JP2002358977A - Solid electrolyte material, its manufacturing method and solid electrolyte cell using the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a solid electrolyte material capable of utilization for fuel cells that is superior in ion conductivity and has a heat conduction property necessary for improving the thermal shock resistance. SOLUTION: A group of silicon nitride monocrystal particles or a group of aluminum nitride particles, that forms a heat conductive passage, is added in the stabilized zirconia powder or lanthane gallate system oxide as a base material of the oxide solid electrolyte. By this composition, while the degradation of ion conductivity is suppressed, the heat conduction is increased and the thermal shock resistance is improved.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a solid electrolyte material,
More specifically, the present invention relates to a solid electrolyte ceramic composite sintered body having excellent heat resistance, high thermal conductivity and high ionic conductivity, a method for producing the same, and a method for producing the same. The present invention relates to a solid oxide fuel cell using the same.

[0002]

BACKGROUND OF THE INVENTION After Nernst discovered a solid electrolyte in 1899, Baur and Preis became one in 1937.
At 000 ° C, a solid electrolyte fuel cell (SOFC: solid
Oxide cells have been in operation, and solid electrolyte fuel cells have continued to make progress, and zirconia ceramics fuel cells having an output of several kW have been operating for tens of thousands of hours. This solid oxide fuel cell can reform hydrocarbon-based fuels in the cell for internal reforming in order to operate at high temperatures above 1000 ° C. For this reason, it is considered that solid combustion fuel cells can achieve high combustion efficiency (> 60%).

[0003] Usually, a solid electrolyte fuel cell generally comprises a solid electrolyte, a fuel electrode, an air electrode and an intermediate layer. All these constituent materials are required to be chemically stable to an oxidation-reduction atmosphere and have appropriate conductivity. In addition, it is necessary that the thermal expansion coefficients of the constituent materials be close to each other, and that the anode and the cathode be porous and gas can pass therethrough. Further, it is naturally desired that these constituent materials have chemical stability as a battery material in an oxidation-reduction atmosphere and are inexpensive.

Therefore, in a so-called ceramic battery using a ceramic solid electrolyte, it is very difficult to select a ceramic material, and it is necessary to use metal parts such as ferritic stainless steel in a container such as a combustor body. It has been. For this reason, it is necessary to select a solid electrolyte and an electrode material which are active at a low temperature. In the future, the selection of ceramic solid electrolytes and electrode materials, the development of new materials, and the manufacturing technology of laminated structures of electrode materials will be important issues.

At present, as a solid electrolyte, stabilized Zr0
₂ are the most actively studied. As a stabilizer, 2
There are rare earth oxides such as oxides of valent alkaline earth element CaO, MgO, oxides of trivalent alkaline earth element Sc ₂ O ₃ , and Y ₂ O ₃ . As a stabilizer in ZrO _2, stabilized ZrO _{2 characteristic} value when CaO-doped, which is an oxide of an alkaline earth element is at 800 ° C. 0.01
(Ωcm) ^-1 .

A ceria-based material is known as a material having high oxygen ion conductivity in a low temperature range. For example, CeO ₂ which is an oxide of ceria has a fluorite-type cubic structure in a temperature range from room temperature to a melting point. When a rare earth element or CaO is added to this oxide (CeO ₂ ), a solid solution is formed over a wide range. Such material systems are described by Kubo and H.S.
Obayashi (J. Electrochem. So
c. , 123 [3], 416-419 (1976), etc.)
Has been reported by Examples of the compound which is the center of the recent _studies, CeO 2 _-Gd 2 _{O 3} system Ce _1-x G
There is d _x O _{(2-x) / 2} . This Ce _1-x Gd _x O
_{At (2-x) / 2} , oxygen vacancies are formed. In this material system, the valence of Ce changes, so that it is reduced to Ce metal in a reducing atmosphere and electron conductivity occurs in a reducing atmosphere, as in the case of the bismuth system, and it is difficult to use it directly in a solid oxide fuel cell.

[0007] In recent years, a material showing high oxide ion conductivity in perovskite oxide has been discovered, and research and development have been actively conducted. The perovskite-type oxide is composed of ABO ₃ , and the two kinds of ions A and B include, for example, BaCe _0.9 Gd _0.1 and La _0.9 S
r _0.1 Ga _0.8 Mg _0.2 O ₃ , CaAl _0.7 T
iO ₃ and SrZr _0.9 Sc _0.1 O ₃ .
In particular, La _1-x Sr _x Ga _1-y Mg _y O ₃ system (LSGM)
Then, T. J. Ishihara et al. Am. Chem.
Soc. , 116, 3801-03 (1994);
Ishihara et al. Feng and J.M. B.
Goodenough, Eur. J. Solid St
ate Inorg. Chem. , 31,663-67
2 (1994), which shows high oxide ion conductivity, particularly at low temperatures and in a redox atmosphere.

[0008]

However, a solid electrolyte (oxide) using such an oxide ion conductor is disclosed.
In order to use the fuel cell as a power source for mobile objects such as automobiles or as a small distributed power source, it can withstand temperature changes due to frequent start / stop and has a short startup time up to the temperature at which oxygen ion conduction starts. Is required. In a solid electrolyte (oxide) fuel cell, many parts are made of a ceramic material, and improvement of the thermal shock resistance of a cell constituent material is an important issue. In particular, a solid electrolyte membrane that separates an oxidizing gas and a fuel gas has a high risk of explosion if broken by thermal shock, and improving the impact resistance of a solid electrolyte material is a very important issue.

