JP2012166987A - Composite ceramic body and method for manufacturing the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a composite ceramic body having high strength and excellent thermal shock resistance and a method for manufacturing the same.SOLUTION: The composite ceramic body 1 is obtained by dispersing zirconia particles 12 having an average particle size of ≤0.3 μm in a matrix of alumina particles 11 having an average particle size of 0.5-1 μm, wherein the content ratio between the alumina particles 11 and the zirconia particles 12 is 80:20 to 95:5 in terms of wt.%. When a fracture surface of the composite ceramic body 1 subjected to a four-point bending test according to JIS R 1601 is observed and the square root of the projected area of an internal defect acting as the starting point of breakdown is regarded as a defect size, the defect size is ≤55 μm.

Description

  The present invention relates to a composite ceramic body in which zirconia particles are dispersed in alumina particles and a method for producing the same.

An exhaust system such as an internal combustion engine for a vehicle is provided with a gas sensor that detects an oxygen concentration or the like in the exhaust gas. The gas sensor includes a gas sensor element made of a ceramic material.
The gas sensor element is configured such that the exhaust gas comes into contact with the surface thereof, but when the internal combustion engine is started, water droplets may fly toward the gas sensor element together with the exhaust gas. Here, the gas sensor element is used in an activated state by being heated to a high temperature. Therefore, when a water droplet adheres to the surface of the gas sensor element, the portion is locally cooled. Thereby, a big thermal shock is added to a gas sensor element, and a crack (water-proof crack) may arise.

Therefore, a composite material in which dispersed particles such as zirconia particles are dispersed in a matrix of alumina particles has been developed as a ceramic material that can increase strength and improve thermal shock resistance.
For example, Patent Document 1 discloses a gas sensor element using the composite material. Patent Document 2 discloses a composite ceramic body in which the ratio of specific pores in the composite material is controlled.

JP 2009-8435 A JP 2010-24128 A

  In the inventions of Patent Documents 1 and 2, the strength of the material itself can be improved by using the composite material. However, if there are internal defects such as foreign matter, coarse particles, and pores in the material, the strength may be reduced due to the internal defects, and the original strength of the material may not be obtained. That is, this internal defect tends to be a starting point of fracture when subjected to stress, and causes a decrease in strength. Therefore, it was not possible to ensure sufficient strength to withstand thermal shock by simply using the composite material.

  The present invention has been made in view of such problems, and an object of the present invention is to provide a composite ceramic body having high strength and excellent thermal shock resistance and a method for producing the same.

In the first invention, zirconia particles having an average particle size of 0.3 μm or less are dispersed in a matrix of alumina particles having an average particle size of 0.5 to 1 μm, and the contents of the alumina particles and the zirconia particles are the same. A composite ceramic body having a weight percent ratio of 80:20 to 95: 5,
When the fracture surface of the composite ceramic body subjected to the four-point bending test based on JIS R 1601 is observed and the square root of the projected area of the internal defect that is the origin of the fracture is defined as the defect size, the defect size is 55 μm or less. The composite ceramic body is characterized in that (Claim 1).

A second invention is a method for producing the composite ceramic body of the first invention,
Adding a solvent to the ceramic raw material containing the alumina particles and the zirconia particles, and crushing the ceramic raw material;
A first mixing step of obtaining a dispersed slurry material in which the alumina particles and the zirconia particles are dispersed by adding a dispersant to the ceramic raw material and mixing with a high-pressure homogenizer;
A second mixing step of obtaining a molding slurry material by adding a binder to the dispersion slurry material and mixing using a high-pressure homogenizer;
A filtration step of filtering the molding slurry material;
A molding step for obtaining a molded body by molding the filtered slurry material for molding, and
And a firing step of obtaining the composite ceramic body by firing the molded body (claim 4).

