gas detector equipped with a COe gas sensor according to Embodiment b of the First Embodiment by providing a heater or the like.

Embodiment 2 is particularly advantageous in that, when controlling the oxygen detection electrode and the COe detection electrode to different temperatures, it allows for the use of a simple method, such as setting the temperature by the distance from the heater.

[Appearance 3]
Figure 9 is a conceptual diagram showing yet another example of a gas detector according to the second embodiment. The gas detector 4 is a direct insertion type gas detector in which a COe gas sensor 40 according to aspect a of the first embodiment and an oxygen gas sensor 46 are built as separate structures in a tubular casing 49 having an open end.

The COe gas sensor 40 has a first detection electrode 42, a counter electrode 43 for the first detection electrode, a second detection electrode 44, and a counter electrode 45 for the second detection electrode, all positioned substantially equidistant from the leading edge of the plate-shaped solid electrolyte substrate 41. The leading edge of the plate-shaped solid electrolyte substrate 41 refers to the end closest to the open end of the casing 49. The oxygen gas sensor 47 has an oxygen detection electrode 48 at the leading edge of the outer wall surface of a test-tube-shaped solid electrolyte substrate 47, and an oxygen detection counter electrode (not shown) at the leading edge of the inner wall surface, and has the same structure as in Embodiments 1 and 2. It also includes a detection circuit (not shown) connecting each electrode.

In embodiment 3, the solid electrolyte substrate 41 on which the electrode for COe detection is provided is configured in a flat plate shape and is provided as a separate structure from the oxygen gas sensor 47, which is different from embodiment 2. This configuration is advantageous in that it allows for the independent manufacturing of the oxygen sensor and the COe sensor, enables independent evaluation of sensor characteristics, and maintains a high yield rate for analyzers combining oxygen detection and COe detection.

In Embodiment 3, the gas detection method is substantially the same as in Embodiment 1, and the same effects can be obtained. Furthermore, Embodiment 3, like Embodiment 1, can also be applied to a gas detector equipped with a COe gas sensor according to Embodiment b of the First Embodiment by providing a heater or the like.

[Aspect 4]
Figure 10 is a conceptual diagram showing yet another example of a gas detector according to the second embodiment. The gas detector 5 is a direct insertion type gas detector in which the first sensor section 50 and the second sensor section 54 of the COe gas sensor according to aspect b of the first embodiment and the oxygen gas sensor 58 are built in as separate structures within a tubular casing 61 having an open end.

The COe gas sensor is formed as a separate structure from a first sensor section 50, which has a first detection electrode 53 and a counter electrode 52 for the first detection electrode provided on a flat solid electrolyte substrate 51, and a second sensor section 54, which has a second detection electrode 57 and a counter electrode 56 for the second detection electrode provided on a similarly flat solid electrolyte substrate 55. The first sensor section 50 and the second sensor section 54 are equipped with heaters (not shown) and are configured to be independently temperature-controllable. The oxygen gas sensor 58 has the same structure as in embodiment 3, with an oxygen detection electrode 60 provided at the tip of the outer wall surface of a test tube-shaped solid electrolyte substrate 59 and an oxygen detection counter electrode (not shown) provided at the tip of the inner wall surface. It also includes a detection circuit (not shown) connecting each electrode.

Embodiment 4 differs from Embodiment 3 in that the first sensor unit 50 and the second sensor unit 54 are provided on different solid electrolyte substrates. By providing the first sensor unit 50 and the second sensor unit 54 on separate, independent solid electrolyte substrates, it becomes possible to accurately control and maintain the first detection electrode 53 at a first temperature and the second detection electrode 57 at a second temperature, enabling accurate COe detection using the temperature difference characteristics of the electrodes, as in Embodiment b. In Embodiment 4, the flow of the gas to be measured and the method of oxygen gas detection are substantially the same as in Embodiment 1, and similar effects can be obtained.

The gas detector according to this embodiment can detect COe, _SO₂ , and optionally oxygen with high sensitivity using a single device, and can be advantageously used for industrial gas measurement.

(Example 1)
A COe gas sensor was manufactured according to embodiment a of the first embodiment of the present invention. An yttria-stabilized zirconia substrate was used as the solid electrolyte substrate, and a first detection electrode, a second detection electrode, and a counter electrode were formed on the substrate. The arrangement of the solid electrolyte substrate, the first detection electrode, the second detection electrode, and the counter electrode was the same as in the embodiments shown in Figures 6 to 8. The first detection electrode, the second detection electrode, and the counter electrode all had the same composition, formed using a paste in which a mixture of Pt alloy particles and yttria-stabilized zirconia particles was dispersed in a solvent. Pt wire was used as wiring and fixed to the electrodes with the respective electrode materials. Next, a COe gas sensor comprising a first sensor section and a second sensor section was manufactured by firing these at 1300°C in air. The film thickness of each electrode after firing was as shown in Table 1 below.

In the preliminary step, the manufactured COe gas sensor was placed in a furnace core heated in a tubular furnace, and the sensor characteristics were measured by flowing gas through it. The target gas was flowed through a furnace core with an inner diameter of 28 mm at a rate of 300 ccm, with a flow velocity of 8.1 mm/s. The COe gas used for measuring the sensor characteristics was a mixture of hydrogen gas and CO gas in a molar ratio of 1:1. The ambient temperature was 650°C. Based on the plots created according to Figures 2 and 3, eight parameters were determined as shown in Table 1 below, and relational equations (1) and (2) were obtained.

