JPH0425209B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to perovskite-type fine powder, and more specifically, provides a method for easily producing perovskite-type fine powder having a large BET specific surface area.

(Prior Art) Perovskite compounds made of oxides of rare earth elements and transition metals have been known, and their fine powders have been widely studied as various catalysts and electronic materials with excellent properties.

(Problem to be solved by the invention) In order for these perovskite compounds to be useful as catalysts, their fine powder must be large.
It is required to have a BET specific surface area, that is, to be a fine powder.

However, in conventional manufacturing methods, for example, the so-called dry method in which oxides of each constituent element or compounds that produce oxides during firing are fired,
Since a high firing temperature of 1100°C is required, the fine powder is sintered violently, making it impossible to obtain a fine powder with a large BET specific surface area.

In addition, this product must be mechanically crushed after firing, and although this crushing requires a large amount of mechanical energy, the resulting crushed product has a large variation in particle size distribution, and it is extremely difficult to remove the coarse particles. It is complicated.

Other new manufacturing methods have been proposed, such as methods using metal alkoxide as raw materials, spray drying methods, freeze drying methods, and mist pyrolysis methods, but all of these methods require large equipment costs. , has disadvantages such as not being suitable for mass production.

Therefore, there is a strong need for a method of producing perovskite-type fine powders having a large BET specific surface area in a low-cost manner.

The inventor of the present invention solved the above-mentioned drawbacks of the conventional technology and, as a result of intensive research to meet the needs of the industry, discovered that when using a specific wet method, a large BET specific surface area can be obtained with simple equipment and at a relatively low calcination temperature. The present invention was completed based on the finding that a perovskite-type fine powder having the following properties can be obtained very easily.

(Means for Solving the Problems) That is, the present invention provides a perovskite-type fine powder represented by the general formula ABO ₃ (A is a rare earth element, and B is a transition metal consisting of Co, Ni, Mn, and Fe). In the method for producing a body, a water-soluble salt of A and a water-soluble salt of B, in which at least one of A and B is divalent, are mixed and precipitated by hydration with an alkaline agent in an aqueous medium. This is a method for producing perovskite-type fine powder, which is characterized by carrying out an oxidation treatment in a liquid phase at the same time or after precipitation, and then sintering the obtained precipitate.

Next, to explain the present invention in detail, the rare earth elements used in the production of the perovskite-type fine powder of the present invention are rare earth elements such as lanthanum, cerium, praseodymium, neodymium, promethium, samarium, europium, and gadolinium. In the invention, these rare earth elements are used as divalent or trivalent water-soluble salts.

These water-soluble salts include chlorides, nitrates,
Any water-soluble compound such as sulfate or acetate may be used, and these compounds may be used alone or as a mixture.

The transition metals used in the present invention are iron, cobalt, nickel, and manganese, and in the present invention, these transition metals are used as divalent or trivalent water-soluble salts.

These water-soluble salts include chlorides, nitrates,
Any water-soluble compound such as sulfate or acetate may be used, and these compounds can be used alone or as a mixture.

In the present invention, it is preferable to use a water-soluble salt of a rare earth element and a water-soluble salt of a transition metal as described above in a metal molar ratio of about 1:1, and It is preferable to use a divalent metal at least one of which is a divalent metal.

Any method may be used to neutralize the above-mentioned water-soluble salts of rare earth elements and water-soluble salts of transition metals and mix and precipitate their hydroxides and/or oxides. For example, (1) A method in which a water-soluble salt of a rare earth element and a water-soluble salt of a transition metal are dissolved in water to prepare an aqueous solution, and an alkali agent or its aqueous solution is added to the solution for neutralization.

(2) A method in which the above aqueous solutions are injected into an aqueous solution of an alkaline agent, either separately or in a mixture.

(3) A method in which a water-soluble salt of a transition metal and a water-soluble salt of a transition metal are added separately or simultaneously to an aqueous solution of an alkaline agent.

(4) In (1) to (3) above, a method of sequentially adding a water-soluble salt of a rare earth element, a water-soluble salt of a transition metal, or an aqueous solution thereof to an aqueous solution of an alkaline agent.

