JPH0465355A - Production of oxide sintered compact having electric conductivity - Google Patents

Abstract

PURPOSE:To inexpensively obtain an oxide sintered compact excellent in heat resistance, electric conductivity, etc., and having high density by mixing a compound of lanthanide element, a Ca or Sr compound, and a Co, Mn, or Ni compound in a specific ratio, subjecting the resulting mixture to heat treatment, to crushing, and to compacting, and then sintering the resulting green compact in an atmosphere with low partial pressure of oxygen. CONSTITUTION:An R compound [e.g. La(OH)3], an A compound (e.g. CaCO3)r a Cr compound (e.g. Cr2O3), and an M compound (e.g. NiO) are blended in the ratio where a sintered compact having a composition represented by formula (where R means lanthanide element, A means Ca or Sr, M means Co, Mn, or Ni, 0.02<=x<=0.25, and 0<y<=0.15) can be obtained, and they are uniformly mixed. Subsequently, the resulting mixture is heat-treated and synthesized into a perovskite type crystalline structure. Then, the synthesized powder is dispersed and crushed and the crushed matter is compacted, and the resulting green compact is sintered at >=1400 deg.C in an atmosphere of <=0.01atm partial pressure of oxygen, by which the oxide sintered compact having heat resistance and electric conductivity represented by the formula can be obtained.

Description

[Detailed description of the invention] Industrial applications The present invention relates to a method for manufacturing a conductive oxide sintered body.

Prior art and its problems A part of R of a sintered body represented by the formula RCr 03 (R represents at least one kind of lanthanide; the same applies hereinafter) is Ca
or R(Ca or 5r)CrO with solid solution substitution with Sr
3, particularly La(Ca or 5r)CrO3, is known as a high melting point, heat resistant, conductive oxide having a perovskite crystal structure. However, since this material is a non-sintered material, it is difficult to obtain a dense sintered body, and it is used in a state with open pores.

Also, the formula: R (Ca or S r) MO3 (M is Mn
, represents at least one of Ni and Co; the same applies hereinafter)
The sintered bodies represented by also have a perovskite crystal structure and are known as oxides that have higher conductivity and are easier to sinter than R(Ca or 5r)CrO3. It has the problem of poor heat resistance and significantly reduced conductivity in a reducing atmosphere.

Conventionally, this type of oxide sintered body, for example, La (Ca or Sr) Com3 sintered body,
It is manufactured by weighing o3, CO203, and CaCO2 or SrCO2 at a predetermined ratio, mixing them, calcining to create a synthetic powder, press-molding, and then firing at 1500°C or higher. However, such a sintered body has low corrosion resistance and lacks stability because the component represented by M easily evaporates and reacts. Furthermore, when using such a sintered body as a fuel cell interconnector, there are problems such as a significant decrease in conductivity, especially on the fuel electrode side, and deterioration due to reaction with contact materials. .

When producing La(Ca or 5r)CrO3 sintered bodies, attempts have also been made to perform sintering at higher temperatures. However, in this case, the amount of evaporation of Cr increases, which not only makes it difficult to obtain a sintered body having a predetermined composition, but also makes it uneconomical in terms of firing equipment and firing energy.

In addition, when producing R(Ca or 5r)Cr03,
By changing the composition ratio in the raw materials and increasing the proportion of R (Ca or Sr), R (Ca or 5r) CrO3 and R (C
a or Sr) has a eutectic point with R(Ca or 5r)C
Attempts have been made to perform sintering by taking advantage of the fact that the melting point is lower than that of r03, but in this case, excess components precipitate at grain boundaries, leading to weathering and reduced conductivity. There is a drawback.

Means to Solve the Problems The inventor of the present invention, while keeping in mind the problems of the prior art as described above, has conducted repeated research and found that the difficulty in sintering R(Ca or 5r)CrO3 is simply due to the difficulty of sintering R(Ca or 5r)CrO3. It was discovered that this is not only because it is a high melting point material, but also because Cr, the main component, evaporates during the sintering process and is precipitated and condensed at the grain boundaries, inhibiting the diffusion of each atom.

