JP2002286680A - Lamination type gas sensor element and its manufacturing method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for efficiently obtaining a lamination type gas sensor element almost not generating a warpage in the element itself by simultaneously burning a non-burned laminate where a non-burned protection layer and a non-burned substrate are laminated so that a non-bumed solid electrolyte layer is pinched. SOLUTION: With the non-burned solid electrolyte layer 15 that becomes a solid electrolyte layer where a pair of electrode patterns 14a and 14a is formed, the non- burned substrate 11 that becomes a ceramic substrate is laminated, a non-burned protection layer 17 that becomes a porous protection layer containing a sublimation powder in a full sphere shape is laminated for forming the non-burned laminated so that at least one of the non-burned electrode patterns 14a and 14b formed on the non-burned solid electrolyte layer is covered, then the non-sintered laminates are burned simultaneously. By using the sublimation powder, the sintering behavior and burning shrinkage of the non-burned protection layer 17 and the non-burned substrate 11 to each sintering temperature can be set nearly equal, thus obtaining the lamination type gas sensor element where the generation of warpage is inhibited having improved manufacturing efficiency without losing the function of the porous protection layer 17.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of manufacturing a laminated gas sensor element for detecting a specific component in a gas to be measured such as exhaust gas discharged from an internal combustion engine, and a laminated gas sensor element obtained by the method. It is about.

[0002]

2. Description of the Related Art Conventionally, in an internal combustion engine such as an automobile engine, various sensors such as an oxygen sensor, a NOx sensor, and an HC sensor have been used as gas sensors for detecting the concentration of a specific component in exhaust gas which serves as an index for air-fuel ratio control and the like. Is being developed. Various types of gas sensor elements incorporated in such a gas sensor are known,
2. Description of the Related Art A laminated gas sensor element (hereinafter, also simply referred to as an “element”) in which a plate-shaped or thin-film solid electrolyte layer formed with a pair of electrodes and a ceramic substrate are laminated has been put to practical use.
This type of device usually has a structure in which at least one electrode in contact with the gas to be measured is covered with a porous protective layer. The reason for forming this porous protective layer is that, for example, the gas to be measured contains a substance (Si, Pb, P or a compound thereof) that poisons the electrode, and protects the electrode from the poisoning. That's why.

[0003] Here, such a laminated element in which a plurality of ceramic layers are laminated is generally manufactured by the following procedure. (1) An unfired solid electrolyte layer serving as a solid electrolyte layer on which a pair of electrode patterns serving as electrodes are formed is laminated on an unfired substrate serving as a ceramic substrate. (2) Forming an unfired protective layer containing a sublimable powder capable of forming pores by sublimation by raising the temperature on the unfired solid electrolyte layer so as to face the unfired substrate with the unfired solid electrolyte layer interposed therebetween An unfired laminated body is manufactured by laminating so as to cover at least one of the unfired electrode patterns. (3) Simultaneously firing this unfired laminate.

[0004]

However, as described above, when an element is obtained by simultaneously firing an unsintered laminate in which an unsintered protective layer and an unsintered substrate are stacked so as to sandwich the unsintered solid electrolyte layer, There is a problem that it is difficult to sufficiently suppress the warpage of the element itself later. If the device is warped in this way, there is a problem that the warp causes cracks in the porous protective layer, and in extreme cases, cracks occur in the device itself.

SUMMARY OF THE INVENTION The present invention solves such a problem. A laminated gas sensor in which an unsintered laminate in which an unsintered protective layer and an unsintered substrate are stacked so as to sandwich an unsintered solid electrolyte layer is simultaneously fired. In forming an element, the element itself is hardly warped, and the porous protective layer is hardly cracked or the like, and a multilayer gas sensor element with good durability can be manufactured. A method and a stacked gas sensor element are provided.

[0006]

Means for Solving the Problems and Effects of the Invention The present inventors simultaneously fire a green laminate in which at least a green protective layer and a green substrate are laminated so as to sandwich a green solid electrolyte layer. In this regard, attention was paid to the relationship between the sintering behavior of the unfired protective layer and the unfired substrate and the firing shrinkage rate during the simultaneous firing, and the study was repeated. Then, while specifying the sublimable powder contained in the unfired protective layer, while specifying the pore shape formed after the sublimable powder is sublimated, the main component constituting the unfired protective layer and the unfired substrate is further determined. By finding that the ceramic components are of the same type, it has been found that both the sintering behavior and the firing shrinkage of the unfired protective layer and the unfired substrate are substantially equal, and have completed the present invention. Furthermore, by limiting the change in porosity of the unfired protective layer (porous protective layer) during simultaneous sintering to a predetermined ratio within a specific firing temperature range, an element with excellent durability can be obtained. And completed the present invention.

[0007] The solution is to provide a solid electrolyte layer provided with a pair of electrodes, a porous protective layer covering at least one of the electrodes, a ceramic component of the same type as the main ceramic component constituting the porous protective layer. A method of manufacturing a laminated gas sensor element comprising at least a porous protective layer and a ceramic substrate facing each other with the solid electrolyte layer interposed therebetween, wherein the pair of electrodes serving as the electrodes are provided. A first step of laminating an unsintered solid electrolyte layer serving as the solid electrolyte layer on which a pattern is formed on an unsintered substrate serving as the ceramic substrate, and forming the porous protective layer containing a true spherical sublimable powder. The unsintered protective layer, the unsintered electrode pattern formed on the unsintered solid electrolyte layer so as to face the unsintered substrate with the unsintered solid electrolyte layer interposed therebetween By stacking so as to cover at least one, a second step of forming an unfired laminated body, a third step and the method of manufacturing a multilayered gas sensing element comprising a cofiring the unfired laminate.

