JP5935548B2 - Alumina / zirconia laminated sintered body, manufacturing method thereof, and gas sensor element including alumina / zirconia laminated sintered body - Google Patents

Description

  The present invention relates to an alumina / zirconia laminated sintered body, a method for producing the same, and a gas sensor element including the alumina / zirconia laminated sintered body.

Conventionally, a gas sensor that is provided in a combustion exhaust passage of an internal combustion engine and detects a specific gas component such as an oxygen concentration contained in a measurement gas such as combustion exhaust has been widely used.
A gas sensor such as an oxygen sensor, a NOx sensor, or an ammonia sensor has at least a pair of counter electrodes on both sides of a substantially flat solid electrolyte body made of a solid electrolyte material that exhibits conductivity with respect to specific ions such as oxygen ions and protons. To form a detection cell.
Since a solid electrolyte body such as zirconia used for this type of gas sensor element becomes active at a high temperature of 300 ° C. or higher, it is usually used in a state heated by a heating element laminated on the solid electrolyte body.
For this reason, when water droplets or oil droplets in the gas to be measured adhere to the gas sensor element, there is a concern that cracks may occur due to thermal shock.
In particular, at the interface between alumina used as an insulator and partially stabilized zirconia (YSZ) used as a solid electrolyte layer, thermal stress due to the difference in thermal expansion coefficient is large, and cracks are likely to occur. ing.

For such a problem, for example, Patent Document 1 discloses a ceramic laminate in which a solid electrolyte layer is integrally provided on a base made of an insulating ceramic, and the solid electrolyte layer is formed of zirconia and The insulating ceramic is contained, and when the total amount of the zirconia and the insulating ceramic is 100% by mass, the content of the insulating ceramic is in the range of 10 to 80% by mass. A ceramic laminate is disclosed.
In Patent Document 1, it is desirable that the relative density of the ceramic layer bonded to the surface of the solid electrolyte layer is 60 to 99.5%.

Patent Document 2 discloses that in a stacked air-fuel ratio sensor element comprising a zirconia solid electrolyte body and an alumina substrate provided with a heater, the zirconia solid electrolyte body contains 5 to 7 mol% of yttria, and a C phase (cubic). Phase), M phase (monoclinic phase) and T phase (tetragonal layer) are mixed, and the relative density of the zirconia solid electrolyte body is 94% or more, and the sintered average particle diameter R _ZR Is 0.5 to 3.0 μm, the relative density of the alumina substrate is 95% or more, the sintered average particle diameter R _AL is 0.5 to 4.0 μm, and the partial stabilization is A laminated air-fuel ratio sensor element is disclosed in which the M / C ratio of zirconia is in the range of 0.05 to 0.25.

However, conventionally, in an alumina / zirconia laminated sintered body in which alumina and zirconia are integrally laminated and fired, the strength of the alumina / zirconia laminated sintered body can be increased by increasing the sintered density of zirconia. However, as a result of intensive studies by the present inventors, when the relative density of alumina is 94% or more and the relative density of zirconia is higher than 95% in the alumina / zirconia laminated sintered body, The effective strength of the alumina / zirconia laminated sintered body is reduced despite the increase in the mechanical strength, and the alumina / zirconia laminate is adjusted by adjusting the relative density of zirconia to the range of 84% to 95%. It has been found that the effective strength of the sintered body can be increased.
This is presumed to be because the theoretical strength increases as the relative density of zirconia increases, but the internal residual stress also increases and the difference between the theoretical strength and the residual stress decreases, so the actual strength decreases. Is done.

  Then, an object of this invention is to provide the gas sensor element containing an alumina / zirconia laminated sintered body with high actual strength, its manufacturing method, and an alumina / zirconia laminated sintered body in view of this situation.

The invention of claim 1 is an alumina / zirconia laminated sintered body in which at least an alumina layer and a zirconia layer are laminated and sintered together, and the relative density of the alumina layer is 94% or more, and The relative density of the zirconia layer is 84% or more and 95% or less (excluding the relative density of 94% or more of the zirconia layer) .

In the invention of claim 2, the relative density of the zirconia layer is 87.5% or more and 92.5% or less.
In the invention of claim 3 , the difference between the thermal expansion coefficient of the alumina layer and the thermal expansion coefficient of the zirconia layer at the phase transformation temperature of the zirconia layer is 0.03% or less.

In the invention of claim 4 , in order to detect a specific component in the gas to be measured, a solid electrolyte layer having conductivity with respect to a specific ion, and a pair of electrodes formed on opposing surfaces of the solid electrolyte layer, And a gas sensor element including an insulating layer containing a heater inside, wherein the solid electrolyte layer is composed of a zirconia layer mainly containing partially stabilized zirconia containing 3 to 8 mol% yttria, and the insulating layer is made of alumina. The said zirconia layer and the said alumina layer comprise the alumina / zirconia laminated sintered body in any one of Claims 1-3.