Furthermore, in subsequent research, when lowering the oxygen partial pressure during sintering and substituting a part of Cr with M, each constituent atomic It was also found that grain boundary diffusion between grains was promoted. The present invention was completed based on such new knowledge.

That is, the present invention provides a method for manufacturing a conductive oxide sintered body as described below, which includes: (1) a sintered body finally obtained; The composition of R,.A,Cr-,M,0
3 (However, R is at least one kind of lanthanide element; A
is at least one of Ca and Sr; M is Co, M
At least one of n and Ni 0.02≦X≦0.25
;0<y≦015), a step of blending the respective compounds of R, A, Cr and M and uniformly mixing them;
(2) A step of heat-treating the obtained mixture to synthesize a perovskite-type crystal structure, (3) A step of dispersing and pulverizing the obtained synthetic powder, (4)
A step of molding the obtained pulverized product, and (5) molding the obtained molded product at 1350°C in an atmosphere with an oxygen partial pressure of 0.1 atm or less.
A method for producing a conductive oxide sintered body, comprising a step of firing at a temperature above. ” The conductive oxide sintered body obtained in the present invention has R, -0A,
Cr,-,M,,03 (wherein, R is at least one of lanthanide elements; A is at least one of Ca and Sr; M is at least one of Co, Mn, and Ni, 0.02≦X≦0. 25.

Q<y≦0.15).

Lanthanide elements are lanthanum with atomic number 57 to 71
It means 15 elements up to lutetium. Lanthanide element sources include oxides, hydroxides, nitrates, carbonates,
It is used in the form of compounds such as sulfates, chlorides, and oxalates. Lanthanide elements may be used alone or in combination of two or more. As the lanthanide element, La5Nd and Pr are more preferable, and it is particularly preferable to use La alone or a mixture of La and other lanthanide elements. As lanthanide elements, La,
When Nd or Pr is used, the conductivity of the sintered body is improved and the heat resistance is also improved. On the other hand, when using these elements, it is necessary to sinter at high temperature in order to obtain a high-density sintered body, so if the purpose is to lower the sintering temperature, some of the It is preferable to replace (approximately 10 to 30 mol %) with another lanthanide element.

In the present invention, a part (0.02 to 0.25 mol) of R is added to Ca and Sr (hereinafter referred to as this) in an oxide with a perovskite structure having a basic composition of RCr,-,,M,03. It is essential that the two be substituted and dissolved in solid solution by at least one of the following (sometimes simply referred to as A). When replacing trivalent R with divalent A, the resulting lack of charge on the cation can be compensated for by replacing the transition metal Cr or M.
Due to the valence variation of , it becomes a complementary structure. As a result, this variation contributes to a significant improvement in conductivity. If the amount of substitution of R by A is less than 2 mol%, the conductivity will not be sufficiently improved, whereas if it exceeds 25 mol%, no further improvement in the conductivity will be observed. As well,
Rather, the sinterability deteriorates during manufacturing. The amount of substitution of R by A is more preferably 5 to 20 mol%. C
As the a source and the Sr source, oxides, hydroxides,
Compound forms such as nitrates, carbonates, sulfates, chlorides, and oxalates are used.

As a Cr source, oxides, hydroxides, nitrates, carbonates,
It is used in the form of compounds such as sulfates, chlorides, and oxalates.

Furthermore, in the present invention, in a perovskite structure whose basic composition is RACrO3, a part of Cr is M
(That is, at least one of Mn, Ni, and Co) must be substituted as a solid solution. Generally, the electrical conductivity and sinterability improve in proportion to the amount of M substituted, but the stability, heat resistance, and corrosion resistance of the sintered body decrease. Individually, these elements include Mn, which reduces the conductivity in a reducing atmosphere, Co, which increases thermal expansion and also reduces the conductivity in a reducing atmosphere, and N1, which reduces the conductivity in a reducing atmosphere. It tends not to improve conductivity as much as Ca. Therefore, the upper limit of the total amount of M should be 0.15 mol, preferably about 0.02 to 0.1 mol, more preferably about 0.02 to 0.05 mol. As an M source,
It is also used in the form of compounds such as oxides, hydroxides, nitrates, carbonates, sulfates, chlorides, and oxalates.