Another solution is to provide a solid electrolyte layer provided with a pair of electrodes, a porous protective layer covering at least one of the electrodes, and a porous protective layer opposed to the porous protective layer with the solid electrolyte layer interposed therebetween. A method of manufacturing a laminated gas sensor element comprising at least a ceramic substrate to be laminated, comprising: an unfired substrate serving as the ceramic substrate; and an unfired protective layer serving as the porous protective layer containing a sublimable powder. As opposed to each other with the unsintered solid electrolyte layer serving as the solid electrolyte layer interposed therebetween, and such that the unsintered protective layer covers at least one of a pair of unsintered electrode patterns formed on the unsintered solid electrolyte layer. Lamination is performed to form an unfired laminate, and when the unfired laminate is simultaneously fired, the change in the porosity of the unfired protective layer is 1 at a firing temperature of 1400 to 1600 ° C. It is a manufacturing method of the multilayered gas sensing element located within%.

The above-mentioned "unfired solid electrolyte layer" is to be fired to become a "solid electrolyte layer" exhibiting oxygen ion conductivity. The unsintered solid electrolyte layer can be obtained by molding a kneaded material (paste or slurry) obtained by kneading a raw material powder for a solid electrolyte layer, a binder, a solvent, and the like. Note that the solid electrolyte layer may be in the form of a plate or a thin film. Specifically, when a screen printing method is used in the above molding, a thin film-shaped (less than 50 μm thick) unsintered solid electrolyte layer is obtained, and the fired solid electrolyte layer can be obtained as a thin film-shaped one. When a doctor blade method is used for molding, a sheet-shaped (50 μm or more in thickness) unfired solid electrolyte layer can be obtained, and the fired solid electrolyte layer can be obtained as a plate-like one.

A typical example of the solid electrolyte layer is zirconia (ZrO ₂ ) in which Y ₂ O ₃ or CaO is dissolved, but other oxides of alkaline earth metal or rare earth metal and ZrO 2 ₂ may be used, and HfO ₂ may be contained in ZrO _{2 serving as} a base. The composition of the solid electrolyte layer is not limited to the above, and a LaGaO ₃ -based sintered body can be used.
In addition, a main component (ceramic component) contained in a layer (specifically, a porous protective layer and a ceramic substrate) laminated on the solid electrolyte layer is replaced with a solid electrolyte layer (unfired solid electrolyte layer). 10) to 80% by weight (preferably 30 to 70% by weight,
More preferably, the unsintered solid electrolyte layer may be formed so as to be contained within the range of 40 to 60% by weight).
In the element obtained by this, the adhesion to other layers laminated on the solid electrolyte layer can be greatly improved.

The unfired electrode pattern which is fired to form a pair of "electrodes" can be formed on one or both surfaces of the unfired solid electrolyte layer. The unfired electrode pattern is mainly composed of, for example, Pt, and is composed of Au, Ag, P
It can be formed containing d, Ir, Ru, Rh and the like. The pair of electrodes specifically constitutes a detection electrode and a reference electrode. The detection electrode is an electrode in contact with the gas to be measured, and the other reference electrode is an electrode in contact with the reference gas, an oxygen pump. An electrode placed under an oxygen atmosphere at a constant pressure formed by the action, or an electrode having a higher potential than the detection electrode when it comes into contact with a combustible gas component in the gas to be measured.

The above-mentioned “green base” is fired to form a “ceramic base”. The unfired substrate can be obtained by molding a kneaded product obtained by kneading a raw material powder for a substrate, a binder, a solvent, and the like by a doctor blade method or the like. The unsintered substrate may be formed in a form in which an unsintered conductive pattern which is to be sintered and becomes a heating resistor lead portion is embedded. In this case, the solid electrolyte layer can be activated early by applying a voltage to the heating resistor in the ceramic substrate obtained after firing.

The unfired substrate preferably has a function of reinforcing the mechanical strength of the element itself, and can exhibit higher insulating properties. In particular, it is preferable that the insulating property at a temperature of 900 ° C. is 100 times or more that of the solid electrolyte layer. When the ceramic substrate embeds a heating resistor inside itself, a layer having another function such as a buffer layer for alleviating thermal expansion is provided by sandwiching the heating resistor. It may be interposed inside. The ceramic substrate can be formed from a ceramic component such as alumina (Al ₂ O ₃ ), mullite, magnesia-alumina spinel, etc., but it is particularly preferable to mainly use alumina. In addition, "subject" in this specification
The term means the component having the highest weight content, and does not necessarily mean the component occupying 50% by weight or more.

The above-mentioned “unfired protective layer” is to be fired to become a “porous protective layer”. The unfired porous protective layer is formed into a thin film by kneading a kneaded product obtained by kneading the raw material powder for the protective layer, the sublimable powder, the binder, the solvent, and the like, by screen printing or the like (multiply if necessary). Can be molded. Further, the above kneaded material can be formed into a plate shape by a doctor blade method or the like. In addition, such an unfired protective layer is laminated so as to cover at least one of a pair of electrode patterns formed on the unfired solid electrolyte layer.

Here, when the porous protective layer is formed, the unfired protective layer contains a sublimable powder for firing to form pores. It is noteworthy that powder is used.

Usually, the sublimable powder is contained in the unfired protective layer in combination with the binder as described above, and does not pass through the liquid phase after the binder is decomposed during the temperature rise of the unfired protective layer. Sublimates to form pores. The pores shrink in the subsequent firing process due to the firing shrinkage of the unfired protective layer due to the reaction activity between the powders of the raw material powder for the protective layer. At this time, if the shape of each pore is irregular, the pore shrinkage becomes non-uniform.Therefore, depending on the firing temperature, the particles located around the pores come into contact due to the shrinkage of the pore, and the burning of the unfired protective layer occurs. The knots may progress excessively. Also, when viewed at the same firing temperature,
The firing shrinkage of the plurality of unfired protective layers may vary.