The composite ceramic body of the first invention is formed by dispersing zirconia particles in a matrix of alumina particles (grain boundaries, intragrains, etc.).
The dispersed zirconia particles are present at the grain boundaries of the alumina particles, whereby the grain boundaries of the alumina particles are reinforced. Moreover, the grain growth of alumina particles can be suppressed and the alumina particles can be made finer. Therefore, the strength of the entire composite ceramic body can be improved.

Further, the presence of the dispersed zirconia particles in the alumina particles causes a compressive residual stress due to a difference in thermal expansion coefficient between the alumina particles and the zirconia particles. Therefore, the strength of the entire composite ceramic body can be improved.
Further, since the zirconia particles are arranged in a dispersed manner, cracks and the like generated at the grain boundaries of the alumina particles are deflected or stopped near the position where the zirconia particles are present. Therefore, it becomes difficult to make a big crack in a composite ceramic body, and the whole intensity | strength can be improved.

In addition, the present inventor has paid attention to internal defects present in the composite ceramic body in order to ensure sufficient strength of the composite ceramic body. The internal defects are foreign matters, coarse particles, pores, and the like present in the composite ceramic body, and are likely to become a starting point of breakage when subjected to stress and cause a reduction in strength.
The inventors have found that the strength required for practical use can be sufficiently ensured in the specific composite ceramic body by controlling the size of the internal defect.

Specifically, as a result of diligent research, the inventor has found that what has the most influence on the strength of the composite ceramic body is not the number or ratio of internal defects, but the internal defect that is the starting point of destruction of internal defects. It was found to be the size of the defect (defect size).
In a composite ceramic body in which zirconia particles having a specific particle size and ratio are dispersed in a matrix of alumina particles having a specific particle size and ratio, the specific test can be performed. It has been found that when the defect size exceeds a certain value (55 μm), the inherent strength of the material cannot be obtained due to internal defects.

For this reason, the composite ceramic body has the defect size of 55 μm or less so that sufficient strength can be secured.
Thereby, the composite ceramic body can sufficiently ensure the strength (for example, 600 MPa or more) required for practical use. And it becomes the thing excellent in the thermal shock resistance which can endure the thermal shock by moisture.

In the method for producing a composite ceramic body of the second invention, as described above, the pulverization step, the first mixing step, the second mixing step, the filtration step, the forming step, and the firing step are performed.
Here, in the pulverization step, the ceramic raw material containing alumina particles and zirconia particles is pulverized. Thereby, it is possible to reduce coarse particles in the ceramic raw material that causes internal defects.

  In the first mixing step, a dispersant is added to the ceramic raw material and mixed using a high-pressure homogenizer. By mixing using a shearing force by a high-pressure homogenizer, alumina particles and zirconia particles can be favorably dispersed without destroying the polymer of the dispersant. Thereby, a dispersed slurry material in which alumina particles and zirconia particles are uniformly dispersed at the primary particle level can be obtained.

In the second mixing step, a binder is added to the dispersed slurry material and mixed using a high-pressure homogenizer. Also here, by mixing using a shearing force by a high-pressure homogenizer, a molding slurry material in which these are well mixed without breaking the binder polymer while maintaining the dispersed state of the alumina particles and zirconia particles is obtained. Can do.
Moreover, the mixing process is divided into two stages, and the effect of the dispersing agent of uniformly dispersing the alumina particles and the zirconia particles is more effectively exhibited by mixing only the dispersing agent in advance in the first mixing process. Can do.

In the filtration step, foreign matters, coarse particles, aggregated particles, undissolved binders, and the like in the molding slurry material that causes internal defects can be removed by filtering the molding slurry material. .
Moreover, the effect which suppresses the residue of the foreign material etc. which become the origin of an internal defect can be improved further by performing the said filtration process just before the said shaping | molding process.

  And after performing said grinding | pulverization process, a 1st mixing process, a 2nd mixing process, and a filtration process, the composite ceramic body of the said 1st invention, ie, the said defect size, is performed by performing the said formation process and the said baking process. And a composite ceramic body having a defect size of 55 μm or less can be obtained. Further, this composite ceramic body has high strength as described above and has excellent thermal shock resistance.

