JP3137128B2 - Manufacturing method of ceramic coating - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a ceramic film, and more particularly to a method for producing a protective layer formed on a measuring electrode of an oxygen concentration detecting element.

[0002]

2. Description of the Related Art Conventionally, as a method of forming a protective layer which is a kind of a ceramic film formed on a measuring electrode in an oxygen concentration detecting element, for example, Japanese Patent Application Laid-Open No. 56-9624
No. 0, Japanese Patent Application Laid-Open No. 55-78245, and the like have proposed many.

[0003]

However, in the above-described method, the firing of the support of the electrode or the detecting element and the firing of the protective layer are performed separately, so that firing is required at least twice. This has been a major factor complicating the manufacturing process of the oxygen concentration detecting element.

For this reason, there has been an increasing demand for simultaneous firing of the protective layer and the detecting element including the support. However, simultaneous firing of the protective layer and the detecting element, particularly when the protective layer has a thickness of 100 μm or more, has been required. In addition, it is necessary to match the firing shrinkage of the protective layer and the detecting element, which is difficult to realize.

Furthermore, it is essential that the electrode protective layer formed on the measurement electrode of the oxygen concentration detecting element allows the measurement gas to permeate and reach the measurement electrode. Therefore, this protection layer is naturally porous. Is required, the protective layer and the detection element can not only be simply fired simultaneously, but after the simultaneous firing, it is necessary to obtain a desired porosity in the protective layer. Simultaneous firing has been made more difficult.

Therefore, in the present invention, when a ceramic film is formed on a support, not only can the support and the ceramic film be fired simultaneously, but also a ceramic film having a desired porosity is provided. A method for producing a ceramic coating is provided.

[0007]

In order to solve the above-mentioned problems, the present inventors have taken as an example a method of forming a protective layer which is a ceramic film formed on an oxygen concentration detecting element which is a support. A number of experiments were conducted to find the best method.

First, the inventors of the present invention have achieved the above object by suppressing the densification by increasing the particle size of the raw material of the protective layer to be larger than the particle size of the base material forming the detection element composed of the solid electrolyte and the support. I found it.

However, simply increasing the particle size of the protective layer raw material as in this method makes the sintering difficult because the particle size of the protective layer raw material is large, and densification does not proceed. For this reason, the distance between the particles is hardly clogged. As a result, the shrinkage of the protective layer becomes too small compared to the shrinkage of the solid electrolyte, causing a problem that the element and the protective layer are warped, cracked, and the like after firing.

[0010] Next, as a method of controlling the shrinkage ratio, the present inventors have adjusted the amount of the binder. This principle is shown in the schematic diagram of FIG. As shown in FIG. 4, as the binder amount increases, the initial distance between the ceramic particles increases. Therefore, if the specific gravity of firing is constant, the moving distance of the particles increases, and the firing shrinkage rate increases.

However, considering moldability, degreasing property, etc.,
There is a limit to the amount of adjustment by the amount of binder, and when the amount of binder is significantly changed, the degreasing shrinkage also changes significantly at the same time, creating a new problem of cracking, peeling, etc. between the detection element and the protective layer. It was found that it was difficult to largely change the shrinkage rate by adjusting the binder amount.

Further, the inventors of the present application have made further studies to enable simultaneous sintering of the ceramic film mainly composed of ceramics and the support, and to set the porosity to a desired value. Thus, a ceramic coating and a method for producing the same could be obtained.

In other words, while the porosity is arbitrarily changed by changing the particle size of the main material of the ceramic film, the specific surface area (bulk density) is controlled according to the production conditions of the material of the protective layer, and the shrinkage of the ceramic film is controlled. To the support, warp,
A protective layer could be formed at low cost between the ceramic film and the support without peeling or cracking.

[0014]

[Function] Generally, raw materials such as a precipitation method are dissolved in a solution.
As shown in the model diagram of FIG. 1, the raw material obtained from the liquid phase has a relatively porous structure in which primary particles A of 0.1 to 0.5 μm are aggregated and bonded to form secondary particles B. It has become. The diameter of this primary particle A is primary particle A and secondary particle B
The temperature can be controlled by the calcination temperature of the ceramic raw material composed of the ceramic raw material . Therefore, as the diameter of the primary particles A is smaller, the secondary particles B have a porous structure including a larger amount of space therein, so that the bulk density becomes smaller and the firing shrinkage becomes larger at the same time. .

