JPS6244614B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for manufacturing an oxygen sensor element for measuring oxygen concentration, and in particular, to measuring the oxygen concentration in exhaust gas discharged from a vehicle engine, and feeding back the results. The present invention relates to a method of manufacturing an oxygen sensor element that can be advantageously used in an exhaust gas purification system configured to appropriately adjust the fuel ratio to enhance the effectiveness of using a catalyst for removing harmful components in exhaust gas.

The oxygen sensor is made of a ceramic material with oxygen ion conductivity, such as a small amount of yttriya (Y ₂ O ₃ ),
An oxygen concentration cell is constructed using a solid electrolyte sintered body made of zirconia (ZrO ₂ ) doped with calcia (CaO) or magnesia (MgO) as a partition wall, and a measured gas portion and a reference gas portion (reference oxygen The oxygen concentration in the gas to be measured portion is detected by measuring the electromotive force generated due to the difference in oxygen partial pressure with the oxygen partial pressure (partial pressure applying means).

This type of oxygen sensor generally has porous electrodes on the inner and outer surfaces of a test tube-shaped solid electrolyte sintered body, and a gas that provides a reference oxygen concentration, such as atmospheric air, is placed inside the solid electrolyte sintered body. It is known that the outside is exposed to exhaust gas, and the electromotive force generated according to the partial pressure of oxygen between the inside and outside is extracted from between the electrodes. Also,
A solid electrode (reference oxygen partial pressure imparting means) made of a sintered body of a metal or a mixture of metal and metal oxide is embedded in the solid electrolyte sintered body, and the inner electrode is formed using the electrical conductivity of the solid electrode itself. Oxygen sensors have been proposed that also serve as an oxygen sensor.

The present invention manufactures a solid electrode sensor element among the above oxygen sensor elements, particularly a solid electrode sensor element which has excellent durability without a decrease in electromotive force even during long-term use, with good workability and without variation in quality between products. The present invention provides a method.

The manufacturing method of the present invention is characterized by including the following steps (a), (b), (c), (d), and (e).

(a) A step of press-molding a solid electrolyte powder to obtain a solid electrolyte temporary molded body having a recess into which a solid electrode is to be inserted; (b) A metal powder or a metal powder and an oxide powder of the metal. A solid electrode temporary molded body made of a mixed powder with a powder, in which one end of an output lead wire is buried, and a heat-resistant metal paste is applied to the surface of the powder, which is electrically connected to the output lead wire. (c) Further solid electrolyte powder is placed on the solid electrolyte temporary molded body holding the solid electrode temporary molded body, and the solid electrolyte powder is integrally press-molded to form the solid electrode. a step of obtaining a structure in which is embedded in a solid electrolyte; (d) a step of firing the above structure in a non-oxidizing or reducing atmosphere at a temperature of approximately 1350°C to 1500°C; (e) a step of sintering the surface of the fired body A step of forming a metal electrode layer on at least a portion.

Hereinafter, the manufacturing method of the present invention will be explained with reference to the drawings.

As shown in Figure 1A, solid electrolyte materials such as ZrO ₂ with small amounts of Y ₂ O ₃ , CaO or MgO
A solid electrolyte temporary molded body 2 having a concave portion is pressure-molded by filling the powder into a molding die 1 and pushing a push rod 4 having a convex portion at the tip into the molding space [(a) process]. For example, a hand press is used to press the push rod 4, and a pressure of about 300 to 1500 kg/cm ² is applied.

Next, as shown in FIG. 1B, the solid electrode temporary molded body 3 prepared in advance is fitted into the recess of the solid electrolyte temporary formed body 2 [step (b)]. The solid electrode temporary formed body 3 is the first
As shown in Figure B', it is a columnar body formed by pressure molding a mixture of metal powder or metal powder and oxide powder of the metal, preferably a mixture of this mixture and an anti-sintering agent powder. , one end of a lead wire 5 made of platinum or a platinum-rhodium alloy is embedded in one end surface, and a metal paste such as platinum is applied to the entire surface of at least one end surface so as to be connected to the lead wire 5 to form an electrode. 6. It is most desirable that the electrode 6 be formed not only on the above-mentioned end surface but also on the entire side surface and bottom surface in contact with the solid electrolyte.

