JP4106442B2 - Method for producing Dy-doped nano-ceria-based sintered body having uniform microstructure - Google Patents

Description

  The present invention relates to a Dy-doped nano-ceria-based sintered body having a high-density and uniform microstructure used for an oxygen sensor, a carbon dioxide sensor, a nitric oxide sensor, a solid electrolyte for a fuel cell, and the like, and a method for producing the same About.

Ceria-based sintered bodies doped with rare earth elements are known to have high electrical conductivity, and ceria-based sintered bodies doped with samarium (Sm) or gadolinium (Gd) as rare earth elements have been published in various literatures. (For example, for the ceria-based sintered body doped with Sm, refer to Non-Patent Documents 1 to 3, and for the ceria-based sintered body doped with Gd, refer to Non-Patent Documents 4 to 6). However, when a sintered body was actually produced and its electrical conductivity was measured, the electrical conductivity was −1.8 and −1.5 (S / cm, respectively) at 700 ° C. by the direct current three-terminal method. ) And was not enough. In order to apply the solid electrolyte to various gas sensors and fuel cells, it is required to ensure high conductivity at a low temperature. Among these, when the ceria-based sintered body doped with the Dy element has a particle diameter of 1 micron or more, the conductivity is lower than the value of the ceria-based sintered body doped with Sm, Gd or the like (0 A Dy _0.2 Ce _0.8 O _1.9 sintered body having a particle diameter of .4 microns has a -3.4 S / cm at 700.degree. C. in a direct current three-terminal method, and is a practically useful material because of its low conductivity. It was not considered to be.

Therefore, as a result of earnest research in the group of the present inventors, the average particle diameter of the sintered body was an average of 100 nm or less and the sintered body density was 95% of the theoretical density using the easily sinterable nanosize fine powder. %, And the measured value of conductivity in the DC three-terminal method at 700 ° C. is −
The inventors succeeded in developing a Dy-doped highly conductive nanoceria-based sintered body of 1 (S / cm) or more and a method for producing the same, and previously filed a patent application for the result (Patent Document 1; Japanese Patent Application No. 2004-066461). The sintered body obtained by the invention according to the earlier application can be expected to have an extremely excellent effect in terms of having high electrical conductivity, and can be said to be an epoch-making invention in that respect, In addition, the following points included problems. In other words, the present invention requires that the sintering temperature not exceed 1100 degrees in order to obtain the conductivity, and finally the sintered body is designed to have a high density of 95% or more of the theoretical density. In addition, there is an extremely difficult technical restriction that it is necessary to control the crystal particles constituting the sintered body to ultrafine particles having an average particle size of 100 nm or less. Therefore, it was necessary to secure nano-sized fine powder with good dispersibility. That is, the starting material requires strict management of the particle size, and it is inevitable that the cost is high, and the sintering conditions are severely limited in temperature management and the like.

C. Milliken, S.M. Guruswamy, A .; Khandkar, J .; Am. Ceram. Soc, 85 [10], 2479 (2002) R. Maric, S.M. Seward, P.M. W. Faguy, M .; Oljaca, J .; Electrochemical and Solid State Letters, 6 [5], A91 (2003) K. Eguchi, T .; Kunisaki, and H.K. Arai, J. et al. Am. Ceram. Soc, 69 [11], C-282 (1986) T.A. Kudo, and H.K. Obayashi, J. et al. Electrochem. Soc. , 123 [3], 415 (1976) I. S. Park, S.M. J. et al. Kim, B.M. H. Lee, S.M. Park, Jpn. J. et al. Appl. Phys. Part 1, 36 [10], 6426 (1997). R. Doshi, V .; L. Richards, J.A. D. Carter, X. Wang, and M.M. Krumpelt, J .; Electrochem. Soc. , 146 [4], 1273 (1999) Japanese Patent Application No. 2004-064616

  Conventional ceria-based sintered bodies doped with rare earth elements, including those according to the above-mentioned patent applications, are not sufficient in terms of conductivity, or the powder as a starting material is extremely dispersible in the manufacturing process. If there is no good and easily sinterable powder, there is a difficult problem in several respects, such as the fact that it does not lead to an improvement in conductivity, and it must be dependent on a specific expensive ceria-based powder. The present invention is intended to solve such problems and to provide a method for producing a Dy-doped ceria-based sintered body having a dense and uniform structure and having high conductive properties.

In light of the above-mentioned problems of the prior art, the present inventors have conducted intensive studies, and as a result, prepared a sinterable Dy-doped nanoceria powder with relatively little particle aggregation, and used this powder as a preliminary. As sintering, after pre-sintering at a predetermined sintering temperature at a temperature rising rate of 400 ° C./min or more from room temperature, sintering is performed by atmospheric pressure sintering, thereby reducing the particle size distribution in the sintered body. By narrowing, it has been found that high conductivity can be obtained without controlling the average particle size in the sintered body to 100 nm or less as in the past, and the present invention has been completed.

That is, the technical configuration taken as a means for solving the above-described problems of the present invention is as described in (1) to (4) below.
(1) Represented by the general formula Dy _x Ce _1-x O _2- δ (where 0.10 ≦ x ≦ 0.3, δ represents the amount of oxygen defects determined from the balance of charges of the cation and anion) A powder particle having a composition having a primary particle diameter of 10 to 30 nanometers and a secondary particle diameter of 50 to 90 nanometers as a starting material powder, This starting material powder is molded, and pre-electrically sintered at a temperature of 1100 ° C. to 1250 ° C. at a temperature increase rate of 400 ° C./min or more from room temperature for a sintering time of 30 minutes or less by an electric current sintering method. Then, it is cooled to room temperature, and the obtained sintered body is subsequently sintered in the air at a heating rate of 3 ° C./min to 10 ° C./min at a temperature not lower than 1100 ° C. and not higher than the pre-energized sintering temperature. So, more than 20 minutes and 30 o'clock By re-sintering, the sintered body density is 95% or more of the theoretical density, the average particle diameter of the crystal particles constituting the sintered body is 100 nm or more and 200 nm or less, and the average particle diameter is twice or more A method for producing a Dy-doped nanoceria-based sintered body having a high density and a uniform fine structure, characterized in that a sintered body having a high density and a uniform fine structure is obtained.
(2) When the starting raw material powder is molded and subjected to current sintering, the starting raw material powder is dispersed in an alcohol liquid in advance, subjected to ultrasonic dispersion treatment, and heated in an inert gas stream after completion of the treatment. The high-density, uniformly fine-structured Dy-doped nanoceria-based sintered body as described in (1) above, wherein the alcohol is evaporated and dried at room temperature, and then subjected to the electric current sintering step. Method.
(3) The method for producing a Dy-doped nanoceria-based sintered body having a high-density, uniform fine structure according to (2), wherein ethanol is used as the alcohol.
(4) The method for producing a Dy-doped nanoceria-based sintered body having a high-density, uniform fine structure according to (2), wherein the ultrasonic dispersion treatment is performed for at least one hour.

