JP2007240152A - Gas sensor and device of measuring combustible gas - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a gas sensor for suppressing a reaction between combustible gas and oxygen in the first processing chamber, introducing the combustible gas into the adjacent second processing chamber with its unchanged concentration, and detecting accurately the concentration of the combustible gas in the second processing chamber. <P>SOLUTION: This gas sensor 10 is equipped with the first processing chamber 36a and the second processing chamber 36b. The first oxygen pump 12 is constituted of the first internal electrode 18a, a solid electrolyte 16a and the first external electrode 20a in the first processing chamber 36a. The second oxygen pump 14 is constituted of the second internal electrode 24, the solid electrolyte 16a and the second external electrode 26 in the second processing chamber 36b. Each electrode is formed from metal particles mainly composed of at least one kind of a metal element selected from a group comprising some metals belonging to a platinum group, gold, silver and nickel. The first internal electrode 18a includes bismuth in the deviated state on the surface of the metal particles. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a gas sensor that outputs an electrical signal corresponding to the concentration of a combustible gas. The present invention also relates to a measuring apparatus that uses the sensor to measure the concentration of combustible gas.

A gas sensor that outputs a voltage corresponding to the concentration of combustible gas has been developed, and is disclosed in Patent Document 1. The gas sensor includes a first processing chamber and a second processing chamber. At least a portion of the wall that partitions the first processing chamber from the periphery is formed of a gas diffusion-controlling layer and a solid electrolyte. Further, at least a portion of the wall that partitions the second processing chamber from the periphery is formed of a solid electrolyte. The first processing chamber and the second processing chamber are adjacent to each other through a gas diffusion control layer.
A first internal electrode is formed on the first processing chamber side of the solid electrolyte partitioning the first processing chamber. A first external electrode is formed on the opposite side of the first internal electrode with the solid electrolyte interposed therebetween. The first internal electrode, the solid electrolyte, and the first external electrode constitute a first oxygen pump that transfers oxygen in the first processing chamber to the surroundings.
Furthermore, the 2nd internal electrode is formed in the 2nd process chamber side of the solid electrolyte which divides a 2nd process chamber. A second external electrode is formed on the opposite side of the second internal electrode across the solid electrolyte. The second external electrode, the solid electrolyte, and the second internal electrode constitute a second oxygen pump that transfers oxygen from the surroundings to the second processing chamber.

In the gas sensor disclosed in Patent Document 1, a test gas containing a combustible gas and oxygen is introduced into the first processing chamber. In the first processing chamber, the first oxygen pump is used to discharge oxygen contained in the test gas to the surroundings. The combustible gas from which oxygen has been removed in the first processing chamber is introduced into the second processing chamber. Oxygen is also introduced into the second processing chamber by the second oxygen pump. In the second processing chamber, the combustible gas reacts with oxygen. The amount of oxygen introduced into the second processing chamber is equal to the amount of oxygen with which the combustible gas reacts with oxygen. Therefore, if the amount of oxygen introduced into the second processing chamber is measured, the amount of combustible gas contained in the test gas can be detected. The amount of oxygen introduced into the second processing chamber is proportional to the current flowing between the second internal electrode and the second external electrode.
The gas sensor of Patent Document 1 is used by being connected to a current detection means for detecting a current flowing between the second internal electrode and the second external electrode, and an electric signal indicating the concentration of the combustible gas contained in the test gas. Converted.

JP-A-8-247995

In the gas sensor disclosed in Patent Document 1, oxygen is removed from a test gas by a first oxygen pump configured by a first internal electrode, a solid electrolyte, and a first external electrode. In the gas sensor of Patent Document 1, since the oxygen concentration in the first processing chamber is sufficiently low, the combustible gas contained in the test gas does not react with oxygen in the first processing chamber.
However, the first internal electrode constituting the first oxygen pump also has a catalytic action. Therefore, in the vicinity of the first internal electrode, it is inevitable that the combustible gas contained in the test gas reacts with oxygen. If the combustible gas contained in the test gas reacts with oxygen in the first processing chamber, the amount of combustible gas introduced into the second processing chamber is lower than the amount of combustible gas contained in the test gas. Resulting in. For this reason, the gas sensor of Patent Document 1 cannot accurately detect the concentration of the combustible gas.
In the present invention, the catalytic action of the first internal electrode constituting the first oxygen pump is inactivated, and the combustible gas contained in the test gas is prevented from reacting with oxygen in the vicinity of the first internal electrode. . If this can be realized, the combustible gas contained in the test gas can be introduced into the second processing chamber without being consumed, and a gas sensor for accurately detecting the concentration of the combustible gas can be realized. .

The gas sensor of the present invention includes a first processing chamber and a second processing chamber, and has the following features.
A gas diffusion-controlling layer and a solid electrolyte are provided on at least a part of the wall defining the first processing chamber from the periphery, and a solid electrolyte is provided on at least a part of the wall defining the second processing chamber from the periphery. The first processing chamber and the second processing chamber are adjacent to each other through a gas diffusion control layer. A first internal electrode is formed on the first processing chamber side of the solid electrolyte partitioning the first processing chamber, and a first external electrode is formed on the opposite side of the first internal electrode with the solid electrolyte interposed therebetween. A second internal electrode is formed on the second processing chamber side of the solid electrolyte partitioning the second processing chamber, and a second external electrode is formed on the opposite side of the second internal electrode with the solid electrolyte interposed therebetween.
The first internal electrode is formed of metal particles mainly composed of at least one metal element selected from the group consisting of any metal belonging to the platinum group, gold, silver, and nickel, and is formed on the surface of the metal particles. The bismuth content (the mass of bismuth / the total mass of the metal particles constituting the electrode) with respect to the total mass of the metal particles constituting the first internal electrode is 0.01 to 10% by mass in a biased state.
The second internal electrode is formed of metal particles mainly composed of at least one metal element selected from the group consisting of any metal belonging to the platinum group, gold, silver, and nickel. The second internal electrode does not contain bismuth. The phrase “not containing bismuth” means that bismuth is not actively added, and a trace amount of bismuth may be mixed as an impurity.

