KR100419346B1 - Method for preparing porous yttria stabilized zirconia - Google Patents

Abstract

The present invention relates to a method for producing porous Yttria stabilized zirconia, and in particular, mechanically stable, which can be used as a support for supporting an electrode material of a solid oxide fuel cell (SOFC) or as a support for a catalyst. And a method for producing a porous YSZ in which pores are evenly distributed.

The present invention for this purpose, in a method for producing a porous yttria stabilized zirconia sintered body, a) mixing a zinc compound, yttria stabilized zirconia; b) molding the mixture; c) sintering the molding; And d) acid treating the sintered product to remove the zinc compound.

Since the production method of the present invention is made of a thermally stable zinc compound and YSZ powder as a starting material, it can be prepared by easily controlling the porosity of the YSZ molded body, in particular, because the porous YSZ is mechanically stable and evenly dispersed pores It can be used as a support of the fuel electrode and the cathode of the fuel cell, a support of the catalyst and the like.

Description

Method for producing porous yttria stabilized zirconia {METHOD FOR PREPARING POROUS YTTRIA STABILIZED ZIRCONIA}

[Industrial use]

The present invention relates to a method for producing porous Yttria stabilized zirconia, and in particular, mechanically stable, which can be used as a support for supporting an electrode material of a solid oxide fuel cell (SOFC) or as a support for a catalyst. And a method for producing a porous YSZ sintered body in which pores are evenly distributed.

[Prior art]

Porous Yttria stabilized zirconia (YSZ) is used as a support for the structure or synthesis components of the cathode or anode in a solid oxide fuel cell (SOFC), and also as a support for the catalyst.

The conventional method for producing porous YSZ is to obtain a porous YSZ by mixing and molding an organic material or carbon and YSZ powder, followed by heating. For example, YSZ and cornstarch mixtures are mixed and then dried, pressed and heated to obtain a porous YSZ (Steven J. Visco, Craig Jacobson, and Lutgard C. De Jonghe. August 26-28, 1997 Fuel Cells '97 Review Meeting, Morgantown, West Virginia. In addition, YSZ powder is gelled and sintered to a sol mixture in which acrylamide, N, N'-methylenebis-acrylamide, or carbon powder, which is an organic monomer, is mixed with YSZ powder. Examples of the preparation of porous YSZ are known (Gu YF, Liu XQ, Meng GY, Peng DK. Ceramics International., 1999, 25, 705).

However, these manufacturing methods have a problem in that the porosity is increased, the mechanical strength of the produced sintered body is weak, and the porosity is lowered when the mechanical strength is increased.

In view of the problems of the prior art, an object of the present invention is to provide a method for producing a porous YSZ sintered body having excellent mechanical strength while being able to easily adjust porosity.

Another object of the present invention is to provide a method for producing a porous YSZ sintered body in which there is no crack and the pores are evenly dispersed.

1 is a surface electron microscope of porous YSZ obtained by mixing and molding the YSZ powder and zinc oxide of Example 1 using a sol gel method at a weight ratio of 50:50, and then sintering at a temperature of 1450 ° C. and treating the obtained sintered body with nitric acid. It is a photograph.

2 is a cross-sectional electron microscope of porous YSZ obtained by mixing and molding the YSZ powder and zinc oxide of Example 1 using a sol gel method at a weight ratio of 50:50, and then sintering at a temperature of 1450 ° C. and treating the obtained sintered body with nitric acid. It is a photograph.

3 is a surface electron micrograph of the sintered compact obtained by mixing and molding the YSZ powder and zinc oxide of Example 1 in a weight ratio of 50:50, and then sintering at a temperature of 1450 ° C.

FIG. 4 is an XRD diagram obtained by sintering YSZ powder, zinc oxide powder, and a mixture of YSZ and zinc oxide of Example 1 at a temperature of 1450 ° C. FIG.

(A) is YSZ, (b) is ZnO, (c) is before the mixture of YSZ powder and zinc oxide is treated with nitric acid, and (d) is a mixture of YSZ powder and zinc oxide treated with nitric acid. The latter one.

FIG. 5 is a surface electron micrograph of the porous YSZ obtained by treating a YSZ powder having a weight ratio of 70:30 and zinc oxide with a sol-gel method and then sintered at a temperature of 1450 ° C. with nitric acid. .

6 is a surface electron micrograph of a sintered compact obtained by sintering a compact obtained by simply mixing YSZ powder and zinc oxide in a weight ratio of 50:50 at 1450 ° C.