The present invention has succeeded in significantly increasing the electric conductivity of the ceria-based sintered body by producing a sintered body obtained by the above-mentioned specific process, and in the future, it will be 700 degrees or less in the past. It is expected to contribute greatly to the development of fuel cells that generate high output at low temperatures. In particular, it is expected to greatly contribute to the application of fuel cells to portable devices that have been attracting attention in recent years and to the widespread use of fuel cells in the home, and its significance is extremely large and serious.

Here, in the method for producing a sintered body according to the present invention, the composition is Dy _x Ce _1-x O _2- δ (where 0.10 ≦ x ≦ 0.3, δ is based on the balance of charges of the cation and the anion) The primary particle diameter is 10 to 30 nanometers, and the secondary particle diameter is 50 to 90 nanometers as the starting powder. It is preferable. In the general formula, x must be 0.10 or more and 0.30 or less. If x is less than 0.10, the amount of oxygen defects is insufficient. Therefore, no matter how small the particle diameter of the sintered body is controlled, improvement in conductivity cannot be expected. On the other hand, if x exceeds 0.30, excessive oxygen defects form defect clusters in the crystal and lower the electrical conductivity. Even if the particle size of the body is controlled to be nano-sized, it is not preferable because an improvement in conductivity cannot be expected.

  Furthermore, the Dy-doped ceria powder, which is a starting material used when producing a sintered body, must have a primary particle size of 10 to 30 nanometers. When the primary particle size is below this range, it is practically impossible, and the minimum value is about 10 nanometers. On the other hand, when it exceeds the above range, the secondary particles are formed by gently associating the primary particles. This is not preferable because the particle diameter becomes too large and the effect of current sintering performed as pre-sintering is lost.

  Moreover, the secondary particle diameter of the sintered compact production raw material powder that satisfies the preferable range of the primary particle diameter must be 50 nanometers or more and 90 nanometers or less, and the finer and more dispersible the smaller the range is, the lower the particle diameter is. Although a powder is obtained, such a powder has poor pressure transmission during molding, and produces a large non-uniformity in the molded body. This non-uniform state is emphasized during sintering, and is larger than twice the average particle size. Since particles are produced in the sintered body and segregation of Dy is likely to occur in these large particles, the movement of oxide ions within the particles is restricted, and the effect of sufficiently reducing the particle size is unlikely to appear. Absent. On the other hand, if it exceeds this range, even if combined with current sintering or atmospheric pressure sintering, such a powder having large agglomeration is difficult to densely sinter, so it is not preferable because high conductive properties cannot be obtained. Absent.

Using the starting powder as described above, preliminary energization is first performed by a current sintering method at a heating rate of 400 ° C./min or more from room temperature to a temperature of 1100 ° C. or more and 1250 ° C. or less for a sintering time of 30 minutes or less. Sintering must be performed. The electric current sintering method is a method in which a starting material powder is sintered while applying a pulsed voltage. According to this method, even if rapid heating of the electric furnace is performed, the temperature in the sample is not changed in the electric furnace. Since the temperature is kept the same, a sintered body having a dense and fine structure can be produced. On the other hand, if this sintering method is not used, no matter how much the heating rate is increased, the temperature in the sample is not necessarily equal to the temperature in the electric furnace, so that a sufficient effect for increasing the heating rate is produced. Since it is not, it is not preferable.

In addition, the rate of temperature increase in current sintering must be from room temperature to 400 ° C./min or more.
Below this rate, dopant segregation occurs during sintering, which causes abnormal grain growth, which is not preferable because a dense sintered body having a uniform and fine grain size cannot be produced. Moreover, even if the heating rate is too fast, only a certain effect is produced, so it is sufficient to secure a rate of up to about 900 ° C./min.

The sintering temperature in this electric sintering must be 1100 degrees or more and 1250 degrees or less, and below this temperature, a sintered body having a density of 85% or more of the theoretical density even in electric sintering is produced. Can not. 85% of the theoretical density means that the middle stage of sintering is almost finished. Sintering includes an initial stage (with a shrinkage of about 5%), a middle stage (after the initial stage, refers to about 90% of the theoretical density), and a final stage (points to the theoretical density after the middle stage). . Abnormal grain growth in the sintered body is assumed to occur during the medium-term sintering. Abnormal grain growth in the sintered body increases the non-uniformity of the structure in the sintered body. This non-uniformity is said to induce the segregation of the dopant, and it is said that the segregation of the dopant induces the generation of microdomains that hinder the ion conduction phenomenon, leading to a large decrease in conductivity. Therefore, if a dense sintered body of 85% or more of the theoretical density can be produced by rapidly terminating the medium-term sintering and suppressing the occurrence of abnormal grain growth, the subsequent normal pressure sintering can achieve 95% of the theoretical density. As described above, it is possible to produce a sintered body having a dense structure and a uniform structure without abnormal grain growth.

For these reasons, the density of the sintered body obtained by current sintering must be 85% or more of the theoretical density. Below this density, abnormal grain growth occurs in the subsequent normal pressure sintering, resulting in hindering improvement in conductivity, which is not preferable.
The current sintering time must be within 30 minutes, and if this sintering time is exceeded, carbon will enter the sample from the carbon mold used for current sintering, and prevent the sintering, or If the sintering is performed for more than 30 minutes, the sample is slightly reduced, and cracking occurs in the sintered body due to the reduction, and a high-density sintered body cannot be obtained. The time must be within 30 minutes. Also, since it has a certain effect even if it is too short, it is more preferable to provide a holding time of at least about 1 minute.