In the gas sensor, the first internal electrode is formed of metal particles mainly composed of at least one metal element selected from the group consisting of any metal belonging to the platinum group, gold, silver, and nickel. Therefore, when a voltage is applied between the first internal electrode and the first external electrode, current easily flows and oxygen transfer efficiency is high. Further, since the surface of the metal particles forming the first internal electrode contains bismuth, the catalytic action of the first internal electrode is inactivated, and the test gas (the surroundings) is in the vicinity of the first internal electrode. This effectively suppresses the combustible gas contained in the gas) from reacting with oxygen.
The combustible gas from which oxygen is removed from the test gas is introduced into the second processing chamber. In the second processing chamber, a second oxygen pump including a second internal electrode, a solid electrolyte, and a second external electrode is prepared, and oxygen is also introduced. In the second processing chamber, the combustible gas reacts with oxygen. The amount of oxygen introduced into the second processing chamber is equal to the amount of oxygen with which the combustible gas reacts with oxygen. Therefore, the amount of combustible gas contained in the test gas can be detected by measuring the amount of oxygen introduced into the second processing chamber. The amount of oxygen introduced into the second processing chamber is proportional to the current flowing between the second internal electrode and the second external electrode.
The test gas introduced into the first processing chamber contains oxygen. If oxygen remains in the gas transferred from the first processing chamber to the second processing chamber, the amount of combustible gas cannot be detected accurately. In the gas sensor, since the oxygen transfer efficiency of the first oxygen pump is high, oxygen contained in the test gas is efficiently removed in the first processing chamber. If the first internal electrode has a catalytic action, combustible gas contained in the test gas is consumed in the vicinity of the first internal electrode, and the amount of combustible gas cannot be detected accurately. In the gas sensor, since the surface of the metal particles forming the first internal electrode contains bismuth, the catalytic action of the first internal electrode is inactivated, and the test gas is detected in the vicinity of the first internal electrode. The combustible gas contained in is not consumed. Together, the gas sensor outputs an electrical signal that accurately corresponds to the concentration of the combustible gas contained in the test gas.

  The gas sensor of the present invention includes a first power source for applying a voltage in a direction for transferring oxygen in the first processing chamber to the surroundings between the first internal electrode and the first external electrode, and between the second internal electrode and the second external electrode. And a second power source for applying a voltage for transferring oxygen contained in the surrounding gas into the second processing chamber, and a current detecting means for detecting a current flowing between the second internal electrode and the second external electrode. Can do. Thereby, a measuring device for combustible gas can be realized.

  The current flowing between the second internal electrode and the second external electrode corresponds to the amount of oxygen introduced into the second processing chamber, and corresponds to the concentration of the combustible gas contained in the test gas. Oxygen is discharged from the first processing chamber by the first power source and the first oxygen pump, and oxygen is introduced into the second processing chamber by the second power source and the second oxygen pump. By detecting the flowing current, the concentration of the combustible gas contained in the test gas can be accurately measured.

In another gas sensor according to the present invention, a pair of internal electrodes are formed inside the gas detection space. An electromotive force corresponding to the concentration of the combustible gas between the pair of internal electrodes when one of the pair of internal electrodes is active with catalytic action and the other with inactive catalytic action. Take advantage of what happens.
This type of gas sensor includes a gas detection space, an oxygen pump element that controls the oxygen concentration in the gas detection space, and a concentration detection element that detects the concentration of the flammable gas in the gas detection space. ing.
The wall that divides the gas detection space from the periphery is provided with a gas diffusion control layer and a solid electrolyte at least in part. In the concentration detection element, a first internal electrode and a second internal electrode are formed on the gas detection space side of the solid electrolyte partitioning the gas detection space, and opposite to the first internal electrode and the second internal electrode with the solid electrolyte interposed therebetween. A common external electrode is formed on the side. In the oxygen pump element, a third internal electrode is formed on the gas detection space side of the solid electrolyte that partitions the gas detection space, and an external electrode is formed on the opposite side of the third internal electrode across the solid electrolyte.
The first internal electrode is formed of metal particles mainly composed of at least one metal element selected from the group consisting of any metal belonging to the platinum group, gold, silver, and nickel. The first internal electrode does not contain bismuth. The phrase “not containing bismuth” means that bismuth is not actively added, and a trace amount of bismuth may be mixed as an impurity.
The second internal electrode is formed of metal particles mainly composed of at least one metal element selected from the group consisting of any metal belonging to the platinum group, gold, silver, and nickel, and is formed on the surface of the metal particles. The bismuth content (the mass of bismuth / the total mass of the metal particles constituting the electrode) with respect to the total mass of the metal particles constituting the second internal electrode including bismuth in a biased state is 0.01 to 10% by mass.
The third internal electrode is formed of metal particles mainly composed of at least one metal element selected from the group consisting of any metal belonging to the platinum group, gold, silver, and nickel, and is formed on the surface of the metal particles. The bismuth content with respect to the total mass of the metal particles that contain bismuth and constitute the third internal electrode in a biased state is 0.01 to 10% by mass.

In the case of the above gas sensor, the first internal electrode does not contain bismuth on the surface, and thus exhibits catalytic activity. In the vicinity of the first internal electrode, the combustible gas and oxygen react with each other, so the oxygen concentration decreases. On the other hand, since the second internal electrode contains bismuth on the surface, the catalytic action is inactive. In the vicinity of the second internal electrode, since the combustible gas and oxygen do not react, the oxygen concentration does not decrease.
As a result, an electromotive force corresponding to a difference in oxygen concentration between the first internal electrode and the second internal electrode is generated. The electromotive force generated between the first internal electrode and the second internal electrode corresponds well to the concentration of the combustible gas contained in the test gas.
In this gas sensor, for example, a first processing chamber in which an oxygen pump element is formed and a second processing chamber in which a concentration detection element is formed may be adjacent to each other via a gas diffusion rate limiting body. Furthermore, if a gas detection space in which the first processing chamber and the second processing chamber are shared is formed, the detection time response is high, the structure is simple, and the manufacturing is easy.

