JP2984750B2 - Calcium Dopran Tank Chromite Powder, Sintered Body Thereof, Solid Electrolyte Fuel Cell Using It, and Method for Synthesizing Calcium Dopran Tank Chromite Powder - Google Patents

Description

Description: FIELD OF THE INVENTION The present invention relates to a calcium doptolan chromite powder, a sintered body thereof, a solid oxide fuel cell using the same, and a method for synthesizing a calcium dope lanthanum chromite powder. . More specifically, the present invention relates to a calcium dopran tank chromite powder for a sintered body that can be sintered at a low temperature for a short time, a method for synthesizing the same, a sintered body, and a solid oxide fuel cell using the same. It is.

(Prior Art) Calcium dopantran chromite (hereinafter abbreviated as lanthanum chromite) -based oxide is not only chemically stable in an oxidation-reduction atmosphere but also has a high electron conductivity. It is suitable as a separator for a solid oxide fuel cell operating at a high temperature as shown in FIG. 3 (A) and FIG. 3 (B). The separator 4 is for connecting a plurality of unit cells 1 in which a fuel electrode 11 and an air electrode 10 are combined so as to sandwich the solid electrolyte 9 by stacking a plurality of cells in series with spacers 2 and 3 interposed therebetween. In FIGS. 3A and 3B, reference numerals 8 and 8 denote pipes for supplying a fuel gas to a space 6 partitioned by the spacer 2, and 7 and 7 denote pipes for supplying the fuel gas to the space 5 partitioned by the spacer 3. It is a pipe for supplying air.

Incidentally, as described above, the sintered body of lanthanum chromite used as the separator 4 is required not only to have excellent chemical stability and electron conductivity in an oxidation-reduction atmosphere and the like, but also to have a cross leak between fuel gas and air. It is required to have high airtightness to prevent (mixing of fuel gas and air through the separator material).

However, in the conventional method for firing lanthanum chromite into a separator component, that is, in the method of firing in air, chromium oxide evaporated from lanthanum chromite powder and hexavalent chromium which is easily evaporated are removed. Since the containing compound sinters in the process of evaporating and re-condensing, it is impossible to obtain an air-tight sintered body because of densification caused by intraparticle diffusion.

Therefore, as a means for solving this problem, conventionally, high-temperature sintering (for example, 1700 ° C) in a reducing atmosphere
Before and after), a method in which aluminum (Al), copper (Cr), zinc (Zn), etc. are added to the B site in the perovskite crystal structure of lanthanum chromite and sintered.
Various means such as a method of adding an alkaline earth metal to the A site or the B site and sintering, and a method of adding and sintering a sintering aid such as a fluoride have been studied.

(Problems to be Solved by the Invention) However, even with these conventional methods, a high firing temperature and a reducing atmosphere are required even if an airtight crystal cannot be obtained or an airtight crystal is obtained. For this reason, there are problems such as difficulty in manufacturing.

Therefore, when lanthanum chromite is used as a separator in a solid oxide fuel cell, the fuel gas and the oxidant gas sent to the fuel electrode and the air electrode cross-leak through the separator, causing a decrease in the battery output, resulting in poor catalytic characteristics. This causes the internal resistance of the battery to decrease and causes an increase in the internal resistance of the battery, the evaporation of the sintering aid causes a decrease in the characteristics of other battery constituent materials, and the sintering temperature of the separator is high. When the firing method, that is, the co-sintering method, is employed, the characteristics of other battery constituent materials are impaired. For this reason, each component of the solid oxide fuel cell,
It cannot be manufactured at once by the co-sintering method, but requires a bonding and assembling process using an adhesive or the like, which causes a problem that the manufacturing cost is increased.

Therefore, the present invention and the like use La
(1-x) Lanthanum chromite mainly composed of CaxCr (1-y) O ₃ , wherein the values of x and y are 0 <x ≦ 0.4 (1) 0 <y ≦ 0.05... (2) y ≦ x... (3)

In the lanthanum chromite raw material powder, chromium is insufficient, and the amount of chromium evaporated can be reduced to improve sinterability, so that a separator having excellent airtightness can be realized. In addition, chemical stability in an oxidation-reduction atmosphere or the like required for a separator, high electron conductivity, and the like can be obtained. However, since the sintering conditions are the sintering conditions (1600 ° C., 5 to 10 hours) that simultaneously inactivate the air electrode material (eliminate the catalytic properties) and diffuse the fuel electrode material, the solid electrolyte type fuel is still used. A battery cannot be manufactured at once by a co-sintering method. For this reason, according to the separator molded with the conventional lanthanum chromite powder,
It must be fired separately from other battery constituent materials and then assembled using an adhesive or the like, and it is very difficult to reduce the manufacturing cost.

