JP4039618B2 - Solid oxide fuel cell - Google Patents

Description

【００７７】
次に、図１は、１４５０℃の焼結温度で焼結した実施例３の焼結体におけるＬａＧａＯ_３の含有量と導電率との関係を示したものである。尚、図１においては比較のために、４ＳｃＳＺ焼結体の導電率と、４ＳｃＳＺに対してＬａＡｌＯ_３を１重量％含有する（以下「４ＳｃＳＺ＋１ｗｔ％ＬａＡｌＯ_３」という）実施例１の焼結体の導電率も合わせて示した。
【００７８】
図１によれば、４ＳｃＳＺに対してＬａＧａＯ_３を０．５〜２重量％含有する（以下「４ＳｃＳＺ＋Ｘｗｔ％ＬａＧａＯ_３」という）実施例３の焼結体の導電率は、全て実用的な範囲であることが分かる。また、３００℃〜８００℃の全温度範囲に亘って実施例１の４ＳｃＳＺ＋１ｗｔ％ＬａＡｌＯ_３の焼結体より高い導電率を示していることも分かる。このことより、４ＳｃＳＺに対してＬａＡｌＯ_３を含有させるよりもＬａＧａＯ_３を含有させた方が、水熱劣化抑制効果が高く、マトリックスである４ＳｃＳＺの導電率の低下をより軽減できることが分かる。
【００７９】
本発明は上記実施例に何ら限定されるものではなく、本発明の趣旨を逸脱しない範囲で種々の改変が可能であることは勿論である。例えば、上記実施例では、４ＳｃＳＺに対してＬａＡｌＯ_３又はＬａＧａＯ_３を所定重量％含有させた焼結体を用いて説明したが、それ以外にも上述した所定モル％のスカンジアを含有するジルコニアに対して、上述した組成式を有するランランガレート系酸化物若しくはランタンアルミネート系酸化物又はこれらの混合物を所定重量％含有させたものであっても本願特有の格別な作用、効果を奏するものである。
【００８０】
【発明の効果】
上記ジルコニア質焼結体によれば、安定化剤としてスカンジアを３〜６モル％含有するジルコニアに対して、ランタンガレート系酸化物若しくはランタンアルミネート系酸化物又はこれらの混合物が０．５〜２重量％含有されているので、Ｓｃ_２Ｏ_３−ＺｒＯ_２系のジルコニア質焼結体が有する高い導電率を大きく低減させることなく強度劣化を抑制することが可能となる。特に、１００℃〜３００℃の温度範囲、かつ、水又は水蒸気の存在する状況下であっても、結晶相の自発的な相転移が生じにくいため、効果的に水熱劣化を抑制することができる。
【００８１】
そのため、このジルコニア質焼結体をＳＯＦＣの固体電解質として用いれば、十分な導電率を有しているので、電池の内部抵抗が減少して発電効率が高められるとともに、ＳＯＦＣの起動停止を繰り返しても固体電解質の強度劣化、特に水熱劣化を招くことがなく、固体電解質としての構造上の信頼性に優れることから、長期に亘って安定して発電可能なＳＯＦＣを得ることが可能となる。
【図面の簡単な説明】
【図１】 １４５０℃の焼結温度で焼結した実施例３の焼結体におけるＬａＧａＯ_３の含有量と導電率との関係を示した図である。[0001]
BACKGROUND OF THE INVENTION
  The present inventionSolid oxide fuel cellFor more details,Solid oxide fuel cell using solid electrolyte composed of zirconia sintered body as constituent materialIt is about.
[0002]
[Prior art]
  In recent years, zirconia (ZrO₂) Sintered compacts are widely used in various applications such as cutting tools that use properties such as high strength and high toughness, ceramic scissors, and engine parts that use properties such as heat resistance. .
[0003]
  In particular, solid oxide fuel cells (hereinafter referred to as “SOFC”) using oxygen ion conductivity of zirconia sintered bodies have high energy conversion efficiency and emit almost no harmful substances, so they are clean and highly efficient. In recent years, it has attracted particular attention because it can build a power generation system.
[0004]
  This type of SOFC uses a zirconia sintered body as a solid electrolyte, and generally has three types of structures of a flat plate shape, a cylindrical shape, and an integral shape. For example, the structure of a flat plate SOFC is roughly classified into a self-supporting membrane type and a supporting membrane type. In the former self-supporting membrane type SOFC, a fuel electrode in contact with a fuel gas such as hydrogen or city gas and an air electrode in contact with an oxidant such as air or oxygen are joined to both sides of a flat solid electrolyte. It has a structure in which a plurality of single cells each having both sides sandwiched by separators are stacked.
[0005]
  On the other hand, in the latter support membrane type SOFC, a very thin solid electrolyte thin film is supported by a thick fuel electrode, and a thin air electrode is joined to the other surface of the solid electrolyte thin film. Furthermore, it has a structure in which a plurality of single cells each having both sides sandwiched by separators are stacked.
