JP2012138256A - Air electrode material powder for solid oxide type fuel battery, and method of manufacturing the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide novel LSCF microparticles (powder) with highly uniform composition suitable as an air electrode material for a solid oxide type fuel battery, and a manufacturing method for obtaining the LSCF microparticles with uniform composition.SOLUTION: There is provided air electrode material powder for a solid oxide type fuel battery expressed by (LaSr)CoFeO. When the average content of a lanthanum element calculated from areal ratios of characteristic X-ray peaks measured by an energy dispersive X-ray spectroscopic system which a scanning electron microscope is equipped with is compared with the average content of one element of cobalt and iron elements which shows a higher content, the variation coefficient (α) of the element higher in average content is 4.0% or less. Further, as a result of the comparison of the average content of the cobalt element calculated likewise with the average content of an iron element, the variation coefficient (β) of the element higher in average content is 2.0% or less.

Description

  The present invention relates to an air electrode material powder for a solid oxide fuel cell that has a perovskite structure and is a composite oxide composed of a lanthanum element, a strontium element, a cobalt element, an iron element, and an oxygen element, and a method for producing the same. Specifically, the present invention relates to an air electrode material powder in which the constituent elements are highly uniform in the composite oxide particles and a method for producing the same.

  A solid oxide fuel cell is a fuel cell that uses a solid electrolyte that exhibits oxygen ion conductivity as an electrolyte. The electrochemical reaction that generates electromotive force is an oxidation reaction of hydrogen, and it does not generate carbon dioxide. Attention has been paid. A solid oxide fuel cell generally has a stack structure in which single cells composed of an oxide air electrode, a solid electrolyte, and a fuel electrode are connected by an interconnector, and the operating temperature is usually about 1000 ° C. There have been various studies, and the minimum temperature of those that have been put to practical use in recent years is still as high as 600 ° C. or higher.

  Due to this cell structure and high operating temperature, the air electrode material constituting the air electrode has (1) high oxygen ion conductivity, (2) high electron conductivity, (3) electrolyte and thermal expansion. Equivalent or approximate, (4) high chemical stability, high compatibility with other constituent materials, (5) the sintered body is porous and has a certain strength, etc. These characteristics are basically required.

As a material satisfying these characteristics, there is a composite oxide represented by (La _1-x Sr _x ) _a Co _y Fe _1-y O ₃ (hereinafter sometimes abbreviated as LSCF) having a perovskite structure. It has been energetically researched and developed as an air electrode material with excellent electrode activity.

For example, Patent Document 1 describes a ceramic powder containing a lanthanum ferrite-based perovskite oxide as a main component, and more specifically, a composition formula (L _1-x AE _x ) _1-y (Fe _z M _1-z ) O _{3 + δ} , L is one or more elements selected from the group consisting of rare earth elements such as lanthanum, scandium (Sc), and yttrium (Y), AE is strontium (Sr) and One or two elements of the group of calcium (Ca), where M is cobalt (Co), magnesium (Mg), scandium (Sc), titanium (Ti), vanadium (V), chromium (Cr), and A ceramic powder is described which is one or more elements selected from the group consisting of nickel (Ni) and has 0 <x <0.5, 0 <y ≦ 0.04, and 0 ≦ z <1. (Special See the scope of the claims.).

As a method of preparing the ceramic powder, lanthanum oxide, strontium carbonate, cobalt oxide, and iron oxide are mixed and ground in a solid using a mortar or the like (solid phase method). And calcining (paragraphs [0032], [0092] to [0094] (Example 1)).
In such a solid phase method, as long as four kinds of raw material element-containing particles are pulverized and mixed in the solid phase, it is difficult in principle to obtain a completely uniform composition at the micro level. is there.

In Examples 2-3 and 6-11 of Patent Document 1, in addition to this solid phase method, (La _0.6 Sr _0.4 ) ₁ having a specific surface area of 4 m ² / g synthesized by the “citrate method” is used. _-z (Co _0.2 Fe _0.8 ) O _{3 + δ} (y = 0, 0.02, 0.04) (manufactured by Seimi Chemical Co., Ltd.) An example is described in which LSCF is pressure-molded after ethanol is added and wet-mixed. Has been. This “citrate method” LSCF was synthesized and provided by the present applicant. (Specifically, raw material powder is mixed and prepared in a solution such as citric acid by the method of Comparative Example 1 described later, and La ₂ O ₃ and Fe ₂ O ₃ which are part of the raw material are completely dissolved. Otherwise, the system is in a slurry state, and a composition having a completely uniform composition cannot be obtained. (In this sense, the “citrate method” is referred to as the “slurry method”).

Patent Document 2 discloses one or more elements represented by the general formula ABO ₃ , wherein the A site is selected from the group of La and rare earth elements, and one or more elements selected from the group of Sr, Ca, and Ba. And a B-site perovskite complex oxide powder composed of one or more elements selected from the group consisting of Mn, Co, Fe, Ni and Cu, having an average particle size of 1 μm or less and a particle size distribution The air electrode raw material powder of a solid oxide fuel cell having a narrow width is described (see claims).

Patent Document 2 relates to an LSCF powder having a fine particle size and a small variation in particle size distribution. As an adjustment means for this purpose, water-soluble nitrates of La, Sr, Co, and Fe, which are raw material elements, are used. It is dissolved in water at a predetermined ratio, NH ₄ OH is added thereto to coprecipitate each insoluble salt, and the precipitate is dried and calcined (coprecipitation method) (paragraph [0032]).
Since this coprecipitation method is precipitated from a uniform solution, it seems that a uniform composition can be easily formed at first glance. In the nitrate of an element, since the pH at which the insoluble salt of each element precipitates and the crystal growth rate thereof are different, precipitation with a uniform composition does not occur. (For example, since the salt of one element first precipitates and grows into large particles, and then the next element microcrystals precipitate on the large particles, so in principle a sufficiently uniform precipitate is obtained. That is difficult.)

JP 2009-35447 A JP 2006-32132 A

  In the conventional LSCF fine particles prepared by a solid phase method, a coprecipitation method, or a slurry method, the present inventors have a problem in principle that the four component elements are not easily uniformed. Recognized. As a result of intensive studies from such a viewpoint, a raw material compound containing La, Sr, Co, and Fe is reacted with the organic acid in the liquid using an aqueous solution of an organic acid such as citric acid or maleic acid, and then complexed. It was found that by completely dissolving as a compound and spray drying in the form of fine droplets, new fine particles having a uniform composition were obtained even at a micro level that did not exist conventionally, and the present invention was completed. did.

  That is, an object of the present invention is to provide novel LSCF fine particles (powder) having a highly uniform composition suitable as an air electrode material for a solid oxide fuel cell, and to obtain LSCF fine particles having such a uniform composition. It is to provide a manufacturing method.

According to the present invention, the following air electrode material powder for a solid oxide fuel cell is provided.

[1] In an air electrode material powder for a solid oxide fuel cell, which has a perovskite structure and is a complex oxide composed of a lanthanum element, a strontium element, a cobalt element, an iron element, and an oxygen element,
The lanthanum element calculated from the peak area ratio of characteristic X-rays measured by an energy dispersive X-ray spectrometer (EDX) attached to the scanning electron microscope at a plurality of positions of the scanning electron microscope image (SEM image) of the powder. The content (w _a (wt%)) and the content (w _b (wt%)) of the element having a large content among the cobalt element or the iron element are determined so as to satisfy the relationship of the formula (1). The average content [w _a ] av (wt%) of the lanthanum element calculated from the contents at a plurality of positions, and the average content [w _b ] av (elements having a high content of the cobalt element or the iron element) wt%), the coefficient of variation (α) of the element having a large average content is 4.0% or less, and similarly the content of cobalt element (w _c (wt%)) and iron content of the element and _{(w d (wt%))} , the formula ( Relationship determined so as to satisfy the), the average content of cobalt element calculated from the content in a plurality of positions _{[w c] av (wt%} ) and the average content of iron element [w _d] av (wt% The air electrode material powder for a solid oxide fuel cell is characterized in that the coefficient of variation (β) of the element having a large average content is 2.0% or less.
w _a + w _b = 100 (wt%) (1)
w _c + w _d = 100 (wt%) (2)

[2] The air electrode material powder for a solid oxide fuel cell according to [1], wherein α is 1.3% or less and β is 2.0% or less.