[0009] For this reason, a method of reducing the thermal shock applied to the cells by devising the fuel cell design has been mainly studied. For example, J. Power
As shown in Sources 71, 268 (1998), a large number of microcells on a small and thin tube having a diameter of 2.4 mm and a thickness of about 200 μm are provided by extrusion molding of a solid electrolyte, and a thermal shock is applied. Ways to mitigate are being considered. Also, for example, Japanese Patent Application Laid-Open No. 2000-
As disclosed in Japanese Patent No. 58102, the flow rate of fuel gas discharge in the solid electrolyte cell is leveled to prevent the occurrence of cracks and the like due to heat spots on constituent materials such as the solid electrolyte, and Attempts have been made to improve the quality.

However, in any of the above cases, the thermal shock resistance is not enough to actually function as a fuel cell, and further improvement in thermal shock resistance, particularly improvement in thermal shock resistance of the solid electrolyte material itself, is desired. I have.

In order to improve the thermal shock resistance of a material, a material which can quickly equalize the temperature of the entire material without creating a heat spot of heat by applying a thermal shock to the material, that is, a material having a high thermal conductivity is used as a constituent material. It is important to use.
The thermal conductivity of yttria-stabilized zirconia or lanthanum gallate used as a solid electrolyte is 2 W / mK.
Since the thermal conductivity of these materials is low, it is considered that if the thermal conductivity of these materials can be improved, the thermal shock resistance will be greatly improved.

The present invention has been made in view of such a conventional situation,
An object of the present invention is to provide a solid electrolyte material having excellent ionic conductivity and also having heat conduction characteristics necessary for improving thermal shock resistance, a method for producing the same, and a solid oxide fuel cell using the same.

[0013]

The present invention is characterized in that a base material of an oxide solid electrolyte contains particles forming a heat conduction path. As a base material of the oxide solid electrolyte, a stabilized zirconia-based oxide or a lanthanum gallate-based oxide is preferable, and as a particle group constituting a heat conduction path, a silicon nitride single crystal particle group or an aluminum nitride particle group, and It is preferable to use a mixture of Further, the diameter of the particle group is preferably 25 μm ± 15 μm. Then, with respect to the cut surface of the solid electrolyte material, the total area of the particle groups having a minor axis diameter of 5 μm or more is an area fraction measured by a line intercept method,
It is preferably 1.5 to 30 area%.

As described above, according to the present invention, the silicon nitride single crystal is compared with amorphous and polycrystalline silicon nitride.
Since the heat conductivity is remarkably high (150 W / mK or more), a good heat conduction path can be formed together with aluminum nitride (230 W / mK). By improving the thermal conductivity of the solid electrolyte material in this way, it is possible to obtain a solid electrolyte material for a fuel cell that improves the thermal shock resistance and does not cause a decrease in the oxide ion conductivity of the solid electrolyte. In addition, these silicon nitride single crystal particles and aluminum nitride particles are chemically stable without interaction with stabilized zirconia-based oxides and lanthanum gallate-based oxides. Can be suppressed.

The present invention also relates to a method for producing a solid electrolyte material, which comprises adding a stabilized zirconia-based oxide powder or a lanthanum gallate-based oxide powder to silicon nitride single crystal powder or aluminum nitride powder in an amount of 10% by weight or more. 50% by weight or less added so that the average particle size is 2 μm or more and 40 μm
After mixing the granules prepared so as to be as follows, and a stabilized zirconia-based oxide powder or a lanthanum gallate-based oxide powder, the granules are mixed so as to be 3% by weight or more and 50% by weight or less. The granules are fired in a temperature range of 1350 ° C. to 1550 ° C. and sintered so that the granules form a heat conduction path. Here, the aspect ratio of the silicon nitride single crystal powder is preferably 5 or more and 100 or less.

According to the present invention, a method of adding a silicon nitride single crystal or aluminum nitride powder having a different particle size in a predetermined ratio as a group of particles (granules) and simultaneously sintering the same is employed. The function of the heat conduction property can be sufficiently exhibited in the solid electrolyte material while keeping the addition ratio of the powder to the minimum. That is, since the silicon nitride single crystal or aluminum nitride to be added as a dispersed phase is added in the form of granules having an appropriate particle size instead of ordinary powder, the reaction with the stabilized zirconia or lanthanum gallate-based oxide is performed at the end of the granulation. The sintered body can be obtained while keeping the inside of the granules with silicon nitride or aluminum nitride while keeping it on the surface. This allows
The silicon nitride single crystal having high thermal conductivity (silicon nitride particles) or the aluminum nitride region (aluminum nitride particles) present in the sintered body plays a role of transferring heat,
Thermal shock resistance can be improved. Furthermore, by using a high-purity silicon nitride single crystal as a particle to be added as a dispersed phase and forming a group of particles into a structure, high thermal conductivity that cannot be achieved with fine silicon nitride particles can be imparted. . And since the sintered body obtained by this manufacturing method has high thermal conductivity while maintaining good oxide ion conduction properties, it can be used as a solid electrolyte material for fuel cells having excellent thermal shock resistance. .

Further, the present invention relates to a solid oxide fuel cell, comprising a solid oxide material in which a group of particles constituting a heat conduction path is contained in a base material of an oxide solid electrolyte; And a pair of electrodes sandwiched therebetween.

According to the present invention, since the solid electrolyte material is provided, a solid oxide fuel cell having excellent thermal shock resistance and good oxide ion conductivity can be realized.

[0019]

According to the present invention, there is an effect that the thermal shock resistance of the solid electrolyte material is improved by greatly improving the heat conduction characteristics.

Further, according to the present invention, a method of adding a silicon nitride single crystal or aluminum nitride powder as a group of particles (granules) at a predetermined ratio and simultaneously sintering the same is adopted. Even if the addition ratio of the powder is minimized, the solid electrolyte material has the effect of sufficiently exhibiting the function of thermal conductivity.

