JP3166333B2 - Ceramic coating method - 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 coating a ceramic substrate having a fine structure and low water absorption, and more particularly to a method for coating a ceramic for forming a ceramic porous electrode of a fuel cell or the like.

[0002]

2. Description of the Related Art As a general method of coating ceramics, there are spraying methods such as plasma torch flame spraying, gas explosion type spraying, PVD method such as sputtering, ion plating and vacuum deposition, CVD method, and slurry coating material. And a slurry coating method in which the slurry is applied to the surface of a ceramic base material to cover the surface.

[0003] Regarding the coating of dense ceramics, for example, in the case of a fuel cell, gas permeates both surfaces of a solid electrolyte membrane which is permeable to oxygen ions but not permeable to non-ionized oxygen gas or hydrogen gas. The structure is such that a porous electrode layer as coarse as possible can be formed. Such a porous electrode layer is formed on the surface of the above-mentioned dense solid electrolyte substrate by, for example, coating by a thermal spraying method.

[0004]

In the above-mentioned thermal spraying method, even when a material other than an electrode of a fuel cell is formed, the structure of the coating layer formed due to the sedimentation of molten particles generally can be controlled. However, there is a problem that it becomes too dense. In addition, thermal spraying, PVD and CVD
The method has disadvantages such as difficulty in increasing the film thickness and increase in cost. Further, the slurry coating method is generally disadvantageous in that it has poor adhesion to a ceramic substrate.

[0005] The characteristics required of an electrode of a fuel cell include excellent gas permeability and electric conductivity. For this purpose, the average pore size is set at 0.
It is necessary to set the porosity to about 1 to 10 μm and the porosity to about 10 to 50% by volume. However, when an electrode is formed by a thermal spraying method as in the prior art, the size of the constituent particles of the electrode cannot be controlled, resulting in an extremely non-uniform structure, lowering gas permeability and lowering the efficiency of the fuel cell.

[0006]

In order to solve the above-mentioned problems, the method of the present invention comprises, as a first step, a step of spray-coating a slurry-like coating material on a fine-textured ceramic substrate to form a porous material having a water-absorbing property. Forming a porous layer. As a second step, the surface of the porous layer is further coated with a skin layer by dipping.

[0007]

In the first step, when a slurry-like coating material is spray-coated on a dense ceramic substrate, the coating material which has become semi-dry during flight is deposited on the ceramic substrate while being dried after being brought into close contact with the ceramic substrate. Will be done. Therefore, it is possible to form a coating layer having a stable composition to an arbitrary thickness. Further, since this coating layer is porous, the adhesion to the coating layer formed by dipping in the second step is also good.

[0008]

Embodiments of the present invention will be described below with reference to the accompanying drawings. Here, FIG. 1 is a schematic view showing an example of the spray coating according to the first step of the present invention, and FIG. 2 is a schematic view of a dipping apparatus according to the second step of the present invention. FIG. 3 is a perspective view of a fuel cell element on which a porous electrode according to the present invention is formed, and FIG. 4 is a view showing a particle structure of the porous electrode of FIG.

In FIG. 1, a hollow dense ceramic base material 1 is fixed to a rotating body 2 in a horizontal direction, and spray coating in the first step is performed while rotating the rotating body 2 at a constant speed. The arrow indicates the direction of the coating material). By spraying the slurry while rotating the ceramic substrate 1 at a constant speed in this manner, a uniform porous layer having water absorption can be formed on the ceramic substrate 1 with good adhesion without dripping. . Further, according to this method, a porous layer having an arbitrary thickness can be formed by adjusting conditions such as a spray time. Spray coating using the rotating body 2 is particularly useful for dense cylindrical ceramics of the oxygen separation element 3 for fuel cells and the like.

As shown in FIG. 3, the oxygen separation element 3 for a solid oxide fuel cell has a porous electrode (air electrode) which is also gas permeable on the surface of a gas permeable cylindrical porous support 4. 5, a dense solid electrolyte layer 6 is formed on the surface of the porous electrode 5 that allows only oxygen ions to pass therethrough and does not allow oxygen gas in a molecular state to pass therethrough, and gas is permeable to the surface of the solid electrolyte layer 6. A porous electrode (fuel electrode) 7 is formed. This porous electrode 7 has a two-layer structure of a porous layer 7a formed by the first step of the present invention and a porous skin layer 7b formed by the second step.