[3] The composition formula of the composite oxide is represented by the general formula (I)
(La _1-x Sr _x ) _a Co _y Fe _1-y O ₃ (I)
(However, in the formula, 0.2 ≦ x ≦ 0.5, 0.1 ≦ y ≦ 0.6, 0.9 ≦ a ≦ 1.0.)
The air electrode material powder for a solid oxide fuel cell as described in the item [1] or [2], characterized in that

Moreover, according to this invention, the manufacturing method of the air electrode material powder for following solid oxide fuel cells is provided.

[4] The method for producing an air electrode material powder for a solid oxide fuel cell according to any one of [1] to [3], wherein the compound containing the metal element constituting the composite oxide is an organic acid. A method for producing an air electrode material powder for a solid oxide fuel cell, wherein the solution is made into a solution using an aqueous solution and calcined.

[5] The compound containing a metal element constituting the composite oxide is made into a solution using an aqueous solution of an organic acid, the solution is spray-dried using a spray dryer, and the dried powder is fired. The method for producing an air electrode material powder for a solid oxide fuel cell as described in the above item [4].

[6] The method for producing an air electrode material powder for a solid oxide fuel cell as described in [4] or [5] above, wherein the firing temperature is from 750 ° C. to 1250 ° C.

[7] The compound containing a metal element constituting the composite oxide is at least one selected from the group consisting of carbonate, oxide, hydroxide and organic acid salt of the metal element. The method for producing an air electrode material powder for a solid oxide fuel cell according to [4] or [5].

[8] The method for producing an air electrode material powder for a solid oxide fuel cell according to [4] or [5], wherein the organic acid is maleic acid or lactic acid.

[9] The organic acid is citric acid, and when the compound containing the metal element constituting the composite oxide is made into a solution using an aqueous solution of an organic acid, an ammonium compound is used at the same time. The method for producing an air electrode material powder for a solid oxide fuel cell according to [4] or [5] above.

[10] The solid oxide fuel according to [9], wherein the ammonium compound is at least one selected from the group consisting of ammonia, ammonium bicarbonate, ammonium carbonate, and ammonium citrate. Manufacturing method of air electrode material powder for battery.

As will be described in detail below, according to the present invention, new LSCF fine particles having a highly uniform composition can be provided as compared with the conventional solid phase method, coprecipitation method, and slurry method.
Further, according to the production method of the present invention, it is possible to obtain such highly uniform LSCF fine particles.

2 is a SEM photograph of LSCF fine particles in Example 1. 6 is an EDX mapping diagram of La in Example 1. FIG. 3 is an EDX mapping diagram of Sr in Example 1. FIG. 3 is an EDX mapping diagram of Co in Example 1. FIG. 3 is an EDX mapping diagram of Fe in Example 1. FIG. 4 is a SEM photograph of LSCF fine particles in Comparative Example 2. 10 is an EDX mapping diagram of La in Comparative Example 2. FIG. 10 is an EDX mapping diagram of Sr in Comparative Example 2. FIG. 6 is an EDX mapping diagram of Co in Comparative Example 2. FIG. 6 is an EDX mapping diagram of Fe in Comparative Example 2. FIG.

The present invention is basically directed to a solid oxide fuel cell air electrode material powder having a perovskite structure, which is a complex oxide having a composition represented by the general formula (I).

(La _1-x Sr _x ) _a Co _y Fe _1-y O ₃ (I)
(However, in the formula, 0.2 ≦ x ≦ 0.5, 0.1 ≦ y ≦ 0.6, 0.9 ≦ a ≦ 1.0.)
The composition of oxygen is stoichiometrically 3. However, depending on the case, it may be partially absent or exist excessively. The composite oxide of the present invention has a perovskite structure as a main component. (La _1-x Sr _x ) _a Co _y Fe _1-y O ₃ only needs to be included, and other impurity phases may exist.

  Here, in the formula, the ranges of x, y, and a are 0.2 ≦ x ≦ 0.5, 0.1 ≦ y ≦ 0.6, and 0.9 ≦ a ≦ 1.0. Is a preferred range for retaining the perovskite structure.

Specifically, examples of the composite compound LSCF represented by the formula (I) include the following, but are not limited thereto.
La _0.6 Sr _0.4 Co _0.2 Fe _0.8 O ₃
(LSCF: 6428, x = 0.4, y = 0.2, a = 1.0)

La _0.8 Sr _0.2 Co _0.2 Fe _0.8 O ₃
(LSCF: 8228, x = 0.2, y = 0.2, a = 1.0)

La _0.6 Sr _0.4 Co _0.4 Fe _0.6 O ₃
(LSCF: 6446, x = 0.4, y = 0.4, a = 1.0)

La _0.64 Sr _0.36 Co _0.18 Fe _0.82 O ₃
(LSCF: 6428, x = 0.36, y = 0.18, a = 1.0)

La _0.54 Sr _0.36 Co _0.2 Fe _0.8 O ₃
(LSCF: 6428, x = 0.4, y = 0.2, a = 0.9)

In the present invention, these composite oxides, LSCF powder (also referred to as fine particles), are obtained by the method defined in the present invention (this is referred to as “complete dissolution method”). Is characterized in that the composition of each component (La, Sr, Co, Fe) in the particles is very uniform with respect to the particles obtained by a conventionally known method.
In the present invention, in the composite oxide fine particles, the dispersion of components is evaluated and defined by relative standard deviation (variation coefficient: CV) as follows.

(I) That is, the characteristic X-ray peaks of the composite oxide fine particles measured by an energy dispersive X-ray spectrometer (EDX) attached to the scanning electron microscope at a plurality of positions of the scanning electron microscope image (SEM image). The content of the lanthanum element calculated from the area ratio (w _a (wt%)) and the content of the element having a high content of the cobalt element or the iron element (w _b (wt%)) are _expressed by the formula (1). determined so as to satisfy the relationship, the content at each location _{[w a] 1, [w} a] 2, [w a] 3, ··· and _{[w b] 1, [w} b] 2, [W _b ] ₃ ,... [Where [w _a ] ₁ + [w _b ] ₁ = 100 (wt%), [w _a ] ₂ + [w _b ] ₂ = 100 (wt%),. average content of the calculated elemental lanthanum from -] and _{[w a] av (wt%} ), of the cobalt element or iron element Average content of more elements of Yuryou when comparing the _{[w b] av (wt%} ), variation coefficient of large elements of average content (alpha) is less than 4.0% and,

(Ii) Similarly, the content of cobalt element (w _c (wt%)) and the content of iron element (w _d (wt%)) are determined so as to satisfy the relationship of formula (2), [W _c ] ₁ , [w _c ] ₂ , [w _c ] ₃ ,... And [w _d ] ₁ , [w _d ] ₂ , [w _d ] ₃ ,. , [W _c ] ₁ + [w _d ] ₁ = 100 (wt%), [w _c ] ₂ + [w _d ] ₂ = 100 (wt%),...] It is specified that the coefficient of variation (β) of elements having a large average content among [w _c ] av (wt%) and the average content of iron elements [w _d ] av (wt%) is 2.0% or less. is doing.
w _a + w _b = 100 (wt%) (1)
w _c + w _d = 100 (wt%) (2)

  In the present invention, weight% (wt%) is used as the same meaning as mass%, and the “element variation coefficient” refers to “the variation coefficient of the average content of elements”. To do.

In this regard, La _0.6 Sr _0.4 Co _0.2 Fe _0.8 O ₃
(LSCF: 6428, x = 0.4, y = 0.2, a = 1.0)
Will be further described with reference to FIG.
The LSCF (6428) is
ABO _3, that is, (La _0.6 Sr _0.4 ) (Co _0.2 Fe _0.8 ) O ₃ ,
The formula (1) w _a + w _b = 100 (wt%) stipulates the sum of the content of La at the A site and the content by weight% of the element having a large content of the B site, Here, the sum of the contents of La and Fe corresponds.
Further, the formula (2) w _c + w _d = 100 (wt%) represents the sum of the contents expressed by weight% of the elements at the B site, and corresponds to the sum of the contents of Co and Fe. .
In the present invention, first, by SEM-EDX measurement, the content [w _a ] _i of Fe (which is an element having a large content in the A site) and Fe (the B site) at a plurality of different measurement points in the SEM image. The content of La and Fe is determined from the peak area ratio of the characteristic X-ray so that the sum of the content of the element is a high content element. [W _a ] ₁ , [w _a ] ₂ , [w _a ] ₃ ,... [W _a ] _n and [w _b ] ₁ , [w _b ] ₂ , [w _b ] ₃ ,. [W _b ] _n is [w _a ] ₁ + [w _b ] ₁ = 100 (wt%), [w _a ] ₂ + [w _b ] ₂ = 100 (wt%),... [W _a ] _n + [W _b ] _n = 100 (wt%) (n ≧ 20) is satisfied. Next, the La and Fe contents at each measurement point are statistically processed to calculate the average contents of La and Fe ([w _a ] av, [w _b ] av) and the standard deviation.
On the other hand, for the Co and Fe elements in the B site, the Co and Fe contents at each measurement point are determined so that the sum of the Co content and the Fe content is 100 (wt%). The average content ([w _c ] av, [w _d ] av) and standard deviation are calculated.

