JP3620800B2 - Method for producing solid electrolyte sintered body - Google Patents

Description

[0001]
[Industrial application fields]
The present invention relates to a manufacturing method of the preferred solid-solid electrolyte sintered body as etc. solid electrolyte used in the solid oxide fuel cell.
[0002]
[Prior art]
In recent years, so-called solid electrolyte materials have been researched and developed in various technical fields and applications.
Among them, for example, solid oxide fuel cells (hereinafter referred to as “SOFC”) have higher power generation efficiency and exhaust heat than other fuel cells such as phosphoric acid type and molten carbonate type that have been developed so far. In recent years, it has attracted particular attention for its ability to build a power generation system that can be used efficiently due to its high temperature.
[0003]
By the way, the SOFC modes are generally classified into a flat plate type shown in FIG. 6 and a cylindrical type (not shown). In the flat plate type shown in FIG. 6, the external manifold type shown in FIG. 7A and the internal manifold type shown in FIG. It is done.
[0004]
The SOFC structure shown in FIG. 6 and FIGS. 7A and 7B will be briefly described. A solid electrolyte plate 30 is sandwiched between a fuel electrode 10 in contact with fuel gas and an oxygen electrode 20 in contact with air. A single cell having a structure in which separators 40a and 40b are respectively provided on the outer side of 10 and the outer side of the oxygen electrode 20 is provided in a laminated manner over a plurality of layers.
[0005]
In the SOFC configured as described above, the fuel gas (hydrogen or carbon monoxide) is in contact with the fuel electrode, and the oxidizing gas (air or oxygen) is in contact with the oxygen electrode. Then, oxygen ions (O ²⁻ ) generated at the oxygen electrode move through the solid electrolyte and reach the fuel electrode, where the oxygen ions react with hydrogen (H ₂ ) to release electrons. As a result, electricity is generated and electricity flows.
[0006]
In this SOFC, the electrical characteristics of the solid electrolyte material used, particularly the electrical conductivity, greatly affects the performance of the battery. Conventionally, stabilized zirconia has been used as this type of solid electrolyte material. This stabilized zirconia is a means for preventing this volume change because zirconia (ZrO ₂ ) undergoes a volume change accompanying a change in crystal structure from monoclinic to tetragonal at a high temperature (about 1150 ° C.). As described above, an oxide such as calcium (Ca) or yttrium (Y) is dissolved to stabilize the crystal structure. At present, yttria-stabilized zirconia (Y ₂ O ₃ Stabilized ZrO ₂ , hereinafter referred to as “YSZ”) is most frequently used. In addition, there is an example in which tetragonal zirconia polycrystal TZP (Tetragonal ZrO ₂ Policrystalline), which is a high-strength material although it has poor electrical characteristics, is used.
[0007]
[Problems to be solved by the invention]
However, although the solid electrolyte material of YSZ alone has excellent conductivity characteristics, when it is intended to provide SOFC using a solid electrolyte sintered body formed in a flat plate shape from this solid electrolyte material of YSZ alone, The plate thickness of the electrolyte sintered body must be increased to 0.2 to 0.3 mm, thereby increasing the internal resistance and lowering the power density (about 0.5 W / cm ² ), high power generation efficiency, There was a problem that a solid oxide fuel cell having power generation performance could not be obtained.
[0008]
On the other hand, as an alternative to the YSZ solid electrolyte material, the present inventors have used a scandia-stabilized zirconia (Sc ₂ O ₃ Stabilized ZrO ₂ , hereinafter referred to as “ScSZ”) simple substance having superior conductivity characteristics. The material was developed first and has already been filed. And it turned out that the electrical conductivity characteristic is most excellent in the range of 8 mol%-15 mol% as a solid solution amount of the scandia in this ScSZ solid electrolyte material.
[0009]
However, this ScSZ solid electrolyte material has higher electrical conductivity than the YSZ solid electrolyte material and has excellent electrical characteristics as a solid electrolyte material of SOFC, but the amount of scandia solid solution is 8 mol%. In the case of the degree, there is a problem that the electrical conductivity is lowered when held at a high temperature for a long time. Therefore, in order to solve this, it is effective to slightly increase the amount of scandia solid solution from 8 mol% to 10 to 15 mol%, but when the amount of scandia solid solution is 11 mol% or more, In addition to the cubic phase (C phase) zirconia, a rhombohedral phase (R phase), which is a compound of zirconia and scandia, is precipitated. This rhombohedral phase has a lower conductivity than the cubic phase, and when heated, the rhombohedral phase transforms from the rhombohedral phase to the cubic phase around 650 ° C., so that a large volume change occurs when the rhombohedral phase increases. There was a problem.