The invention of claim 5 is a method for producing an alumina / zirconia laminated sintered body according to any one of claims 1 to 3 , comprising at least alumina powder as a main raw material, a predetermined amount of a sintering aid, a binder, An alumina sheet forming step of forming an alumina green sheet using an alumina slurry having a median diameter of 1 μm or less after being dispersed in a dispersion medium together with a plasticizer and a dispersing agent, and 3 to 3 as a stabilizer A zirconia slurry containing 8 mol% yttria as a main raw material, dispersed in a dispersion medium together with a predetermined amount of a binder, a plasticizer, and a dispersant, and having a median diameter of 1 μm or less through a pulverization / mixing process is used. The zirconia sheet forming process for forming the zirconia green sheet and the obtained alumina green sheet and zirconia green sheet are stacked. Zirconia sintering in which the alumina / zirconia laminate is formed to form an alumina / zirconia laminate, and the obtained alumina / zirconia laminate is integrally fired at a firing temperature of 1450 to 1500 ° C. for a holding time of 1 to 2 hours. And a density range-limited integrated firing step.

The invention of claim 6 includes a thermal expansion difference relaxation heat treatment step that repeats at least one thermal expansion difference relaxation heat treatment held at a temperature of 900 to 1200 ° C. for 1 to 2 hours.

  According to the present invention, the inventors of the present invention have made it possible to reduce the difference between the thermal expansion coefficient of the zirconia layer and the thermal expansion coefficient of the alumina layer before and after the phase transformation temperature Tc, and It has been found that the actual strength can be improved by increasing the difference between the theoretical strength of the sintered body and the stress remaining in the sintered body.

According to invention of Claim 3 , high durability with respect to a thermal shock can be exhibited.

According to invention of Claim 4 , the gas sensor element excellent in durability with respect to a thermal shock is realizable.

According to the invention of claim 5 , it is possible to realize the alumina / zirconia laminated sintered body having excellent durability according to claim 1 or 2.

According to the invention of claim 6 , the difference between the thermal expansion coefficient of the zirconia layer and the thermal expansion coefficient of the alumina layer before and after the phase transformation temperature Tc is further reduced, and the actual strength of the alumina / zirconia laminated sintered body is further increased. be able to.

The expansion | deployment perspective view which shows the outline | summary of the gas sensor element which has an alumina / zirconia laminated sintered body in the 1st Embodiment of this invention. The cross-sectional schematic diagram which shows the basic composition of the alumina / zirconia laminated sintered body in the 1st Embodiment of this invention. The cross-sectional schematic diagram which shows the modification of the basic composition of the alumina / zirconia laminated sintered body in the 1st Embodiment of this invention. The flowchart which shows the outline | summary of the manufacturing method of the alumina / zirconia laminated sintered body of this invention. The characteristic view which shows the three-point curvature strength test result performed in order to confirm the effect of this invention. The characteristic view which shows the variation of the result of FIG. 4A. The characteristic view which shows the change of the thermal expansion coefficient in a comparative example. The characteristic view which shows the change of the thermal expansion coefficient in Example 1 of this invention. The characteristic view which shows the change of the thermal expansion coefficient in Example 2 of this invention. It is a figure for demonstrating the effect of this invention, Comprising: The characteristic view which shows the change of the internal stress with respect to the temperature of a zirconia layer. It is a figure for demonstrating the effect of this invention, Comprising: The characteristic view which shows the change of theoretical strength with respect to the relative density of a zirconia layer, and a residual stress. The characteristic view showing the critical significance of the present invention and showing the relationship between the sintered density of the zirconia layer and the difference in thermal expansion coefficient at the transition temperature. The characteristic view which shows the thermal expansion coefficient difference reduction effect of the secondary heat processing in this invention.

With reference to FIG. 1, as an example of the alumina / zirconia laminated sintered body in the first embodiment of the present invention, at least a solid electrolyte layer 100 made of yttria-stabilized zirconia and formed in a substantially flat plate shape, and alumina. An outline of the gas sensor element 1 including an alumina / zirconia laminated sintered body integrally laminated and sintered with a substantially flat insulating layer (130, 190) and detecting a specific component in a gas to be measured. Will be described.
As shown in FIG. 1, the gas sensor element 1 includes a solid electrolyte layer 100, an adhesive layer 110, a measurement electrode 120, a measurement gas chamber forming layer 130, a burned-out layer 140, diffusion resistance layers 150a and 150b, a shielding layer. The layer 160, the reference electrode 170, the adhesive layer 180, the reference gas chamber forming layer 190, the heating element 210, and the insulating layers 200 and 220 are laminated and fired to be integrated.

