JP2002316872A - Lanthanum gallate-base solid electrolytic material, method for manufacturing the same and solid electrolyte type fuel battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a lanthanum gallate-base solid electrolytic material which is usable in a low-temperature region as a component of a solid electrolyte type fuel battery and is good in mechanical strength. SOLUTION: A lanthanum gallate-base solid electrolyte layer 2 consisting of a sintered compact formed by adding silicon nitride or titanium nitride as particle groups at a ratio from >=0.5 to <=10 wt.% to a lanthanum gallate-base oxide is grasped between electrodes 3 and 4, by which the solid electrolyte type fuel battery 1 is constituted. The solid electrolyte type fuel battery can be used for a longer time and its stable characteristics can be maintained by adapting such constitution.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a solid electrolyte material and a fuel cell using the same, and more particularly, a lanthanum gallate-based solid electrolyte material which is a perovskite-type ceramic solid electrolyte, a method for producing the same, and a solid material using the same. The present invention relates to an electrolyte fuel cell.

[0002]

2. Description of the Related Art After Nernst discovered a solid electrolyte in 1899, Baur and Preis decided to use a solid oxide fuel cell (SOFC) at 1000 ° C. in 1937.
, The solid electrolyte fuel cell has continued to advance,
Zirconia-based ceramic fuel cells with an output of several kW have been operated for tens of thousands of hours. This solid fuel cell has 1
In order to operate at a high temperature of 000 ° C. or higher, it is considered that a hydrocarbon-based fuel can be reformed in a cell, and a high combustion efficiency of 60% or higher can be obtained.

[0003] Usually, the structure of a solid electrolyte combustion battery is composed of a solid electrolyte, a combustion electrode and an intermediate layer. All constituent materials must be stable in an oxidation-reduction atmosphere and have appropriate conductivity. Further, the thermal expansion coefficients of the constituent materials are close to each other, and it is necessary that the anode and the cathode are porous bodies and gas can pass therethrough. Naturally, it is desired that the battery material be chemically stable in an oxidation-reduction atmosphere and inexpensive. From the viewpoint of stability during operation, a material system having high ionic conductivity at a temperature as low as possible is desirable as a basic requirement of the ionic conductor. Further, in order to improve the power generation efficiency, studies have been made mainly on zirconia materials to reduce the internal resistance of the solid electrolyte by thinning the solid electrolyte. Therefore, development of a material system having both high oxygen ion conductivity and strength capable of forming a thin film is strongly desired.

At present, stabilized ZnO is used as a solid electrolyte.
_Two are the most actively studied. As a stabilizer, 2
Oxide of alkaline earth element CaO, MgO, Sc ₂
0 ₃ and the like rare earth oxides such as such or Y ₂ O _3. When doped with CaO, which is an oxide of an alkaline earth element, the characteristic value shows an ion conductivity of 0.01 (Ωcm) ⁻¹ at 800 ° C. As indicated in the paper (H. Tannenberger
Proc. Int'l Etude Piles Combust, 19-26 (1965) Ion conductivity when doped with rare earth oxides (Y2O3, Yb2O3, and Gd2O3) is 1 × 10 ^-1 to 1 × 10 at 800 ° C.
^-2 (Ωcm) ^-1 . 2x when the temperature drops below 650 ° C
The output falls below 10 -2 (Ωcm) -1. Also,
In order to reduce the electrolyte resistance in the low temperature range, it has been studied to reduce the thickness of the solid electrolyte membrane to about 5 to 10 μm. However, the internal resistance can be reduced to some extent, but the electrode performance is low due to low ionic conductivity. The problem of not being able to fully demonstrate is becoming apparent.

[0005] Rare earth alone stabilized zirconia is 197
It has been known by the year 0, and for the stabilized zirconia of rare earth and alkaline earth, Japanese Patent Publication No. 57-5074
No. 8 discloses this.

