JP2014178303A - Method for manufacturing gas sensor element - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for manufacturing a gas sensor element capable of easily forming an electrode on the surface of a solid electrolyte and suppressing reduction of gas detection accuracy.SOLUTION: The method for manufacturing a gas sensor element 3 in manufacturing the gas sensor element having an electrode formed on a solid electrolyte 3s and on its surface includes: a core sticking process of forming a nucleus formation part by adhering noble metal particles to electrode planned parts 450x, 450y at which electrodes are planned to be formed among the surfaces; and a plating process of applying plating to the nucleus formation part and forming an electrode. The core sticking process includes: a coating process of coating the electrode planned part with a solution or a paste containing a solvent and noble metal particles composed of a single noble metal element in which particle diameter (D90) whose accumulated numbers are 90% is less than 100 nm; and a removable process of heating the electrode planned part coated with the solution or the paste to a heating temperature equal to or more than a lower temperature of either a volatilization temperature of the solvent or a boiling point.

Description

  The present invention relates to a method of manufacturing a gas sensor element that detects the concentration of a gas to be detected.

As a gas sensor for detecting an oxygen concentration in an exhaust gas of an automobile or the like, a gas sensor that extends in an axial direction and has a substantially cylindrical gas sensor element that is inserted and held inside a cylindrical metal shell is known. Yes. This gas sensor element has a cylindrical solid electrolyte body and inner and outer electrodes formed on the inner and outer surfaces of the solid electrolyte body, respectively.
As a method of forming these inner electrode and outer electrode, after applying an organic compound of platinum to the electrode forming portion on the surface of the solid electrolyte body by printing or the like, it is reduced by heating above the thermal decomposition temperature of this compound. A method of forming a platinum nucleus composed of a single platinum and then electrolessly plating platinum on the nucleus has been developed (Patent Document 1).
Further, a method for forming the above-described platinum nucleus by physical vapor deposition (PVD) has been developed (Patent Document 2).

JP-A-9-304334 JP 2004-170404 A

However, in the case of the technique described in Patent Document 1, platinum metal particles deposited by heating an organic compound of platinum at a temperature equal to or higher than the thermal decomposition temperature aggregate to make the size of the finally obtained platinum nucleus nonuniform. There is a problem. Therefore, the thickness of the electrode plated on the surface of the nucleus also becomes uneven, and the gas detection accuracy of the obtained gas sensor element may be lowered.
On the other hand, in the case of the technique described in Patent Document 2, since the platinum is directly deposited on the surface of the solid electrolyte body, it is possible to prevent the size of the platinum nucleus from becoming non-uniform, but the deposition equipment becomes complicated and the manufacturing cost increases. Invite.
Accordingly, an object of the present invention is to provide a method of manufacturing a gas sensor element that can easily form an electrode on the surface of a solid electrolyte body and suppresses a decrease in gas detection accuracy.

In order to solve the above-described problems, a method of manufacturing a gas sensor element according to the present invention provides a gas sensor element having a solid electrolyte body and an electrode formed on the surface of the solid electrolyte body. A nucleation step for forming a nucleation portion by attaching noble metal particles to an electrode planned portion to be formed, and a plating step for forming the electrode by plating the nucleation portion, In the nucleation step, a solution or paste containing a solvent and the noble metal particles composed of a single noble metal element having a particle diameter (D90) of 90% and a cumulative number of less than 100 nm is used as the electrode planned portion. The application step of applying, and the electrode portion to which the solution or paste has been applied are heated to a heating temperature equal to or higher than the volatile temperature or boiling point of the solvent, to remove the solvent. Having a removal step of forming the nucleation section.
According to this method of manufacturing a gas sensor element, when a nucleation part is formed using a solution or a paste on a predetermined electrode part, the solvent is removed by heating to a temperature lower than its volatilization temperature or boiling point, whichever is lower. Therefore, the heating temperature becomes relatively low, and the noble metal particles hardly aggregate. Thereby, the size and thickness of the core of the noble metal particles finally obtained become uniform, the thickness of the electrode plated on the surface of the core also becomes uniform, and the deterioration of the gas detection accuracy of the obtained gas sensor element is suppressed. be able to.