SUMMARY OF THE INVENTION An object of the present invention is to provide a calcium dopran tank chromite powder for a sintered body that can be sintered at a low temperature for a short time and a method for synthesizing the same. Another object of the present invention is to provide a solid oxide fuel cell which is suitable as a separator material and can be produced by a co-sintering method with other cell components.

(Means for Solving the Problems) In order to achieve the above object, the lanthanum chromite powder of the present invention has a molar ratio of each element of the main components of the mixture before synthesizing the calcium dope lanthanum chromite powder.
La: Ca: Cr = (1-x): x: (1-y) and x, y, z
Satisfying (1), (2), (3) 0 <x ≦ 0.4 (1) 0 <y ≦ 0.05 (2) y ≦ x (3) The mixture is degreased at a temperature of 400 ° C or less,
The temperature is raised rapidly to a temperature of about 900-1100 ° C. at a rate of 300 ° C./hour or more, and the reaction is carried out at that temperature for 5 hours or more.

Further, the dense calcium dopantran chromite sintered body of the present invention is obtained by firing the above powder at a relatively low temperature.

Further, the solid oxide fuel cell of the present invention, by a separator or connection terminal made by firing the above powder,
It is characterized in that unit batteries are connected in series and in parallel.

Here, the lanthanum chromite oxide of the present invention, that is,
A lanthanum chromite having La (1-x) CaxCr (1-y) O ₃ as a component, wherein x and y are the above (1), (2),
The mixture having the composition region of the formula (3) is not particularly limited to the method for producing the mixture, and any mixture produced by any method such as a powder method, a coprecipitation method, and a sol-gel method can be used. 400 ° C for the mixture prepared by any method
Degreasing at the following temperature, 9
The temperature is rapidly raised to a temperature of about 00-1100 ° C., and the reaction is carried out at this temperature for 5 hours or more, whereby the calcium doprantan chromite powder of the present invention can be obtained. The powder can then be heated rapidly and hermetically sintered at low temperature in a short time.

(Action) When the above unheated mixture in which the mixing ratio of the main components of La, Ca, and Cr is within a predetermined value is degreased at a temperature of 400 ° C. or more, the powder is cooled to a temperature lower than the conventional sintering temperature (for example, 1200 ~ 1400 ℃)
Cannot be sintered densely. But 400 ° C
If degreased at the following temperature, it can be densely sintered at a low temperature (1200-1400 ° C.). To explain this state physically,
Although it is not clear yet, it is considered that if the temperature is raised to 400 ° C. or more, a compound containing hexavalent chromium, which is difficult to be sintered in the powder, is produced.

When the temperature of the defatted powder is rapidly increased at a rate of 300 ° C./h or more, a compound containing hexavalent chromium, which is difficult to sinter, does not appear in the powder, and pure calcium dough which is easy to sinter is obtained. Plantan chromite can be synthesized. By using this powder, a dense sintered body can be produced at a low temperature (1200 to 1400 ° C.). A dense sintered body cannot be produced at a low temperature with a calcium dopantran chromite powder fired at a heating rate of less than 300 ° C./hour.

Since calcium dopantran chromite has a unique crystal structure called a perovskite structure, diffusion of ions during the reaction is extremely unlikely to occur. But,
After the above-mentioned temperature rise, the powder is held for 5 hours or more to promote the diffusion of ions and to synthesize calcium doptolan chromite more purely. Retention time 5
If the time is less than the time, the diffusion of ions may be insufficient.

(Examples) Hereinafter, the configuration of the present invention will be described in detail based on examples shown in the drawings.

The calcium dopantran chromite powder of the present invention is a ceramic containing La, Ca, and Cr as main components. The main component of the mixture before synthesizing this powder is that the molar ratio of each element is La: Ca: Cr = (1-x): x: (1-y), and x,
The values of y and z are adjusted so as to satisfy the conditions of 0 <x ≦ 0.4, 0 <y ≦ 0.05, and y ≦ x. The mixture having the above-mentioned composition range is not particularly limited to the production method, and the mixture produced by any method such as a powder method, a coprecipitation method, and a sol-gel method can be used.