  Thus, according to the present invention, a composite ceramic body having high strength and excellent thermal shock resistance and a method for producing the same can be provided.

FIG. 3 is an explanatory diagram schematically showing a composite ceramic body in Example 1. FIG. 3 is an explanatory view showing a four-point bending test method for a composite ceramic body in Example 1. 2 is an SEM photograph showing a fracture surface of a composite ceramic body in Example 1. FIG. The SEM photograph which shows the internal defect used as the starting point of destruction of the composite ceramic body in Example 1. FIG. FIG. 3 is an explanatory diagram illustrating a projected internal defect in the first embodiment. 3 is a graph showing the relationship between the defect size and the strength at the defect position in Example 1. Explanatory drawing which shows the structure of the gas sensor in Example 2. FIG. Explanatory drawing which shows the structure of the gas sensor element in Example 2. FIG.

In the first invention, the composite ceramic body is obtained by dispersing zirconia particles having an average particle size of 0.3 μm or less in a matrix of alumina particles having an average particle size of 0.5 to 1 μm.
When the average particle size of the alumina particles is less than 0.5 μm, the firing temperature becomes low and it becomes difficult to maintain a high relative density, so that the strength of the composite ceramic body may be lowered. On the other hand, when the average particle size of the alumina particles exceeds 1 μm, it is difficult to suppress the particle growth of the alumina particles, and the strength of the composite ceramic body may be reduced.
Moreover, when the average particle diameter of a zirconia particle exceeds 0.3 micrometer, stress will generate | occur | produce in the part which has a zirconia particle, it may become a starting point of a crack etc., and there exists a possibility that the intensity | strength of a composite ceramic body may fall.

In the composite ceramic body, the weight ratio of alumina particles to zirconia particles is 95: 5 to 80:20.
When the weight ratio of zirconia increases beyond the above weight ratio, the zirconia particles tend to aggregate, and zirconia particles having a large particle diameter are present as defects in the matrix of alumina particles, so that the strength of the composite ceramic body is increased. May decrease. On the other hand, if the weight ratio of zirconia is smaller than the above weight ratio, the strength of the grain boundaries of the alumina particles is lowered, and it is difficult to suppress the grain growth of the alumina particles, and the strength of the composite ceramic body may be lowered. There is.

Further, the composite ceramic body is obtained by observing the fracture surface of the composite ceramic body that has been subjected to a four-point bending test based on JIS R 1601, and setting the square root of the projected area of the internal defect that is the starting point of the fracture as the defect size. The defect size is 55 μm or less.
If the defect size exceeds 55 μm, the inherent strength of the material may not be obtained due to internal defects. That is, there is a possibility that sufficient strength cannot be secured.

Moreover, the said defect size can be calculated | required as follows, for example.
That is, a four-point bending test based on JIS R 1601 is performed on the test body of the composite ceramic body. Next, the fracture surface (fracture surface) of the specimen after the four-point bending test is observed with an SEM (scanning electron microscope) or the like. Next, the internal defect that is the starting point of destruction is specified. Here, the internal defects are foreign matters, coarse particles, pores and the like existing in the composite ceramic body. Next, the projected area A of the identified internal defect is obtained, and the defect size B is obtained from the projected area A. The defect size B is the square root √A of the projected area A.

  In order to identify the internal defect that is the starting point of the destruction, first, the part that is the starting point of the destruction is specified based on the flow pattern of the fracture surface of the specimen. For example, if a pattern is formed radially from a part having a fracture surface, it can be estimated that the part is the starting point of the destruction. Next, an internal defect existing in the part that is the starting point of destruction is confirmed, and this is specified as the internal defect that is the starting point of destruction.

Moreover, it is preferable that the size of the internal defect is 25 μm or less.
In this case, the composite ceramic body has higher strength and better thermal shock resistance.