Further, according to the present invention, the solid electrolyte type fuel cell can be used, for example, in automobiles by improving the thermal conductivity of the solid electrolyte material layer disposed between the pair of electrodes to enhance the thermal shock resistance. Improves the durability of solid oxide fuel cells because it has good thermal conductivity when used as a power source for mobile units or small distributed power sources, even if temperature changes occur with frequent starting and stopping of mobile units. Has the effect of doing

[0022]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The details of the solid electrolyte material according to the present invention and the method for producing the same will be described below based on embodiments.

(Solid Electrolyte Material) The base material of the solid electrolyte material according to the present invention includes a stabilized zirconia-based oxide and a lanthanum gallate-based oxide. In addition, as the stabilized zirconia-based oxide, for example, YSZ (yttrium-stabilized zirconia), ScSZ (scandium-stabilized zirconia), C
SZ (calcium stabilized zirconia) and the like are preferred. The composition of the lanthanum gallate-based oxide is not particularly limited as long as it is a Ga-based oxide having a perovskite structure _{. 9} Sr _{0 . 1} Ga _0.8 M
g _0.2 O _3-δ or (La _0.9 Sr _0.1 ) _0.9
Those having a composition such as _{Ga 0 .8 Mg 0.2 O 3-} δ is preferred.

In this embodiment, silicon nitride single crystal particles or aluminum nitride particles are included in the base material so as to form a heat conduction path. FIG. 2 schematically shows a state in which the additive particles form a heat conduction path in a substantially mesh shape in, for example, lanthanum gallate. FIG. 2 shows additive particles (particle groups) having substantially the same particle size.
Shows the state where was mixed and sintered.

As the silicon nitride single crystal, a silicon nitride whisker produced by a gas phase reaction method or the like can be used. The silicon nitride single crystal is not particularly limited, but from the viewpoint of thermal conductivity, it is preferable to use a β-type silicon nitride single crystal having few internal defects produced by a reaction between molten silicon and nitrogen gas.

(Solid Electrolyte Fuel Cell) As shown in FIG. 1, a solid electrolyte fuel cell 1 of this embodiment
It comprises a solid electrolyte material layer 2 of the present embodiment and a pair of electrodes 3 and 4 sandwiching the solid electrolyte material layer 2. By combining a solid oxide fuel cell (single cell) having such a configuration, a high-output fuel cell can be realized. Air and fuel are supplied to the solid oxide fuel cell (unit cell) 1 while being heated to 500 to 800 ° C. Here, the solid electrolyte material layer 2 functions to carry oxygen ions from the air electrode serving as one electrode to the fuel electrode side serving as the other electrode, thereby generating an electromotive force.

The solid electrolyte material layer 2 having such a structure is
When used in the solid oxide fuel cell 1 having different temperatures depending on parts, stable characteristics can be obtained.
Further, the device can be a device that can stably exhibit characteristics even in a situation where the temperature of the oxygen sensor used in the exhaust pipe of the vehicle is drastic, despite its small size, and the performance tends to change easily.

(Vehicle Oxygen Sensor) Such a solid electrolyte material can also be applied to a vehicle oxygen sensor 10 as shown in FIG. As shown in FIG. 4, the vehicle oxygen sensor 10 includes a conductive hermetic seal 12 in a container-like case 11 in which a plurality of ventilation holes 11A are formed.
A solid electrolyte material layer 15 made of the above-described material sandwiched between the standard electrode (Pt) 13 and the detection electrode (Pt) 14 is housed. Note that the outer surface of the detection electrode 14 is covered with a protective film 16. An exhaust gas duct wall 17 is provided around the upper part of the case 11 so as to guide exhaust gas from outside the case 11 to the ventilation hole 11A. The standard gas SG is introduced into the space inside the standard electrode 13.

By applying the solid electrolyte material of the present invention to such a vehicle oxygen sensor 10, a vehicle oxygen sensor having excellent durability and stability can be realized.

For this reason, the solid electrolyte according to the present embodiment has a high heat conduction characteristic as described above, and can be sufficiently used for a fuel cell such as an automobile or a distributed power source which requires a fast start-up characteristic. is there.

(Method of Manufacturing Solid Electrolyte Material) Next, an embodiment of a method of manufacturing a solid electrolyte material according to the present embodiment will be described.

(A) Stabilized zirconia-based oxide powder or lanthanum gallate-based oxide powder is added to silicon nitride single crystal powder or aluminum nitride powder in an amount of 10% by weight or more.
0% by weight or less so that the average particle size is 2 μm or more.
A granulated body prepared to be 0 μm or less is produced. The silicon nitride single crystal powder has an aspect ratio of 5
It is preferably at least 100 and at most 100.

(B) Next, the stabilized zirconia-based oxide powder or lanthanum gallate-based oxide powder was mixed with
It is mixed so as to be at least 50% by weight.

(C) Thereafter, the granules are fired in a temperature range of 1350 ° C. to 1550 ° C. and sintered so that the above-mentioned granules form a continuous structure forming a heat conduction path.

In the manufacturing method of the present embodiment, a method is adopted in which silicon nitride single crystal or aluminum nitride powder having different particle diameters are added as particles (granules / granules) at a predetermined ratio and simultaneously sintered. Thereby, the function of heat conduction properties can be sufficiently exhibited in the solid electrolyte material while the addition ratio of the silicon nitride single crystal or aluminum nitride powder is minimized.

Hereinafter, examples and comparative examples to which the present invention is applied will be described.

(Examples) (Examples 1 to 6, Comparative Examples 4 to 7) A lanthanum gallate-based oxide which is a base material (matrix) of a solid electrolyte material is as follows:
Each raw material (La ₂ O ₃ , SrCO ₃ , Ga ₂ O ₃ , Mg
O) was weighed and mixed in a ball mill for 24 hours in alcohol. After drying the slurry obtained by this mixing, it was calcined in the atmosphere at a temperature of 1150 ° C. for 6 hours.
The powder was again pulverized in an alcohol so as to have an average particle diameter of 0.8 μm or less by a ball mill, and then dried to obtain a base material powder.