The heating temperature is preferably equal to or lower than a temperature at which the noble metal particles aggregate.
According to this method for manufacturing a gas sensor element, aggregation of noble metal particles is reliably suppressed, and the size and thickness of the nuclei of the noble metal particles become even more uniform.

The paste may further contain a binder.
According to this method for manufacturing a gas sensor element, since the paste has viscosity, it becomes easy to apply the paste to the planned electrode part.

The particle size distribution width (D90-D10) based on the number of the noble metal particles is preferably 50 nm or less.
According to this method for manufacturing a gas sensor element, the size and thickness of the nuclei of the noble metal particles become even more uniform.

  According to the present invention, an electrode can be easily formed on the surface of the solid electrolyte body, and a gas sensor element in which a decrease in gas detection accuracy is suppressed can be obtained.

It is sectional drawing which cut | disconnected the gas sensor which assembled | attached the gas sensor element manufactured by this invention by the surface in alignment with an axial direction. It is a perspective view which shows the structure of the inner side electrode of a gas sensor element, and an outer side electrode. It is process drawing which shows the manufacturing method of a gas sensor element.

Hereinafter, embodiments of the present invention will be described.
FIG. 1 shows a cross-sectional structure of a gas sensor 100 having a gas sensor element 3 manufactured according to the present invention, cut along a plane along the axis O direction. In this embodiment, the gas sensor 100 is an oxygen sensor that is inserted into an exhaust pipe of an automobile and has a tip exposed to the exhaust gas to detect the oxygen concentration in the exhaust gas. The gas sensor element 3 is a known oxygen sensor element that constitutes an oxygen concentration cell in which a pair of electrodes are laminated on an oxygen ion conductive solid electrolyte body and outputs a detection value corresponding to the amount of oxygen.
In addition, let the lower side of FIG. 1 be the front end side of the gas sensor 100, and let the upper side of FIG.

The gas sensor 100 is assembled so that a substantially cylindrical (hollow shaft-shaped) gas sensor element (in this example, an oxygen sensor element) 3 having a closed tip is inserted and held inside a cylindrical metal fitting body (main metal fitting) 20. It has been. The gas sensor element 3 includes a cylindrical solid electrolyte body 3s having a tapered diameter toward the tip, an inner electrode 50 (see FIG. 2) and an outer electrode formed on the inner and outer peripheral surfaces of the solid electrolyte body, respectively. 450 (see FIG. 2). Further, a round bar heater 15 is inserted into the hollow portion of the gas sensor element 3 so as to raise the temperature of the solid electrolyte body 3s to the activation temperature.
The inner electrode 50 and the outer electrode 450 correspond to “electrodes” in the claims.
A cylindrical outer tube 40 that holds lead wires and terminals (described later) provided on the rear end side of the gas sensor element 3 and covers the rear end portion of the sensor element 3 is joined to the rear end portion of the metal fitting body 20. ing. Further, an insulating and cylindrical separator 121 is caulked and fixed inside the outer cylinder 40 on the rear end side of the gas sensor element 3. On the other hand, the detection part at the tip of the gas sensor element 3 is covered with a protector 7. The male screw part 20d of the metal fitting body 20 of the gas sensor 100 manufactured in this way is attached to a screw hole such as an exhaust pipe, so that the detection part at the tip of the gas sensor element 3 is exposed in the exhaust pipe and the gas to be detected (exhaust gas) Gas). A polygonal flange 20c for engaging a hexagon wrench or the like is provided near the center of the metal fitting body 20, and the step between the flange 20c and the male thread 20d is attached to the exhaust pipe. A gasket 14 is inserted to prevent the gas from leaking when it is blown.

