JP7374530B2 - Porous ceramic sintered body and applications using it - Google Patents

Description

The present invention relates to a porous ceramic sintered body and uses thereof. In particular, the present invention relates to a porous ceramic sintered body made of an oxide ion/electronic mixed conductor using starch as a pore-forming agent, and uses thereof.

Porous materials are used in adsorbents, filters, catalyst carriers, reactors, insulation materials, sound deadening materials, building materials, etc. Among such porous materials, methods for producing ceramic porous bodies (also referred to as porous ceramics) having communicating pores and high porosity are known (see, for example, Patent Documents 1 and 2).

According to Patent Document 1, a method for manufacturing a ceramic porous body by gelling, freezing, thawing, drying, and sintering a slurry in which ceramic powder is dispersed in an aqueous solution of a gelatable water-soluble polymer is disclosed. Ru. According to Patent Document 1, gelation and freezing of a water-soluble polymer generates ice crystals in the water-soluble polymer gel, which are removed by drying to form pores. Further, Patent Document 1 discloses the use of starch as a water-soluble polymer, but the water-soluble polymer only temporarily fixes the structure of ceramic powder, etc., and functions as a pore source. do not. Furthermore, Patent Document 1 has a problem in that the size of ice crystals becomes coarse during gelation and freezing.

According to Patent Document 2, the problem of Patent Document 1 is solved by using an ice crystal coarsening inhibitor such as sodium ion, potassium ion, magnesium ion, calcium ion, hydroxide ion, carbonate ion, etc. A porous body with a controlled size of 10 μm to 300 μm is produced. However, there was a problem in that the ions added as an ice crystal coarsening inhibitor were not removed and remained in the porous body. Therefore, it is desirable to develop a method for producing a porous body that does not contain unnecessary ions and controls the pore diameter and the like.

Furthermore, an oxygen separation membrane is known that has a support layer made of porous ceramics made of a mixed oxide ion/electron conductor and an oxygen separation active layer thereon (see, for example, Patent Document 3). According to Patent Document 3, the support layer and the oxygen separation active layer have the general formula:
A _x A' _1-X B _y B' _1-y O _3-α
Disclose that it is expressed in . Here, in the formula, 0<x, y<0.5, α is a numerical value for maintaining electrical neutrality, and A is a group consisting of lanthanide elements, Ca, Sr, and Ba. A' is at least one element selected from the group consisting of lanthanide elements, Ca, Sr, and Ba, excluding the elements selected in A above. , B is at least one element selected from the group consisting of Ti, Zr, Ce, Nb, Ta, and Ga, and B' is at least one element selected from the group consisting of Fe, Co, Cr, and Y. At least one element selected from

However, even in this case, the continuity of the support layer was not sufficient, and further improvements were required.

JP2008-201636A Japanese Patent Application Publication No. 2011-038072 Japanese Patent Application Publication No. 2009-101310

In light of the above, an object of the present invention is to provide a porous ceramic sintered body made of an oxide ion/electronic mixed conductor with excellent connectivity, and applications using the same.

The porous ceramic sintered body according to the present invention includes lanthanum strontium manganese oxide (LSM), lanthanum strontium iron oxide (LSF), lanthanum strontium cobalt oxide (LSC), lanthanum strontium cobalt iron oxide (LSCF), samarium strontium Cobalt oxide (SSC), bismuth sternium oxide, barium strontium cobalt iron oxide (BSCF), lanthanum strontium gallium cobalt oxide, lanthanum strontium gallium iron oxide, lanthanum strontium gallium nickel oxide, calcium titanium iron oxide, Cerium praseodymium oxide, Gatrinium cerium praseodymium oxide, Yttrium stabilized bismuth-silver (BYS/Ag), Erbium stabilized bismuth-gold (ESB/Au), Bismuth calcium oxide, Bismuth yttrium copper oxide, Bismuth yttrium It is made of an oxide ion/electronic mixed conductor selected from the group consisting of samarium oxide and bismuth erbium oxide, has communicating pores, and has an open porosity that satisfies the range of 50% to 75%. and has a closed porosity that satisfies the range of 0.05% or more and 4.0% or less, has a relative density that satisfies the range of 23% or more and 50% or less, and satisfies the range of 0.5 μm or more and 20 μm or less. It has a pore size, thereby solving the above problem.
The oxide ionic/electronic mixed conductor may be barium strontium cobalt iron oxide (BSCF).
It may have an electrical conductivity of 1.5×10 ⁻³ S·cm ⁻¹ or more.
In the air electrode for a solid oxide fuel cell containing a mixed oxide ion and electron conductor according to the present invention, the mixed oxide ion and electron conductor is the above-mentioned porous ceramic sintered body. Solve the above issues.
An oxygen permeable membrane comprising a support according to the present invention and an oxygen separation active layer located on the support, wherein the support is made of the above-mentioned porous ceramic sintered body, and the oxygen separation active layer is made of the above-mentioned porous ceramic sintered body. It is made of the same oxide ion/electron mixed conductor as the oxide ion/electron mixed conductor constituting the porous ceramic sintered body, thereby solving the above problem.
The support may have a thickness in the range of 500 μm or more and 1500 μm or less.
The oxygen separation active layer may have a thickness of 10 μm or more and 500 μm or less.