Next, using the average content and the standard deviation obtained as described above, (i) La, which is an element in the A site, and La, which is an element having a large average content, among Fe, which is an element in the B site. The variation coefficient is obtained by dividing the standard deviation (variation) of the average content by the average value of the content.
Further, (ii) the coefficient of variation is similarly obtained for the variation in the average content of Fe having a large average content among Co and Fe as elements in the B site.
Note that, for the convenience of statistical processing, the EDX measurement is preferably performed at 20 points or more, and is performed at measurement points uniformly dispersed in the SEM image. For example, measurement is performed on 20 different points (n = 20) that are uniformly distributed in a lattice shape in the SEM image.

In the present invention, the element having a high content focused in this way is characterized by a very small coefficient of variation when the composition is evaluated by a coefficient of variation (CV) which is a measure of variation. . Specifically, in the above example,
C. of La which is an element having a larger average content of La and Fe. V. (Α) ≦ 4.0%
C. of Fe which is an element having a larger average content of Co and Fe. V. (Β) ≦ 2.0%,
More preferably,
C. of La which is an element having a larger average content of La and Fe. V. (Α) ≦ 1.3%
C. of Fe which is an element having a larger average content of Co and Fe. V. (Β) ≦ 2.0%.
(As shown in the comparative examples described later, the LSCF powder prepared by the conventional method varies greatly in composition, and its coefficient of variation CV (α, β) is defined by the present invention. It is shown to be much larger beyond the range.)

Hereafter, the general formula (I) according to the present invention
(La _1-x Sr _x ) _a Co _y Fe _1-y O ₃ (I)
The manufacturing method of the air electrode material for solid oxide fuel cells which has a composition represented by these is demonstrated.

(Adjustment of raw material powder)
The powder as a raw material of the air electrode material for a solid oxide fuel cell having the composition represented by the general formula (I) (La _1-x Sr _x ) _a Co _y Fe _1-y O ₃ according to the present invention is: Those usually used can be suitably used, and examples thereof include oxides, hydroxides, nitrates, carbonates, nitrates, and organic acid salts containing La, Sr, Co, and Fe.

In particular, carbonates, hydroxides or oxides are preferable from the viewpoint of environmental aspects and availability, and organic acid salts such as citrates are also preferable because of the high reactivity of the raw materials.
In addition, as the raw material, any two or more kinds of compounds selected from carbonates, oxides, hydroxides, nitrates, and the like per element can be selected as the element source.

The raw material powder is weighed so that each element of La, Sr, Co, and Fe has a target composition represented by the general formula (I).
In addition, it is preferable that each weighed raw material powder is pulverized and refined in advance so that the dissolution reaction can proceed rapidly. A part or all of them may be mixed uniformly in advance. Mixing may be performed by dry mixing. However, since a homogeneous raw material powder can be obtained in a relatively short time, it is preferable to perform mixing by a wet mixing method, and pulverization may be performed at the same time as mixing.

  An apparatus for carrying out the wet mixing method is not particularly limited, but an apparatus for carrying out pulverization at the same time is preferable. For example, a ball mill, a bead mill, an attrition mill, a colloid mill and the like are preferable. Of these, a type using a grinding medium such as zirconia balls, such as a ball mill and a bead mill, is more preferably used. For example, the above pulverization medium may be added to the raw material powder and pulverized and mixed for 12 to 24 hours using a ball mill. It is preferable to perform pulverization and mixing with a pulverizing medium such as a ball mill because a stronger shearing force can be applied and a more homogeneous raw material mixed powder can be obtained.

(Organic acid aqueous solution)
On the other hand, an aqueous solution of an organic acid is prepared in advance. The organic acid is not particularly limited as long as it can react with a compound containing the above metal element to form a complex thereof, and can be dissolved. For example, maleic acid, citric acid, malic acid, formic acid, acetic acid One or more selected from the group consisting of oxalic acid and lactic acid are preferred. Maleic acid, lactic acid or citric acid is particularly preferred.

  Here, when citric acid is used as the organic acid, and the compound containing the metal element constituting the composite oxide is made into a solution with an aqueous solution of the organic acid, the dissolution reaction ( Complex formation) is preferred because it can proceed more easily. Such an ammonium compound is preferably at least one selected from the group consisting of ammonia, ammonium bicarbonate, ammonium carbonate, and ammonium citrate. The ammonium compound is not particularly limited as long as it can dissolve the raw material powder. Since the raw material powder easily dissolves, it is preferable to use 1 to 10 equivalents with respect to the lanthanum compound.

  The amount of the organic acid used is preferably equal to or more than an equivalent amount capable of forming a complex with the metal element and completely dissolving it. The concentration of the aqueous solution of the organic acid is not particularly limited, but is 10 to 70% by weight, preferably 20 to 60% by weight, and more preferably 30 to 50% by weight because of ease of operation and a requirement to sufficiently increase the reaction rate. %.

(Dissolution reaction)
As described above, the powder of the compound containing the metal element constituting the adjusted composite oxide is made into a solution using the above-described aqueous solution of organic acid.
The apparatus for carrying out this dissolution reaction is not particularly limited. For example, the apparatus comprises a stirring means, a heating means, a raw material powder supply means, and an organic acid aqueous solution supply means, without causing the supplied raw material powder to precipitate. A tank-type reaction vessel that can be suspended and reacted with an organic acid in a suspended state is preferred. As the stirring means, any of ordinary stirrers such as a vertical stirrer, a propeller stirrer, a turbine stirrer and the like is preferably used. In the case of a small scale reaction, a flask type container may be provided with a stirrer.

The contact method of the metal element-containing compound powder and the organic acid aqueous solution is not particularly limited, but the reaction is grasped as a solid-liquid heterophasic reaction in chemical engineering, so that the reaction is carried out efficiently, There is no particular limitation as long as a uniform solution is finally obtained. Usually, it is preferable to first prepare an organic acid aqueous solution in a reaction vessel and add a raw material powder to the reaction vessel with stirring to react and dissolve.
The raw material powder to be added may be added sequentially for each powder, or the raw material powders may be mixed in advance, and the mixed powder may be supplied and reacted at the same time. Further, these supply methods may be combined.

  In addition, when adding raw material powder sequentially, first, a raw material compound containing one metal element, for example, lanthanum oxide powder, is supplied to an organic acid aqueous solution and dissolved under heating, and then the remaining elemental compound (for example, strontium carbonate) , Cobalt carbonate, iron citrate, etc.) may be added and reacted at the same time.

  The reaction temperature is preferable because the dissolution reaction is promoted by carrying out the reaction under a certain degree of heating. Usually, it is 30-100 degreeC, Preferably it is 50-90 degreeC, More preferably, it is 60-80 degreeC. The reaction time, that is, the time until a uniform solution is formed may vary depending on the reaction temperature, the organic acid concentration, the type of organic acid or the starting metal element-containing compound, its particle size, etc., but usually 10 minutes to 10 hours , Preferably 30 minutes to 5 hours, more preferably about 1 to 3 hours.

(Spray drying, etc.)
In the present invention, the solution thus obtained is dried using a box-type dryer such as a shelf dryer or a spray dryer such as a spray dryer. In particular, spray drying using a spray dryer is preferred.

  In spray drying, a solution in which each raw metal element is completely dissolved in an organic acid aqueous solution is supplied to a drying apparatus such as an air dryer or a spray dryer to perform drying. The solution supplied to the drying device becomes fine droplets in the device, which forms a fluidized bed with hot air for drying, and is dried in a very short time while being transported by the hot air. It is preferable because the obtained metal powder has high homogeneity of La, Sr, Co, and Fe metal elements.

  As a sprayer when using a spray dryer, a rotating disk, a two-fluid nozzle, a pressure nozzle, or the like can be appropriately employed. The hot air temperature for drying is 150 to 300 ° C. at the inlet and 100 to 150 ° C. at the outlet. It is preferable to make it about.