  The gas sensor detects a voltage generated between the first internal electrode or the second internal electrode and the common external electrode, and a power source for controlling the oxygen concentration in the gas detection space between the third internal electrode and the external electrode. Voltage detecting means for controlling the voltage applied between the third internal electrode and the external electrode so that the voltage detected by the voltage detecting means is maintained at a constant value, and the first internal electrode and the second internal electrode It is preferably used in combination with an output voltage detecting means for detecting an output voltage generated during the period. Thereby, a measuring device for combustible gas can be realized.

By providing a power source between the third internal electrode and the external electrode, oxygen can be transferred from the periphery of the gas sensor to the gas detection space, and oxygen can also be transferred from the gas detection space to the periphery of the gas sensor.
When the capacity of the oxygen pump element composed of the third internal electrode, the solid electrolyte, and the external electrode is adjusted so that the voltage generated between the first internal electrode or the second internal electrode and the common external electrode is kept constant, The electromotive force generated between the first internal electrode and the second internal electrode corresponds well to the concentration of the combustible gas contained in the test gas. By detecting the electromotive force generated between the first internal electrode and the second internal electrode, the concentration of combustible gas contained in the test gas can be accurately measured.

  In the present invention, of the pair of internal electrodes constituting the gas detection element, one internal electrode uses an active catalyst and the other internal electrode uses an inactive catalytic function. Furthermore, since the oxygen concentration in the space where the combustible gas is detected is controlled by the oxygen pump, the concentration of a small amount of combustible gas can be detected at a high output. Further, since the oxygen concentration in the space where the combustible gas is detected can be accurately managed, the concentration of the combustible gas can be detected accurately.

Embodiments of the present invention will be described below.
(First embodiment)
FIG. 1 schematically illustrates the gas sensor of the first embodiment. The gas sensor 10 includes a first processing chamber 36a and a second processing chamber 36b. The first processing chamber 36a is configured to introduce gas formed in the first solid electrolyte layer 30, the second solid electrolyte layer 16a, the insulating sheet 32b, the second gas diffusion rate controlling layer 40, and the first solid electrolyte layer 30. It is surrounded by a first gas diffusion limiting layer 38 covering the hole 34.
The second processing chamber 36b is surrounded by the first solid electrolyte layer 30, the second solid electrolyte layer 16a, the insulating sheet 32a, and the second gas diffusion rate controlling layer 40.
The first processing chamber 36 a and the second processing chamber 36 b are adjacent to each other through the second gas diffusion rate controlling layer 40.
A first internal electrode 18a is formed on the first processing chamber 36a side of the second solid electrolyte layer 16a. A first external electrode 20a is formed on the opposite side of the first internal electrode 18a across the second solid electrolyte layer 16a. The first internal electrode 18a, the second solid electrolyte layer 16a, and the first external electrode 20a constitute the first oxygen pump 12a. The first internal electrode 18a and the first external electrode 20a are electrically connected to a power supply circuit 22a provided with an ammeter. The first internal electrode 18a is exposed to the first processing chamber 36a, and the first external electrode 20a is exposed to the outside of the gas sensor 10 through the outside air port 42.
A second internal electrode 24 is formed on the second processing chamber 36b side of the second solid electrolyte layer 16a. A second external electrode 26 is formed on the opposite side of the second internal electrode 24 across the second solid electrolyte layer 16a. The second internal electrode 24, the second solid electrolyte layer 16a, and the second external electrode 26 constitute the second oxygen pump 14. The second internal electrode 24 and the second external electrode 26 are electrically connected to a power circuit 28 provided with an ammeter. The second internal electrode 24 is exposed to the second processing chamber 36 b, and the second external electrode 26 is exposed to the outside air of the gas sensor 10 through the outside air port 42.
32d of illustration is an insulating sheet, and the heater 44 is formed in the inside. The insulating sheet 32d is fixed to the second solid electrolyte layer 16a via the insulating sheet 32c.

The gas diffusion limiting layer 38 can limit the gas diffusion rate, and can introduce a test gas (also referred to as ambient gas) existing outside the gas sensor 10 into the first processing chamber 36a.
The first solid electrolyte layer 30 and the second solid electrolyte layer 16a are made of yttria-stabilized zirconia (YSZ) plates having oxygen ion permeability.
The first internal electrode 18a is formed of metal particles mainly composed of platinum, and contains bismuth while being biased toward the surface of the metal particles. The bismuth content with respect to the total mass of the metal particles constituting the first internal electrode 18a is 1% by mass. Instead of platinum, at least one metal element selected from the group consisting of metals other than platinum belonging to the platinum group, gold, silver, and nickel may be used. For example, the first internal electrode 18a may be formed of metal particles mainly composed of gold. Further, it may be formed from metal particles mainly composed of gold and metal particles mainly composed of platinum and / or at least one metal element of a metal other than platinum belonging to the platinum group.
The second internal electrode 24 is formed of metal particles mainly composed of platinum. Bismuth is not added. Instead of platinum, at least one metal element selected from the group consisting of metals other than platinum belonging to the platinum group, gold, silver, and nickel may be used.
The first external electrode 20a is formed of metal particles mainly composed of platinum. Bismuth is not added. Instead of platinum, at least one metal element selected from the group consisting of metals other than platinum belonging to the platinum group, gold, silver, and nickel may be used.
The second external electrode 26 is formed of metal particles mainly composed of platinum. Bismuth is not added. Instead of platinum, at least one metal element selected from the group consisting of metals other than platinum belonging to the platinum group, gold, silver, and nickel may be used.