That is, by controlling the diameter of the primary particles A, that is, the specific surface area (bulk density) of the primary particles A, the firing shrinkage of the ceramic film can be controlled.

On the other hand, the porosity of the ceramic coating material is
The diameter of the secondary particles B, which is an aggregate of the primary particles A, can be controlled. The diameter of the secondary particles B depends on the solution temperature, the stirring conditions, and the like during precipitation from the liquid phase. Can be controlled independently.

In other words, the growth rate of the secondary particles can be adjusted by the solution temperature, and the secondary particle diameter decreases as the stirring speed increases, and the secondary particle diameter increases as the stirring speed decreases. can do.

As described above, according to the present invention, the diameter of the primary particles A is controlled by preliminarily firing the ceramic raw material, thereby controlling the firing shrinkage ratio, and is a general dispersed particle. The diameter of the secondary particles B is the solution temperature,
The porosity can be controlled by controlling the stirring conditions and the like .

[0019]

As described above, by setting the specific surface area of the ceramic coating to a predetermined area value, the ceramic coating can be co-fired satisfactorily without warping or cracking with the support.

Further, the porosity and the shrinkage can be controlled independently by the secondary particle diameter of the ceramic coating.
Not only can the type of porosity for each of the obtained ceramic coatings be made desired, but also the porosity gradient can be arbitrarily set by laminating a plurality of ceramic coatings having different particle sizes.

[0021]

FIG. 2 shows the relationship between the specific surface area of the ZrO ₂ raw material and the firing shrinkage rate, for example, in which ZrO ₂ raw materials having different specific surface areas and secondary particle diameters were prepared.

As a scale representing the primary particle diameter and bulk density (specific surface area) of a ceramic film formed by firing a ZrO ₂ raw material, the method is a specific surface area measuring method which is easy to measure, has high sensitivity and high reproducibility. Blowsorb 2300 manufactured by Shimadzu Corporation, which is an apparatus for measuring by the BET method, was used, and as the secondary particle diameter, a volume average particle diameter measured by Nikkiso's Microtrac SPA was adopted. In FIG. 2, the number on the right side in parentheses at each measurement point indicates the porosity (%), and the number on the left side in parentheses indicates the secondary particle diameter (μ).
m).

As is apparent from FIG. 2, the firing shrinkage increased in proportion to the specific surface area, and the porosity could be controlled independently of this by the secondary particle diameter.

For example, as shown in FIG.
If the specific surface area is adjusted to 5 to 7 m ² / g, the secondary particle diameter is set to 0.6 to 4 μm while the firing shrinkage is kept constant at approximately 18%.
It can be seen that the porosity can be changed by 15 to 50% by changing Further, for example, when the specific surface area is set to 8 to 10 m ² / g, the firing shrinkage rate can be increased to 20%, and the secondary particle diameter is set to 1.3 to 10 m ² / g.
By changing the porosity to 5 μm, the porosity is 25 to 50%.
It can be seen that it can be changed.

FIG. 3 is a developed view showing one embodiment of the oxygen concentration detecting element 1 employing the ceramic film of the present invention as a protective layer. In FIG. 3, reference numeral 101 denotes a rectangular cylindrical support having through-holes open at both ends, which is made of alumina porcelain, zirconia porcelain, or the like. Is a continuous slope from one of the side surfaces, and when viewed from the side,
This tip has a wedge shape, and the other end is provided with an atmosphere introduction hole 111 for introducing the atmosphere. 103
Is a heating element mainly made of a platinum material, and a heating section of the heating element 103 of the inclined surface opening 101a is projected onto a surface facing the inclined surface of the support 101 via an insulating material 102 such as alumina. Are laminated so as to cover completely, and the insulating material 10 is formed in a portion except for the terminal electrode portions 114a and 114b.
An insulating layer 104 of the same material as that of No. 2 is laminated. Reference numeral 106 denotes a solid electrolyte made of, for example, zirconia to which yttrium is added. The solid electrolyte 106 has a reference electrode 105 and a measurement electrode 107.
5 are stacked so as to coincide with each other. The reference electrode 105 is fixed to a reference electrode terminal 112b via a through hole 113 provided in the solid electrolyte 106, and the measurement electrode 107 is fixed to a measurement electrode terminal 112a.