A flange portion 3 a is provided at the center side of the gas sensor element 3, and a step portion that is reduced in diameter is provided on the inner peripheral surface near the tip of the metal fitting body 20. In addition, a cylindrical ceramic holder 5 is disposed on the surface facing the rear end of the step portion via a washer 12. The gas sensor element 3 is inserted inside the metal fitting body 20 and the ceramic holder 5, and the flange 3 a of the gas sensor element 3 is in contact with the ceramic holder 5 through the washer 13 from the rear end side.
Furthermore, a cylindrical talc powder 6 and a cylindrical ceramic sleeve 10 are arranged in the radial gap between the gas sensor element 3 and the metal fitting body 20 on the rear end side of the flange 3a. And the ceramic sleeve 10 is pressed to the front end side by arranging the metal ring 30 on the rear end side of the ceramic sleeve 10 and bending the rear end portion of the metal fitting body 20 inward to form the crimped portion 20a. Thereby, the talc ring 6 is crushed and the ceramic sleeve 10 and the talc powder 6 are caulked and fixed, and the gap between the gas sensor element 3 and the metal fitting body 20 is sealed.

The separator 121 disposed on the rear end side of the gas sensor element 3 is provided with insertion holes (four in this example), and two of the insertion holes are plate-like base portions of the inner terminal fitting 71 and the outer terminal fitting 91, respectively. 74 and 94 are inserted and fixed. Connector portions 75 and 95 are formed at the rear ends of the plate-like base portions 74 and 94, respectively, and lead wires 41 and 41 are crimped to the connector portions 75 and 95, respectively. Further, a heater lead wire 43 (only one is shown in FIG. 1) drawn from the heater 15 is inserted into two insertion holes (heater lead holes) (not shown) of the separator 121.
A cylindrical grommet 131 is caulked and fixed inside the outer cylinder 40 on the rear end side of the separator 121, and two lead wires 41 and two heater lead wires 43 are respectively inserted from the four insertion holes of the grommet 131. Has been pulled out.
A through hole 131 a is formed at the center of the grommet 131 and communicates with the internal space of the gas sensor element 3. A water-repellent ventilation filter 140 is interposed in the through-hole 131a of the grommet 131 so that the reference gas (atmosphere) is introduced into the internal space of the gas sensor element 3 without passing outside water.

  On the other hand, a cylindrical protector 7 is fitted on the distal end side of the metal fitting body 20, and the distal end side of the gas sensor element 3 protruding from the metal fitting body 20 is covered with the protector 7. The protector 7 is configured by attaching a bottomed cylindrical metal (for example, stainless steel, etc.) double outer protector 7b and an inner protector 7a having a plurality of holes (not shown) by welding or the like.

  Next, the configuration of the outer electrode 450 and the inner electrode 50 will be described with reference to FIG. As shown in FIG. 2, the inner electrode 50 is formed on the inner peripheral surface of the solid electrolyte body 3 s and is located on the front end side and formed over the entire circumference in the circumferential direction. And an elongated inner lead portion 52 that is formed in a part in the circumferential direction and narrower in the radial direction than the inner detection portion 51, and an inner terminal connection portion 53 that extends to the rear end side from the inner lead portion 52 are integrated. Have. In this example, the inner side detector 51 is also formed on the bottom of the inner peripheral surface of the solid electrolyte body 3s. The inner terminal connection portion 53 is wider than the inner lead portion 52 and is formed on a part of the inner peripheral surface of the solid electrolyte body 3s in the circumferential direction. However, the inner terminal connection portion 53 may have the same width as the inner lead portion 52 or may be formed over the entire circumference in the circumferential direction.

  On the other hand, the outer electrode 450 is formed on the outer peripheral surface of the solid electrolyte body 3s, is located on the front end side and is formed over a part of the circumferential direction, and extends from the outer detector 451 toward the rear end. The outer lead portion 452 that is formed in a part in the circumferential direction and is narrower in the radial direction than the outer detection portion 451, and the outer terminal connection portion 453 that extends to the rear end side from the outer lead portion 452 are integrally provided. . In this example, the outer side detector 451 is also partially formed at the bottom of the inner peripheral surface of the solid electrolyte body 3s. The outer terminal connection portion 453 is wider than the outer lead portion 452 and is formed in the circumferential direction of the outer surface of the solid electrolyte body 3s by a length of 1/3 of the entire circumference. However, the outer terminal connection portion 453 may have the same width as the outer lead portion 452, or may be formed over the entire circumference in the circumferential direction.

