JP2005276683A - Fuel electrode, electrochemical cell and method of manufacturing fuel electrode - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To further improve the working efficiency of an electrochemical cell in a composition system that can prevent cracks resulting from a difference in thermal expansion coefficient between a fuel electrode and a solid electrolyte. <P>SOLUTION: A material for the fuel electrode is composed of 30-40 capacity % of nickel, 25-40 vol.% of zirconia, and 25-40 vol.% of a nickel-aluminum composite oxide. The fuel electrode made of this material is in contact with a solid electrolyte layer. The material for the fuel electrode is made by mixing a nickel oxide powder having a mean particle diameter of 1.0 μm or less, a zirconia powder having a mean particle diameter of 1.0 μm or less and an Al<SB>2</SB>O<SB>3</SB>powder having a mean particle diameter of 1.0 μm or less, and by sintering the mixture. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a fuel electrode for an electrochemical cell and a method for producing the same.

  Solid oxide fuel cells are roughly classified into so-called flat plate types and cylindrical types. In a flat type solid oxide fuel cell, a stack for power generation is configured by alternately stacking so-called separators and power generation layers. That is, a fuel electrode and an air electrode are respectively formed on a solid electrolyte membrane to produce a power generation layer, and an interconnector is prepared, and ceramic powder and an organic binder are contained between the power generation layer and the interconnector. The power generation layer and the interconnector are joined by sandwiching the thin film and heat-treating the thin film.

  However, since the thermal expansion coefficient of the nickel-zirconia fuel electrode used in the solid oxide fuel cell is larger than the thermal expansion coefficient of the solid electrolyte, it breaks when the thermal cycle is repeated. Further, since the porosity is large when exposed to a reducing atmosphere, deformation due to a difference in thermal expansion occurs due to low strength. For this reason, in order to maintain consistency with thermal expansion, the thermal expansion coefficient is adjusted by using spinel such as nickel aluminum composite oxide or magnesium aluminum composite oxide as a material replacing zirconia. In addition, zirconia, nickel aluminum composite oxide, magnesium aluminum composite oxide, etc. are mixed to prevent nickel sintering.

For example, Patent Documents 1, 2, and 3 describe the use of a nickel-yttria stabilized zirconia-nickel spinel mixture as the material of the fuel electrode.
JP-A-6-243872 Japanese Patent No. 3327789 JP2003-242985

Particularly in Patent Document 1, for example, nickel oxide powder 60 vol% of the specific surface area of 0.23 m ² / g, 3 mol% yttria-stabilized zirconia powder 10 vol% of the specific surface area of 14.3m ² / g, and the alumina powder 30 vol% The mixture was molded and fired at 1450 ° C. for 3 hours (0014) (10015).

  However, in SOFCs as described in Patent Documents 1 to 3, it is difficult to increase the power generation performance in some cases, and sufficient power generation performance may not be obtained. This seems to be because there is little generation of a reaction field (three-phase interface) that can contribute to power generation along the interface between the fuel electrode and the solid electrolyte, and therefore the contribution to power generation is not sufficient.

  An object of the present invention is to further improve the operating efficiency of an electrochemical cell in a composition system that can prevent cracking due to a difference in thermal expansion coefficient between a fuel electrode and a solid electrolyte.

  The invention according to the first aspect is a fuel electrode material comprising 30 to 40% by volume of nickel, 25 to 40% by volume of zirconia, and 25 to 40% by volume of nickel aluminum composite oxide. It is concerned.

  In addition, the present invention relates to a fuel electrode characterized by including the fuel electrode material, and further comprising the fuel electrode, a solid electrolyte layer, and an air electrode. It concerns chemical cells.

  In the invention according to the second aspect, nickel oxide powder having an average particle diameter of 1.0 μm or less, zirconia powder having an average particle diameter of 1.0 μm or less, and alumina powder having an average particle diameter of 1.0 μm or less are mixed and sintered. The present invention relates to a method for producing a fuel electrode material.

  According to the invention according to the first aspect, the three-phase interface is increased by arranging and contacting the fuel electrode material in which nickel, zirconia and nickel aluminum composite oxide are mixed in the above-described ratio in the vicinity of the electrolyte surface. In addition, since the sufficient electrical conductivity can be ensured, the effective three-phase interface that can contribute to power generation also increases, so that the operation efficiency of the electrochemical cell is remarkably improved.