7 is a surface electron micrograph of a porous YSZ obtained by treating a sintered compact obtained by sintering a compact obtained by simply mixing YSZ powder and zinc oxide in a weight ratio of 50:50 at 1450 ° C. with nitric acid.

In order to achieve the above object, the present invention provides a method for producing a porous yttria stabilized zirconia sintered body,

a) mixing a zinc compound and yttria stabilized zirconia;

b) molding the mixture;

c) sintering the molding; And

d) acid treating the sintered product

It provides a method for producing a porous YSZ sintered body comprising a.

Hereinafter, the present invention will be described in more detail.

The present invention is different from the conventional method for producing porous YSZ by oxidizing or decomposing carbon or organic material in the process of sintering carbon or organic material into a mixture of YSZ, and forming a metal compound such as zinc by mixing with powder of YSZ. After sintering and chemically treating the sintered body to provide a method for producing a porous YSZ characterized in that porosity is obtained by eluting the added zinc component. In particular, thermally stable ZnO powders can be used to form YSZ thin films with no cracks and evenly dispersed pores.

First, the preparation of the mixture of zinc compound and YSZ includes a simple mixing method of simply mixing the zinc compound and YSZ, and a sol-gel mixing method of transferring the sol and gel phases and mixing them.

In the simple mixing method, at least one zinc compound selected from the group consisting of zinc chloride, zinc nitrate, zinc sulfate, zinc oxide, and the like is added so that the amount of zinc is 50 to 250 parts by weight based on 100 parts by weight of YSZ. Grinding and mixing.

The sol-gel mixing method is one or more selected from the group consisting of zinc chloride, zinc nitrate, zinc sulfate, zinc oxide and the like so that the amount of zinc component is 50 to 250 parts by weight based on 100 parts by weight of YSZ. After adding and mixing the zinc compound, the mixture is poured into water, a dispersant is added with stirring and stirred for another 6 to 48 hours. In the process, the mixture is converted into a sol state. The emulsifier is added to the sol so dispersed and water is evaporated again while stirring or shaking to obtain a gelled mixture after 6 to 48 hours. The amount of water and dispersant added to the mixture here affects the time the sol gels. For example, the amount of water to be used based on 10 g of YSZ powder and 10 g of zinc compound is suitably 5 to 15 ml. The greater the amount of water, the longer the sol gels, and the shorter the amount of water, the more zinc compounds or the YSZ powders may clump together. Mixing a zinc compound of unequal size and YSZ powder results in an uneven distribution of pores in the final molded product, resulting in low mechanical strength.

In the dispersant used in the sol-gel mixing method, the amount thereof is preferably 3 to 12 parts by weight based on 100 parts by weight of the total of the zinc compound and the YSZ powder. In addition, as a dispersant, anionic surfactants such as ethyl acrylate and polycarboxylate, cationic surfactants such as ammonium salt and amine salt, and ethylene glycol and polyether ( One or more types can be selected from the group containing neutral surfactants, such as polyether), and DURAMAX D-3021 (made by ROHM and HAAS) can be used as a commercial product.

In the emulsifier used in the sol-gel mixing method, the amount thereof is preferably 14 to 51 parts by weight based on 100 parts by weight of the total of the zinc compound and the YSZ powder. In addition, the emulsifier may be selected from the group consisting of polymers such as acrylic polymers and organic compounds capable of condensation polymerization or addition polymerization similarly to dispersants. 3 ml of DURAMAX B-1014, DURAMAX B-1000 (manufactured by ROHM and HAAS) can be used.

The simple mixing method refers to a method in which the zinc compound powder and the powder of YSZ are mixed in a solid state or evenly mixed using a medium such as water. The simple mixing method is suitable for producing porous YSZ molded bodies, and the sol-gel mixing method is suitable for producing porous YSZ thin films.

Next, the steps of molding the mixture will be described.

The shaping | molding method of the sintered compact of this invention can be divided into two types.

One is to put the zinc compound and YSZ mixture simply mixed in the mixing step into a cast mold and pressurized by applying pressure. In this process, in order to give more strength to the molded body before sintering, it may be molded by mixing an organic binder such as starch or starch, and the mixing ratio or the pressure during molding may vary depending on the purpose of use of the final molded product.

Another molding method is to apply a mixture of zinc compound and YSZ mixed by the sol-gel method in the mixing step to a predetermined thickness on a suitable plane such as a polymer film and to solidify it. Here, the sol-gel mixture is unfolded to a certain thickness and left to solidify, and the solidified plate can be cut into a shape to be used. The application thickness is preferably several tens of microns to several mm.

Next, the step of sintering the molded product will be described.