For example, FIG. 1 shows a method for synthesizing a lanthanum chromite powder by a coprecipitation method.

First, lanthanum nitrate A, calcium nitrate B, and chromium nitrate C are dropped into an ethanol solution D in which excess oxalic acid is dissolved (step). Next, the mixed solution is dried by means such as blowing or heating (step). Further, it is heated at a temperature of 400 ° C. or less to degrease it (step). Thereafter, using an organic solvent or the like, mixing is performed in a ball mill or the like (step). The obtained mixture is rapidly heated to a temperature of 900 ° C. to 1100 ° C. at a temperature increasing rate of 300 ° C./h or more, and further kept at that temperature range for 5 hours or more to obtain a lanthanum chromite powder (step).

Example 1 lanthanum nitrate _{(La (NO 3) 3 ·} 6H 2 O) 401g, calcium nitrate _{(Ca (NO 3) 2 ·} 4H 2 O) 100g, chromium nitrate (Cr (N
_{O 3) 3 · 9H 2 O} ) 529g were mixed and added dropwise to this excess oxalic acid ((COOH) in ₂ · 2H ₂ O) ethanol solution prepared by dissolving the. Thereafter, the mixed solution was dried to obtain La: Ca: Cr = (1
-X): x: (1-y) and the values of x, y, z are 0 <x ≦ 0.4,
A mixture having a composition ratio satisfying 0 <y ≦ 0.05 and y ≦ x, that is,
A mixture having a composition ratio of La _0.7 Ca _0.32 CrO ₃ was obtained. Then, the temperature was raised rapidly to 1000 ° C at a rate of 300 ° C / h or more, and
After holding for 0 hour, lanthanum chromite powder was obtained. This lanthanum chromite powder was mixed with a ball mill using ethanol to obtain the lanthanum chromite powder of the present invention.

Sintering experiment The powder obtained by the above-mentioned synthesis method is pressed into a pellet having a diameter of 20 mm and a thickness of 1 to 2 mm using a pelletizer as a raw material, and a relatively low temperature region of 1100 to 1400 ° C. in air. Was fired for an arbitrary time, and the time required for the sintered body to have the required hermeticity was determined. Here, the relatively low temperature region is a temperature lower than the firing temperature of the conventional lanthanum chromite, for example, higher than the conventional firing temperature of 1600 to 1700 ° C.
It means a region that is lower by about 200 ° C. and does not affect other battery constituent materials.

The result is shown in FIG. FIG. 2 is a diagram showing the relationship between the sintering temperature and the sintering time and the relative density. The hatched area in the figure indicates that gas permeation, which is suitable for use as a separator of a solid oxide fuel cell, Shows no airtight sintered body area. Specifically, it indicates a region where the relative density of the sintered body is 94% or more.

From this experimental result, when the lanthanum chromite powder of the present invention is used, when the maximum sintering temperature is 1300 ° C., 5
It can be understood that a dense sintered body can be obtained without a holding time when the maximum temperature is set to 1400 ° C. with the firing time within the time. The firing conditions, that is, the firing conditions of 5 hours at 1300 ° C. and no holding time at 1400 ° C. are firing conditions that have little effect on the characteristics of other fuel cell components such as the fuel electrode and the air electrode. is there.

Therefore, if the sintered body obtained by firing the calcium doptolan chromite powder of the present invention is used as a separator 4 of a solid oxide fuel cell as shown in FIG. 3, for example, or as a connector such as spacers 2 and 3 If used, it can be manufactured at once by a co-sintering method with the main components of the electrolyte fuel cell. As shown in FIGS. 3 (A) and (B), an example of a configuration as a separator of a flat solid electrolyte fuel cell is shown in an exploded perspective view. In the fuel cell, a flat unit cell 1 and a separator 4 are alternately stacked via spacers 2 and 3, and an air supply space 5 and a combustion gas supply space 6 formed by the unit cell 1 and the separator 4 are formed.
At this time, the combustion gas and the air are supplied via the fuel gas supply pipe 7 and the air supply pipe 8, respectively. Furthermore, the cell 1
Are the air electrode 10 and the fuel electrode 11 on the front and back sides of the solid electrolyte 9.
Is formed. As the separator 4 or the spacers 2 and 3 of such a fuel cell, the calcium dopran tank chromite sintered body according to the present invention is used.