The porous ceramic sintered body of the present invention is made of the above-mentioned oxide ion/electron mixed conductor, has communicating pores, has an open porosity that satisfies the range of 50% to 75%, and has an open porosity of 50% to 75%. It has a closed porosity that satisfies the range of 0.5% or more and 4.0% or less, a relative density that satisfies the range of 23% or more and 50% or less, and a pore diameter that satisfies the range of 0.5 μm or more and 20 μm or less. , excellent breathability and handling. Such a porous ceramic sintered body is made of a mixed oxide ion/electronic conductor and has excellent air permeability, so it is advantageous for the air electrode of a fuel cell. In addition, the porous ceramic sintered body of the present invention maintains strength while having high air permeability, so it functions as a support for forming an oxygen separation active layer thereon, and the porous ceramic sintered body has excellent strength as a whole. Can provide a permeable membrane.

The method of manufacturing porous ceramics made of an oxide ion/electronic mixed conductor and having communicating pores according to the present invention involves mixing ceramic particles, which are oxide ion/electronic mixed conductors, and starch with at least water. mixing in a dispersion medium containing the starch, heating the mixture at a temperature range of 50°C to 150°C to gelatinize the starch, and heating the gelatinized product at a temperature range of -5°C to 10°C. a step of aging the starch by holding it under a first condition satisfying a temperature range of −10° C. or lower; and a step of drying the aged product and removing the dispersion medium. , and firing the molded body. Through these steps, starch functions as a pore-forming agent, and by utilizing the gelatinization and aging phenomena of starch, it is possible to produce porous ceramics having communicating pores.

A diagram schematically showing a porous ceramic sintered body of the present invention Flowchart showing steps for manufacturing the porous ceramic sintered body of the present invention Diagram showing the procedure for manufacturing the porous ceramic sintered body of the present invention Schematic diagram showing an oxygen permeable membrane using the porous ceramic sintered body of the present invention A diagram showing SEM images of fractured surfaces of molded bodies of Examples 16, 19, 23, and 27. Diagrams showing SEM images of fractured surfaces of various examples of sintered bodies Diagrams showing SEM images of fractured surfaces of sintered bodies of various other examples A diagram showing a SEM image of a fracture surface of a sintered body in yet another example Diagram showing the relationship between water content in the dispersion medium, open porosity, and relative density Diagram showing the relationship between firing temperature and open porosity

Embodiments of the present invention will be described below with reference to the drawings. Note that similar elements are given similar numbers and their explanations will be omitted.

(Embodiment 1)
In Embodiment 1, a porous ceramic sintered body of the present invention and a method for manufacturing the same will be described.

FIG. 1 is a diagram schematically showing a porous ceramic sintered body of the present invention.

The porous ceramic sintered body 100 of the present invention is composed of an oxide ion/electronic mixed conductor 110. The oxide ion/electronic mixed conductor 110 may be any mixed conductor, but perovskite type mixed conductors, fluorite type mixed conductors, cermet type mixed conductors, spinel type oxides, etc. are known. . Specifically, lanthanum strontium manganese oxide (LSM), lanthanum strontium iron oxide (LSF), lanthanum strontium cobalt oxide (LSC), lanthanum strontium cobalt iron oxide (LSCF), and samarium strontium cobalt oxide (SSC). , bismuth sternium oxide, barium strontium cobalt iron oxide (BSCF), lanthanum strontium gallium cobalt oxide, lanthanum strontium gallium iron oxide, lanthanum strontium gallium nickel oxide, calcium titanium iron oxide, cerium praseodymium oxide, trinium cerium praseodymium oxide, yttrium stabilized bismuth-silver (BYS/Ag), erbium stabilized bismuth-gold (ESB/Au), bismuth calcium oxide, bismuth yttrium copper oxide, bismuth yttrium samarium oxide, and selected from the group consisting of bismuth erbium oxide; These materials are known as oxide ion/electronic mixed conductors, and are easily available as raw materials for producing the porous ceramic sintered body of the present invention. Although it is selected depending on the intended use, for example, when the porous ceramic sintered body of the present invention is used for an oxygen permeable membrane or an air electrode of a fuel cell, BSCF having excellent oxygen permeability is preferable. Among these, Ba _0.5 Sr _0.5 Co _0.8 Fe _0.2 O _3-δ (δ is a numerical value indicating electrical neutrality, 0.2<δ<0.6) is preferable.