Each of the molded bodies, which are mixed by the simple mixing method and the sol-gel mixing method, are sintered at a temperature of 1000 to 1600 ° C for 30 minutes to 12 hours. As for the temperature increase rate at the time of sintering, 1-5 degreeC per minute is preferable, and 1-5 degreeC per minute is preferable for a descending rate.

In the sintering process, the zinc compound changes to zinc oxide, and YSZ is not found on the surface of the sintered body. This fact suggests that zinc oxide with a melting point of 1970 ° C has more fluidity at sintering temperatures than YSZ particles with higher melting points (the melting points of zirconia and yttrium oxides are 2700 ° C and 2400 ° C, respectively). I can explain that there is. At room temperature, the density of zinc oxide and YSZ is around 5.6 in both cases, so the YSZ particles do not rise or sink during this sintering process, so the YSZ particles appear to be uniformly distributed throughout the solid and sinter the adjacent YSZ particles. In particular, since the Mohs hardness of zinc oxide is 4, which is lower than the Mohs hardness of zirconia 7 to 8, unstrained sintered compact is formed by effectively dispersing the stress of the sintered compact without disturbing the sintered bonding between YSZ particles.

Next, the step of treating the sintered body with an acid will be described.

When the sintered compact is added to an acid solution such as nitric acid, hydrochloric acid, sulfuric acid, and treated at a temperature of 25 to 100 ° C., some or all of the zinc components in the sintered compact may be eluted into the solution. The zinc-eluted sintered body has a porosity, and the porosity can be easily varied with the relative amount of zinc compound and the concentration and amount of acid or base to be treated.

The present invention will be described in more detail with reference to the following examples. However, an Example is for illustrating this invention and is not limited only to these.

EXAMPLE

Example 1

Preparation of Porous YSZ Sintered Thin Film

(Sol-gel mixing of zinc oxide and YSZ)

10 g of YSZ powder and 10 g of zinc oxide powder were added to the beaker with 10 ml of water and 1 ml of DURAMAX D-3021 as a dispersant to block the beaker inlet to prevent water from evaporating and to stir slowly at room temperature to prevent bubbles for 24 hours. )

After 24 hours, 3 ml of DURAMAX B-1014 and 5 ml of DURAMAX B-1000 were added to the mixture as an emulsifier, and the beaker inlet was opened to allow the moisture in the beaker to evaporate and stirred for 24 hours at room temperature. A gel of the compound-YSZ mixture was obtained.

(apply)

After spreading the gel to a polymer film in a thickness of about 1 mm and dried, it was prepared into a disc shape having a diameter of about 2 cm.

(Sinter)

The molded sample was heated to 1450 ° C. at a temperature increase rate of 2 ° C./min, sintered at this temperature for 2 hours, and then lowered at a drop rate of 2 ° C./min.

(Acid treatment)

The sintered sample was heated in boiling water for 30 minutes, then placed in 1 M HNO ₃ and heated again for 30 minutes. Again, the sample was heated in boiling water for 30 minutes to remove residual HNO ₃ and dried to prepare a porous YSZ thin film.

(Test result)

Table 1 shows the results of component analysis (EDX) before and after treatment with pure YSZ and a sintered compact having a weight ratio of 50:50 of zinc oxide and YSZ. From this, it was confirmed that zinc was eluted by nitric acid treatment.

TABLE 1

sample % Mole by element O Zn Sr Y Zr Before treatment with nitric acid 34.98 15.86 1.09 0.30 47.77 After treatment with nitric acid 48.28 2.53 0.83 0.27 48.10 Pure YSZ 46.27 0 0.65 0.22 52.86

1 is a surface electron micrograph of the porous YSZ obtained after the acid treatment of the sintered body, Figure 2 is an electron micrograph of the cross section, Figure 3 is a surface electron micrograph of the sintered body before the acid treatment.

While FIG. 3 shows a large particle size and few voids, it can be observed that FIG. 1 has many voids. In other words, zinc oxide is filled between the YSZ particles which are partially connected to the sintered body before acid treatment, and it is thought that porous YSZ is generated while zinc oxide is removed by acid treatment. The porosity of the sample was measured by the amount of water soaked into the acid-treated sintered compact was 40% by volume.

FIG. 4 is a chart of XRD (X-ray Diffraction) obtained by sintering and acidifying the YSZ powder, zinc oxide powder, and a mixture of YSZ and zinc oxide in a weight ratio of 50:50 at 1450 ° C. FIG. Here, reference numeral (a) is YSZ, (b) is ZnO, (c) is before the sintered compact of YSZ powder and zinc oxide is treated with nitric acid, and (d) is a sintered compact of YSZ powder and zinc oxide. After treatment with nitric acid.