On the other hand, in the present invention, as described above, a true spherical sublimable powder is used, and the pore shape after sublimation is substantially spherical, reflecting the shape before sublimation. Accordingly, when the reaction between the powders of the protective layer raw material powder proceeds during the sintering process and shrinkage due to firing occurs, the pores are uniformly spherical and shrink uniformly. Therefore, even at each sintering temperature, each pore acts to maintain its shape although shrinkage occurs, and particles located around the pores hardly come into contact due to shrinkage of the pores. Thereby, the firing shrinkage rate for each firing temperature is stable, and the firing shrinkage rates of the plurality of unfired protective layers when viewed at the same firing temperature are also stable.

In the present invention, a ceramic substrate is provided in which a porous protective layer (unfired protective layer) containing a spherical sublimable powder is laminated to face each other with a solid electrolyte layer (unfired solid electrolyte layer) interposed therebetween. It should be further noted that the main component is composed mainly of the same type of ceramic component as that of the (unfired substrate).
In such a configuration, since the unsintered protective layer and the unsintered base are mainly composed of the same type of ceramic component, the progress of the sintering reaction of both can be made substantially equal, and the above-described true spherical sublimation is achieved. The sintering behavior of the unfired protective layer and the unfired substrate and the sintering shrinkage of the unfired protective layer with respect to each firing temperature are substantially equal to each other, in combination with the effect of stabilization of the firing shrinkage for each firing temperature provided by the conductive powder It can be. As a result, even when the unfired laminate is fired at the same time, no warpage occurs, and furthermore, the porous protective layer has a highly durable laminated gas sensor element in which peeling and cracking hardly occur.
It becomes possible to obtain with good manufacturing efficiency.

The unfired protective layer and the unfired substrate are mainly composed of the same type of ceramic substrate, and the mixing ratio R2 of the ceramic component which is the main component of the raw material powder for the protective layer in the unfired protective layer is as described above. It is more preferable that the mixing ratio R1 of the ceramic component constituting the main component of the raw material powder for the substrate in the unfired substrate is 90% or more. If the compounding ratio is less than 90%, the effect of making the sintering behavior substantially equal may be reduced. The blending ratio is more preferably 95% or more. It is preferable that the main ceramic components constituting the protective raw material powder and the base raw material powder are of the same kind, and that the average particle size, the particle size distribution, the specific surface area, and the like are closer.

Further, as the above-mentioned "sublimable powder", spherical carbon powder, spherical graphite powder, spherical theobromine powder and the like can be used, but it is preferable to use spherical carbon powder in consideration of handling properties and the like. The term “true sphere” as used herein means a spherical shape, and the ratio of (maximum diameter) / (minimum diameter) in one particle (spherical body) is 1.2 or less.

The spherical sublimable powder preferably has a particle size distribution of 2 to 30 μm and an average particle size of 4 to 15 μm. When the average particle size is larger than 15 μm, the number of true spheres per volume decreases, and most of the barriers through which the gas originally passes in the fired porous protective layer tend to be closed pores, and the response variation of the element (gas sensor) is large. May be. On the other hand, when the average particle diameter is less than 4 μm, the pores tend to increase in the porous protective layer after firing, and the rate control is weakened. As a result, the trapping ability in the exhaust gas is reduced, and the poisoning of the electrode cannot be prevented. is there. When the average particle size of the sublimable powder satisfies 4 to 15 μm but the particle size distribution is out of the range of 2 to 30 μm, coarse particles are largely present in the thickness direction in the cross section of the unfired protective layer. For this reason, the function of the porous protective layer after firing may be reduced, and specifically, the response variation of the element (gas sensor) may be increased, or the assurance of poisoning resistance may be reduced. .

When the total of the sublimable powder and the raw material powder for the protective layer mainly composed of the ceramic component excluding the sublimable powder is 100% by volume, the unfired protective layer is 35% of the sublimable powder. It is preferable to contain it in the range of 65% by volume. If the sublimable powder is less than 35% by volume, it is difficult to obtain sufficient pores (that is, open pores) after firing (simultaneous firing), and it becomes difficult for the gas to be measured to reach the detection electrode. On the other hand, when the content exceeds 65% by volume, the mechanical strength of the obtained porous protective layer may not be sufficiently obtained, and Si,
There is a tendency that it is difficult to sufficiently prevent the electrode (detection electrode) from being poisoned by P, Pb and these compounds.

When simultaneously firing an unsintered laminate in which the unsintered protective layer, unsintered solid electrolyte layer, and unsintered substrate are stacked, preferred firing conditions are 1400 to 16
It is to hold at a firing temperature of 00 ° C (more preferably 1425 to 1550 ° C) for 1 to 2 hours. When the sublimable powder is contained in the range of 35 to 65% by volume with respect to the unfired protective layer as described above, the porosity of the obtained porous protective layer changes depending on the firing temperature. However, the porosity of the porous protective layer after firing is desirably 25 to 50%. In order to obtain a porosity in such a range, the firing temperature is determined in consideration of the content of the sublimation powder. Then, the temperature may be appropriately adjusted within the range of 1400 to 1600 ° C.

