JPH0891846A - Production of multiple oxide having large specific surface area - Google Patents

Abstract

PURPOSE: To produce a superior multiple oxide having a large specific surface area and fit for various uses. CONSTITUTION: In a 1st process, a molten alloy is prepd. from metallic and/or metalloid elements constituting a multiple oxide and an element which is selectively leached by an acid or base. In a 2nd process, a supercooled body is formed by rapidly cooling the molten alloy. In a 3rd process, the element which is selectively leached by an acid or base is leached from the supercooled body. In a 4th process, a material obtd. in the 3rd process is sintered. The objective multiple oxide is produced through those processes.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a composite oxide having a small particle size and a large specific surface area, which can be used in applications such as a catalyst, a superconductor, a piezoelectric material, a sensor and an electrolyte of a fuel cell. It is a thing.

[0002]

2. Description of the Related Art The characteristics of materials such as catalysts and sensors that utilize interaction between substances depend on the size of the point of action on the surface. Therefore, the greater the specific surface area, the greater the activity expected.

However, the specific surface area of the complex oxide obtained by the conventional methods such as the coprecipitation method, the evaporation-drying method, and the powder mixing method is less than 10 m ² / g, which is not a sufficient value. When used as a catalyst or sensor, sufficient performance may not be obtained in some cases. This is because the particle size of the raw material used in the conventional method is relatively large, at least on the order of submicron. Further, if the particle size is large, the constituent elements must diffuse over a long distance in order to form the composite oxide, and therefore it is necessary to perform firing at a high temperature, which also causes the particles to grow.
Therefore, a method for producing a composite oxide having a small particle size and a large specific surface area is required, and various techniques have been disclosed so far.

For example, a method of mixing an organic substance before firing a material to suppress grain growth after firing (JP-A-2-2)
No. 84649), a method in which a solution of a mixed salt of metal salts is impregnated with a catalyst carrier and the metal salt is supported on the surface of the carrier is subjected to low-temperature plasma treatment in advance to form a composite oxide and then firing. JP-A-64-67260) and the like.

[0005]

However, in the former method, organic components may remain in the catalyst, and in the latter method, the growth of the particle size can be suppressed by the low temperature plasma treatment, so that the specific surface area can be suppressed. However, due to the difference in solubility of each salt in the impregnation step, the precipitation of each salt on the carrier becomes non-uniform, and since each salt sticks to the carrier, solid-phase reaction is less likely to occur, so that the composition of Uniformity is not resolved,
As a result, there is a problem that the homogeneity of the catalyst is poor. The present invention has been made against the background of the technical problems as described above, and provides a method for producing an excellent composite oxide having a large specific surface area and a wide range of applications as compared with the conventional techniques. With the goal.

[0006]

Means for Solving the Problems The present invention includes the following (a)-
The present invention provides a method for producing a high specific surface area composite oxide, which comprises the step (d). (A) Metal element and / or metalloid element constituting the composite oxide or less (also referred to as "element for forming composite oxide")
And a first step of forming a molten alloy from an element selectively eluted by an acid or a base (hereinafter also referred to as “element to be eluted”). (B) A second step of making a supercooled body by rapidly cooling the molten alloy obtained in the first step. (C) A third step of eluting an element selectively eluted with an acid or a base from the supercooled body obtained in the second step. (D) A fourth step of firing the material obtained in the third step.

The complex oxide obtained by the production method of the present invention is preferably a complex oxide represented by the following general formula (I). La _1-x A _x BO ₃ (I) (In the formula, A is at least one selected from the group of Ca, Sr, and Ce, and B is Cr, Mn, Fe,
It is at least one selected from the group consisting of Co, Ni, Cu and Ta, and 0 ≦ X ≦ 0.4. )

The present invention will be described in detail below for each step. (A) First Step This step is a step of forming a molten alloy from the metal element and / or metalloid element forming the composite oxide and the element selectively eluted by the acid or base. Here, as the complex oxide forming element, an element constituting the complex oxide intended to be manufactured by the present invention is used. This complex oxide may be any type of complex oxide such as perovskite type, ilmenite type, spinel type, K ₂ NiF ₄ type and the like. Among the complex oxide forming elements that form the complex oxide, the metal elements include 1A element, 1B element, 2A element, 2B element, 3B element, 3A to 7A element in the periodic table.
8B element can be mentioned, but preferably Cr, Mn, F
e, Co, Ni, Cu, La, Nd, Ba, Ca, S
r, Ce, Ta, Ti, Y, Zr, Nb, Pb and Mg.