[0006]
  When a fuel gas and an oxidant are respectively supplied to the fuel electrode and the air electrode of the flat plate SOFC having such a configuration, the difference between the oxygen partial pressure on the air electrode side and the oxygen partial pressure on the fuel side is different. Therefore, oxygen becomes ions in the air electrode, and is carried to the fuel electrode through the solid electrolyte. The oxygen ions that have reached the fuel electrode react with the fuel gas and emit electrons. Therefore, if a load is connected to the fuel electrode and the air electrode, the change in the free energy of the cell reaction can be directly taken out as electric energy to generate electric power.
[0007]
  Specifically, as the zirconia sintered body used for the various applications described above, yttria (Y₂O₃) And Scandia (Sc₂O₃A stabilized zirconia to which a predetermined amount of a rare earth metal oxide such as) is added is widely known.
[0008]
  This stabilized zirconia is composed of a single component zirconia (ZrO₂) Occurs at about 1150 ° C. as the crystal phase changes from monoclinic to tetragonal, the yttria (Y₂O₃) And Scandia (Sc₂O₃) Or the like is used as a stabilizer to form a solid solution in zirconia to stabilize the crystal phase.
[0009]
  As such a zirconia sintered body, for example, JP-B-2-20587 discloses Y₂O₃Is disclosed, and a zirconia sintered body whose crystal phase is mainly stabilized in tetragonal crystal is disclosed.
[0010]
  Japanese Patent Laid-Open No. 61-26562 discloses YZ as a zirconia sintered body that can suppress deterioration over time due to heat and has high strength.₂O₃Containing 1.5 to 5 mol% of ZrO₂And a zirconia sintered body comprising 1 to 40% by weight of a zirconia-based double oxide containing alumina, alumina-based oxide, La, Nd and the like is disclosed.
[0011]
  JP-A-6-329468 discloses a zirconia sintered body having excellent thermal shock resistance and thermal stability and high strength.₂O₃, Ho₂O₃, Er₂O₃, Yb₂O₃A zirconia sintered body is disclosed in which an oxide such as La, Pr, or Nd is added as a characteristic improver.
[0012]
  In addition, JP 2000-95564 A discloses a zirconia sintered body having excellent mechanical strength and thermal stability.₂O₃ZrO containing 1.5-4 mol%₂On the other hand, a zirconia sintered body containing 0.1 to 3 mol% of a rare earth metal element composed of La, Pr and Nd and having a crystal phase mainly composed of tetragonal crystals is disclosed.
[0013]
[Problems to be solved by the invention]
  However, the conventional zirconia sintered body as shown in Japanese Patent Publication No. 2-20587 has a drawback that significant strength deterioration occurs when left in the vicinity of 100 ° C. to 300 ° C. for a long time. Yes. This is because tetragonal crystals, which are metastable at room temperature among the crystalline phases of zirconia sintered bodies, spontaneously undergo phase transition to stable monoclinic crystals. This is because cracks occur. In particular, it has been found that the strength deterioration caused by this phase transition is accelerated in the presence of water or water vapor (hereinafter, this kind of deterioration is referred to as “hydrothermal deterioration”).
[0014]
  Therefore, for example, when this zirconia sintered body is used as a solid electrolyte for SOFC, hydrothermal degradation is not a problem under normal SOFC operating conditions (about 1000 ° C.). At the time of stopping, there may be a temperature range of 100 ° C. to 300 ° C. and the presence of water or water vapor, so the problem of hydrothermal deterioration becomes obvious.
[0015]
  That is, in the SOFC, there is a possibility that moisture remains in the SOFC because a fuel gas may be humidified by several percent or a large amount of water may be added to reform the city gas. Therefore, when the SOFC is started and stopped, the zirconia sintered body as the solid electrolyte in the SOFC is repeatedly exposed to a temperature range of 100 ° C. to 300 ° C. in the presence of water or water vapor. Become. Therefore, cracks occur in the zirconia sintered body due to the hydrothermal deterioration, and there is a problem in that the destruction of the zirconia sintered body cannot be maintained even in the form, and the power generation effective as a battery cannot be maintained.
[0016]
  Moreover, in order to avoid this problem of hydrothermal deterioration, the thermal stability disclosed in JP-A-61-26562, JP-A-6-329468, JP-A-2000-95564, etc. is excellent, When a zirconia sintered body having a high strength is applied as a solid electrolyte, the hydrothermal deterioration itself is certainly improved to some extent, but it is still insufficient, and one of the important characteristics as a solid electrolyte is also present. The problem is that the electrical conductivity is low.