Further, in the present invention, when the unsintered laminate in which the unsintered protective layer containing the sublimable powder and the unsintered substrate are laminated to face each other with the unsintered solid electrolyte layer interposed therebetween, Preferably, the change in the porosity of the unfired protective layer is controlled within 10% within a firing temperature range of 1400 to 1600 ° C. In other words, in the simultaneous firing of the unsintered laminate, the key point is to stabilize the firing shrinkage of the unsintered protective layer at each firing temperature, as described above. Stabilization of the porosity leads to stabilization of a change in porosity of the unfired protective layer with respect to each firing temperature. Therefore, when simultaneously firing the unsintered laminate, the change in the porosity of the unsintered protective layer is made to be within 10% within the above-mentioned sintering temperature, so that a good device in which warpage is suppressed can be obtained. It is possible to obtain. It should be noted that such a change in porosity can be adjusted within 10% with respect to each firing temperature by specifically using a true spherical sublimable powder.

[0025]

BEST MODE FOR CARRYING OUT THE INVENTION FIG. 1 shows an example of an oxygen sensor B, which is a gas sensor incorporating a laminated gas sensor element A of the present invention and is attached to an exhaust pipe of an internal combustion engine and used for measuring the oxygen concentration in exhaust gas. FIG.

The stacked gas sensor element A (hereinafter, also simply referred to as “element A”) incorporated in the oxygen sensor B is
The front side is inserted into an insertion hole 32 formed in the metal shell 3 so as to protrude from the tip of the metal shell 3, and a gap between the inner peripheral surface of the insertion hole 32 and the outer peripheral surface of the element A is formed by glass ( For example, it is sealed by a sealing material layer 41 mainly composed of crystallized zinc silica borate glass). Metallic double protectors 61 and 62 covering the protruding portion of the element A are fixed to the outer periphery of the distal end portion of the metal shell 3. The protectors 61 and 62 have a cap shape, and gas introduction holes 61a and 62a for guiding exhaust gas flowing through the exhaust pipe into the protectors 61 and 62 are formed at the ends and around the caps. On the other hand, the rear end portion of the metal shell 3 is inserted inside the front end portion of the outer cylinder 7, and the overlapped portion is joined by laser welding or the like in the circumferential direction. In addition, on the outer peripheral portion of the metal shell 3, a mounting screw portion 3 for screwing the oxygen sensor B (metal shell 3) into the exhaust pipe and mounting it.
1 is screwed.

The element A is electrically connected to an external circuit (not shown) via the first connector 51, the elongated metal thin plate 52, the second connector portion 53 and an insulating plate (not shown), and the lead wire 9. It is connected to the. The four lead wires 9 extend through the grommet 8 located at the rear end side of the outer cylinder 7. In addition, the longitudinal direction of element A (axial direction)
In this embodiment, a porous inorganic substance (for example, talc talc) is disposed adjacent to at least one side of the sealing material layer 41 (adjacent to the end face of the sealing material layer 41 close to the detection portion X in this embodiment). The buffer layer 42 is formed of a powder compact of inorganic material powder or a porous calcined body. This buffer layer 4
The element 2 supports the element A projecting in the axial direction from the sealing material layer 41 so as to wrap the element A from the outside, and plays a role of suppressing excessive bending stress and thermal stress from being applied to the element A.

2. Manufacturing and Structure of Laminated Gas Sensor Element Next, a laminated gas sensor element which is a main component of the present invention will be described with reference to FIG. FIG. 2 is an exploded perspective view of the element A provided in the oxygen sensor B shown in FIG. In the following manufacturing method, each pattern is printed and laminated on a sheet (unfired body) having a size of one element for easy understanding. In the actual process,
After printing and laminating a required number of green sheets (unfired ceramic sheets) having a size capable of manufacturing ten elements, a green laminate having an element shape is cut out, degreased, and fired. Thus, a device was manufactured. Further, in one manufacturing process, 300 elements are manufactured at a time.

(1) Preparation of Unfired Substrate Alumina powder (purity 99.99%
Above, average particle size 0.4 to 0.5 μm, specific surface area 4 to 5 m
² / g), 115 g of butyral resin as a binder for a substrate, and 47.5 g of dibutyl phthalate.
And a predetermined amount of a mixed solvent consisting of toluene and methyl ethyl ketone to form a slurry, and then a first unfired substrate and a second unfired substrate were produced by a doctor blade method. The first unfired substrate has a thickness of 0.55 mm, a length in the longitudinal direction of 5.0 cm, and a width of 4 mm, and becomes the first ceramic substrate 11a after firing. The second green substrate has a thickness of 0.5
The length is 5 mm, the length in the longitudinal direction is 5.0 cm, and the width is 4.0 mm. After firing, the second ceramic base 11b is obtained.

(2) Formation of heater pattern Alumina powder (purity 99.99% or more, average particle size 0.3
6 parts by weight) and 100 parts by weight of platinum powder, a binder and a solvent were added and kneaded to form a paste for a conductive layer on a first green base (after firing, the first ceramic base 1).
1a), a meandering heating element pattern (after firing,
The heating part 121) is printed and dried, and thereafter, alumina powder (purity of 99.99% or more, average particle diameter of 0.4 to 0.5 μm)
m) A pair of heater lead patterns (after firing, heater lead portions 122) are printed and dried with a conductive layer paste containing 2 parts by weight of platinum powder and 100 parts by weight of platinum powder. 12) was formed.

Next, two through-holes (through-holes 111a after sintering) are formed in the vicinity of one end of the first unsintered base so as to conduct with the heating resistor 12 so as to penetrate in the thickness direction of the base. Then, the same conductive layer paste as that of the heater lead pattern was printed and dried on the inner wall surface of each through hole. Further, the terminal pattern for the heating resistor is formed at the position corresponding to the through hole on the surface of the second unfired substrate opposite to the surface facing the heater pattern of the first unfired substrate by using the same conductive layer paste. After firing, two heating resistor terminals 19a) were printed and dried. After that, the second unfired substrate (after firing, the second ceramic substrate 11b) is laminated on the surface of the first unfired substrate on which the heater pattern is formed, pressure-bonded, and unfired substrate (fired, A ceramic substrate (specifically, a ceramic heater) 11) was obtained.