The porous ceramic sintered body 100 of the present invention has communicating pores 120 (also referred to as a pore communication structure). By having the pore communication structure 120, air permeability can be improved. The pore communication structure 120 is confirmed by microscopic observation using a scanning electron microscope or the like. For example, the pore communication structure 120 is observed as pores penetrating the porous ceramic or pores formed by spherical pores connected to each other in a beaded manner.

The porous ceramic sintered body 100 of the present invention has the above-mentioned pore communication structure 120, but also has an open porosity (when the external volume of the sintered body is 1) that satisfies the range of 19% to 81%. (percentage of the volume of open pores in this). By controlling the conditions in the manufacturing method described below, a porous ceramic sintered body having a desired open porosity can be provided. The open porosity is measured by the Archimedes method, gravimetric porosity method, mercury porosity method, or the like.

The porous ceramic sintered body 100 of the present invention has a relative density in the range of 19% to 80%. If the relative density is within this range, the porous ceramic sintered body will not become brittle and break, making it easy to handle. The relative density is calculated from the ratio between the density of the sintered body measured by the Archimedes method and the theoretical density.

The porous ceramic sintered body 100 of the present invention has the above-mentioned pore communication structure 120, but the pore diameter 130 satisfies the range of 0.5 μm or more and 100 μm or less. Here, the pore diameter 130 in this specification is intended to be the length of the communicating pores 120 in the transverse direction, and the pore diameter distribution may be obtained from an adsorption/desorption isotherm, but it is simply observed by microscopic observation. The diameters of about 100 pores may be calculated from the images obtained by the method and averaged. Having a pore diameter within this range provides excellent air permeability.

Since the porous ceramic sintered body 100 of the present invention is obtained by the manufacturing method described below, ice crystals of sodium ions, potassium ions, magnesium ions, calcium ions, hydroxide ions, carbonate ions, etc. described in Patent Document 2 are used. The above-mentioned pore diameter 130 can be controlled without using a coarsening inhibitor. As a result, a porous ceramic sintered body containing no unnecessary ions can be provided, and the original characteristics of the oxide ion/electronic mixed conductor 110 can be exhibited.

The porous ceramic sintered body 100 of the present invention preferably has an open porosity that satisfies the range of 50% or more and 75% or less, a relative density that satisfies the range of 23% or more and 50% or less, and has a relative density that satisfies the range of 23% or more and 50% or less. It has a pore diameter that satisfies the range of 5 μm or more and 20 μm or less. This allows for better air permeability and better handling.

The porous ceramic sintered body 100 of the present invention preferably has a closed porosity that satisfies the range of 0.05% to 4.0%. This ensures the pore communication structure, resulting in particularly excellent air permeability. The closed porosity is measured by Archimedes method, X-ray CT method, etc.

In particular, the porous ceramic sintered body 100 of the present invention is made of an oxide ion/electronic mixed conductor, which is BSCF, and satisfies the above-mentioned open porosity, relative density, and particle size of 1.5×10 ⁻ It has an electrical conductivity of ³ S·cm ⁻¹ or more. That is, the porous ceramic sintered body 100 of the present invention achieves high electrical conductivity because the ceramics are maintained in contact with each other by employing the manufacturing method described below.

Next, a method for manufacturing the above-described porous ceramic sintered body 100 of the present invention will be explained with reference to FIGS. 2 and 3. The inventors of the present application focused on using starch as a pore-forming agent, and in particular, succeeded in forming a pore-communicating structure by utilizing the gelatinization and aging phenomena of starch. Explain in detail.

FIG. 2 is a flowchart showing steps for manufacturing the porous ceramic sintered body of the present invention.
FIG. 3 is a diagram showing a procedure for manufacturing the porous ceramic sintered body of the present invention.

S210: Ceramic particles 310, which are oxide ion/electronic mixed conductors, and starch 320 are mixed in a dispersion medium 330 containing at least water. Here, the ceramic particles 310 are the oxide ion/electronic mixed conductor described above with reference to FIG. Starch 320 is a carbohydrate represented by (C ₆ H ₁₀ O ₅ ) _n (n is a natural number of 10 or more) and is composed of amylose and amylopectin. ) Contains a lot. This makes it possible to provide a highly viscous slurry during gelatinization, which will be described later, and makes it easier to control aging. Starch 320 containing any ratio of amylose and amylopectin can be used, but among them, one that satisfies amylose:amylopectin = 5:95 to 40:60 is preferable because it promotes the gelatinization and aging phenomenon described below. . More preferably, one that satisfies amylose:amylopectin=15:85 to 25:75 is employed. Specifically, rice starch, corn, wheat, etc. can be used as the starch 320.