  According to the second aspect of the invention, a nickel oxide powder having an average particle size of 1.0 μm or less, a zirconia powder having an average particle size of 1.0 μm or less, and an alumina powder having an average particle size of 1.0 μm or less are mixed and sintered. Let In this way, by using fine nickel powder, zirconia powder, and alumina powder as starting materials, the nickel aluminum composite oxide phase, zirconia phase, and nickel phase are uniformly deposited as fine particles when the nickel aluminum composite oxide is produced. To do. As a result, the three-phase interface is increased, the operating efficiency of the cell is improved, and the thermal expansion coefficients of the solid electrolyte and the fuel electrode can be easily matched.

  In the invention according to the first aspect, the proportion of nickel is 30 to 40% by volume, more preferably 35% by volume or more. The proportion of zirconia is still 25 to 40% by volume, more preferably 30% by volume or more. Moreover, although the ratio of nickel aluminum complex oxide is 25-40 volume%, it is still more preferable that it is 30 volume% or more.

  The fuel electrode of the present invention is entirely or partially made of the fuel electrode material of the present invention. Here, in a preferred embodiment, at least a portion of the fuel electrode that contacts the solid electrolyte is made of the fuel electrode material of the present invention. For example, the entire fuel electrode may be made of the fuel electrode material of the present invention, or the fuel electrode is made of a first fuel electrode layer made of the fuel electrode material of the present invention and a second electrode made of another material. And a fuel electrode layer.

Zirconia constituting the fuel electrode material of the present invention is an oxide obtained by adding another metal oxide to ZrO ₂ . As such other metal oxides, rare earth elements are preferable, neodymium oxide (Nd ₂ O ₃ ), samarium oxide (Sm ₂ O ₃ ), yttrium oxide (Y ₂ O ₃ ), gadolinium oxide (Gd ₂ O ₃ ), Scandium oxide (Sc ₂ O ₃ ) is particularly preferred.

  The ratio of other metal elements in the zirconia is preferably 12 mol% or less, and particularly preferably 10 mol% or less. The ratio of other metal elements in the zirconia is preferably 2 mol% or more, and particularly preferably 3 mol% or more. Particularly preferably, the zirconia is 3 to 10 mol% yttria stabilized zirconia.

The electrochemical cell of the present invention can be used as a solid oxide fuel cell, an oxygen pump, and a high temperature steam electrolysis cell. The high-temperature steam electrolysis cell can be used for a hydrogen production apparatus and a steam removal apparatus. In this case, the following reaction is caused at each electrode.
Cathode: H ₂ O + 2e ⁻ → H ₂ + O ²⁻
Anode: O ²⁻ → 2e ⁻ + 1 / 2O ₂

  Moreover, an electrochemical cell can be used as a decomposition cell for NOx and SOx. This decomposition cell can be used as a purification device for exhaust gas from automobiles and power generation devices. In a preferred embodiment, the electrochemical cell is a solid oxide fuel cell.

Although the material which can be used as a solid electrolyte will not be specifically limited if it has ionic conductivity, The following can be illustrated.
Stabilized zirconia in which neodymium oxide (Nd ₂ O ₃ ), samarium oxide (Sm ₂ O ₃ ), yttrium oxide (Y ₂ O ₃ ), gadolinium oxide (Gd ₂ O ₃ ), calcium oxide (CaO) and the like are dissolved Partially stabilized zirconia.
Ceria (CeO ₂ ) in which neodymium oxide (Nd ₂ O ₃ ), samarium oxide (Sm ₂ O ₃ ), yttrium oxide (Y ₂ O ₃ ), gadolinium oxide (Gd ₂ O ₃ ), and the like are dissolved.
Lanthanum gallate (LaGaO ₃ ) in which Sr, Mg and the like are dissolved.

  The material of the air electrode is preferably a perovskite complex oxide containing lanthanum, more preferably lanthanum manganite or lanthanum cobaltite, and even more preferably lanthanum manganite. Lanthanum manganite may be doped with strontium, calcium, chromium, cobalt, iron, nickel, aluminum or the like. Further, palladium, platinum, ruthenium, platinum-zirconia cermet, palladium-zirconia cermet, ruthenium-zirconia cermet, platinum-cerium oxide cermet, palladium-cerium oxide cermet, ruthenium-cerium oxide cermet may be used.

