JPH04193701A - Production of perovskite type oxide powder - Google Patents

Abstract

PURPOSE:To easily produce the perovskite type oxide powder which is useful as an electrode material for fuel batteries and is uniform in two kinds of grain sizes in a large amt. by separately treating and calcining the org. acid salt and carbonate of the metal elements constituting the perovskite type oxide. CONSTITUTION:The org. acid salts, such as acetate, of the metal element constituting the perovskite type oxide, for example, La1-xA'MO3 (A' is Sr, Ba, M is Co, Cr, Mn, Ni, Fe) are mixed to prescribed ratios to prepare a soln. and this soln. is evaporated to dryness. The resulted product is pulverized and calcined and the calcined matter is pulverized to obtain the powder of the perovskite type oxide having <=1mum grain diameter. On the other hand, at least one of the metal elements constituting the above-mentioned oxide is formed of the carbonate and the other is formed of the simple substance or oxide. The above-mentioned powder is calcined while the oxygen is supplied, by which the powder having 5 to 10mum grain diameter is obtd.

Description

DETAILED DESCRIPTION OF THE INVENTION A. Field of Industrial Application The present invention relates to a method for producing perovskite-type oxides.

B0 Summary of the Invention The present invention provides a method for producing perovskite oxide powder with uniform particle size by supplying the raw material metal constituting the perovskite oxide in the form of an organic acid salt or a carbonate compound and treating each of them. It's something you get.

C0 Prior Art In general, a fuel cell main body is constructed by arranging anode and cathode electrode plates on both sides of a solid electrolyte to form a unit cell, and stacking a plurality of these unit cells so as to connect them in series.

The single cell structure of this battery uses a porous substrate as a support structure through which fuel gas such as hydrogen flows appropriately, and a thin film cathode, a thin film solid electrolyte, and a thin film anode are sequentially laminated on the surface of this porous substrate. It is formed into a structure. and,
Hydrogen gas (hydrogen) is supplied as a fuel to the thin film cathode side of the single cell, and air (oxygen) is supplied as an oxidizing agent to the thin film anode side to cause the hydrogen and oxygen to react and generate electricity. water is produced.

In a single cell of such a battery, the thickness of the solid electrolyte should be thinner in order to reduce the voltage drop due to the resistance bones of the thin film solid electrolyte itself.

If the current flowing through the thin film solid electrolyte is i (A), the resistance of the solid electrolyte is R (Ωam), and the thickness of the solid electrolyte is t (μm), then the voltage drop Vd in the solid electrolyte is: Vd= It can be expressed as i-R-tX 10-',
From Equation 1, it can be seen that the thinner the thin film solid electrolyte is, the less the voltage drop will be.

On the other hand, since the solid electrolyte of this thin film is formed on a porous substrate, considering the coverage of the thin film, it is not possible to configure it unconditionally.
It has been found that it is best to form the film to a thickness of about 1 m.

Generally available porous substrates have a pore diameter of, for example, 0.
．． When electrodes and thin film solid electrolyte are laminated on the surface of this porous substrate, there is a problem that pinholes are likely to form in the thin film solid electrolyte in the two parts with large pore diameters. Ta.

A fuel cell forms a type of oxygen concentration cell when the oxygen partial pressure across the thin film solid electrolyte is different, and an electromotive force is generated at both ends of the thin film solid electrolyte.The electromotive force E at this time. is expressed by the following formula.

Eo=(RT/4F)XIn(P+/P2) From the above formula, the electromotive force E. increases in proportion to the ratio of oxygen partial pressures. In addition. In the formula, R is a gas constant, T is an absolute temperature, F is a Faraday constant, and P, P2 are oxygen partial pressures across the solid electrolyte.

As mentioned above, if a pinhole is formed in the thin film solid electrolyte, the oxygen partial pressure ratio will decrease, so in a fuel cell using such a single cell, the electromotive force will decrease, or in the worst case, an electromotive force will occur. There was an inconvenience that it stopped working.

Therefore, perovskite-type oxide powders with two different particle sizes were manufactured and coated on a porous stainless steel substrate, and the surface roughness was
An oxygen electrode was formed that had a film thickness of about 1710 mm that of the solid electrolyte and had enough porosity to allow gas to pass through.

The two types of particle sizes mentioned above are those with a particle size of 5 to 1011 m that fills the large pores of the porous stainless steel substrate and smoothes the surface;
Cover the electrode surface and make the undulations of the surface 1 of the solid electrolyte film thickness.
There are two types of perovskite-type oxide powders: one with a particle size of 1 μm or less, which suppresses the particle size to about 710, and increases the surface area and increases the catalytic ability. As a result, a thin and gas-tight solid electrolyte thin film having a thickness of about 110 l1 could be formed on the porous stainless steel substrate 2.

