JP2005106691A - Ceramic structure, its manufacturing method, and gas sensor element - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a ceramic structure having excellent strength and thermal conductivity, its manufacturing method, and a gas sensor element. <P>SOLUTION: This ceramic structure 1 comprises a layered body 19 made by layering a plurality of ceramic layers 11 to 15, and is equipped with an internal space 16 within the layered body 19, with the width of a vertical cross-section of the internal space 16 being decreased from an upper part of the layered body 19 toward its lower part. This gas sensor element is equipped with the ceramic structure and a heater attached to a lower surface of the ceramic structure. At least, a ceramic layer facing on an upper part of the internal space in the ceramic structure is a solid electrolyte layer, with a measurement electrode formed on an upper surface of the electrolyte layer and a reference electrode formed on a lower surface of the electrolyte layer. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a ceramic structure suitable as a structural component used for applications such as a gas sensor element typified by an oxygen sensor element for detecting oxygen concentration in automobile exhaust gas, a method for producing the ceramic structure, and The present invention relates to a gas sensor element.

  In general, a ceramic structure used for an oxygen sensor for automobiles having a plate shape is formed by laminating ceramic green sheets formed by a known technique such as a doctor blade method, an extrusion molding method, a calendar method, etc. It is obtained through a predetermined heat treatment step after producing a laminate having

  On the surface of the ceramic green sheet, a conductor paste is printed by a screen printing method as necessary to form circuit wiring, electrodes, and the like. The laminate is usually formed by laminating two or more similar ceramic green sheets. As a green sheet laminating method, a thermocompression bonding method described in Patent Document 1 or the like, or an adhesive material method in which an adhesive liquid composed of ceramic powder and an organic binder is applied to the green sheet and then pressure-bonded is known. .

  By the way, as a structural component used for an oxygen sensor for automobiles, for example, a ceramic structure having an internal space is used. FIG. 11 is a cross-sectional view showing an example of an automobile oxygen sensor element using this ceramic structure. As shown in FIG. 11, this oxygen sensor element is made of a solid electrolyte and has a green sheet 81 on which a pair of electrodes 80, 80 are formed on both sides, and a green sheet on which a through portion for forming an internal space 82 is formed. 83 and the heater substrate in which the heating element 85 is disposed inside the insulating green sheet 84 are laminated and integrated and fired (see, for example, Patent Document 2).

  In this oxygen sensor element, when a voltage is applied between the pair of electrodes 80, 80, oxygen ions flow from one electrode to the other through the solid electrolyte. The oxygen concentration in the atmosphere to be measured can be measured by utilizing the speed at which oxygen ions flow, that is, the current value depends on the oxygen concentration.

However, since the internal space 82 is formed as a reference gas passage in the oxygen sensor element as described above, the strength of the ceramic structure is lowered, and in some cases, cracks and breakage may occur. Further, when measuring the oxygen concentration, it is necessary to heat the solid electrolyte to a high temperature of about 400 to 1000 ° C. with a heater substrate provided with a heating element 85 in order to increase the conductivity of oxygen ions. Therefore, there is a problem that the thermal conductivity of the ceramic structure is lowered and sufficient rapid heating cannot be performed.
JP 2001-126852 A JP 2002-236104 A

  The subject of this invention is providing the ceramic structure which has the outstanding intensity | strength and thermal conductivity, its manufacturing method, and a gas sensor element.

In order to solve the above-described problems, a ceramic structure, a manufacturing method thereof, and a gas sensor element of the present invention have the following configurations.
(1) A ceramic structure comprising a laminate in which a plurality of ceramic layers are laminated, and having an internal space inside the laminate, wherein the width of the vertical cross section of the internal space is from the top to the bottom of the laminate. A ceramic structure characterized by decreasing toward the surface.
(2) The ceramic structure according to (1), wherein an inner wall surface of the internal space is smooth.
(3) The ceramic structure according to (1) or (2), wherein the shape of the internal space in the vertical section is a triangle or a trapezoid.
(4) The ceramic structure according to (3), wherein two inner angles θ1 and θ2 on the lower side of the trapezoid are the same or different and are in a range of more than 90 ° and not more than 175 °.
(5) A step of laminating at least one second ceramic green sheet having a penetrating portion on the first ceramic green sheet to form a laminate having a recess on the upper surface, and at least the width of the tip portion Is pressed into the recess to reduce the width of the recess from the top to the bottom of the laminate, and the inside of the recess. A step of smoothing the wall surface, a step of laminating a third ceramic green sheet on the laminate so as to close the upper opening of the recess, and forming a laminate having an internal space; and firing the laminate And a process for producing the ceramic structure.
(6) The method for manufacturing a ceramic structure according to (5), wherein the height of the convex portion in the jig can be adjusted according to the depth of the concave portion.
(7) A step of cutting the surface of a single ceramic green sheet or the surface of a laminate of a plurality of ceramic green sheets to form a recess whose width decreases from the top to the bottom, and an upper opening of the recess The ceramic green sheet is laminated on the single ceramic green sheet or the laminated body to form a laminated body having an internal space, and the laminated body is fired. A method for producing a ceramic structure.
(8) In the cutting process, the processing blade is linearly moved while being rotated, the rotation speed X of the processing blade is set to 800 rpm ≦ X ≦ 3000 rpm, and the linear operation speed Y of the processing blade is 1 cm / min ≦ Y ≦ The method for producing a ceramic structure according to (7), wherein the rate is 10 cm / min.
(9) The ceramic structure according to any one of (1) to (4), and a heater attached to a lower surface of the ceramic structure, and at least an upper surface of the internal space in the ceramic structure A gas sensor element in which the ceramic layer is a solid electrolyte layer, a measurement electrode is formed on the upper surface of the solid electrolyte layer, and a reference electrode is formed on the lower surface of the solid electrolyte layer.