Moreover, it is preferable that the said composite ceramic body comprises a part of gas sensor element for detecting the specific gas density | concentration in to-be-measured gas (Claim 3).
That is, the composite ceramic body has high strength and excellent thermal shock resistance. For this reason, when the gas sensor element is used as a ceramic material, water cracking of the gas sensor element can be prevented.

  In the second aspect, in the pulverization step, the ceramic raw material can be pulverized by a ball mill or the like.

Example 1
A composite ceramic body according to an embodiment of the present invention and a manufacturing method thereof will be described with reference to the drawings.
In this example, five composite ceramic bodies (samples E1 to E5) were prepared as examples of the present invention, and two composite ceramic bodies (samples C1 and C2) were manufactured as comparative examples of the present invention. And the strength characteristic was evaluated about these composite ceramic bodies.
This will be described in detail below.

As shown in FIG. 1, the composite ceramic bodies (samples E1 to E5) of the examples are obtained by dispersing zirconia particles 12 having a particle size of 0.3 μm or less in a matrix of alumina particles 11 having an average particle size of 0.5 to 1 μm. In the composite ceramic body 1, the content of the alumina particles 11 and the zirconia particles 12 is 80:20 to 95: 5 in terms of a weight percent ratio of both.
When the fracture surface of the composite ceramic body 1 subjected to the four-point bending test based on JIS R 1601 is observed, and the square root of the projected area of the internal defect that is the starting point of the fracture is defined as the defect size, the defect size is 55 μm or less.

  On the other hand, the composite ceramic bodies of the comparative examples (samples C1 and C2) have the same basic configuration as the composite ceramic bodies of the examples (samples E1 to E5), and are different in that the defect size exceeds 55 μm. It is.

Next, the manufacturing method of the composite ceramic body (samples E1-E5) of an Example is demonstrated.
The composite ceramic body of the example was manufactured by the following manufacturing method including a pulverization step, a first mixing step, a second mixing step, a filtration step, a forming step, and a firing step.

In the pulverization step, a solvent is added to the ceramic raw material containing alumina particles and zirconia particles, and coarse particles of the ceramic raw material are pulverized.
In the first mixing step, a dispersing agent is added to the ceramic raw material and mixed using a high-pressure homogenizer to obtain a dispersed slurry material in which alumina particles and zirconia particles are dispersed.
In the second mixing step, a molding slurry material is obtained by adding a binder to the dispersed slurry material and mixing using a high-pressure homogenizer.
In the filtration step, the molding slurry material is filtered.
In the molding step, a molded body is obtained by molding the filtered molding slurry material.
In the firing step, a composite ceramic body is obtained by firing the formed body.

  Specifically, in the pulverization step, alumina raw material (AKP-53: manufactured by Sumitomo Chemical Co., Ltd.) and zirconia raw material (KZ-0Y-LSF: manufactured by Kyoritsu Material) are used at a predetermined weight% ratio (80:20 to 95: 5). Ethanol or the like as a solvent is added to the ceramic raw material. And in order to grind | pulverize the coarse particle of a ceramic raw material, it grind | pulverizes for 24 hours using a ball mill.

  Next, in the first mixing step, foreign matters such as pot casks are removed with a filter having an opening of 200 μm, and then a dispersant (Floren WK-13E: manufactured by Kyoeisha Chemical Co., Ltd.) is added to the ceramic raw material. The dispersant is added in an amount of 2% by weight based on 100% by weight of the ceramic raw material. Then, by mixing for 10 minutes using a high-pressure homogenizer, a dispersed slurry material in which alumina particles and zirconia particles are dispersed at the primary particle level is obtained.