  The obtained sintered body is continuously heated in air at a rate of temperature of 3 ° C./min to 10 ° C./min at a sintering temperature of 1100 ° C. or higher and a pre-energized sintering temperature or lower for 20 minutes to 30 hours. The following normal pressure sintering must be performed. In this normal pressure sintering, if the heating rate exceeds the above range, impurities such as carbon that are slightly mixed in the electric current sintering are left as “soot” in the sintered body, causing a decrease in the density of the sintered body. It is not preferable.

On the other hand, even if the rate of temperature increase in atmospheric pressure sintering is made too slow, only a certain effect appears. Therefore, it is preferable to control the sintering at 3 ° C./min or higher for sintering. In addition, the atmospheric pressure sintering temperature is
The temperature must be at least 1100 ° C. and below the pre-energization sintering temperature. Below this temperature, no further improvement in density can be expected even if atmospheric pressure sintering is performed, and voids in the sintered body are removed. Therefore, it is not preferable because the conductivity of the sintered body is reduced. On the other hand, when normal pressure sintering is performed at a temperature exceeding the temperature of the first stage electric current sintering (referred to as pre-current current sintering), it has a fine, uniform particle size and a theoretical density of 85. The sintered body densified to more than% is caused by non-uniform grain growth by further high-temperature treatment, resulting in a decrease in the density of the sintered body and a decrease in the conductivity of the sintered body. Moreover, this atmospheric pressure sintering time must be 20 minutes or more and 30 hours or less. Exceeding this range is not preferable because abnormal grain growth due to long-term sintering increases non-uniformity in the microstructure of the sintered body, leading to a decrease in conductivity. Further, if the normal pressure sintering time is less than this range, it is not preferable because sufficient effects required for densification cannot be obtained.

The density of the sintered body thus obtained must be 95% or more of the theoretical density. Below this range, the pores in the sintered body lower the electrical conductivity, which is not preferable.
Further, the average particle size of the sintered body having a uniform structure obtained by the above production method should be 100 nm or more and 200 nm or less and does not include particles having a particle size twice or more of the average particle size. The improvement in conductivity cannot be expected. When the average particle size is larger than 200 nm, the grain boundary in the sintered body becomes a large resistance, which is not preferable because the electrical conductivity of the entire sintered body is lowered. In addition, when the average particle size is below the above range, there is a high possibility that excellent characteristics will be obtained as in this range, but for that purpose, it is finer and less agglomerated than the starting materials defined in this specification. It is necessary to use a particularly expensive powder as a starting material, which is not preferable. However, even when the range of the average particle size of the sintered body is satisfied, coarse particles having a size exceeding twice the average particle size must not be included. The presence of such coarse particles in the sintered body is not preferable because segregation of the dopant occurs therein and the conductivity is not sufficiently improved.

More preferably, the above-mentioned composition is Dy _x Ce _1-x O _2- δ (where 0.10 ≦ x ≦ 0.3, δ represents the amount of oxygen defects determined from the charge balance between the cation and the anion) ), A primary particle diameter of 10 nanometers to 30 nanometers, and a secondary particle diameter of 50 nanometers to 90 nanometers are used as a starting powder. Before sintering, disperse it in a solution using ethanol as a solvent, perform ultrasonic dispersion treatment for 1 hour or more, and then evaporate the alcohol at room temperature without heating in an inert gas stream. After that, by conducting the above-mentioned current sintering and atmospheric pressure sintering, the cracking of the sample, which may occur during current sintering, is prevented, the density is increased to 95% or more of the theoretical density, and further sintering is performed. Average grain of body Diameter at 100nm or 200nm or less, and it is possible to stably produce a sintered body containing no particles having a particle size of at least 2 times the average particle diameter.

At this time, the solvent is not particularly limited, but an organic solvent having a high volatility makes it difficult to perform ultrasonic treatment for a long time, and an organic solvent extremely harmful to the human body is substantially difficult to handle. It is preferable to use anhydrous ethanol that has been dehydrated overnight using zeolite or the like, and eliminates agglomeration slightly remaining on the powder, resulting in a high-density, unbreakable product. Can be manufactured. Cracks in the sintered body, which can be seen during electric current sintering, mainly occur during electric current sintering due to uneven filling of the powder. To solve this problem, it remains in the powder. It is necessary to reduce the aggregation. Therefore, the ultrasonic dispersion treatment time must be 1 hour or longer, and if the treatment time is shorter than this, it is not preferable because a sufficient dispersion effect does not appear. Moreover, even if the treatment is performed for a very long time, only a certain effect can be obtained, so it is sufficient to perform the treatment for a maximum of 3 hours.
In addition, when the powder dispersed in ethanol is to be dried, it must be carried out at room temperature under a dry inert gas flow. When it is dried by heating or using a humid gas, the dispersed powder is not removed. Since it aggregates again, it is not preferable.

As described above, the properties of the starting powder, the combination of electric current sintering and atmospheric pressure sintering, the heating rate during sintering, the sintering time, the average particle size of the sintered body, its distribution, and the sintered body density It was clarified that satisfying all of the conditions, a value of −1 (S / cm) or higher at 700 ° C., which is a high conductive property, can be obtained.

  Next, this invention is demonstrated based on an Example, drawing, and a comparative example. However, these examples are disclosed only as an aid for specifically showing and easily understanding the present invention, and the contents of the present invention are not limited by these examples.