On the other hand, as an additional phase, a high-purity silicon nitride single crystal and a lanthanum gallate-based oxide powder separately prepared by a silicon nitride molten nitrogen gas synthesis method were used in a ball mill in ethanol at a predetermined ratio for 48 hours. After mixing and grinding,
The particles were shaken from an average particle size of 2 ± 1 μm to 50 ± 5 μm, mixed at a predetermined volume ratio, and mixed by a V-type blender to obtain a particle group powder.

This lanthanum gallate-based oxide particle group powder was compacted with a mold, molded at a pressure of ² ton / cm ² by a hydrostatic pressure press, and sintered at 1450 ° C. for 6 hours to obtain a solid electrolyte.

In the sintering, a co-fabric torch and an alumina sheath are preferably used, but the torch may be made of alumina. Incidentally, the tochi is a plate on which the green compact is fired, and preferably has a thermal expansion coefficient similar to that of the fired material and low reactivity. Saya is a ceramic enclosure for keeping the temperature conditions during firing and protecting the sample from dust and the like. Usually, it is used for sintering a large number of samples in a multi-layered manner such as Tochi, Saya, Tochi and Saya. Then, each 10 × 10 × 0.5 mm test piece was prepared.

Comparative Example 1 (lanthanum gallate alone) A lanthanum gallate-based oxide was prepared using various raw materials (La ₂ O ₃ , S
rCO ₃ , Ga ₂ O ₃ , MgO) were weighed and mixed in an alcohol using a ball mill for 24 hours. After drying the obtained slurry, it was calcined in the air at a temperature of 1150 ° C. for 6 hours. The average particle size is 0.8μ again using a ball mill.
m and then dried in alcohol.

The lanthanum gallate-based oxide powder was compacted with a mold, molded at a pressure of ² ton / cm ^{2 by} a hydrostatic press, and sintered at a predetermined temperature (1450 ° C.) for 6 hours to form a solid electrolyte. Obtained.

In the sintering, a co-textured torch and an alumina sheath are preferably used, but the torch may be made of alumina. Next, a test piece of 10 × 10 × 0.5 mm was prepared.

Comparative Example 2 (Addition of Silicon Nitride Powder) Lanthanum gallate was obtained from each raw material (La ₂ O ₃ , SrC
O ₃ , Ga ₂ O ₃ , and MgO) were weighed and mixed in an alcohol using a ball mill for 24 hours. After drying the obtained slurry, it was calcined in the air at a temperature of 1150 ° C. for 6 hours. The powder was again pulverized in an alcohol so as to have an average particle diameter of 0.8 μm or less by a ball mill, and then dried.

On the other hand, commercially available β-Si ₃
N ₄ 48 in a ball mill powder (manufactured by Ube Industries, Ltd.) and lanthanum gallate-based oxide powder in ethanol at a predetermined ratio
After mixing and grinding for an hour, the average particle size of the granules is 2 ± 1 μm to 50
The mixture was shaken to ± 5 μm, mixed at a predetermined volume ratio, and mixed by a V-type blender to obtain a particle group powder.

The lanthanum gallate-based oxide powder was compacted with a mold, molded at a pressure of ² ton / cm ^{2 by} a hydrostatic press, and sintered at a predetermined temperature (1450 ° C.) for 6 hours to obtain a solid electrolyte. Was. Next, a test piece of 10 × 10 × 0.5 mm was prepared. At the time of sintering, it is preferable to use a co-fabric torch and an alumina sheath, but the torch may be made of alumina.

Comparative Example 3 (Silicon Nitride Single Crystal Uniform Dispersion) Lanthanum gallate-based oxide as a base material
₂ O ₃ , SrCO ₃ , Ga ₂ O ₃ , MgO)
The mixture was mixed in an alcohol by a ball mill for 24 hours. After drying the obtained slurry, it was calcined at 1150 ° C. for 6 hours in the air. The average particle size is 0.8μm again using a ball mill
After pulverizing in alcohol as described below, it was dried to obtain a base material powder. This powder was mixed with a high-purity silicon nitride single crystal separately prepared by a silicon nitride molten nitrogen gas synthesis method at a predetermined volume ratio, and mixed with a V-type blender.

This lanthanum gallate particle group powder was compacted with a mold, molded at a pressure of ² ton / cm ^{2 by} a hydrostatic press, and sintered at 1450 ° C. for 6 hours to obtain a solid electrolyte.

At the time of firing, it is preferable to use a co-fabric torch and an alumina sheath, but the torch may be made of alumina.

Next, test specimens of 10 × 10 × 0.5 mm were prepared.

Evaluation of characteristics (1) Evaluation of microstructure of particle group: The sample was polished with diamond particles (0.26 μm) and then subjected to an optical microscope. The particle diameter was determined by averaging the diameters of the particles contained in a 4 × 4 mm area of the micrograph. The diameter of the particle group was determined by taking a photograph of the silicon nitride particle group on the polished surface, randomly drawing a straight line on the photograph, obtaining the particle diameters of all the silicon nitride particle groups intersecting the straight line, and averaging the average. The line intercept method was used to determine the diameter of the particle group by an image analyzer as the number average of the group.

(2) Thermal shock test: A sample was placed in a crucible made of alumina, heated in an electric furnace to 500 ° C. for 10 minutes, held at 500 ° C. for 10 minutes, and thereafter at a rate of 10 ° C./min. And cooled. The removed sample was visually observed, and whether or not a crack was observed in the sample was determined as a thermal shock test.

The following Table 1 shows Examples 1 to 6 and Comparative Examples 1 to
9 shows the composition of Comparative Example 7, the structure of added particles, the dispersed structure, and the results of a thermal shock test obtained based on the above evaluation method.