  Next, in the second mixing step, a binder (PVB: manufactured by Denki Kagaku Kogyo) and a plasticizer (benzyl butyl falarate: manufactured by Wako Pure Chemical Industries, Ltd.) are added to the dispersed slurry material. The binder and the plasticizer are added at 9% by weight and 5.5% by weight, respectively, with respect to 100% by weight of the ceramic raw material. Further, the binder and the plasticizer are previously dissolved in ethanol or the like as a solvent and added to the dispersed slurry material. And the slurry material for shaping | molding is obtained by mixing for 10 minutes using a high voltage | pressure homogenizer. Thereafter, a part of the solvent is evaporated while stirring the molding slurry material in a reduced-pressure atmosphere, and adjusted to a predetermined slurry viscosity (7 to 10 Pa · s).

  Next, in the filtration step, the molding slurry material is filtered. At this time, a filter having a particle size after filtration of 10 μm or less is used, and filtration is performed by passing the molding slurry material through the filter. This removes foreign matters, coarse particles, aggregated particles, undissolved binders, and the like in the molding slurry material.

Next, in the forming step, the forming slurry material is used to form a sheet by a doctor blade method and then dried. Thereby, an alumina sheet (molded body) is obtained.
Next, in the firing step, a plurality of the obtained alumina sheets are stacked, pressed by a cold isostatic press (CIP) under the conditions of 85 ° C. and 50 MPa, and then cut into a predetermined dimension. And degreasing is performed on the conditions of 500 degreeC and 25 hours. At this time, the temperature rise to 500 ° C. takes about 5 days. Thereafter, the temperature is raised to a predetermined temperature at 150 ° C./hour in an electric furnace (atmosphere) and held for 1 hour to perform firing.
The composite ceramic body (samples E1-E5) of an Example is obtained by the above.

Next, a method for manufacturing the composite ceramic body (samples C1 and C2) of the comparative example will be described.
The composite ceramic body of the comparative example was produced by the following manufacturing method.

  Specifically, first, a ceramic containing an alumina raw material (AKP-53: manufactured by Sumitomo Chemical Co., Ltd.) and a zirconia raw material (KZ-0Y-LSF: manufactured by Kyoritsu Materials Co., Ltd.) in a predetermined weight% ratio (80:20 to 95: 5). Ethanol or the like as a solvent is added to the raw material. Further, 2% by weight of a dispersant (Floren WK-13E: manufactured by Kyoeisha Chemical Co., Ltd.) is added to 100% by weight of the ceramic raw material.

  Furthermore, a binder (PVB: manufactured by Denki Kagaku Kogyo) and a plasticizer (benzyl butyl furarate: manufactured by Wako Pure Chemical Industries, Ltd.) are respectively added at 9% by weight and 5.5% by weight with respect to 100% by weight of the ceramic raw material. The binder and the plasticizer are previously dissolved in ethanol as a solvent and added. And the slurry material for shaping | molding is obtained by grind | pulverizing and mixing for 24 hours using a ball mill.

Next, after removing foreign matters such as pot residue with a filter having an opening of 200 μm, a part of the solvent is evaporated while stirring the molding slurry material in a reduced-pressure atmosphere to obtain a predetermined slurry viscosity (7 to 10 Pa · s). adjust.
Thereafter, the same steps as the filtration step, the forming step, and the firing step described in the method for producing the composite ceramic body of the example are performed.
Thus, the composite ceramic body (samples C1 and C2) of the comparative example is obtained.

Next, strength characteristics of the produced composite ceramic bodies (samples E1 to E5, samples C1 and C2) were evaluated.
Specifically, first, a bending strength test was performed on the composite ceramic body specimen, and the strength at the defect size and defect position was measured using the specimen subjected to the bending strength test.

<Bending strength test>
The bending strength test was a four-point bending test according to the bending strength test method of JIS R 1601. And the load at the time of breaking was measured, and 4 point | piece bending strength was calculated | required from the load.
In the bending strength test, as shown in FIG. 2, a test body 2 processed to have a length of 40.0 mm, a width of 4.0 mm, and a thickness of 3.0 mm was used. The distance between the fulcrums 31 (distance between fulcrums) was set such that the upper fulcrum distance D1 was 10.0 mm, the lower fulcrum distance D2 was 30.0 mm, and the load F was applied to the upper fulcrum 31.

