JPH05249071A - Oxygen sensor of threshold current type - Google Patents

Abstract

PURPOSE:To increase the mechanical strength of the bonded part of a solid electrolyte and a porous gas diffusion member and to prevent oxygen from being leaked from the bonded part by a method wherein the solid electrolyte and the porous gas diffusion member are bonded at a high temperature by using a platinum plate. CONSTITUTION:An oxygen-ion conductive solid electrolyte 1 is obtained in the following manner: a metal oxide by Y2O3 is mixed with a metal oxide by ZrO2; an oxide which has been obtained is formed to be a cylindrical shape; and a dense sintered body is formed. One side of the solid electrolyte 1 is coated with a noble-metal paste such as platinum or the like as an anode 2; the paste is baked in the air. A cathode 3 and a porous gas diffusion member 4 which is provided with diffusion holes of a gas under test are installed on a face which is opposite to the anode 2. The cathode 3 is obtained in the following manner: the powder of a perovskite-type composite oxide is mixed with turpentine; the face of the cathode is coated with the mixture; and the mixture is baker in the air. The diffusion member 4 is obtained in the following manner: a coarse-particle oxide and a fine-particle oxide which have mixed a metal oxide by ZrO2 with Y2O3 are mixed and reshaped; and the mixture is sintered in the air. When the solid electrolyte 1 to which the electrodes have been baked and the diffusion member 4 are bonded, they are bonded at a high temperature by using a platinum plate and by exerting a pressure to the direction of a circle-center axis.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a limiting current type oxygen sensor.

[0002]

2. Description of the Related Art It has been conventionally known that an oxygen sensor using zirconia, which is an oxygen ion conductive solid electrolyte, is used for measuring the oxygen concentration contained in an atmospheric furnace, combustion exhaust gas and the like. In this oxygen sensor, a solid electrolyte zirconia plate is used as a partition wall, and precious metal electrodes such as platinum are provided on both sides of the zirconia plate at 800 ° C to 900 ° C.
When the test gas is introduced to one electrode at a high temperature and the reference gas whose oxygen concentration is known is introduced to the other electrode, an electromotive force determined by the temperature is generated by the function of the oxygen concentration battery, and this electromotive force causes The oxygen concentration of is determined. However, in the oxygen concentration sensor using the action of such an oxygen concentration battery, the electromotive force becomes minute when the difference in oxygen concentration between the test gas and the reference gas approaches, and the electromotive force changes depending on the oxygen concentration. Since it is proportional to the logarithm of, it is difficult to read a slight change in oxygen concentration. Further, the sensor device is complicated because it requires a reference gas and needs to operate at a high temperature. Therefore, in order to solve such a drawback, a limiting current type oxygen sensor utilizing an oxygen pump phenomenon is known.
An example of a limiting current type oxygen sensor using the oxygen gas diffusion phenomenon and the oxygen pump phenomenon is shown in FIG. In the figure, the oxygen gas that has diffused through the porous gas diffusion member 4 having gas diffusion holes receives electrons at the cathode 3, becomes oxygen ions, moves in the solid electrolyte 1, and becomes oxygen gas again at the anode 2. At that time, if the diffusion holes are controlled so as to control the gas diffusion,
A limiting current value corresponding to the oxygen concentration in the test gas appears in the current value. By controlling the diffusion holes, the oxygen concentration and the limiting current value show a linear relationship, so that the oxygen concentration can be known. A platinum lead wire 5 is connected to apply to the anode 2 and the cathode 3, and the diffusion member 4 and the solid electrolyte 1 are joined by an inorganic adhesive 6.

[0003]

However, the joint portion between the solid electrolyte and the porous gas diffusion member of the limiting current type oxygen sensor having the above-mentioned characteristics is such that oxygen does not leak from the outside of the sensor element to the cathode portion, and it operates. It is necessary that both are in close contact with each other while maintaining mechanical strength. Conventionally, as a joining method, an inorganic adhesive is used, or both are stacked when they are raw material plates, and heat treatment is performed, but both methods are sufficient for obtaining mechanical strength. However, the sensor malfunctions due to the leakage of oxygen from the outside of the device. The present invention has been proposed in view of such circumstances, the bonding between the solid electrolyte and the porous gas diffusion member has a sufficient mechanical strength, without the leakage of oxygen from the bonding portion. Therefore, it is an object of the present invention to provide a limiting current type oxygen sensor free from malfunction.

[0004]

Therefore, the present invention provides an anode on one surface of an oxygen ion conductive solid electrolyte, a cathode on the other surface of the solid electrolyte opposite to the anode, the cathode and the In a limiting current type oxygen sensor, each of which is provided with a porous gas diffusion member in contact with the solid electrolyte, a power source for applying a voltage between the both electrodes, and an ammeter for detecting a current flowing between the both electrodes is provided. A high temperature bonding using a platinum plate is used for bonding the solid electrolyte and the porous gas diffusion member.

[0005]

According to this structure, the solid electrolyte of the limiting current type oxygen sensor and the porous gas diffusion member are firmly bonded to each other, oxygen does not leak from the bonded portion, and malfunction does not occur.