D8 Problems to be Solved by the Invention However, in order to obtain perovskite-type oxide powder with uniform particle size as described above, it is necessary to perform classification repeatedly.

In particular, in order to obtain perovskite-type oxide powder with a particle size of 1 μm or less, it is necessary to grind the powder over several days using a batch method such as a bot mill, which makes it easy for impurities to enter from balls or pots during grinding. Moreover, it takes a lot of time and effort to obtain a large amount of electrode material.

In addition, when producing powder with a particle size of 5 to 10 μm, the firing time becomes longer due to the lack of oxygen during firing.
Furthermore, there is a problem in that when the firing temperature is increased to shorten the firing time, abnormal grain growth occurs.

The present invention was made against this background, and it is an object of the present invention to easily and mass-produce two types of perovskite-type oxide powders having uniform particle sizes as described above.

E9 Means for Solving Problems In order to solve the above problems, the present invention prepares a solution containing a mixture of organic acid salts of metal elements constituting a perovskite type oxide, and dries the solution to produce a product. It is characterized in that it is ground, mixed and fired, and the fired product is ground to obtain a powder.

Furthermore, at least one of the metal elements constituting the perovskite-type oxide is carbonate, and other metal elements constituting the perovskite-type oxide are used alone or as oxides,
The particle size of the above-mentioned raw materials is smaller than the particle size of the target perovskite oxide, and these powders are mixed and fired while supplying oxygen directly into the powder to obtain the powder. Features.

F1 action In the present invention, by supplying the raw material metal of perovskite type oxide as an organic acid salt such as acetate, the fired product becomes porous, and by using carbonate as the raw material metal, carbonic acid decomposes during firing. oxygen is generated.

Therefore, the amount of oxygen during firing increases, and firing progresses smoothly.
By pulverizing this product, a powder with small and uniform particle size can be obtained.

G. Examples Oxygen electrode materials usually used in fuel cells are A B
03 perovskite type oxides are known, mainly L
In the a1-xA'xMO3 system, M is Co, CrXM
n-, 'N 1% Fe, etc. alone or as a mixture, and those in which A' is replaced with Sr, Ba, etc. at the A site are used.

In this example, Lao6 is used as the perovskite oxide.
Although srO, 4c00.911NiO, and [12o3 are used, other perovskite-type oxides can also be produced using a similar method.

Furthermore, in this example, acetate of each metal is used as a starting material to obtain perovskite oxide powder with a particle size of 1 μm or less, but other organic acid salts such as napfranate and ophthalate may also be used. Powders can be easily obtained in the same manner by dissolving each raw material in a solvent such as butanol, ethanol, or water in which it is soluble.

First, the particle size is 1. Lao below ttm, aS ro, 4
To obtain a powder of co0.911Njoo203, (
CH3COO)2Co・4H20, (CH3COO)2
sr”o, 5H20, L a (CH3C00) 3・1
,5H20,(CH3COO)2Ni・4H20,L
a:Sr:Co:N1=0.6+0.4+0.098:
0.02, put it in a bottle or cup, add ion-exchanged water at a ratio of 500 cc to 150 g of mixed powder, and emulsify with a shaker mixer to prepare a solution.

This solution is placed in a vat with a shallow bottom and a large area to facilitate drying, and is dried and decomposed in a dryer at around 250° C. while rotating a fan to prevent bumping, thereby obtaining an intermediate product.

This is crushed and mixed in a miller, and then heated in the atmosphere or in an oxygen stream using a Matsufuru furnace, etc.
Firing is performed at 1000°C for about 10 hours.

The product thus obtained becomes porous due to the release of the reaction gas, and by simply pulverizing it with a sieve, it becomes a powder with a particle size of 1 μm or less as shown in the SEM images in Figures 2 and 3. or can be obtained.

Figures 6(a) and 6(b) show the results of X-ray diffraction of this powder. This confirms that a perovskite oxide having a single composition can be obtained by firing at a low temperature of 700 to 1000°C.

In addition, the fluorescence X shown in FIGS. 7(a), (b), and (C)
Linear diffraction reveals that each of the metals La, Sr, Co, and Ni is contained according to the composition ratio.

Next, a method for obtaining powder having a particle size of 5 to 10 mm will be shown below.

In this example, Ni powder and 5rCOh powder with a particle size of 3 to 7 μm and La20 powder with a particle size of 11-2tt were used.
．． .

Powder and Co powder are used as raw materials.