[0017]
  The present invention has been made to solve such problems, and the problem to be solved by the present invention is that strength deterioration can be suppressed while reducing the decrease in electrical conductivity, particularly 100 ° C to 300 ° C. A zirconia sintered body capable of suppressing strength deterioration even in the presence of water or steam.A solid oxide fuel cell used as a solid electrolyteIs to provide.
[0018]
[Means for Solving the Problems]
  In order to achieve such an object, the present inventors have conducted extensive research on various material properties, and as a result,₂O₃-ZrO₂Sc superior in oxygen ion conductivity to the zirconia sintered body₂O₃-ZrO₂This is an improvement of the zirconia sintered body of the system.
[0019]
  That is,Solid oxide fuel cell according to the present inventionContains lanthanum gallate oxide or lanthanum aluminate oxide or a mixture thereof with respect to zirconia containing 3 to 6 mol% of scandia as a stabilizer.Solid electrolyte made of sintered zirconia sintered body was used as a constituent materialthingNeedLet ’s do it.
[0020]
  Where aboveZirconia sintered body,UpContent of lanthanum gallate oxide, lanthanum aluminate oxide or a mixture thereofBut,Up0.5 to 2% by weight based on zirconiaWithin the range ofAhThe
[0021]
  In the solid oxide fuel cell according to the present invention,The lanthanum gallate oxide has a composition formula La_1-xA_xGa_1-yB_yO₃(Where A is one or more elements selected from Sr, Ca and Ba, 0 ≦ x ≦ 0.5, B is one or two selected from Mg, Al, Fe and In) Represented by more than seed elements, 0 ≦ y ≦ 0.5),UpThe lanthanum aluminate-based oxide has a composition formula La_{1-x '}C_{x '}Al_{1-y '}D_{y '}O₃(Wherein, C is one or more elements selected from Sr, Ca and Ba, 0 ≦ x ′ ≦ 0.5, D is one or more elements selected from Ga and In. Element, 0 ≦ y ′ ≦ 0.5)Is preferred.
[0022]
  Also,UpThe lanthanum gallate oxide is LaGaO.₃AndUpThe lanthanum aluminate oxide is LaAlO₃BeIs preferred.
[0023]
  Also,Zirconia aboveCrystal phase of sintered bodyIsConsists mainly of a tetragonal phase or a mixed phase of tetragonal and cubic crystalsIs preferred.
[0024]
  The zirconia sintered body preferably has no hydrothermal deterioration after aging in hot water or steam at 250 ° C. for 50 hours.
[0025]
DETAILED DESCRIPTION OF THE INVENTION
  Below, according to the present inventionSolid oxide fuel cell (SOFC)Will be described in detail. According to the present inventionSOFCContains lanthanum gallate oxide or lanthanum aluminate oxide or a mixture thereof with respect to zirconia containing 3 to 6 mol% of scandia as a stabilizer.Solid electrolyte made of zirconia sintered body is used as a constituent material.
[0026]
  In the above zirconia sintered bodyScandia as a stabilizer (Sc₂O₃) Content of zirconia (ZrO₂) To 3 to 6 mol%, preferably 3.5 to 5 mol%. This is because Scandia (Sc₂O₃) Content in the range of 3 to 6 mol%, the crystal phase of the sintered body does not substantially contain a monoclinic phase and is mainly tetragonal or a mixture of tetragonal and cubic crystals. phaseThanThis is because the balance between electrical conductivity and mechanical strength is excellent.
[0027]
  When the scandia content is less than 3 mol%, a large amount of monoclinic zirconia particles precipitate, which is not preferable. This monoclinic zirconia particle has a remarkably low electrical conductivity and hinders ion conduction, and therefore increases the total electrical resistance of the sintered body when used as a solid electrolyte. Further, the presence of monoclinic zirconia particles is not preferable because it is a main cause of volume change accompanying a phase transition due to temperature change (occurs at about 1150 ° C.).
[0028]
  On the other hand, when the content of scandia is more than 6 mol%, the proportion of cubic zirconia particles increases, and the desired mechanical strength cannot be obtained. Further, since the content of expensive scandia is increased, it is not preferable in that the zirconia sintered body cannot be reduced in price.
[0029]
  Next, the content of the lanthanum gallate-based oxide or lanthanum aluminate-based oxide or a mixture thereof is in the range of 0.5 to 2% by weight with respect to the zirconia containing the predetermined amount of scandia, preferably The range of 0.5 to 1% by weight is good. This is the matrix Sc₂O₃-ZrO₂This is because it is possible to suppress the strength deterioration without greatly reducing the high electrical conductivity of the zirconia sintered body of the system, in particular, the temperature range of 100 ° C. to 300 ° C., and water or water vapor. This is because, even under existing conditions, the spontaneous phase transition of the crystal phase is unlikely to occur, so that it is possible to effectively suppress hydrothermal degradation.
