JP2612584B2 - Manufacturing method of oxygen detection element - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a method for manufacturing an oxygen detection element for measuring an oxygen concentration in exhaust gas of, for example, an internal combustion engine or various combustion equipment.

[Related Art] Conventionally, an oxygen detecting element for detecting an oxygen concentration in a measurement gas such as an exhaust gas has been used in order to control an air-fuel ratio of an internal combustion engine, various combustion devices, and the like.

As such an oxygen detecting element, there is an element in which a pair of porous electrodes is provided on the front and back surfaces of an oxygen ion conductive solid electrolyte such as zirconia.

This oxygen detection element detects the partial pressure of oxygen gas in the surrounding atmosphere by, for example, the following method.

One porous chamber electrode is exposed to the surrounding atmosphere, and the other porous electrode is exposed to a reference oxygen source such as the atmosphere, and the partial pressure of oxygen gas in the surrounding atmosphere is detected by an electromotive force generated between the two porous electrodes.

One of the porous electrodes is exposed to the measurement gas chamber communicating with the surrounding atmosphere through the gas diffusion restricting section, and the oxygen gas in the measurement gas chamber is discharged out of the element or supplied from outside the element by applying a current between the two electrodes. The partial pressure of oxygen gas in the measurement gas chamber is set to a predetermined value, and the partial pressure of oxygen gas in the surrounding atmosphere is detected by a pump current flowing between both electrodes at that time.

An oxygen sensor using such an oxygen detecting element will be described with reference to a partially cutaway perspective view of FIG.

In the oxygen sensor 10, an oxygen detecting element 16 is supported by an insulating spacer 18 inside a metal shell 14 having a screw portion 12 serving as a mounting portion to an internal combustion engine. In addition, metal shell
A protector 20 is attached to 14.

The oxygen detection element 16 has a measurement gas side electrode 22 on one surface, a solid electrolyte plate 24 having a reference gas side electrode (not shown) on the other surface, and an atmosphere introduced into the reference gas side electrode. And a shielding plate 26 having a passage (not shown). The electromotive force generated between the measurement gas side electrode 22 and the reference gas side electrode is output from a signal extraction unit (not shown).

[Problems to be Solved by the Invention] As shown in FIG. 4, a conventional oxygen sensor 10 is an oxygen detecting element.
The solid electrolyte plate 24 and the metal shell 14 are electrically insulated by supporting the insulating spacer 16 with the insulating spacer 18.

However, the measurement gas containing conductive particles such as carbon particles, such as exhaust gas from an internal combustion engine, is used for the oxygen sensor 10.
When exposed, the conductive particles accumulate on the surface of the oxygen detecting element 16 and on the spacers 18.

Then, due to this deposition, the insulation resistance between the measurement gas side electrode 22 or the reference gas side electrode provided on the solid electrolyte plate 24 of the oxygen detection element 16 and the metal shell 14 is reduced.

As a result, while the oxygen sensor 10 has been used for a long period of time, the insulation resistance decreases, and noise is added to the output signal of the oxygen detection element 16, and the accurate oxygen gas partial pressure is measured. It turns out that there are times when it becomes impossible.

An object of the present invention is to provide a method for manufacturing an oxygen detection element that maintains good insulation resistance between the measurement gas side electrode 22 or the reference gas side electrode of the oxygen detection element 16 and the metal shell 14 over a long period of time. .

[Means for Solving the Problems] The gist of the present invention for solving the above problems includes: a solid electrolyte made of an oxygen ion conductive solid electrolyte; and a pair of porous electrodes provided on the solid electrolyte body. A method for manufacturing an oxygen detection element for detecting a partial pressure of oxygen gas in a measurement gas, comprising: ceramic particles having a ceramic particle diameter of 0.3 to 0.2 μm;
A ceramic paste containing the following flux is adhered to the surface exposed to the measurement gas except for at least the porous electrode on the green sheet surface of the solid electrolyte body to form a paste layer, and then the paste layer and the paste A method for manufacturing an oxygen detection element, comprising simultaneously firing a green sheet of a solid electrolyte body and a dense layer impermeable to a conductive substance and a gas on the surface of the solid electrolyte body.

Here, as a material of the solid electrolyte having oxygen ion conductivity, a solid solution of zirconia and yttria or calcia is typical, and other solid solutions of cerium dioxide, thorium dioxide, hafnium dioxide, and perovskite type An oxide solid solution, a trivalent metal oxide solid solution and the like can be used.

Further, as a material of the porous electrode, platinum, gold, or the like can be used. These materials are formed by pasting the material powder of the porous electrode as a main component, printing using a thick film technique, and then sintering the porous electrode. A porous electrode can be formed, or a porous electrode can be formed using a thin film technique such as flame spraying or chemical plating or vapor deposition.

Furthermore, the conductive substance and the gas-impermeable dense layer constituting the surface of the solid electrolyte body exposed to the measurement gas need to have no communicating pores, for example, having a porosity of about 5% or less. It is necessary. The porosity of the conventional protective layer formed by spraying is 10 to 40%, and a conductive substance may be deposited in the pores.