[0006] Stabilized bismuth is known as another solid electrolyte material. The high temperature phase (δ phase) of Bi ₂ O ₃ has a defective fluorite structure (Bi ₄ O ₆ □ ₂ ), has low activation energy for oxide ion transfer, and exhibits high oxide ion conductivity. The high-temperature phase can be stabilized to a low temperature by dissolving the rare-earth oxide, and exhibits high oxygen ion conductivity. T. Takahashi et al., J. APPL. Electrochemistry, 5 (3), 18
As shown in 7-195 (1975), rare earth stabilized zirconia, for example, (Bi ₂ O ₃ ) _1-x (Y ₂ O ₃ ) _x is 0.1 (Ωcm) ⁻¹ at 700 ° C. and 0 at 500 ° C. 0.001 (Ωcm)
^-1 , which is 10 to 100 times larger than that of stabilized zirconia. JP-B-62-45191 discloses a mixture of stabilized bismuth oxide and stabilized zirconium oxide.
Results of greater than 0.1 (Ωcm) ⁻¹ at 0 ° C. are disclosed. For this reason, it is expected that high ionic conductivity can be obtained in a temperature range of less than 1000 ° C., but in a reducing atmosphere, it is reduced to Bi metal, so that electron conductivity occurs.
When used as a solid electrolyte, efficiency is reduced, and it is difficult to directly use it.

As another solid electrolyte material, a ceria-based material is known. CeO ₂ has a fluorite-type cubic structure in the temperature range from room temperature to the melting point. When a rare earth element or CaO is added to this oxide, a solid solution is formed over a wide range. This material system is based on Kudo and H. Obayashi (J. Electrochem. S
oc., 123 [3], 416-419 (1976)). In the CeO ₂ -Gd ₂ O ₃ system, which is the central compound of recent research, Ce _{1 -x} Gd _x O _{(2-x ) / 2} is formed, and oxygen vacancies are formed. Since the valence of Ce changes in this system, it is reduced to Ce metal in a reducing atmosphere, as in the case of the bismuth system, so that electron conductivity occurs and direct use is difficult.

As another candidate material that can be used at a low temperature, there is a perovskite oxide, which has been actively researched and developed in recent years. The perovskite-type oxide is composed of ABO ₃ , A,
Two ions of B, for example BaCe _0.9 Gd _0.1 , La
_0.9 Sr _0.1 Ga _0.8 Mg _0.2 O ₃ , CaAl _0.7 TiO ₃ and SrZr _0.9 Sc _0.1 O ₃ . In particular, La _1-x Sr _x
For Ga _1-y Mg _y O ₃ system (LSGM), T. Ishihara et al., JA
m. Chem. Soc., 116, 3801-03 (1994), T. Ishihara et al., MF
eng and JBGoodenough, Eur.J. Solid State Inorg.Ch
em., 31, 663-672 (1994), which can be expected to have high oxide ion conductivity at low temperatures and in a redox atmosphere.

[0009]

However, since the output of a single cell of a battery using such a material is limited to several volts, it is necessary to adopt a laminated structure in order to obtain a high voltage. In such a ceramic battery, it is very difficult to select a ceramic material system, and a metal part such as a ferritic stainless steel must be effectively used for a container such as a combustor body. Therefore, there is a need to select a solid electrolyte and an electrode material that are active at a low temperature. In the future, the selection of ceramic solid electrolytes and electrode materials (development of new materials) and the manufacturing technology of laminated structures will be important issues.

As a solid electrolyte for operating a solid electrolyte fuel cell in a low temperature range where such metal parts can be used, zirconia has a low ionic conductivity at a low temperature, and bismuth and ceria have an electron conductivity in a reducing atmosphere. Therefore, it is not suitable for a solid electrolyte for a fuel cell at a low temperature. On the other hand, lanthanum gallate has better ionic conductivity at low temperatures than other compounds, but because of its low material strength, the solid electrolyte must be thickened when used as a fuel cell. However, there is a problem that the resistance increases. Therefore, when the lanthanum gallate material is used as a solid electrolyte material for a solid electrolyte fuel cell in a low temperature region, it is necessary to improve the mechanical strength.