  According to the ceramic structure described in the above (1), the width of the internal space decreases from the upper part to the lower part of the multilayer body, and therefore, compared with the substantially rectangular parallelepiped internal space of the conventional ceramic structure. Even if the area of the lower surface of the ceramic layer forming the upper part of the internal space is the same as the conventional one, the volume of the entire internal space can be reduced. Thereby, the strength and thermal conductivity of the ceramic structure can be improved. Therefore, even when this ceramic structure is used as a structural part of a gas sensor element such as an oxygen sensor element, the strength and thermal conductivity of the gas sensor element can be improved without changing the area of the reference electrode. .

  When the inner wall surface of the inner space is smooth as described in the above (2), the heat conduction on the inner wall surface of the inner space becomes uniform, thereby suppressing the occurrence of uneven stress concentration on the inner wall surface. Can do. Thereby, durability with respect to the heat | fever of a ceramic structure can be improved. Therefore, even if the ceramic structure is heated to a high temperature, it is possible to prevent cracks and destruction.

  As described in (3) above, the vertical cross-sectional shape of the internal space in the ceramic structure is preferably a triangle or a trapezoid. Thus, by making the vertical cross-sectional shape of the internal space a simple shape such as a triangle or a trapezoid, an internal space in which the width of the vertical cross-section decreases from the upper part toward the lower part can be easily formed.

  In addition, as described in (4) above, since the inner angles θ1 and θ2 on the lower side of the trapezoid are in the above range, the strength and thermal conductivity of the ceramic structure can be improved, and the ceramic structure Even when the gas sensor element is used as, for example, a gas sensor element, it is possible to prevent the volume of the internal space from becoming excessively small, so that the function of the internal space as a reference gas passage is not impaired.

  According to the method for producing a ceramic structure according to the above (5), using the above-described jig, the width of the concave portion is reduced from the upper part toward the lower part of the laminate, and the inner wall surface of the concave part is smoothed. A ceramic structure excellent in smoothness of the inner wall surface of the internal space can be easily obtained. Moreover, since the jig has a convex shape, there is almost no friction between the inner wall surface of the recess and the jig when the jig is removed from the recess after smoothing. As a result, stress applied to the inner wall surface (side surface and bottom surface) of the recess and the corner portion where the side surface and bottom surface of the recess intersect can be reduced, thereby preventing the inner wall surface and corner portion of the recess from cracking. Can do.

  According to the method for manufacturing a ceramic structure according to (6), since the height of the convex portion in the jig can be adjusted according to the depth of the concave portion, the depth of the concave portion due to thickness variation of the ceramic green sheet or the like. Even if it fluctuates, the convex portion can be adjusted to the optimum height according to the depth of the concave portion in the smoothing process. Thereby, the convex part of a jig can always be adapted to a concave part.

  The ceramic structure of the present invention can also be produced by the method as described in (7) above. In this case, by setting the rotational speed X of the machining blade within the range described in (8) above, the impact of the machining blade on the ceramic green sheet can be reduced, so that chipping is prevented from occurring at the edge of the recess. While being able to do, high smoothness can be provided to the inner wall surface of a recessed part. In addition, by setting the linear operation speed Y of the processing blade within the range described in (8), it is possible to prevent the occurrence of problems such as chips adhering or adhering to the edge of the recess or chipping. it can.

  Since the gas sensor element described in (9) uses the ceramic structure as described above, the gas sensor element has excellent strength and thermal conductivity, and is excellent in reliability without being easily cracked or broken.

  Hereinafter, a ceramic structure of the present invention, a manufacturing method thereof, and a gas sensor will be described in detail with reference to the drawings. Fig.1 (a) is a perspective view which shows the ceramic structure concerning one Embodiment of this invention, FIG.1 (b) is the sectional view on the AA line.

  As shown in FIGS. 1 (a) and 1 (b), the ceramic structure 1 of the present invention comprises a laminated body 19 in which a plurality of ceramic layers 11, 12, 13, 14, and 15 are laminated. An internal space 16 is provided inside. The shape of the internal space 16 in the vertical cross section is a trapezoid in which two opposite sides are substantially parallel to the upper surface of the laminate 19 and the long side of the two sides is located at the top. Thereby, the width of the internal space 16 in the cross section decreases from the upper part to the lower part of the stacked body 19.

  Thus, in the present invention, it is important that the width of the internal space 16 decreases from the upper part to the lower part of the stacked body 19. Therefore, the two inner angles θ1 and θ2 on the lower side of the trapezoid should be in the range of more than 90 ° and not more than 175 °, preferably 95 ° to 125 °, more preferably 105 ° to 115 °. Further, the inner angles θ1 and θ2 may be the same angle or different.