Next, as shown in FIG. 1C, the solid electrolyte powder 7 is placed on the solid electrolyte temporary molded body 2 holding the solid electrode temporary molded body 3 until its surface reaches a height that matches the tip of the lead wire 5. For example, by pressing a push rod 8 having a center rod 8', the parts are press-formed into one piece [step (c)]. By releasing the mold, a structure 9 in which a solid electrode is embedded in a solid electrolyte as shown in FIG. 1D is obtained. By using the push rod 8, it is possible to uniformly compress the solid electrolyte powder 7 without displacing the lead wire 5.

The obtained structure 9 is fired at a temperature of 1350 to 1500° C. in a non-oxidizing or reducing atmosphere to form a sintered body [step (d)]. The firing time depends on the type and amount of the solid electrode material and the solid electrolyte material, the firing temperature, etc., but can usually be selected within the range of 1 to 6 hours.

Next, as shown in FIG. 1E, an electrode 10 is formed on at least a portion of the outer surface of the sintered structure 9 exposed to the gas to be measured [step (e)]. The electrode 10 is
This is done by conventional techniques such as applying and firing a paste of heat-resistant conductive metal material such as platinum or platinum-rhodium (without glass frit). Also,
A porous protective layer 11 of a refractory metal oxide, such as a sprayed layer of magnesium spinel, is preferably formed on the electrode 10 exposed to the gas to be measured.
Further, as shown in the figure, a paste such as platinum is applied in the radial direction to the upper end surface of the structure 9 so as to connect to the upper end of the output lead wire 5, and the internal lead wire 12 is
If this is formed, it is convenient to lead the lead wires to the outside.

The shape of the oxygen sensor element is not particularly limited and may be disc-shaped, cylindrical, spherical, or prismatic, but preferably disc-shaped or cylindrical. Further, it is preferable that the output lead wire is arranged so as to coincide with or be parallel to the central axis of the disk or cylindrical sensor element.

The solid electrolyte may be composed of a conventionally well-known solid electrolyte material for oxygen concentration batteries, such as zirconia (ZrO ₂ ), and a small amount of Y ₂ O ₃ , CaO or MgO is added to this solid electrolyte material for thermal stabilization. It is advantageous to use a solid solution obtained by performing a pre-calcination treatment. A particularly preferable solid electrolyte layer 4 is made of ZrO ₂ containing 4 to 10 mol % of Y ₂ O ₃ as a solid solution.

A solid electrode is obtained from a metal powder or a mixture of a metal powder and an oxide powder of the metal, but it is manufactured using only a metal powder rather than a metal powder-metal oxide powder mixture. However, when an oxygen sensor is used, some of the metals are converted into oxides by receiving oxygen ions guided through the solid electrolyte.
The reference oxygen partial pressure applying means is substantially composed of a sintered body of a metal-metal oxide mixture. The metal components used in the production of solid electrodes include iron, molybdenum,
Examples include chromium, tungsten, nickel, cobalt, silicon and manganese.

In addition to the above-mentioned metal-metal oxide components and platinum group element components, the solid electrode material may include ZrO ₂ , which is the same as the solid electrolyte, or Al ₂ O ₃ , Al ₂ O ₃・MgO,
It is desirable to mix an appropriate amount of a sintering inhibitor made of a metal oxide such as SiO ₂ or Al ₂ O ₃ .SiO ₂ . By blending these metal oxides, the solid electrode is prevented from being excessively sintered during the sintering process during its manufacture, and the thermal shrinkage rates of the solid electrode and the electrolyte layer are made equal. It is possible to prevent problems such as deformation, damage, and electrode peeling of the sensor element during the sintering and use process.