In the sintered body of the present invention, (R,, A,) and (Cr, □
Although it is desirable that the ratio of M, ) is equimolar, a range of 0.98 to 1.02 moles of the latter to 1 mole of the former is acceptable. If the ratio of both is slightly away from equimolar within the above range, oxides of R, A, Cr and M are formed and eutectic at a temperature lower than the melting point of the perovskite crystal. , sintering may be easier than in the case of equimolar compositions. If the ratio of (Cr i-y M, This is undesirable because it causes the formation of

On the other hand, the ratio of (cr 1-y 'M, ) is 1.02
If it exceeds the molar amount, a small amount of Cr2 is present at the grain boundaries of the sintered body.
O3 and M2O3 are formed and the conductivity decreases.

The method of the present invention is carried out as follows.

First, raw materials serving as Ri, A source, Cr source, and M source are blended so that the ratio of each component at the time of producing a sintered body is within a predetermined range, and mixed and pulverized to obtain a uniform powder mixture. Although the particle size of the powder is not particularly limited, it is preferably 5 μm or less.

Generally, in the synthesis process, etc., it is preferable to mix a slightly larger amount of the M source or the M source and the C source because M tends to diffuse into the container. This point can be determined as appropriate by considering the sintering temperature and time, but for example,
When sintering at 1650°C for 3 hours, the Cr source or M source should be added to about 0.2% by weight (C
It is preferable to add a large amount of the compound (as r203 or M2O3). The mixing may be performed by either wet mixing or dry mixing of powders, or by mixing aqueous solutions of each raw material.

Next, the powder mixture obtained above is heat-treated at a temperature or higher at which 70% or more thereof becomes a perovskite structure of R(Ca,Sr)(CrM)03 to obtain a synthetic powder. This heat treatment temperature may vary depending on the type, particle size, mixing method, etc. of each raw material compound constituting the powder mixture, but is usually 600
~1500°C, more preferably 80°C
It is within the range of 0 to 1350°C. If the heat treatment temperature is too low, shrinkage during sintering, which will be described later, will increase, causing sintering distortion, which is not preferable. On the other hand, if the heat treatment temperature is too high, the crystal grain size of the synthesized powder becomes too large, which reduces sinterability, which is also not preferable.

The heat treatment time is also related to the heat treatment temperature, but usually O15
It takes about 3 hours.

Next, the synthetic powder obtained above is dispersed or pulverized.

This dispersion or pulverization is preferably carried out in the presence of an organic solvent such as water or alcohol. Dispersion or grinding is
The average particle size of the obtained powder is 2 μm or less and the specific surface area is 2c [li/g or more, more preferably the average particle size is 1 μm.
The specific surface area is 4 cr! It is preferable to carry out the treatment to the extent that it is 1/g or more. When dispersing or pulverizing this synthetic powder, A
At least one of 9203, MgO1Ti02 and Zr2O3 may be added in an amount not exceeding 2 parts by weight. These exhibit the effect of improving sinterability during sintering, which will be described later, without substantially reducing the conductivity and heat resistance of the sintered body.

Next, the powder dispersed or pulverized to a predetermined particle size is molded into a predetermined shape according to conventional methods for molding ceramics, that is, by methods such as CIP, mechanical press, casting, injection, extrusion, and tape molding. At this time, it goes without saying that additives such as known acrylic molding aids may be used in combination.