  Thereby, the volume of the internal space 16 can be reduced, the strength and thermal conductivity of the ceramic structure 1 can be improved, and the internal space 16 can be used even when the ceramic structure 1 is used as a gas sensor element, for example. Therefore, the internal space 16 does not lose its function as a reference gas passage. In addition, cracks due to stress concentration are less likely to occur at the corners of the internal space 16 (near the inner angles θ1 and θ2).

  The inner wall surface of the internal space 16 is preferably smooth. Specifically, the maximum width Rmax of the irregularities on the inner wall surface is 60 μm or less, preferably 40 μm or less, more preferably 20 μm or less. As described above, since the inner wall surface in the inner space 16 has high smoothness, the heat conduction on the inner wall surface of the inner space 16 becomes uniform, thereby suppressing the occurrence of uneven stress concentration on the inner wall surface. can do. The maximum width Rmax of the unevenness is, for example, a line segment that cuts the ceramic structure 1 in the vertical cross section shown in FIG. 1B and forms the internal space 16 (in the case of FIG. 1B, the side forming the trapezoid). Unevenness is obtained by measuring the roughness with a surface roughness meter and calculating the difference between the highest and lowest locations.

  On the other hand, when the maximum width of the unevenness exceeds 60 μm, the non-uniformity of heat conduction due to the surface deformation generates a non-uniform accumulation portion of stress during rapid temperature rise and cooling. As a result, the ceramic structure 1 Serious problems such as cracks and breakage may occur, and reliability may be reduced. In this way, by reducing the maximum width of the unevenness on the inner wall surface of the internal space 16 to the above range, when the internal space 16 is exposed to a locally or totally unsteady heating environment, in particular, Even when heated to 500 ° C. or higher, stress can be dispersed and durability can be enhanced.

Hereinafter, the manufacturing method of the ceramic structure 1 according to the present embodiment will be described.
<First manufacturing method>
FIG. 2 is an exploded perspective view for explaining the first manufacturing method of the ceramic structure 1. In the first production method, first, ceramic powder and an organic binder are mixed, and further, an organic-inorganic mixture is prepared by mixing a plasticizer, an antifoaming agent, a dispersing agent and the like as an auxiliary material together with an organic solvent. Then, this mixture is formed into a sheet having a thickness of 2 to 2000 μm, particularly 100 to 600 μm, by a doctor blade method, a calender roll method, a press molding method, an extrusion molding method or the like. Next, the penetrating portion 16a is formed by die punching to obtain U-shaped ceramic green sheets 12a to 14a. The width of each through portion 16a of the green sheets 12a to 14a is such that the green sheet 12a is the largest and the green sheet 14a is the smallest.

  Next, the ceramic green sheets 12a to 14a are sandwiched and laminated by the ceramic green sheets 11a and 15a that are not provided with the penetrating portion 16a, thereby producing a laminate 19a. In general, when the internal space is formed of a plurality of layers of ceramic green sheets as shown in FIG. 2, a step is likely to occur at the lamination interface. Therefore, it is important to accurately set the ceramic green sheet at the time of stacking and die punching to reduce these variations.

  When laminating the above ceramic green sheets 11a to 15a, by laminating while applying a pressure higher than the yield stress value of the green sheet, peeling between the green sheets due to the springback phenomenon and occurrence of stacking faults are further increased. It can be surely prevented. As the pressure application method, a known technique such as a uniaxial press method or an isotropic pressurization method (dry method, wet method) can be used.

  In addition, since the corners 17 and 18 at the upper part of the internal space 16 are acute angles, stress tends to concentrate. Therefore, if excessive pressure is applied during lamination, defects such as cracks may occur near the corners 17 and 18. is there. In such a case, after the ceramic green sheets 12a to 15a are laminated while applying a pressure equal to or higher than the yield stress value of the green sheet, the ceramic green sheet 11a is placed on top of the obtained laminate, and the yield stress of the green sheet is obtained. Lamination may be performed while applying a pressure that is less than the value and does not cause peeling. Specifically, after the ceramic green sheets 12a to 15a are laminated at a temperature of 60 to 90 ° C. while applying a pressure of about 50 to 100 MPa, the ceramic green sheets 11a are added to the top of the obtained laminate at a room temperature. Lamination is performed while applying a pressure of about 01 to 3 MPa. Thereby, it is possible to more reliably prevent the occurrence of defects such as cracks in the vicinity of the corners 17 and 18 in the upper part of the internal space 16.

  Moreover, you may provide an adhesive material layer between the ceramic green sheets 11a-15a as needed. Examples of the adhesive layer include a mixture of ceramic powder, an organic binder, and an organic solvent. As the ceramic powder, the same ceramic powder as that used in the ceramic green sheet is preferably used. Specifically, as an adhesive, an organic solvent is added and mixed at a ratio of 20 to 10000 parts by mass with 100 parts by mass of a solid component composed of ceramic powder 0 to 85% by volume and an organic binder 15 to 100% by volume. The slurry which becomes is mentioned. What is necessary is just to apply | coat this slurry on the green sheet surface, and to laminate | stack and adhere | attach. By interposing such an adhesive layer between the ceramic green sheets, the ceramic particles form a bonding layer when fired, so that defects are hardly generated at the joints of the green sheets, and a stable laminate 19a is formed. easy.