  When the first fuel electrode layer in contact with the solid electrolyte is formed of the fuel electrode material of the present invention and the second fuel electrode layer is formed of a material different from this, the material of the second fuel electrode layer is There is no particular limitation. For example, a sintered body of metal, mixed powder of metal particles and solid electrolyte particles, or mixed powder of metal particles and composite oxide can be used.

  As such a metal, nickel, palladium, platinum, ruthenium, and alloys thereof are preferable. However, from the viewpoint of compatibility and durability of the thermal expansion coefficient with the first fuel electrode layer, a sintered powder of a mixed powder of metal particles and solid electrolyte particles or a mixed powder of metal particles and composite oxide is used. It is particularly preferred to use it. As such metal particles, particles made of nickel, palladium, platinum, ruthenium, and alloys thereof are particularly preferable. Examples of solid electrolyte particles include zirconia and ceria. Particularly preferably, the metal particles are made of nickel, and the solid electrolyte particles are made of stabilized or partially stabilized zirconia. Moreover, it is preferable to use a sintered body in which the metal particles are made of nickel and the composite oxide particles are made of nickel aluminum composite oxide.

  Hereinafter, the invention according to the first and second aspects will be described in more detail with a focus on a preferable manufacturing process of the electrochemical cell.

  1 and 2 show the steps of a production process suitable for producing the electrochemical cell substrate of the present invention. FIGS. 3A and 3B are views showing the electrochemical cell 12 and the cell substrate 7 according to an embodiment of the present invention.

  As shown in FIG. 1 (a), a coating layer 15 for the first fuel electrode layer is formed on the main surface 5a of the second green molded body 5 for the fuel electrode layer. Next, as shown in FIG. 1B, the green molded body 3 of the solid electrolyte membrane is laminated on the coating layer 15, and the resin sheet 4 is laminated thereon. 5b is a main surface of the green molded body 5, and 5c is a side surface. The entire laminate 2 of the green molded bodies 5 and 3 and the resin sheet 4 is covered with the coating 1 and subjected to cold isostatic pressing. Thereby, a uniform pressure is applied over the entire surface of the laminate 2.

  Alternatively, as shown in FIG. 1C, the first fuel electrode layer coating layer 15 is formed on the green molded body 3 of the solid electrolyte membrane, and then the molded body 3 and the coating layer 15 are formed into the second fuel. It can laminate | stack with respect to the green molded object 5 for pole layers, and can use this for a cold isostatic press.

  In this example, in the invention according to the second aspect, nickel oxide powder having an average particle diameter of 1.0 μm or less, zirconia powder having an average particle diameter of 1.0 μm or less, and alumina powder having an average particle diameter of 1.0 μm or less are mixed. The coating layer 15 is produced.

  From the viewpoint of the present invention, the average particle diameter of the nickel oxide powder is preferably 0.8 μm or less, and more preferably 0.6 μm or less. Although there is no particular lower limit, it is practically, for example, 0.05 μm or more.

  From the viewpoint of the present invention, the average particle size of the zirconia powder is preferably 0.8 μm or less, and more preferably 0.6 μm or less. Although there is no particular lower limit, it is practically, for example, 0.05 μm or more.

  From the viewpoint of the present invention, the average particle size of the alumina powder is preferably 0.8 μm or less, and more preferably 0.6 μm or less. Although there is no particular lower limit, it is practically, for example, 0.05 μm or more.

  Next, the coating film 1 is peeled from the obtained pressure-molded body to obtain a laminate 6 shown in FIG. Next, the resin sheet 4 is peeled off from the pressure-molded body 6 and the pressure-molded body 6 is sintered to obtain the electrochemical cell substrate 7 shown in FIG. The substrate 7 includes a second fuel electrode layer 8, a solid electrolyte membrane 9, and a first fuel electrode layer 16 formed along the interface between the second fuel electrode layer 8 and the solid electrolyte membrane 9. Become.

  When the electrochemical cell is manufactured, for example, as shown in FIG. 3A, an air electrode molded body 10 is provided on the surface of the solid electrolyte layer 9 of the electrochemical cell substrate 7. And by sintering this molded object 10, as shown in FIG.3 (b), the air electrode 11 is formed and the electrochemical cell 12 is obtained.