The semi-metal element is an element having both metal and non-metal properties, for example, B, Si, Ge and A.
Examples include s, Sb, and Te. These metal elements and / or metalloid elements are used in combination of two or more to form a composite oxide. Specific combinations of metal elements and / or metalloid elements include:
As the catalyst material, La and Cu, Nd and Cu, La and C
o, La and Mn, La and Ni, Sr and Fe, La and Sr
And Co, La and Sr and Cr, La and Sr and Mn, La and Sr and Fe, La and Sr and Cu, La and Ba and Cu, L
a and Ta and Mn, La and Ta and Co, La and Ca and C
o, good conductors for sensors are La, Ti, Sr
And V, Ca and Cr, Sr and Cr, Sr and Co, and as the capacitor material, Mg and Ti, Ca and Ti, Sr and Ti,
Ba and Ti, Pb and Ti, and Y and Ba as the superconductor
And Cu, La, Sr, Cu, and the like.

In the composite oxide represented by the general formula (I), A is at least one selected from the group consisting of Ca, Sr and Ce, and B is Cr, Mn and F.
At least one selected from the group consisting of e, Co, Ni, Cu and Ta is used. In the composite oxide of the general formula (I), trivalent La is added to divalent Ca, Sr, and tetravalent C.
By substituting with e, oxygen lattice defects are introduced, and the lattice defects serve as a catalyst having a particularly large activity, and the perovskite phase can be obtained at a low temperature. Further, in the general formula (I), the relationship between the element ratio of La and the element A is
The range is 0 ≦ X ≦ 0.4. Here, when X exceeds 0.4, the main phase perovskite phase is changed from LaBO ₃ to AB.
The lattice defects of oxygen are reduced due to the change to O ₃ .
The activity decreases.

Further, as elements to be eluted, Al, Z
Although n, Sn, Ga and the like can be mentioned, Al is preferable. The complex oxide-forming element and the element to be eluted are powdery, as long as they can be melted as a button-shaped ingot.
Either a lump shape or a plate shape may be used. The ratio of the element for complex oxide formation to the element to be eluted is usually 30/70 in terms of element ratio.
It is -10/90, preferably 20/80. When the ratio of the complex oxide forming element is less than 10 element%, the recovery rate after elution is low, while when it exceeds 30 element%, the specific surface area is not sufficiently large.

In the first step, the melting for producing the molten alloy is not particularly limited, but is preferably performed by arc melting or high frequency melting. In the case of arc melting, for example, 5 × 10 ⁻⁵ to 1 × 10 ⁻⁴ To
After evacuating to rr, Ar300-400 Tor
It is melted at an arc current of 200 to 300 A in an r atmosphere. In the case of high frequency melting, for example, 5 × 10 ⁻⁵ to 1 × 10
After vacuuming to ^-4 Torr, Ar200-300
Melt in a Torr atmosphere.

(B) Second Step This step is a step of rapidly cooling the molten alloy obtained in the first step to produce a supercooled body in which alloy components are uniformly dispersed. Here, in the state where the alloy components are uniformly dispersed,
Including amorphous state. Further, as a method of the rapid solidification treatment, a single roll method, an atomizing method and the like can be mentioned. In the case of the single roll method, for example, a complex oxide forming element which becomes a mother alloy is high-frequency melted in a quartz nozzle, and a molten alloy on a rotating copper roll is injected to rapidly solidify. At this time, the condition of the condition is that the nozzle hole diameter is 0.2 to 0.3 mm, the roll rotation speed is 3,000 to 4,000 rpm, and the roll diameter is 20.
0 to 300 mmφ, atmosphere Ar 150 to 200 Tor
r, and the injection pressure is 0.5 to 0.8 kgf. When the atomization method is used, the mother alloy is melted in a graphite crucible under an inert gas atmosphere, the molten metal is made to flow from a nozzle, pulverized by high pressure gas, and rapidly solidified. In this case, the condition is, for example, cooling gas He and gas pressure 100.
kg / cm ² and nozzle hole diameter 1.5 mmφ. The material obtained by the single roll method is ribbon-shaped, and the material obtained by the atomizing method is powdery.

(C) Third Step This step is a step of eluting an element that is selectively eluted with an acid or a base (hereinafter also referred to as “leaching”). The leaching is performed by immersing the ribbon-shaped or powder-shaped material in an aqueous solution containing one of an acid and a base. The acid or base aqueous solution used here is preferably one that selectively elutes the element to be eluted in the first step and that can be used under relatively mild conditions.