According to the result of manufacturing a solid oxide fuel cell using the separator made of the raw material powder of the present invention, it is expected that a fuel cell having better power generation performance than the conventional one can be manufactured easily and at low cost.

The above-described embodiment is an example of a preferred embodiment of the present invention, but is not limited thereto, and various modifications can be made without departing from the spirit of the present invention. For example,
In the above-described embodiment, only the case where the present invention is applied to a solid oxide fuel cell is described. However, the present invention is not particularly limited to this, and the lanthanum chromite powder of the present invention is chemically stable and has electronic conductivity. Therefore, even when used as an electrode of an air furnace heater or an MHD generator that operates at a high temperature, a combustion catalyst, or the like, an effect can be obtained.

(Effects of the Invention) As is clear from the above description, according to the lanthanum chromite powder of the present invention, a calcium dopran tank chromite sintered body that is excellent in chemical stability, electron conductivity, and airtightness is of the same type. Can be fired at a relatively low temperature and in a shorter time than the conventional product. Therefore, when molding a sintered body having excellent airtightness using the lanthanum chromite powder, for example, a separator of a solid oxide fuel cell, the maximum sintering temperature lower than before, for example, 1300 to 1400 ° C. and manufactured in a short time Therefore, other constituent materials of the solid oxide fuel cell such as the air electrode and the fuel electrode are not adversely affected. For this reason, since the separator and other cell constituent materials of another solid oxide fuel cell can be fired at a time, the manufacturing cost can be significantly reduced. Of course, this also applies to the case where the present invention is applied to other high-temperature operating bodies requiring chemical stability, electron conductivity, and the like.

[Brief description of the drawings]

FIG. 1 is an explanatory diagram showing an example of the method for producing a lanthanum chromite raw material powder of the present invention. FIG. 2 is a graph showing the relationship between the calcination conditions and the degree of hermeticity during calcination of the calcium dopantran chromite powder of the present invention. FIG. 3A is a perspective view illustrating an example of the configuration of a solid oxide fuel cell, and FIG. 3B is a longitudinal sectional view thereof. 2,3 ... Spacer as connection terminal, 4 ... Separator.

Continuing from the front page (72) Inventor Tatsuya Kawada 1-1-1 Higashi, Tsukuba, Ibaraki Pref., Institute of Chemical Technology, Industrial Technology Institute (72) Inventor Natsuko Sakai 1-1-1, Higashi, Higashi, Tsukuba, Ibaraki Pref. Investigator Daiji Daikohara (56) References JP-A-2-111632 (JP, A) JP-A-3-261621 (JP, A) (58) Fields investigated (Int. Cl. ⁶ , DB name) C01G 37 / 00 C04B 35/00

Claims (4)

(57) [Claims] (1) The molar ratio of each element of the main components of the mixture before the synthesis of calcium dopantran chromite powder is as follows:
La: Ca: Cr = (1-x): x: (1-y) and x, y, z
Satisfying (1), (2), (3) 0 <x ≦ 0.4 (1) 0 <y ≦ 0.05 (2) y ≦ x (3) The mixture was degreased at a temperature of 400 ° C or less, rapidly heated to a temperature of 900-1100 ° C at a rate of 300 ° C / hour or more, and reacted at this temperature for 5 hours or more. A calcium dopamine chromite powder. 2. A calcium dopantlan chromite sintered body produced by firing the calcium dopantlan chromite powder according to claim 1 at a relatively low temperature for a short time. 3. A solid electrolyte type wherein unit cells are connected in series and in parallel by a separator or a connection terminal formed by firing the calcium dopantran chromite powder according to claim 1. Fuel cell. 4. The molar ratio of each of the main components of the mixture before the synthesis of the calcium dopantran chromite powder is as follows:
La: Ca: Cr = (1-x): x: (1-y) and x, y, z
(1), (2), (3) 0 <x ≦ 0.4 (1) 0 <y ≦ 0.05 (2) A mixture satisfying y ≦ x (3) Is degreased at a temperature of 400 ° C or less, and then 3
A method for synthesizing a calcium dopran tank chromite powder, wherein the temperature is rapidly raised to a temperature of about 900 to 1100 ° C. at a temperature rising rate of 00 ° C./hour or more, and the reaction is further performed at this temperature for 5 hours or more.