In short, any method can be used as long as the hydroxide and/or oxide of the rare earth element and the hydroxide and/or oxide of the transition metal can be obtained in a uniformly mixed state. It may be a method.

The alkaline agent used in such a mixed precipitation method may be any alkaline agent such as sodium hydroxide, potassium hydroxide, or sodium carbonate.

The amount of alkaline agent used may be any amount that can neutralize the water-soluble salt of the rare earth element and transition metal, but it is preferable to use an excess amount of the alkaline agent.

Further, the slurry concentration of the hydroxide and/or oxide of the rare earth element and transition metal produced by these neutralization is preferably about 2 to 8% by weight.

In the present invention, it is necessary to oxidize the divalent metal ions in the slurry thus obtained into trivalent metal ions in the slurry.

Oxidizing agents used include hydrogen peroxide, oxygen,
Any oxidizing agent such as sodium chlorate may be used, but preferred is an oxidizing agent that does not produce impurities upon oxidation, such as hydrogen peroxide or oxygen gas.

The amount of the oxidizing agent to be used may be the amount necessary to oxidize the divalent metal to trivalent metal ions, but it is preferable to use the oxidizing agent in a somewhat excessive proportion in order to complete the oxidation.

In this oxidation, the above slurry may be used as it is, or unnecessary cations and anions, such as cations such as sodium ions and potassium ions, chloride ions, and various acid ions may be removed from the slurry in advance. You can go after that.

If the oxidation is performed using the slurry as it is, after the oxidation is completed, the various unnecessary ions mentioned above are removed by filtering the slurry, washing with water, etc., and by drying the slurry, the precursor of the perovskite type compound is removed. Obtainable.

In the present invention, such precursors are prepared under a normal atmosphere, preferably a non-reducing atmosphere, from about 600 to
At a temperature of 1000℃, preferably around 800℃
By firing for 20 minutes to 1 hour, it is possible to obtain a perovskite-type fine powder having a BET specific surface area of 5 m ² /g or more, which is the object of the present invention.

(Function/Effect) According to the present invention as described above, since the firing temperature in the production method of the present invention is lower than that in conventional methods, the fine powder of the perovskite compound is not excessively sintered. It has a very soft state and has a large BET specific surface area of 5 m ² /g or more, making it useful as a variety of catalysts and other materials. It is something.

In addition, the manufacturing method does not require particularly expensive equipment, and the firing process does not require an oxygen stream, etc., so it is possible to provide the above-mentioned excellent perovskite-type fine powder at a low manufacturing cost. .

Next, the present invention will be specifically explained with reference to Examples.

In the text, percentages are based on weight unless otherwise specified.

Example 1 32.6 g of lanthanum oxide La ₂ O ₃ was added to a 60% nitric acid aqueous solution.
43 c.c. and 58.2 g of cobalt nitrate Co(NO ₃ ) ₂ .6H ₂ O is dissolved in this aqueous solution, and water is added to make the total amount 300 c.c.

On the other hand, an aqueous solution prepared by dissolving 45 g of sodium hydroxide in 200 c.c. of water is prepared, and the above two aqueous solutions are simultaneously poured into a container equipped with a stirrer and previously filled with 500 c.c. of water. During this time, the pH of the slurry liquid is maintained around 9, and the temperature is maintained below 30°C.

After the precipitation reaction is completed, the entire amount of excess sodium hydroxide aqueous solution is added. The pH of the liquid in this state was 13.4.

Next, add 15% hydrogen peroxide solution to this slurry.
After gradually adding 100 c.c., heat and mature at 80°C for 10 hours.

The obtained black and colored product is washed with water by decantation to remove impurities such as unnecessary cations and anions, then filtered and thoroughly dried at 100°C.

This dried material was calcined at 800° C. for 30 minutes to obtain a fine powder of the perovskite compound of the present invention.

The X-ray diffraction pattern of this fine powder was as shown in Figure 1, and completely matched the LaCoO ₃ perovskite type phase. Further, according to transmission electron micrographs, the particle diameter of these fine powders was approximately 0.1 to 0.2 μm. Moreover, the BET specific surface area was 13 m ² /g.