Example 1;
After preparing a 0.20 mol / liter cerium nitrate solution and a 0.05 mol / liter dysprosium nitrate solution as starting materials so that the blending was Dy _0.2 Ce _0.8 O _1.9 , this liquid was mixed. An aqueous ammonium hydrogen carbonate solution was dropped into the mixed solution at 2 drops / second, and after completion of the dropping, an aging treatment was performed at room temperature for 1 hour.
The precipitate thus obtained is repeatedly washed with water and filtered three times alternately, dried in dry nitrogen gas, then calcined at a temperature of 700 ° C. in air for 2 hours through a 120 mesh sieve, Ceria compound powder was prepared. It was confirmed by an X-ray diffraction test that the obtained calcined powder was composed of a single crystal phase of fluorite. The calcined powder was confirmed by a scanning electron microscope (SEM) to have a primary particle size of 20 nanometers and a secondary particle size of about 70 nanometers. The observation results are shown in FIG.
This powder was put into a carbon mold and uniaxially molded at 250 kg / cm ² , and then at 500 ° C. /
Current heating was performed at 1200 ° C. for 2 minutes at a heating rate of 1 minute. The obtained sintered body was slightly blackened by carbon. However, when the black portion of the surface was removed by polishing and the sintered body density was measured, it was increased to 87% of the theoretical density. Then, when a normal pressure sintering was performed at 1200 ° C. for 30 minutes at a rate of temperature increase of 5 ° C./min, a yellow sintered body having an appearance was obtained. When the density of the sintered body was measured, the density was increased to 97% of the theoretical density, and it was found that no large voids were observed on the surface of the sintered body and the densification was progressing. The obtained sintered body had an average particle size of 150 nanometers, and the maximum particle size in the sintered body was 260 nanometers, indicating that it had a uniform structure.
The conductivity measured at 700 ° C. by the direct current three-terminal method showed a high value of −0.9 (S / cm). The results of Example 1 are shown in Table 1.

Example 2;
A 0.20 mol / liter cerium nitrate solution and a 0.025 mol / liter dysprosium nitrate solution were prepared as starting materials so that the blending would be Dy _0.1 Ce _0.9 O _1.95 , and then this liquid was mixed. An aqueous ammonium hydrogen carbonate solution was dropped into the mixed solution at 2 drops / second, and after completion of the dropping, an aging treatment was performed at room temperature for 1 hour.
The precipitate thus obtained is repeatedly washed with water and filtered three times alternately, dried in dry nitrogen gas, then calcined at a temperature of 700 ° C. in air for 2 hours through a 120 mesh sieve, Ceria compound powder was prepared. It was confirmed by an X-ray diffraction test that the obtained calcined powder was composed of a single crystal phase of fluorite. This calcined powder was also SEM as in Example 1.
As a result of observing the powder, the primary particle size was 20 nanometers, and the secondary particle size was about 80 nanometers.
This powder was put into a carbon mold, uniaxially molded at 250 kg / cm ² , and then subjected to current sintering at 1100 ° C. for 2 minutes at a heating rate of 700 ° C./min. The obtained sintered body was very slightly blackened by carbon, but when the black portion of the surface was removed by polishing and the sintered body density was measured, the density was increased to 86% of the theoretical density. . Then, when sintered at 1100 ° C. for 4 hours at a rate of temperature increase of 5 ° C./min, a sintered body having a yellow appearance was obtained. When the density of the sintered body was measured, the density was increased to 96% of the theoretical density, and it was found that no large pores were observed on the surface of the sintered body and the densification was progressing. The obtained sintered body had an average particle diameter of 130 nanometers, and the maximum particle diameter in the sintered body was also 210 nanometers, indicating that it had a uniform structure.
The conductivity measured at 700 ° C. by the direct current three-terminal method showed a high value of −1.0 (S / cm). As in Example 1, the obtained results are shown in Table 1.

Example 3;
A 0.20 mol / liter cerium nitrate solution and a 0.056 mol / liter dysprosium nitrate solution were prepared as starting materials so that the _composition was Dy _0.28 Ce _0.78 O _1.86 , and then this liquid was mixed. An aqueous ammonium hydrogen carbonate solution was dropped into the mixed solution at 2 drops / second, and after completion of the dropping, an aging treatment was performed at room temperature for 1 hour.
The precipitate thus obtained is repeatedly washed with water and filtered three times alternately, dried in dry nitrogen gas, then calcined at a temperature of 700 ° C. in air for 2 hours through a 120 mesh sieve, Ceria compound powder was prepared. It was confirmed by an X-ray diffraction test that the obtained calcined powder was composed of a single crystal phase of fluorite. Also, this calcined powder is SEM as in Example 1.
As a result of observing the powder, the primary particle size was 20 nanometers, and the secondary particle size was about 75 nanometers.
This powder was put in a carbon mold, uniaxially molded at 250 kg / cm ² , and then subjected to current sintering at 1250 ° C. for 1 minute at a heating rate of 900 ° C./min. Although the obtained sintered body was slightly blackened by carbon, the black portion of the surface was removed by polishing and the sintered body density was measured. As a result, the sintered body was densified to 90% of the theoretical density. Then, when a normal pressure sintering was performed at 1100 ° C. for 6 hours at a rate of temperature increase of 5 ° C./min, a sintered body having a yellow appearance was obtained. When the density of the sintered body was measured, the density was increased to 98% of the theoretical density, and it was found that no large voids were observed on the surface of the sintered body and the densification was progressing. The obtained sintered body had an average particle size of 110 nanometers, and the maximum particle size in the sintered body was also 190 nanometers, indicating that it had a uniform structure.
The conductivity measured at 700 ° C. by the direct current three-terminal method showed a high value of −1.0 (S / cm). As in Example 1, the obtained results are shown in Table 1.

Example 4;
After preparing a 0.20 mol / liter cerium nitrate solution and a 0.05 mol / liter dysprosium nitrate solution as starting materials so that the blending was Dy _0.2 Ce _0.8 O _1.9 , this liquid was mixed. An aqueous ammonium hydrogen carbonate solution was dropped into the mixed solution at 2 drops / second, and after completion of the dropping, an aging treatment was performed at room temperature for 1 hour.
The precipitate thus obtained is alternately washed with water and filtered three times, dried in dry nitrogen gas, then calcined for 2 hours at a temperature of 700 ° C. in an oxygen stream through a 120-mesh sieve. A ceria compound powder was prepared. It was confirmed by an X-ray diffraction test that the obtained calcined powder was composed of a single crystal phase of fluorite. Further, as a result of observing the powder by SEM as in Example 1, this calcined powder was a particle having a primary particle size of 20 nanometers and a secondary particle size of about 70 nanometers.
This powder was put in a carbon mold, uniaxially molded at 250 kg / cm ² , and then subjected to current sintering at 1150 ° C. for 5 minutes at a heating rate of 700 ° C./min. The obtained sintered body was slightly blackened by carbon, but when the black portion of the surface was removed by polishing and the density of the sintered body was measured, the density was increased to 85% of the theoretical density. Then, when a normal pressure sintering was performed at 1100 ° C. for 24 hours at a rate of temperature increase of 5 ° C./min, a yellow sintered body having an appearance was obtained. When the density of the sintered body was measured, the density was increased to 98% of the theoretical density, and it was found that no large voids were observed on the surface of the sintered body and the densification was progressing. The obtained sintered body had an average particle size of 180 nanometers, and the maximum particle size in the sintered body was also 300 nanometers, indicating that it had a uniform structure.
The conductivity measured at 700 ° C. by the direct current three-terminal method showed a high value of −0.8 (S / cm). As in Example 1, the obtained results are shown in Table 1.