This dense layer can be formed as follows.

For example, a material that becomes the dense layer after sintering, for example, Al ₂ O
₃ + a sintering agent is applied to the oxygen sensing element before firing is formed by sintering.

[Operation] In the method for manufacturing an oxygen detection element of the present invention, a ceramic paste containing ceramic particles having a ceramic particle diameter of 0.3 to 0.2 μm and containing a flux of 15% by weight or less based on the ceramic particles is used. A paste layer is formed by attaching the paste layer to the surface exposed to the measurement gas except for at least the porous electrode on the surface of the green sheet, and then the paste layer and the green sheet of the solid electrolyte body are simultaneously fired to form the solid electrolyte body. A dense layer impermeable to a conductive substance and a gas is formed on the surface of the substrate.

Therefore, the oxygen detection element thus manufactured is
Even if the conductive particles are deposited on the surface of the oxygen detecting element or the spacer, the insulation resistance between the porous electrode and the metallic shell of the oxygen detecting element is not limited unless the porous electrode and the metallic shell are connected by the deposited layer of the conductive particles. Does not decrease.

Therefore, accurate measurement of the oxygen gas partial pressure can be performed over a long period of time.

Example A first example of the present invention will be described with reference to FIG. In this embodiment, the present invention is applied to a method of manufacturing a plate-shaped oxygen detection element 100.

The oxygen detection element 100 is provided with a reference gas side electrode 110 of a porous chamber on one surface, a measurement gas side electrode 120 on the other surface, and a solid made of ZrO ₂ partially stabilized with Y ₂ O _3. Electrolyte plate 130 and introduction path for introducing air to reference gas side electrode 110
U-shaped frame 150 and shielding plate 160 forming 140,
Protective layer 1 such as a lead (not shown) of measurement gas side electrode 120
70 are laminated.

The measurement gas side electrode 120 is provided with a catalyst support layer 180 made of a porous heat-resistant metal oxide (spinel) supporting platinum as a catalyst.

In addition, the side surface of the stacked body constituting the oxygen detection element has a dense layer 190 impermeable to a conductive substance and a gas made of alumina.
Covered in.

The oxygen detection element 100 of the present embodiment is manufactured as follows.

The zirconia powder adjusted to a composition that is partially stabilized by Y ₂ O ₃ is mixed with an organic resin, and a zirconia green sheet having a thickness of about 0.4 mm serving as a solid electrolyte plate 130 is formed by a doctor blade method, and is formed into a predetermined shape. Disconnect.

Alumina powder mixed with organic resin, by doctor blade method, thickness of about 0.4 m to become the frame 150 and the shielding plate 160
An m green alumina green sheet is prepared and cut into a predetermined shape. In addition, in the same manner, the thickness of the protective layer 170 becomes about 0.05 mm.
Is prepared and cut into a predetermined shape.

On the front and back surfaces of the zirconia green sheet, electrode patterns serving as porous reference gas side electrodes 110 and measurement gas side electrodes 120 are formed by screen printing a paste containing platinum as a main component.

For materials with the same composition as alumina green sheet,
25 wt /% of an organic binder, toluene and methyl ethyl ketone (MEK) are added to form a slurry, and a viscous agent of about 30 watts is added.
Adjust the paste-like alumina viscous material by adding t /%.
Similarly, a paste-like zirconia viscous material is prepared using a material having the same composition as the zirconia sheet.

An alumina viscous body is applied to the bonding surface of the alumina green sheet serving as the frame 150 and the shielding plate 160, and the bonding surface and the solid electrolyte plate 130 of the alumina green sheet serving as the frame 150 and the zirconia sheet serving as the solid electrolyte plate 130 are applied. A zirconia viscous material is applied to the bonding surface between the zirconia sheet to be formed and the alumina green sheet to be the protective layer 170, and is pressed to form a laminate.

As the dense layer 190, an alumina paste composed of alumina powder having a particle size of 0.3 to 2.0 μm and a flux of 15% or less is applied to the side surface of the laminate.

1% on the electrode pattern of the measurement gas side electrode 120
Consists of Al ₂ O ₃ paste containing platinum powder, stacking pattern to be a catalyst supporting layer 180, porous membrane thickness of about 40μm by screen printing.

The laminate is simultaneously fired at 1450 to 1500 ° C. to obtain the oxygen detection element 100.

When the dense layer 190 of the oxygen detecting element 100 manufactured as described above was subjected to a dye impregnation method (red check method), it was confirmed that there was no colored portion and the dense layer was dense.

The oxygen detecting element 100 is exposed to a strong reducing atmosphere having an assembling temperature of 500 ° C. and an air-fuel ratio of λ = 0.8 in the same manner as the oxygen sensor 10 described in the related art, and the measurement gas side electrode 120 and the metallic shell 14 are exposed.
Was measured, and the change with time of the insulation resistance was examined. This result is shown by a solid line in FIG.

Further, as a comparison, a similar experiment was performed on an oxygen sensor using a conventional oxygen detection element having no dense layer around it. This result is shown by a broken line in FIG.