[0030]
  When the content of the lanthanum gallate oxide or lanthanum aluminate oxide or a mixture thereof is less than 0.5% by weight, the hydrothermal deterioration of the zirconia sintered body cannot be sufficiently suppressed. Since there is a tendency, it is not preferable. On the other hand, when the content of the lanthanum gallate-based oxide or lanthanum aluminate-based oxide or a mixture thereof is more than 2% by weight, although there is an effect of suppressing hydrothermal deterioration, the decrease in conductivity tends to increase. This is not preferable. Further, it is not preferable in that the zirconia sintered body cannot be reduced in price.
[0031]
  At this time, the lanthanum gallate oxide has a composition formula La_1-xA_xGa_1-yB_yO₃A is one or more elements selected from Sr, Ca, and Ba, and B is one or more elements selected from Mg, Al, Fe, and In. Preferably, the A element is Sr and the B element is Mg.
[0032]
  X is an atomic ratio of the A element, and is set in the range of 0 to 0.5, preferably 0 to 0.2. y is the atomic ratio of the B element, and is set in the range of 0 to 0.5, preferably 0 to 0.2. The reason why both x and y are limited to the range of 0 to 0.5 is that the characteristics when used as a solid electrolyte are excellent, for example, good conductivity can be obtained within the range.
[0033]
  In the above compositional formula, the atomic ratio of oxygen is represented as 3. However, as is apparent to those skilled in the art, for example, when x is not 0, oxygen vacancies are generated. The atomic ratio often takes a value smaller than 3. However, since the number of oxygen vacancies varies depending on the types of additive elements A and B and the manufacturing conditions, the oxygen atomic ratio is represented as 3 for convenience.
[0034]
  On the other hand, the lanthanum aluminate-based oxide has a composition formula La_{1-x '}C_{x '}Al_{1-y '}D_{y '}O₃Wherein C is one or more elements selected from Sr, Ca and Ba, and D is one or more elements selected from Ga and In. Preferably, the C element is Sr and the D element is Ga.
[0035]
  X 'is the atomic ratio of the C element, and is set in the range of 0 to 0.5, preferably 0 to 0.2. y ′ is the atomic ratio of the D element, and is set in the range of 0 to 0.5, preferably 0 to 0.2. The reason why both x 'and y' are limited to the range of 0 to 0.5 is that excellent characteristics are obtained when used as a solid electrolyte, for example, good conductivity can be obtained within the range. Note that in the above composition formula, the atomic ratio of oxygen expressed as 3 is the same as in the case of the lanthanum gallate oxide described above.
[0036]
  Here, both the lanthanum gallate oxide and the lanthanum aluminate oxide are lanthanum gallate (LaGaO) which is a perovskite oxide.₃) And lanthanum aluminate (LaAlO)₃) In which the oxygen ion conductivity is improved by substituting La, Ga, and Al metal ions, which are main components, with dissimilar metal ions having different valences.
[0037]
  In the present application, lanthanum gallate (LaGaO), which is a basic structure of a lanthanum gallate oxide and a lanthanum aluminate oxide, with respect to zirconia containing a predetermined amount of scandia.₃), Lanthanum aluminate (LaAlO₃) Is contained, it is possible to effectively suppress hydrothermal deterioration while maintaining practical conductivity.
[0038]
  Therefore, lanthanum gallate (LaGaO) as lanthanum gallate oxide and lanthanum aluminate oxide.₃), Lanthanum aluminate (LaAlO₃) Has the advantage that the zirconia sintered body can be easily made cheaper because the other subcomponents are not contained and the sintered body manufacturing process is simplified. That is,the aboveThe lanthanum gallate-based oxide and lanthanum aluminate-based oxide contained in the zirconia sintered body have the above-described composition according to the specifications and costs such as conductivity, mechanical strength, etc. required for the zirconia sintered body. Various adjustments are possible within the range of the formula.
[0039]
  Also onWritingIn the sulconia sintered body, only lanthanum gallate oxide or lanthanum aluminate oxide may be contained in zirconia containing a predetermined amount of scandia, or lanthanum gallate oxide and What mixed lanthanum aluminate type oxide with arbitrary ratios may be contained, and it is not limited in particular.
[0040]
  However, with regard to the mixing ratio of both, the lanthanum gallate oxide is a matrix Sc compared with the lanthanum aluminate oxide.₂O₃-ZrO₂It can be said that it is preferable to mix only the lanthanum gallate-based oxide or a large amount of the lanthanum gallate-based oxide because the decrease in the conductivity of the zirconia-based sintered body can be further suppressed.