A method for measuring the concentration of the combustible gas with the gas sensor 10 will be described.
When the gas sensor 10 is installed in a space where a test gas containing a combustible gas and oxygen exists, the test gas passes through the gas diffusion control layer 38 in a state where the diffusion speed is limited, and is introduced into the first processing chamber 36a. The At this time, oxygen is also introduced into the first processing chamber 36a simultaneously with the combustible gas.
When the power supply circuit 22a connected to the first internal electrode 18a and the first external electrode 20a is turned on, oxygen introduced into the first processing chamber 36a passes through the inside of the second solid electrolyte layer 16a from the first internal electrode 18a. Then, it moves to the first external electrode 20a side. That is, oxygen is discharged from the first processing chamber 36a. At this time, since the catalytic action of the first internal electrode 18a is inactive, the combustible gas does not react with oxygen.

  The combustible gas from which oxygen is removed in the first processing chamber 36a is introduced from the first processing chamber 36a into the second processing chamber 36b in a state where the diffusion rate is limited by the gas diffusion control layer 40. As will be described later, the combustible gas introduced into the second processing chamber 36b reacts with oxygen supplied from the second oxygen pump 14 and is consumed. The transfer of the combustible gas from the first processing chamber 36a to the second processing chamber 36b is caused by the difference between the concentration of the combustible gas in the first processing chamber 36a and the concentration of the combustible gas in the second processing chamber 36b, or the first processing. This is caused by the flow of combustible gas in the chamber 36a and the second processing chamber 36b.

In the second processing chamber 36b, the combustible gas reacts with oxygen by the catalytic action of the second internal electrode 24. Oxygen for reacting with the combustible gas is supplied from the ambient gas. When the power supply circuit 28 connected to the second internal electrode 24 and the second external electrode 26 is turned on, oxygen contained in the test gas that has entered from the outside air port 42 passes through the second solid electrolyte layer 16a and is subjected to the second treatment. It is introduced into the chamber 36b.
The amount of oxygen introduced into the second processing chamber 36b is equal to the amount of oxygen with which the combustible gas reacts with oxygen. Therefore, if the amount of oxygen introduced into the second processing chamber 36b is measured, the amount of combustible gas contained in the test gas can be detected. The amount of oxygen introduced into the second processing chamber 36 b is proportional to the current flowing between the second internal electrode 24 and the second external electrode 26. By reading the value of the current flowing through the power supply circuit 28, the concentration of the combustible gas contained in the test gas can be measured.
The heater 44 keeps the temperature of the gas sensor 10 constant. By keeping the temperature of the gas sensor 10 constant, the temperature of the ambient gas entering from the first processing chamber 36a, the second processing chamber 36b, and the outside air port 42 becomes constant.

(Second Embodiment)
FIG. 2 schematically illustrates the gas sensor of the second embodiment. The gas sensor 50 includes a gas detection space 58. The gas detection space 58 is a gas diffusion rate controlling layer covering the first solid electrolyte layer 16b, the second solid electrolyte layer 48, the insulating sheet 56b, and the gas introduction hole 68 formed in the first solid electrolyte layer 16b. 66.
A first internal electrode 60 and a second internal electrode 62 are formed on the gas detection space 58 side of the second solid electrolyte layer 48. A common external electrode 64 is formed on the opposite side of the first internal electrode 60 and the second internal electrode 62 across the second solid electrolyte layer 48. The common electrode 64 is exposed to the outside (for example, the atmosphere) of the gas sensor 50 through the outside air port 54. Alternatively, an atmosphere chamber for introducing the atmosphere to the common external electrode 64 may be installed. A gas detection cell 46 is formed by the second solid electrolyte 48, the first internal electrode 60, the second internal electrode 62, and the common external electrode 64. A voltmeter V3 for detecting an electromotive force generated between the first internal electrode 60 and the second internal electrode 62 is provided between the first internal electrode 60 and the second internal electrode 62. Between the first internal electrode 60 and the common external electrode 64, a voltmeter V1 for detecting an electromotive force generated between the two is provided. Between the second internal electrode 62 and the common external electrode 64, a voltmeter V2 for detecting an electromotive force generated between the two is provided.
A third internal electrode 18b is formed on the gas detection space 58 side of the first solid electrolyte layer 16b. An external electrode 20b is formed on the opposite side of the third internal electrode 18b across the first solid electrolyte layer 16b. The third internal electrode 18b and the external electrode 20b constitute an oxygen pump. The external electrode 20b is exposed to the outside of the gas sensor 50 (for example, a test gas).
The third internal electrode 18b and the external electrode 20b are electrically connected to a power supply circuit 22b provided with an ammeter.
56d of illustration is an insulation sheet, and the heater 53 is formed in the inside. The insulating sheet 56d is fixed to the second solid electrolyte layer 48 via the insulating sheet 56c.

The gas diffusion rate controlling layer 66 can limit the gas diffusion rate, and can introduce a test gas (also referred to as ambient gas) existing outside the gas sensor 50 into the gas detection space 58.
The first solid electrolyte layer 16b and the second solid electrolyte layer 48 are made of yttria-stabilized zirconia (YSZ) plates having oxygen ion permeability.
The first internal electrode 60 is formed from metal particles mainly composed of platinum. Bismuth is not added. Instead of platinum, at least one metal element selected from the group consisting of metals other than platinum belonging to the platinum group, gold, silver, and nickel may be used.
The 2nd internal electrode 62 and the 3rd internal electrode 18b are formed from the metal particle which has platinum as a main, and contain bismuth in the state biased to the surface of the metal particle. The bismuth content with respect to the total mass of the metal particles constituting the second internal electrode 62 and the third internal electrode 18b is 0.6% by mass. Instead of platinum, at least one metal element selected from the group consisting of metals other than platinum belonging to the platinum group, gold, silver, and nickel may be used. For example, the second internal electrode 62 and the third internal electrode 18b may be formed of metal particles mainly composed of gold. Further, it may be formed of metal particles mainly composed of gold and metal particles mainly composed of platinum and / or at least one metal element of a metal other than platinum belonging to the platinum group.
The common external electrode 64 and the external electrode 20b are formed of metal particles mainly composed of platinum. Bismuth is not added. Instead of platinum, at least one metal element selected from the group consisting of metals other than platinum belonging to the platinum group, gold, silver, and nickel may be used.