As an attempt to improve the strength of the lanthanum gallate material, a method of substituting Al for the Ga site of lanthanum gallate, a method of mixing a plurality of Al-substituted phases,
A method of dispersing l ₂ O ₃ particles has been proposed.
The improvement in strength is not enough. A contained in the additive
Since l reacts with lanthanum gallate, if the solid electrolyte fuel cell is used for a long time under power generation conditions, A
There is a problem in that 1 is diffused, the ionic conductivity is gradually reduced, and at the same time, the mechanical strength is also reduced.

Therefore, an object of the present invention is to enable use in a low temperature region as a constituent material of a solid oxide fuel cell,
An object of the present invention is to provide a lanthanum gallate-based solid electrolyte material having good mechanical strength.

[0013]

Means for Solving the Problems Accordingly, the present inventors have:
In order to achieve the above object, when silicon nitride or titanium nitride is used as the strength-enhancing particle material to be dispersed in the lanthanum gallate-based oxide, the strength can be greatly improved, and at the same time, it does not react with the lanthanum gallate, It has been found that the solid electrolyte material of an excellent solid electrolyte fuel cell can be obtained without causing a decrease in the oxide ion conductivity because it is electrically stable.

Attention has also been paid to a particle group sintering technique utilizing a coarse particle group, which has been conventionally excluded as an agglomerate, and silicon nitride or titanium nitride powder is added as a particle group (granules) at a predetermined ratio and simultaneously sintered. By producing a multi-phase ceramic material by the bonding method, it is possible to sufficiently develop the function of imparting mechanical strength characteristics while minimizing the addition ratio of silicon nitride or titanium nitride. The above problem has been solved by using a dispersed microstructure. The sintered body thus obtained has good oxide ion conduction properties and good mechanical strength properties.

That is, the invention according to claim 1 is a lanthanum gallate-based solid electrolyte material, which is a sintered body obtained by adding silicon nitride or titanium nitride powder to a lanthanum gallate-based oxide. .

According to a second aspect of the present invention, the silicon nitride or the titanium nitride is a sintered body in which 0.5% by weight or more and 10% by weight or less are added to the lanthanum gallate-based oxide as a particle group. It is characterized by.

The invention according to claim 3 is characterized in that the sintered body is made of a multi-phase ceramic mainly composed of particles of the silicon nitride or the titanium nitride having a diameter of 25 μm ± 15 μm.

According to a fourth aspect of the present invention, the area of the silicon nitride or titanium nitride particles having a minor axis diameter of 5 μm or more with respect to the cut surface of the sintered body is measured by a line intercept method. It is characterized in that the area fraction is 1.5 to 30 area%.

According to a fifth aspect of the present invention, there is provided a method for producing a lanthanum gallate-based solid electrolyte material, comprising adding a silicon nitride or titanium nitride powder to a lanthanum gallate-based oxide to a temperature of 1350 ° C. to 1550 ° C. It is characterized by sintering.

According to a sixth aspect of the present invention, there is provided a method for producing a lanthanum gallate-based solid electrolyte material, wherein the silicon nitride or the titanium nitride is contained in the lanthanum gallate-based oxide in a particle group in an amount of 0.5 wt% to 10 wt%. It is characterized by being added at the following ratio.

According to a seventh aspect of the present invention, there is provided a solid oxide fuel cell, comprising: the lanthanum gallate-based solid electrolyte material according to any one of the first to fourth aspects; and a pair of conductive electrodes. Characterized in that they are composed of unit cells composed of

[0022]

According to the first to fourth aspects of the present invention, a lanthanum gallate-based solid electrolyte material which can be used in a low temperature region and has good mechanical strength can be used as a constituent material of a solid electrolyte fuel cell. There is an effect to be realized.