Example 2 32.6 g of lanthanum oxide La ₂ O ₃ was added to 60% nitric acid aqueous solution 43
Cobalt nitrate in this aqueous solution is completely dissolved in cc.
Dissolve 58.2 g _of Co(NO ₃ ) 2.6H ₂ O and add water to make a total volume of 300 c.c.

On the other hand, prepare a solution of 38 g of sodium hydroxide dissolved in 200 c.c. of water and 100 c.c. of a 15% hydrogen peroxide aqueous solution, and place the above three solutions in a container equipped with a stirrer and previously filled with 500 c.c. of water. inject at the same time. During this time, the pH of the slurry liquid is maintained at around 9 and the temperature is maintained at 50°C.

After the precipitation reaction and oxidation reaction were completed, excess sodium hydroxide aqueous solution was added to adjust the pH to 10, and then to 80.
Heat and ripen at ℃ for 1 hour.

The obtained black and colored product is filtered and washed with water to remove impurities such as unnecessary cations and anions, and then thoroughly dried at 100°C.

This dried material was calcined at 700° C. for 30 minutes to obtain a fine powder of the perovskite compound of the present invention. The X-ray diffraction pattern of this fine powder was as shown in Figure 1, and completely matched the LaCoO ₃ perovskite type phase. Further, according to transmission electron micrographs, the particle diameter of these fine powders was approximately 0.1 μm.
Moreover, the BET specific surface area was 20 m ² /g.

Example 3 29 g of lanthanum oxide La ₂ O ₃ was added to 40 c.c. of 60% nitric acid aqueous solution.
In this aqueous solution, 8.7 g of cerous nitrate Ce (NO ₃ ) _{3.6H 2} O and cobalt nitrate Co
Dissolve 58.2 g of (NO ₃ ) 2.6H _{2 O} and add water to make a total volume of 300 c.c.

Thereafter, an oxidation product was obtained in the same manner as in Example 1, dried, and the dried product was calcined at 850° C. for 30 minutes to obtain a fine powder of the perovskite compound of the present invention. The X-ray diffraction pattern of this fine powder was almost the same as that shown in FIG. 1, and completely corresponded to the La _0.9 Ce _0.1 O ₃ perovskite type phase. Furthermore, according to transmission electron micrographs, the particle size of these fine powders is approximately 0.1~
It was around 0.2 μm. Also, the BET specific surface area is 10
m ² /g.

Example 4 Neodymium oxide instead of lanthanum oxide
A NdCoO ₃ perovskite type fine powder of the present invention was obtained in the same manner as in Example 1 except that 33.6 g of Nd ₂ O ₃ was used. The X-ray diffraction pattern of this fine powder was as shown in Figure 2, and completely matched the NdCoO ₃ perovskite type phase. Furthermore, according to transmission electron micrographs, the particle size of these fine powders is approximately 0.1 to 0.2μ.
It was around m. Also, the BET specific surface area is 12m ² /g
It was hot.

Example 5 Samarium oxide instead of lanthanum oxide
A SmCoO ₃ perovskite type fine powder of the present invention was obtained in the same manner as in Example 1 except that 34.9 g of Sm ₂ O ₃ was used. The X-ray diffraction pattern of this fine powder was almost the same as that shown in FIG. 2, and completely corresponded to the SmCoO ₃ perovskite type phase. Furthermore, according to transmission electron micrographs, the particle size of these fine powders is approximately 0.1~
It was around 0.2 μm. Also, the BET specific surface area is 11.5
m ² /g.

Example 6 The present invention was carried out in the same manner as in Example 1, except that instead of lanthanum oxide, mixed rare earth element REX 70 manufactured by Santoku Metal Co., Ltd. or mixed rare earth element 32.7 g manufactured by Nissan Rare Earth Element Co., Ltd. was used. A perovskite-type fine powder of the invention was obtained. The X-ray diffraction pattern of these fine powders is as shown in FIG. 3, and according to transmission electron micrographs, the particle diameters of these fine powders were approximately 0.1 to 0.2 μm.
Moreover, the BET specific surface area was 10 m ² /g.