  By the way, when the laminated body 19a is formed by interposing an adhesive layer between the ceramic green sheets 11a to 15a, the organic solvent in the adhesive often penetrates and diffuses into the ceramic green sheet. May swell and soften. Therefore, in the ceramic structure 1, when the positional accuracy of each green sheet to be laminated requires a strict tolerance of 100 μm or less, particularly 50 μm or less, the softening of the green sheet is one factor that deteriorates the positional accuracy. In such a case, lamination is performed without interposing an adhesive layer made of ceramic and / or organic binder or organic solvent between laminated sheets.

  When the adhesive layer is not interposed, for example, when the glass transition point Tg of the organic binder used for the ceramic green sheet is −50 ° C. to 0 ° C., particularly −50 ° C. to −10 ° C. When using an organic binder, the pressure during the pressure lamination is preferably 30 ° C. or higher, more preferably 50 ° C. or higher than Tg, and the pressure applied is set to a pressure higher than the yield stress value. Thereby, since the organic binder in the ceramic green sheets to be laminated moves with each other at the lamination interface, it is possible to more reliably obtain the laminated body 19a of ceramic green sheets having no lamination defects.

  On the other hand, when the plasticizer is used even when the glass transition point Tg of the organic binder used for the ceramic green sheet is 0 ° C. or higher, for example, Tg> 50 ° C., such as polyvinyl butyral, the glass transition point of the organic binder is used. The plasticizer in the ceramic green sheets to be laminated is applied by applying a pressure higher than the yield stress value while applying a temperature of Tg or higher, preferably 50 ° C or higher than Tg, more preferably 90 ° C or higher. It exudes to the surface of the green sheet, and the binder on the surface of the ceramic green sheet is redissolved. As a result, the ceramic green sheet laminate 19a is obtained without stacking faults. And the ceramic structure 1 which has the internal space 16 in which the width | variety of a vertical cross section is reducing toward the lower part from the upper part of the laminated body 19 is obtained by baking the obtained laminated body 19a at about 800-1600 degreeC. be able to.

  In the case where the ceramic green sheet 11a and / or the ceramic green sheet 15a is formed by a laminate of two or more layers, the green sheet 11a and / or the ceramic green sheet 15a are prepared in advance by laminating, respectively, By laminating with the ceramic green sheets 12a to 14a in which the through portions 16a are formed, peeling between the sheets can be reliably prevented.

  In general, when a ceramic green sheet is opened by a mold or the like, a cutting method such as die punching is a cutting method based on a push-off action, and therefore the wall surface of the opening that becomes the inner wall surface of the internal space tends to be rough, Defects such as burrs are likely to occur. This tendency becomes prominent when the yield stress value of the green sheet increases. This is because the Young's modulus is generally improved when the yield stress value of the ceramic green sheet increases. When the hole wall surface becomes rough or defects such as burrs occur as described above, the following second manufacturing method may be used.

<Second production method>
3A to 3D are cross-sectional views illustrating a second method for manufacturing the ceramic structure 1. In the second production method, first, ceramic green sheets 11a to 15a are produced in the same manner as in the first method. Next, as shown in FIG. 3 (a), a U-shaped ceramic green sheet 12a in which a through portion 16a for forming the internal space 16 is formed on the surface of the ceramic green sheet 15a (first ceramic green sheet). ˜14a (second ceramic green sheet) is laminated to form a laminate 19a ′ having a recess 16a ′.

  Next, as shown in FIG. 3 (b), a convex press punch (a jig) comprising a convex portion 32 having a width that decreases from the upper portion toward the lower portion and a smooth surface and an upper punch 30 that supports the convex portion 32. By press-fitting 31 into the recess 16a ′, the width of the recess 16a ′ is reduced from the upper part to the lower part of the stacked body 19a ′ by a predetermined dimension, and the inner wall surface of the recess 16a ′ is smoothed. The surface of the convex portion 32 preferably has a surface roughness Ra of 1 μm or less, particularly 0.4 μm or less. As a result, as shown in FIG. 3C, the width of the inner wall surface of the recess 16a 'can be reduced from the upper part toward the lower part, and the inner wall surface can be smoothed. Further, the maximum width Rmax of the unevenness on the inner wall surface of the recess 16a 'may be 60 μm or less, preferably 40 μm or less, more preferably 20 μm or less.

  Since the ceramic green sheets 12a to 15a are accommodated in the space formed by the pressing die 34 and the lower punch 33 having a flat surface, the ceramic green sheets 12a to 15a are smoothed by the convex press punch 31. Deformation can be effectively suppressed. Here, the tolerance between the convex portion 32 and the concave portion 16a and the tolerance between the mortar 34 and the laminated body 19a 'may be set within a range in which the function imparted to the laminated body 19a' is not impaired. In particular, for a heater having a screen-printed heating element, an oxygen sensor having a screen-printed electrode, etc., if the tolerance is 0 to 150 μm, preferably the tolerance is 0 to 100 μm, more preferably the tolerance is 0 to 50 μm, the printed body Therefore, the intended function is effectively protected.