According to the fifth and sixth aspects of the present invention,
By setting the addition ratio of silicon nitride or titanium nitride, there is an effect that a solid electrolyte material having high mechanical strength can be easily manufactured.

According to the seventh aspect of the present invention, there is an effect of realizing a solid oxide fuel cell having stable cell characteristics even when used for a long time and having high mechanical strength.

[0025]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A lanthanum gallate-based solid electrolyte material according to the present invention, a method for producing the same, and a solid oxide fuel cell using the same will be described based on embodiments.

The lanthanum gallate-based oxide used in this embodiment is not particularly limited as long as it is a gallium (Ga) -based oxide having a perovskite structure. Considering the characteristics, L
a _0.9 Sr _0.1 Ga _0.8 Mg _0.2 O _3-δ , or (La
Those having a composition such as _0.9 Sr _0.1 ) _0.9 Ga _0.8 Mg _0.2 O _3-δ are preferable.

Further, the solid electrolyte fuel cell of the present embodiment is a combination of a unit cell composed of a pair of electrodes having conductivity of the lanthanum gallate-based solid electrolyte material of the present invention. FIG. 1 is an explanatory view schematically showing a solid electrolyte fuel cell 1 according to the present embodiment. The solid electrolyte fuel cell 1 has a lanthanum gallate-based solid electrolyte layer 2
Is sandwiched between a pair of electrodes (air electrode, fuel electrode) 3 and 4. In such a cell, 500 to 800
When heated to ° C, air and fuel are supplied, and the electrolyte acts to carry oxygen ions from the air-side electrode to the fuel-side electrode, thereby generating an electromotive force. Such a solid electrolyte fuel cell can exhibit stable characteristics when used in a fuel cell having different temperatures depending on parts. In addition, a small-sized oxygen sensor used in an automobile exhaust pipe can be a device that can stably exhibit characteristics even under a situation in which the temperature changes drastically and the performance easily changes.

Further, the solid electrolyte of the present invention has high strength and high toughness, which can be used as a material for a fuel cell used at a high temperature, and can sufficiently cope with an increase in the size of the cell.

EXAMPLES Next, Examples 1 to 12 and Comparative Examples 1 to 11 having the respective compositions will be described.

(Examples 1 to 6 and Comparative Examples 4 to 6) Lanthanum gallate was prepared from each raw material (La ₂ O ₃ , SrCO ₃ , Ga).
₂ O ₃ , MgO) were weighed and mixed by a ball mill in alcohol for 24 hours. After drying the obtained slurry, it was calcined at 1150 ° C. for 6 hours in the air. Next, it 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 dried to obtain a matrix powder.

As the additional phase, silicon nitride granules 10 ± 2
μm to 55 ± 5 μm (Examples 1 to 5 shown in Table 1 below)
6, see Comparative Examples 4 to 6), mixed at a predetermined volume ratio, and mixed with a V-type blender to obtain a particle group powder. This lanthanum gallate particle group powder is compacted with a mold, and is molded with a hydrostatic press at a pressure of 2 ton / cm 2,
Sintering was performed at a predetermined temperature (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. 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.

Next, JIS-shaped test pieces were prepared. In the following description, a sintered body from the particle group powder is referred to as a particle group sintered material.

Table 1 below shows Examples 1 to 6 and Comparative Examples 1 to 6.
7 shows the composition and various characteristics.

[0034]

[Table 1] Comparative Example 1 (lanthanum gallate alone) Lanthanum gallate was obtained from each raw material (La ₂ O ₃ , SrCO ₃ ,
Ga ₂ O ₃ , MgO) were weighed and mixed in a ball mill for 24 hours in alcohol. After drying the obtained slurry, it was calcined in the atmosphere at 1150 ° C. for 6 hours. Again, it was pulverized in alcohol so as to have an average particle diameter of 0.8 μm or less by a ball mill, and then dried. This lanthanum gallate powder is compacted with a mold, and pressed with a hydrostatic press for 2 tons.
Molded at a pressure of n / cm2 and at a specified temperature (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.