  According to such spray drying, a solution in which a homogeneous phase is formed and all the raw metal elements are dissolved forms a microdroplet state, and each droplet is evaporated or removed instantaneously or in a very short time. As a result, a dry powder (mixed powder) in which a solid phase having a completely uniform composition is deposited to a micro level in principle can be obtained.

(Baking)
Next, preferably, the spray-dried mixed powder is transferred to a firing container and fired in a firing furnace. Firing is preferably basically composed of three steps with different firing temperatures for rough firing, preliminary firing, and main firing, but may be two steps of rough firing and main firing, or two steps of preliminary firing and main firing, Moreover, the process which consists only of this baking which raises temperature one by one may be sufficient. The material of the firing container is not particularly limited, and examples thereof include mullite and cordierite.

  The firing furnace may be an electric or gas type shuttle kiln as a heat source, or may be a roller hearth kiln or a rotary kiln, and is not particularly limited.

(Coarse firing)
In the rough firing step, the temperature of the firing furnace is increased to a target firing temperature (300 to 500 ° C.) at a temperature rising rate of 20 to 800 ° C./hour. It is preferable to set the heating rate to 20 ° C./hour or more because the time to reach the target firing temperature is shortened and the productivity is improved. In addition, it is preferable to set the rate of temperature rise to 800 ° C./hour or less because the chemical change of the reactants at each temperature sufficiently proceeds.

  300-500 degreeC is preferable and the firing temperature at the time of rough baking has more preferable 350-450 degreeC. Setting the temperature to 300 ° C. or higher is preferable because the carbon component hardly remains. Moreover, since it becomes difficult to segregate a constituent element by making it 500 degrees C or less, it is preferable.

  The firing time for the rough firing is preferably 4 to 24 hours, and more preferably 8 to 20 hours. By setting it as 4 hours or more, since a carbon component becomes difficult to remain, it is preferable. Moreover, even if it exceeds 24 hours, there is no change in the product, but the productivity decreases, so it is preferable to make it 24 hours or less. This rough calcination may be held at a constant temperature, for example, 400 ° C. for 8 hours, or may be gradually increased from 300 ° C. to 460 ° C. at 20 ° C./hour.

  The atmosphere of the firing furnace at the time of rough firing is an oxygen-containing atmosphere, and is preferably in the air (in the air) or in an atmosphere having an oxygen concentration of 21% by volume or less. When the oxygen concentration exceeds 21% by volume, the carbon component in the raw material mixed powder burns, and as a result of partial oxidation reaction, the constituent elements of the product may be localized. It is preferable to make it. The oxygen concentration is preferably 15% by volume or less.

  After roughly firing for a predetermined time, the temperature is lowered to room temperature. The cooling rate is preferably 100 to 800 ° C./hour, more preferably 100 to 400 ° C./hour. The productivity is improved by setting the temperature lowering rate to 100 ° C./hour or more, which is preferable. Moreover, since the possibility that the baking container used by making this 800 degrees C / hr or less will be cracked by a thermal shock falls, it is preferable. In addition, when not changing a baking container and not crushing, you may transfer to the next temporary baking process, without lowering temperature from a rough baking process.

  Next, the oxide obtained in the rough firing step is crushed as necessary. For crushing, a crusher such as a cutter mill, a jet mill, or an atomizer is generally used and is dry. The volume average particle size after crushing is preferably 1 to 50 μm. More preferably, it is 10-20 micrometers.

(Temporary firing)
Subsequently, the coarsely fired powder pulverized as necessary is temporarily fired at a temporary firing temperature (500 to 800 ° C.).
In the preliminary firing step, the temperature of the firing furnace is raised to the target firing temperature at a temperature increase rate of 100 to 800 ° C./hour, preferably 100 to 400 ° C./hour. It is preferable to set the heating rate to 100 ° C./hour or more because the time to reach the target firing temperature is shortened and the productivity is improved. Further, it is preferable that the rate of temperature increase is 800 ° C./hour or less because the chemical change of the reactant at each temperature is sufficiently advanced.

  500-800 degreeC is preferable and the temperature of temporary baking is more preferable 500-700 degreeC. A temperature of 500 ° C. or higher is preferable because no carbon component remains. Moreover, since it becomes difficult to sinter a sintered powder excessively when it is 800 degrees C or less, it is preferable.

  The firing time is preferably 4 to 24 hours, and more preferably 8 to 20 hours. If it is 4 hours or longer, the carbon component hardly remains, which is preferable. Moreover, it is preferable that it is 24 hours or less because the product is not changed and the productivity is improved.

The atmosphere of the firing furnace at the time of temporary firing is preferably an oxygen-containing atmosphere similar to that during rough firing.
After pre-baking for a predetermined time, the temperature is lowered to room temperature. The cooling rate is preferably 100 to 800 ° C./hour, more preferably 100 to 400 ° C./hour. It is preferable that the temperature is 100 ° C./hour or more because productivity does not decrease. Moreover, since the target substance produces | generates that it is 800 degrees C / hr or less, it is preferable.

  Next, the oxide obtained by the preliminary calcination is crushed as necessary in the same manner as performed after the rough calcination. Crushing is generally performed by a dry method using a pulverizer such as a cutter mill, a jet mill, or an atomizer. The volume average particle size after crushing is preferably 1 to 50 μm. More preferably, it is 10-20 micrometers.

(Main firing)
Further, the calcined temporary pulverized powder is calcined at a main calcining temperature (700 to 1400 ° C.) as necessary.
In the main firing step, the temperature of the firing furnace is raised to the target firing temperature at a temperature rising rate of 50 to 800 ° C./hour, preferably 100 to 400 ° C./hour. A temperature increase rate of 50 ° C./hour or more is preferable because the time to reach the target firing temperature is shortened and productivity is improved. Further, when the rate of temperature increase is 800 ° C./hour or less, the chemical change of the reactant at each temperature does not proceed sufficiently, and the reactant does not reach the target firing temperature in a non-uniform state. Therefore, it is preferable because no by-product is generated in the fired product.

  700-1300 degreeC is preferable and the temperature of this baking is more preferable 750-1250 degreeC. It is preferable that the temperature is 700 ° C. or higher or 1300 ° C. or lower because a target crystal phase is generated.

  The firing time is preferably 4 to 24 hours, and more preferably 5 to 20 hours. It is preferable that the reaction time is 4 hours or longer because a product having a single crystal phase can be obtained without mixing unreacted substances in the target oxide. Moreover, when it is 24 hours or less, there is no change in the product and productivity is not lowered, which is preferable.

The firing furnace atmosphere during the main firing is preferably an oxygen-containing atmosphere similar to that during rough firing or temporary firing.
After performing the main baking for a predetermined time, the temperature is lowered to room temperature. The temperature lowering rate is preferably 100 to 800 ° C./hour. It is preferable that the temperature is 100 ° C./hour or more because productivity does not decrease. Moreover, since the target substance produces | generates that it is 800 degrees C / hr or less, it is preferable.

Next, the oxide obtained by the main firing is crushed in the same manner as performed after the rough firing. For crushing, a crusher such as a cutter mill, a jet mill, or an atomizer is generally used and is dry. The volume average particle size of the powder after pulverization is preferably 1 to 50 μm. More preferably, it is 10-20 micrometers. Thereafter, it may be pulverized in a wet manner to adjust the particle size as necessary.
Note that the above-described rough firing, temporary firing, and main firing may be performed continuously without lowering the temperature to room temperature after the completion of each step and without crushing after firing. That is, temporary baking may be performed continuously after rough baking, main baking may be performed continuously after temporary baking, or three steps of rough baking, temporary baking, and main baking may be performed continuously.

(Molded body, sintered body)
The powder (fine particles) obtained by the main firing as described above has a completely uniform composition (La _1-x Sr _x ) _a Co _y Fe _1-y O ₃ even when each fine particle is at a micro level. (LSCF), and by sintering this as a molded body, the molded sintered body can be suitably used as an air electrode for a solid oxide fuel cell. That is, it is understood that the molded sintered body supports a highly uniform fine particle composition as it is, and thus forms an extremely uniform LSCF sintered body in principle.

As a means for forming the formed body and the sintered body, a means known per se is applied. For example, first, powder of (La _1-x Sr _x ) _a Co _y Fe _1-y O ₃ is mixed with a binder, filled in a mold having a certain volume, and pressure is applied from above. Create a molded body.
The method of applying the pressure is not particularly limited, such as a mechanical uniaxial press, a cold isostatic press (CIP) press and the like.