A method for measuring the concentration of the combustible gas with the gas sensor 50 will be described.
When the gas sensor 50 is installed in a space where a test gas containing a combustible gas and oxygen exists, the test gas moves in a state where the diffusion speed is limited by the gas diffusion control layer 66 and is introduced into the gas detection space 58. . At this time, oxygen is also introduced into the gas detection space 58 simultaneously with the combustible gas.
When the power supply circuit 22b connected to the third internal electrode 18b and the external electrode 20b is turned on, oxygen introduced into the gas detection space 58 passes through the first solid electrolyte layer 16b from the third internal electrode 18b, and the external electrode 20b. Move to the side. That is, since the third internal electrode 18b has an inactive catalytic action, oxygen can be discharged from the gas detection space 58 without affecting the combustible gas.

The combustible gas introduced into the gas detection space 58 reacts with oxygen introduced into the gas detection space 58 by the catalytic action of the first internal electrode 60. Therefore, the oxygen concentration near the surface of the first internal electrode 60 is lower than the average oxygen concentration in the gas detection space 58.
On the other hand, since the catalytic action of the second internal electrode 62 is inactive, the reaction between the combustible gas and oxygen does not occur in the vicinity of the second internal electrode 62. Therefore, the oxygen concentration near the surface of the second internal electrode 62 is equal to the average oxygen concentration in the gas detection space 58. Therefore, an oxygen concentration difference is generated between the first internal electrode 60 and the second internal electrode 62, and an oxygen concentration electromotive force is generated. Since the difference in oxygen concentration generated in both electrodes correlates with the amount of combustible gas to be burned, the concentration of combustible gas can be detected from the electromotive force.
The oxygen concentration in the gas detection space 58 is controlled to a desired concentration by the oxygen pump 12b. That is, oxygen may be discharged from the gas detection space 58 to the surrounding gas, or oxygen may be introduced from the surrounding gas to the gas detection space 58.

  In the present embodiment, the oxygen discharge capacity of the oxygen pump 12b is adjusted so that the detected value of the voltmeter V1 or the voltmeter V2 is kept constant. That is, the oxygen discharge capacity of the oxygen pump 12b is adjusted so that the oxygen concentration near the surface of the first internal electrode 60 or the second internal electrode 62 is kept constant. For example, when the oxygen concentration in the gas detection space 58 increases, the electromotive force V1 between the first internal electrode 60 and the common external electrode 64 decreases unless the oxygen pump 12b is controlled. Therefore, the oxygen pump 12b is controlled so as to keep the detection value of the voltmeter V1 constant. That is, the oxygen discharge capacity of the oxygen pump 12b is increased, and the oxygen concentration in the gas detection space 58 is lowered.

Embodiments will be described in detail below with reference to the drawings.
(First embodiment)
A gas sensor 10 having the configuration shown in FIG. 1 was manufactured. That is, yttria-stabilized zirconia (ZrO ₂ -6 mol% Y ₂ 0 ₃ : hereinafter referred to as YSZ) shaped into a flake (70 mm × 6 mm × 1 mm) plate (solid electrolyte) 16a is electrically connected to each of two positions. A platinum electrode forming paste having a composition of 90% by mass of platinum (Pt) powder and 10% by mass of YSZ (excluding organic components such as a vehicle) was screen-printed so as not to contact the substrate.
Next, a gas diffusion rate controlling layer 40 was formed between the Pt electrode (first internal electrode) 18a and the Pt electrode (second internal electrode) 24 on the upper surface of the YSZ plate 16a. Next, an alumina sheet for forming insulating sheets 32a and 32b (70a × 6mm × 2mm) of insulating sheets 32a and 32b (32a and 32b in the figure are substantially the same) having alumina as a main component is placed, and the alumina sheet and YSZ are placed. A plate (solid electrolyte) 30 was bonded.
Next, an insulating sheet 32d having a heater 44 formed therein was bonded to the lower surface of the YSZ plate 16a via a thin film (70 mm × 6 mm × 2 mm) insulating sheet 32c. Thereafter, baking was performed at 1500 ° C. for 2 hours.
Further, 30 μL of 0.01 mol / L bismuth nitrate aqueous solution was dropped onto the Pt electrode 18a. The bismuth content of the Pt electrode 18a is 1% by mass.
After applying the bismuth nitrate aqueous solution, heat treatment was performed at 850 ° C. Furthermore, in order to make bismuth unevenly distributed on the metal surface of the Pt electrode 18a, an energization treatment was performed in nitrogen gas containing 1% hydrogen. Further, a gas diffusion rate limiting layer 38 is formed on the upper surface of the YSZ plate 30 so as to block the gas introduction hole 34, the power circuit 22a is connected between the Pt electrodes 18a and 20a, and the power circuit 28 is connected between the Pt electrodes 24 and 26. Connected.

Next, the gas sensor 10 is heated to 700 ° C. by the heater 44, and a combustible gas is added in an atmosphere of nitrogen gas containing 1% oxygen (hereinafter referred to as “first reference test gas”). The gas detection performance of was evaluated. The combustible gas was prepared by changing the concentration to 0 to 1000 ppm for three types of propane gas (C ₃ H ₈ ), hydrogen gas (H ₂ ), and carbon monoxide gas (CO).
A voltage of 0.6 V was applied to the first oxygen pump 12a by the power supply circuit 22a, and oxygen was discharged from the first processing chamber 36a to the outside air port 42.
FIG. 5 shows the relationship between the current value flowing through the power supply circuit 28 of the gas sensor 10 and the concentration of the combustible gas. The vertical axis indicates the current value (μA) flowing through the power supply circuit 28, and the horizontal axis indicates the concentration (ppm) of the combustible gas. A curve 90 shows a case where the combustible gas is propane gas, a curve 92 shows a case where the combustible gas is hydrogen gas, and a curve 94 shows a case where the combustible gas is carbon monoxide gas.
As is apparent from the curve 90, as the propane gas concentration increases, the current flowing through the power supply circuit 28 increases in proportion. It was confirmed that the gas sensor 10 can measure the concentration of propane gas.
Further, as is apparent from the curves 92 and 94, when the combustible gas is hydrogen gas or carbon monoxide gas, even if the gas concentration increases, almost no current flows through the power supply circuit 28. That is, it was confirmed that the gas sensor 10 is not affected by the concentration of hydrogen gas or carbon monoxide gas.