Comparative Example 2 (Addition of Alumina Particles) Lanthanum gallate was prepared from each raw material (La ₂ O ₃ , SrCO ₃ ,
Ga ₂ O ₃ , MgO) were weighed and mixed in a ball mill for 24 hours in alcohol. After drying the obtained slurry, it was calcined in the atmosphere at 1150 ° C. for 6 hours. Again, it was pulverized in alcohol so as to have an average particle diameter of 0.8 μm or less by a ball mill, and then dried. This powder was mixed with Al2O3 powder at a predetermined volume ratio and mixed with a V-type blender. The lanthanum gallate powder was compacted with a mold, molded by a hydrostatic press at a pressure of 2 ton / cm 2, and sintered at a predetermined temperature (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.

Comparative Example 3 (Ga-site Al-substituted) Lanthanum gallate was prepared using various raw materials (La ₂ O ₃ , SrCO ₃ ,
Ga ₂ O ₃ , MgO, Al ₂ O ₃ ) were weighed and mixed in an alcohol by a ball mill for 24 hours. After drying the obtained slurry, it was calcined in the atmosphere at 1150 ° C. for 6 hours. Again, it was pulverized in alcohol so as to have an average particle diameter of 0.8 μm or less by a ball mill, and then dried.
This lanthanum gallate powder is compacted with a mold, molded at a pressure of 2 ton / cm 2 by a hydrostatic pressure press, and cooled to a predetermined temperature (1
(450 ° 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.

(Evaluation of Characteristics) (1) Bending strength: A four-point bending test described in JIS-R1601 was performed.

(2) Measurement of transport number: A sample is set at the center of the furnace as a partition at the center of the furnace. While flowing argon (Ar) gas to the fuel electrode side and the air electrode side, the temperature was raised to 600 ° C., the Ar gas was stopped, humidified hydrogen was supplied to the fuel electrode, and air was supplied to the air electrode. After allowing to stand for 30 minutes, the natural potential between the anode and the cathode is measured and calculated as a percentage of the theoretical natural potential.

As a sample, a platinum (Pt) paste was applied using a disk processed to a diameter of 13 mm and a thickness of 1 mm.
It dried at ° C and used as an electrode.

Transport number (%) = measured potential / theoretical potential × 100 (3) Ionic conductivity: A DC four-terminal method was used. Platinum wires were fixed at regular intervals with a platinum paste using a JIS bending test piece, and then fired at 1000 ° C. to obtain a test piece. In the measurement, after maintaining the temperature at a predetermined temperature, the resistivity was measured and the reciprocal number was multiplied by the transport number to obtain the ion conductivity (σ). The following formula was used for the calculation.

Σ (S / m) = current (A) × cross-sectional area of test specimen / voltage (V) × effective test specimen length (m) × transport number (%) (0.26 μm) and then polished 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. Furthermore, the diameter of the particle group is determined by taking a photograph of the silicon nitride particle group on the polished surface, drawing a straight line at random on the photograph, obtaining the particle diameters of all the silicon nitride particle groups intersecting the straight line, and averaging the average. A line intercept method was used in which the diameter of the particle group was determined by an image analyzer as the number average of the silicon particle group.

In the sintering of lanthanum gallate, if the calcination temperature is lower than 1100 ° C., the solid phase reaction becomes insufficient and
If the temperature is higher than 200 ° C., there are particles that cause sintering, resulting in non-uniformity.

The calcination time of lanthanum gallate is 2 hours.
When the time is shorter than the time, the solid phase reaction is insufficient, and when the time is longer than 10 hours, grain growth occurs.