This inner side detection unit 51 is exposed to a reference gas atmosphere introduced into the internal space of the gas sensor element 3. On the other hand, the outer electrode 450 formed on the outer surface of the gas sensor element 3 is exposed to the gas to be detected, and the inner electrode 50 (the inner detection unit 51) and the outer electrode 450 (the outer detection unit 451) through the solid electrolyte body 3s. Gas is detected between the two.
The inner terminal connecting portion 53 is electrically connected to the inner terminal fitting 71 inserted in the opening of the solid electrolyte body 3s, and the detection output of the gas sensor element 3 is taken out from the inner terminal fitting 71 to the outside. The outer terminal connection portion 453 is electrically connected to the outer terminal fitting 91 fitted in the solid electrolyte body 3s, and the detection output of the gas sensor element 3 is taken out from the inner terminal fitting 91 to the outside.

Next, with reference to FIG. 3, the manufacturing method of the gas sensor element which concerns on embodiment of this invention is demonstrated. Although the present invention is applied to at least one of the outer electrode 450 and the inner electrode 50, the case where the present invention is applied to the outer electrode 450 and manufactured is illustrated.
FIG. 3 shows a planned electrode portion 450x that is to form the outer electrode 450 on the outer peripheral surface (surface) of the solid electrolyte body 3s. The planned electrode portion 450x is a region having the same dimensions as the outer electrode 450, and integrally includes a planned outer detection portion 451x, a planned outer lead portion 452x, and a planned outer terminal connection portion 453x.

First, in the nucleation step, noble metal particles are attached to the planned electrode portion 450x to form a nucleation portion. In the nucleation step, a solution or paste containing a solvent and a noble metal particle made of a single noble metal element having a particle diameter (D90) with a cumulative number of 90% of less than 100 nm is applied to the planned electrode portion 450x. An application step, and a removal step of removing the solvent by heating the pre-electrode portion 450x to which the solution or paste has been applied to a heating temperature equal to or higher than the solvent's volatilization temperature or boiling point.
Examples of the noble metal particles include particles composed of one kind of platinum group or alloys thereof (this is referred to as “single”), and platinum particles and palladium particles are preferable. The average particle diameter of the noble metal particles is preferably 100 nm or less. When the average particle diameter exceeds 100 nm, when the noble metal particles are formed on the planned electrode part, the unevenness of the film becomes large, and the thickness of the electrode formed on the film may be nonuniform.

Here, the particle diameter of the noble metal particles is measured as follows. First, the solution or paste is applied to a flat plate made of alumina. Next, heat treatment is performed at a lower temperature of the volatilization temperature or boiling point of the solvent (in the case where the following organic binder is further included, the higher one of the volatilization temperature or boiling point of the solvent and the organic binder). Then, 100 particles are randomly selected from a SEM (scanning electron microscope) photograph at a magnification of 100,000 (on the SEM photograph, noble metal particles are distinguished as a white image with respect to alumina as a background). Analytical software measures the particle size (diameter equivalent of particle area) for each particle. For 100 particles, the fine particle side is zero, and the particle diameter at which the cumulative number of particles is 90% is defined as D90. The particle diameter at which the cumulative number of particles is 10% is D10, and the particle diameter at which the cumulative number of particles is 50% is D50.
When the D90 of the noble metal particles is 100 nm or more, the noble metal particles are aggregated, the size and thickness of the finally obtained nucleus become non-uniform, and the thickness of the electrode plated on the surface of the core becomes non-uniform. The gas detection accuracy of the obtained gas sensor element is lowered. The lower limit of D90 is not particularly limited, but is set to 10 nm, for example. Those having a D90 of 10 nm or less are difficult to produce.

  The particle size distribution width (D90-D10) based on the number of noble metal particles is preferably 50 nm or less. When (D90-D10) is 50 nm or less, the particle size distribution of the noble metal particles is sharp, and the core size and thickness of the noble metal particles become even more uniform. In addition, although the minimum of (D90-D10) is not specifically limited, For example, you may be 10 nm. Those having (D90-D10) of 10 nm or less are difficult to produce.