(3) Formation of Buffer Layer Pattern On the second green substrate of the green substrate prepared in (2), a buffer paste containing 80 parts by weight of alumina powder and 20 parts by weight of zirconia powder was used. The buffer layer pattern (after baking, buffer layer 13) was printed to a thickness of 40 ± 10 μm and dried.

(4) Formation of Reference Electrode Pattern On the buffer layer pattern formed in (3), 87 parts by weight of platinum powder and 13 parts by weight of zirconia powder containing coprecipitated yttria are added, and a binder and a solvent are added. Using the kneaded conductive layer paste, a reference electrode pattern (after firing, the reference electrode portion 142a) and a reference electrode pattern (after firing, the reference electrode portion 142a) comprising a reference electrode portion pattern (after firing, the reference electrode portion 141a). 14a) was printed to a thickness of 20 ± 10 μm and dried.

(5) Formation of unfired solid electrolyte layer Zirconia powder (purity 99.9% or more, average particle diameter 0.3
~ 0.4 μm) and 50 parts by weight of alumina powder (purity: 99.
9% or more, average particle diameter 0.4 to 0.5 μm) 50 parts by weight together with 0.5 part by weight of a dispersant are mixed in a predetermined amount of acetone, and kneaded in a resin pot for 3 hours to form a slurry. Prepared. On the other hand, a binder solution was prepared by mixing 15 parts by weight of a binder, 33.3 parts by weight of butyl carbitol, and 0.8 part by weight of dibutyl phthalate in predetermined acetone.
This binder solution was added to the slurry, and the acetone was evaporated while kneading to prepare a solid electrolyte layer paste. Note that butyl carbitol was further added to the prepared paste to adjust the clay of the paste. Then, the solid electrolyte layer paste is coated with a thickness of 45 ± 5 so as to cover at least the reference electrode pattern on the buffer layer pattern.
An unsintered solid electrolyte layer (sintered, solid electrolyte layer 15) was formed by printing and drying 10 μm, a longitudinal length of 7.0 mm, and a width of 4.0 mm.

(6) Formation of Insulating Layer Pattern A first unfired substrate is separately prepared according to the procedure of (1),
To this substrate, 45 parts by weight of butyl carbidol and a predetermined amount of acetone were added and dissolved. After mixing for 4 hours, the acetone was evaporated to prepare an insulating layer paste. This insulating layer paste was applied to a portion on the buffer layer pattern where the unsintered solid electrolyte layer was not formed by 45 ± 10 μm.
Print and dry with the thickness of the insulation layer pattern (after firing,
An insulating layer 16) was formed. However, this insulating layer pattern was formed in a form in which a through hole (through hole 161 after firing) was provided.

(7) Forming a sensing electrode pattern On the unsintered solid electrolyte layer and the insulating layer pattern formed in (5) and (6), using the conductive layer paste prepared in (4), the sensing electrode pattern is formed. Pattern (after firing, sensing electrode 1
41b) and the detection electrode lead pattern (after firing, the detection electrode lead 142b) and the detection electrode pattern (after firing, the detection electrode 14b) were printed and dried at a thickness of 20 ± 5 μm.

(8) Preparation of green body for reinforcing layer A first green reinforcing layer and a second green reinforcing layer were prepared by the doctor blade method using the slurry prepared in (1). The first green reinforcing layer has a thickness of 0.55 mm, a length in the longitudinal direction of 4.0 cm, and a width of 4.0 mm, and becomes the first reinforcing layer 18a after firing. It should be noted that a through-hole (after firing, a through-hole 181 is provided) near one end of the first unsintered reinforcing layer for establishing electrical connection with the reference electrode 14a and the detection electrode 14b.
a) was formed so as to penetrate in the thickness direction of the substrate. The second green reinforcing layer has a thickness of 0.55 mm, a length of 4.0 cm, and a width of 4.0 mm, and after firing, becomes the second reinforcing layer 18b. In addition, also in the vicinity of one end of the second unsintered reinforcing layer, a through hole (after sintering, a through hole 1) for achieving conduction with the reference electrode 14a and the detection electrode 14b is provided.
82a) were formed so as to be coaxial with the through-holes (after-firing, through-holes 181a) of the unfired first reinforcing layer and to penetrate in the thickness direction of the base.

Thereafter, a first unsintered reinforcing layer is formed so as to cover the detection electrode lead portion pattern of the detection electrode pattern formed in (7), and to pass through the through-hole (after firing, the through-hole 1).
81a) was laminated so as to be coaxial with the through hole provided in the insulating layer pattern. Next, the second unsintered reinforcing layer is formed by placing both of the through holes (after sintering, the through holes 181b) on the surface of the first unsintered reinforcing layer opposite to the surface on which the detection electrode lead pattern is formed. 1 Laminated so as to be coaxial with the through holes provided in the unsintered reinforcing layer.

(9) Formation of Pattern for Electrode Terminal Using the conductive paste prepared for forming the heater lead pattern in (2), the first unfired reinforcing layer and the second
The inner wall surfaces of the through holes formed in each of the green reinforcing layer and the buffer layer pattern were printed and dried. Further, using the same conductive layer paste as that of the heater lead pattern, the reference electrode is placed at a position corresponding to the through hole on the surface of the unfired second reinforcement layer opposite to the surface facing the unfired first reinforcement layer. 14
The electrode terminal pattern (after firing, the electrode terminal 19b) for inputting and outputting a signal to and from each of the detection electrode 14a and the detection electrode 14b,
Two pieces were printed and dried.