[0010]
Therefore, when a solid electrolyte sintered body is formed from such a ScSZ solid electrolyte material and applied as a solid electrolyte of SOFC, the electrical resistance cannot be stably maintained over a long period of time, so that the internal resistance increases. Degradation of power generation performance occurs, strain or thermal stress is generated inside the battery due to volume expansion during heating and cooling of the solid oxide fuel cell, or electrode material peels off when the volume expansion is large There was a problem.
[0011]
The present invention has been made to solve such problems, and the object of the present invention is to maintain a high electrical conductivity over a long period of time without causing phase transformation, and the crystalline phase is It is to provide a method of producing a stabilized solid body electrolyte sintered body cubic phase. Thereby, for example, the deterioration of the power generation performance of the solid oxide fuel cell (SOFC) is suppressed, and the volume change at the time of heating and cooling is eliminated to achieve permanent use.
[0012]
[Means for Solving the Problems]
Manufacturing method of engaging Ru solid body electrolyte sintered body in the present invention, as described in claim 1, zirconia within the range of _Sc 2 _O 3 / molar ratio of ZrO ₂ is 11 / 89-15 / 85 scandia a scandia-stabilized zirconia powder but solid-dissolved by mixing alumina powder in the range of 0.3 to 5 wt%, molding the resultant mixed powder is calcined, stabilize the crystal phase in the cubic phase it is an gist Rukoto is.
[0013]
According to the above production method , 0.3 to 5 wt.% In scandia-stabilized zirconia in which scandia is solid-solved in zirconia within a range of the Sc ₂ O ₃ / ZrO ₂ molar ratio of 11/89 to 15/85. %, A solid electrolyte sintered body in which alumina is mixed and dispersed and the crystal phase is stabilized to a cubic phase is obtained.
[0014]
The resulting solid electrolyte sintered body, while maintaining a high conductivity over a long period, the phase transformation is almost Do Ino causing conductivity is lowered increases the internal resistance of the solid electrolyte sintered body In addition, there is no occurrence of distortion or thermal stress due to volume changes during heating and cooling.
[0015]
Therefore, in the case of using a solid electrolyte sintered body this as a solid electrolyte of the solid electrolyte fuel cell, without causing output reduction per cell, a reduction in power generation efficiency, stably for a long period of time good power generation efficiency It is possible to obtain a solid oxide fuel cell from which the battery can be obtained, thereby enabling permanent use of the battery. In addition, it is possible to avoid problems such as volume expansion during heating and cooling during battery use and distortion inside the battery, and problems such as peeling of the electrode material formed on the solid electrolyte sintered body. As a result, the reliability is excellent.
[0016]
At this time, the scandia-stabilized zirconia powder is preferably produced by using a solid phase method, a sol-gel method or a coprecipitation method as described in claim 2.
[0017]
【Example】
Will be described in detail a manufacturing method of the engaging Ru solid body electrolyte sintered body to an embodiment of the present invention are described below. In the examples described below, a description is given assuming a solid electrolyte sintered body used for a solid oxide fuel cell (SOFC). In the drawings described below, for convenience,% by weight is written as Wt%.
FIG. 1 shows a manufacturing process of a solid electrolyte plate formed in a flat plate shape according to an embodiment of the present invention . According to this, first, powder particles of zirconia (ZrO ₂ ) as a main material and powder particles of scandia (Sc ₂ O ₃ ) as a stabilization material are mixed at an appropriate blending ratio. Here, it is mechanically mixed by a ball mill or the like. The average particle diameter of this mixed powder is about 3 μm. If a liquid phase production process such as a sol-gel method or a coprecipitation method is applied as a method for preparing a mixed powder of zirconia and scandia, a uniform mixed powder with few impurities can be obtained. The blending ratio of zirconia and scandia is appropriately selected within the range of 92 to 85 mol% zirconia and 8 to 15 mol% scandia.
[0018]
Then, this mixed powder of zirconia and scandia is heat-treated at a high temperature (600 to 700 ° C.) to obtain scandia-stabilized zirconia (ScSZ) in which scandia is solid-solved in zirconia, and then the scandia stabilized by pulverization. Zirconia powder is obtained.
Next, alumina (Al ₂ O ₃ ) powder as a crystal phase stabilizing material is mixed with the scandia-stabilized zirconia powder at an appropriate blending ratio. The mixing ratio of alumina is suitably in the range of 0.3 to 5 % by weight based on the scandia-stabilized zirconia powder.