Note that a binder may be added in order to maintain the molded body described later. Such a binder is preferably an organic binder that is burned out during sintering, which will be described later, and examples thereof include polyvinyl alcohol (PVA), methylcellulose, and acrylic resin. Such an organic binder is effective in binding the ceramic particles 310 if mixed in an amount of 0.1 part by weight or more and 0.3 parts by weight or less with respect to 100 parts by weight of the ceramic particles 310 . Further, the organic binder may be used after being dissolved in a dispersion medium.

Further, if the size of the ceramic particles 310 and the starch 320 is set to be smaller than that of the starch 320, the starch 320 will be surrounded by the ceramic particles 310 due to electrostatic interaction, and the ceramic particles 310 will be surrounded by the ceramic particles 310. and starch 320 are in a mutually dispersed state (state 340 in FIG. 3). More preferably, the ceramic particles 310 have a particle size in the range of 0.3 μm or more and 1 μm or less, and the starch 320 has a particle size in the range of greater than 1 μm and 50 μm or less. This promotes good dispersion of the ceramic particles 310 and starch 320 without agglomerating each other.

The water contained in the dispersion medium 330 is distilled water, ion-exchanged water, ultrapure water, or the like. The dispersion medium 330 may be water alone, or may contain alcohol in addition to water. It is preferable that the dispersion medium 330 contains not only water but also alcohol in order to suppress the gelatinization phenomenon and control the structure and open porosity. Alcohols include, but are not particularly limited to, methanol, ethanol, 2-propanol, t-butyl alcohol, and the like. When the dispersion medium 330 contains alcohol in addition to water, the open porosity and relative density of the resulting porous ceramic sintered body can be controlled simply by controlling the water content.

When the dispersion medium 330 contains alcohol and water, the alcohol and water are preferably mixed so that alcohol:water=0:100 to 70:30 in mass% (here, 0 :100 means that the dispersion medium 330 is not water alone, but contains a very small amount of alcohol). If the water content is less than 30% by mass, gelatinization and aging phenomena will not be sufficiently promoted, and the molded product before sintering will not be maintained. More preferably, alcohol and water are mixed so that alcohol:water=5:95 to 60:40 in terms of mass %. Within this range, a porous ceramic sintered body having strength while maintaining a high open porosity can be obtained. More preferably, alcohol and water are mixed so that alcohol:water=20:80 to 40:60 in terms of mass %.

Furthermore, in step S210, ceramic particles 310 and starch 320 are mixed so that 20 parts by weight or more and starch 320 in a range of 75 parts by weight or less is filled with respect to 100 parts by weight of ceramic particles 310. When the amount of starch 320 is less than 20 parts by weight, oxygen permeability may not be expected because a pore communication structure is not sufficiently formed. If the amount of starch 320 exceeds 75 parts by weight, the amount of pore-forming agent will be too large, and the molded product before sintering may not be maintained. More preferably, the ceramic particles 310 and the starch 320 are mixed so that 30 parts by weight or more and 70 parts by weight or less of the starch 320 are contained per 100 parts by weight of the ceramic particles 310 . Within this range, a porous ceramic sintered body having the above-mentioned open porosity and relative density can be obtained. More preferably, the ceramic particles 310 and the starch 320 are mixed so that the proportion of the starch 320 is 30 parts by weight or more and 35 parts by weight or less per 100 parts by weight of the ceramic particles 310 . This results in a porous ceramic sintered body 310 containing more ceramic particles 310, so that the reaction field can be particularly increased.

Further, in step S210, ceramic particles 310 and starch 320 are mixed such that the concentration of ceramic particles 310 and starch 320 in dispersion medium 330 satisfies 0.2 g/mL or more and 0.6 g/mL or less. Within this range, the ceramic particles 310 and starch 320 are dispersed in the dispersion medium 330, so that the gelatinization phenomenon described below can be promoted. More preferably, the concentration of ceramic particles 310 and starch 320 satisfies 0.3 g/mL or more and 0.5 g/mL or less. Within this range, the gelatinization phenomenon is ensured.

Step S220: The mixture 340 obtained in step S210 is heated in a temperature range of 50° C. or higher and 150° C. or lower to gelatinize the starch 320. FIG. 3 shows gelatinized starch 350. If the temperature is lower than 50°C, the gelatinization phenomenon of starch 320 may not proceed. If the temperature exceeds 150° C., the gelatinization phenomenon of starch 320 proceeds rapidly, and a good pore communication structure may not be obtained.

