JP7184270B2 - Manufacturing method of porous ceramic sintered body - Google Patents

Description

The present invention relates to a method for producing a porous ceramic sintered body . In particular, the present invention relates to a method for producing a porous ceramic sintered body comprising an oxide ion/electron mixed conductor using starch as a pore-forming agent.

Porous materials are used for adsorbents, filters, catalyst carriers, reactors, heat insulators, sound deadeners, building materials and the like. Among such porous materials, methods for producing ceramic porous bodies (also referred to as porous ceramics) having continuous pores and high porosity are known (see, for example, Patent Documents 1 and 2).

Patent Document 1 discloses a method of producing 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 gellable water-soluble polymer. be. According to Patent Document 1, gelation and freezing of the water-soluble polymer produces ice crystals in the water-soluble polymer gel, which are removed by drying to form pores. In addition, 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 or the like, and functions as a pore source. do not do. Moreover, in Patent Document 1, there is a problem that the size of ice crystals becomes coarse during gelation and freezing.

According to Patent Document 2, by using an ice crystal coarsening inhibitor such as sodium ion, potassium ion, magnesium ion, calcium ion, hydroxide ion, carbonate ion, etc., the problem of Patent Document 1 is solved, and pores A porous body with a size controlled at 10 μm to 300 μm is produced. However, there is a problem that the ions added as an ice crystal coarsening inhibitor remain in the porous body without being removed. Therefore, it is desirable to develop a method for producing a porous body in which the pore size and the like are controlled without containing unnecessary ions.

Also known is an oxygen separation membrane comprising a support layer made of porous ceramics made of an oxide ion/electron mixed 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 are represented by the general formula,
A _x A' _1-X B _y B' _1-y O _3-α
Disclose that it is represented by Here, in the formula, 0 < x, y < 0.5, α is a numerical value for maintaining electrical neutrality, A is a lanthanoid element, Ca, Sr, and the group consisting of Ba and A' is at least one element selected from the group consisting of lanthanoid 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 from the group consisting of Fe, Co, Cr, and Y is at least one element selected from

However, even in this case, the continuity of the support layer is not sufficient, and further improvement has been desired.

Japanese Patent Application Laid-Open No. 2008-201636 JP 2011-038072 A JP 2009-101310 A

In view of the above, an object of the present invention is to provide a method for producing a porous ceramic sintered body comprising an oxide ion/electron mixed conductor with excellent connectivity. A further object of the present invention is to provide a method for producing a porous ceramic sintered body with controlled pore diameter and open porosity and excellent communication.