  Or as shown in FIG.3 (c), the fuel electrode 20 can be made into a single layer, and the whole fuel electrode 20 can be produced from the material for fuel electrodes of this invention.

  The green molded body for the fuel electrode and the coating layer for the fuel electrode layer are preferably composed of a mixture in which each raw material is mixed with an organic binder, a pore former, and water. Examples of the organic binder include polymethyl acrylate, nitrocellulose, polyvinyl alcohol, polyvinyl butyral, methyl cellulose, ethyl cellulose, starch, wax, acrylic acid polymer, and methacrylic acid polymer. When the weight of the main raw material is 100 parts by weight, the addition amount of the organic binder is preferably 0.5 to 5 parts by weight.

  The method for forming the green molded body for the fuel electrode is not limited, and may be an ordinary ceramic molding technique such as a doctor blade method, a slip casting method, an extrusion molding method, or a die press molding method. The method for forming the fuel electrode coating layer is not limited, and a known film forming method such as a screen printing method, a doctor blade method, a slurry dipping method, a spin coating method, a dip coating method, or a casting method is preferable.

  The method for forming the green molded body of the solid electrolyte membrane is not limited, and may be an ordinary ceramic forming technique such as a doctor blade method, a dip method, or an extrusion method. When molded by the doctor blade method, polyethylene glycol, polyalkylene glycol, dibutyl phthalate, etc. as plasticizers other than the above binder, glycerin, oleic acid, sorbitan triol, etc. as peptizers, toluene, ethanol, butanol etc. as solvents preferable.

  The green molded body of the solid electrolyte membrane is preferably a molded body obtained by molding a mixture of an organic binder and water or an organic solvent into the main raw material of the solid electrolyte membrane. As the organic binder, those described above can be used. When the weight of the main raw material is 100 parts by weight, the amount of the organic binder added is preferably 0.5 to 20 parts by weight.

The pressure at the time of cold isostatic pressing the stack, from the viewpoint of enhancing the adhesion of each green body of the laminate, 500 kgf / cm ² or more, more preferably to 1000 kgf / cm ² or more, pressure Is practically 10 tf / cm ² or less. The firing temperature is usually 1000 ° C to 1500 ° C.

(Experiment 1)
The electrochemical cell 12 shown in FIG. 3B was produced according to the procedure described with reference to FIGS.

(Manufacture of molded body 3 for solid electrolyte)
Put an alumina ball with a ball diameter of 10 mm in a nylon plastic container, add 100 parts by weight of 3 mol yttria-added zirconia (3YSZ), 20 parts by weight of toluene, 11 parts by weight of ethanol, and 2 parts by weight of butanol as the rotation speed of the mill. Ball mill mixing was performed at 60 rpm. Thereafter, 8 parts by weight of polyvinyl butyral, 3 parts by weight of dibutyl phthalate, 26 parts by weight of toluene and 15 parts by weight of ethanol were added to this mixture, followed by ball mill mixing. The obtained slurry was subjected to sheet molding on a polyethylene terephthalate sheet (100 μm thick) (resin sheet 4) by a doctor blade method, and a green molded body 3 of 3 mol% yttria added zirconia (3YSZ) having a width of 50 mm and a thickness of 20 μm. (Molded body for solid electrolyte membrane) was produced.

(Manufacture of first fuel electrode layer coating layer 15)
The coating layer using nickel oxide powder, 8 mol% yttria stabilized zirconia (8YSZ) powder and alumina powder as raw materials becomes a composite material having a nickel-8YSZ-nickel aluminum composite oxide composition by reduction during power generation after firing.
8YSZ powder and the average particle size 0.6 .mu.m in average particle size 0.6 .mu.m (specific surface area 6.1 m ² / g) nickel oxide powder and the average particle diameter 0.5μm of (specific surface area 8m ² / g) (specific surface area 6.8 m ² / After weighing the alumina powder of g) so as to have the composition shown in Table 1, an organic binder and a solvent were added to the mixed powder and mixed in an alumina mortar to form a paste. Thereafter, screen printing was performed on the solid electrolyte membrane molded body 3 to form a first fuel electrode layer coating layer 15. The film thickness of screen printing at this time was 15 μm.