Next, the obtained molded body is fired. The atmosphere during firing may be any one of reduced pressure, normal pressure, and increased pressure, but it is essential that the oxygen partial pressure in the atmosphere be maintained at 0.1 atmosphere or less. Examples of means for maintaining the oxygen partial pressure in the atmosphere below 0.1 atm include reducing the pressure and replacing the atmosphere with an inert gas such as N2, Ar, or He. Alternatively, carbon may be present to create a CO atmosphere. When firing in such an atmosphere, the material of the present invention, which is difficult to sinter, can be sintered densely at a relatively low temperature. This densification of the sintered body is not only due to the reduction in evaporation of Cr and M under low oxygen partial pressure, but also due to the active interaction of their diffusion energy with each constituent atom. It is assumed that. The oxygen partial pressure in the firing atmosphere is 10-2 to 1
It is more preferable to set the pressure to about 0-6 atm. Further, the firing temperature is usually within a range of about 1350 to 1850°C, and more preferably about 1450 to 1750°C. When pressure sintering is performed, the sintered body can be densified at a lower temperature. If the amount of A component and M component is small, it may be necessary to increase the firing temperature.

The oxide sintered body thus obtained is estimated to have R, -8A, (Cr, M) 03-13, and has decreased conductivity. Therefore, in the present invention, the oxide sintered body is heated at 1000°C in an atmosphere with an oxygen partial pressure of 0.1 atm or more, more preferably 0.2 atm or more.
The conductivity can be improved by heat treatment at a temperature higher than
- It is preferable to do so.

The higher the oxygen partial pressure, the more significant the improvement in conductivity becomes. The upper limit of the heating temperature is not particularly limited, but is 13
The purpose is fully achieved at about 50°C. When the above firing is performed in an N2 atmosphere or in the presence of carbon, C
It is presumed that a small amount of nitrides or carbides such as r and M components are formed to further promote densification, but these nitrides or carbides are also converted into oxides by this heat treatment. Note that this heat treatment does not necessarily need to be performed subsequent to the sintering treatment, and may be performed as a result during the process of using the oxide sintered body, as long as the above conditions are satisfied.

The density of the conductive oxide sintered body produced by the method of the present invention reaches 95% or more of the theoretical density.

Effect of the invention According to the present invention, the following remarkable effects can be achieved.

(1) High-density La (Ca) with excellent heat resistance stability and conductivity, which was impossible to produce using conventional technology.

S r ) (Cr, M) 03 sintered body can be manufactured at low cost.

(2) Because of its excellent heat resistance at high temperatures, the sintered body according to the present invention can be used, for example, as a heating element, an electrode, etc.
Its period of use will be significantly extended.

(3) Furthermore, because of its high density, the sintered body of the present invention maintains a high degree of airtightness even in an oxidizing or reducing atmosphere when used, for example, as an interconnector for solid fuel cells. Can maintain conductivity over a long period of time.

(4) Therefore, the conductive oxide sintered body according to the present invention is economical in use.

EXAMPLES Examples and comparative examples are shown below to further clarify the features of the present invention.

Examples 1 to 4 and Comparative Example 1 Each powder of La (OH)3, Cr203, CodSNi○ and CaCO3 was converted to La0.9 Cao l Cro9Coo 05N j
o Co0 or 0.0 than 0503 composition. After mixing and dispersing the mixture in a wet manner in the presence of water, it is dried and heat-treated at 1100°C for 2 hours to achieve a ratio of 2% by weight or more. A powder was obtained.

The obtained synthetic powder was milled in the presence of water for 24 hours using a whole mill.
The powder was wet-milled for hours to obtain a powder with an average particle size of 1.0 μm. Next, after adding an acrylic molding aid to this, a spray dryer is used to form granular powder (average particle size 60 μm) for molding.
was prepared. This granular powder was molded under a pressure of 2 ton/c♂
Machine press molded into 60mm x 60mm x 5m
After obtaining a molded article of m, it was fired under the conditions shown in Table 1, and then heat treated in the air at 1300° C. for 2 hours.

The properties of the obtained sintered body are shown in Table 2.

Example Comparative Example 1 Table 1 Firing conditions Atmosphere oxygen partial pressure (atm) Yu○-2 1,510-' In reduced pressure carbon (air+N2) Firing conditions (°C) Table 2 Characteristics of sintered body Relative density Conductivity Electric skewer (%) (10006C8/cm) Example 1
96 17 Comparative Example 1 '87
13 As is clear from the results shown in Table 2, according to the present invention, a sintered body with high density and high conductivity was developed.