Next, this molded body is heat-treated to obtain a sintered body. The heat treatment temperature is preferably 1000 to 1450 ° C. When the heat treatment temperature is 1000 ° C. or higher, the mechanical strength of the molded body is sufficiently maintained, and when it is 1450 ° C. or lower, a part of the generated LSCF is decomposed to form impurities and the composition may be nonuniform. It is preferable because it is not.
The heat treatment time is preferably 2 to 24 hours.

  Hereinafter, specific examples (Examples 1 to 5) of the present invention will be described in comparison with comparative examples (Comparative Examples 1 and 2). However, these examples are examples of embodiments of the present invention, and the present invention is not particularly limited to these examples, and is not construed as being limited thereto. In the following, “%” means mass (or weight) unless otherwise specified.

[Example 1]
(1) (Preparation of raw material powder and organic acid)
Each raw material was weighed so as to form La _0.6 Sr _0.4 Co _0.2 Fe _0.8 O ₃ .
That is, as shown in Table 1, 356.8 g of lanthanum oxide (La ₂ O ₃ ) as the La source, 215.7 g of strontium carbonate (SrCO ₃ ) as the Sr source, and Nihon Kagaku having a Co content of 46.58% as the Co source. 92.16 g of cobalt carbonate (CoCO ₃ ) manufactured by Sangyo Co., Ltd. and 876.7 g of iron citrate (FeC ₆ H ₅ O ₇ .nH ₂ O) having an Fe content of 18.56% as an Fe source (in terms of atomic ratio, La : Sr: Co: Fe is 0.6: 0.4: 0.2: 0.8)).

  On the other hand, in a 20 L separable flask, 3 equivalents to the number of moles of La ions, 2 equivalents to the number of moles of Sr ions and Co ions, respectively, and the number of moles of Fe ions are already in iron citrate. Since 1 mol of citric acid is present, an equivalent amount of 2908 g of citric acid was added to 4.0 L (liter) of pure water at 55 ° C. to prepare a citric acid solution. To this, 1037 g of ammonium bicarbonate (6 equivalents relative to the number of moles of La ions) was added and dissolved at 28 ° C. in a stirred tank reaction vessel.

(2) (Intermediate product and drying)
Lanthanum oxide was added to the citric acid solution, heated to 70 ° C., and reacted at that temperature for 2 hours. Lanthanum oxide was completely dissolved, and a colorless transparent solution was obtained.
To this, strontium carbonate, cobalt carbonate and iron citrate were added and reacted at the same temperature for another 2 hours. Each metal salt was completely dissolved, and a blackish brown transparent solution was obtained.

  After completion of the reaction, the resulting solution was dried with a spray dryer to obtain a composite citrate dry powder as an intermediate product. As a spray dryer, a BDP-10 type spray bag dryer (manufactured by Okawara Chemical Co., Ltd.) was used, and drying was performed under conditions of an inlet temperature: 200 ° C., an outlet temperature: 125 ° C., and an atomizer rotational speed: 15000 rpm.

(3) (Rough firing, provisional firing, main firing)
The obtained dry powder was filled into 4 mullite 30 cm square sheaths and baked in the electric furnace at 400 ° C. for 10 hours in the atmosphere to decompose the organic matter (coarse calcination). The rate of temperature increase from room temperature to 400 ° C. was 400 ° C./3 hours, and the rate of temperature decrease from 400 ° C. to room temperature was 400 ° C./4 hours.

  The obtained coarsely baked powder was filled in a mullite 30 cm square sheath and baked in the electric furnace at 600 ° C. for 10 hours in the atmosphere to decompose the remaining carbon (temporary calcination). The temperature increase rate from room temperature to 500 ° C. is 500 ° C./3 hours, the temperature increase time from 600 ° C. is 100 ° C./2 hours, and the temperature decrease rate from 600 ° C. to room temperature is 600 ° C./6 hours. I got a powder.

The calcined powder is packed in a mullite 30 cm square sheath and fired in an electric furnace at 800 ° C. for 6 hours in the air to obtain the final LSCF final powder (La _0.6 Sr _0.4 Co _0.2 Fe _0.8 O ₃ ) (Main firing) The temperature rising rate from room temperature to 700 ° C. is 700 ° C./4 hours, the temperature rising time from 800 ° C. is 100 ° C./1 hour, and the temperature decreasing rate from 800 ° C. to room temperature is 100 ° C./1 hour. It was. After the main firing, the fired powder was crushed to obtain La _0.6 Sr _0.4 Co _0.2 Fe _0.8 O ₃ powder.

(4) (Component analysis)
(I) XRD analysis A small amount of La _0.6 Sr _0.4 Co _0.2 Fe _0.8 O ₃ final powder was collected, and powder X-ray diffraction measurement using CuKα as an X-ray source was performed in order to identify the crystal phase. For the X-ray diffraction measurement, RINT2200V manufactured by Rigaku Corporation was used. As a result, a perovskite structure having rhombohedral crystals (113 phase) was confirmed.

(Ii) SEM and EDX analysis The powder was analyzed with a scanning electron microscope (SEM) and an energy dispersive X-ray spectrometer (EDX) attached thereto. The SEM used was FE-SEM S-4300 manufactured by Hitachi, and the EDX detector was EDX EMAX6853-H manufactured by Horiba, Ltd., with a resolution of 137 eV. Measurement conditions were tube voltage 40 kV, tube current 40 mA, magnification 3000 times, WD 15 mm, process time 4, and 4 million counts or more.

FIG. 1 is an SEM photograph (magnification × 3000) of the powder. 2 to 5 are mapping diagrams of La, Sr, Co, and Fe by EDX. From this, the segregation of each component was not confirmed but it was confirmed that it was distributed uniformly. On the SEM image of the powder as shown in FIG. 1, each side is divided into a lattice shape of about 8 μm, and 20 lattice points are used as point analysis points. Lanthanum element, strontium element, cobalt element at each lattice point, The characteristic X-ray of the iron element was measured. From the peak area, the content of the content and iron lanthanum element such that the content (w _a) and the content of iron element of lanthanum element in each measurement point (w _b) satisfies the relationship of formula (1) When the amount was calculated and the average of 20 points was taken, the average content of lanthanum and iron was 65.4 wt% and 34.6 wt%, respectively, as shown in Table 2, and the standard deviation was 0.57 w%. there were. Therefore, the variation coefficients of the lanthanum element and the iron element are 0.87% and 1.6%, respectively. V. (Α) was 0.87% (≦ 4.0%).

Further, the content of cobalt element (w _c (wt%)) and the content of iron element (w _d (wt%)) at 20 measurement points are determined so as to satisfy the relationship of formula (2). The average content of cobalt element and the average content of iron element were 21.5 wt% and 78.5 wt%, respectively, and the standard deviation was 0.74 wt%. Therefore, the coefficient of variation C.C. V. (Β) was 0.94% (≦ 2.0%).
w _a + w _b = 100 (wt%) (1)
w _c + w _d = 100 (wt%) (2)

(Iii) Particle size distribution measurement A sample was prepared by dispersing a small amount of La _0.6 Sr _0.4 Co _0.2 Fe _0.8 O ₃ in ion-exchanged water as follows. Using an aqueous solution having a concentration of 0.24% by weight using sodium diphosphate decahydrate manufactured by Wako Pure Chemical Industries, Ltd. as a dispersant, about 0.1 g of La _0.6 Sr _0.4 Co _0.2 Fe _0.8 O ₃ and a dispersion A dispersion was prepared so that the total volume was 10 ml, and a sample irradiated with ultrasonic waves for 3 minutes was used as a sample. The particle size distribution of La _0.6 Sr _0.4 Co _0.2 Fe _0.8 O ₃ was measured from the sample using a laser diffraction / scattering particle size distribution device LA-920 manufactured by HORIBA. Immediately before the measurement, ultrasonic treatment with an output of 30 W was performed for 180 seconds. As a result, the volume average particle diameter D ₅₀ was 15.1 μm.