In (c), both the characteristic peak of YSZ seen in (a) and the characteristic peak of zinc oxide seen in (b) can be observed. However, in (d), it can be seen that the characteristic peak of zinc oxide shown in (c) does not appear.

In addition, as a result of confirming the air permeability of the porous YSZ thin film through a vacuum test, the air permeation diffusion coefficient was 2.4 × 10 ^-5 m ² / s.

Example 2

Preparation of Porous YSZ Sintered Thin Film

A porous YSZ thin film was manufactured in the same manner as in Example 1, except that 14 g of YSZ powder and 6 g of ZnO powder were used by changing the weight mixing ratio of the YSZ powder and the ZnO powder to 70:30.

FIG. 5 shows a surface electron scanning microscope (SEM) photograph of this thin film, indicating that there are few pores as compared with Example 1 above. The porosity of this sample was 35% by volume.

In addition, as a result of confirming the air permeability of the porous YSZ thin film through a vacuum test, the air permeation diffusion coefficient was 0.52 × 10 ^-5 m ² / s.

Therefore, it can be seen that the porosity of the porous YSZ thin film can be easily adjusted by controlling the mixing weight ratio of the zinc compound and the YSZ powder.

Example 3

Preparation of Porous YSZ Sintered Body

10 g of the YSZ powder and 10 g of the ZnO powder were simply mixed into a solid form, placed in a cast mold, and molded into a pellet shape by applying pressure (20 to 40 kgf / cm ² ). The molded sample was heated to 2 ° C./min, sintered at 1450 ° C. for 2 hours, and then lowered to 2 ° C./min. 6 is a surface electron micrograph of the sintered body thus obtained.

The sintered sample was heated in boiling water for 30 minutes and then placed in 1M HNO ₃ and heated again for 30 minutes. The sample was then heated in boiling water for 30 minutes to remove residual HNO ₃ and the sample was dried to form a porous YSZ thin film.

7 is a surface electron micrograph of the porous YSZ obtained after the acid treatment of the sintered body. It can be seen that when the sintered body is acid treated as in the case of mixing by the sol gel method, porous YSZ is obtained.

The porosity of the sample was measured by the amount of water soaked into the acid-treated sintered compact was 16% by volume.

Since the production method of the present invention is made of a thermally stable zinc compound and YSZ powder as a starting material, it can be prepared by easily adjusting the porosity of the YSZ molded body, in particular, since the porous YSZ to be manufactured is mechanically stable and evenly dispersed pores It can be used as a support of the fuel electrode and the cathode of the fuel cell, a support of the catalyst and the like.

Claims (9)

In the production method of porous yttria stabilized zirconia, i) a zinc compound; And ii) mixing yttria stabilized zirconia (YSZ), wherein the zinc compound is mixed in an amount of 50 to 250 parts by weight based on 100 parts by weight of the yttria stabilized zirconia. ; b) molding the mixture; c) sintering the molding at a temperature of 1000 to 1600 ° C. for 30 minutes to 12 hours; And d) adding the sintered product to an acid solution and treating at a temperature of 25 to 100 ℃ Manufacturing method comprising a. delete The method of claim 1, The zinc compound of step a) is selected from the group consisting of zinc chloride, zinc nitrate, zinc sulfate, and zinc oxide. delete The method of claim 1, The acid solution of step d) is selected from the group consisting of nitric acid, hydrochloric acid and sulfuric acid solution. The method of claim 1, Iii) powder by mixing zinc compound powder and yttria stabilized zirconia powder Preparing a mixture; Ii) pressure molding the powder mixture to produce a molded body; Iii) sintering the molded body to produce a sintered molded body; And Iii) acid treating the sintered compact to produce a porous YSZ sintered compact Manufacturing method comprising a. The method of claim 6, The pressure molding of step ii) is carried out by further mixing 1 to 10 parts by weight of the organic binder of starch or starch components with respect to 100 parts by weight of the powder mixture. The method of claim 1, Iii) preparing a sol-gel mixed solution of zinc compound and yttria stabilized zirconia Making; Ii) applying the mixed solution onto a substrate and solidifying to prepare a thin film; Iii) sintering the thin film to produce a sintered thin film; And Iii) acid treating the sintered thin film to produce a porous YSZ sintered thin film Manufacturing method comprising a. The method of claim 8, Preparing a dispersion sol by dispersing the yttria stabilized zirconia powder and the zinc compound powder in water, and adding an emulsifier to the dispersion sol and evaporating water to prepare a dispersion gel. Manufacturing method.