(Second embodiment)
A gas sensor 50 having the configuration shown in FIG. 2 was manufactured. That is, the platinum electrode forming paste having the composition used in Example 1 was screen-printed on both surfaces of the YSZ plate 16b in which the gas introduction holes 68 were formed. Thereafter, baking was performed at 1500 ° C. for 2 hours to form thin Pt electrodes 18b and 20b formed by sintering Pt particles on both surfaces of the YSZ plate 16b. Next, the platinum electrode forming paste having the composition used in Example 1 was screen-printed so that the YSZ plate (solid electrolyte) 48 was not electrically in contact with the upper surface of the YSZ plate 48 (solid electrolyte) 48. The platinum electrode forming paste having the composition used in 1 was screen-printed. Thereafter, baking was performed at 1500 ° C. for 2 hours, and thin film-like Pt electrodes 60, 62, 64 formed by sintering Pt particles on both surfaces of the YSZ plate 48 were formed.
Next, 10 μL of 0.01 mol / L bismuth nitrate aqueous solution was dropped onto the Pt electrode (third internal electrode) 18 b and the Pt electrode 62. The bismuth content of the Pt electrode 18b and the Pt electrode 62 is 0.6% by mass. After applying the bismuth nitrate aqueous solution, heat treatment was performed at 850 ° C. Furthermore, in order to make bismuth unevenly distributed on the metal surfaces of the Pt electrode 18b and the Pt electrode 62, an energization process was performed in nitrogen gas containing 1% hydrogen.
Next, a gas diffusion control layer 66 was formed on the upper surface of the YSZ plate 16b so as to close the gas introduction hole 68. Next, the YSZ plate 16b and the YSZ plate 48 were bonded via the insulating sheet 56b, and the insulating sheet 56d in which the YSZ plate 48 and the heater 53 were formed was bonded via the insulating sheet 56c. Thereafter, baking was performed at 600 ° C. for 1 hour.
Next, the power supply circuit 22b is connected between the Pt electrodes 18b and 20b, and a voltage is applied between the Pt electrode (first internal electrode) 60, the Pt electrode (second internal electrode) 62, and the Pt electrode (common external electrode) 64. A control circuit 52 was formed.

Next, the gas sensor 50 was heated by the heater 53, and a combustible gas was added to the first reference test gas atmosphere to evaluate the gas detection performance of the gas sensor 50.
The gas detection performance was evaluated by introducing the atmosphere into the outside air port 54. That is, the Pt electrode 64 is not exposed to the flammable gas but is exposed to the atmosphere. The combustible gas was prepared by changing the concentration from 0 to 1000 ppm for three types of propane gas (C3H8), hydrogen gas (H2), and carbon monoxide gas (CO).
The value of the current flowing through the variable power supply circuit 22b was changed by the electric signal from the voltmeter V1 of the voltage control circuit 52 so that the electromotive force generated between the Pt electrode 60 and the Pt electrode 64 was constant at 110 mV.
FIG. 6 shows the relationship between the value of the voltmeter V3 of the voltage control circuit 52 of the gas sensor 50 and the concentration of the combustible gas. The vertical axis indicates the value (mV) of the voltmeter V3, and the horizontal axis indicates the concentration (ppm) of the combustible gas. A curve 96 shows a case where the combustible gas is propane gas, a curve 98 shows a case where the combustible gas is hydrogen gas, and a curve 100 shows a case where the combustible gas is carbon monoxide gas.
As apparent from the curve 96, the value of the voltmeter V3 increases as the concentration of propane gas increases. It was confirmed that the gas sensor 50 can measure the concentration of propane gas.
Further, as is apparent from the curve 98 and the curve 100, when the combustible gas is hydrogen gas or carbon monoxide gas, the value of the voltmeter V3 hardly changes even when the gas concentration increases. That is, it was confirmed that the gas sensor 50 is not affected by the concentration of hydrogen gas or carbon monoxide gas.

(Third embodiment)
In Example 1 or Example 2, an electrode in which bismuth is added to the surface of the internal electrode is used. In this example, the amount of bismuth added and its effect were investigated.
12 types of gas sensors 80 shown in FIG. 3 having different bismuth contents of the internal electrodes 86 were manufactured.
That is, a platinum electrode forming paste having the composition used in Example 1 was screen-printed on both surfaces of a YSZ plate 82 formed into a thin plate shape (diameter 17 mm, height 1 mm). Thereafter, baking was performed at 1500 ° C. for 1 hour, and Pt particles were sintered on both surfaces of the YSZ plate 82 to form thin Pt electrodes 86 and 88. The physical properties of the obtained Pt electrodes 86 and 88 are shown below. (Thickness: 10 μm, area: about 0.5 cm ² , porosity: about 40%, density: 21.45 g / cm ³ , Pt mass: about 6.4 mg)
Next, an appropriate amount (see Table 1) of an aqueous bismuth nitrate solution having any concentration shown in Table 1 was dropped onto the Pt electrode 86. After dropping the aqueous bismuth nitrate solution, a gas diffusion rate-determining body 84 made of alumina having a predetermined shape (diameter 17 mm, height 0.5 mm) was adhered onto the Pt electrode 86. Next, heat treatment at 800 ° C. was performed in the atmosphere. By this method, bismuth (bismuth oxide) was added to the surface of the Pt particles constituting the internal electrode 86 disposed in the space 85 surrounded by the gas diffusion rate controlling body 84. Next, a power supply circuit 81 capable of applying a voltage to the Pt electrodes 86 and 88 was formed between the Pt electrodes 86 and 88. Thus, a total of 12 types of gas sensors 80 (sample 1 to sample 12) shown in Table 1 were prepared. Manufactured. Table 1 shows the concentration of bismuth nitrate used in the production of each sample, the dripping amount, the bismuth addition amount, and the bismuth mass content relative to the total mass of the electrode constituent metal elements in the internal electrode 86 to which bismuth was added ((bismuth Mass / mass of platinum particles + mass of bismuth) × 100).