The solid electrolyte layer 100 is made of an oxygen ion conductive solid electrolyte material such as yttria stabilized zirconia or calcia stabilized zirconia, and is fired to have a relative density of 84% or more and 95% or less.
The adhesive layer 110 includes an alumina / zirconia mixed layer, which is an intermediate material between the solid electrolyte layer 100 made of zirconia and the measurement gas chamber forming layer 130 made of alumina, and is a measurement electrode for embedding the measurement electrode 120. The embedded space 111 is partitioned, and the solid electrolyte layer 100 and the measurement gas chamber forming layer 130 are firmly joined.

The measurement electrode layer 120 is made of a known electrode material such as Pt, and is exposed to the measurement gas introduced into the measurement gas chamber 131.
The measurement electrode layer 120 is connected to the outside via the measurement electrode lead 121, the measurement side through-hole electrodes 123 and 124, and the measurement electrode terminal 122.
The measurement gas chamber forming layer 130 is made of alumina, is formed in a substantially flat plate shape, and is fired to have a relative density of 94% or more.

In the measurement gas chamber forming layer 130, a measurement gas chamber 131 and measurement gas introduction holes 132a and 132b for introducing the measurement gas into the measurement gas chamber 131 are defined.
Diffusion resistance layers 150a and 150b using a porous material such as alumina are formed in the measurement gas introduction holes 132a and 132b in order to give a predetermined diffusion resistance.

The burned-out layer 140 is mainly composed of a material that burns down by firing, such as carbon, is filled in the space forming the measurement gas chamber 131, and has a function of preventing cracks from occurring around the reference gas chamber 131 in the stacking process. Demonstrated and burned out when the gas sensor element 1 is completed.
The shielding layer 160 is made of alumina and is formed in a substantially flat plate shape. The surface of the measurement gas chamber forming layer 130 is formed so that the measurement gas is not introduced into the measurement gas chamber 131 without passing through the diffusion resistance layers 150a and 150b. Covering.

The reference electrode layer 170 is connected to the outside via a reference electrode lead portion 171, reference side through-hole electrodes 173, 174, 175, 176 and a reference electrode terminal 172.
Similar to the adhesive layer 110, the adhesive layer 180 includes an alumina / zirconia mixed layer that is an intermediate material between the solid electrolyte layer 100 made of zirconia and the reference gas chamber forming layer 190 made of alumina. And the reference gas chamber forming layer 190 are firmly bonded.

The reference gas chamber forming layer 190 is made of alumina, is made of alumina, is formed in a substantially flat plate shape, and is fired to have a relative density of 94% or more.
The reference gas chamber forming layer 190 has a reference gas chamber 191 that is laminated on the reference electrode layer 170 side and introduces air into the element as a reference gas.
The heating element 120 is formed of a known resistance heating element such as Pt, and is connected to the outside through heating element lead portions 211a and 211b, heating element through-hole electrodes 213a and 213b, and heating element electrode terminals 212a and 212b. .
Note that the adhesive layers 110 and 180 may be omitted.

In the present invention, if the alumina layer (130, 190) and the zirconia layer (100) are laminated and integrally sintered, the alumina layer as shown in FIG. Even when the (130, 190) and the zirconia layer (100) are directly laminated and sintered, there is an intermediate between the alumina layer (130, 190) and the zirconia layer (100) as shown in FIG. 2B. It can be appropriately employed even when an adhesive layer (alumina / zirconia mixed layer) (110, 180) made of any material is formed.
The most important thing in the present invention is not to aim for complete sintering of the zirconia layer, but by adjusting the relative density of the zirconia layer to be in the range of 84% or more and 95% or less. It is intended to improve the actual strength of the.

With reference to FIG. 3, the outline | summary of the manufacturing method of the alumina / zirconia laminated sintered body of this invention is demonstrated.
In the first step (alumina sheet forming step) P1, after firing, an alumina green sheet to be an insulating layer (130, 160, 190, 200, 220) is produced.
Alumina powder, which is an insulating ceramic, is used as a main raw material, yttria, silica, calcia, magnesia and the like as a sintering aid, a required amount of a binder such as butyral resin, a plasticizer such as dibutyl phthalate, a nonionic polyether, A dispersing agent such as a cationic polyalkylene polyamine and an anionic carboxylic acid is blended.
At this time, the blending ratio is adjusted so that the relative density becomes 94% or more when fired under conditions of a firing temperature of 1450 to 1500 ° C. and a holding time of 1 to 2 hours.
In the test to be described later, alumina contains 1 to 3 wt% zirconia, and a low melting point sintering aid such as other flux is not particularly added, and the raw material is slurried with an aqueous solvent, Further, granules having an average granule diameter of 50 to 100 μm are formed through a spray drying process.
Thereafter, the median diameter is reduced to 1 μm or less by the granulation step of this granule, a mixed solution of a carboxylic acid ester solution and an alcohol solution as an organic solvent is 80 to 90 wt% with respect to alumina, and polyvinyl butyral as a binder with respect to alumina. 10 to 20 wt%, a phthalate ester solution as a plasticizer was prepared at a ratio of 5 to 10 Wt% with respect to alumina, and a slurry was prepared by ball milling for 24 hours.