[Example 2]
(1) Example 1, the citric acid solution was added ammonium carbonate 797g in place of ammonium bicarbonate, also addition to the main baking temperature and 1200 ° C. is performed the same experiment as in Example 1, La _0.6 A final powder represented by Sr _0.4 Co _0.2 Fe _0.8 O ₃ was obtained. (See Table 1)

In addition, the temperature program of the main firing is as follows: the temperature increase rate from room temperature to 700 ° C. is 700 ° C./4 hours; the temperature increase rate up to 1000 ° C. is 100 ° C./1 hour; the temperature increase rate up to 1200 ° C. is 200 ° C. / 3 hours. The rate of temperature decrease from 1200 ° C. to room temperature was 100 ° C./1 hour. After the main firing, the fired powder was crushed to obtain La _0.6 Sr _0.4 Co _0.2 Fe _0.8 O ₃ powder.

(2) (Component analysis)
(I) XRD analysis A small amount of the final powder of La _0.6 Sr _0.4 Co _0.2 Fe _0.8 O ₃ was collected and subjected to powder X-ray diffraction measurement in the same manner as in Example 1. As a result, it was confirmed that the powder had a perovskite structure having rhombohedral crystals (113 phase).

(Ii) SEM and EDX analysis The powder was analyzed with a scanning electron microscope (SEM) and an energy dispersive X-ray spectrometer (EDX) attached thereto in the same manner as in Example 1.
The surface state of the powder by SEM photograph and the mapping diagram of La, Sr, Co, and Fe by EDX were the same as in Example 1, but slight segregation was observed for Co, but overall It was confirmed that the distribution was almost uniform.

The content of the calculated elemental lanthanum from the peak intensity ratio of EDX characteristic X-ray measured in the same manner as in Example 1 and _{(w a (wt%))} , the content of iron element (w _b (wt%)) and Was determined so as to satisfy the relationship of the formula (1), and the average content of the lanthanum element and the average content of the iron element were calculated. As shown in Table 2, 66.4 wt%, 33 The coefficient of variation of the element with the larger average content (ie, La) is 6 wt%. V. (Α) was 2.1% (≦ 4.0%).

Further, when the content of cobalt element (w _c (wt%)) and the content of iron element (w _d (wt%)) are determined so as to satisfy the relationship of formula (2), The average contents of the iron element are 21.6 wt% and 78.4 wt%, respectively, and the coefficient of variation C. of the element having the higher average content (ie, Fe) is obtained. V. (Β) was 1.5% (≦ 2.0%) or less.
w _a + w _b = 100 (wt%) (1)
w _c + w _d = 100 (wt%) (2)

(Iii) Particle size distribution measurement The particle size distribution measurement was performed in the same manner as in Example 1. As a result, the volume average particle diameter D ₅₀ of La _0.6 Sr _0.4 Co _0.2 Fe _0.8 O ₃ was 15.7 μm.

[Comparative Example 1]
(1) (Intermediate product formed by adding raw material powder and organic acid)
Each raw material was weighed so as to form La _0.6 Sr _0.4 Co _0.2 Fe _0.8 O ₃ in the same manner as in Example 1. (See Table 1)
On the other hand, 2 L (liter) of pure water is added to a 20 L separable flask, lanthanum oxide is added and the liquid temperature is kept at 50 ° C., and the hydration reaction is performed for 2 hours (La ₂ O ₃ + 3H ₂ O → 2La (OH) ₃ ) Strontium carbonate, cobalt carbonate, and iron citrate were added thereto and dispersed for 1 hour. Further, 816 g of citric acid was added and reacted for 2 hours to obtain a brown slurry.
The amount of citric acid required is equivalent to the number of moles of La ions, Co ions, and Fe ions, and 2/3 equivalent to the number of moles of Sr ions.

(2) (Drying of intermediate product)
The prepared slurry obtained by adding citric acid was transferred to a stainless steel vat and dried for 1 day in a shelf dryer set at 110 ° C.

(3) (Rough firing, provisional firing, main firing)
The obtained dry powder was filled in four mullite 30 cm square sheaths, roughly baked in the same manner as Example 1 in an electric furnace in the atmosphere, and further pre-fired and main-fired. After the main firing, the fired powder was crushed to obtain La _0.6 Sr _0.4 Co _0.2 Fe _0.8 O ₃ powder.

(4) (Component analysis)
(I) XRD analysis A small amount of the final powder of La _0.6 Sr _0.4 Co _0.2 Fe _0.8 O ₃ was collected and subjected to powder X-ray diffraction measurement in the same manner as in Example 1. As a result, the powder is rhombohedral (113 phase): 84.0wt%, 214 _{Phase: 13.8wt%, La 2 O 3} : 0.2wt%, SrCO 3: and 2.0 wt%, impurity phase Many were included.

(Ii) SEM and EDX analysis The powder was analyzed with a scanning electron microscope (SEM) and an energy dispersive X-ray spectrometer (EDX) attached thereto in the same manner as in Example 1.
In the surface state of the powder by SEM photograph and the mapping diagram of La, Sr, Co, and Fe by EDX, considerable segregation was observed for La and Fe.

The content of the calculated elemental lanthanum from the peak intensity ratio of EDX characteristic X-ray measured in the same manner as in Example 1 and _{(w a (wt%))} , the content of iron element (w _b (wt%)) and Was determined so as to satisfy the relationship of the formula (1), and the average content of the lanthanum element and the average content of the iron element were calculated. As shown in Table 2, 66.6 wt%, 33 The coefficient of variation of the element with the higher average content (ie, La) is 4 wt%. V. (Α) was 6.4% (> 4.0%).

Further, when the content of cobalt element (w _c (wt%)) and the content of iron element (w _d (wt%)) are determined so as to satisfy the relationship of formula (2), The average contents of the iron element are 21.6 wt% and 78.4 wt%, respectively, and the coefficient of variation C. of the element having the higher average content (ie, Fe) is obtained. V. (Β) was 1.4% (≦ 2.0%) or less.
w _a + w _b = 100 (wt%) (1)
w _c + w _d = 100 (wt%) (2)

(Iii) Particle size distribution measurement The particle size distribution measurement was performed in the same manner as in Example 1. As a result, the volume average particle diameter D ₅₀ of La _0.6 Sr _0.4 Co _0.2 Fe _0.8 O ₃ was 15.3 μm.

[Comparative Example 2]
(1) In Comparative Example 1, the same experiment was conducted except that 162.7 g of iron oxide (Fe ₂ O ₃ ) was used instead of iron citrate as the Fe source, and the amount of citric acid to be added was 1429 g. The final powder represented by La _0.6 Sr _0.4 Co _0.2 Fe _0.8 O ₃ was obtained. (See Table 1)

(2) (Component analysis)
(I) XRD analysis A small amount of the final powder of La _0.6 Sr _0.4 Co _0.2 Fe _0.8 O ₃ was collected and subjected to powder X-ray diffraction measurement in the same manner as in Example 1. As a result, the powder was rhombohedral (113 phase): 40.6 wt%, 214 phase: 24.5 wt%, La ₂ O ₃ : 16.1 wt%, SrCO ₃ : 6.9 wt%, α-Fe _2. O ₃ : 9.3 wt% and SrFe ₁₂ O ₁₉ : 2.6 wt% consisted of a large number of impurity phases.

(Ii) SEM and EDX analysis The powder was analyzed with a scanning electron microscope (SEM) and an energy dispersive X-ray spectrometer (EDX) attached thereto in the same manner as in Example 1.
FIG. 6 shows an SEM photograph (magnification × 3000) of the powder. In addition, mapping diagrams of La, Sr, Co, and Fe by EDX are shown in FIGS. Considerable segregation was observed for La, Sr, and Fe.

The content of the calculated elemental lanthanum from the peak intensity ratio of EDX characteristic X-ray measured in the same manner as in Example 1 and _{(w a (wt%))} , the content of iron element (w _b (wt%)) and Was determined so as to satisfy the relationship of the formula (1), and the average content of the lanthanum element and the average content of the iron element were calculated. As shown in Table 2, 67.3 wt% and 32.32 respectively. The coefficient of variation of the element having a higher average content (ie, La) of 7 wt% C.I. V. (Α) was 37% (> 4.0%).

Further, the cobalt element when the content of the cobalt element (w _c (wt%)) and the content of the iron element (w _d (wt%)) are determined so as to satisfy the relationship of the formula (2) The average contents of iron and iron elements are 33.9 wt% and 66.1 wt%, respectively. V. (Β) was 43% (> 2.0%).
w _a + w _b = 100 (wt%) (1)
w _c + w _d = 100 (wt%) (2)

(Iii) Particle size distribution measurement The particle size distribution measurement was performed in the same manner as in Example 1. As a result, the volume average particle diameter D ₅₀ of La _0.6 Sr _0.4 Co _0.2 Fe _0.8 O ₃ was 15.5 μm.