Using the COe gas sensor of this embodiment, the electromotive force _Em1 of the first sensor and the electromotive force Em2 of the second sensor were measured for COe gas and _SO2 gas, both of known concentrations, under the same conditions as the measurement conditions for the sensor characteristics. Next, the gas concentration was calculated using the derived relational _equation . The result showed that the difference between the calculated concentration and the known concentration was within the acceptable error range.

(Example 2)
A COe gas sensor was manufactured according to embodiment b of the first embodiment of the present invention. The electrode material and manufacturing method were the same as in Example 1. The arrangement of the solid electrolyte substrate, first detection electrode, second detection electrode, and counter electrode was the same as in the embodiment shown in Figure 10. As a temperature holding mechanism, heaters were installed to individually heat the first detection electrode and the second detection electrode, thereby fabricating a COe gas sensor comprising a first sensor section and a second sensor section. The film thickness of each electrode after firing was as shown in Table 2 below. In the preliminary step, gas was flowed under the same conditions as in Example 1, and the first detection electrode and the second detection electrode were heated to the predetermined temperatures shown in Table 2 to measure the sensor characteristics. As a result of plotting according to Figures 2 and 3, eight parameters were determined as shown in Table 2 below, and relational equations (1) and (2) were obtained.

Using the COe gas sensor of this embodiment, the electromotive force _Em1 of the first sensor and the electromotive force Em2 of the second sensor were measured for target gases with known concentrations of COe gas and _SO2 gas, under the same conditions as the measurement conditions for the sensor characteristics. Next, the gas concentration was calculated using the derived relational _equation . As a result, similar to Embodiment 1, the difference between the calculated concentration and the known concentration was within the acceptable error range.

Although preferred embodiments of the present invention have been described above, the present invention is not limited to these specific embodiments, and various modifications and changes are possible within the scope of the gist of the invention as described in the claims.

The COe gas sensor according to the present invention can be inserted into the flue of a boiler or the like to enable accurate monitoring of the COe concentration in the combustion exhaust. It is particularly suitable for systems using raw materials with high sulfur content, such as coal fuel. Furthermore, by combining it with existing oxygen concentration sensors, it becomes possible to construct a combustion control system for boilers and the like, contributing to energy conservation.

1 COe gas sensor 10 Solid electrolyte substrate, 11 First detection electrode, 12 Counter electrode, 13 First sensor unit 14 Solid electrolyte substrate, 15 Second detection electrode, 16 Counter electrode, 17 Second sensor unit

Claims (9)

A first sensor unit including a first detection electrode and a counter electrode connected ionically via a solid electrolyte substrate,
A COe gas sensor comprising a second sensor section including a second detection electrode and a counter electrode connected ionically via a solid electrolyte substrate,
a) The film thickness of the first detection electrode is smaller than the film thickness of the second detection electrode, or
b) A mechanism is provided that can maintain the temperature of the first detection electrode lower than the temperature of the second detection electrode.
COe gas sensor. The COe gas sensor according to claim 1, wherein the first detection electrode and the second detection electrode are sintered bodies containing platinum-containing alloy particles and solid electrolyte particles, and the counter electrode is a sintered body containing platinum-containing metal particles and solid electrolyte particles. The COe gas sensor according to claim 1, wherein the film thickness of the first detection electrode is configured to be 10 μm or more thinner than the film thickness of the second detection electrode. The COe gas sensor according to claim 3, wherein the film thickness of the first detection electrode is 15 μm to 90 μm. The COe gas sensor according to claim 1, wherein the mechanism is a heating unit capable of independently controlling the temperatures of the first detection electrode and the second detection electrode. A gas detector comprising a COe gas sensor as described in claim 1, housed in a tubular casing having an open end, wherein the first detection electrode, the second detection electrode, and the counter electrode are configured to be in contact with the target gas flowing in from the open end. The tubular casing having the open end further comprises an oxygen gas sensor,
The oxygen gas sensor includes a solid electrolyte substrate and at least a pair of electrodes that are ionically conductively connected via the solid electrolyte substrate.
The pair of electrodes includes an oxygen-sensing electrode made of a sintered body containing platinum-containing metal particles and solid electrolyte particles, and a counter electrode for oxygen detection made of a sintered body containing platinum-containing metal particles and solid electrolyte particles.
The gas detector according to claim 6, wherein the oxygen sensing electrode is configured to be in contact with the gas to be measured flowing in from the open end, and the counter electrode for oxygen detection is isolated from the atmosphere of the gas to be measured. A method for detecting COe gas using the gas sensor described in claim 1,
A step of obtaining the electromotive force Em ₁ of the first sensor unit and the electromotive force Em ₂ of the second sensor unit,
The process includes a step of calculating the COe gas concentration Xcoe and the SO2 gas concentration XSO2 based on the correlation between the parameters _a11 , _a21 , _b11 , _b21 obtained in advance for the first sensor unit, the parameters _a12 , _a22 , _b12 , _b22 obtained in advance for the _second sensor unit _, and _Em1 , _Em2 .
_a11 and _a12 are constants that show the concentration dependence of the COe gas electromotive force.
b ₁₁ and b ₁₂ are constants that indicate the sensitivity limit concentration of COe gas.
_a21 and _a22 are constants that show the concentration dependence of the _SO2 gas electromotive force.
_b21 and _b22 are constants that indicate the sensitivity limit concentration of _SO₂ gas.
Detection method. The aforementioned constant is a constant obtained by setting the first detection electrode to a first temperature and the second detection electrode to a second temperature.
The process of obtaining the electromotive force is carried out with the first detection electrode at a first temperature and the second detection electrode at a second temperature.
The method according to claim 8, wherein the first temperature is 580 to 650°C and the second temperature is 30 to 100°C higher than the first temperature.