Using a dispersing means such as a ball mill, a rolling mill, a high shear rotor mixer, etc., the above raw materials are dispersed in water or an organic solvent, an alumina slurry having a median diameter of 1 μm or less is prepared, and the viscosity is adjusted by vacuum defoaming. An alumina green sheet having a thickness of 0.2 to 0.3 mm (by measurement, becomes the measurement gas chamber forming layer 130, the shielding layer 160, the reference gas chamber forming layer 190, and the insulating layers 200 and 220) by the blade method. .
Layers that will become the measurement gas chamber forming layer 130, the shielding layer 160, the reference gas chamber forming layer 190, and the insulating layers 200 and 220 after firing, such as by punching an alumina green sheet into a predetermined shape and overlaying as necessary. Partition.

In the second step (zirconia sheet forming step) P2, after firing, a zirconia green sheet to be a solid electrolyte layer (100) is produced.
Oxygen ion conductive ceramic, yttria-stabilized zirconia powder containing 3 to 8 mol% of yttria, a required amount of a binder such as butyral resin, a plasticizer such as dibutyl phthalate, a nonionic polyether, a cationic binder A dispersant such as an alkylene polyamine or an anionic carboxylic acid is blended.
At this time, the relative density when firing at a firing temperature of 1450 to 1500 ° C. and a holding time of 1 to 2 hours is 84% or more and 95% or less, and the relative density when firing at a temperature higher than 1500 ° C. is 95. The blending ratio is adjusted to be at least%.
In addition, in the test described later, an auxiliary agent such as a flux other than yttria is not added to zirconia, the raw material is slurried with an aqueous solvent, and an average granule diameter of 50 to 100 μm is passed through a spray drying process. Granules were formed.

Thereafter, the median diameter is reduced to 1 μm or less by a granulation process, a mixed solution of a carboxylic acid ester-based solution and an alcohol-based aqueous solution as an organic solvent is 50 to 60 Wt% with respect to zirconia, and polyvinyl butyral as a binder with respect to zirconia. The slurry was prepared by ball milling the phthalate ester solution as a plasticizer for 5 to 10 Wt% and zirconia for 5 to 10 Wt% for 24 hours.
Using a dispersing means such as a ball mill, a rolling mill, a high shear rotor mixer, etc., the above raw materials are dispersed in water or an organic solvent, a zirconia slurry having a median diameter of 1 μm or less is prepared, and the viscosity is adjusted by vacuum defoaming. A zirconia green sheet having a thickness of 0.2 to 0.3 mm is produced by a blade method.

Here, the sub-process P _SUB that can be appropriately changed according to the specific configuration of the gas sensor will be briefly described.
In the sub-process P _SUB , the measurement electrode 110, the reference electrode 170, the measurement gas chamber forming layer 130, the burned-out layer 140, the diffusion resistance layers 150a and 150b, the reference gas chamber forming layer 190, the heating element 210, and the like are formed as necessary. I do. Specifically, the following procedure is followed.

In the heating element forming step, predetermined heater patterns (heating element 210, heating element lead portions 211a and 211b, through-hole electrodes 213a and 213b, heat generation) are formed at predetermined positions on the alumina grease sheet (which becomes the insulating layers 200 and 220 after firing). The body conduction terminals 212a and 212b) are formed by a known method such as thick film printing using a known conductive material such as platinum paste.
In the electrode forming step, a predetermined electrode pattern (measurement electrode 120, measurement electrode lead portion 121, reference electrode 170, reference electrode lead portion 171 and through electrode is formed on the opposing surface of the zirconia sheet (which becomes the solid electrolyte layer 100 after firing). The hole electrode 173) is formed by a known method such as thick film printing using a known conductive material such as platinum paste.
In the measurement gas chamber formation layer forming step, a measurement gas chamber formation layer 130 having a predetermined shape is formed by dividing the portions to be the measurement gas chamber 131 and the measurement gas introduction holes 132a and 132b using an alumina green sheet.
In the burnt-out layer forming step, a burnt-out sheet 140 mainly composed of a burnt-out material such as carbon and a binder that is burnt down by firing is formed and embedded in a space serving as the measurement gas chamber 131 provided in the measurement gas chamber forming layer 130. .
In the diffusion resistance forming step, a diffusion resistance layer sheet mainly composed of a large-diameter alumina powder to become porous diffusion resistance layers 150a and 150b having a predetermined diffusion resistance and a burned-out material for adjusting pores is formed. Then, the measurement gas chamber forming layer 130 is embedded in the portions to be the measurement gas introduction holes 132a and 132b.