[0041]
  Next, have the above configurationRujiA manufacturing method for manufacturing a Luconia sintered body will be described.the aboveIn order to produce a zirconia sintered body, a lanthanum gallate oxide or a lanthanum aluminate oxide or a mixture thereof is added to zirconia containing 3 to 6 mol% of scandia.0.5-2% by weightA raw material preparation step of preparing a raw material mixture using a zirconium compound and a scandium compound and a lanthanum gallate oxide and / or a lanthanum aluminate oxide so as to contain, a temporary baking of the raw material mixture at 600 to 800 ° C. It can be manufactured by going through a firing process, a calcining / molding process in which the obtained calcined body is pulverized and molded to form a molded body, and a sintering process in which the molded body is sintered at 1300-1500 ° C. it can. Hereinafter, each step will be described.
[0042]
  First, in the raw material preparation step, the zirconium compound and scandium compound and the lanthanum gallate oxide and / or lanthanum aluminate oxide arethe aboveWhat is necessary is just to measure so that it may become a composition in a zirconia sintered compact, and to prepare a raw material mixture. That is, for the zirconium compound and the scandium compound, scandia (Sc₂O₃) Is usually about 3 to 6 mol%, preferably 3.5 to 5 mol%.
[0043]
  The content of the lanthanum gallate-based oxide, lanthanum aluminate-based oxide, or a mixture thereof is scandia (Sc₂O₃) Containing zirconia (ZrO)₂For)0. What is necessary is just to mix | blend so that it may become 5 to 2 weight%, preferably 0.5 to 1 weight%. These contents can be appropriately adjusted according to the type of zirconium compound, scandium compound, lanthanum gallate-based oxide, lanthanum aluminate-based oxide, etc. used, the use of the zirconia sintered body, and the like.
[0044]
  Here, as the zirconium compound, specifically, zirconia, zirconium hydroxide, zirconium inorganic acid salt (zirconium oxychloride, zirconium chloride, zirconium nitrate, zirconium sulfate, etc.), zirconium organic acid salt (zirconium acetate, Zirconium oxalate, zirconium citrate, zirconium malonate, etc.).
[0045]
  Specific examples of scandium compounds include zirconia, scandium hydroxide, scandium carbonate, scandium inorganic acid salts (scandium nitrate, scandium chloride, scandium sulfate, etc.), and scandium organic acid salts (scandium acetate, scandium oxalate). , Scandium citrate, scandium malonate, etc.).
[0046]
  Further, as the lanthanum gallate oxide, specifically, LaGaO₃, La_0.9Sr_0.1Ga_0.8Mg_0.2O₃, La_0.8Sr_0.2Ga_0.8Mg_0.2O₃As the lanthanum aluminate-based oxide, specifically, LaAlO₃, La_0.9Ca_0.2AlO₃Etc.
[0047]
  As a method for preparing the raw material mixture, a known method can be adopted. For example, in addition to a chemical synthesis method such as neutralization coprecipitation method, hydrolysis method, alkoxide method (sol-gel method), oxide mixing method, etc. Can be prepared.
[0048]
  For example, in the case of the neutralization coprecipitation method, an appropriate amount of a lanthanum gallate oxide, a lanthanum aluminate oxide or a mixture thereof is added to and dissolved in a scandia nitrate solution, and the zirconium oxychloride aqueous solution or the like To obtain a mixed aqueous solution having a predetermined composition. The mixed solution is neutralized and coprecipitated with an alkali such as ammonia or sodium hydroxide, and the resulting precursor (mainly hydroxide) is washed with water and filtered as necessary to obtain a raw material mixture.
[0049]
  In addition, for example, in the case of an oxide mixing method, lanthanum gallate oxide, lanthanum aluminate oxide or a mixture thereof is blended with zirconia and scandia to have a predetermined composition, and wet-mixed with a ball mill or the like, A raw material mixture can be obtained by drying.
[0050]
  In the method of preparing the raw material mixture, a zirconium compound and a scandium compound and a lanthanum gallate oxide and / or a lanthanum aluminate oxide may be mixed at a time, or a predetermined amount of scandia may be added. The zirconia contained and the lanthanum gallate-based oxide or lanthanum aluminate-based oxide or a mixture thereof may be prepared separately, and these may be mixed later, and is not particularly limited.
[0051]
  Moreover, you may mix | blend a sintering aid, a well-known binder (for example, polyvinyl alcohol binder, an acrylic binder, etc.) etc. with a raw material mixture suitably as needed.
[0052]
  Next, in the calcining step, the obtained raw material mixture is calcined. The calcining temperature is usually about 500 to 900 ° C., preferably 600 to 800 ° C. This calcination is performed mainly by homogenizing the raw material composition by thermal diffusion, and further by using ZrO in advance.₂This is to promote the sintering in the sintering process by causing a part of the crystal to undergo a phase transition to tetragonal crystal.
[0053]
  When the calcination temperature is less than 500 ° C., there is a tendency that such an effect cannot be sufficiently obtained. When the calcination temperature exceeds 900 ° C., aggregated particles remain even after pulverization, which is large. This is not preferable because the strength of the zirconia sintered body may be reduced due to a failure point.