(10) Preparation of Unfired Protective Layer The same alumina powder as the first and second unfired substrates of (1) (purity of 99.99% or more, average particle diameter of 0.4 to 0) was used as the protective layer raw material powder. 0.5 μm, specific surface area 4-5 m ² / g) 780
g and spherical carbon powder (average particle size: 5 μm, particle size distribution: 2.27 to 17.38 μm), which is a true spherical sublimable powder 2
20 g, a dispersant, and a mixed solvent composed of toluene and methyl ethyl ketone were mixed, and then 97 g of butyral resin and 47 g of dibutyl phthalate as a binder for a protective layer were added and mixed to form a slurry. In this case, the protective layer raw material powder excluding the spherical carbon powder was 35 to 6
When the volume is 5% by volume, the spherical carbon powder has the opposite of 6%.
It is contained at a ratio of 5 to 35% by volume (that is, the total of the spherical carbon powder and the protective layer raw material powder is 100% by volume). Then, the slurry was 270 μm thick and 10.0 mm long in the longitudinal direction by a doctor blade method.
Unfired protective layer having a width of 4.0 mm (after firing, porous protective layer 1)
7) was molded. Then, the obtained unfired protective layer is first reinforced so as to cover the detection electrode portion pattern (detection electrode portion 141b after firing) of the detection electrode pattern formed in (7) and on the unfired solid electrolyte layer. The layers were laminated so as not to overlap with each other to obtain an unfired laminated body (laminated gas sensor element A after firing).

(11) Degreasing and firing The unfired laminate obtained in (1) to (10) was heated from room temperature to 420 ° C. in an air atmosphere at a rate of 10 ° C. /
The temperature was raised over a period of time, and the temperature was maintained for 2 hours to perform a degreasing treatment (a debinding process). Then, in an air atmosphere, 11
The temperature was increased to 00 ° C. at a rate of 100 ° C./hour, and further increased to 1520 ° C. at a rate of 60 ° C./hour, and the temperature was maintained for 1 hour and baked to obtain a multilayer gas sensor element A. . No warpage was observed in the obtained laminated gas sensor element A, and neither cracking nor peeling was observed in the porous protective layer 17.

[0042]

[Experimental example] Relationship between firing behavior and firing shrinkage First, what is the tendency of firing shrinkage of each of the unfired protective layer serving as the porous protective layer 17 and the unfired substrate serving as the ceramic substrate 11 shown in FIG. Was observed using a test piece prepared according to the following procedure. In addition, as a ceramic component which is a main component of the raw material powder for protection and the raw material powder for the substrate constituting the unfired protective layer and the green substrate, only the same alumina powder is used in order to make firing behavior substantially equal. I went.

The test piece was prepared by using alumina powder (purity of 99.99% or more, average particle diameter of 0.4 to 0.5) as a raw material powder.
μm, specific surface area of 4 to 5 m ² / g) 780 g, a carbon powder as a sublimable powder, a mixed solvent comprising a dispersant, toluene and methyl ethyl ketone, and then 97 g of a butyral resin as a binder and dibutyl phthalate After adding and mixing 47 g to obtain a slurry, a slurry (unfired ceramic sheet) having a thickness of 0.27 mm, a length of 50 mm in a longitudinal direction, and a width of 4.0 mm was obtained by a doctor blade method. . Nine test pieces of three types were prepared for this test piece. Sample No. 1 was used as a sublimable powder as a spherical carbon powder having a true spherical shape (average particle size of 5 μm, particle size distribution of 2.27-1.
7.38 μm) as 55% by volume assuming 45% by volume, and Sample No. 2 is a sublimable powder as a spherical carbon powder having a true spherical shape (average particle size 10 μm, particle size distribution 6.72 to 2).
9.91 μm) is 45
By volume%, sample No. 3 is an amorphous carbon powder (average particle size 3 μm, particle size distribution 0.9 to 1) as a sublimable powder.
2.0 μm) were contained at a ratio of 55% by volume, based on the above raw material powder at 45% by volume.

The test pieces of Sample Nos. 1 to 3 are all assumed to have a porous protective layer. Observe the difference in firing shrinkage rate from the test pieces assuming the porous protective layer. So, as sample number 4,
A test piece assuming the ceramic substrate 11 shown in FIG. 2 was manufactured by the following procedure. As the test piece of sample No. 4, an alumina powder (purity of 99.99% or more, average particle size of 0.4 to 0.5 μm, specific surface area of 4 to 5 m ² / g)
And butyral resin 115 as a binder.
g and 47.5 g of dibutyl phthalate, and a predetermined amount of a mixed solvent composed of toluene and methyl ethyl ketone were mixed to form a slurry, and then the mixture was subjected to a doctor blade method.
0.55mm thickness, 50mm length in the longitudinal direction, 4.0 width
9 mm (unfired ceramic sheets) were manufactured. In addition, sample numbers 1 to 3 assuming a porous protective layer,
Sample No. 4 assuming a ceramic substrate was prepared by mainly using alumina powder as a raw material powder (specifically, 100% by weight of alumina powder) in order to make firing behaviors equal.