As a result of the analysis, the sintered bodies of Example 1 and Comparative Example 1 lacked Ni by 0.05% compared to the blended composition, and the other examples had an approximately equimolar ratio. It turned out that it was.

Examples 5 to 6 Sintered bodies obtained in the same manner as in Example 2 were subjected to oxygen partial pressures of 1 atm (Example 5) and 5 atm (Example 6).
) at 1300℃ for 1 hour, the density of the sintered body did not change, but the electrical conductivity decreased by 2.
53/cm and 33S/cm.

Examples 7-10 and Comparative Examples 2-3 La A sintered body was produced in the same manner.

Table 3 shows the properties of the obtained sintered body.

Table 3 Properties of sintered body X Firing temperature Relative density Electrical conductivity (%) (%) (1000℃8/(1) Comparative example 2
0.01 1670 93 1. 5 Example 7 0
．． 03 1670 96 68 0.08 1620
98 26 9 0.15 1620 99 36 10 0.25 ], 620 96 30 Comparative Example 3
0.3 1620 94 20 As is clear from the results shown in Table 3, the sintered body of the present invention in the range of 0.02≦X0125 has high density and high conductivity.

In addition, in the same firing process as in Example 8, 1
50kg/cr! When sintering was performed under a pressure of 1,600 °C, the temperature was 1,600 °C! A 99.5% sintered body was obtained.

Examples 11 to 13 and Comparative Example 4 La)-x-z Cat Srx Cro, 9 Co
Example 3 except that the values of X and 2 of the sintered body having the composition shown by o, o, Nio, 0503 were changed to those shown in Table 4.
A sintered body was produced in the same manner.

Table 4 shows the properties of the obtained sintered body.

Table 4 Characteristics of sintered body xz Relative density Electrical conductivity (%') (1000℃S/a) Example 11 0 0.03 97 612
0 0.1099 2613 0.05 0
．． 10 98 37 Comparative Example 4 0.15 0.1
5 94 21 As is clear from the results shown in Table 4, even when Ca and Sr are used together, the total amount is 0.
The sintered body of the present invention having a content in the range of 0.02 to 0.25 mol% has a high density and high conductivity.

Examples 14-21 and Comparative Examples 5-8 Lao 9 Cao, ossro, os (Cr,
-y M y ) Cr of the sintered body having the composition shown by 03
Amount and M (at least one of C○, Mn and Ni)
A sintered body was produced in the same manner as in Example 3, except that the amount and firing temperature were changed as shown in Table 5.

Table 6 shows the properties of the obtained sintered body.

Table 5 Example 14 Comparative example 5 Example 16 Comparative example 6 C.

C.

C.

Mn Mn n 0.01 0.1 0.1B 0.01 0.1 0.2 Yu620 Table 5 (continued) Example] 8 Example 19 Comparative example 7 Ni I C.

Mn Mn Ni C.

Ni C.

Mn 0.01 0.1 O2O3 0,02 0,05 0,05 0,1 0,1 0,06 0,05 0,05 Example 14 Comparative example 5 ■7 Comparative example 6 Example 18 Comparative example 7 6 Sintered Relative Density (%) Characteristic Electrical Conductivity of Surface (1000°C 8/cm) All the obtained sintered bodies had high density and high electrical conductivity. However, the conductivity in the atmosphere (6th
Table), the conductivities at 1000°C in a hydrogen atmosphere are 115 or more for the sintered bodies of Examples 14, 16, 18, 19 and 20, and the sintered bodies of Examples 15, Near and 21 have a In the case of the compact, it was 1/8 or more, whereas in the sintered compacts of Comparative Examples 5, 6, 7 and 8, it was significantly reduced to 1/10 or less.

Furthermore, the sintered bodies of Comparative Examples 5.6.7 and 8 lacked thermal stability, had poor thermal shock resistance, and were easily corroded by contact with ZrO2.