In the intermediate layer forming step, the above-described alumina slurry and zirconia slurry are appropriately mixed to prepare an alumina / zirconia mixed slurry or an alumina / zirconia mixed paste to be an alumina / zirconia mixed layer (111, 180). Accordingly, an alumina / zirconia mixed layer is formed at a position serving as a boundary between the alumina layer and the zirconia layer.
At this time, an alumina / zirconia mixed layer prepared in a paste form may be used instead of the adhesive, or an alumina / zirconia mixed layer formed in a sheet form may be superposed and thermocompression bonded.

  In the third step (alumina / zirconia lamination step) P3, for example, as shown in FIG. 1, the measurement gas formation layer 130, the shielding layer 160, the reference gas chamber formation layer 190, and the insulating layer 200 provided as an alumina layer. Then, the insulating layer 220 and the solid electrolyte layer 100 provided as a zirconia layer are laminated, heated, and pressure-bonded to form a gas sensor element molded body (1) that is an integral alumina / zirconia laminate.

In the fourth step (Zirconia sintering density range limited integral firing step) P4 which is the main part of the present invention, the obtained alumina / zirconia laminate is held in an air atmosphere at, for example, 420 ° C. for 2 hours, and degreased. After that, in the air atmosphere, the relative density of the alumina layer (130, 160, 190, 200, 220) is 94% or more, and the relative density of the zirconia layer 100 is maintained at 85% to 95%. The gas sensor element 1 which is an alumina / zirconia laminated sintered body is obtained by holding at ˜1500 ° C. for 1-2 hours.
In this step, it is particularly important to adjust the firing temperature and time so that the relative density of the zirconia layer 100 does not exceed 95%.
Even in this state, if the relative density of the zirconia layer 100 is 85% to 95%, the effect of the present invention can be exhibited, but more desirably, the heat treatment step P5 for thermal expansion difference relaxation described later is more reliably performed. The actual strength of the alumina / zirconia laminate can be increased.

In the fifth step (heat treatment step for thermal expansion difference relaxation) P5 which is the main part of the present invention, the fired gas sensor element 1 is held at 900 to 1200 ° C. for 1 to 2 hours in an air atmosphere. The heat treatment for reducing the thermal expansion difference is performed at least once.
Thereby, the difference between the thermal expansion coefficient of the alumina layer and the thermal expansion coefficient of the zirconia layer at the phase transformation temperature Tc (= 460 ° C.) of zirconia is further reduced (specifically, 0.03% or less). The gas sensor element 1 which is an alumina / zirconia laminated sintered body having a large difference between the theoretical strength and the residual stress and a high actual strength is completed.
When the heat treatment is repeated about 3 times by the present inventors' diligent test, the difference in thermal expansion between the alumina layer and the zirconia layer becomes the smallest, and the effect changes even if the heat treatment is repeated 5 to 8 times or more. On the other hand, when it was repeated 9 times or more, it was found that the sintering progressed gradually, the relative density of zirconia increased, and the thermal expansion difference increased on the contrary.

With reference to FIG. 4A and FIG. 4B, the result of the three-point bending strength test performed to confirm the effect of the present invention will be described.
Alumina grease sheet and zirconia green sheet are laminated and pressure-bonded, and 10 test pieces punched into a predetermined shape are prepared for each level. The sintered density of the alumina layer is 94% or more, and the sintered density of the zirconia layer is Samples were prepared in which the firing temperature was changed in the range of 1400 ° C. to 1600 ° C. so that the relative density was 75.0% to 97.5% and 0.5% intervals. The obtained alumina / zirconia laminated sintered body was measured for three-point bending strength (based on JIS R1601), and the results are shown in FIGS. 4A and 4B.
Note that FIG. 3B shows a comparison of the coefficient of variation (standard deviation σ / average value μ) (%) calculated as an evaluation of variation at each level.

As shown in FIG. 3A, the three-point bending strength (220 MPa) when the sintered density of the conventional zirconia layer exceeds 95% is used as a comparative example, and 200 MPa (average value μ + 3σ) is considered in consideration of variations in the comparative example. ) The case where the above high strength was demonstrated was judged to be effective.
As a result, it was found that when the relative density of zirconia was 84% or more and 95% or less, the three-point bending strength of the alumina / zirconia laminated sintered body was larger than that of the comparative example.
Further, as shown in FIG. 4B, it was found that within this range, the three-point bending strength variation of the alumina / zirconia laminated sintered body was also smaller than the variation of the comparative example.