[0054]

[Table 1] Effect of added particle group: (Example 1 and Comparative Example 1, Comparative Example 2) By adding the silicon nitride single crystal particle group, the thermal shock resistance is improved as compared with the case of no addition. This indicates that the silicon nitride single crystal particles efficiently form a heat conduction path without excessive reaction of the silicon nitride with the base material of the lanthanum gallate-based oxide. Even with the same silicon nitride material, the thermal shock resistance is improved by adding the silicon nitride single crystal particles. This is because silicon nitride powder other than a single crystal has a low thermal conductivity (about 40 to 70 W / mK) and does not efficiently serve as a heat conduction path. The results show that the silicon nitride single crystal particle group is very effective in improving the thermal shock resistance. Particle Group Structure Addition Effect: Example 2 and Comparative Example 3 Even with the same silicon nitride single crystal particle group addition area ratio, the particle group The system added as a group of particles (Example 2) has improved thermal shock resistance as compared with the system uniformly added (Comparative Example 3), indicating that the effect of adding as a group of particles is large. ing. This is because a multiphase ceramic material is produced by adding silicon nitride single crystal powder as a group of particles (granules) at a predetermined ratio and simultaneously sintering, thereby minimizing the thermal conductivity by adding silicon nitride. Improve the characteristics,
This is an effect obtained by forming a particle group dispersed microstructure capable of sufficiently exhibiting a function of imparting thermal shock resistance.

Effect of Particle Group Diameter: Examples 2, 5, 6 and Comparative Examples 6, 7 The thermal shock resistance can be improved by using the silicon nitride particle group of 25 μm ± 15 μm as the added phase. When the diameter of the particle group is 40 μm or more, the thermal diffusion path of the single crystal particles is not continuous, but is dispersed.

Area fraction: Examples 1 to 4 and Comparative examples 4 and 5 When the cut surfaces of the sintered bodies were observed, the total area of the silicon nitride particles having a minor axis diameter of 5 μm or more was determined by the line intercept method. In terms of the area fraction measured in the above, it is more preferable to be 1.5 to 30 area%, and if the area of the silicon nitride particle group is small, sufficient thermal shock resistance tends to be unable to be given. When the area of the silicon nitride particles is large, the crystals collide with each other, and the sintered density tends to be low. Therefore, it is more preferable that the area be 30 area% or less. .

(Examples 7 to 12 and Comparative Examples 8 to 11) A lanthanum gallate-based oxide as a base material was prepared by using each raw material (La ₂ O).
₃ , SrCO ₃ , Ga ₂ O ₃ , MgO ) Was weighed and mixed in a ball mill for 24 hours in alcohol. After drying the obtained slurry, it was calcined at 1150 ° C. for 6 hours in the air. The powder was again pulverized in an alcohol so as to have an average particle diameter of 0.8 μm or less by a ball mill, and then dried to obtain a base material powder.

On the other hand, as an additional phase, aluminum nitride powder and high-purity lanthanum gallate oxide powder manufactured by Kojundo Chemical Co., Ltd. were mixed and pulverized at a predetermined ratio in ethanol in a ball mill for 48 hours, and then the average particle size of the granules was 2 ± 2. From 1 μm to 50 ± 5
The mixture was shaken down to μm, mixed at a predetermined volume ratio, and mixed by a V-type blender to obtain a particle group powder.

This lanthanum gallate particle group powder was compacted with a mold, molded at a pressure of ² ton / cm ^{2 by} a hydrostatic press, and sintered at 1450 ° C. for 6 hours to obtain a solid electrolyte.

At the time of sintering, it is preferable to use a co-fabric torch and an alumina sheath, but the torch may be made of alumina.

Next, test pieces of 10 × 10 × 0.5 mm were prepared.

Comparative Example 12 (Aluminum Nitride Uniform Dispersion) A lanthanum gallate-based oxide as a base material
₂ O ₃ , SrCO ₃ , Ga ₂ O ₃ , MgO)
The mixture was mixed in an alcohol by a ball mill for 24 hours. After drying the obtained slurry, it was calcined at 1150 ° C. for 6 hours in the air. The average particle size is 0.8μm again using a ball mill
After pulverizing in alcohol as described below, it was dried to obtain a base material powder. This powder was mixed with aluminum nitride powder manufactured by Kojundo Chemical Co., Ltd. at a predetermined volume ratio, and mixed with a V blender.

The lanthanum gallate particle group powder was compacted with a mold, molded at a pressure of ² ton / cm ^{2 by} a hydrostatic press, and calcined at 1450 ° C. for 6 hours to obtain a solid electrolyte.

A 10 × 10 × 0.5 mm test piece was prepared.

(Evaluation of Characteristics) (1) Evaluation of microstructure of particle group: The sample was polished with diamond particles (0.26 μm), and then subjected to an optical microscope. The particle diameter was determined by averaging the diameters of the particles contained in a 4 × 4 mm area of the micrograph. The diameter of the particle group was determined by taking a photograph of the silicon nitride particle group on the polished surface, randomly drawing a straight line on the photograph, obtaining the particle diameters of all the silicon nitride particle groups intersecting the straight line, and averaging the average. The line intercept method was used to determine the particle size of the particle group by an image analyzer as the number average of the group.

(2) Thermal shock test: A sample was placed in a crucible made of alumina, heated in an electric furnace to 500 ° C. for 10 minutes, held at 500 ° C. for 10 minutes, and then at a rate of 10 ° C./min. Cool. The removed sample was visually observed, and whether or not a crack was observed in the sample was determined as a thermal shock test. Table 2 below shows Examples 7 to 12 and Comparative Examples 8 to 12.
2 shows the results of a thermal shock test of a lanthanum gallate-based material obtained based on the above evaluation method.