Further, the sintering temperature of the lanthanum gallate is
If the temperature is lower than 1350 ° C., sintering is insufficient and pores remain, and 1
If the temperature is higher than 550 ° C., sintering proceeds too much, causing grain boundary cracking.

If the sintering time of the lanthanum gallate is shorter than 2 hours, sintering is insufficient and pores remain. If the sintering time is longer than 8 hours, sintering proceeds excessively and grain boundary cracks occur.

Hereinafter, Examples 1 to 11 and Comparative Examples 1 to 1
With respect to 0, the results of bending strength and ionic conductivity obtained based on the above evaluation method are compared from each viewpoint.

Effects of adding silicon nitride particles: (Example 1 and Comparative Examples 1, 2, and 3) It can be seen that the addition of the silicon nitride particles increased the bending strength as compared with the case where no silicon nitride particles were added.
Also, it can be seen that the strength is increased by the addition of the Si ₃ N ₄ particles as compared with those of Al ₂ O ₃ particles or element substitution (Al to Ga site).

Effect of adding particle group structure: (Example 1 and Comparative Example 7) Even with the same addition amount of silicon nitride particles, a system added as a particle group (Comparative Example 7) compared with a system not added as a particle group (Comparative Example 7) Example 1) maintains high ionic conductivity after increasing the strength, indicating that the effect of adding as a particle group is great. This is because the multi-phase ceramic material is manufactured by adding silicon nitride powder as a group of particles (granules) in a predetermined ratio and simultaneously sintering, so that the addition ratio of silicon nitride is minimized and the ion conductivity is reduced. This is an effect obtained by providing a particle group dispersed microstructure capable of sufficiently exhibiting a function of imparting mechanical strength characteristics while suppressing a decrease. FIG. 2 is a cross-sectional explanatory view schematically showing a cross section of a solid electrolyte to which additional particles (silicon nitride granules) having a particle diameter are added.

Effect of addition amount of particle group: (Examples 1 to 4 and Comparative Examples 4 and 5) At 1 wt% to 10 wt%, the addition of silicon nitride particles improves the bending strength and suppresses the decrease in ionic conductivity. You can see that This is because addition of 1 wt% or less is insufficient for increasing strength, while
If the content is not less than wt%, the proportion of the ion-insulating silicon nitride is too large, and the ionic conductivity is greatly reduced.

Effect of Particle Group Diameter: (Examples 1, 5, 6 and Comparative Example 6) By using a silicon nitride particle group of 25 μm ± 15 μm, it is possible to suppress a decrease in ion conductivity with respect to an increase in strength. When the diameter of the particle group is 40 μm or more, the particles are excessively localized, so that the mechanical strength is reduced and ion conduction is hindered.

Area fraction: (Examples 1-4 and Comparative Example 4,
5) 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 the area fraction measured by the line intercept method. If the area of the silicon nitride particles is small, it tends to be impossible to impart sufficient mechanical strength characteristics. Is large, the oxide ion conductivity tends to decrease.
It is more desirable to set the following.

(Examples 7 to 12 and Comparative Examples 8 to 11) Lantangalate, which is a matrix, was prepared by using each raw material (La
₂ O ₃ , SrCO ₃ , Ga ₂ O ₃ , MgO) were 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. Next, the average particle size is set to 0.
After pulverizing in alcohol so as to be 8 μm or less, it was dried to obtain a matrix powder.

As an additional phase, silicon nitride granules 10 ± 2
μm to 80 ± 5 μm (Examples 1 to
6, see Comparative Examples 4 to 6), mixed at a predetermined volume ratio, and mixed with a V-type blender to obtain a particle group powder. This lanthanum gallate particle group powder is compacted with a mold, and is molded with a hydrostatic press at a pressure of 2 ton / cm 2,
Sintering was performed at a predetermined temperature (1450 ° C.) for 6 hours 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. 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.

Next, each JIS-shaped test piece was prepared. In the following description, a sintered body from the particle group powder is also referred to as a particle group sintered material.