The solid electrolyte layer 6 partitions the low oxygen side region S1 and the high oxygen side region S2.
The oxygen in the high oxygen side region S2 passes through the solid electrolyte layer 6 as ions by applying a voltage between the low oxygen side regions S1
Can be moved to

The porous support 4 is prepared by extruding a ceramic compound such as alumina to obtain a green body, and then firing the green body by means such as hanging grilling. Also, the porous electrodes 5, 7a, 7b
As shown in FIG. 4, it is necessary that the constituent particles 12 (black portions in the figure) are sufficiently bonded to each other and that a predetermined average pore diameter and porosity are secured.

An example of a slurry-like coating material for forming the porous layer 7a on the dense solid electrolyte layer 6 of the solid oxide fuel cell by spraying is shown below. Metal oxide fine particles (particle size selected depending on the application.) NiO, ZrO _2, etc. 2 to 40 wt% binder such as ethyl cellulose 2 to 14 wt% solvent ethanol 5-95% (preferably 40 to 60% by weight) alpha -Terpineol 5 to 95% by weight (preferably 40 to 60% by weight) In addition, a dispersant and a defoaming agent are added as necessary. The viscosity of the slurry is preferably 10 to 1000 cps,
0 to 300 cps is more preferable. The porous layer 7a having a water absorbing property can be formed by forming the porous layer 7a to a thickness of about several tens of μm using such a slurry-like coating material and performing drying and baking.

Next, coating of the skin layer 7b by dipping, which is the second step, is performed. The method as shown in FIG. 2, for example, to a container 8 for example NiO and ZrO ₂
Slurry 9 made of the composite oxide of
By rotating the stirrer 10 in the slurry 9
Is stirred, and the ceramic substrate 1 covered with the porous layer is immersed therein, whereby the unfired composite oxide skin layer 7b can be formed on the surface of the ceramic substrate 1. After thoroughly drying this layer under conditions that do not cause cracks,
A film is formed by firing.

By changing the dipping time or the number of times of dipping in the dipping slurry, the skin layer 7 b
Can be adjusted in thickness.

[0016]

According to the ceramic coating method of the present invention, a firm coating layer having good adhesion can be formed even on a dense ceramic substrate having no water absorption. The coating layer to be formed has a uniform composition and its thickness can be freely adjusted.

[Brief description of the drawings]

FIG. 1 is a schematic view showing an example of spray coating according to a first step of the present invention.

FIG. 2 is a schematic diagram of a dipping apparatus according to a second step of the present invention.

FIG. 3 is a perspective view of a fuel cell element having a porous electrode according to the present invention.

FIG. 4 is a view showing a particle structure of the porous electrode of FIG. 3;

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Ceramic base material, 2 ... Rotating body, 3 ... Oxygen separation element,
4 ... porous support, 5, 7a ... porous layer, 7b ... skin layer, 11 ... stirrer.

──────────────────────────────────────────────────続 き Continuation of the front page (58) Field surveyed (Int. Cl. ⁷ , DB name) C04B 41/80-41/91 B05D 1/00-7/26

Claims (4)

(57) [Claims] In a method of coating on a ceramic substrate having a dense structure, a slurry-like coating material is spray-coated to form a water-absorbing porous layer on the surface of the ceramic substrate. The first to form
And a second step of further coating the skin layer by dipping on the surface of the porous layer. 2. The spray coating in the first step, wherein the ceramic substrate is horizontally fixed to a rotating body,
The coating method according to claim 1, wherein the coating is performed while rotating the rotating body at a constant speed. 3. The coating method according to claim 1, wherein the ceramic substrate has a cylindrical shape. 4. The fuel cell according to claim 1, wherein the ceramic substrate is a solid electrolyte layer of a solid oxide fuel cell, and the coating layer formed in the first and second steps is a fuel electrode. The coating method according to claim 1.