Next, the effect of the present invention on the coefficient of thermal expansion will be described with reference to FIGS. 5A, 5B, and 5C.
FIG. 5A shows, as a comparative example, a zirconia sintered body having a sintered density of 5.59 g / cm ³ (relative density 96.4% (the theoretical density of YSZ is 5.80)) used for the gas sensor element. Of the thermal expansion coefficient when heating from room temperature to 1000 ° C, and cooling from 1000 ° C to room temperature, and heating the alumina sintered body from room temperature to 1000 ° C and cooling from 1000 ° C to room temperature It is the characteristic view which piled up the change of the thermal expansion coefficient at the time of doing.
As shown in FIG. 5A, the coefficient of thermal expansion of the zirconia sintered body shows different values when the temperature is raised and when the temperature is lowered, and becomes a hysteresis curve.
In particular, before and after the phase transformation temperature Tc (460 ° C.) at which phase transformation occurs in the zirconia layer, there is a large difference from the thermal expansion coefficient of alumina, and this is a factor causing cracks in the alumina / zirconia laminated sintered body due to stress. It has become.

On the other hand, when the sintered density of the zirconia layer is controlled to a relative density in the range of 84% or more and 95% or less, it has been found that the difference between the coefficient of thermal expansion at the time of temperature rise and the coefficient of thermal expansion at the time of temperature decrease decreases. .
As shown in Example 1 in FIG. 5B, a zirconia sintered body having a sintered density of 5.34 g / cm ³ (relative density 92.4%) was heated from room temperature to 1000 ° C. and cooled from 1000 ° C. to room temperature. When the alumina sintered body was heated from room temperature to 1000 ° C. and the change in coefficient of thermal expansion when cooled from 1000 ° C. to room temperature was superimposed, the change in thermal expansion coefficient at the time was shown in FIG. 4A as a comparative example. It can be seen that the difference between the thermal expansion coefficient of alumina around the phase transformation temperature Tc is smaller than when the sintered density of the zirconia sintered body is 5.59 g / cm ₃ .

  Further, as shown in Example 2 in FIG. 5C, a plurality of heat treatments for reducing the thermal expansion difference are held for holding a zirconia sintered body having a sintered density of 5.59 g / cm 3 at a temperature of 900 to 1200 ° C. for 1 to 2 hours. It was found that the difference between the thermal expansion coefficient of alumina before and after the phase transformation temperature Tc was smaller than that of the comparative example in which the heat treatment was not performed after repeating the process once (5 times in this example).

The results of the rapid cooling test conducted for investigating the effects of the present invention with reference to Table 1 will be described. The alumina green sheet and the zirconia green sheet obtained by the above-described alumina sheet forming step P1 and zirconia sheet forming step P2 are punched and laminated and bonded to a predetermined size, a test piece is prepared, and degreased at a predetermined temperature. In the range of 1400 to 1600 ° C., a rapid cooling test was performed with n = 10 samples each having a sintered density of zirconia ranging from 75.0% to 97.5% in terms of relative density. Is shown in Table 1.
In the rapid cooling test, each sample is placed in an autoclave, and the temperature in the autoclave is rapidly changed from 1000 ° C. higher than the phase transformation temperature Tc (460 ° C.) of zirconia to room temperature lower than the phase transformation temperature Tc. The presence or absence of breakage when added was examined.
When the number of cracks r is 0, it is judged that there is an excellent effect, and ◎ is marked, and when the number of cracks r is 1 to 3 is judged to be effective, the mark is marked ○. The crack occurrence number r at the same level as the current comparative example is determined to be ineffective from 4 to 6, and a Δ mark is attached, and the crack occurrence number at a level worse than the comparative example is 7 or more. It was determined that there was an adverse effect, and a cross was marked.

The operation principle of the present invention will be described with reference to FIGS. 6A and 6B.
As shown in FIG. 6A, the internal stress of partially stabilized zirconia increases with a decrease in temperature. For example, a phase transformation from T phase (cubic) to M phase (monoclinic) occurs around 460 ° C. A sudden change in internal stress is observed.
In addition, a relatively large residual stress exists at room temperature.
In partially stabilized zirconia, cracks are prevented from progressing due to partial phase transformation by imperfectly stabilizing rapid volume changes associated with phase transitions.
As shown in FIG. 6B, the theoretical strength increases as the relative density of the zirconia layer increases, but at the same time, the residual stress also increases. As a result, the difference between the theoretical strength and the residual stress is small in a high density state. It is inferred that the actual strength is lowered.
If the relative density of the zirconia layer is suppressed to 84% or more and 95% or less, it is considered that the difference between the theoretical strength and the residual stress can be increased and the actual strength can be increased.
This result is also in good agreement with the experimental results shown above.