Preferably, the mixture 340 may be heated while stirring at a temperature range of 100° C. to 130° C. for 30 minutes to 2 hours. As a result, the gelatinization phenomenon of the starch 320 progresses uniformly throughout, resulting in a pore communication structure whose shape is controlled. Note that the progress of the gelatinization phenomenon can be determined by visually confirming that the product has viscosity. The product thus obtained is called a gelatinized product 360.

Stirring may be performed manually or using a stirrer using a magnetic stirrer or the like. Stirring is preferably performed at a rotation speed of 700 rpm to 1200 rpm. As a result, the gelatinized starch is uniformly located in the gelatinized body 360, so that uniform pores can be formed.

Step S230: The gelatinized body 360 obtained in step S220 is held under a first condition that satisfies a temperature range of -5°C or higher and 10°C or lower, and then a second condition that satisfies a temperature range of -10°C or lower. to age the starch 350. By holding under the first condition, water is dehydrated from the starch. By holding the starch under the second conditions, the starch aging phenomenon progresses, resulting in recrystallized starch 370. The water 380 dehydrated from the starch is frozen. The product thus obtained is called aged body 390.

In step S230, the first condition is preferably to hold the gelatinized body 360 at a temperature range of -2° C. or higher and 5° C. or lower for a period of 30 minutes or more and 2.5 hours or less. Within this range, dehydration of water from starch may be accelerated and aging phenomena may be induced.

In step S230, the second condition is preferably that the gelatinized body 360 is maintained at a temperature of -200°C or more and -100°C or less for a period of 5 seconds or more and 10 seconds or less, or at a temperature higher than -100°C. Maintain at a temperature range of -15°C or lower for 1 hour or more and 24 hours or less. Under these conditions, the dehydrated water is frozen and the aged body 390 is reliably obtained. The former condition can be carried out using liquid nitrogen or the like, but in addition to water, alcohol can also be frozen as a dispersion medium.

Step S240: The aged body 390 obtained in step S230 is dried and the dispersion medium is removed. Here, the frozen dispersion medium (water or both water and alcohol) is removed by drying, and a molded body 391 consisting of recrystallized starch 370 and ceramic particles 310 is obtained.

Drying may be performed by either atmospheric pressure drying or vacuum freeze drying. In the case of atmospheric pressure drying, drying may be performed at room temperature, but since it takes a long time, it is preferably carried out at a temperature range of 40° C. or higher and 100° C. or lower. If the temperature exceeds 100° C., the dispersion medium will be rapidly removed, so there is a possibility that the molded body 391 will collapse. More preferably, drying may be carried out at a temperature range of 40° C. or higher and 60° C. or lower for a period of 1 hour or more and 3 hours or less. Within this range, a molded body 391 with suppressed cracks and warpage can be obtained.

The vacuum freeze-drying may preferably be carried out at a pressure of 1×10 ⁻³ atm or less for a period of more than 24 hours and less than 72 hours. If the time is less than 24 hours, the dispersion medium may not be sufficiently removed. If vacuum freeze-drying is performed, the frozen dispersion medium also functions as a pore-forming agent, so an increase in open porosity can be expected. Note that the lower limit is not particularly limited, but there is no problem as long as it is 1×10 ⁻⁶ atm or more.

In step S240, drying is preferably performed until the molded body 391 has an open porosity in the range of 40% to 90%. As a result, it is possible to obtain a sintered body that is hard and fixed by subsequent firing without causing the molded body 391 to break.

Step S250: The molded body 391 obtained in step S240 is fired. As a result, the recrystallized starch 370 is removed, communicating pores (pore communication structure) 392 are formed, and the porous ceramic sintered body 100 of the present invention is obtained. The firing conditions are not particularly limited as long as the temperature is higher than the burnout temperature of starch and the ceramic particles 310 are fixed and form a neck, but for example, firing is performed at a temperature of 800°C or higher and 1500°C or lower for 2 hours. This will be carried out for a period of at least 24 hours. The firing atmosphere depends on the type of ceramic particles, but in the case of oxides, it may be in the air.

Note that starch may be dried and removed prior to baking. That is, by controlling the temperature profile up to the calcination temperature, starch can be dried and removed, and finally sintered. For example, the starch in the molded product can be dried by holding the molded product at a temperature of 150° C. to 450° C. for 1 to 6 hours. Next, the starch can be removed from the molded body by holding it at 450°C to 600°C for 30 minutes to 3 hours. Further, starch may be dried in two stages: holding at 150° C. to 250° C. for 1 hour to 3 hours and holding at 250° C. to 450° C. for 1 hour to 3 hours. Thereby, the starch can be reliably dried while maintaining the molded body.

(Embodiment 2)
In Embodiment 2, applications using the porous ceramic sintered body of the present invention will be described.
FIG. 4 is a schematic diagram showing an oxygen permeable membrane using the porous ceramic sintered body of the present invention.