[0067]

[Table 2] Effect of added particle group: (Example 8 and Comparative Example 1) By adding the aluminum nitride particle group, the thermal shock resistance is improved as compared with the case of no addition. This is because aluminum nitride does not cause an extreme reaction with the lanthanum gallate-based oxide material, and the silicon nitride single crystal particles efficiently form a heat conduction path. From this result, it can be seen that the aluminum nitride particles are very effective in improving the thermal shock resistance.

Effect of adding particle group structure: Example 8 and Comparative Example 1
2. Even with the same aluminum nitride single crystal particle group area ratio, the system added as the particle group (Example 8) is improved in thermal shock resistance as compared with the system added uniformly as the particle group (Comparative Example 12). Shows that the effect of adding as a particle group is great. This is because aluminum nitride is added as a group of particles (granules) in a predetermined ratio and sintered at the same time to produce a multi-phase ceramic material, thereby improving the heat transfer characteristics by minimizing the addition ratio of aluminum nitride. And
This is an effect obtained by forming a particle group dispersed microstructure capable of sufficiently exhibiting a function of imparting thermal shock resistance.

Effects of Particle Group Diameter: Examples 8, 11, and 12
And Comparative Examples 8 and 11 By setting the added phase to a silicon nitride particle group of 25 μm ± 15 μm, the thermal shock resistance can be improved.
When the diameter of the particle group is 40 μm or more, the thermal diffusion path of the single crystal particles is not continuous, but is dispersed.

Area fraction: Examples 7 to 10 and Comparative Examples 9 and 1
0 When observing the cut surface of the sintered body, the total area of the silicon nitride particles having a minor axis diameter of 5 μm or more is 1.5 to 30 area% as an area fraction measured by a line intercept method. If the area of the aluminum nitride particles is small, sufficient thermal shock resistance tends not to be imparted. Therefore, the area is preferably 1.5% by area or more. If the area is large, crystals will collide with each other, and the sintering density tends to decrease.

(Examples 13 to 18, Comparative Examples 15 to 18)
The stabilized zirconia was obtained by pulverizing commercially available 8 mol% yttrium-stabilized zirconia (manufactured by Tosoh Corporation) in an alcohol so as to have an average particle diameter of 0.8 μm or less by a ball mill, and then drying to obtain a matrix powder.

On the other hand, as an additional phase, a high-purity silicon nitride single crystal and a stabilized zirconia powder separately prepared by a silicon nitride molten nitrogen gas synthesizing method were mixed and pulverized in ethanol at a predetermined ratio in a ball mill for 48 hours. After that, shake the granule from 2 ± 1μm to 50 ± 5μm,
The particles were mixed at a predetermined volume ratio and mixed by a V-type blender to obtain a particle group powder.

This stabilized zirconia particle group powder is compacted with a mold, molded by a hydrostatic press at a pressure of ² ton / cm ² , and sintered at a predetermined temperature (1600 ° C. to 1800 ° C. for 6 hours). Thus, a solid electrolyte was obtained.

In the sintering, it is preferable to use a co-fabric torch and an alumina sheath, but the torch may be made of alumina.

Next, test specimens of 10 × 10 × 0.5 mm were prepared.

Comparative Example 13 (YSZ alone) Stabilized zirconia was obtained by using a commercially available 8 mol% yttrium-stabilized zirconia (manufactured by Tosoh Corporation) with a ball mill having an average particle size of O.D. After pulverizing in alcohol to 8 μm or less, it is dried. This stabilized zirconia powder is compacted with a mold, and molded with a hydrostatic press at a pressure of ² ton / cm ² .
Sintering was performed at a predetermined temperature to obtain a solid electrolyte. At the time of sintering, it is preferable to use a co-fabric torch and an alumina sheath, but the torch may be made of alumina.

Comparative Example 14 (Addition of Silicon Nitride Powder) Stabilized zirconia was obtained by pulverizing a commercially available 8 mol% yttrium stabilized zirconia (manufactured by Tosoh Corporation) in an alcohol so that the average particle size would be 0.8 μm or less. After that, commercially available β-Si ₃ N _{4 is} added to the powder at a predetermined volume ratio.
Powder (made by Ube Industries) was blended and mixed by a V blender.

The lanthanum gallate-based oxide powder was compacted with a mold, molded at a pressure of ² ton / cm ^{2 by} a hydrostatic press, and sintered at a predetermined temperature to obtain a solid electrolyte. At the time of sintering, it is preferable to use co-fabric tochi and alumina sheath, but the tochi may be made of alumina. Next, a test piece of 10 × 10 × 0.5 mm was prepared.

Comparative Example 19 (Silicon Nitride Single Crystal Uniform Dispersion) As the stabilized zirconia, commercially available 8 mol% yttrium stabilized zirconia (manufactured by Tosoh Corporation) was subjected to ball milling to obtain an average particle diameter of O.I. After pulverizing in alcohol to 8 μm or less, it was dried to obtain a base material powder. This powder was mixed with a high-purity silicon nitride single crystal separately prepared by a silicon nitride molten nitrogen gas synthesis method at a predetermined volume ratio, and mixed with a V-type blender.

The lanthanum gallate-based oxide particle group powder was compacted with a mold, molded at a pressure of ² ton / cm ^{2 by} a hydrostatic press, and sintered at a predetermined temperature to obtain a solid electrolyte. At the time of sintering, it is preferable to use co-fabric tochi and alumina sheath, but the tochi may be made of alumina. Next, a test piece of 10 × 10 × 0.5 mm was prepared.