Table 2 below shows Examples 7 to 12 and Comparative Example 8.
11 to 11 show the compositions and various characteristics.

[0056]

[Table 2] (Characteristic evaluation) (1) Bending strength: A four-point bending test described in JIS-R1601 was performed.

(2) Measurement of transport number: A sample is set at the center of the furnace as a partition at the center of the furnace. While flowing argon (Ar) gas to the fuel electrode side and the air electrode side, the temperature was raised to 600 ° C., the Ar gas was stopped, humidified hydrogen was supplied to the fuel electrode, and air was supplied to the air electrode. After allowing to stand for 30 minutes, the natural potential between the anode and the cathode is measured and calculated as a percentage of the theoretical natural potential.

As a sample, a platinum (Pt) paste was applied using a disk processed to a diameter of 13 mm and a thickness of 1 mm.
It dried at ° C and used as an electrode.

Transport number (%) = measured potential / theoretical potential × 100 (3) Ion conductivity: A DC four-terminal method was used. Platinum wires were fixed at regular intervals with a platinum paste using a JIS bending test piece, and then fired at 1000 ° C. to obtain a test piece. In the measurement, after maintaining the temperature at a predetermined temperature, the resistivity was measured and the reciprocal number was multiplied by the transport number to obtain the ion conductivity (σ). The following formula was used for the calculation.

Σ (S / m) = current (A) × cross-sectional area of test specimen / voltage (V) × effective test specimen length (m) × transport number (%) (0.26 μm) and then polished 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. Further, the diameter of the particle group is 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 diameter of all the silicon nitride particle groups crossing the straight line, and averaging the average. A line intercept method was used in which the diameter of the particle group was determined by an image analyzer as the number average of the silicon particle group.

Effect of adding titanium nitride particles: (Example 7 and Comparative Examples 1, 2, and 3) It can be seen that the addition of the titanium nitride particles increased the bending strength as compared with the case where no titanium nitride particles were added.
Also, it can be seen that the strength is increased by the addition of the titanium nitride particles as compared with those of alumina particles or those with element substitution (substitution with Al at the Ga site).

Effect of adding particle group structure: (Example 7 and Comparative Example 8) Even when the same amount of titanium nitride was added, a system was added as a particle group as compared with a system not added as a particle group (Comparative Example 8) (Example 7). 7) shows that the high ion conductivity is maintained after the strength is increased, and that the effect of adding as a particle group is large. A multi-phase ceramic material is manufactured by adding titanium nitride powder as a group of particles (granules) at a predetermined ratio and simultaneously sintering, thereby suppressing the decrease in ion conductivity by minimizing the addition ratio of titanium nitride. However, this is an effect obtained by providing a particle group dispersed microstructure that allows the function of imparting mechanical strength characteristics to be sufficiently exhibited.

Effect of addition amount of particle group: (Examples 7 to 10 and Comparative Examples 9 and 10) At 1 wt% or more and 10 wt% or less, the addition of titanium nitride particles improves the bending strength and suppresses the decrease in ionic conductivity. You can see that This is because addition of 1 wt% or less is insufficient for increasing strength, while
If the content is not less than wt%, the proportion of the oxide ion insulating titanium nitride is too large, and the oxide ion conductivity is greatly reduced.

Effect of Particle Group Diameter: (Examples 7, 11, 1
2 and Comparative Example 11) By using a titanium nitride particle group of 25 μm ± 15 μm, it is possible to suppress a decrease in ion conductivity with respect to an increase in strength. When the diameter of the particle group is 40 μm or more, the particles are excessively localized, so that the mechanical strength is reduced and the oxide ion conduction is inhibited.

Area fraction: (Examples 7 to 10 and Comparative Example 9,
10) When the cut surface of the sintered body was observed, the total area of the titanium 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. If the area of the titanium nitride particles is small, it tends to be impossible to impart sufficient mechanical strength characteristics. Therefore, it is preferable that the area be 1.5 area% or more. Is large, the oxide ion conductivity tends to decrease. Therefore, it is preferable to set the area to 30% by area or less.