  In the case where there are irregularities on the inner wall surface of the recess 16a before the smoothing process, the irregularity is plastically deformed along the surface of the convex part 32 to apply a sufficient pressure to form a smooth surface, and the smoothing process is performed. It is desirable to apply a pressure higher than the yield stress value of the ceramic green sheet. Moreover, you may pressurize, heating at the temperature of 50 to 150 degreeC at this time.

  Next, a laminated body 19a having an internal space 16a is formed by laminating ceramic green sheets 11a (third ceramic green sheets) so as to close the upper openings of the recesses 16a ′ (FIG. 3D). By firing the obtained laminated body 19a at about 800 to 1600 ° C., the ceramic structure 1 having the internal space 16 in which the width of the vertical cross section decreases from the upper part to the lower part of the laminated body 19 is obtained. Can do.

  The pressure when laminating the ceramic green sheets 11a is preferably not less than the yield stress value of the ceramic green sheets and not more than 10 times the yield stress value. However, when stress concentrates on the upper corner portion of the internal space 16 and there is a risk that a defect such as a crack may occur in the vicinity of the corner portion, the ceramic green sheets 12a to 15a should be equal to or higher than the yield stress value of the green sheet. It is preferable that the ceramic green sheets 11a be laminated while applying pressure so that the ceramic green sheets 11a are less than the yield stress value of the green sheets and do not cause peeling.

  Further, in place of the above-described convex press punch 31, as shown in FIG. 4, a convex press punch 31 ′ whose height of the convex portion 32 ′ can be adjusted according to the depth of the concave portion 16 a is used. Also good. In this convex press punch 31 ′, the height of the convex portion 32 ′ can be changed by holding the convex portion 32 ′ through a through hole provided in the upper punch 30 ′. Thereby, it can adjust freely so that the height of convex part 32 'can be adapted with respect to the dispersion | variation in the thickness of green sheet 12a-15a. Therefore, when a large number of pieces are taken during mass production, the height of the convex portion 32 ′ can be varied during the pressure treatment, so that variations in the depth of the concave portion can be absorbed, and the convex portion 32 ′ and the concave portion 16 a can always be connected. As a result of the adaptation, the maximum width of the irregularities on the inner wall surface of the internal space 16 can always be controlled to 60 μm or less even during mass production. Note that the vertical movement of the convex portion 32 ′ may be controlled by a servo cylinder, or may be controlled so as to equalize pressure by providing a buffer material.

<Third production method>
5A to 5C are explanatory views showing a third manufacturing method of the ceramic structure 1. In the third manufacturing method, the recess 16b ′ is formed by cutting. First, as shown in FIG. 5A, ceramic green sheets 11b to 15b are produced in the same manner as in the first method described above. Next, among these, the ceramic green sheets 12b to 15b are laminated, and a laminated body 19b ′ integrally laminated in advance is produced by the aforementioned pressure lamination method (FIG. 5B).

  Next, the surface of the obtained laminate 19b 'is cut with the processing blade 41 to form the recess 16b' (FIG. 5C). The formation of the recess 16b 'by cutting is preferably performed by a process in which the processing blade 41 rotates and linearly moves. In particular, it is desirable to perform cutting with the machining blade 41 connected in advance to a machining device (for example, NC drill, NC drilling machine, machining device, etc.) that can control the operation content of the machining blade 41 by programming. Among them, it is desirable to process using an NC drill. Since the smoothness of the inner wall surface of the recess 16b 'obtained by such a method can be determined only by the cutting accuracy, the smoothness can be easily controlled.

  In the above-described cutting process, when the rotational speed of the processing blade 41 is X, it is preferable that the edge of the recess 16b is not damaged by chipping or the like by the processing blade 41 if 800 rpm ≦ X ≦ 3000 rpm. In particular, in order to smooth the surface, it is desirable that 1300 rpm ≦ X ≦ 2000 rpm, and further 1500 rpm ≦ X ≦ 1800 rpm.

  On the other hand, in the case of 3000 rpm <X, the impact of the rotated processing blade 41 on the green sheet increases, and there is a possibility that the problem of frequent chipping at the edge of the recess 16b cannot be suppressed. Further, in the case of X <800 rpm, the cutting surface of the green sheet tends to be rough due to the low rotation speed of the processing blade 41. Further, excessive shearing stress may be generated in the processing blade 41 and the processing blade 41 may be broken.

  Further, when the linear operation speed of the machining blade 41 is Y, when 1 cm / min ≦ Y ≦ 10 cm / min, there are no problems such as chipping, chip adhesion, and adhesion on the edge of the recess 16 b ′. Furthermore, in order to further improve the smoothness of the inner wall surface of the recess 16b ', it is desirable that 2 cm / min≤Y≤6 cm / min, particularly 3 cm / min≤Y≤4 cm / min.

  On the other hand, when Y <1 cm / min, chips during cutting are likely to bite between the processing blade 41 and the green sheet, and there is a risk that the chips soften due to frictional heat and adhere to the inner wall surface. . Further, when 10 cm / min <Y, as described above, the impact of the rotated processing blade 41 on the green sheet increases, and there is a possibility that the chipping frequently occurs at the edge of the recess 16 b ′.