Examples 22 to 24 A sintered body of the present invention was obtained by carrying out the same operation as in Example 3 except that the firing temperature was set to 1600° C. and the following points were changed. The results are also shown below.

*Example 22 Nd was used instead of La.

Relative density of sintered body -98% Electrical conductivity of sintered body = 13 (1000°C S/cm) *Example 23: 20% of La was changed to Nd.

Relative density of sintered body -97% Electrical conductivity of sintered body -25 (1000°C 8/cm) *Example 24: 10% of La was changed to Gd.

Relative density of sintered body -99% Electrical conductivity of sintered body -22 (1000°C 8/cm) Example 2
5 La(NO3):+, Cr in aqueous solution state as raw materials, respectively
(NO3) 3, CO (NO3) 3, N i (
Using NOq)3 and Ca(NO3)2,
After mixing these, neutralizing, and drying the precipitate, 750
A synthetic powder with a perovskite structure was produced by heat treatment at ℃.

Next, using this synthetic powder, the same operation as in Example 2 was carried out (however, the firing temperature was 1600°C) to obtain a sintered body with a relative density of 97%.

Example 26 A sintering aid of 0.00% AQ203 was added to the synthetic powder obtained in the same manner as in Examples 1 to 4. An amount of AR corresponding to 5% by weight
(OC3H7)3 was blended and a sintered body was obtained in the same manner as in Example 3.

While the relative density at 1580°C of the sintered body of Example 3, which did not use a sintering aid, was 96%, the relative density of the sintered body of this example was improved to 98%, and the electrical conductivity was also 24%. (
IO00℃8/cm) Ni improvement LJ, -0 (or more) Procedural filing (spontaneous) August 8, 1990 1990 Patent Application No. 178870 2 Relationship with the title of invention case Patent applicant Nihon Kagaku Togyo Co., Ltd. 4 agent Sawanotsuru Building flD6, 2-1-2 Hirano-cho, Chuo-ku, Osaka (
203) [1941 (652)) Patent attorney Eiji Saegusa --> (Fuku 5 Date of amendment %, "Voluntary 6 Amendment subject to amendment page 13 line 14 r2cut/gJ"
Correct it to '1''/gJ.

Specification page 13 line 16 r4cd/g J's r4r
Correct it as rl''/g J.

Specification page 14, line 1 “Zr2O3” is corrected as “Zr02J.

a a a (Hereafter Up)

Claims (1)

[Claims] (1) A method for producing a conductive oxide sintered body, comprising: (1)
The composition of the finally obtained sintered body is R_1_-_x Ax Cr_1_-_y M_y O
_3 (However, R is at least one kind of lanthanide element; A is at least one kind of Ca and Sr; M is Co
, at least one of Mn and Ni; 0.02≦x≦0
．． 25; R, A, C with a ratio of 0<y≦0.15)
A step of blending the respective compounds of r and M and mixing them uniformly. (2) A step of heat-treating the obtained mixture to synthesize a perovskite-type crystal structure. (3) Dispersing and pulverizing the obtained synthetic powder. (4)
A step of molding the obtained pulverized product, and (5) molding the obtained molded product at 1350°C in an atmosphere with an oxygen partial pressure of 0.1 atm or less.
A method for producing a conductive oxide sintered body, comprising a step of firing at a temperature above. (2) The method according to claim 1, wherein the atmosphere having an oxygen partial pressure of 0.1 atm or less is created by reducing pressure. (3) The method according to claim 1, wherein the atmosphere having an oxygen partial pressure of 0.1 atmosphere or less is formed in the presence of an inert gas. (4) The method according to claim 1, wherein an atmosphere having an oxygen partial pressure of 0.1 atm or less is formed in the presence of carbon. (5) Conductive oxide sintering, characterized in that the sintered body produced by the method according to claim 1 is further subjected to oxidation heat treatment at a temperature of 1000° C. or higher in an atmosphere with an oxygen partial pressure of 0.1 atm or higher. How the body is manufactured. (6) A conductive oxide sintered body produced by the method according to claim 1 or 5, wherein the density is 95% or more of the theoretical density.