[0006]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described with reference to the drawings. FIG. 1 is a sectional view thereof. In the figure, an oxygen ion conductive solid electrolyte 1 used in the oxygen sensor according to the present invention.
Is a cylinder having a thickness of 0.5 mm and a diameter of 10 mm obtained by mixing ZrO ₂ metal oxide with Y ₂ O ₃ metal oxide at a ratio of 8 mol% and firing at 1800 ° C. for 10 hours. It is formed into a plate and made into a dense sintered body. A noble metal paste such as platinum is applied to one surface of the solid electrolyte 1 as the anode 2 and baked in air at 1000 ° C. for 1 hour.
Further, a cathode 3 and a porous gas diffusion member 4 having a test gas diffusion hole are provided on the surface of the solid electrolyte 1 facing the anode 2. The cathode is La _1-x M _x MnO ₃ (M = Sr, Ca; O
A perovskite complex oxide having a composition of <x <1). The perovskite type complex oxide is prepared by the following method. That is, the starting material is lanthanum oxide (La).
₂ O ₃ ), strontium carbonate (or calcium carbonate)
And manganese oxide (Mn ₂ O ₃ ) such that the composition ratio of strontium (or calcium) in the oxide state after firing is 0.1 to 0.5 mol%, preferably 0.4 to 0.5 mol%. Mix and fire in air at 1500 ° C. for 10 hours. The calcined oxide powder is wet-milled by a ball mill to make the particle size 0.5 to 1 μm. The thus-obtained perovskite-type composite oxide powder and turpentine oil were mixed in a weight ratio of 3: 1 to form a paste, which was applied to the cathode surface and baked in air at 1100 ° C. for 1 hour to form a cathode. To do. The porous gas diffusion member 4 having test gas diffusion holes is obtained by mixing the metal oxide of ZrO _{2 with} the metal oxide of Y ₂ O ₃ at a ratio of 8 mol% and firing at 1800 ° C. for 10 hours. 3 to 4 μm of coarse-grained oxide and wet-milled this with a ball mill to pulverize to 0.2-0.5 μm of finely divided oxide and mix them in a weight ratio of 2: 1 to obtain a thickness of 1 m.
m at 1300 ℃ after molding into pellets with a diameter of 10 mm
Sinter in air for 0 hours. Bonding of the solid electrolyte 1 having the electrodes baked and the diffusion member 4 having the gas diffusion holes is performed by the following method. That is, outer diameter 10 mm, inner diameter 8 mm, thickness 5
After fixing the 0 μm platinum plate 8 between the solid electrolyte and the diffusion member having gas diffusion holes, 0.5 kg / cm ² to 1 kg /
Applying a pressure of cm ² along the axis of the circle at 1500 ° C for 1 hour,
Hold in air. After lowering the temperature to room temperature,
As shown in, the platinum lead wire 5 is fixed so that a voltage can be applied to the cathode and anode, a direct current power source 7 is connected, and a current system for detecting a current corresponding to the applied voltage constitutes a limiting current type oxygen sensor.

[0007]

As described above, according to the present invention, in a limiting current type oxygen sensor using yttria-stabilized zirconia which is an oxygen ion conductive solid electrolyte, platinum is used for joining the solid electrolyte and the porous gas diffusion member. By using the high-temperature pressure welding through the plate, oxygen does not leak from the outside of the element as compared with the conventional joining method, and the oxygen concentration in the target gas can be accurately detected. In short, according to the present invention, an anode is provided on one surface of the oxygen ion conductive solid electrolyte, a cathode is provided at a position opposite to the anode on the other surface of the solid electrolyte, and the cathode and the solid electrolyte are in contact with each other to form a porous film. In the limiting current type oxygen sensor, each of which is provided with a gas diffusion member, a power source for applying a voltage between the electrodes, and an ammeter for detecting a current flowing between the electrodes, wherein the solid electrolyte and the porosity are By using high temperature bonding using a platinum plate for bonding with the gas diffusion member, the solid electrolyte and the porous gas diffusion member have sufficient mechanical strength and oxygen leakage from the bonding part. The present invention is extremely useful industrially because it provides a limiting current type oxygen sensor which is compact and therefore does not malfunction.

[Brief description of drawings]

FIG. 1 is a sectional view of a limiting current type oxygen sensor according to an embodiment of the present invention.

FIG. 2 is a sectional view of a conventional limiting current type oxygen sensor.

[0008]

[Explanation of symbols]

 1 Solid Electrolyte 2 Anode 3 Cathode 4 Diffusing Member 5 Platinum Lead Wire 6 Inorganic Adhesive 7 DC Power Supply 8 Platinum Plate

Claims (1)

[Claims] 1. An anode is provided on one surface of an oxygen ion conductive solid electrolyte, a cathode is provided on a surface of the other surface of the solid electrolyte opposite to the anode, and a porous gas is in contact with the cathode and the solid electrolyte. A limiting current type oxygen sensor comprising a diffusing member, a power source for applying a voltage between the electrodes, and an ammeter for detecting a current flowing between the electrodes, wherein the solid electrolyte and the porous gas are diffused. A limiting current type oxygen sensor characterized in that a high temperature bonding using a platinum plate is used for bonding with a member.