Next, the samples 1 to 12 are heated to 700 ° C., the limiting current in the nitrogen gas containing 0.1% oxygen (hereinafter referred to as “second reference test gas”), and the second reference test gas. The limit current in the propane-containing second test gas into which propane was introduced so that the concentration was 200 ppm was obtained. When the limit current value in the propane-containing second test gas is 80% of the limit current value in the second reference test gas that does not contain propane, it is shown in Table 1 that there is an effect of containing bismuth. ○ indicates. When the difference between the limit current values was 80% or less, it was indicated by x in Table 1 because there was no substantial effect of containing bismuth.
As can be seen from Table 1, in Samples 3 to 12 containing 0.0016% by mass or more of bismuth in the internal electrode, the limit current value was not affected by the flammable gas (propane in this case), and the propane-containing second The limit current value in the test gas was maintained at 80% of the limit current value in the second reference test gas not containing propane. On the other hand, although detailed data are not shown, the resistance value increased in Samples 11 to 12 in which the bismuth content of the internal electrode exceeded 10 mass% (Δ in the figure). Accordingly, when the gas sensor provided by the present invention is used as an oxygen sensor, it is recognized that the bismuth content of the internal electrode is suitably about 0.002 to 10% by mass, and preferably about 0.01 to 10% by mass. It was.

(Fourth embodiment)
The electrode to which bismuth is added is formed of metal particles mainly composed of at least one metal element selected from the group consisting of any metal belonging to the platinum group, gold, silver, and nickel, and the surface of the metal particles It is preferable to apply an aqueous bismuth nitrate solution to the surface of the metal particles so that bismuth is included in a biased state.
In the said Example, the method of apply | coating bismuth nitrate aqueous solution is employ | adopted as a method of including bismuth on the surface of an electrode. This is because, in order to include bismuth in the electrode used in the gas sensor, the method of applying an aqueous solution can provide higher oxygen pump performance than other methods.
FIG. 4 shows a component 70 produced to verify the ion permeability of an electrode used for a gas sensor. A YSZ plate 72 formed into a thin piece (diameter 17 mm, height 1 mm) was prepared, and a platinum electrode forming paste having the composition used in Example 1 was screen printed on one side of the YSZ plate 72 at 1500 ° C. for 1 hour. The Pt electrode 88 was formed by firing. Thereafter, the following two types of Pt / Bi electrodes 74 were produced on the other surface of the YSZ plate 72.
Condition 1: A Pt / Bi electrode forming paste having a composition of 75 mol% platinum powder and 25 mol% bismuth was screen-printed, and then heat-treated at 850 ° C. in an oxygen atmosphere.
Condition 2: A platinum electrode forming paste having the composition used in Example 1 was screen-printed and baked at 1500 ° C. for 1 hour, and then a 0.002 mol / L bismuth nitrate aqueous solution was applied, and then 850 in an oxygen atmosphere. Then, heat treatment was performed at 800 ° C. for 1 hour in a hydrogen atmosphere. Next, a power supply circuit 81 capable of applying a voltage to the Pt electrodes 74 and 88 was formed between the Pt electrodes 74 and 88.

About the obtained component of this Example, it heated at 700 degreeC in 2nd reference | standard test gas, the voltage of the power supply circuit 81 was changed, and the electric current value at that time was measured.
In the graph shown in FIG. 7, the vertical axis represents the current value (mA), and the horizontal axis represents the voltage (V) of the power supply circuit 81. A curve 104 shows the result of producing the Pt / Bi electrode 74 under condition 1, and a curve 102 shows the result of producing the Pt / Bi electrode 74 under condition 2.
The curve 104 does not increase much in current value even when the voltage of the power supply circuit 81 is increased. That is, the amount of oxygen ions passing between the electrodes does not increase much even when the voltage is increased. In the curve 102, when the voltage is increased, the current value is also proportionally increased. That is, when the voltage is increased, the amount of oxygen ions passing between the electrodes increases in proportion. When a voltage of 1 V is applied between the electrodes, the component 70 in which the Pt / Bi electrode 74 is produced under the condition 1 and the component 70 in which the Pt / Bi electrode 74 is produced under the condition 2 cause the current flowing between the Pt electrodes 74 and 88 to flow. The difference was about 10 times.
An oxygen pump used for a gas sensor has a higher oxygen ion permeability, and can move more oxygen ions from an internal electrode to an external electrode (or from an external electrode to an internal electrode) at a lower voltage. In order to include bismuth in the electrode used in the gas sensor, a method in which a solution is applied and bismuth is unevenly distributed on the surface provides higher oxygen pump performance than other methods.
Further, about 26% by mass of bismuth is used on the surface of the Pt / Bi electrode 74 under condition 1, and about 0.5% by mass of bismuth is used on the surface of the Pt / Bi electrode 74 under condition 2. Yes.
It was confirmed that when the Pt / Bi electrode 74 was produced by a method of applying a solution, high oxygen pump performance was obtained with a small amount of bismuth added.