[0019]
When a mixed powder of scandia-stabilized zirconia powder and alumina powder is obtained in this manner, the mixed powder is then formed into a plate (approximately 20 cm square plate) having a plate thickness of 100 to 300 μm. As this forming means, in this embodiment, pressure forming is performed by using a hydrostatic press (CIP) with a pressing force of 1 t / cm ² . However, it is not limited to this forming means, and a thin plate may be manufactured by a doctor blade method or a calender roll method generally used conventionally. Then, the molded plate is fired at a temperature of 1500 to 1700 ° C. Thus, in the scandia-stabilized zirconia in which scandia is solid-dissolved in zirconia within the range of Sc ₂ O ₃ / ZrO ₂ in the range of 8/92 to 15/85 , in the range of 0.3 to 5 % by weight. alumina mixture is dispersed and crystalline phases that Do is stabilized in the cubic phase (C phase) solid body electrolyte plate is obtained.
[0020]
Next, when forming a fuel electrode or an oxygen electrode on this solid electrolyte plate (hereinafter referred to as “ScSZA solid electrolyte plate”), the ScSZA solid electrolyte is formed by making a ceramic powder of these electrode materials into a mud and using a so-called slurry coating method. Each of the plates is applied to one side and the opposite side, and then fired at a predetermined temperature.
In the case of the fuel electrode, for example, nickel (Ni) 40 wt% -zirconia (ZrO ₂ ) 60 wt% nickel-zirconia cermet is coated on one side of the ScSZA solid electrolyte plate with a thickness of about 50 μm, and 1400-1500 Bake at a temperature of ° C. As a result, a thin-film fuel electrode is formed on one side of the ScSZA solid electrolyte plate.
[0021]
In the case of an oxygen electrode, for example, lanthanum strontium manganate (La (Sr) MnO ₃ ) is coated on the surface of the ScSZA solid electrolyte plate on the side opposite to the above-mentioned fuel electrode at a thickness of about 50 μm. Firing at a temperature of As a result, a thin-film oxygen electrode is formed on the opposite surface of the ScSZA solid electrolyte plate. The mixing ratio of the oxygen electrode material is suitably about 5 to 15 mol% of strontium with respect to 95 to 85 mol% of lanthanum manganate.
Next, various experiments were conducted on the SOFC ScSZA solid electrolyte plate manufactured as described above, and these will be described.
[0022]
First, FIG. 2 shows the results of examining the temperature dependence of the conductivity characteristics of each ScSZA solid electrolyte plate in which the amount of alumina (Al ₂ O ₃ ) mixed and dispersed in scandia-stabilized zirconia was changed. Is. In this experiment, the amount of scandia solid solution in scandia-stabilized zirconia was 12 mol%, and alumina was mixed in an amount of 0,0.3,0.7,3,5,10,20% by weight. ing.
In the drawing, the horizontal axis indicates the temperature variable 1000 / T [1 / K] (K: absolute temperature), and the vertical axis indicates the conductivity variable log σ [S / cm].
[0023]
As a result, as the temperature variable 1000 / T [1 / K] increases for any of the test materials, the conductivity characteristics decrease, but no scandia-stabilized zirconia is compounded with alumina (12Sc0A). In particular, it can be seen that the decrease in conductivity characteristics tends to be conspicuous at a temperature variable of 1.1 or more (approximately 650 K or more). And when the amount of alumina blended even in a small amount (12Sc0.3A) is compared with the amount of alumina blended more (~ 12Sc20A), it can be seen that there is almost no significant difference in conductivity characteristics. .
[0024]
Next, FIG. 3 shows the amount and conductivity (at 870 ° C. and 1000 ° C.) of alumina (Al ₂ O ₃ ) mixed and dispersed in scandia-stabilized zirconia in the ScSZA solid electrolyte plate obtained by this production method . It shows the relationship.
At this time, as the scandia-stabilized zirconia, 12 mol% Sc ₂ O ₃ -88 mol% ZrO ₂ was used, and alumina was mixed and dispersed in the range of 0 wt% to 20 wt%. In the drawing, the horizontal axis represents the amount of Al ₂ O ₃ [wt%], and the vertical axis represents the conductivity σ [S / cm].
[0025]
As a result, the conductivity of the ScSZA solid electrolyte plate is highest in a state where no alumina is mixed and dispersed in both temperature environments of 870 ° C. and 1000 ° C., and it decreases as the amount of alumina increases. I understand. However, up to about 20% by weight of alumina can be used as a conductivity value.
Next, FIG. 4 shows X-ray analysis data of the ScSZA solid electrolyte plate obtained by this manufacturing method . Here, as the scan Kanjia stabilized zirconia, 12 _mol% Sc ₂ O 3 used as the -88 mol% ZrO _2, the tested those alumina was 0,0.3,3,5 blending each weight percent to ing. In FIG. 4, the horizontal axis represents the intensity in the range of 2θ = 20 to 90 °, and the vertical axis represents the intensity.