  In this way, it is possible to form the concave portion 16b 'having a predetermined width and decreasing from the upper part to the lower part of the stacked body 19b'.

  Next, by laminating the ceramic green sheets 11b so as to close the upper opening of the recess 16b ', a laminated body 19b having the internal space 16b is formed (FIG. 5 (d)). The pressure when laminating the ceramic green sheets 11b is preferably not less than the yield stress value of the ceramic green sheets and not more than 10 times the yield stress value. However, in the case where stress concentrates on the upper corner of the internal space 16b and there is a possibility that a defect such as a crack may occur in the vicinity of the corner, the ceramic green sheet 11b is less than the yield stress value of the green sheet and It is good to laminate | stack, applying the pressure of the grade which does not produce peeling. And the ceramic structure 1 can be obtained by baking the laminated body 19b obtained above at about 800-1600 degreeC.

  FIG. 6 is a cross-sectional view showing a ceramic structure according to another embodiment of the present invention. The ceramic structure includes a laminated body 20 in which a plurality of ceramic layers 11, 12 ′, 13 ′, 14 ′, and 15 are laminated, and an internal space 16 ′ is provided inside the laminated body 20. The shape of the vertical cross section of the internal space 16 'is an inverted triangle. Thereby, the width of the internal space 16 ′ in the cross section decreases from the upper part to the lower part of the stacked body 20.

  As described above, in the ceramic structure of the present invention, the shape of the internal space is not particularly limited as long as the width decreases from the upper part toward the lower part. Further, the internal space does not necessarily have a continuously decreasing width like the trapezoid or the triangle shown in the above embodiment, and there may be a portion where the width does not change.

<Oxygen sensor element>
Hereinafter, an oxygen sensor element (gas sensor element) according to an embodiment of the present invention will be described. FIG. 7 is a cross-sectional view showing the oxygen sensor element of the present embodiment, and FIG. 8 is an exploded perspective view thereof. The oxygen sensor element includes a ceramic structure 61 of the present invention having an air introduction hole (internal space) 63 therein, and a heater portion 72 attached to the lower surface of the ceramic structure 61.

  The ceramic structure 61 is formed of a laminate in which a plurality of ceramic layers are laminated, that is, a laminate in which the solid electrolyte layer 64 facing the upper portion of the air introduction hole 63 and ceramic layers 65 and 66 are laminated. A measurement electrode 62 is formed on the upper surface of the solid electrolyte layer 64, and a reference electrode 67 is formed on the lower surface of the solid electrolyte layer 64. The vertical cross-sectional shape of the air introduction hole 63 is a trapezoid in which the long side is located at the upper part of the two parallel parallel sides. Thereby, the width of the air introduction hole 63 in the cross section decreases from the upper part to the lower part.

  Electrode leads 68 and 69 are connected to the measurement electrode 62 and the reference electrode 67, respectively. The electrode lead 68 is connected to an extraction electrode 70 formed on the surface of the solid electrolyte layer 64, and the electrode lead 69 is connected to the solid electrolyte layer 64 through a through hole (not shown) formed in the thickness direction of the solid electrolyte layer 64. It is connected to an extraction electrode 71 formed on the surface.

  The measurement electrode 62, the reference electrode 67, the electrode leads 68 and 69, and the extraction electrodes 70 and 71 can be formed by printing an electrode material on a ceramic green sheet that becomes the solid electrolyte layer 64 after firing by screen printing or the like. As the electrode material, for example, platinum or an alloy of platinum and one selected from the group consisting of rhodium, palladium, lutetium, and gold can be used.

  The heater portion 72 is sandwiched between insulating layers 74 and 75 disposed on the lower surface of the ceramic layer 66 together with the power supply lead 73, and is attached to the heater substrate 76. The power feed lead 73 is electrically connected to a power feed pad 78 attached to the lower surface of the heater substrate 76 through a through hole 77 formed in the insulating layer 75 and the heater substrate 76.

The solid electrolyte layer 64 is formed of a solid electrolyte. The solid electrolyte that can be used in the present invention is made of ceramics containing zirconia, and Y ₂ O ₃ , Yb ₂ O ₃ , Sc ₂ O ₃ , Sm ₂ O ₃ , Nd ₂ O ₃ , Dy ₂ as stabilizers. O ₃ partially stabilized ZrO ₂ or stabilized ZrO ₂ to rare earth oxide containing 3 to 15 mol% in terms of oxide, such as, such as ZrO ₂ and the like in which a solid solution of alkaline earth elements. Further, as the materials of the ceramic layers 65 and 66 and the heater substrate 76, various ceramic materials such as a solid electrolyte similar to the solid electrolyte layer 64 and an alumina-containing material can be used. The insulating layers 74 and 75 are made of an insulating material such as an alumina-containing material in order to electrically insulate the ceramic layer 66 from the heater portion 72 and the power supply lead 73 on the heater substrate 76. . Insulating layers 74 and 75 may not be provided when an insulating material such as an alumina-containing material is used as ceramic layer 66 and heater substrate 76, for example.