(Evaluation of Characteristics) (1) Evaluation of microstructure of particle group: After polishing a sample with diamond particles (0.26 μm), observation was performed with an optical microscope. The particle diameter was determined by averaging the diameters of the particles contained in a 4 × 4 mm area of the micrograph. The diameter of the particle group was determined by taking a photograph of the silicon nitride particle group on the polished surface, randomly drawing a straight line on the photograph, obtaining the particle diameters of all the silicon nitride particle groups intersecting the straight line, and averaging the average. The line intercept method was used to determine the diameter of the particle group by an image analyzer as the number average of the group.

(2) Thermal shock test: The sample was placed in a crucible made of alumina, heated in an electric furnace to 500 ° C. for 10 minutes, held at 500 ° C. for 10 minutes, and then at a rate of 10 ° C./min. And cooled. The removed sample was visually observed, and whether or not a crack was observed in the sample was determined as a thermal shock test. Table 3 below shows Examples 13 to 18 and Comparative Example 13.
19 to 19 show the results of a thermal shock test of a lanthanum gallate-based oxide material obtained based on the above evaluation method.

[0083]

[Table 3] Effect of additive particle group: (Example 13 and Comparative Examples 13 and 14) By adding the silicon nitride single crystal particle group, the thermal shock resistance is improved as compared with the case where no silicon nitride single crystal particle is added. This indicates that the silicon nitride single crystal particles efficiently form a heat conduction path without the silicon nitride causing an extreme reaction with the stabilized zirconia material. Even with the same silicon nitride material, the thermal shock resistance is improved by adding the silicon nitride particles. This is because the thermal conductivity of silicon nitride powder (4
(Approximately 0-70 W / mK), which does not efficiently serve as a heat conduction path. From this result, it can be seen that the silicon nitride single crystal particles are very effective in improving the thermal shock resistance.

Effect of adding particle group structure: (Example 14 and Comparative Example 19) Even with the same silicon nitride single crystal particle group addition area ratio, a particle group was added as compared with a system (Comparative Example 19) which was not uniformly added but a particle group. The system added (Example 14) has improved thermal shock resistance, indicating that the effect of adding as a particle group is large. This is achieved by producing a multi-phase ceramic material by a method in which silicon nitride single crystal powder is added as a group of particles (granules) at a predetermined ratio and simultaneously sintered.
This is an effect obtained by providing a particle group dispersed microstructure that can improve the thermal conductivity while minimizing the addition ratio of silicon nitride and sufficiently exhibit the function of imparting thermal shock resistance.

Effect of Particle Group Diameter: (Examples 14, 17,
18 and Comparative Examples 17 and 18) By using the silicon nitride particles having a diameter of 25 μm ± 15 μm, the thermal shock resistance can be improved. If the diameter of the particle group exceeds 40 μm, the thermal diffusion paths of the single crystal particles are not continuous, but are dispersed.

Area fraction: Examples 13 to 16 and Comparative Example 1
5, 16 When the cut surface of the sintered body was observed, the total area of the silicon nitride particles having a minor axis diameter of 5 μm or more was 1.5 to 30% by area in terms of the area fraction measured by the line intercept method. Is more preferable. If the area of the silicon nitride particles is small, sufficient thermal shock resistance tends not to be imparted. Therefore, the area is preferably 1.5% by area or more. Furthermore, if the area of the silicon nitride particles is large, the crystals will collide with each other, and the sintering density tends to decrease. Therefore, it is more preferable to set the area to 30% by area or less.

Examples 18 to 23 and Comparative Examples 17 to 20 Stabilized zirconia was prepared by using a commercially available 8 mol% yttrium-stabilized zirconia (manufactured by Tosoh Corporation) in an alcohol so that the average particle size would be 0.8 μm or less in a ball mill. And then dried to obtain a base material powder.

On the other hand, as an additive phase, aluminum nitride powder (manufactured by Kojundo Chemical Co., Ltd.) and stabilized zirconia powder are dissolved in ethanol or the like at a predetermined ratio, and the mixture is subjected to 48 ball milling.
After mixing and grinding for an hour, the average particle size of the granules is 2 ± 1 μm to 50
The mixture was shaken to ± 5 μm, mixed at a predetermined volume ratio, and mixed by a V-type blender to obtain a particle group powder.

The stabilized zirconia particle group powder was compacted with a mold, molded at a pressure of ² ton / cm ^{2 by} a hydrostatic press, and sintered at a predetermined temperature (1600 ° C. to 1800 ° C.) for 6 hours. A solid electrolyte was obtained. At the time of sintering, it is preferable to use a co-fabric torch and an alumina sheath, but the torch may be made of alumina. Then each 10 × 10 ×
A test piece of 0.5 mm was prepared.

Comparative Example 24 (Aluminum Nitride Uniform Dispersion) Stabilized zirconia was obtained by pulverizing commercially available 8 mol% yttrium stabilized zirconia (manufactured by Tosoh Corporation) in an alcohol so that the average particle size would be 0.8 μm or less. After that, it was dried to obtain a base material powder. An aluminum nitride powder manufactured by Kojundo Chemical Co., Ltd. was blended with this powder in a predetermined volume ratio and mixed with a V-type blender. This stabilized zirconia powder was compacted with a mold, molded by a hydrostatic press at a pressure of ² ton / cm ² , and sintered at 1450 ° C. for 6 hours to obtain a solid electrolyte. At the time of sintering, it is preferable to use a co-fabric torch and an alumina sheath, but the torch may be made of alumina. Next, a test piece of 10 × 10 × 0.5 mm was prepared.

Table 4 below shows the results of the thermal shock resistance of the stabilized zirconia material obtained based on the above evaluation method for Examples 19 to 24 and Comparative Examples 13 and 20 to 24.

[0092]

[Table 4] Effect of added particle group: Example 20 and Comparative Example 13 By adding the aluminum nitride particle group, the thermal shock resistance is improved as compared with the case without the addition. This is because aluminum nitride does not cause an extreme reaction with the stabilized zirconia base material, and the silicon nitride single crystal particles efficiently form a heat conduction path. From these results, it can be seen that the aluminum nitride particles are very effective in improving the thermal shock resistance.