The oxygen permeable membrane 400 of the present invention includes a support 410 and an oxygen separation active layer 420 located on the support 410. Here, since the support body 410 is made of the porous ceramic sintered body 100 (FIG. 1) of the present invention, it has sufficient mechanical strength, and when it functions as an oxygen permeable membrane, the oxygen partial pressure difference However, the oxygen separation active layer 420 located thereon will not be destroyed. Further, since the porous ceramic sintered body 100 of the present invention has a high open porosity, a sufficient reaction field can be secured, and the surface exchange reaction is promoted at the interface with the oxygen separation active layer 420. Oxygen separation ability can be achieved.

Furthermore, since the oxygen separation active layer 420 is made of the same material as the porous ceramic sintered body 100 of the present invention, that is, the same oxide ion/electron mixed conductor, there is a gap between the support 410 and the oxygen separation active layer 420. No interfacial reaction phase is formed.

Illustratively, the thickness of the support 410 in the oxygen permeation direction is in the range of 500 μm or more and 1500 μm or less, and the thickness of the oxygen separation active layer 420 is in the range of 10 μm or more and 500 μm or less. Note that such an oxygen separation active layer 420 can be formed using existing methods such as a physical vapor deposition method, a chemical vapor deposition method, a sol-gel method, an alternate layer deposition method, and an electrophoretic deposition (EPD) method using the support body 410 as a substrate. Manufactured by the method.

The operation of the oxygen permeable membrane 400 will be explained. When the oxygen-containing air that has passed through the pore communication structure 120 in the porous ceramic sintered body 100 that constitutes the support body 410 reaches the oxygen separation active layer 420, the oxygen receives electrons and becomes O ₂ +4e ⁻ →2O. By the reaction ^2- , it becomes an oxide ion. The generated oxide ions diffuse through the oxygen separation active layer 420, combine with each other on the opposite surface of the layer 420, and become oxygen through the reaction O ^2- + O ^2- → O ₂ + ^4e- , and the oxygen content is reduced. It is released to the side of the oxygen separation active layer 420 facing the support 410 where the pressure is low. In this way pure oxygen can be separated from air. In the present invention, the support 410 is composed of the porous ceramic sintered body 100, and the oxygen separation active layer 420 made of the same material is located on the support 410, so that the oxygen separation active layer 420 has excellent adhesion. 420 can be prevented from being destroyed.

With reference to FIG. 4, an oxygen permeable membrane 400 has been described as an application of the porous ceramic sintered body 100 of the present invention, but the porous ceramic sintered body 100 of the present invention is used for solid oxide fuel cells. It can also be used for air electrodes, methane partial oxidation membrane reactors, and sensors.

Next, the present invention will be described in detail using specific examples, but it should be noted that the present invention is not limited to these examples.

[Preparation of raw materials]
Ba _0.5 Sr _0.5 Co _0.8 O _3-δ (BSCF, manufactured by Kusaka Rare Metal Research Institute Ltd., average particle size: 0.5 to 1 Rice starch (amylose: amylopectin = 20:80 (mass ratio), particle size: 2.0 to 8.0 μm, manufactured by Sigma-Aldrich) was used as the starch. Distilled water and ethanol were used as necessary as a dispersion medium. These were mixed to satisfy the compositions of Mixtures 1 to 7 shown in Table 1 (Step S210 in FIG. 2). As a binder, polyvinyl alcohol (PVA) (98% aqueous solution, manufactured by Sigma-Aldrich) was added in an amount of 0.2 parts by weight based on the BSCF (100 parts by weight) of Mixtures 1 to 7. The mixture was also dispersed using an ultrasonic homogenizer.

[Heating, refrigeration, freezing, drying]
The mixture was treated under various conditions shown in Table 2 to obtain molded bodies. Specifically, the mixture was heated according to conditions A and B in Table 2 to obtain a gelatinized body, which was cast and filled on a metal plate, and left to stand in a refrigerator to obtain an aged body ( Steps S220 to S230 in FIG. 2). Next, it was held in a freezer and subjected to atmospheric pressure drying using a drying oven and vacuum freeze drying (freeze drying) using a vacuum freeze dryer to obtain a molded product (step S240 in FIG. 2). Condition C in Table 2 was the same as Condition B, except that it was frozen in a liquid nitrogen environment and vacuum freeze-dried. Condition D in Table 2 involved only freezing and drying similar to Condition C, without refrigeration or freezing. Condition E means that no heating, refrigeration, freezing, or drying treatment is performed.

[Firing]
Next, the processed molded bodies were fired under various conditions shown in Table 3 to obtain sintered bodies (Step S250 in FIG. 2). Prior to calcination, starch was dried and removed. Specifically, to dry the starch, it was held at 200°C (temperature increase rate: 0.2°C/min) for 2 hours, and then to 350°C (heated rate: 0.25°C/min) to further dry the starch. ) for 2 hours, and then held at 500° C. (heating rate: 0.5° C./min) for 1 hour to burn off the starch. Note that the condition d means that no firing was performed.