(Formation of second molded body 5 for fuel electrode layer)
A molded body made of nickel oxide powder and alumina powder as a raw material becomes a composite material having a nickel-nickel aluminum composite oxide composition after firing and reduction during power generation.
A nickel oxide powder having an average particle diameter of 1 μm and an alumina powder having an average particle diameter of 1 μm are weighed to a composition of 35% by volume of nickel and 65% by volume of a nickel aluminum composite oxide, and then added with an organic binder and water in a ball mill. Wet mixed, the mixture was dried and granulated. This granulated powder was molded in a mold to produce a second molded article 5 for the fuel electrode layer having a thickness of 3 mm.

(Integration of solid electrolyte / first fuel electrode layer / second fuel electrode layer)
The produced solid electrolyte molded body 3, the first fuel electrode layer coating layer 15 and the second fuel electrode layer molded body 5 were laminated. This laminate was covered with a vacuum bag film bag and cold isostatic pressed (pressure: ² ton / cm ² holding time: 1 minute). The obtained press-molded body was taken out from the mold and the film was peeled off to obtain a press-molded body.

(Baking of pressure-molded body)
This press-molded body was fired in air at a maximum temperature of 1400 ° C. for 2 hours to obtain a laminated sintered body 7.

(Formation of air electrode)
100 parts by weight of lanthanum manganite powder having an average particle size of 1 μm, 3 parts by weight of alkyl acetate polyvinyl alcohol, and 30 parts by weight of TVneol were mixed in an alumina mortar to form a paste. The kneaded material thus obtained was applied with a screen printer, dried after film formation, and baked at a temperature of 1250 ° C. for 1 hour to form the air electrode 11.

(Power generation test)
The initial power generation output was measured for each example SOFC. Specifically, the laminated sintered body was set in a power generation test apparatus. A platinum mesh was sandwiched between the air electrode part and the fuel electrode part to collect current. The temperature was raised while flowing air at 500 cc / min on the air electrode side and nitrogen at 500 cc / min on the fuel electrode side. The temperature was maintained at 750 ° C., and hydrogen was supplied to the fuel electrode side at 500 cc / min to replace the gas. Table 1 shows the results of measuring the output (initial output) after 10 hours have passed after energization of 0.7 V after the atmosphere has stabilized.

(Confirmation of crystal phase)
Separately, in order to confirm the crystal phase, the first fuel electrode layer coating layer 15 and the second fuel electrode molded body 5 were not integrated, but were fired under the above firing conditions, and then 1% at 750 ° C. in a hydrogen atmosphere. It cooled after the time reduction process. Thereafter, as a result of measurement by an X-ray analysis apparatus, the first fuel electrode layer 16 is composed of nickel (Ni), zirconia (YSZ), and nickel aluminum composite oxide (NiAl ₂ O ₄ ). The fuel electrode layer 8 confirmed the precipitation of nickel (Ni) and nickel aluminum composite oxide (NiAl ₂ O ₄ ). In any case, unreacted crystals of Al ₂ O ₃ were not precipitated.

  From the above results, it was confirmed that when the fuel electrode is formed using the fuel electrode material of the invention according to the first and second aspects, the power generation performance is remarkably improved. That is, high output was obtained from Experiment 1-1 to 1-5. In Experiment 1-6, the nickel aluminum composite oxide was not contained, but the output decreased. In Experiment 1-7, zirconia was not contained, but the output decreased. In Experiment 1-8, the amount of zirconia was small and the amount of nickel aluminum composite oxide was large, but the output decreased. In Experiment 1-9, the amount of nickel was large, but the output decreased.

(Experiment 2)
In Experiments 2-1, 2-2, 2-3, and 2-4, the cell 12 shown in FIG. 3B was manufactured as in Experiment 1-1.
However, the fuel electrode was manufactured by changing the average particle size of nickel oxide powder, 8 mol% yttria-stabilized zirconia powder, and alumina powder as raw materials for the fuel electrode. The composition of the first fuel electrode was the same as in Experiment 1-1, and the particle size of the raw material powder was controlled by the pulverization time. The average particle size was measured with SALD-2000A manufactured by Shimadzu Corporation. The second molded article for the fuel electrode layer is a nickel oxide powder having an average particle diameter of 1 μm and an 8YSZ powder having an average particle diameter of 1 μm so as to have a composition of 35% by volume of nickel and 65% by volume of zirconia composite oxide. And water were added and wet mixed in a ball mill, and the mixture was dried and granulated. This granulated powder was molded in a mold to produce a second molded body for the fuel electrode layer having a thickness of 3 mm. Subsequent cells were prepared in the same manner as in Experiment 1, and a power generation test was performed. Table 2 shows the measurement results.