The mixed rare earth element used here is La ₂ O ₃ 50
~70% as main component, other 20 _~ 30% _Nd2O3 ,
It contains 5-13% of Pr ₆ O ₁₁ and 0.5-2% of Sm ₂ O ₃ .

Example 7 26 g of lanthanum oxide La ₂ O ₃ was added to 37 c.c. of 60% nitric acid aqueous solution.
In this aqueous solution, 8.5 g of strontium nitrate Sr (NO ₃ ) ₂ and cobalt nitrate Co (NO ₃ ) ₂ are completely dissolved.
Dissolve 58.2 g of 6H ₂ O and add water to make a total volume of 300 c.c.

Meanwhile, dissolve 37 g of sodium hydroxide and 5 g of sodium carbonate in 200 c.c. of water.

Thereafter, in the same manner as in Example 1, a fine powder of a perovskite compound of the present invention was obtained. The X-ray diffraction pattern of this fine powder was almost the same as that shown in FIG. Further, according to transmission electron micrographs, the particle diameter of these fine powders was approximately 0.1 to 0.2 μm. Also
The BET specific surface area was 10 m ² /g.

Example 8 The same procedure was carried out except that 50.2 g of manganese nitrate Mn (NO ₃ ) ₂ ·4H ₂ O was used in place of 58.2 g of cobalt nitrate Co (NO ₃ ) ₂ ·6H ₂ O, and the calcination temperature was 900°C. Example 1
In the same manner as above, a LaMnO ₃ perovskite type fine powder of the present invention was obtained.

The X-ray diffraction pattern of these fine powders is as shown in FIG. 4, and according to transmission electron micrographs, the particle diameters of these fine powders were approximately 0.1 to 0.2 μm. Moreover, the BET specific surface area was 9 m ² /g.

Example 9 Same as Example 1 except that 57.6 _{g of ferrous nitrate Fe (NO 3 ) 2.6H 2 O was used} instead of 58.2 g of cobalt nitrate Co (NO ₃ ) 2.6H ₂ O. of the present invention
LaFeO ₃ perovskite type fine powder was obtained. The X-ray diffraction pattern of this fine powder is shown in Figure 5.
Further, according to transmission electron micrographs, the particle diameter of these fine powders was approximately 0.1 to 0.2 μm. Moreover, the BET specific surface area was 10 m ² /g.

Example 10 The same procedure was carried out except that 58.2 g of nickel nitrate ₍ NO ₃ ) 2.6H _{2 O} was used instead of 58.2 g of cobalt nitrate Co (NO ₃ ) 2.6H ₂ O, and the firing temperature was 1000°C. A LaNiO ₃ perovskite type fine powder of the present invention was obtained in the same manner as in Example 1. The X-ray diffraction pattern of this fine powder is similar to that shown in Figure 1, and according to the transmission electron micrograph, the particle size of these fine powders is approximately 0.1 to 0.2μ.
It was around m. Also, the BET specific surface area is 8m ² /g
It was hot.

Comparative Example 1 The same procedure as in Example 1 or 2 was carried out except for the step of oxidizing with hydrogen peroxide, but no perovskite phase was obtained. The X-ray diffraction pattern of the product was as shown in FIG.

[Brief explanation of drawings]

1 to 5 show the X-ray diffraction pattern of the perovskite compound of the present invention, and FIG. 6 shows the X-ray diffraction pattern of the comparative product. The X-rays used
It is CoKα radiation. The vertical axis of the figure is the diffraction intensity, and the horizontal axis is the diffraction angle (2θ).

Claims (1)

[Claims] 1 General formula ABO ₃ (A is a rare earth element, B is
In a method for producing a perovskite-type fine powder represented by a transition metal consisting of Co, Ni, Mn, and Fe, a water-soluble salt of A and a water-soluble salt of B, in which at least one of A and B is divalent, are mixed. , mixed and precipitated by neutralization with an alkali agent in an aqueous medium,
Oxidation treatment is performed in the liquid phase at the same time as precipitation or after precipitation,
A method for producing a perovskite-type fine powder, the method comprising: then firing the obtained precipitate.