When Zn, Mn or Mg is used as the element to be eluted, an acidic aqueous solution, particularly preferably a nitric acid aqueous solution can be used. When a nitric acid aqueous solution is used as the acidic aqueous solution, the nitric acid concentration is 5 to 10% by weight, the liquid temperature is normal temperature, and the immersion time is 3 to 10 minutes. When Al, Zn, Sn, or Ga is used as the element to be eluted, a basic aqueous solution, particularly preferably an NaOH aqueous solution can be used. When NaOH is used as the basic aqueous solution, the concentration of NaOH is 5 to 20% by weight and the liquid temperature is 50 to 50%.
The immersion time is 60 ° C. and the time is 5 to 30 minutes.

The leached molten alloy is taken out from the acidic aqueous solution or the basic aqueous solution, and subjected to a washing treatment with ion-exchanged water until the metal (for example, Na ion) forming the acid or the base is not detected in the filtrate. Then, a drying process is performed. By leaching, the ribbon-shaped material is usually decomposed into powder, and its surface layer becomes a mixed layer of complex oxide forming elements. However, in the leaching, the material can be made into a ribbon shape or a flaky shape by adjusting the immersion time.

(D) Fourth Step This step is a step of firing the material obtained in the third step to form a composite oxide. Therefore, firing is performed in the air or in an oxygen stream. The firing conditions are a firing temperature of 500 to 90.
0 ° C., preferably 550 to 650 ° C., firing time 60 to
It is 600 minutes, preferably 300 to 400 minutes. If the firing temperature is lower than 500 ° C, no perovskite is generated, while if it exceeds 900 ° C, the specific surface area is reduced due to grain growth. If the firing time is less than 60 minutes, the formation of perovskite becomes insufficient, while if it exceeds 600 minutes, the specific surface area decreases due to grain growth.

Thus, by rapidly cooling and solidifying the molten alloy, an amorphous or supersaturated solid solution alloy is obtained. The grain size of the chemically leached alloy is
Very fine with several tens of nm, and its specific surface area is 60 to 10
Remarkably large at 0 m ² / g. Therefore, by firing this, a composite oxide having a high specific surface area can be obtained.

In the composite oxide obtained by the present invention, the adsorption process, which is the rate-determining step of the reaction, proceeds smoothly due to the increase in the specific surface area, and the catalytic activity is improved especially at low temperatures. Here, as the catalyst, a CH oxidation (combustion) catalyst,
An exhaust gas purifying catalyst (NO _x, etc.) can be used. Examples of the catalyst material composed of the composite oxide of the present invention include LaM
nO ₃ , LaCoO ₃ , LaNiO ₃ , La _0.8 Sr
_0.2 CoO ₃ , La _0.8 Ce _0.2 CoO ₃ , La _0.8 S
r _0.2 MnO ₃ , LaMn _0.7 Ta _0.3 O ₃ , La _0.8
Sr _0.2 CrO ₃ , La _0.8 Sr _0.2 FeO ₃ La _1.5
Sr _0.5 CuO ₄ , La _1.8 Ba _0.2 CuO ₄ , SrF
eO _{3 and the} like can be mentioned.

Further, the gas sensor utilizing the semiconductor characteristics of the complex oxide uses the characteristic that the resistance of the material changes depending on the gas concentration. When the specific surface area of the material is large like the complex oxide of the present invention, the number of gas adsorption points is increased, and the response (responsiveness, sensitivity, etc.) as a sensor becomes sharper. The sensor material which can be manufactured by the present _invention, and the like LaMnO 3, LaCoO _3. Further, when the crystal grains of the composite oxide become fine, the coercive force (Hc) improves. As a result, the composite oxide of the present invention has improved BH _{max and} high characteristics as a hard magnet.