Next, in order to measure the firing shrinkage rate at each firing temperature of these sample numbers 1 to 4, the length of the test piece corresponding to each sample number in the longitudinal direction was set to L1, and each test piece was put into a furnace and each hour until 1100 ° C. The temperature was raised by 100 ° C. in increments of 100 ° C.
° C, 1200 ° C, 1300 ° C, 1350 ° C, 1400
℃, 1450 ℃, 1500 ℃, 1550 ℃, 1600
° C), and held at this predetermined temperature for 1 hour.
Next, assuming that the length in the longitudinal direction of each test piece taken out from the furnace after cooling is L2, a ratio S (%) represented by the following formula [1] is defined as a firing shrinkage ratio. S (%) = (L1−L2) / L1 × 100 [1] Then, the firing shrinkage ratio calculated by the above formula [1] at each firing temperature of sample numbers 1 to 4 is shown in the graph of FIG. Shown.

As can be seen from FIG. 3, Sample Nos. 1 and 2 using a true spherical spherical carbon powder as the sublimable powder were mainly made of the same kind of raw material powder and contained no sublimable powder. As compared with No. 4, the firing shrinkage ratio at each firing temperature changes substantially the same. On the other hand, Sample No. 3 in which amorphous carbon powder was used as the sublimable powder shows a change in the firing shrinkage at a firing temperature of 1450 ° C. or later different from that of Sample No. 4. From this, the unsintered protective layer is composed mainly of the same type of ceramic component as the unsintered substrate laminated opposite to the unsintered solid electrolyte layer, and the unsintered protective layer has a spherical sublimation. By containing conductive powder (spherical carbon powder)
It can be seen that both the firing shrinkage and firing behavior of the unfired protective layer and the unfired substrate can be made substantially equivalent.

Porosity of Porous Protective Layer Of the test pieces of Sample Nos. 1 to 3 obtained above, firing temperatures of 1400 ° C., 1450 ° C., 1500 ° C.,
The porosity at each firing temperature of 550 ° C. and 1600 ° C. was measured. In addition, the porosity is defined as an apparent volume (including a pore volume) V of each test piece, a weight m1 in the air,
Weight m2 just immersed in water and enough water in pores after immersion in water (by vacuum defoaming, boiling defoaming, etc.)
Using the weight m3, a ratio P (%) calculated by the following equation [2] is used. P (%) = {(m3-m1) / (m3-m2)} × 100 [2] Then, the porosity calculated by the above formula [2] at each firing temperature of sample numbers 1 to 3 is This is shown in the graph of FIG.

As can be seen from FIG. 4, for Sample Nos. 1 and 2 in which a true spherical carbon powder was used as the sublimable powder, the temperature varied within 10% within the firing temperature range of 1400 to 1600 ° C. I have. On the other hand, Sample No. 3 in which amorphous carbon powder was used as the sublimable powder changed nearly 30% within the above-mentioned firing temperature range. From this, a true spherical sublimable powder (spherical carbon powder)
In the unsintered protective layer containing, it is considered that each pore at each sintering temperature acts to maintain its shape although shrinkage occurs, and the change in porosity with respect to each sintering temperature is controlled. At the same time, it can be seen that it is stable.

Electron micrographs Two types of laminated gas sensor elements were manufactured in accordance with the steps (1) to (11) described above. Here, the above (10)
As a sublimable powder used in the step (1), spherical carbon powder (average particle size 5 μm, particle size distribution 2.27 to 17.38 μm) is used in one element (hereinafter, referred to as an example element).
In the other element (hereinafter, referred to as a comparative element), an amorphous carbon powder (average particle size 3 μm, particle size distribution 0.9 to 1)
2.0 μm). In addition, each sublimation powder contained 55% by volume of the protective layer raw material powder at 45% by volume. In the above step (11), the firing temperature of the unfired laminate was set to 1520 ° C., but in order to manufacture these two types of elements, the firing temperature was set to 1450 ° C.
And

Then, the cross-sections of the example device and the comparative example device obtained after the calcination were taken at right angles to the stacking direction of the devices so as to include the porous protection layer. Using an electron microscope (Model JSM-5410, manufactured by JEOL (JEOL Datum)).
Photos taken at 0x and 5000x magnifications and taken are shown in FIGS. FIG. 5 shows that the surface of the porous protective layer of the device of the example was 50
FIG. 6 is a photograph magnified 5000 times of the surface of the porous protective layer of the device of the example, FIG. 7 is a photo magnified 500 times of the surface of the porous protective layer of the device of the comparative example, and FIG. It is the photograph which expanded the porous protective layer surface of the comparative example element 500 times.

In FIGS. 5 and 6, substantially spherical pores are respectively formed, reflecting the use of the spherical spherical carbon powder. When the pores are adjacent to each other, the porous protective layer is formed. A hole is opened in a part of the wall of the constituent aggregate to form a communication hole. On the other hand, in FIGS. 7 and 8, the shape of the original carbon powder is difficult to understand due to the use of amorphous carbon, and the cross-sectional structure has numerous gaps. It can be seen that the pore diameter and the pore shape clearly show cross-sectional structures.

In the above, the present invention has been described with reference to the embodiments. However, the present invention is not limited to the embodiments, and it is needless to say that the present invention can be appropriately modified and applied without departing from the gist thereof. Absent. For example, as a configuration of the stacked gas sensor element, it can be applied to elements of any configuration such as an element that can be used in an ICP (reference oxygen generation) method and an element that can be used in a reference gas introduction method. Further, in forming the porous protective layer, instead of using one unfired protective layer as in the above-described example, two unfired protective layers having different spherical carbon powder contents were formed, By manufacturing the device after laminating them, it is possible to change the porosity of the obtained porous protective layer into a layer.

[Brief description of the drawings]

FIG. 1 is a schematic view showing a cross section of an oxygen sensor in which a laminated oxygen sensor element of the present invention is incorporated.