” 1. The raw materials listed in item 1 are converted into the target products Lao, 6Sro,
4Co(,911NiO0203)
:Sr:C.

:N1=0.6+0.4+0.098:0.02, and after adding ion-exchanged water to 1 kg of this mixed powder], 1 kg of ion-exchanged water was added using a ball mill for 10
Mix for at least an hour.

This slurry is placed in a vat with a shallow bottom and a large area to facilitate drying, and is dried in a dryer using a fan at a temperature of about 120° C. without bumping to obtain a cake.

Put this in the port and use the Matsufuru furnace for 1200~1300
Bake at °C for about 10 hours.

At this time, an alumina tube or the like is inserted into the mixed powder to supply oxygen gas directly to the powder.

This accelerates the reaction, completes the reaction at a relatively low temperature and in a short period of time, and suppresses abnormal grain growth.

Figures 4 and 5 are SEM analysis images of the powder produced as described above. From these diffraction images, the particle size distribution shown in Table 1 below was obtained, and the particle size of the powder was determined. 4~10μ
It can be seen that it falls within the range of m.

The following margins and FIGS. 8(a) and 8(b) show the results of X-ray analysis, showing that a perovskite type oxide of a single composition was obtained.

In the above starting materials, C01La20 in this example
3, the raw material that is the main component of perovskite grows during firing and the particle size increases, so the particle size is 5.
It is preferable to use powder with a small particle size of about μm or less.

Furthermore, a carbonate such as SrCO3 may be used to lower the firing temperature.

On the other hand, for carbonate that decomposes during firing and raw materials with a small content, powder with a larger particle size than the above-mentioned main component raw materials may be used, and in this example, carbonate SrCO3 and Ni with a small content both have particle sizes of 3 to 3.
It is approximately 7 μm, which is larger than that of the main raw material.

In addition, perovskite-type oxide powder can be obtained easily and in large quantities using the above-mentioned formation method, and a fuel with good water drainage in which an oxygen electrode, a solid electrolyte, and a fuel electrode are laminated in this order on the above-mentioned porous substrate is also available. The battery can be easily configured.

■9 Effects of the invention According to the invention, when producing a powder of a perovskite-type oxide with a particle size of 1 μm or less, an organic acid salt of a metal element, which is a raw material for the perovskite-type oxide, is used. , reactive gas evolution occurs during calcination, which makes the product porous.

Therefore, when this product is pulverized, the particle size of the powder becomes smaller than when a normal product is pulverized, and this production method allows powder with a particle size of 1 μm or less to be obtained easily and in large quantities. Manufacturing time is significantly reduced compared to traditional manufacturing methods,
Also, the risk of contamination with impurities is extremely reduced.

In addition, when manufacturing perovskite oxide powder with a particle size of 5 to 10 μm, the particle size of the raw material is made smaller than the target particle size, and at least one of the constituent metal elements of the perovskite oxide is In addition, an alumina tube or the like is inserted into the powder to supply oxygen directly into the powder during firing.

By the method described in item 1, oxygen is sufficiently supplied during firing to promote the reaction, thereby making it possible to shorten the firing time and keep the firing temperature low.

Therefore, the grain growth of the raw material is suppressed, and a perovskite oxide having the desired grain size can be obtained.

[Brief explanation of the drawing]

Figures 1 to 5 are photographs showing the particle structure of the powder according to this example, Figures 6 (a), (b), and Figure 7 (a), (b).
, (c), FIGS. 8(a) and (b) are X-ray diffraction graphs of the powder according to this example, and FIG. 9 is a configuration diagram of the fuel cell. 1... Stainless steel pipe, 2... Porous stainless steel substrate, 3... Electrode, 4... Solid electrolyte, 5... Electrode, Figure 1 Figure 2 Figure 3 Figure 4 PA Eye- Kenmoe mail eb Shima 00 farm stitch 1 □ Gas B Stainless steel pipe...Porous stainless steel substrate/Electrode...Solid electrolyte/Electrode-14=

Claims (2)

[Claims] (1) Prepare a solution in which organic acid salts of metal elements constituting the perovskite oxide are mixed, dry this solution, crush the resulting product, mix and sinter, and pulverize this sintered product. A method for producing perovskite-type oxide powder, characterized in that the powder is obtained by (2) At least one of the metal elements constituting the perovskite-type oxide is carbonate, and the other metal elements constituting the perovskite-type oxide are used alone or as oxides,
The particle size of the above-mentioned raw materials is smaller than the particle size of the target perovskite oxide, and these powders are mixed and fired while supplying oxygen directly into the powder to obtain the powder. Characteristic method for producing perovskite-type oxides.