The critical significance of the present invention will be described with reference to FIG. FIG. 7 shows samples having different sintered densities of the zirconia sintered body, and the thermal expansion coefficient at the phase transformation temperature Tc (460 ° C.) and the thermal expansion coefficient of the alumina sintered body when the temperature is lowered from 1000 ° C. to room temperature. The difference in thermal expansion coefficient due to the difference in zirconia sintered density is plotted.
As shown in this figure, the difference between the thermal expansion coefficient of the zirconia sintered body having a sintered density exceeding 95% in the conventional relative density and the thermal expansion coefficient of the alumina sintered body is about 0.05%. On the other hand, the difference between the thermal expansion coefficient of the zirconia sintered body having a relative density of 84% or more and 95% or less and the thermal expansion coefficient of the alumina sintered body is about 0.01 to 0.02. It is getting smaller rapidly.
Even when the relative density of the zirconia sintered body is lower than 84%, the difference in thermal expansion coefficient is expected to be small and the influence of residual stress is expected to be small, but the strength of the zirconia sintered body itself is reduced. In order to increase the effect, the lower limit of the zirconia sintered body was set to 84% in terms of relative density.

With reference to FIG. 8, the thermal expansion coefficient difference reduction effect at the time of performing the heat processing for a thermal expansion difference reduction of 900-1200 degreeC and 1-2 hours which is the principal part of this invention is demonstrated.
The difference between the thermal expansion coefficient of a zirconia sintered body with a sintered density of 91.3% in relative density and the thermal expansion coefficient of an alumina sintered body was measured, and the change when this was heat-treated multiple times was investigated. .
As shown in FIG. 8, when the heat treatment for reducing the thermal expansion difference at 900 to 1200 ° C. for 1 to 2 hours was performed once, the difference in thermal expansion coefficient was from 0.05% to less than 0.005%. When the heat treatment for reducing the thermal expansion difference is performed again, the difference in thermal expansion coefficient is further reduced, and when the heat treatment is repeated three times, the difference in thermal expansion coefficient is 0.001% or less, and the highest effect is exhibited. Further, even when heating was repeated, the effect of reducing the difference in thermal expansion coefficient was not obtained.
However, if the heat treatment for reducing the expansion difference is repeated 5 to 8 times or more, the sintering of the zirconia sintered body gradually proceeds, and the difference in the thermal expansion coefficient gradually increases. On the contrary, it has been found that there is a possibility that the difference in thermal expansion coefficient may be larger than the conventional one.

The following knowledge was acquired by the above test.
(1) At least alumina powder as a main raw material, and a predetermined amount of sintering aid, binder, plasticizer, and dispersant are dispersed in a dispersion medium, and the median diameter is reduced to 1 μm or less through pulverization / mixing steps. Alumina green sheet formed using alumina slurry and zirconia powder containing 3-8 mol% yttria as a stabilizer are the main raw materials, and are dispersed in a dispersion medium together with a predetermined amount of binder, plasticizer, and dispersant. In an alumina / zirconia laminated sintered body obtained by laminating and firing integrally with a zirconia green sheet formed using a zirconia slurry having a median diameter of 1 μm or less after pulverization and mixing steps, the firing temperature is 1450-1500 ° C. The holding time is set to 1 to 2 hours, the relative density of the alumina layer is set to 94% or more, and the relative density of the zirconia layer is set to 84% or more. 95% or less, the difference between the thermal expansion coefficient of the zirconia layer and the thermal expansion coefficient of the alumina layer before and after the phase transformation temperature Tc is reduced, and the theoretical strength and the sintered body of the alumina / zirconia laminated sintered body are reduced. The actual strength can be improved by increasing the difference from the stress remaining inside.
(2) In the alumina / zirconia laminated sintered body, the heat treatment for relaxing the thermal expansion difference, which is maintained at 900 to 1200 ° C. for 1 to 2 hours, is repeated at least once or more so that the zirconia layer before and after the phase transformation temperature Tc. The difference between the thermal expansion coefficient and the thermal expansion coefficient of the alumina layer can be further reduced, and the actual strength of the alumina / zirconia laminated sintered body can be further increased.
(3) As the actual strength of the alumina / zirconia laminated sintered body is improved, the occurrence of water cracking can be suppressed.
(4) By using the alumina / zirconia laminated sintered body of the present invention in part, a solid electrolyte layer mainly composed of zirconia, a pair of electrodes provided on the opposing surface, and a heater are incorporated, It is possible to improve the durability of the gas sensor element in which an insulating layer mainly composed of alumina is laminated.