Table 1 shows the results of actual measurement of the particle size distribution state of the noble metal particles, and the number of each data section in Table 1 represents the number of particles having the corresponding particle size. In addition, about Examples 1-3, and 2 of Table 1, since each particle | grain was substantially circular on a SEM photograph, it was considered that it was a single particle (that is, two or more particle | grains have not aggregated).
In Examples 1 to 3 in Table 1, a solution in which platinum particles, which are noble metal particles having different D90, were mixed with a solvent (terpineol and alkylamine) was used. Then, this solution was applied onto alumina, heated to 250 ° C. to remove the solvent, and D10, D50, and D90 of the noble metal particles were measured by the method described above.
As a “conventional example”, a solution in which a platinum complex salt and a reducing agent are mixed was used. And this solution was apply | coated on the alumina, it heated at 70 degreeC, the reduction reaction was produced, and the nucleus was deposited. Thereafter, the temperature was raised to 120 ° C. to volatilize the water, and nuclei D10, D50, and D90 were measured by the method described above.

The noble metal particles can be blended, for example, in an amount of 0.5 to 5.0% by mass with respect to the entire solution or paste.
As the solvent, water, an aqueous solvent, and an organic solvent (for example, alcohol, toluene, chloroform, hexane, terpineol) can be used. Specific examples of the organic solvent include alkyl acetalized polyvinyl alcohol.
In addition, in order to disperse the noble metal particles in the solvent without agglomerating, known dispersants such as polycarboxylic acid, urethane, acrylic resin, esters, amines, imines, thiols and the like can be used. Specific examples of the dispersant include alkylamine, carboxylic acid amide, fatty acid, alkoxysilyl, polyethyleneimine, and polyvinylpyrrolidone. The dispersant covers the noble metal particles and is dispersed in the solvent as a metal colloid. Further, a dispersant and noble metal particles may be mixed.
Furthermore, it can be set as a paste by adding a various organic binder with respect to the solution containing a solvent and a noble metal particle, and raising a viscosity. Examples of the organic binder when the solvent is an organic solvent include acrylic resins and urethane resins. Moreover, a cellulose resin is mentioned as an organic binder when a solvent is an aqueous solvent.
As described above, a solution or paste can be prepared.

In the application step, the solution or paste can be applied to the electrode planned portion 450x by, for example, printing (including transfer), spraying, a dip (immersion) method, an ink jet method, or the like.
In the application step, at least a part of the planned electrode portion 450x may be applied. For example, the outer detection portion planned portion 451x of the planned electrode portion 450x in FIG. 3 and the flange portion 3a of the planned outer lead portion 452x. Even if the solution or paste is applied only to the tip side portion (the regions are combined and represented as the electrode predetermined portion 450y in FIG. 3), and the other portions may be formed with an electrode by a method different from that of the present invention. Good.
The dipping method can be preferably used when the entire surface of the solid electrolyte body 3s is applied in the circumferential direction. For example, when forming the inner side detection part 51 of FIG. 2, it can apply | coat by a dip (immersion) method by filling the said solution from the bottom face (tip) side of the internal space of 3 s of solid electrolyte bodies to the predetermined depth. . Similarly, when the outer side detection unit 451 is formed on the entire circumference in the circumferential direction of the outer surface of the solid electrolyte body 3s, the solid electrolyte body 3s is applied by the dip (immersion) method by immersing the solid electrolyte body 3s from the tip side to a predetermined depth. It can be performed.
As described above, the solution or paste can be applied to the predetermined electrode portion 450x having a predetermined shape without using a mask.