FIG. 2 is an exploded perspective view of an element obtained by the manufacturing method of the present invention.

FIG. 3 shows sample numbers 1 and 2 corresponding to an unfired ceramic sheet containing a true spherical carbon powder (assuming the unfired protective layer of the present invention), and a sample number corresponding to an unfired ceramic sheet containing an amorphous carbon powder. 3 is a graph showing the change in firing shrinkage at each firing temperature for each of Sample No. 4 corresponding to an unfired ceramic sheet mainly composed of a ceramic component constituting these unfired ceramic sheets.

FIG. 4 shows sample numbers 1 and 2 corresponding to an unfired ceramic sheet containing a true spherical carbon powder (assuming the unfired protective layer of the present invention), and a sample number corresponding to an unfired ceramic sheet containing an amorphous carbon powder. 3 is a graph showing a change in porosity at each firing temperature for each of Sample No. 4 which is an unfired ceramic sheet mainly composed of a ceramic component constituting these unfired ceramic sheets.

FIG. 5 is an electron micrograph showing a cross section of a porous protective layer at a magnification of 500 times in a laminated gas sensor element fired using an unfired porous layer containing spherical carbon powder.

FIG. 6 is an electron micrograph of a cross section of a porous protective layer of a laminated gas sensor element fired using an unfired porous layer containing spherical carbon powder at a magnification of 5,000.

FIG. 7 is an electron micrograph showing a cross section of a porous protective layer at a magnification of 500 times in a laminated gas sensor element fired using an unfired porous layer containing amorphous carbon powder.

FIG. 8 is an electron micrograph showing a cross section of a porous protective layer at a magnification of 5,000 in a laminated gas sensor element fired using an unfired porous layer containing amorphous carbon powder.

[Explanation of symbols]

A: Laminated gas sensor element, 11, ceramic substrate (ceramic heater), 11a; first ceramic substrate, 11
b; 2nd ceramic base, 111a, 161, 181
a, 181b; Through hole, 12; Heating resistor, 12
1; heating section; 122; heater lead section; 13; buffer layer;
14a; reference electrode, 14b; detection electrode, 15; solid electrolyte layer, 16; insulating layer, 17; porous protective layer, 18a; first reinforcing layer, 18b; second reinforcing layer, B; oxygen sensor (gas sensor)

 ────────────────────────────────────────────────── ─── Continued on the front page (72) Inventor Kunio Yanagi 14-18 Takatsuji-cho, Mizuho-ku, Nagoya F-term (reference) in Japan Special Ceramics Co., Ltd. 2G004 BB04 BE19 BF01 BM07

Claims (8)

[Claims] A solid electrolyte layer provided with a pair of electrodes;
A porous protective layer covering at least one of the electrodes, and a ceramic component of the same type as the main ceramic component constituting the porous protective layer are mainly formed, and the porous protective layer and the solid electrolyte layer are sandwiched between the porous protective layer and the solid electrolyte layer. A method for manufacturing a laminated gas sensor element comprising at least laminating a ceramic substrate facing the above, wherein the unsintered solid electrolyte layer serving as the solid electrolyte layer on which the pair of electrode patterns serving as the electrodes is formed is formed using the ceramic A first step of laminating an unfired substrate serving as a substrate, and an unfired protective layer serving as the porous protective layer containing a spherical sublimable powder, the unfired substrate being sandwiched between the unfired solid electrolyte layers. An unsintered laminated body is formed by stacking so as to face each other and to cover at least one of the unsintered electrode patterns formed on the unsintered solid electrolyte layer. The second step and the method of manufacturing a multilayered gas sensing element, characterized in that it comprises a third step of the firing an unfired laminate simultaneously, the that. 2. The sublimable powder has a particle size distribution of 2 to 30.
and a mean particle size in the range of 4 to 15 μm.
A manufacturing method of the laminated gas sensor element according to the above. 3. The method according to claim 1, wherein the sublimable powder is a spherical carbon powder. 4. The unsintered protective layer, when the total of the sublimable powder and the raw material powder for a protective layer mainly composed of a ceramic component excluding the sublimable powder is 100% by volume, the sublimable powder. The method for producing a laminated gas sensor element according to any one of claims 1 to 3, wherein the content is in the range of 35 to 65% by volume. 5. The compounding ratio R2 of the ceramic component forming the main component of the raw material powder for the protective layer in the unfired protective layer is determined by the mixing ratio R1 of the ceramic component forming the main component of the raw material powder for the base in the green substrate. The method for producing a multilayer gas sensor element according to any one of claims 1 to 4, which is 90% or more. 6. The method for manufacturing a multilayer gas sensor element according to claim 1, wherein the ceramic component is alumina. 7. A solid electrolyte layer provided with a pair of electrodes,
A method for manufacturing a laminated gas sensor element, comprising: laminating at least a porous protective layer covering at least one of the electrodes, and a ceramic substrate facing the porous protective layer and the solid electrolyte layer, wherein the ceramic layer comprises: The unfired substrate serving as the substrate and the unfired protective layer serving as the porous protective layer containing the sublimable powder are opposed to each other with the unfired solid electrolyte layer serving as the solid electrolyte layer interposed therebetween. An unfired laminate is formed by laminating the fired protective layer so as to cover at least one of the pair of unfired electrode patterns formed on the unfired solid electrolyte layer,
In firing the unsintered laminate at the same time, the change in the porosity of the unsintered protective layer is caused by the sintering temperature of 1400 to 1600.
A method for manufacturing a laminated gas sensor element, wherein the temperature is within 10% within the range of ° C. 8. A multilayer gas sensor element obtained by the method for manufacturing a multilayer gas sensor element according to claim 1.