Example 5
After preparing a 0.20 mol / liter cerium nitrate solution and a 0.05 mol / liter dysprosium nitrate solution as starting materials so that the blending was Dy _0.2 Ce _0.8 O _1.9 , this liquid was mixed. An aqueous ammonium hydrogen carbonate solution was dropped into the mixed solution at 2 drops / second, and after completion of the dropping, an aging treatment was performed at room temperature for 1 hour.
The precipitate thus obtained is alternately washed with water and filtered three times, dried in dry nitrogen gas, then calcined for 2 hours at a temperature of 700 ° C. in an oxygen stream through a 120-mesh sieve. A ceria compound powder was prepared. It was confirmed by an X-ray diffraction test that the obtained calcined powder was composed of a single crystal phase of fluorite. Further, as a result of observing the powder by SEM as in Example 1, this calcined powder was a particle having a primary particle size of 20 nanometers and a secondary particle size of about 70 nanometers.
This powder was put into a carbon mold, uniaxially molded at 250 kg / cm ² , and then subjected to current sintering at 1100 ° C. for 5 minutes at a heating rate of 700 ° C./min. The obtained sintered body was slightly blackened by carbon. However, when the black portion of the surface was removed by polishing and the sintered body density was measured, it was increased to 86% of the theoretical density. Then, when a normal pressure sintering was performed at 1100 ° C. for 24 hours at a rate of temperature increase of 4 ° C./min, a yellow sintered body having an appearance was obtained. When the density of the sintered body was measured, the density was increased to 97% of the theoretical density, and it was found that no large voids were observed on the surface of the sintered body and the densification was progressing. The obtained sintered body had an average particle size of 170 nanometers, and the maximum particle size in the sintered body was also 280 nanometers, indicating that it had a uniform structure.
The conductivity measured at 700 ° C. by the direct current three-terminal method showed a high value of −0.9 (S / cm). As in Example 1, the obtained results are shown in Table 1.

Example 6
After preparing a 0.20 mol / liter cerium nitrate solution and a 0.05 mol / liter dysprosium nitrate solution as starting materials so that the blending was Dy _0.2 Ce _0.8 O _1.9 , this liquid was mixed. An aqueous ammonium hydrogen carbonate solution was dropped into the mixed solution at 2 drops / second, and after completion of the dropping, an aging treatment was performed at room temperature for 1 hour.
The precipitate thus obtained is alternately washed with water and filtered three times, dried in dry nitrogen gas, then calcined for 2 hours at a temperature of 700 ° C. in an oxygen stream through a 120-mesh sieve. A ceria compound powder was prepared. It was confirmed by an X-ray diffraction test that the obtained calcined powder was composed of a single crystal phase of fluorite. Further, as a result of observing the powder by SEM as in Example 1, this calcined powder was a particle having a primary particle size of 20 nanometers and a secondary particle size of about 70 nanometers. This powder was further dispersed in ethanol in a beaker, the beaker was placed in a tabletop ultrasonic cleaner, and subjected to ultrasonic dispersion treatment for 1 hour. After this treatment, ethanol was dried by blowing dry nitrogen gas, and again passed through a 120-mesh sieve to obtain a powder for sintering.
This powder was put into a carbon mold, uniaxially molded at 250 kg / cm ² , and then subjected to current sintering at 1100 ° C. for 5 minutes at a heating rate of 700 ° C./min. The obtained sintered body was slightly blackened by carbon, but the black portion of the surface was removed by polishing and the density of the sintered body was measured. As a result, the density was increased to 89% of the theoretical density. Then, when a normal pressure sintering was performed at 1100 ° C. for 24 hours at a rate of temperature increase of 9 ° C./min, a yellow sintered body having an appearance was obtained. When the density of the sintered body was measured, the density was increased to 98% of the theoretical density, and it was found that no large voids were observed on the surface of the sintered body and the densification was progressing. The obtained sintered body had an average particle diameter of 180 nanometers, and the maximum particle diameter in the sintered body was also 210 nanometers, indicating that it had a uniform structure.
The conductivity measured at 700 ° C. by the direct current three-terminal method showed a high value of −0.8 (S / cm). As in Example 1, the obtained results are shown in Table 1.

Comparative Example 1;
A 0.20 mol / liter cerium nitrate solution and a 0.01 mol / liter dysprosium nitrate solution were prepared as starting materials so that the _composition would be Dy _0.05 Ce _0.95 O _1.975 , and then this liquid was mixed. An aqueous ammonium hydrogen carbonate solution was dropped into the mixed solution at 2 drops / second, and after completion of the dropping, an aging treatment was performed at room temperature for 1 hour.
The precipitate thus obtained is alternately washed with water and filtered three times, dried in dry nitrogen gas, then calcined for 2 hours at a temperature of 700 ° C. in an oxygen stream through a 120-mesh sieve. A ceria compound powder was prepared. It was confirmed by an X-ray diffraction test that the obtained calcined powder was composed of a single crystal phase of fluorite. Further, as a result of observing the powder by SEM as in Example 1, this calcined powder was a particle having a primary particle diameter of 20 nanometers and a secondary particle diameter of about 80 nanometers.
This powder was put into a carbon mold, uniaxially molded at 250 kg / cm ² , and then subjected to current sintering at 1100 ° C. for 5 minutes at a heating rate of 700 ° C./min. The obtained sintered body was slightly blackened by carbon. However, when the black portion of the surface was removed by polishing and the sintered body density was measured, it was increased to 86% of the theoretical density. Then, when a normal pressure sintering was performed at 1100 ° C. for 24 hours at a rate of temperature increase of 5 ° C./min, a yellow sintered body having an appearance was obtained. When the density of the sintered body was measured, the density was increased to 95% of the theoretical density, and it was found that no large voids were observed on the surface of the sintered body and the densification was progressing. The obtained sintered body had an average particle size of 190 nanometers, and the maximum particle size in the sintered body was also 310 nanometers, indicating that it had a uniform structure.
However, the conductivity measured at 700 ° C. by the direct current three-terminal method is −2.7 (S / c
m) and a low value. The results thus obtained are shown in Table 2.