[0021]

The present invention will be described below with reference to examples.
The present invention is not limited to these examples. The ratio and% are based on the number of elements unless otherwise specified. Examples 1 to 4 are cases where two kinds of elements are used as complex oxide forming elements, while Examples 5 to 6 are cases where Ta and Ca are added to Example 1, and Examples 7 to 8 are Shows the case where Sr and Ta were added to Example 2. Examples 1 to 8 Example 1; La: Co: Al = 10: 10: 80 Example 2; La: Mn: Al = 10: 10: 80 Example 3; La: Cu: Al = 7.5: 10 : 82.5 Example 4; Nd: Cu: Al = 10: 10: 80 Example 5; La: Ta: Co: Al = 10: 3: 7: 80 Example 6; La: Ca: Co: Al = 8: 2: 10: 80 Example 7; La: Sr: Mn: Al = 8: 2: 10: 80 Example 8; La: Ta: Mn: Al = 10: 3: 7: 80

Each of the constituent elements was weighed to a predetermined element ratio using the above-mentioned elements and blending recipe, and then melted into a button-shaped ingot by arc melting. This was pulverized to a size of about 2 mm square, a molten alloy was prepared by high frequency melting in a quartz nozzle, and then the molten metal was subjected to a rapid solidification treatment by applying a single roll method to prepare a ribbon-shaped catalyst material. In the single roll method, the diameter of the cooling roll is 200 mm, the rotation speed of the cooling roll is 4,000 rpm, the size of the jet nozzle of the quartz nozzle is 0.3 mm, the jet pressure of the molten metal is 0.4 kgf / c.
m ² and chamber pressure Ar100 Torr, and a ribbon material having a width of 1 mm and a thickness of 20 to 30 μm was manufactured. In order to selectively elute Al from this quench ribbon, a 20% NaOH aqueous solution 100 kept at 60 ° C. in advance
It was immersed in ml for 5 to 30 minutes until the generation of H ₂ due to the dissolution reaction of Al stopped. The ribbon material was washed with ion-exchanged water until Na ions were not detected in the filtrate, and dried with a drier. The compositions of the ribbon material after leaching and before firing are shown in Tables 1 to 7. This is 500, 55
0, 600, 650, 700, 750, 800, 85
Firing was performed at 0 and 900 ° C. for 5 hours each.

The powder obtained by this calcination was subjected to X-ray diffraction to examine the produced phase. The results are shown in Tables 1-7. In the table, amorphous was abbreviated as "amo." According to these, it was possible to synthesize at a low temperature a perovskite-type composite oxide, which conventionally required high-temperature firing.
An X-ray diffraction pattern demonstrating that perovskites are formed at low temperature in Example 1 is shown in FIG. Furthermore, in the case where Ca and Sr were added (Examples 6 to 7), the perovskite phase was formed at a temperature lower by about 50 ° C. than in the case where Ca and Sr were not added (Examples 1 and 2).

The specific surface area was measured by the BET method. The results are also shown in Tables 1 to 7. According to this, 55
The specific surface area is 40 m ² / g by firing at 0 to 650 ° C.
It was possible to obtain a composite oxide having a sufficient specific surface area before and after. Furthermore, when Ta is added (Examples 5 and 8), the decrease in specific surface area when firing at high temperature is suppressed, and as a result, a composite oxide having a very large specific surface area can be obtained. . At this time, the substitution amount of Ta for Co or Mn is preferably 0.1 to 0.9, more preferably 0.3 to 0.7, and most preferably 0.
It is 3 to 0.5. If it is less than 0.1, the effect of adding Ta is not remarkable, while if it exceeds 0.9, the properties of LaBO ₃ as an active ingredient are impaired, and Ta hinders the formation of perovskite to form the second phase. Because it does.

[0025] Comparative Example 1 (Preparation of LaCoO ₃₎ (a) coprecipitation La (NO ₃₎ and _{3 · 6H 2 O, Co (} NO 3) 2 · 6
H ₂ O was dissolved in a predetermined amount of water in a molar ratio of 1: 1 and stirred for 10 hours. Next, an excess of 0.1 N ammonia water and 30% hydrogen peroxide water were simultaneously added dropwise to coprecipitate, and the precipitate was dried at 100 ° C. Then 300 ° C
After decomposing nitrate ions in the air, further in the atmosphere
It was baked at 00 ° C. for 5 hours. The specific surface area was measured by the BET method. Table 1 shows the product phase and specific surface area after firing.

(B) Evaporation and Drying Method La (COOCH ₃ ) ₃ · 1.5H ₂ O and Co (CO
The _{OCH 3) 2 · 4H 2 O} , 1 in a molar ratio: in the 1 was dissolved in a predetermined amount of water, and stirred for 10 hours. Next, water was removed by evaporation with an evaporator, the acetate was decomposed in the air at 300 ° C., and then the mixture was calcined in the air at 800 ° C. for 5 hours. The specific surface area was measured by the BET method. Table 1 shows the product phase and specific surface area after firing.