As described above, the present invention makes it possible to easily manufacture a solid electrode sensor element in which a solid electrode is embedded in a solid electrolyte and sintered integrally. Regarding the manufacturing method of this type of sensor element, methods such as vapor deposition or sputtering of a solid electrolyte material around a solid electrode have been proposed, but compared to this method, the method of the present invention Density etc. can be adjusted extremely easily.

Thus, the oxygen sensor element manufactured according to the present invention can be effectively used as a means for detecting oxygen concentration in exhaust gas in a vehicle air-fuel ratio control system as described at the beginning. In particular, the solid state polar oxygen sensor element obtained according to the present invention can stably generate a predetermined electromotive force over a long period of time. In other words, in a solid electrode oxygen sensor that uses the electrical conductivity of the solid electrode itself to double as an inner electrode, if it is used at high temperatures and in an oxidizing atmosphere, oxides may form on the surface of the solid electrode contained in the solid electrolyte. An insulating layer is formed, increasing the sensor's internal resistance.
There was a problem where the regular electromotive force was no longer generated. In the element according to the present invention, a heat-resistant porous metal electrode is formed on the surface of the solid electrode to connect with the output lead wire on the solid electrode side, so that the internal resistance does not increase even after durability and the normal electromotive force is maintained. You can force it.

Next, examples of the present invention will be specifically described.

The first _ZrO2 powder stabilized _with 5.5 mol% _Y2O3
As shown in Figure A, a solid electrolyte temporary molded body 2 having a concave portion was obtained by temporary molding. Separately, platinum with a diameter of 0.3 mm.
Using a hand press, the cylindrical solid electrode temporary molded body 3 with one end of the rhodium alloy lead wire 5 buried therein was
It was manufactured by pressure molding at Kg/cm ² for 3 minutes. A mixture of 40% by weight of carbonyl decomposed iron powder, 20% by weight of ZrO ₂ powder, and 40% by weight of NH ₄ HCO ₃ powder was used as the material for the solid temporary compact 3.

A platinum paste (without glass frit), which is a mixture of platinum powder and volatile organic solvents such as nitrocellulose and butyl acetate, is applied to the entire surface of the solid electrode temporary molded body 3, and electrically connected to the output lead wire 5. A porous metal electrode 6 to be connected was formed [Fig.
B′].

Insert the solid electrode temporary molded body 3 into the recess of the solid electrolyte temporary molded body 2 [Fig. 1B], and place the same as above on it.
Filled with Y ₂ O ₃ mixed ZrO ₂ powder, using a hand press, press the push rod 8 with the middle rod 8' at a molding pressure of 600 kg/
cm ² , and the molding time was 3 minutes, and the mold was released to obtain a structure 9 in which the solid electrode 3 was embedded in the solid electrolyte 2 [Fig. 1C, D] This structure 9 was mixed with 1% by volume of hydrogen. Heat treatment was performed at 1450°C for 3 hours in an argon stream to obtain a sintered body. This sintered body was etched for 5 minutes using concentrated hydrofluoric acid, then washed with water, and a platinum paste (without glass frit) was applied and baked to form a platinum electrode layer 10. Further, on the upper surface of the sintered body, platinum paste was applied and baked in the radial direction in the same manner as described above to form internal lead wires 12 to be connected to the output lead wires 5. In addition, the platinum electrode layer 10
A porous protective coating layer 11 was formed by thermally spraying spinel (MgO.Al ₂ O ₃ ) powder on the [first
Figure E].

Next, FIG. 2 shows a specific example of a sensor for measuring oxygen in exhaust gas, which includes the oxygen sensor element obtained as described above.