Comparative Example 2;
A 0.20 mol / liter cerium nitrate solution and a 0.08 mol / liter dysprosium nitrate solution were prepared as starting materials so that the _composition was Dy _0.4 Ce _0.6 O _1.95 , and then this liquid was mixed. An aqueous ammonium hydrogen carbonate solution was dropped into the mixed solution at 2 drops / second, and after completion of the dropping, an aging treatment was performed at room temperature for 1 hour.
The precipitate thus obtained is alternately washed with water and filtered three times, dried in dry nitrogen gas, then calcined for 2 hours at a temperature of 700 ° C. in an oxygen stream through a 120-mesh sieve. A ceria compound powder was prepared. It was confirmed by an X-ray diffraction test that the obtained calcined powder was composed of a single crystal phase of fluorite. Further, as a result of observing the powder by SEM as in Comparative Example 1, this calcined powder was a particle having a primary particle size of 20 nanometers and a secondary particle size of about 70 nanometers.
This powder was put into a carbon mold, uniaxially molded at 250 kg / cm ² , and then subjected to current sintering at 1100 ° C. for 5 minutes at a heating rate of 700 ° C./min. The obtained sintered body was slightly blackened by carbon, but when the black portion of the surface was removed by polishing and the density of the sintered body was measured, the density was increased to 85% of the theoretical density. Then, when a normal pressure sintering was performed at 1100 ° C. for 24 hours at a rate of temperature increase of 5 ° C./min, a yellow sintered body having an appearance was obtained. When the density of the sintered body was measured, the density was increased to 96% of the theoretical density, and it was found that no large pores were observed on the surface of the sintered body and the densification was progressing. The obtained sintered body had an average particle size of 190 nanometers, and the maximum particle size in the sintered body was also 310 nanometers, indicating that it had a uniform structure.
However, the conductivity measured at 700 ° C. by the direct current three-terminal method is −3.1 (S / c
m) and a low value. As in Comparative Example 1, the obtained results are shown in Table 2.

Comparative Example 3;
After preparing a 0.20 mol / liter cerium nitrate solution and a 0.04 mol / liter dysprosium nitrate solution as starting materials so that the blending was Dy _0.2 Ce _0.8 O _1.9 , this liquid was mixed. An aqueous ammonium hydrogen carbonate solution was dropped into the mixed solution at 2 drops / second, and after completion of the dropping, an aging treatment was performed at room temperature for 1 hour.
The precipitate thus obtained is alternately washed with water and filtered three times, dried in dry nitrogen gas, and then calcined for 10 hours at a temperature of 1000 ° C. in an oxygen stream through a 120-mesh sieve. A ceria compound powder was prepared. It was confirmed by an X-ray diffraction test that the obtained calcined powder was composed of a single crystal phase of fluorite. Further, this calcined powder was observed by SEM as in Comparative Example 1. As a result, the primary particle diameter was 20 nanometers, but the calcined powder was agglomerated and the secondary particle diameter was about 150 nanometers. It was a particle.
This powder was put into a carbon mold, uniaxially molded at 250 kg / cm ² , and then subjected to current sintering at 1100 ° C. for 5 minutes at a heating rate of 700 ° C./min. The obtained sintered body was slightly blackened by carbon, but when the black portion of the surface was removed by polishing and the sintered body density was measured, it was about 72% of the theoretical density. Therefore, when a normal pressure sintering was performed at 1100 ° C. for 24 hours at a rate of temperature increase of 5 ° C./min, a yellow sintered body was obtained. The density of this sintered body was measured. It has a density of 92% of the theoretical density, and some large pores are observed on the surface of the sintered body, and it has been found that the densification is not necessarily sufficiently advanced. The obtained sintered body had an average particle size of 160 nanometers, and the maximum particle size in the sintered body was also 290 nanometers, indicating that it had a uniform structure.
However, the conductivity measured at 700 ° C. by the direct current three-terminal method is −2.9 (S / c
m) and a low value. As in Comparative Example 1, the obtained results are shown in Table 2.

Comparative Example 4;
After preparing a 0.20 mol / liter cerium nitrate solution and a 0.04 mol / liter dysprosium nitrate solution as starting materials so that the blending was Dy _0.2 Ce _0.8 O _1.9 , this liquid was mixed. An aqueous ammonium hydrogen carbonate solution was dropped into the mixed solution at 2 drops / second, and after completion of the dropping, an aging treatment was performed at room temperature for 1 hour.
The precipitate thus obtained is alternately washed with water and filtered three times, dried in dry nitrogen gas, then calcined for 2 hours at a temperature of 700 ° C. in an oxygen stream through a 120-mesh sieve. A ceria compound powder was prepared. It was confirmed by an X-ray diffraction test that the obtained calcined powder was composed of a single crystal phase of fluorite. Further, this calcined powder was observed by SEM as in Comparative Example 1. As a result, the primary particle size was 20 nanometers, and the secondary particle size was about 80 nanometers.
This powder was put in a carbon mold, uniaxially molded at 250 kg / cm ² , and then subjected to current sintering at 1000 ° C. for 20 minutes at a heating rate of 700 ° C./min. In the obtained sintered body, a blackened portion due to carbon was not recognized, and a yellow characteristic of the ceria-based sintered body was exhibited. When the density of the sintered body was measured, it was about 68% of the theoretical density. Then, when the atmospheric pressure sintering was performed at 1100 ° C. for 24 hours at a rate of temperature increase of 5 ° C./min, the density of the sintered body was about 90% of the theoretical density. When large vacancies were observed, it was found that densification was not sufficiently advanced. The obtained sintered body had an average particle size of 130 nanometers, and the maximum particle size in the sintered body was also 200 nanometers, indicating that it had a uniform structure.
However, the conductivity measured at 700 ° C. by the direct current three-terminal method is −3.2 (S / c
m) and a low value. As in Comparative Example 1, the obtained results are shown in Table 2.