[0054]
  Next, in the pulverization / molding step, the obtained calcined body is pulverized and molded. As the pulverization method, a known method can be used. For example, the pulverization can be performed by a ball mill, a crusher mill, a sand mill, a vibration mill, a bead mill or the like. The calcined body is obtained in the form of a powdery material, a lumpy material or the like, but may be further pulverized to a desired shape if necessary. The degree of pulverization can be set as appropriate, but the average particle size is usually about 0.1 to 1.0 μm, preferably 0.3 to 0.7 μm.
[0055]
  On the other hand, a publicly known method can be used also about a forming method, for example, press forming method, extrusion forming method, cast forming method, CIP method, HIP method, etc. are employable. In addition,the aboveIn the production method, prior to molding, kneading or granulation can be performed using a binder in advance. As the binder, a known binder such as a polyvinyl alcohol-based binder can be used as described above.
[0056]
  Finally, in the sintering step, the molded body is sintered. As this sintering method, pressure sintering is particularly preferable. This is because a denser zirconia sintered body can be produced. The sintering temperature is usually about 1300 to 1500 ° C, preferably 1350 to 1450 ° C. When the sintering temperature is less than 1300 ° C., only a sintered body having low mechanical properties can be obtained. This is not preferable, and when it exceeds 1600 ° C., abnormal grain growth or the like occurs in the desired grain. It is not preferable because the mechanical characteristics cannot be obtained.
[0057]
  As abovethe aboveA zirconia sintered body can be obtained. On this occasion,the aboveUsing zirconia sintered body as SOFC solid electrolyteNiIn the above pulverization / molding step, a flat plate is formed using a press molding method, a tape molding method, or the like, or a cylindrical shape or a honeycomb shape is formed using an extrusion molding method, an injection molding method, or the like. It ’s fine. And if the compact | molding | casting obtained in this way is sintered at the optimal temperature according to a composition in a sintering process, the solid electrolyte for SOFC will be obtained.
[0058]
  In this case, the thickness of the solid electrolyte of SOFC is in the range of 50 to 300 μm, preferably in the range of 100 to 200 μm. This is because when the thickness is less than 50 μm, the reliability as a structural material tends to decrease, and when the thickness is more than 300 μm, the electrical resistance tends to increase and the conductivity tends to decrease.
[0059]
  Then, on one surface of the solid electrolyte thus obtained, for example, a fuel electrode material in which nickel-zirconia cermet of nickel 40% by weight-zirconia 60% by weight is made into a slurry is applied and sintered at a predetermined temperature. To form a fuel electrode and, on the other surface of the solid electrolyte, for example, apply an air electrode material in a slurry form of lanthanum strontium manganate and sinter at a predetermined temperature to form an air electrode. If a fuel gas introduction means, an oxidant gas introduction means and the like are attached to the solid electrolyte provided with the fuel electrode and the air electrode, SOFC can be obtained.
[0060]
  Specific examples of the method for applying the fuel electrode and the air electrode include a screen printing method, a doctor blade method, a brush coating method, a spray method, a dipping method, and the like. There is no particular limitation.
[0061]
  next,the aboveThe operation of the zirconia sintered body will be described. According to the zirconia sintered body, the lanthanum gallate-based oxide or lanthanum aluminate-based oxide or a mixture thereof with respect to zirconia containing 3 to 6 mol% of scandia as a stabilizer.0.5-2% by weightSince it is contained, Sc₂O₃-ZrO₂It becomes possible to suppress the strength deterioration without greatly reducing the high electrical conductivity of the zirconia sintered body of the system. In particular, even in a temperature range of 100 ° C. to 300 ° C. and in a situation where water or water vapor is present, since the spontaneous phase transition of the crystal phase hardly occurs, it is possible to effectively suppress hydrothermal deterioration. It becomes possible.
[0062]
  At this time, the lanthanum gallate oxide is converted into the composition formula La described above._1-xA_xGa_1-yB_yO₃The lanthanum aluminate-based oxide is represented by the composition formula La described above._{1-x '}C_{x '}Al_{1-y '}D_{y '}O₃In the case of lanthanum gallate oxide, high oxygen ion conductivity is expressed by replacing metal ions such as La and Ga, which are main components, with other metal ions having different valences. Moreover, the fall of the electrical conductivity of a sintered compact by containing a lanthanum aluminate type oxide can be made still smaller.
[0063]
  Further, lanthanum gallate (LaGaO) as lanthanum gallate oxide and lanthanum aluminate oxide.₃), Lanthanum aluminate (LaAlO₃), It is possible to effectively suppress hydrothermal deterioration while maintaining the practical conductivity of the zirconia sintered body, and other sub-substances such as Sr. Since the component is not contained, the sintered body manufacturing process is simplified, so that there is an advantage that it is easy to reduce the cost of the zirconia sintered body.