  From the above results, even in the composition within the scope of the first invention, when a fuel electrode is formed using a fuel electrode material having a small starting material particle size (Experiment Nos. 2-1, 2-2, 2-3). ), It was found that the power generation performance was further improved.

(Experiment 3)
In Experiments 3-1, 3-2, and 3-3, the cell 12 shown in FIG. 3B was manufactured in the same manner as in Experiment 1-1.

  However, the second fuel electrode layer 8 was manufactured as follows. That is, nickel oxide powder having an average particle diameter of 1 μm, 8 mol% yttria-stabilized zirconia powder having an average particle diameter of 1 μm, and alumina powder having an average particle diameter of 1 μm are weighed to have the composition shown in Table 3, and an organic binder and water are added. The mixture was wet mixed in a ball mill, and the mixture was dried and granulated. This granulated powder was molded in a mold to produce a green molded body having a thickness of 3 mm. Thereafter, the cell 12 was manufactured in the same manner as in Experiment 1.

  In Experiments 3-1, 3-2, and 3-3, the first fuel electrode layer 16 in contact with the solid electrolyte layer is made of the fuel electrode material of the present invention, and therefore the output is high. That is, if the fuel electrode in contact with the solid electrolyte layer is the fuel electrode material of the present invention regardless of the second fuel electrode layer, the power generation output is increased.

(Experiment 4)
A single-layer fuel electrode 20 shown in FIG. 3C was produced in the same manner as the second fuel electrode layer in Experiment 1-1. The composition of the fuel electrode was Ni: 35% by volume, 8YSZ: 32.5% by volume, and NiAl ₂ O ₄ : 325% by volume. Otherwise, the solid electrolyte layer and the air electrode layer were formed in the same manner as in Experiment 1-1, and the cell shown in FIG. 3C was obtained. This cell was also subjected to a power generation test in the same manner as in Experiment 1, and the same result was obtained.

(A), (b), (c) is a schematic diagram which shows the manufacturing process of the board | substrate 7 for electrochemical cells. (A), (b) is a schematic diagram which shows the manufacturing process of the board | substrate 7 for electrochemical cells. (A) has shown the state which formed the green molded object 10 for air electrodes on the electrochemical cell substrate 7, (b) has shown the state which formed the air electrode 11 on the electrochemical cell substrate 7 (C) is the schematic diagram which shows the electrochemical cell which the fuel electrode 20 consists of a single phase.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Coating 2 Laminate 3 Solid electrolyte membrane molded body 4 Resin coating 5 Second fuel electrode layer 8 molded body 7 Electrochemical cell substrate 8 Second fuel electrode layer 9 Solid electrolyte membrane 11 Air electrode 12 Electrochemical Cell 15 Coating layer for first fuel electrode layer 16 16 First fuel electrode layer 20 Fuel electrode composed of a single phase

Claims (6)

  A fuel electrode material comprising 30 to 40% by volume of nickel, 25 to 40% by volume of zirconia, and 25 to 40% by volume of nickel aluminum composite oxide.   A fuel electrode comprising the fuel electrode material according to claim 1.   The fuel electrode according to claim 2, comprising a single-layer fuel electrode made of the fuel electrode material.   The fuel electrode according to claim 2, comprising a first fuel electrode layer made of the fuel electrode material and a second fuel electrode layer made of a material other than the fuel electrode material.   An electrochemical cell comprising the fuel electrode according to any one of claims 2 to 4, a solid electrolyte layer, and an air electrode.   A fuel electrode material comprising: a nickel oxide powder having an average particle size of 1.0 μm or less, a zirconia powder having an average particle size of 1.0 μm or less, and an alumina powder having an average particle size of 1.0 μm or less, and sintering. Production method.

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