Comparative Example 5;
After preparing a 0.20 mol / liter cerium nitrate solution and a 0.04 mol / liter dysprosium nitrate solution as starting materials so that the blending was Dy _0.2 Ce _0.8 O _1.9 , this liquid was mixed. An aqueous ammonium hydrogen carbonate solution was dropped into the mixed solution at 2 drops / second, and after completion of the dropping, an aging treatment was performed at room temperature for 1 hour.
The precipitate thus obtained is alternately washed with water and filtered three times, dried in dry nitrogen gas, then calcined for 2 hours at a temperature of 700 ° C. in an oxygen stream through a 120-mesh sieve. A ceria compound powder was prepared. It was confirmed by an X-ray diffraction test that the obtained calcined powder was composed of a single crystal phase of fluorite. Moreover, as for this calcined powder, as a result of observing powder by SEM like the comparative example 1, a primary particle diameter is 20 nanometers and a secondary particle diameter is
The particles were about 80 nanometers.
This powder was put into a carbon mold, uniaxially molded at 250 kg / cm ² , and then subjected to current sintering at 1100 ° C. for 5 minutes at a heating rate of 700 ° C./min. In the obtained sintered body, an extremely large blackening phenomenon due to carbon was observed, and when the density of the sintered body was measured, it was about 85% of the theoretical density. Then, when the normal pressure sintering was performed at 1100 ° C. for 40 hours at a rate of temperature increase of 5 ° C./min, the density of the sintered body was about 88% of the theoretical density. On the other hand, large vacancies were observed and it was found that the densification was not sufficiently advanced. The obtained sintered body had an average particle diameter of 250 nanometers, and the maximum particle diameter in the sintered body was also 600 nanometers, indicating that it had a non-uniform structure.
The conductivity measured at 700 ° C. by the direct current three-terminal method showed a low value of −4.1 (S / cm). As in Comparative Example 1, the obtained results are shown in Table 2.

Comparative Example 6;
After preparing a 0.20 mol / liter cerium nitrate solution and a 0.04 mol / liter dysprosium nitrate solution as starting materials so that the blending was Dy _0.2 Ce _0.8 O _1.9 , this liquid was mixed. An aqueous ammonium hydrogen carbonate solution was dropped into the mixed solution at 2 drops / second, and after completion of the dropping, an aging treatment was performed at room temperature for 1 hour.
The precipitate thus obtained is alternately washed with water and filtered three times, dried in dry nitrogen gas, then calcined for 2 hours at a temperature of 700 ° C. in an oxygen stream through a 120-mesh sieve. A ceria compound powder was prepared. It was confirmed by an X-ray diffraction test that the obtained calcined powder was composed of a single crystal phase of fluorite. Moreover, as for this calcined powder, as a result of observing powder by SEM like the comparative example 1, a primary particle diameter is 20 nanometers and a secondary particle diameter is
The particles were about 80 nanometers.
This powder was put in a carbon mold, uniaxially molded at 250 kg / cm ² , and then subjected to current sintering at 1300 ° C. for 1 minute at a heating rate of 700 ° C./min. In the obtained sintered body, an extremely large blackening phenomenon due to carbon was observed, and when the density of the sintered body was measured, it was about 80% of the theoretical density. Then, when the normal pressure sintering was performed at 1300 ° C. for 2 hours at a rate of temperature increase of 5 ° C./min, the density of the sintered body was about 92% of the theoretical density. On the other hand, large vacancies were observed and it was found that the densification was not sufficiently advanced. The obtained sintered body had an average particle size of 230 nanometers, and the maximum particle size in the sintered body was also 550 nanometers, indicating that it had a non-uniform structure.
The conductivity measured at 700 ° C. by the direct current three-terminal method showed a low value of −3.5 (S / cm). As in Comparative Example 1, the obtained results are shown in Table 2.

Comparative Example 7;
After preparing a 0.20 mol / liter cerium nitrate solution and a 0.04 mol / liter dysprosium nitrate solution as starting materials so that the blending was Dy _0.2 Ce _0.8 O _1.9 , this liquid was mixed. An aqueous ammonium hydrogen carbonate solution was dropped into the mixed solution at 2 drops / second, and after completion of the dropping, an aging treatment was performed at room temperature for 1 hour.
The precipitate thus obtained is alternately washed with water and filtered three times, dried in dry nitrogen gas, then calcined for 2 hours at a temperature of 700 ° C. in an oxygen stream through a 120-mesh sieve. A ceria compound powder was prepared. It was confirmed by an X-ray diffraction test that the obtained calcined powder was composed of a single crystal phase of fluorite. Moreover, as for this calcined powder, as a result of observing powder by SEM like the comparative example 1, a primary particle diameter is 20 nanometers and a secondary particle diameter is
The particles were about 80 nanometers.
This powder was put into a carbon mold, uniaxially molded at 250 kg / cm ² , and then subjected to current sintering at 1200 ° C. for 2 minutes at a temperature rising rate of 700 ° C./min. In the obtained sintered body, a blackening phenomenon that carbon slightly intruded into the sintered body was observed, but when the black portion of this surface was removed by polishing and the sintered body density was measured, It was about 87% of the theoretical density. Then, when the atmospheric pressure sintering was performed at 1200 ° C. for 2 hours at a rate of temperature increase of 20 ° C./min, the density of the sintered body was about 95% of the theoretical density. It was found that no large vacancies were observed and the densification was progressing. However, although the obtained sintered body had an average particle diameter of 180 nanometers, the maximum particle diameter in the sintered body was also 480 nanometers, and it was found that the sintered body had a non-uniform structure.
The conductivity measured at 700 ° C. by the direct current three-terminal method showed a low value of −3.2 (S / cm). As in Comparative Example 1, the obtained results are shown in Table 2.