[Examples 1 to 33]
Samples 1 to 33 of molded bodies or sintered bodies were produced according to the sample conditions in Table 4. The sample conditions in Table 4 will be explained. For example, the sample of Example 1 is shown to have been produced under sample condition 1-Aa. In detail, "1" represents composition 1 of the mixture in Table 1, "A" represents heating, refrigeration, freezing and drying conditions A in Table 2, and "a" represents baking conditions in Table 3. The sample of Example 1 is a sample obtained by a combination of these conditions.

The microstructures of the molded body and sintered body before firing were observed using a scanning electron microscope (SEM, JSM-6510 manufactured by JEOL). At this time, the operating voltage was 15.0 kV. The relative density and open porosity of the molded body and sintered body were measured using a simple specific gravity measuring device. At this time, kerosene (density: 0.789 g/cm ³ ) was used as a solvent. Note that the closed porosity was calculated by the Archimedes method. Further, the electrical conductivity of the sintered body was measured at room temperature by a direct current two terminal method. These results are shown in FIGS. 5 to 10 and Tables 5 to 6.

FIG. 5 is a diagram showing SEM images of the fractured surfaces of the molded bodies of Examples 16, 19, 23, and 27.

According to FIGS. 5(A) to 5(C), the starch used as the raw material no longer had a granular shape and was in an interconnected state. On the other hand, according to FIG. 5(D), the starch used as the raw material remained granular. From this, by heating starch under the conditions shown in Table 2, and then refrigerating and freezing it, the starch used as a raw material changes from a granular form to an interconnected form, and gelatinization and aging phenomena occur appropriately. It was shown that

FIG. 6 is a diagram showing SEM images of fractured surfaces of various examples of sintered bodies.
FIG. 7 is a diagram showing SEM images of fractured surfaces of various other examples of sintered bodies.
FIG. 8 is a diagram showing a SEM image of a fractured surface of a sintered body of still another example.

Table 5 summarizes the properties of the molded bodies or sintered bodies of Examples 1 to 33.

6 (A) to (H), in which starch was gelatinized and aged under the first and second conditions, as explained with reference to FIG. Comparing Figures 6 (I) to (K) in which starch was gelatinized and aged, the sintered bodies of Examples 13 to 15, 17, 18, and 20 to 22 are different from the sintered bodies of Examples 24 to 26. In comparison, it showed more communicating pores. Comparing each sintering temperature, the open porosity of the sintered bodies of Examples 13 to 15, 17, 18, and 20 to 22 is higher overall than that of the sintered bodies of Examples 24 to 26; It was shown that introducing the process of the following conditions is effective for the gelatinization and aging phenomena of starch.

Furthermore, when comparing FIGS. 6(A) to 6(C) and FIGS. 6(D) to (H) in terms of sintering temperature, the open porosity of the sintered bodies of Examples 13 to 15 is the same as that of Examples 17, 18, Compared to the sintered bodies No. 20 to 22, it was higher overall. This suggests that by performing vacuum freeze-drying when removing the dispersion medium in the molded body, the dispersion medium in addition to starch also functioned as a pore-forming agent.

Focusing on the pore diameter, as shown in Figures 6(A) to (C), if atmospheric pressure drying is performed, connected pores with a uniform and small pore diameter (0.5 μm to 1 μm) can be obtained. Do you get it. On the other hand, as shown in Figures 6(F) to (H), if vacuum freeze-drying is performed, the dispersion medium in addition to starch also functions as a pore-forming agent, resulting in uniform and relatively large pore diameters (1 μm to 1 μm). It was found that open pores with a diameter of 5 μm) were obtained.

7(A) to (C), the sintering temperature is the same (900° C.), but the content of ethanol in the dispersion medium is different. Similarly, in FIGS. 7(D) to (F), the sintering temperature is the same (1100° C.), but the content of ethanol in the dispersion medium is different. According to FIGS. 7(A) and (D), it was found that when the dispersion medium did not contain water, it did not have communicating pores. This indicates that when utilizing the gelatinization and aging phenomena of starch, the dispersion medium needs to contain at least water.

A comparison between FIGS. 7(E) and (F) shows that the open porosity tends to increase as the content of ethanol in the dispersion medium decreases. The same applies to FIGS. 7(B) and (C). This suggests that the open porosity can be controlled by adjusting the amounts of water and alcohol in the dispersion medium.

