JPH0597536A - Production of porous ceramic product - Google Patents

Abstract

PURPOSE:To readily obtain a porous ceramic product having a high opened pore degree by mixing a powdery ceramic raw material with finely cut carbon fibers, molding the mixture and subsequently calcining the molded product. CONSTITUTION:A powdery ceramic raw material (e.g. nickel oxide) and carbon fibers cut into a length of approximately <=500mum and having a diameter of approximately 7mum are mixed with each other, and further mixed with a binder, a solvent, a plasticizer, etc., in suitable amounts, respectively, to form a slurry, which is formed into a sheet by a doctor blade method, etc., to form a sheet. The suitable number of the sheets are superposed on each other, pressed, and subsequently cut into a molded product having a prescribed size. The molded product is heated to scatter the binder, and further calcined at a higher temperature to obtain a porous ceramic product. Thereby, the product having a high opened pore degree is readily obtained, because the carbon fibers are eliminated on the calcination to leave long fibrous pores communicated with each other.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to a method for producing a porous ceramic product.

[0002]

2. Description of the Related Art Among fuel cells which directly convert the chemical energy of fuel into electrical energy by an electrochemical means, in a solid oxide fuel cell operated at a high temperature of about 1000 ° C., an electrolyte is sandwiched. A porous ceramic film is used as the fuel (hydrogen) side electrode and the air side electrode facing each other. And, as a general manufacturing method of such an electrode, there is a method of applying an electrode paste to a sintered body of a solid electrolyte and baking it. According to this method, sintering of the solid electrolyte and baking of the electrode paste are performed. There is an inconvenience that the number of steps is increased because it is necessary.

The present inventor, as a method for producing a porous ceramic product capable of reducing the number of steps as compared with such a method, uses a solid electrolyte green sheet,
We are investigating the method of co-sintering by press-bonding with a green sheet that becomes an electrode. In this case, as the sheet material for forming the electrode made of porous ceramics,
Add the required amount of additives to the ceramic raw material that will be burned down below the sintering temperature of the ceramic raw material, make this mixture into a sheet, and co-sinter with the green electrolyte sheet. Is done. As such an additive, an organic substance such as a binder added in excess of an amount necessary for maintaining the strength of the sheet or a separately added cellulose powder is usually used.

[0004]

By the way, in the air side electrode of the fuel cell, a reaction in which oxygen gas is combined with an electron to form an oxygen ion and then diffuses into the electrolyte, and in the fuel side electrode, an oxygen ion It is necessary to smoothly proceed the reaction in which is coupled with hydrogen to become water and at the same time, emits an electron. Then, in order to efficiently proceed these reactions, a portion where the electrolyte through which oxygen ions pass, the fuel-side electrode and the air-side electrode, and the gas phase such as hydrogen or air flowing outside these are in contact with each other. A large number of pores must be present, and a large number of open pores through which the gas phase can reach the electrolyte must be formed in the porous ceramic product that serves as each electrode.

However, the binder as an additive added to form the voids that form the open pores is thinly distributed so as to enclose the powdery ceramic raw material, and the cellulose powder has a substantially spherical shape. Therefore, the aspect ratio of the void shape in the porous ceramic product obtained by sintering is often small, and the open pores do not necessarily increase. Therefore, when it is attempted to increase the amount of open pores formed by the continuous voids formed inside the porous ceramic product to increase the open porosity, a larger amount of organic substances such as cellulose powder is added. Need to be added. However, even if a large amount of organic matter is added to the ceramic raw material, it is not useful for leading the gas phase to the electrolyte, and the apparent density is lowered, and the electrical conductivity is also lowered, resulting in closed pores. The reality is that many results are formed.

The present invention was devised in view of such inconvenience, and an object thereof is to provide a manufacturing method by which a porous ceramic product having a high open porosity can be easily obtained.

[0007]

In order to achieve such an object, the method for producing a porous ceramic product according to the present invention comprises adding powdered ceramic raw material with carbon fibers that have been shredded in advance. It is characterized in that it is molded and fired after being mixed.

[0008]

According to the above construction, since the chopped carbon fiber is added to the ceramic raw material, when a molded body made of a mixture of these is fired,
The carbon fiber will disappear, and a fibrous long void will remain in the trace where the carbon fiber has disappeared. And, since these voids are fibrous with each other, it is easy for them to be continuous with each other. As a result, the amount of open pores increases and the open porosity increases even if the amount of carbon fiber added is small. .

[0009]

EXAMPLES Examples of a method for producing a porous ceramic product according to the present invention will be described below.

First, nickel oxide and yttrium-stabilized zirconium oxide, which are powdery ceramic raw materials, are prepared and mixed in required amounts, and then a predetermined amount of carbon fiber, that is, a predetermined amount of carbon fiber prepared in advance with respect to these mixtures, , Diameter about 7 cut to a length of less than 500 μm
Add μm carbon fiber and mix. Then, 15% by weight of polyvinyl butyral binder and ethanol, toluene, relative to 100% by weight of the obtained mixture,
Add an appropriate amount of plasticizer to make a slurry.

Next, a sheet material made of a slurry is formed by a doctor blade method, an appropriate number of the obtained sheet materials are superposed on each other and pressed, and then cut into a predetermined size to obtain a so-called rectangular parallelepiped shape. Obtain a molded body. Then, the molded body was heated at a temperature of 400 ° C. for 3 hours to scatter the binder, and then 1 ° C./min.
The temperature was raised to 1300 ° C. at a rate of 1, the temperature was maintained for 2 hours for firing, and then the temperature was cooled to room temperature to obtain a porous ceramic product (hereinafter referred to as an example product) as a sintered body. It was

Further, in order to evaluate the method of this embodiment,
Prepare a substantially spherical cellulose powder, add it to a mixture of nickel oxide and yttrium-stabilized zirconium oxide, which are ceramic raw materials, and follow the same procedure as described above to obtain a porous body as a sintered body. Ceramics products (hereinafter referred to as conventional products) were manufactured. Then, when the relative density and open porosity of each of the example product and the conventional product were measured, the measurement results shown in Table 1 were obtained. In addition, sample numbers 1 to 5 in Table 1
Indicates an example product, and sample numbers 6 to 10 indicate conventional example products.

[0013]

[Table 1]

From Table 1, it can be seen that the open porosity of the example product using carbon fiber is significantly higher than the open porosity of the conventional product using cellulose powder. Further, according to Table 1, even when the relative densities are the same, the open porosity of the example product is higher than that of the conventional product, so that the open pores equivalent to those of the conventional product are obtained. If the ratio is satisfactory, it is clear that the amount of carbon fiber added for forming open pores may be small.

When manufacturing a solid oxide fuel cell, a green sheet made of cubic zirconia stabilized by the addition of a solid electrolyte, for example, yttria, is added to a green sheet made of a porous ceramic electrode. The method of pressure bonding and sintering will be implemented.

In the above description, the porous ceramic product is the fuel side electrode and the air side electrode of the fuel cell, but it goes without saying that it may be used for other purposes. is there.

[0017]

As described above, according to the method for producing a porous ceramic product of the present invention, since the shredded carbon fiber is added to the powdery ceramic raw material, the molding of a mixture of these is performed. When the body is fired, the carbon fibers disappear and voids formed in a fibrous shape are left, and these voids are easily continuous with each other. As a result, the amount of open pores increases even if the amount of carbon fiber added is small, and a porous ceramic product with a high open porosity can be easily obtained.

Claims (1)

[Claims] 1. A method for producing a porous ceramic product, which comprises mixing a powdery ceramic raw material and shredded carbon fiber, and then molding and firing.