Although the present embodiment and examples have been described above, the present invention is not limited to these.
The lanthanum gallate-based solid electrolyte material described above can also be applied to an automobile oxygen sensor 10 as shown in FIG. As shown in FIG. 3, the vehicle oxygen sensor 10
A standard electrode (Pt) is inserted through a conductive airtight seal 12 into a container-like case 11 in which a plurality of ventilation holes 11A are formed.
A lanthanum gallate-based solid electrolyte layer 15 sandwiched between 13 and a detection electrode (Pt) 14 is housed. Note that the outer surface of the detection electrode 14 is covered with a protective film 16. Also,
An exhaust gas duct wall 17 is provided around the upper part of the case 11 so that exhaust gas from the outside of the case 11 can pass through the vent hole 11.
A. The standard gas SG is introduced into the space inside the standard electrode 13.

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

[Brief description of the drawings]

FIG. 1 is a schematic explanatory view showing an embodiment of a solid oxide fuel cell using a lanthanum gallate-based solid electrolyte material according to the present invention.

FIG. 2 is an explanatory cross-sectional view schematically showing a lanthanum gallate-based solid electrolyte material obtained by mixing and sintering particles added to regular granules.

FIG. 3 is a schematic sectional view of an automobile oxygen sensor to which the lanthanum gallate-based solid electrolyte material of the present invention is applied.

[Explanation of symbols]

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

Continuing from the front page (72) Inventor Ryoichi Sengokutani Nissan Motor Co., Ltd., 2 Takaracho, Kanagawa-ku, Yokohama, Kanagawa Prefecture (72) Inventor Masaharu Hatano 2 Takaracho, Kanagawa-ku, Yokohama, Kanagawa Prefecture, Nissan Motor Co., Ltd. (72) Invention Fumio Munakata 2 Takaracho, Kanagawa-ku, Yokohama, Kanagawa Prefecture F-term (reference) 5G301 CA02 CA03 CD01 5H026 AA06 BB01 BB08 EE11 EE13 HH01 HH02 HH05 HH08

Claims (7)

[Claims] 1. A lanthanum gallate solid electrolyte material comprising a sintered body obtained by adding silicon nitride or titanium nitride powder to a lanthanum gallate oxide. 2. The lanthanum gallate-based oxide may contain 0.5% of the silicon nitride or the titanium nitride as particles.
2. The lanthanum gallate-based solid electrolyte material according to claim 1, comprising a sintered body added at a ratio of not less than 10 wt% and not more than 10 wt%. 3. The sintered body has a diameter of 25 μm ± 15 μm.
The lanthanum gallate-based solid electrolyte material according to claim 2, comprising a multiphase ceramic mainly composed of the silicon nitride or the titanium nitride particles. 4. An area fraction of the silicon nitride or titanium nitride particles having a minor axis diameter of 5 μm or more with respect to a cut surface of the sintered body as an area fraction measured by a line intercept method. The lanthanum gallate-based solid electrolyte material according to any one of claims 1 to 3, wherein the content is 5 to 30% by area. 5. A powder of silicon nitride or titanium nitride is added to a lanthanum gallate-based oxide.
A method for producing a lanthanum gallate-based solid electrolyte material, comprising sintering at a temperature of 50 ° C. 6. The silicon nitride or the titanium nitride as a particle group in the lanthanum gallate-based oxide is 0.5%.
The method for producing a lanthanum gallate-based solid electrolyte material according to claim 5, wherein the lanthanum gallate-based solid electrolyte material is added at a ratio of not less than 10 wt% and not more than wt%. 7. A combination of a unit cell composed of the lanthanum gallate-based solid electrolyte material according to claim 1 and a pair of electrodes having conductivity. Solid oxide fuel cell.