[0064]
  Therefore, such a zirconia sintered bodySWhen used as a solid electrolyte of OFC, it has sufficient conductivity, so that the internal resistance of the battery is reduced and the power generation efficiency is increased, and the strength of the solid electrolyte is deteriorated even if the SOFC is repeatedly started and stopped, particularly water. Since it does not cause thermal degradation and is excellent in structural reliability as a solid electrolyte, it is possible to obtain a SOFC that can stably generate power over a long period of time.
[0065]
【Example】
  The zirconia sintered body according to the present invention will be described more specifically with reference to examples.
[0066]
Example 1
  Lanthanum aluminate (LaAlO) with respect to zirconia (hereinafter referred to as “4ScSZ”) containing 4 mol% of scandia₃4ScSZ and LaAlO so that 1) wt.₃Were weighed, and pure water was added to the ball mill (ZrO).₂Wet mixing was used). The mixture was then dried and calcined at 1000 ° C. Next, the calcined powder obtained was crushed with the above ball mill, and after adding an acrylic binder and spray granulation, a molding pressure of 1000 kgf / cm²A uniaxial die was molded to form a molded body. Subsequently, each zirconia sintered body was obtained by firing at 1350 ° C., 1400 ° C., 1450 ° C., and 1500 ° C. for 2 hours.
[0067]
  In addition, 4ScSZ used the thing made from a 1st rare element chemical industry company. Lanthanum aluminate (LaAlO₃) La₂O₃And Al₂O₃Were weighed, and pure water was added thereto and wet-mixed with the above ball mill, and then prepared by firing at 1200 ° C. for 2 hours.
[0068]
(Example 2)
  For 4ScSZ, lanthanum aluminate (LaAlO₃) Lanthanum gallate (LaGaO)₃Each zirconia sintered body was obtained according to the same procedure as in Example 1, except that the above was used.
[0069]
(Example 3)
  For 4ScSZ, lanthanum aluminate (LaAlO₃) Lanthanum gallate (LaGaO)₃4) ScSZ and LaGaO so as to contain 0.5, 0.7, 1.0, 1.5, and 2.0 wt%₃Were weighed, and pure water was added to the ball mill (ZrO).₂Each zirconia sintered body was obtained according to the same procedure as in Example 1, except that the mixture was wet-mixed using cobblestone) and each molded body was fired at a firing temperature of 1450 ° C. for 2 hours. At this time, lanthanum gallate (LaGaO₃4ScSZ sintered body not containing) was used as a comparison.
[0070]
  Lanthanum gallate (LaGaO₃) La₂O₃And Ga₂O₃Were weighed, and pure water was added thereto and wet-mixed with the above ball mill, and then prepared by firing at 1200 ° C. for 2 hours.
[0071]
(Various characteristic evaluation tests)
  About each zirconia sintered compact of Example 1, Example 2, and Example 3 obtained as mentioned above, the autoclave test, the crystal phase, and the measurement of the electrical conductivity were performed. That is, in the autoclave test, each zirconia sintered body of Example 1, Example 2 and Example 3 was put in an autoclave and aged for 50 hours in 250 ° C. hot water or steam (medium: ion-exchanged water). After performing, the presence or absence of hydrothermal deterioration was judged by confirming the external appearance state of each sintered compact.
[0072]
  The crystal phase was measured by polishing each zirconia sintered body of Example 1, Example 2 and Example 3 with a # 600 diamond grindstone and then finishing the mirror surface with 1-5 μm diamond grains. The surface was measured by powder X-ray diffraction. In addition, the measurement was performed also about the thing after a hydrothermal deterioration test.
[0073]
  In addition, the conductivity was measured by baking a platinum paste as an electrode at 1000 ° C. on each zirconia sintered body of Example 1, Example 2 and Example 3 (20 mm × 3 mm × 4 mm). Was performed at temperatures of 300 ° C., 400 ° C., 500 ° C., 600 ° C., 700 ° C., and 800 ° C. At this time, the conductivity was measured by the AC impedance method (frequency: 100 to 10 MHz, in still air), and the conductivity was obtained from the measured resistance value and the size of the test piece according to the following equation.
[0074]
[Expression 1]
  Conductivity σ (S / cm) = (1 / resistance value R (Ω))
                        X Test piece length L (cm) / Test piece cross-sectional area S (cm²)
[0075]
(Test results)
  As shown in Table 1, LaAlO against 4ScSZ₃LaGaO with respect to Example 1, 4ScSZ containing 1 wt% (wt%)₃For the sintered bodies of Example 2 and Example 3 in which 0.5 to 2 wt% (wt%) was contained, hydrothermal deterioration could be sufficiently suppressed, so even after the autoclave test The morphology of the sintered body could be maintained. The crystal phase is tetragonal before and after the autoclave test, indicating that no phase transition has occurred.