The present invention is not limited to the above embodiment. For example, as an example of the alumina / zirconia laminated sintered body of the present invention, an oxygen sensor element having the most basic structure is shown as an example. Various gas sensor elements such as an ammonia sensor can be used as appropriate, and a structure having a plurality of detection cells or an oxygen pumping cell may be used.
The present invention can also be applied to a PM sensor element or the like in which a pair of electrodes formed in a comb-teeth shape is formed on a solid electrolyte layer, and an insulating layer containing a heater is laminated and baked integrally.
Further, the present invention is not limited to the gas sensor element, and can be applied to, for example, a laminated piezoelectric element in which an electrode layer, a zirconia layer, and an insulating layer are repeatedly laminated.

1 Gas sensor element 100 Solid electrolyte layer (zirconia layer)
110 Adhesive layer (alumina / zirconia mixed layer)
111 Electrode layer embedded space 120 Measurement electrode layer 121 Measurement electrode lead part 122 Measurement electrode terminal part 123, 124 Through-hole electrode 130 Measurement gas chamber forming layer (alumina layer)
131 Measuring gas chambers 132a, 132b Measuring gas introduction hole 140 Burned-out layer 150a, 150b Diffusion resistance layer (porous ceramic layer)
160 Shielding layer (alumina layer)
170 Reference electrode layer 171 Reference electrode lead portion 172 Reference electrode terminal portion 173, 174, 175, 176 Through-hole electrode 180 Adhesive layer (alumina / zirconia mixed layer)
190 Reference gas chamber formation layer (alumina layer)
191 Reference gas chamber 200, 220 Insulating layer (alumina layer)
210 Heating element 211a, 211b Heating element lead part 212a, 212b Heating element energization terminal part 213a, 213b Through-hole electrode

JP 2001-66280 A JP-A-11-316211

Claims (6)

At least an alumina / zirconia laminated sintered body in which an alumina layer and a zirconia layer are laminated and sintered together,
The relative density of the alumina layer is 94% or more, and the relative density of the zirconia layer is 84% or more and 95% or less (excluding the relative density of 94% or more of the zirconia layer). Alumina / zirconia laminated sintered body. 2. The alumina / zirconia laminated sintered body according to claim 1, wherein the relative density of the zirconia layer is 87.5% or more and 92.5% or less . The alumina / zirconia laminated sintered body according to claim 1 or 2 , wherein the difference between the thermal expansion coefficient of the alumina layer and the thermal expansion coefficient of the zirconia layer at the phase transformation temperature of the zirconia layer is 0.03% or less. In order to detect a specific component in the gas to be measured, a solid electrolyte layer having conductivity with respect to specific ions, a pair of electrodes formed on opposite surfaces of the solid electrolyte layer, and a heater inside are incorporated. A gas sensor element including an insulating layer,
The solid electrolyte layer comprises a zirconia layer mainly composed of partially stabilized zirconia containing 3 to 8 mol% yttria,
The insulating layer is made of an alumina layer mainly composed of alumina,
The gas sensor element, wherein the zirconia layer and the alumina layer constitute the alumina / zirconia laminated sintered body according to any one of claims 1 to 3 . It is a manufacturing method of the alumina / zirconia laminated sintered body according to any one of claims 1 to 3 ,
At least an alumina slurry having alumina powder having a median diameter of 1 μm or less after being dispersed in a dispersion medium together with a predetermined amount of a sintering aid, a binder, a plasticizer, and a dispersing agent using alumina powder as a main raw material. An alumina sheet forming step P1 for forming an alumina green sheet by using,
The main raw material is zirconia powder containing 3-8 mol% yttria as a stabilizer, and it is dispersed in a dispersion medium together with a predetermined amount of a binder, a plasticizer, and a dispersant. A zirconia sheet forming step P2 for forming a zirconia green sheet using the zirconia slurry obtained, and
An alumina / zirconia lamination step P3 in which the obtained alumina green sheet and zirconia green sheet are laminated to form an alumina / zirconia laminate;
And a zirconia sintered density range-limited integrated firing step P5 in which the obtained alumina / zirconia laminate is integrally fired at a firing temperature of 1450 to 1500 ° C. for a holding time of 1 to 2 hours. A method for producing an alumina / zirconia laminated sintered body. The alumina / zirconia laminated sintering according to claim 5 , comprising a thermal expansion difference relaxation heat treatment step that repeats at least one thermal expansion difference relaxation heat treatment held at a temperature of 900 to 1200 ° C for 1 to 2 hours. Body manufacturing method.

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