Example 3
(1) (Preparation of raw material powder and organic acid)
Each raw material was weighed so as to form La _0.8 Sr _0.2 Co _0.2 Fe _0.8 O ₃ . That is, as shown in Table 1, 847.1 g of lanthanum carbonate (La ₂ (CO ₃ ) ₃ .8H ₂ O) as La source, 102.3 g of strontium carbonate (SrCO ₃ ) as Sr source, water as Co source 65.17 g of cobalt oxide (Co (OH) ₂ ) and 338.7 g of hydrous iron hydroxide (Fe (OH) ₃ ) having an Fe content of 45.58% as an Fe source (at an atomic ratio, La: Sr: Co : Fe is 0.8: 0.2: 0.2: 0.8)). On the other hand, 2078 g maleic acid and 4.0 L (55 liters) of pure water at 55 ° C. are added to a 20 L separable flask to prepare a maleic acid solution, which is stirred without adding an ammonium source such as ammonium bicarbonate. And dissolved at 28 ° C.

(2) (Intermediate product and drying)
Lanthanum carbonate was added to the above maleic acid solution, heated to 70 ° C., and reacted at that temperature for 2 hours. Lanthanum carbonate was completely dissolved, and a colorless transparent solution was obtained.
To this, strontium carbonate, cobalt hydroxide, and iron hydroxide were added and reacted at the same temperature for another 2 hours. Each metal salt was completely dissolved, and a blackish brown transparent solution was obtained.

  After completion of the reaction, the obtained solution was dried with a spray dryer to obtain a dry powder of complex maleate as an intermediate product. In addition, as a spray dryer, the same BDP-10 type spray bag dryer (made by Okawara Kako Co., Ltd.) as Example 1 was used, and it dried on the conditions similar to Example 1. FIG.

(3) (Rough firing, provisional firing, main firing)
The obtained dry powder was roughly fired and temporarily fired under the same conditions as in Example 1.

The calcined powder is packed in a mullite 30 cm square sheath, fired in the air in an electric furnace at 750 ° C. for 6 hours, and after pulverization, the LSCF final powder (La _0.8 Sr _0.2 Co _0.2 Fe _0.8 O ₃ ) got. (Main firing)
The temperature increase rate from room temperature to 750 ° C. was 750 ° C./4 hours, and the temperature decrease rate from 750 ° C. to room temperature was 750 ° C./6 hours.

(4) (Component analysis)
(I) XRD analysis A small amount of La _0.8 Sr _0.2 Co _0.2 Fe _0.8 O ₃ final powder was collected, and powder X-ray diffraction measurement using CuKα as an X-ray source was performed in order to identify the crystal phase. For the X-ray diffraction measurement, RINT2200V manufactured by Rigaku Corporation similar to Example 1 was used. As a result, a perovskite structure having rhombohedral crystals (113 phase) was confirmed.

(Ii) SEM and EDX analysis The powder was analyzed with a scanning electron microscope (SEM) used in Example 1 and an energy dispersive X-ray spectrometer (EDX) attached thereto.
The surface state of the powder by SEM photograph and the mapping diagram of La, Sr, Co, and Fe by EDX were the same as in Example 1, and no segregation was observed.

The content of the calculated elemental lanthanum from the peak intensity ratio of EDX characteristic X-ray measured in the same manner as in Example 1 and _{(w a (wt%))} , the content of iron element (w _b (wt%)) and Was determined so as to satisfy the relationship of the formula (1), and the average content of the lanthanum element and the average content of the iron element were calculated. As shown in Table 2, 85.2 wt% and 14.5 respectively. The coefficient of variation of the element having a higher average content (ie, La) of 8 wt% C.I. V. (Α) was 0.90% (≦ 4.0%).

Further, when the content of cobalt element (w _c (wt%)) and the content of iron element (w _d (wt%)) are determined so as to satisfy the relationship of formula (2), The average content of the iron element is 21.4 wt% and 78.6 wt%, respectively, and the coefficient of variation C. of the element with the higher average content (ie, Fe) is as follows. V. (Β) was 1.0% (≦ 2.0%) or less.
w _a + w _b = 100 (wt%) (1)
w _c + w _d = 100 (wt%) (2)

(Iii) Particle size distribution measurement The particle size distribution measurement was performed in the same manner as in Example 1. As a result, the volume average particle diameter D ₅₀ of La _0.8 Sr _0.2 Co _0.2 Fe _0.8 O ₃ was 15.9 μm.

Example 4
(1) (Preparation of raw material powder and organic acid)
Each raw material was weighed so as to form La _0.6 Sr _0.4 Co _0.4 Fe _0.6 O ₃ .
That is, as shown in Table 1, 414.4 g of lanthanum hydroxide (La (OH) ₃ ) as a La source, 178.9 g of strontium hydroxide (Sr (OH) ₂ ) as a Sr source, and Co content as a Co source Cobalt carbonate (CoCO ₃ ) 183.8 g made by Nippon Chemical Industry Co., Ltd. with an amount of 46.58%, and 267.0 g hydrous iron hydroxide (Fe (OH) ₃ ) with an Fe content of 45.58% as an Fe source ( In terms of atomic ratio, La: Sr: Co: Fe is set to 0.6: 0.4: 0.4: 0.6). On the other hand, 2082 g of lactic acid and 4.0 L (liter) of 55 ° C. pure water were prepared in a 20 L separable flask to prepare a lactic acid solution, which was stirred without adding an ammonium source such as ammonium bicarbonate. It was dissolved at 28 ° C.

(2) (Intermediate product and drying)
Lanthanum hydroxide was added to the lactic acid solution, heated to 70 ° C., and reacted at that temperature for 2 hours. Lanthanum hydroxide was completely dissolved, and a colorless transparent solution was obtained.

  To this, strontium hydroxide, cobalt carbonate and hydrous iron hydroxide were added and reacted at the same temperature for another 2 hours. Each metal salt was completely dissolved, and a blackish brown transparent solution was obtained.

  After completion of the reaction, the obtained solution was dried with a spray dryer to obtain a dry powder of complex lactate as an intermediate product. In addition, as a spray dryer, the same BDP-10 type spray bag dryer (made by Okawara Kako Co., Ltd.) as Example 1 was used, and it dried on the conditions similar to Example 1. FIG.

(3) (Rough firing, provisional firing, main firing)
The obtained dry powder was roughly fired and temporarily fired under the same conditions as in Example 1.

The pre-fired powder is filled in a mullite 30 cm square sheath and fired in an electric furnace at 1000 ° C. for 6 hours in the atmosphere to obtain the final LSCF final powder (La _0.6 Sr _0.4 Co _0.4 Fe _0.6 O ₃ ) (Main firing)
The rate of temperature increase from room temperature to 700 ° C. was 700 ° C./4 hours, and the rate of temperature increase to 1000 ° C. was 100 ° C./1 hour. The rate of temperature decrease from 1000 ° C. to room temperature was 100 ° C./1 hour.

(4) (Component analysis)
(I) XRD analysis A small amount of the final powder of La _0.6 Sr _0.4 Co _0.4 Fe _0.6 O ₃ was collected, and powder X-ray diffraction measurement using CuKα as an X-ray source was performed in order to identify the crystal phase. For the X-ray diffraction measurement, RINT2200V manufactured by Rigaku Corporation similar to Example 1 was used. As a result, a perovskite structure having rhombohedral crystals (113 phase) was confirmed.

(Ii) SEM and EDX analysis The powder was analyzed with a scanning electron microscope (SEM) used in Example 1 and an energy dispersive X-ray spectrometer (EDX) attached thereto.
The surface state of the powder by SEM photograph and the mapping diagram of La, Sr, Co, and Fe by EDX were the same as in Example 1, and no segregation was observed.

The content of the calculated elemental lanthanum from the peak intensity ratio of EDX characteristic X-ray measured in the same manner as in Example 1 and _{(w a (wt%))} , the content of iron element (w _b (wt%)) and Was determined so as to satisfy the relationship of the formula (1), and the average content of the lanthanum element and the average content of the iron element were calculated. As shown in Table 2, 66.2 wt% and 33.3%, respectively. The coefficient of variation of the element having a higher average content (ie, La) of 8 wt% C.I. V. (Α) was 1.6% (≦ 4.0%).