Next, in the removal step, the solvent is removed by heating the electrode planned portion 450x coated with the solution or paste to a heating temperature equal to or higher than the lower one of the volatilization temperature and boiling point of the solvent, and the noble metal particles are removed. The nucleation part including the film is uniformly formed on the surface of the planned electrode part 450x. Here, the lower the volatilization temperature or the boiling point of the solvent, the lower the heating temperature, so that the noble metal particles are less likely to aggregate. Thereby, the size and thickness of the core of the noble metal particles finally obtained become uniform, the thickness of the electrode plated on the surface of the core also becomes uniform, and the deterioration of the gas detection accuracy of the obtained gas sensor element is suppressed. be able to.
For example, when water is used as the solvent, the heating temperature can be about 120 ° C., and aggregation of noble metal particles can be suppressed. In particular, the volatilization temperature or boiling point of the solvent is preferably less than 200 ° C, and the heating temperature is preferably less than 200 ° C.
Further, the heating temperature is preferably not more than the temperature at which the noble metal particles aggregate. Here, “the temperature at which the noble metal particles agglomerate” varies depending on the particle size of the noble metal particles, the type of the dispersant, and the like. Therefore, when the solution or paste is heated, the above-mentioned particle diameter measurement method (SEM photograph) Thus, the temperature is the temperature at which at least one aggregate of two or more particles is confirmed.
In addition, you may add the aggregation inhibitor which suppresses aggregation of a noble metal particle to a solution or a paste. Examples of the aggregation inhibitor include those containing an organometallic compound of any of zirconium, aluminum, titanium, and magnesium and a resin. Examples of the resin include cellulose resins and vinyl resins, and specific examples include ethyl cellulose, nitrocellulose, polyvinyl acetal, and polyvinyl alcohol.

Next, proceeding to the plating step, using a plating solution in which the nucleation part formed in the planned electrode part 450x acts as a catalyst, a noble metal (platinum, etc.) in the plating solution is deposited on the surface of the planned electrode part 450x, The outer electrode 450 is formed.
Specifically, the plating solution is heated in a state in which the solid electrolyte body 3s including the planned electrode portion 450x is immersed in the plating solution, and then left for a predetermined time. Thereby, the noble metal (platinum etc.) in a plating solution can be deposited on the said electrode scheduled part 450x of 3 s of solid electrolyte bodies. Thereafter, the process proceeds to a heat treatment process, and the plated solid electrolyte body 3s is heat-treated at 1200 ° C., for example. As a result, the outer electrode 450 (plating layer) can be baked onto the inner surface of the solid electrolyte body 3s to give predetermined characteristics. The outer electrode 450 is formed in this way, and the obtained gas sensor element 3 can be assembled to the gas sensor 100 (see FIG. 1) by a known assembling method (for example, see Japanese Patent Application Laid-Open No. 2004-053425). Note that organic substances such as a dispersant and a binder are burned out in the heat treatment step.
As the plating solution, for example, a composition prepared by mixing an aqueous platinum complex salt solution (platinum concentration: 15 g / L) and an aqueous solution of hydrazine (concentration: 85 mass%) can be used.
When the inner electrode 50 is formed, a plating solution may be injected into the internal space of the solid electrolyte body 3s using a liquid injection device.

  It goes without saying that the present invention is not limited to the above-described embodiment, but extends to various modifications and equivalents included in the spirit and scope of the present invention. For example, the shapes of the inner electrode and the outer electrode are not limited to the above.

3 Gas sensor element 3s Solid electrolyte body 50, 450 Electrode 450x, 450y Electrode scheduled part

Claims (4)

In manufacturing a gas sensor element having a solid electrolyte body and an electrode formed on the surface of the solid electrolyte body,
A nucleation step of forming a nucleation part by adhering noble metal particles to an electrode planned part to form the electrode of the surface;
A plating step of plating the nucleation part to form the electrode;
A gas sensor element manufacturing method comprising:
In the nucleation step, a solution or paste containing a solvent and the noble metal particles made of a single noble metal element having a particle diameter (D90) with a cumulative number of 90% of less than 100 nm is the electrode portion. Heating the coating portion to which the solution or the paste is applied to a heating temperature equal to or higher than the lower one of the volatile temperature and boiling point of the solvent to remove the solvent. And a removing step of forming the nucleation part.   The method for manufacturing a gas sensor element according to claim 1, wherein the heating temperature is equal to or lower than a temperature at which the noble metal particles aggregate.   The method for manufacturing a gas sensor element according to claim 1, wherein the paste further contains a binder.   The method for producing a gas sensor element according to any one of claims 1 to 3, wherein a particle diameter distribution width (D90-D10) based on the number basis of the noble metal particles is 50 nm or less.

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