Comparative Example 8;
After preparing a 0.20 mol / liter cerium nitrate solution and a 0.04 mol / liter dysprosium nitrate solution as starting materials so that the blending was Dy _0.2 Ce _0.8 O _1.9 , this liquid was mixed. An aqueous ammonium hydrogen carbonate solution was dropped into the mixed solution at 2 drops / second, and after completion of the dropping, an aging treatment was performed at room temperature for 1 hour.
The precipitate thus obtained is alternately washed with water and filtered three times, dried in dry nitrogen gas, then calcined for 2 hours at a temperature of 700 ° C. in an oxygen stream through a 120-mesh sieve. A ceria compound powder was prepared. It was confirmed by an X-ray diffraction test that the obtained calcined powder was composed of a single crystal phase of fluorite. Moreover, as for this calcined powder, as a result of observing powder by SEM like the comparative example 1, a primary particle diameter is 20 nanometers and a secondary particle diameter is
The particles were about 80 nanometers.
This powder was put in a carbon mold, uniaxially molded at 250 kg / cm ² , and then subjected to current sintering at 1200 ° C. for 2 minutes at a temperature rising rate of 200 ° C./min. In the obtained sintered body, a blackening phenomenon that carbon slightly intruded into the sintered body was observed, but when the black portion of this surface was removed by polishing and the sintered body density was measured, It was about 86% of the theoretical density. Therefore, when atmospheric pressure sintering was performed at 1200 ° C. for 2 hours at a rate of temperature increase of 5 ° C./min, the density of the sintered body was about 96% of the theoretical density. It was found that no large vacancies were observed and the densification was progressing. However, although the obtained sintered body had an average particle diameter of 210 nanometers, the maximum particle diameter in the sintered body was also 500 nanometers, and it was found that the sintered body had a non-uniform structure.
The conductivity measured at 700 ° C. by the direct current three-terminal method showed a low value of −3.4 (S / cm). As in Comparative Example 1, the obtained results are shown in Table 2.

Comparative Example 9;
After preparing a 0.20 mol / liter cerium nitrate solution and a 0.04 mol / liter dysprosium nitrate solution as starting materials so that the blending was Dy _0.2 Ce _0.8 O _1.9 , this liquid was mixed. An aqueous ammonium hydrogen carbonate solution was dropped into the mixed solution at 2 drops / second, and after completion of the dropping, an aging treatment was performed at room temperature for 1 hour.
The precipitate thus obtained is alternately washed with water and filtered three times, dried in dry nitrogen gas, then calcined for 2 hours at a temperature of 700 ° C. in an oxygen stream through a 120-mesh sieve. A ceria compound powder was prepared. It was confirmed by an X-ray diffraction test that the obtained calcined powder was composed of a single crystal phase of fluorite. Moreover, as for this calcined powder, as a result of observing powder by SEM like the comparative example 1, a primary particle diameter is 20 nanometers and a secondary particle diameter is
The particles were about 80 nanometers. This powder is subjected to ultrasonic dispersion treatment in ethanol using a tabletop ultrasonic cleaner for 1 hour, and then the ethanol is evaporated on a hot plate heated to 80 ° C. and set to a temperature of 100 ° C. The dried material was dried for 12 hours to obtain a sintered compact raw material.
This powder was put into a carbon mold, uniaxially molded at 250 kg / cm ² , and then subjected to current sintering at 1200 ° C. for 2 minutes at a temperature rising rate of 700 ° C./min. When the obtained sintered body was taken out from the carbon mold, it was broken into six, and it was not in a state where the density and conductivity could be measured.

  Summarizing the above examples and comparative examples, the powders formulated based on the blending defined in the claims of the present invention, the primary particle diameter, the secondary particle diameter, the current sintering temperature rise rate, When the current sintering temperature, the current sintering time, the sintered body density, the atmospheric pressure sintering temperature, the atmospheric pressure sintered body density, the average particle size within the sintered body, and the maximum particle size have specific values, It has been clarified that it has an extremely high conductivity as compared to outside the range. In other words, according to this data, it can be said that each requirement defined in the scope of claims defines a matter of exceptional significance.

  In recent years, reduction of carbon dioxide has been called out as part of global warming countermeasures, while development of high-power small fuel cells has been actively promoted to meet increasing energy demand. For the development of such a fuel cell, research and development of a solid electrolyte for a fuel cell exhibiting a high output in a temperature range of 500 ° C. to 700 ° C. is indispensable. The present invention provides a method for producing a ceria-based sintered solid electrolyte exhibiting a large electrical conductivity at a temperature of 700 ° C. exactly corresponding to this need, and is expected to be used greatly in the future. In the future, it is expected to be used and used as an excellent solid electrolyte in various technical fields as well as fuel cells. In particular, since it is a solid electrolyte with excellent heat resistance, its range of use is wide and it is expected to develop into the creation of new industries.

SEM observation drawing of sintered raw material synthesized by the production method of the present invention

Claims (4)

The composition represented by the general formula Dy _x Ce _1-x O _2- δ (where 0.10 ≦ x ≦ 0.3, δ represents the amount of oxygen defects determined from the balance of charges of the cation and anion) A powder particle having a primary particle diameter of 10 to 30 nanometers and a secondary particle diameter of 50 to 90 nanometers as a starting material powder. Molding the powder, by the current sintering method, at a temperature rising rate of 400 ° C./min or more from room temperature,
Pre-energization sintering is performed at a temperature of 1100 ° C. or more and 1250 ° C. or less for a sintering time of 30 minutes or less, and then cooled to room temperature. The obtained sintered body is subsequently kept at 3 ° C./min to 10 ° C. in the air. The sintering density is 95% of the theoretical density by performing sintering again at a sintering temperature not lower than 1100 ° C. and not higher than the pre-current sintering temperature at a heating rate of not higher than 1 / min. As described above, it is characterized in that a sintered body having a high density and a uniform fine structure is obtained which does not include an average particle diameter of 100 nm or more and 200 nm or less of crystal grains constituting the sintered body, and does not include a particle diameter more than twice the average particle diameter. A method for producing a Dy-doped nanoceria-based sintered body having a high density and a uniform fine structure. When the starting raw material powder is molded and subjected to current sintering, the starting raw material powder is dispersed in an alcohol liquid in advance and subjected to ultrasonic dispersion treatment, and after the treatment is completed, without heating in an inert gas stream The method for producing a Dy-doped nano-ceria-based sintered body having a high density and a uniform fine structure according to claim 1, wherein the alcohol is evaporated and dried at room temperature and then subjected to the electric current sintering step. Ethanol is used as this alcohol, The manufacturing method of the Dy dope nano ceria-type sintered compact with a high-density and uniform fine structure of Claim 2 characterized by the above-mentioned. The method for producing a Dy-doped nanoceria-based sintered body having a high density and uniform microstructure according to claim 2, wherein the ultrasonic dispersion treatment is performed for at least one hour.

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