Further, when the content of cobalt element (w _c (wt%)) and the content of iron element (w _d (wt%)) are determined so as to satisfy the relationship of formula (2), The average content of iron element is 41.3 wt% and 58.7 wt%, respectively, and the coefficient of variation C. of the element with the higher average content (ie, Fe) is shown. V. (Β) was 1.2% (≦ 2.0%).
w _a + w _b = 100 (wt%) (1)
w _c + w _d = 100 (wt%) (2)

(Iii) Particle size distribution measurement The particle size distribution measurement was performed in the same manner as in Example 1. As a result, the volume average particle diameter D ₅₀ of La _0.6 Sr _0.4 Co _0.4 Fe _0.6 O ₃ was 16.1 μm.

Example 5
(1) (Final powder preparation)
Each raw material was weighed so as to form (La _0.6 Sr _0.4 ) _0.9 Co _0.2 Fe _0.8 O ₃ . That is, as shown in Table 1, 342.8 g of lanthanum oxide (La ₂ O ₃ ) as a La source, 207.3 g of strontium carbonate (SrCO ₃ ) as a Sr source, and Co content of 46.58% as a Co source 98.40 g of cobalt carbonate (CoCO ₃ ) manufactured by Nippon Chemical Industry Co., Ltd. and 936.0 g of iron citrate (FeC ₆ H ₅ O ₇ .nH ₂ O) having an Fe content of 18.56% as an Fe source (atomic ratio) Then, La: Sr: Co: Fe is 0.54: 0.36: 0.2: 0.8)). On the other hand, 2893 g of citric acid equivalent to the number of moles of La ions, 2 equivalents of moles of Sr ions and Co ions, and 2 moles of moles of Fe ions were added to a 20 L separable flask at 55 ° C. In addition to 4.0 L (liter) of pure water, a citric acid solution was prepared. To this was added 996 g of ammonium bicarbonate (6 equivalents to La metal) and dissolved at 28 ° C.
Thereafter, the same treatment as in Example 1 was carried out to obtain (La _0.6 Sr _0.4 ) _0.9 Co _0.2 Fe _0.8 O ₃ powder.

(2) (Component analysis)
(I) XRD analysis A small amount of (La _0.6 Sr _0.4 ) _0.9 Co _0.2 Fe _0.8 O ₃ final powder was fractionated, and powder X-ray diffraction measurement using CuKα as an X-ray source was performed to identify the crystal phase. . For the X-ray diffraction measurement, RINT2200V manufactured by Rigaku Corporation similar to Example 1 was used. As a result, a Co ₃ O ₄ phase was observed as an impurity phase in addition to a phase having a perovskite structure having rhombohedral crystals (113 phase). However, as will be described later, no segregation of Co is observed in the EDX analysis, and it is considered that Co ₃ O ₄ as an impurity is because very fine crystals are uniformly dispersed among particles of perovskite crystals.

(Ii) SEM and EDX analysis The powder was analyzed with a scanning electron microscope (SEM) used in Example 1 and an energy dispersive X-ray spectrometer (EDX) attached thereto.
The surface state of the powder by SEM photograph and the mapping diagram of La, Sr, Co, and Fe by EDX were the same as in Example 1, and no segregation was observed.

The content of the calculated elemental lanthanum from the peak intensity ratio of EDX characteristic X-ray measured in the same manner as in Example 1 and _{(w a (wt%))} , the content of iron element (w _b (wt%)) and Was determined so as to satisfy the relationship of the formula (1), and the average content of the lanthanum element and the average content of the iron element were calculated. As shown in Table 2, 60.5 wt% and 39. The coefficient of variation of the element having a higher average content (ie, La) of 5 wt% C.I. V. (Α) was 1.1% (≦ 4.0%).

Further, the cobalt element when the content of the cobalt element (w _c (wt%)) and the content of the iron element (w _d (wt%)) are determined so as to satisfy the relationship of the formula (2) The average contents of iron and iron elements are 21.3 wt% and 78.7 wt%, respectively, and the coefficient of variation C. of the element with the larger average content (ie, Fe) is obtained. V. (Β) was 1.1% (≦ 2.0%).
w _a + w _b = 100 (wt%) (1)
w _c + w _d = 100 (wt%) (2)

(Iii) Particle size distribution measurement The particle size distribution measurement was performed in the same manner as in Example 1. As a result, the volume average particle size D ₅₀ of (La _0.6 Sr _0.4 ) _0.9 Co _0.2 Fe _0.8 O ₃ was 15.1 μm.
The above results are summarized in Tables 1 and 2.

As described in detail above, according to the present invention, the air electrode for a solid oxide fuel cell having a perovskite structure and being a complex oxide composed of a lanthanum element, a strontium element, a cobalt element, an iron element, and an oxygen element In the material powder, new LSCF fine particles having a more highly uniform composition than those obtained by the conventional solid phase method, coprecipitation method, and slurry method are provided. When this highly uniform LSCF fine particle is sintered as a molded body, the sintered body supports this uniform composition, so that it is reasonably expected that an LSCF sintered body of extremely uniform composition can be obtained in principle. Can do.
Further, according to the production method of the present invention, it is possible to obtain such highly uniform LSCF fine particles, so that the industrial applicability is great.

Claims (10)

In the air electrode material powder for a solid oxide fuel cell, which has a perovskite structure and is a complex oxide composed of a lanthanum element, a strontium element, a cobalt element, an iron element, and an oxygen element,
The lanthanum element calculated from the peak area ratio of characteristic X-rays measured by an energy dispersive X-ray spectrometer (EDX) attached to the scanning electron microscope at a plurality of positions of the scanning electron microscope image (SEM image) of the powder. The content (w _a (wt%)) and the content (w _b (wt%)) of the element having a large content among the cobalt element or the iron element are determined so as to satisfy the relationship of the formula (1). The average content [w _a ] av (wt%) of the lanthanum element calculated from the contents at a plurality of positions, and the average content [w _b ] av (elements having a high content of the cobalt element or the iron element) wt%), the coefficient of variation (α) of the element having a large average content is 4.0% or less, and similarly the content of cobalt element (w _c (wt%)) and iron content of the element and _{(w d (wt%))} , the formula ( Relationship determined so as to satisfy the), the average content of cobalt element calculated from the content in a plurality of positions _{[w c] av (wt%} ) and the average content of iron element [w _d] av (wt% The air electrode material powder for a solid oxide fuel cell is characterized in that the coefficient of variation (β) of the element having a large average content is 2.0% or less.
w _a + w _b = 100 (wt%) (1)
w _c + w _d = 100 (wt%) (2)
2. The air electrode material powder for a solid oxide fuel cell according to claim 1, wherein the α is 1.3% or less and β is 2.0% or less.
The composite oxide has a general formula (I)
(La _1-x Sr _x ) _a Co _y Fe _1-y O ₃ (I)
(However, in the formula, 0.2 ≦ x ≦ 0.5, 0.1 ≦ y ≦ 0.6, 0.9 ≦ a ≦ 1.0.)
The air electrode material powder for a solid oxide fuel cell according to claim 1, wherein the air electrode material powder is represented by:
The method for producing an air electrode material powder for a solid oxide fuel cell according to any one of claims 1 to 3, wherein the compound containing the metal element constituting the composite oxide is dissolved using an aqueous solution of an organic acid. And a method for producing an air electrode material powder for a solid oxide fuel cell, characterized by firing.
5. The compound containing a metal element constituting the composite oxide is made into a solution using an aqueous solution of an organic acid, the solution is spray-dried using a spray dryer, and the dried powder is fired. The manufacturing method of the air electrode material powder for solid oxide fuel cells as described in any 1 item | term.
6. The method for producing an air electrode material powder for a solid oxide fuel cell according to claim 4, wherein the firing temperature is from 750 ° C. to 1250 ° C.
The compound containing a metal element constituting the composite oxide is at least one selected from the group consisting of carbonate, oxide, hydroxide and organic acid salt of the metal element. The manufacturing method of the air electrode material powder for solid oxide fuel cells of Claim 4 or Claim 5.
The method for producing an air electrode material powder for a solid oxide fuel cell according to claim 4 or 5, wherein the organic acid is maleic acid or lactic acid.
The organic acid is citric acid, and when the compound containing the metal element constituting the composite oxide is made into a solution using an aqueous solution of an organic acid, an ammonium compound is used at the same time. A method for producing an air electrode material powder for a solid oxide fuel cell according to claim 4 or 5.
The air electrode material for a solid oxide fuel cell according to claim 9, wherein the ammonium compound is at least one selected from the group consisting of ammonia, ammonium bicarbonate, ammonium carbonate, and ammonium citrate. Powder manufacturing method.

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