As is clear from FIG. 2, the oxygen detecting element 100 of the present embodiment, in which the periphery is covered with the gas-impermeable dense layer 190, has a very small change in insulation resistance.

As a result, it was confirmed that an accurate oxygen gas partial pressure can be detected over a long period of time.

A second embodiment of the present invention will be described with reference to FIG. The oxygen detection element 200 of the present embodiment has a structure in which a solid electrolyte body 220 is wound around a hollow cylindrical body 210.

 The configuration of the present oxygen detection element 200 will be described together with the manufacturing method.

Zirconia powder adjusted to a composition partially stabilized by Y ₂ O ₃ is mixed with an organic resin, and a zirconia green sheet having a thickness of about 0.25 to 0.4 mm to be a solid electrolyte plate 220 is formed by a doctor blade method.

On the front and back surfaces of the zirconia green sheet, electrode patterns serving as porous reference gas side electrodes 230 and measurement gas side electrodes 240 are formed by screen printing a paste containing platinum as a main component.

The alumina powder is mixed with an organic resin, and a dense layer 250 impermeable to a conductive substance and gas is formed by a doctor blade method.
An alumina green sheet having a thickness of about 0.05 mm is formed and cut into a predetermined shape having an opening 260 corresponding to the measurement gas side electrode 240.

A paste-like viscous zirconia material is prepared in the same manner as in the first embodiment.

Zirconia green sheet is coated with a zirconia viscous material, and an alumina green sheet is laminated on the zirconia green sheet.

A porous catalyst supporting layer 2 made of an Al ₂ O ₃ paste containing 1% of platinum powder is superposed on the electrode pattern of the measurement gas side electrode 240 in the opening 260 of the alumina green sheet.
A pattern of 70 is laminated by screen printing to a thickness of about 40 μm.

A zirconia viscous body is applied to a zirconia cylindrical body 290 having a communication hole 280, and the laminate manufactured in the above steps (1) to (4) is wound and fixed. Then, the lid 300 is bonded to one end of the cylindrical body 290.

The above-prepared product is integrally fired at 1450-1500 ° C.

In the axial groove 310 on the surface of the fired body obtained in
_A gas-impermeable dense layer 320 is formed by applying a fine particle colloidal cement of ₂ O ₃ and MgO and performing a heat treatment to obtain a cylindrical oxygen detection element 200.

In addition, although the laminated body manufactured by the above-mentioned may be manufactured one by one, after manufacturing a plurality of laminated bodies collectively, it cuts one by one and winds it around the cylindrical body 290. Is also good.

When an experiment similar to that of the first embodiment was performed on the oxygen detection element 200 of the present embodiment, the insulation resistance between the measurement gas side electrode 240 and the metal shell over a long period of time was the same as in the first embodiment. It was confirmed that high resistance was maintained.

[Effect of the Invention] As described above, the oxygen detecting element manufactured by the method for manufacturing an oxygen detecting element of the present invention has a conductive property except for at least the porous electrode on the surface of the solid electrolyte body exposed to the measurement gas. It is covered with a dense layer that is impermeable to substances and gases. Therefore, in this oxygen detecting element, the insulation resistance between the porous electrode and the metal shell does not decrease due to deposition of conductive particles or the like.

Therefore, accurate measurement of the oxygen gas partial pressure can be performed over a long period of time.

[Brief description of the drawings]

FIG. 1 is a partially cutaway perspective view of a first embodiment of the present invention, FIG. 2 is a diagram illustrating the effect thereof, FIG. 3 is a partially cutaway perspective view of a second embodiment of the present invention, and FIG. It is a partially broken perspective view explaining a conventional example. 16,100,200 …… Oxygen detecting element 24,130,220 …… Solid electrolyte 22,110,120,230,240 …… Porous electrode 170,190,250,320… Dense layer

 ──────────────────────────────────────────────────続 き Continuation of front page (72) Inventor Yoshitake Kawaji 14-18 Takatsuji-cho, Mizuho-ku, Nagoya-shi, Aichi Japan Special Ceramics Co., Ltd. (56) References JP-A-59-166854 (JP, A) JP-A-57-182156 (JP, A) JP-A-62-222159 (JP, A) JP-A-60-113550 (JP, U)

Claims (1)

(57) [Claims] An oxygen detecting element comprising: a solid electrolyte comprising an oxygen ion conductive solid electrolyte; and a pair of porous electrodes provided on the solid electrolyte body, wherein the oxygen detecting element detects a partial pressure of oxygen gas in a measurement gas. In the manufacturing method, a ceramic paste containing ceramic particles having a ceramic particle diameter of 0.3 to 0.2 μm and a flux of 15% by weight or less with respect to the ceramic particles is coated on at least a surface of the green sheet of the solid electrolyte body. A paste layer is formed by attaching the paste layer to the surface exposed to the measurement gas except for the porous electrode, and then the paste layer and the green sheet of the solid electrolyte body are simultaneously fired, whereby the surface of the solid electrolyte body is Forming a dense layer that is impermeable to a conductive substance and a gas.