Comparing FIGS. 7(B) and 7(E) with FIGS. 8(A) to 8(B), the open porosity of Examples 31 to 32, in which the amount of starch to the ceramic particles was increased, is that of Examples 1 and 3. Compared to that, it showed a tendency to increase. This also indicates that pore-forming agents that utilize the gelatinization and aging phenomena of starch are effective. Furthermore, according to FIG. 8(C), the tendency was the same even when the dispersion medium was water alone.

FIG. 9 is a diagram showing the relationship between water content in the dispersion medium, open porosity, and relative density.

According to FIG. 9(A), as the water content in the dispersion medium increased, the open porosity increased. According to FIG. 9(B), as the water content in the dispersion medium increased, the relative density decreased. This also indicates that the open porosity and relative density can be controlled by adjusting the amounts of water and alcohol in the dispersion medium.

FIG. 10 is a diagram showing the relationship between firing temperature and open porosity.

As the firing temperature increased, the open porosity decreased, and as the water content in the dispersion medium increased, the open porosity tended to increase. This indicates that by appropriately selecting the firing temperature and the content of water in the dispersion medium, it is possible to provide a porous ceramic sintered body having an open porosity depending on the application.

Table 6 lists the electrical conductivity of the sintered bodies of Examples 22, 26 and 30. The electrical conductivity of the sintered body of Example 22 in which the starch was gelatinized and aged was higher than that of the sintered bodies of Examples 26 and 30 in which the starch was not gelatinized and aged. This suggests that the use of starch gelatinization and aging phenomena can not only generate connected pores but also promote contact between ceramic particles through sintering.

The porous ceramic sintered body according to the present invention has a high open porosity and is excellent in air permeability and handling, so it can be used as a support for an air electrode of a fuel cell or an oxygen permeable membrane. The manufacturing method of the present invention can provide a porous ceramic sintered body with controlled open porosity, relative density, and pore diameter by simply adjusting the dispersion medium, sintering temperature, etc. It can be advantageously used for air electrodes for physical fuel cells, methane partial oxidation membrane reactors, sensors, etc.

100 Porous ceramic sintered body 110 Oxide ion/electron mixed conductor 120, 392 Connecting pores (pore communication structure)
130 Pore diameter 310 Ceramic particles 320 Starch 330 Dispersion medium 350 Gelatinized starch 360 Gelatinized body 370 Recrystallized starch 380 Frozen water 390 Aged body 391 Molded body 400 Oxygen permeable membrane 410 Support body 420 Oxygen separation active layer

Claims (7)

Lanthanum strontium manganese oxide (LSM), lanthanum strontium iron oxide (LSF), lanthanum strontium cobalt oxide (LSC), lanthanum strontium cobalt iron oxide (LSCF), samarium strontium cobalt oxide (SSC), bismuthternium oxide barium strontium cobalt iron oxide (BSCF), lanthanum strontium gallium cobalt oxide, lanthanum strontium gallium iron oxide, lanthanum strontium gallium nickel oxide, calcium titanium iron oxide, cerium praseodymium oxide, gathrinium cerium praseodymium oxide from bismuth-stabilized bismuth-silver (BYS/Ag), erbium-stabilized bismuth-gold (ESB/Au), bismuth calcium oxide, bismuth yttrium copper oxide, bismuth yttrium samarium oxide, and bismuth erbium oxide. consisting of an oxide ion/electronic mixed conductor selected from the group consisting of
It has communicating pores,
It has an open porosity that satisfies the range of 50% or more and 75% or less,
It has a closed porosity that satisfies the range of 0.05% or more and 4.0% or less,
It has a relative density that satisfies the range of 23% or more and 50% or less,
A porous ceramic sintered body having a pore diameter in the range of 0.5 μm or more and 20 μm or less. The porous ceramic sintered body according to claim 1, wherein the oxide ion/electronic mixed conductor is barium strontium cobalt iron oxide (BSCF). The porous ceramic sintered body according to claim 2, having an electrical conductivity of 1.5×10 ⁻³ S·cm ⁻¹ or more. An air electrode for a solid oxide fuel cell containing an oxide ion/electronic mixed conductor,
An air electrode, wherein the oxide ion/electronic mixed conductor is a porous ceramic sintered body according to any one of claims 1 to 3. An oxygen permeable membrane comprising a support and an oxygen separation active layer located on the support,
The support body is made of the porous ceramic sintered body according to any one of claims 1 to 3,
The oxygen separation active layer is an oxygen permeable membrane made of the same oxide ion/electron mixed conductor as the oxide ion/electron mixed conductor constituting the porous ceramic sintered body. The oxygen permeable membrane according to claim 5, wherein the support has a thickness in a range of 500 μm or more and 1500 μm or less. The oxygen permeable membrane according to claim 5 or 6, wherein the oxygen separation active layer has a thickness in a range of 10 μm or more and 500 μm or less.