<Measurement of defect size>
First, the fracture surface of the specimen subjected to the bending strength test is observed with an SEM (scanning electron microscope) to identify the internal defect that is the starting point of the fracture.
Specifically, as shown in FIG. 3, the entire fractured surface 20 of the specimen 2 is observed, and the part that is the starting point of the fracture is specified from the flow of the pattern on the fractured surface 20. Here, in the four-point bending test, as shown in FIG. 2, compressive stress acts on one surface (compression surface 201) in the thickness direction, and tensile stress acts on the other surface (tensile surface 202). Since ceramic is generally weak to tensile stress, the starting point of fracture exists on the side on which tensile stress acts (the tensile surface 202 side). In FIG. 3, since the pattern is formed radially from the P portion on the tensile surface 202 side of the fracture surface 20, the P portion is specified as the portion that is the starting point of the fracture.

Next, as shown in FIG. 4, the portion specified as the starting point of destruction (P portion in FIG. 3) was enlarged to observe internal defects 21 such as foreign matters, coarse particles, pores, and the like, which became the starting point of destruction The internal defect 21 is specified.
Next, as shown in FIG. 5, only the identified internal defect 21 portion is projected, and the projection area A is obtained. Then, the defect size B (= √A) is obtained from the projected area A.

<Strength at defect position>
In the specimen subjected to the bending strength test, the stress acting at the intermediate position in the thickness direction is zero. Therefore, when the distance from the internal defect that is the starting point of fracture to the intermediate position in the thickness direction of the specimen is L (FIG. 3), and the four-point bending strength measured in the bending strength test is σ, The intensity at the position of the internal defect, that is, the intensity σk at the defect position can be obtained from the following equation. Thereby, the intensity σk at the defect position is obtained.
σk = σ (L / 1.5)

Next, the evaluation results of strength characteristics are shown in FIG. In this figure, the horizontal axis represents the defect size (μm), and the vertical axis represents the strength (MPa) at the defect position.
As can be seen from the figure, all of the samples E1 to E5 of the example had a defect size of 55 μm or less and a strength at the defect position of 600 MPa or more. On the other hand, the samples C1 and C2 of the comparative example both had a defect size exceeding 55 μm, and the strength at the defect position was also less than 600 MPa.

From this result, it can be seen that the composite ceramic body of the present invention has high strength and excellent thermal shock resistance.
In addition, since the bending strength required when the composite ceramic body is applied to a gas sensor element or the like is 600 MPa or more, the strength required for practical use is sufficiently ensured by setting the defect size to 55 μm or less. You can see that

  It can also be seen from the figure that there are regions where the strength decreases as the defect size increases, and regions where the strength is almost constant regardless of the defect size. This boundary has a defect size of around 25 μm. Therefore, it can be seen that the defect size is preferably 25 μm or less in order to more surely obtain the practically required strength.

(Example 2)
In this example, as shown in FIGS. 7 and 8, the composite ceramic body of the present invention is applied to a part of the gas sensor element 7 built in the gas sensor 8.
As shown in FIG. 7, the gas sensor element 7 is built in the gas sensor 8 for detecting a specific gas concentration (oxygen concentration) in the gas to be measured (exhaust gas).

The gas sensor 8 includes a gas sensor element 7, an insulator 81 that inserts and holds the gas sensor element 7 inside, a housing 82 that inserts and holds the insulator 81 inside, and an atmosphere-side cover disposed on the base end side of the housing 82. 83 and an element cover 84 that is disposed on the front end side of the housing 82 and protects the gas sensor element 7.
The element cover 84 is configured by a double-structured cover including an outer cover 841 and an inner cover 842, and is provided with a conduction hole 843 for conducting a gas to be measured.