  In the above embodiment, the case where the ceramic structure of the present invention is applied to an oxygen sensor has been described. However, the ceramic structure of the present invention can be applied to various gas sensor elements in addition to an oxygen sensor element.

  EXAMPLES Hereinafter, although an Example is given and this invention is demonstrated further in detail, this invention is not limited to a following example.

The oxygen sensor element having the configuration as shown in FIGS. 9 and 10 was manufactured by the following procedure, and various evaluations were performed.
As a material of the solid electrolyte layer 64, zirconia (5YSZ) in which 5 mol% of Y ₂ O ₃ was dissolved was used. Further, Al ₂ O ₃ was used as a material for the ceramic layers 65 and 66 and the heater substrate 76.

(1) Preparation of Green Sheet In manufacturing the oxygen sensor element shown in FIGS. 9 and 10, a predetermined amount of an organic binder, 2 parts by weight of dibutyl phthalate and 2 parts by weight of dioctyl phthalate are added to zirconia powder. After adding ~ 110 parts by weight of toluene, the mixture was mixed by a ball mill to prepare a slurry mixture. Thereafter, the slurry was stirred and degassed under reduced pressure, and a zirconia green sheet 64 having a thickness of 300 μm was produced by a doctor blade method.

  Similarly, a predetermined amount of an organic binder, 2 parts by weight of dibutyl phthalate and 2 parts by weight of dioctyl phthalate are added to the alumina powder, 70 to 110 parts by weight of toluene is added, and then the mixture is mixed by a ball mill. A mixture was made. Thereafter, this slurry was stirred and degassed under reduced pressure, and alumina green sheets 65, 66, and 76 were produced by a doctor blade method. The green sheet 65 has a thickness of 400 μm, and the green sheets 66 and 76 have a thickness of 200 μm.

(2) Fabrication of heater Next, a platinum paste prepared by using platinum powder having an average particle diameter of 2 μm and a magnesia-alumina composite oxide material on a green sheet 76 for the heater substrate 76 has a predetermined resistance value. Screen printing was performed to form a heater portion 72 and a power supply lead 73, which were dried at 70 ° C. The power feed lead 73 was connected to a power feed pad 78 printed on the back surface of the green sheet 76 through a through hole 77 filled with platinum paste.

(3) Formation of electrode Screen printing method using platinum paste for electrode prepared by using platinum powder containing 30% by volume of zirconia containing 8% by mole of yttria and having an average particle diameter of 0.1 μm. Thus, the measurement electrode 62, the reference electrode 67, and the electrode leads 68 and 69 were disposed on the front and back surfaces of the ceramic green sheet 64 for the solid electrolyte plate, respectively. The reference electrode 67 was electrically connected to electrode pads 70 and 71 provided on the surface of the solid electrolyte 64 through an electrode lead 69 and a through hole (not shown).

(4) Formation of air introduction hole In order to evaluate the performance of the inner wall surface of the air introduction hole 63, various oxygen sensor elements having different inner angles located below the air introduction hole 63 were produced by various methods.

(4-1) Convex punch uniaxial press In order to form the air introduction hole 63 on the green sheet 65, a penetration portion was formed in a predetermined shape by a die punching method. Next, a green sheet 65 having a penetrating portion, a green sheet 66 not having a penetrating portion, and a heater substrate 76 on which a heater portion 72 and the like have been printed, are preheated to 80 ° C. as shown in FIG. Then, thermocompression bonding was performed for 1 minute at a pressure of 40 MPa using the upper punch 30 having a tapered convex portion 32 set in a space formed by the lower punch 33 having a flat surface and preheated at 80 ° C. Subsequently, an adhesive layer composed of a zirconia material and an organic binder was applied to the upper surface of the opening of the recessed portion after pressurization, and the solid electrolyte layer 64 was placed thereon, and a pressure of 3 MPa was maintained at room temperature for 1 minute. A laminate was obtained.

(4-2) NC machine cutting The green sheets 65 and 66 and the printed heater substrate 76 on which no penetrating part was formed were subjected to thermocompression bonding at 80 ° C. and a pressure of 40 MPa for 1 minute. Subsequently, as shown in FIG. 5 (c), a concave portion was formed by cutting with an NC processing machine using a carbide drill. The rotation speed of the drill was 1600 rpm, and the operation speed was 3 cm / min. Finally, the adhesive layer described above was applied to the upper surface of the opening of the recess after cutting, and the solid electrolyte layer 64 was placed thereon, and a pressure of 3 MPa was maintained for 1 minute at room temperature to obtain a laminate.

(5) Baking and Evaluation of Oxygen Sensor Element Each laminate for an oxygen sensor element produced as described above was baked at 1500 ° C. for 2 hours to obtain an oxygen sensor element. In the obtained oxygen sensor elements (20 in each condition), the occurrence of cracks at the lower corners (near the inner angles θ1 and θ2) of the air inlet hole 63 of the oxygen sensor elements by dyeing, X-rays, and ultrasonic flaw detection. evaluated. The results are shown in Table 1.

  From Table 1, sample No. which is out of the scope of the present invention. It can be seen that 10 to 12 have a high crack generation rate at the corners of 40% or more. On the other hand, Samples Nos. 1 to 9 and Nos. 13 to 15 within the scope of the present invention have a low crack generation rate of 15% or less regardless of the internal space formation method, and can produce highly reliable elements. I know that there is.