Specific examples of the present invention have been described in detail above, but these are merely examples and do not limit the scope of the claims. The technology described in the claims includes various modifications and changes of the specific examples illustrated above.
In the above embodiment, the heater is installed in the gas sensor. However, it is only necessary that the gas sensor is heated, and the heater is not necessarily installed in the gas sensor. In that case, the gas sensor may be arranged in a region where the gas sensor can be heated.
In the first embodiment, the first processing chamber and the second processing chamber are adjacent to each other via the gas diffusion rate limiting body. However, if the gas diffusion rate between the first processing chamber and the second processing chamber is limited. Well, it does not necessarily have to be partitioned. For example, the gas diffusion rate may be limited by reducing the space volume of the first processing chamber and the second processing chamber.
In Example 1, firing was performed after the YSZ plate before firing, the alumina sheet before firing, and the insulating sheet before firing were attached, but the YSZ plate, the alumina sheet, and the insulating sheet were fired in advance. Finally, it may be glued.
In Example 2, the YSZ plate and the insulating sheet were fired in advance and bonded last, but may be fired after the YSZ plate and insulating sheet are bonded.
Further, in Example 2, the entire gas sensor was exposed to the test gas, and the atmosphere was introduced to the outside air port, but the external electrode side of the oxygen pump was partitioned, and only the section was exposed to the test gas. The common external electrode side of the gas detection cell may be partitioned and only the inside of the partition may be exposed to the atmosphere.
For example, in the second embodiment, the operation of the oxygen pump is controlled so as to keep the detection value of the voltmeter V1 constant. However, the operation of the oxygen pump may be controlled so as to keep the detection value of the voltmeter V2 constant. .
The technical elements described in this specification or the drawings exhibit technical usefulness alone or in various combinations, and are not limited to the combinations described in the claims at the time of filing.

The gas sensor of Example 1 is shown. The gas sensor of Example 2 is shown. The gas sensor of Example 3 is shown. The component of the gas sensor of Example 4 is shown. The graph which shows the combustible gas of the gas sensor of Example 1, and output current value. The graph which shows the combustible gas of the gas sensor of Example 2, and an output voltage value. Example 4 A graph showing current-voltage characteristics of components of a gas sensor.

Explanation of symbols

10: gas sensor 12: oxygen pump 14: second oxygen pump 16, 30, 48: solid electrolyte 18: internal electrode 20: external electrodes 22, 28, 81: power supply circuit 24: internal electrode 26: external electrodes 32, 56: insulation Sheets 34, 68: Gas introduction holes 36: Processing chambers 42, 54: Outside air ports 38, 40, 66: Gas diffusion rate controlling bodies 44, 53: Heater 46: Gas detection cell 50: Gas sensor 52: Voltage control circuit 58: Gas detection Space 60: Internal electrode 62: Internal electrode 64: Common external electrode

Claims (4)

A gas sensor comprising a first processing chamber and a second processing chamber;
A gas diffusion control layer and a solid electrolyte are provided on at least a part of a wall defining the first processing chamber from the surroundings;
A solid electrolyte is provided on at least a part of a wall defining the second processing chamber from the surroundings;
The first processing chamber and the second processing chamber are adjacent to each other through a gas diffusion control layer,
A first internal electrode is formed on the first processing chamber side of the solid electrolyte partitioning the first processing chamber;
A first external electrode is formed on the opposite side of the first internal electrode across the solid electrolyte;
A second internal electrode is formed on the second processing chamber side of the solid electrolyte partitioning the second processing chamber;
A second external electrode is formed on the opposite side of the second internal electrode across the solid electrolyte;
The first internal electrode is formed of metal particles mainly composed of at least one metal element selected from the group consisting of any metal belonging to the platinum group, gold, silver, and nickel, and is formed on the surface of the metal particles. The bismuth content (mass of bismuth / total mass of metal particles constituting the electrode) with respect to the total mass of the metal particles constituting the first internal electrode is 0.01 to 10% by mass, including bismuth in a biased state,
The gas sensor, wherein the second internal electrode is formed of metal particles mainly composed of at least one metal element selected from the group consisting of any metal belonging to the platinum group, gold, silver, and nickel. A gas sensor according to claim 1;
A first power source for applying a voltage in a direction to transfer oxygen in the first processing chamber to the surroundings between the first internal electrode and the first external electrode;
A second power source for applying a voltage in a direction to transfer oxygen contained in the surrounding gas into the second processing chamber between the second internal electrode and the second external electrode;
A combustible gas measuring device having current detection means for detecting a current flowing between a second internal electrode and a second external electrode. A gas sensor having a gas detection space,
A gas diffusion control layer and a solid electrolyte are provided on at least a part of the wall that divides the gas detection space from the surroundings,
A first internal electrode and a second internal electrode are formed on the gas detection space side of the solid electrolyte partitioning the gas detection space;
A common external electrode is formed on the opposite side of the first internal electrode and the second internal electrode across the solid electrolyte,
A third internal electrode is formed on the gas detection space side of the solid electrolyte partitioning the gas detection space;
An external electrode is formed on the opposite side of the third internal electrode across the solid electrolyte,
The first internal electrode is formed of metal particles mainly composed of at least one metal element selected from the group consisting of any metal belonging to the platinum group, gold, silver, and nickel,
The second internal electrode is formed of metal particles mainly composed of at least one metal element selected from the group consisting of any metal belonging to the platinum group, gold, silver, and nickel, and is formed on the surface of the metal particles. The bismuth content (the mass of the bismuth / the total mass of the metal particles constituting the electrode) with respect to the total mass of the metal particles constituting the second internal electrode is 0.01 to 10% by mass, including bismuth in a biased state,
The third internal electrode is formed of metal particles mainly composed of at least one metal element selected from the group consisting of any metal belonging to the platinum group, gold, silver, and nickel, and is formed on the surface of the metal particles. A gas sensor comprising bismuth in a biased state and having a bismuth content of 0.01 to 10% by mass relative to the total mass of metal particles constituting the third internal electrode. A gas sensor according to claim 3;
A power source for applying a voltage for controlling the oxygen concentration in the gas detection space between the third internal electrode and the external electrode;
Voltage detecting means for detecting a voltage generated between the first internal electrode or the second internal electrode and the common external electrode;
A device for controlling the voltage applied between the third internal electrode and the external electrode so that the voltage detected by the voltage detection means is maintained at a constant value;
A combustible gas measuring device having output voltage detection means for detecting an output voltage generated between a first internal electrode and a second internal electrode.

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