Solid electrolyte material 2A and output lead wire 5
The sensor element A, which is integrally formed with the solid electrode 3A to which the solid electrode 3A is attached, is disposed within the tip of a protective cover 13 provided with a large number of ventilation holes 14. Sensor element A
A rod-shaped insulating member 15 made of sintered ceramic is connected to the upper end with a glass adhesive 16, and on the side surface of the insulating member 15 are leads formed by applying platinum paste in a belt shape in the axial direction. line 17
a, 17b are provided. Solid electrolyte material 2A
One end of the platinum electrode 10 formed on the outer surface of the solid electrode 3A is connected to the lead wire 17b, and the output lead wire 5 has one end buried in the solid electrode 3A and connected to the platinum electrode 6 formed on the surface of the solid electrode. Internal lead wire 12
The lead wire 17a is connected to the lead wire 17a through the lead wire 17a.
Then, an insulating member 15 provided with lead wires 17a and 17b and a solid electrolyte material 3 provided with a platinum electrode 10.
A protective ceramic coating layer 11 is placed on the surface of the
is formed.

A flange 18 is formed at one end of the protective cover 13, and a cylindrical housing 19 is connected to the protective cover 13 via the flange 18. The rod-shaped insulating member 15 extends within the housing 19,
Lead wires 20a and 20b (not shown) are embedded in the upper end thereof, and lead wire 20a is connected to output terminal 22a via lead wire 21a, and lead wire 20b is similarly connected to output terminal 22b. There is. Further, the band-shaped lead wire 17a is connected to a lead wire 20a, and the band-shaped lead wire 17b is connected to a lead wire 20b, and an inorganic connection material 23 is applied to the connecting portions of these to be fixed. Note that an insulating ceramic ring 24 is interposed between the rod-shaped insulating member 15 and the inner circumferential surface of the housing 19 and is joined to the member 15. In addition, the lead wire 20
An insulating filler 25 is filled between a, 20b, 21a, and 21b to prevent mutual contact. Output terminals 22a and 22b are insulating bushes 2
It is fixed by 6.

The oxygen sensor is attached to the exhaust pipe of the vehicle at the flange 18, and the protective cover 13 containing the sensor element A is disposed inside the exhaust pipe.

As described above, the present invention provides a solid-state polar oxygen sensor element that has a stable electromotive force and excellent durability and is suitable for detecting oxygen concentration in vehicle exhaust gas, with easy workability.
Moreover, it can be manufactured without any variation in product quality.

[Brief explanation of the drawing]

1A to 1E are explanatory views of the manufacturing process of the oxygen sensor according to the present invention, FIG. 2A is a half-sectional view of the entire oxygen sensor, and FIG. 2B is a sectional view of the main part thereof. 1... Molding mold, 2... Solid electrolyte temporary molded body,
3... Solid electrode temporary molded body, 5... Lead wire for output extraction, 6, 10... Metal electrode, 13... Protective cover, A... Oxygen sensor element.

Claims (1)

[Claims] 1 (a) A step of press-molding solid electrolyte powder to obtain a solid electrolyte temporary molded body having a recess into which a solid electrode is to be inserted; (b) Metal powder or metal powder and It is made of a mixed powder of oxide powder of the metal, one end of the output lead wire is buried in it, and a heat-resistant metal paste is coated on the surface of the powder, which is electrically connected to the output lead wire. A step of placing the solid electrode temporary molded body in the recess of the solid electrolyte temporary molded body; (c) Further placing solid electrolyte powder on the solid electrolyte temporary molded body holding the solid electrode temporary molded body, A step of pressure forming to obtain a structure in which a solid electrode is embedded in a solid electrolyte; (d) a step of firing the above structure at a temperature of about 1350°C to 1500°C in a non-oxidizing or reducing atmosphere; (e) A step of forming a metal electrode on at least a part of the surface of the fired body; and a process of forming a metal powder or a mixture of metal powder and oxide powder of the metal to which an output lead wire is connected. A solid electrode made of a sintered body and serving as a reference oxygen partial pressure imparting means is completely embedded in the solid electrolyte sintered body, a metal electrode is formed on the surface of the solid electrolyte sintered body layer, and the above-mentioned solid electrode is formed on the surface of the solid electrode. A method for manufacturing an oxygen sensor element having a metal electrode connected to an output lead wire.