(C) Powder Mixing Method La ₂ O ₃ and CoO were mixed in a ball mill at a molar ratio of 1: 2 (pot volume 0.86 liter, ball amount; 5 mmφ and 10 mmφ were 15 times the pot volume). %, Ball material zirconia, dispersion medium ethanol 200 m
1, mixing time 20 hours), ethanol was removed by evaporation with an evaporator, and the mixture was calcined in the air at 850 ° C. for 5 hours. The specific surface area was measured by the BET method. Table 1 shows the product phase and specific surface area after firing.

Comparative Example 2 (Preparation of LaMnO ₃ ) La ₂ O ₃ and MnO ₂ were mixed at a molar ratio of 1: 2,
A composite oxide was prepared according to the powder mixing method (c) of Comparative Example 1. The specific surface area was measured by the BET method. Table 2 shows the produced phase and specific surface area after firing.

Comparative Example 3 (Preparation of La ₂ CuO ₄ ) La (COOCH ₃ ) ₃ · 1.5H ₂ O and Cu (CO
OCH ₃ ) ₂ · H ₂ O was mixed at a molar ratio of 2: 1 to prepare a composite oxide according to the evaporation dryness method (b) of Comparative Example 1. The specific surface area was measured by the BET method. Table 3 shows the produced phase and specific surface area after firing.

Comparative Example 4 (Preparation of Nd ₂ CuO ₄ ) Nd (NO ₃ ) ₃ .6H ₂ O and Cu (COOCH ₃ )
₂ · H ₂ O was mixed at a molar ratio of 2: 1 to prepare a composite oxide according to the dry dry evaporation method of Comparative Example 1 (b). The specific surface area was measured by the BET method. Table 4 shows the produced phase and specific surface area after firing.

Comparative Example 5 (Adjustment of LaSrMnO ₃ ) La (COOCH ₃ ) .1.5H ₂ O and Sr (COO
CH ₃ ) ₂ · 0.5H ₂ O and Mn (COOCH ₃ ) ₂
4H ₂ O was mixed at a molar ratio of 1: 1 to prepare a composite oxide according to the powder mixing method of Comparative Example 1 (a) and the evaporation dryness method of (b). Table 6 shows the produced phase and specific surface area after firing.

[0032]

[Table 1]

[0033]

[Table 2]

[0034]

[Table 3]

[0035]

[Table 4]

[0036]

[Table 5]

[0037]

[Table 6]

[0038]

[Table 7]

[0039]

INDUSTRIAL APPLICABILITY According to the method for producing a composite oxide of the present invention, the composite oxide can be synthesized at a low temperature by using a material which has been made fine by chemical treatment. It makes it possible to obtain. Therefore, since it can be expected to exhibit excellent performance as a composite oxide, it can be used in various applications such as catalysts, superconductors, piezoelectric materials, sensors, and electrolytes for fuel cells.

[Brief description of drawings]

FIG. 1 is an X-ray diffraction pattern of a produced phase after leaching and after firing in Example 1.

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[Procedure amendment]

[Submission date] November 1, 1994

[Procedure Amendment 1]

[Document name to be amended] Statement

[Name of item to be corrected] 0032

[Correction method] Change

[Correction content]

[0032]

[Table 1]

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification code Internal reference number FI Technical display location C01G 45/00 // H01M 8/02 M 9444-4K (72) Inventor Shigeki Koyama Wako City, Saitama Prefecture Chuo 1-4-1 No. 1 inside Honda R & D Co., Ltd. (72) Inventor Akihisa Inoue Kawauchi Mubanchi, Aoba-ku, Sendai City, Miyagi Prefecture Kawauchi Housing 11-806

Claims (2)

[Claims] 1. A method for producing a high specific surface area composite oxide, which comprises the following steps (a) to (d): (A) A first step of forming a molten alloy from a metal element and / or a semimetal element forming a composite oxide and an element selectively eluted by an acid or a base. (B) A second step of making a supercooled body by rapidly cooling the molten alloy obtained in the first step. (C) A third step of eluting an element selectively eluted with an acid or a base from the supercooled body obtained in the second step. (D) A fourth step of firing the material obtained in the third step. 2. A composite oxide represented by the following general formula (I), which is obtained by the production method according to claim 1. La _1-x A _x BO ₃ (I) (In the formula, A is at least one selected from the group of Ca, Sr, and Ce, and B is Cr, Mn, Fe,
It is at least one selected from the group consisting of Co, Ni, Cu and Ta, and 0 ≦ X ≦ 0.4. )