Here, the support body 101 is formed by injection molding or the like, the solid electrolyte layer 106 is formed by extrusion molding or the like, and the electrode layers 105 and 107, the heating element 103 and the insulating layers 102 and 104 are provided by printing or the like. After laminating these in an unsintered state, they are simultaneously fired to form a sensor element.

Reference numeral 108 denotes an electrode protection layer obtained by the manufacturing method of the present invention, and is formed so as to cover at least the wide end portion of the electrode 107. This protective layer 108
Is formed by bonding or screen printing a sheet made of a protective film material obtained by a doctor blade method, an extrusion molding method, or the like, so as to cover the electrode 107 before firing, and is fired simultaneously with the sensor element portion. Is done.

Hereinafter, for example, a method using a sheet obtained by a doctor blade method will be described in detail. Particle size 0.
6 μm, porosity of specific surface area 5.5 m ² / g 15%, shrinkage 1
8% and comprising zirconia (Zr0 ₂₎ protective layer material on yttria _{(Y 2 O 3) 4~8mol%} , a molding binder of polyvinyl butyral (PVB), 5 wt%, respectively dibutyl phthalate, further solvents ethanol, butanol A total amount of 40 wt% was added to the ZrO ₂ powder, and the mixture was added in a ball mill using nylon balls containing iron balls.
Mix for hours.

The slurry thus obtained is formed into a sheet by a doctor blade method, cut into a desired size, and adhered onto the electrode 107. As a method for bonding, the solvent is applied to the protective layer sheet bonding surface, or adhered to manner a part, Zr0 ₂ protective layer was adjusted to a Y ₂ O ₃ amount in the protective layer sheet and colleagues There is a method of applying and bonding an acrylic adhesive to which a raw material is added.

Under the conditions of baking at 1470 ° C. for 2 hours, the support 101 or the solid electrolyte 10 having a baking shrinkage of 18% was used.
6. Simultaneous firing of each of the electrodes 105 and 107, the heating element 103 and the insulators 102 and 104,
A good sensor element 1 without cracks or the like was obtained.

The firing shrinkage of the electrode protection layer 108 is 1
If it is less than 6%, the tip of the sensor element will be warped,
If it is 20% or more, cracks occur in the protective layer, and a good fired product cannot be obtained.

In the above embodiment, an acrylic adhesive is used for bonding the solid electrolyte and the substrate, but a PVB adhesive may be used. In the above embodiment, the ceramic film is employed as the protective layer of the oxygen concentration detecting element, but the ceramic film of the present invention is not limited to this, and may be used for a ceramic filter or the like having a changed porosity. it can.

In the above embodiment, a method for producing a ceramic coating made of zirconia was described. However, the present invention is not limited to zirconia, but may be any ceramic obtained in a liquid phase, such as alumina or titania. Good.

[Brief description of the drawings]

FIG. 1 is a schematic diagram showing a state of primary particles and secondary particles.

FIG. 2 is a characteristic diagram showing the relationship between the specific surface area of each particle having each specific surface area and porosity, and the firing shrinkage.

FIG. 3 is a development view of an oxygen concentration detecting element.

FIG. 4 is an explanatory diagram showing a degree of shrinkage of a fired product according to a binder amount.

[Explanation of symbols]

 101 Support 113 Solid electrolyte 108 Protective layer

──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Toshitaka Saito 1-1-1, Showa-cho, Kariya-shi, Aichi Japan Inside Denso Co., Ltd. (72) Inventor Katsuhiro Ishikawa 1-1-1, Showa-cho, Kariya-shi, Aichi Nihon Denso Co., Ltd. (72) Inventor Satoru Nomura 1-1-1 Showa-cho, Kariya-shi, Aichi Japan Inside Denso Co., Ltd. (58) Field surveyed (Int. Cl. ⁷ , DB name) C04B 35/622-35/64

Claims (3)

(57) [Claims] 1. A ceramic raw material comprising primary particles and secondary particles formed by cohesive joining of the primary particles, wherein a shrinkage rate of the ceramic raw material after firing is adjusted by the particle size of the primary particles. A method for producing a ceramic film, wherein the porosity of the ceramic material after firing is adjusted by the particle size of the secondary particles. 2. The method according to claim 1, wherein the adjustment of the particle size of the primary particles is performed by a calcining temperature at which the ceramic raw material is calcined . 3. The method for adjusting the particle size of the secondary particles from the liquid phase
A method for producing a ceramic film, wherein the method is carried out under the conditions of a solution temperature and a stirring condition during precipitation .