Effect of adding particle group structure: Example 20 and Comparative Example 24 Even with the same aluminum nitride single crystal particle group area ratio, a system in which particles were added as a particle group compared to a system in which particles were not uniformly added but a uniform group (Comparative Example 24) (Example 20) shows that the thermal shock resistance is improved and the effect of adding as a particle group is large. This is by producing a multi-phase ceramic material by a method in which aluminum nitride is added as a group of particles (granules) at a predetermined ratio and simultaneously sintered.
This is an effect obtained by using a particle group-dispersed microstructure capable of improving the heat conduction characteristics by minimizing the addition ratio of aluminum nitride and sufficiently exhibiting the function of imparting thermal shock resistance.

Effect of particle group diameter: Examples 20, 23, 2
4 and Comparative Examples 20 and 23 By using silicon nitride particles having a diameter of 25 μm ± 15 μm, the thermal shock resistance can be improved. When the diameter of the particle group is 40 μm or more, the thermal diffusion path of the single crystal particles is not continuous, but is dispersed.

Area fraction: Examples 19 to 22 and Comparative Example 2
1,22 Observation of the cut surface of the sintered body revealed that the total area of the silicon nitride particles having a minor axis diameter of 5 μm or more was 1.5 to 30 area% as the area fraction measured by the line intercept method. If the area of the aluminum nitride particles is small, sufficient thermal shock resistance tends not to be imparted. Therefore, the area is preferably 1.5% by area or more. If the area of the aluminum particle group is large, the crystals collide with each other, and the sintering density tends to decrease. Therefore, it is more preferable to set the area to 30% by area or less.

Although the embodiments and examples of the present invention have been described above, it should not be understood that the description and drawings constituting a part of the disclosure of the above embodiments limit the present invention. From this disclosure, various alternative embodiments, examples, and operation techniques will be apparent to those skilled in the art.

For example, in the above-described embodiment, YSZ (yttrium-stabilized zirconia), ScSZ (scandium-stabilized zirconia), and CSZ (calcium-stabilized zirconia) have been described as stabilized zirconia-based oxides. It is of course possible to apply stabilized zirconia.

In the above-described embodiment, La _0.9 Sr _0.1 Ga is used as the lanthanum gallate-based oxide.
_0.8 Mg _0.2 O _3-δ or (La _0.9 Sr
_0.1 ) An oxide having a composition such as _0.9 Ga _0.8 Mg _0.2 O _3-δ was mentioned, but it is not particularly limited as long as it is a Ga-based oxide having a perovskite structure. is not.

Further, in the above embodiment, the silicon nitride single crystal particles or the aluminum nitride particles are added, respectively. However, the silicon nitride single crystal particles and the aluminum nitride particles are mixed in the base material. It may be configured to be added by adding.

[Brief description of the drawings]

FIG. 1 is an explanatory view showing an embodiment of a solid oxide fuel cell according to the present invention.

FIG. 2 is an explanatory view schematically showing a structure of a solid electrolyte material according to the present invention.

FIG. 3 is a sectional view showing an example in which the solid electrolyte material according to the present invention is applied to an automobile oxygen sensor.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 solid oxide fuel cell 2 lanthanum gallate solid electrolyte layer 3, 4 electrodes

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Fumio Munakata 2 Takaracho, Kanagawa-ku, Yokohama, Kanagawa Prefecture, Nissan Motor Co., Ltd. (72) Inventor Shoji Hatano 2 Takaracho, Kanagawa-ku, Yokohama City, Kanagawa Nissan Motor Co. Terms (reference) 4G031 AA04 AA07 AA08 AA12 AA38 BA03 BA07 BA23 CA01 CA04 GA01 GA03 GA14 5H026 AA06 BB01 BB08 CC01 CV02 CX05 EE11 EE12 HH00 HH01 HH02 HH05 HH08

Claims (8)

[Claims] 1. A solid electrolyte material characterized in that a matrix of particles forming a heat conduction path is contained in a base material of the oxide solid electrolyte. 2. The solid electrolyte material according to claim 1, wherein the base material is made of a stabilized zirconia-based oxide or a lanthanum gallate-based oxide. 3. The solid electrolyte material according to claim 1, wherein the particle group comprises a silicon nitride single crystal particle group and / or an aluminum nitride particle group. 4. The base material having a diameter of 25 μm ± 15 μm.
The solid electrolyte material according to any one of claims 1 to 3, wherein the solid electrolyte material is made of a multiphase ceramic mainly composed of the particles. 5. A method according to claim 1, wherein the total area of the particle groups having a minor axis diameter of 5 μm or more with respect to the cut surface is 1.5 to 30 area% as an area fraction measured by a line intercept method. The solid electrolyte material according to any one of claims 1 to 4, wherein 6. A stabilized zirconia-based oxide powder or a lanthanum gallate-based oxide powder is added to a silicon nitride single crystal powder or an aluminum nitride powder at a ratio of 10% by weight or more and 50% by weight or less to obtain an average particle size. 2μm or more and 40μ
m and a stabilized zirconia-based oxide powder or a lanthanum gallate-based oxide powder were mixed with each other so that the granulated body was 3% by weight or more and 50% by weight or less. And baking at a temperature in the range of 1350 ° C. to 1550 ° C. to sinter the granules so as to form a heat conduction path. 7. The method for producing a solid electrolyte material according to claim 6, wherein the silicon nitride single crystal powder has an aspect ratio of 5 or more and 100 or less. 8. A solid electrolyte fuel cell, comprising: the solid electrolyte material according to claim 1; and a pair of electrodes sandwiching the solid electrolyte material.