[0076]
[Table 1]

[0077]
  Next, FIG. 1 shows LaGaO in the sintered body of Example 3 sintered at a sintering temperature of 1450 ° C.₃It shows the relationship between the content of and the electrical conductivity. For comparison, in FIG. 1, the conductivity of the 4ScSZ sintered body and LaAlO with respect to 4ScSZ.₃1 wt% (hereinafter “4ScSZ + 1 wt% LaAlO₃The electrical conductivity of the sintered body of Example 1 is also shown.
[0078]
  According to FIG. 1, LaGaO for 4ScSZ₃In an amount of 0.5-2 wt% (hereinafter referred to as “4ScSZ + Xwt% LaGaO₃It can be seen that the conductivity of the sintered body of Example 3 is in a practical range. Further, the 4ScSZ + 1 wt% LaAlO of Example 1 over the entire temperature range of 300 ° C. to 800 ° C.₃It can also be seen that the conductivity is higher than that of the sintered body. From this, LaAlO for 4ScSZ₃Rather than containing LaGaO₃It can be seen that the inclusion of sucrose has a higher effect of suppressing hydrothermal deterioration and can further reduce the decrease in the conductivity of 4ScSZ as a matrix.
[0079]
  The present invention is not limited to the above-described embodiments, and various modifications can be made without departing from the spirit of the present invention. For example, in the above embodiment, LaAlO is used for 4ScSZ.₃Or LaGaO₃The lanthanum gallate-based oxide or lanthanum aluminum having the above-described composition formula with respect to zirconia containing the predetermined mol% of scandia other than that described above is used. Even if the nate-based oxide or a mixture thereof is contained in a predetermined weight percent, the particular action and effect peculiar to the present application are exhibited.
[0080]
【The invention's effect】
  the aboveAccording to the zirconia sintered body, a lanthanum gallate oxide or a lanthanum aluminate oxide or a mixture thereof with respect to zirconia containing 3 to 6 mol% of scandia as a stabilizer.0.5-2% by weightSince it is contained, Sc₂O₃-ZrO₂It becomes possible to suppress the strength deterioration without greatly reducing the high electrical conductivity of the zirconia sintered body of the system. In particular, even in a temperature range of 100 ° C. to 300 ° C. and in a situation where water or water vapor is present, since the spontaneous phase transition of the crystal phase hardly occurs, it is possible to effectively suppress hydrothermal deterioration. it can.
[0081]
  Therefore, this zirconia sintered bodySWhen used as a solid electrolyte of OFC, it has sufficient conductivity, so that the internal resistance of the battery is reduced and the power generation efficiency is increased, and the strength of the solid electrolyte is deteriorated even if the SOFC is repeatedly started and stopped, particularly water. Since it does not cause thermal degradation and is excellent in structural reliability as a solid electrolyte, it is possible to obtain a SOFC that can stably generate power over a long period of time.
[Brief description of the drawings]
FIG. 1 LaGaO in a sintered body of Example 3 sintered at a sintering temperature of 1450 ° C.₃It is the figure which showed the relationship between content of and the electrical conductivity.

Claims (5)

Against zirconia containing 3-6 mol% scandia as a stabilization agent, distearate zirconia sintered to lanthanum gallate-based oxide or lanthanum aluminate-based oxide or a mixture thereof 0.5 to 2 wt% A solid oxide fuel cell characterized in that a solid electrolyte comprising a ligation is used as a constituent material . The lanthanum gallate-based oxide has a composition formula La _1-x A _x Ga _1-y B _y O ₃ (where A is one or more elements selected from Sr, Ca and Ba, 0 ≦ x ≦ 0.5, B is represented by one or more elements selected from Mg, Al, Fe and In, 0 ≦ y ≦ 0.5), and the lanthanum aluminate oxide is Composition formula La _{1-x ′} C _{x ′} Al _{1-y ′} D _{y ′} O ₃ (wherein C is one or more elements selected from Sr, Ca and Ba, 0 ≦ x ′ ≦ The solid oxide form according to claim 1, wherein 0.5 and D are represented by one or more elements selected from Ga and In, 0 ≦ y ′ ≦ 0.5) Fuel cell . The lanthanum gallate-based oxide is LaGaO _3, a solid oxide fuel cell according to claim 1 or 2, wherein the lanthanum aluminate-based oxide is characterized by a LaAlO _3. Solid oxide fuel cell according to any one of claims 1 to 3, characterized in that the crystalline phase of the zirconia sintered body is mainly composed of tetragonal phases or tetragonal and cubic mixed phase of. The zirconia sintered body, a solid oxide according to any one of claims 1 to 4, characterized in that there is no hydrothermal degradation after 50 hours aging at 250 ° C. in hot water or water vapor Fuel cell .

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