[0026]
As a result, it is found that the crystal phase of the conventional scandia-stabilized zirconia solid electrolyte material (12Sc0A) in which no alumina is blended is filled with the rhombohedral phase (R phase). However, it can be seen that all of the compounds containing alumina (Al ₂ O ₃ ) (12Sc0.3A, 12Sc3A, 12Sc5A) are filled with the cubic phase (C phase). Therefore, from this test data, the crystal phase is filled with a cubic phase having a higher conductivity than the rhombohedral phase by adding a small amount of alumina in a scandia-stabilized zirconia in the range of 0.3 to 5% by weight. Since no phase transformation from rhombohedral phase to cubic phase during heating can occur, it can be said that there is little volume change due to thermal expansion.
[0027]
Next, FIG. 5 shows conductivity change characteristics after aging at 1000 ° C. in the ScSZA solid electrolyte plate obtained by this production method . Also in this experiment, 12 mol% Sc ₂ O ₃ -88 mol% ZrO ₂ was used as scandia-stabilized zirconia, and alumina was added to this with 0.3, 0.7, ₃ , 5, 10, 20 Tested with each weight% blended.
In the drawings, the horizontal axis indicates aging time [hr], and the vertical axis indicates conductivity [S / cm]. Aging time was plotted from 0 to 1600 hours.
[0028]
As a result, it can be seen that in the ScSZA solid electrolyte plate, the greater the amount of alumina, the lower the conductivity. And when the amount of alumina is in the range of 0 to 5% by weight, it can be used as a conductivity characteristic value, but when the amount of alumina is 20% by weight or more, it can be said that it cannot be used as a conductivity characteristic value. . In addition, it turns out that the fluctuation | variation of the electrical conductivity by the short aging time is hardly recognized.
[0029]
From the above various experimental data, the amount of alumina in the ScSZA solid electrolyte plate should not be blended as much as possible from the viewpoint of conductivity characteristics, but it is better to disperse and blend in a small amount from the viewpoint of crystal phase stabilization. From the viewpoint of stabilizing the crystal phase, it is sufficient to disperse and mix in a small amount in the range of 0.3 to 5% by weight, and it can be said that the electrical conductivity characteristics do not decrease so much with such an amount of alumina.
[0030]
【The invention's effect】
As shown in the various embodiments above, according to the manufacturing method of the engaging Ru solid body electrolyte sintered body of the present invention, while maintaining a high conductivity for a long time, without causing a phase transformation, crystalline phase it is possible to obtain a cubic phase stabilized solid body electrolyte sintered body (C phase), also this be used as a solid electrolyte of a solid oxide fuel cell (SOFC), power generation performance of the S oF C It can be said that the industrial benefits are extremely high, such as suppressing the deterioration of the material and eliminating the volume change of the material at the time of heating and cooling and achieving the permanent use.
[Brief description of the drawings]
1 is a diagram showing a manufacturing process of engaging Ru flat plate shape formed solid electrolyte plate to an embodiment of the present invention.
FIG. 2 is a graph showing temperature dependence data on conductivity characteristics of each ScSZA solid electrolyte plate in which the amount of alumina (Al ₂ O ₃ ) mixed and dispersed in scandia-stabilized zirconia is changed.
FIG. 3 is a diagram showing the relationship between the amount of alumina (Al ₂ O ₃ ) mixed and dispersed in scandia-stabilized zirconia and conductivity in a ScSZA solid electrolyte plate obtained by this production method .
FIG. 4 is a diagram showing X-ray analysis data of a ScSZA solid electrolyte plate obtained by the present manufacturing method .
FIG. 5 is a graph showing conductivity change characteristic data after aging at 1000 ° C. in a ScSZA solid electrolyte plate obtained by the present manufacturing method .
FIG. 6 is a diagram showing an example of a plate-type SOFC single cell structure generally known in the past, to which a solid electrolyte sintered body obtained by the present manufacturing method is applied.
7A is a diagram showing a schematic configuration of an external manifold type in the flat plate type SOFC shown in FIG. 6, and FIG.

Claims (2)

Scandia-stabilized zirconia powder in which scandia is dissolved in zirconia within a molar ratio of Sc ₂ O ₃ / ZrO ₂ in the range of 11/89 to 15/85, and alumina powder in the range of 0.3 to 5 % by weight. It was mixed, forming a mixed powder obtained, baking, manufacturing method of the solid electrolyte sintered body, characterized in Rukoto to stabilize the crystal phase to cubic phase. The method for producing a solid electrolyte sintered body according to claim 1, wherein the scandia-stabilized zirconia powder is produced using a solid phase method, a sol-gel method, or a coprecipitation method.

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