The oxygen sensor element was produced in the same manner as in Example 1 except that the variable height convex variable punch single screw press shown in FIG. 4 was used, and the integrated convex punch single screw press in Example 1 was used. Compared to when used. At this time, the inner angle of the corner located below the air introduction hole 63 was fixed at 100 °, and 20 samples were prepared for each condition. The cross section of the oxygen sensor element after firing was observed, and the correlation between the maximum variation tmax in the thickness of the ceramic green sheet and the cracks generated at the corners of the air introduction hole 63 was evaluated. The results are shown in Table 2. The maximum variation tmax in the thickness of the green sheet means the difference between the maximum thickness and the minimum thickness in the green sheet 65 that forms the air introduction hole 63.

  As is apparent from the results in Table 2, in the case of the integrated convex punch uniaxial press (sample Nos. 16 to 19), when the maximum variation tmax in the thickness of the ceramic green sheet increases, the crack occurrence rate at the corner portion of the air introduction hole Tended to be larger. On the other hand, when using a variable convex punch uniaxial press (sample Nos. 20 to 23), even if the maximum variation tmax of the thickness of the ceramic green sheet increases, the crack generation rate does not change and is good. Met.

(a) is a perspective view which shows the ceramic structure concerning one Embodiment of this invention, (b) is the AA sectional view taken on the line. It is a disassembled perspective view for demonstrating the 1st manufacturing method of the ceramic structure shown in FIG. (a)-(c) is sectional drawing which shows the 2nd manufacturing method of a ceramic structure. It is sectional drawing which shows other embodiment of the 2nd manufacturing method. (a)-(c) is explanatory drawing which shows the 3rd manufacturing method of a ceramic structure. It is sectional drawing which shows the ceramic structure concerning other embodiment of this invention. It is sectional drawing which shows the oxygen sensor element of this embodiment. It is a disassembled perspective view which shows the oxygen sensor element of this embodiment. It is sectional drawing which shows the oxygen sensor element used for evaluation in an Example. It is a disassembled perspective view which shows the oxygen sensor element used for evaluation in an Example. It is sectional drawing which shows the conventional oxygen sensor element.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Ceramic structure 11-15 Ceramic layer 16 Internal space 19 Laminated body 61 Ceramic structure 62 Measuring electrode 63 Atmospheric introduction hole (internal space)
64 Solid electrolyte layer (ceramic layer)
65, 66 Ceramic layer 67 Reference electrode 68, 69 Electrode lead 70, 71 Lead electrode 72 Heater part 73 Power supply lead 74, 75 Insulating layer 76 Heater substrate 77 Through hole 78 Power supply pad

Claims (9)

  A ceramic structure having a laminated body in which a plurality of ceramic layers are laminated and having an internal space inside the laminated body, wherein the width of the vertical cross section of the internal space decreases from the upper part to the lower part of the laminated body A ceramic structure characterized by being made.   The ceramic structure according to claim 1, wherein an inner wall surface of the internal space is smooth.   The ceramic structure according to claim 1 or 2, wherein a shape of the internal space in the vertical cross section is a triangle or a trapezoid.   4. The ceramic structure according to claim 3, wherein two inner angles θ <b> 1 and θ <b> 2 on the lower side of the trapezoid are the same or different and are in a range of more than 90 ° and 175 ° or less. A step of laminating at least one second ceramic green sheet having a penetrating portion on the first ceramic green sheet to form a laminate having a recess on the upper surface;
At least a jig having a convex part with a smooth surface that decreases in width from the upper part to the lower part is pressed into the concave part, and the width of the concave part is reduced from the upper part to the lower part of the laminate. Smoothing the inner wall surface of the recess,
A step of laminating a third ceramic green sheet on the laminate so as to close the upper opening of the concave portion to form a laminate having an internal space;
A method for producing a ceramic structure comprising the step of firing the laminate.   The method for manufacturing a ceramic structure according to claim 5, wherein the height of the convex portion in the jig can be adjusted according to the depth of the concave portion. Cutting a surface of a single ceramic green sheet or a laminate of a plurality of ceramic green sheets to form a recess whose width decreases from the top to the bottom;
A step of laminating a ceramic green sheet on a single ceramic green sheet or the laminate to form a laminate having an internal space so as to close the upper opening of the recess;
A method for producing a ceramic structure comprising the step of firing the laminate.   In the cutting process, the processing blade is linearly moved while being rotated, the rotational speed X of the processing blade is set to 800 rpm ≦ X ≦ 3000 rpm, and the linear operation speed Y of the processing blade is 1 cm / min ≦ Y ≦ 10 cm / min. A method for producing a ceramic structure according to claim 7. The ceramic structure according to any one of claims 1 to 4,
A heater attached to the lower surface of the ceramic structure,
At least the ceramic layer facing the upper part of the internal space in the ceramic structure is a solid electrolyte layer,
A gas sensor element in which a measurement electrode is formed on the upper surface of the solid electrolyte layer and a reference electrode is formed on the lower surface of the solid electrolyte layer.

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