  As shown in FIG. 8, the gas sensor element 7 has an oxygen ion conductive solid electrolyte body 71 made of zirconia. On one surface of the solid electrolyte body 71, a measurement gas side electrode 72 made of platinum is provided. A reference gas side electrode 73 made of platinum is provided on the other surface of the solid electrolyte body 71.

  A reference gas chamber forming layer 74 is laminated on the other surface of the solid electrolyte body 71. The reference gas chamber forming layer 74 is provided with a groove 741, and a reference gas chamber 740 is formed by the groove 741. The reference gas chamber 740 is configured to be able to introduce a reference gas (atmosphere).

  A heater layer 75 is laminated on the surface of the reference gas chamber forming layer 74 opposite to the solid electrolyte body 71. The heater layer 75 is provided with a heating element (heater) 751 that generates heat when energized so as to face the reference gas chamber forming layer 74. The heating element 751 is configured to heat the gas sensor element 7 to the activation temperature by generating heat by energization.

An insulating layer 76 having an opening 761 is stacked on one surface of the solid electrolyte body 71. A gas permeable porous diffusion resistance layer 77 is laminated on the surface of the insulating layer 76 opposite to the solid electrolyte body 71. A gas chamber 760 to be measured is formed at a location covered by the solid electrolyte body 71, the opening 761 of the insulating layer 76, and the diffusion resistance layer 77. The measured gas chamber 760 is configured such that the measured gas (exhaust gas) can be introduced from the diffusion resistance layer 77.
A shielding layer 78 is laminated on the surface of the diffusion resistance layer 77 opposite to the insulating layer 76.

In this example, in the gas sensor element 7, the heater layer 75, the reference gas chamber forming layer 74, the insulating layer 76, the diffusion resistance layer 77, and the shielding layer 78 are composed of the composite ceramic body of the present invention.
That is, these layers are the composite ceramic body of the present invention in which zirconia particles are dispersed in a matrix of alumina particles.

Next, the function and effect of this example will be described.
In the case of this example, the composite ceramic body constitutes a part of the gas sensor element 7 for detecting the specific gas concentration in the gas to be measured. The composite ceramic body is high in strength and excellent in thermal shock resistance. Thereby, the water crack of the gas sensor element 7 can be prevented.

DESCRIPTION OF SYMBOLS 1 Composite ceramic body 11 Alumina particle 12 Zirconia particle

Claims (4)

A zirconia particle having a particle size of 0.3 μm or less is dispersed in a matrix of alumina particles having an average particle size of 0.5 to 1 μm, and the content of the alumina particles and the zirconia particles is 80:20 in a weight ratio of both. A composite ceramic body of ~ 95: 5,
When the fracture surface of the composite ceramic body subjected to the four-point bending test based on JIS R 1601 is observed and the square root of the projected area of the internal defect that is the origin of the fracture is defined as the defect size, the defect size is 55 μm or less. A composite ceramic body characterized by   2. The composite ceramic body according to claim 1, wherein the defect size is 25 μm or less. 3.   3. The composite ceramic body according to claim 1, wherein the composite ceramic body constitutes a part of a gas sensor element for detecting a specific gas concentration in a gas to be measured. A method for producing the composite ceramic body according to claim 1,
Adding a solvent to the ceramic raw material containing the alumina particles and the zirconia particles, and crushing coarse particles of the ceramic raw material;
A first mixing step of obtaining a dispersed slurry material in which the alumina particles and the zirconia particles are dispersed by adding a dispersant to the ceramic raw material and mixing with a high-pressure homogenizer;
A second mixing step of obtaining a molding slurry material by adding a binder to the dispersion slurry material and mixing using a high-pressure homogenizer;
A filtration step of filtering the molding slurry material;
A molding step for obtaining a molded body by molding the filtered slurry material for molding, and
A method for producing a composite ceramic body, comprising: a firing step of obtaining the composite ceramic body by firing the molded body.