The porous ceramic sintered body according to the present invention is composed of an oxide ion/electron mixed conductor, has communicating pores, has an open porosity satisfying the range of 19% to 81%, and has an open porosity of 19% to 80%. % or less, and has a pore diameter that satisfies the range of 0.5 μm or more and 100 μm or less, thereby solving the above problems.
The oxide ion/electron mixed conductor includes 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), bismusternium 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, gatolinium 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 may be selected from the group consisting of samarium oxide and bismuth erbium oxide.
It has an open porosity that satisfies the range of 50% or more and 75% or less, has a relative density that satisfies the range of 23% or more and 50% or less, and has a pore diameter that satisfies the range of 0.5 μm or more and 20 μm or less. good.
It may have a closed porosity that satisfies the range of 0.05% or more and 4.0% or less.
The mixed oxide ion-electron conductor may be barium strontium cobalt iron oxide (BSCF) and have an electrical conductivity of 1.5×10 ⁻³ S·cm ⁻¹ or higher.
According to the present invention, there is provided a method for producing a porous ceramic comprising a mixed oxide ion/electron conductor and having communicating pores, comprising: adding at least water to ceramic particles of the oxide ion/electron mixed conductor; mixing in the containing dispersion medium; heating the mixture obtained in the mixing step in a temperature range of 50° C. or higher and 150° C. or lower to gelatinize the starch; The gelatinized product obtained in the step is held under a first condition that satisfies a temperature range of −5° C. or higher and 10° C. or lower, then held under a second condition that satisfies a temperature range of −10° C. or lower, and the starch is drying the aged body obtained in the aging step to remove the dispersion medium; and firing the molded body obtained in the removing step, whereby To solve the above problems.
In the mixing step, 20 parts by weight or more and 75 parts by weight or less of the starch may be mixed with 100 parts by weight of the ceramic particles in the dispersion medium.
In the mixing step, 30 parts by weight or more and 70 parts by weight or less of the starch may be mixed with 100 parts by weight of the ceramic particles in the dispersion medium.
In the mixing step, the concentration of the ceramic particles and the starch in the dispersion medium may be 0.2 g/mL or more and 0.6 g/mL or less.
In the mixing step, the concentration of the ceramic particles and the starch in the dispersion medium may be 0.3 g/mL or more and 0.5 g/mL or less.
In the mixing step, the dispersion medium may contain an alcohol, and the alcohol and the water may be mixed in a mass % ratio of 0:100 to 70:30.
In the mixing step, the starch may contain amylose and amylopectin, and the amylopectin may contain more mass % than the amylose.
The amylose and the amylopectin may satisfy amylose:amylopectin=5:95 to 40:60 in mass %.
The amylose and the amylopectin may satisfy amylose:amylopectin=15:85 to 25:75 in mass %.
In the mixing step, the ceramic particles may have a particle size ranging from 0.3 μm to 1 μm, and the starch may have a particle size ranging from 1 μm to 50 μm.
In the gelatinization step, the mixture may be heated in a temperature range of 100° C. or higher and 130° C. or lower for a period of 30 minutes or longer and 2 hours or shorter while being stirred.
In the aging step, the first condition may be that the gelatinized product is held in a temperature range of −2° C. or higher and 5° C. or lower for 30 minutes or longer and 2.5 hours or shorter.
In the aging step, the second condition is that the gelatinized product is held in a temperature range of -200°C or higher and -100°C or lower for 5 seconds or longer and 10 seconds or shorter, or higher than -100°C. A temperature range of −15° C. or lower may be maintained for 1 hour or more and 24 hours or less.
The step of removing the dispersion medium may be performed by atmospheric pressure drying or vacuum freeze drying.
In the atmospheric pressure drying, the aged body may be dried in a temperature range of 40° C. or higher and 60° C. or lower for 1 hour or longer and 3 hours or shorter.
The vacuum freeze-drying may dry the aged body at a pressure of 1×10 ⁻³ atm or less for a time of greater than 24 hours and less than or equal to 72 hours.
The step of removing the dispersion medium may be performed until a molded article having an open porosity in the range of 40% to 90% is obtained from the aged article.
An air electrode for a solid oxide fuel cell containing an oxide ion/electron mixed conductor according to the present invention, wherein the oxide ion/electron mixed conductor is the porous ceramic sintered body described above, To solve the above problems.
According to the present invention, there is provided an oxygen permeable membrane comprising a support and an oxygen separation active layer positioned on the support, wherein the support comprises the porous ceramic sintered body described above, and the oxygen separation active layer comprises the above It consists 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 problems.

The porous ceramic sintered body of the present invention comprises an oxide ion/electron mixed conductor, has communicating pores, has an open porosity satisfying the range of 19% to 81%, and has an open porosity of 19% to 80%. % or less and has a pore diameter in the range of 0.5 μm or more and 100 μm or less. Such a porous ceramic sintered body is made of a mixed oxide ion/electron conductor and is excellent in air permeability, so it is advantageous for the air electrode of a fuel cell. In addition, since the porous ceramic sintered body of the present invention has high air permeability and maintains strength, it functions as a support for forming an oxygen separation active layer thereon, and as a whole has excellent strength. A permeable membrane can be provided.

The method for producing a porous ceramic comprising an oxide ion/electron mixed conductor and having communicating pores according to the present invention comprises mixing particles of a ceramic that is an oxide ion/electron mixed conductor, starch, and at least water. a step of mixing in the containing dispersion medium, a step of heating the mixture in a temperature range of 50° C. or higher and 150° C. or lower to gelatinize the starch, and a step of gelatinizing the gelatinized product in a temperature range of −5° C. or higher and 10° C. or lower. and then holding at a second condition satisfying a temperature range of −10° C. or less to retrograde the starch; , and firing the compact. Through these steps, the starch functions as a pore-forming agent, and the gelatinization and aging phenomena of starch can be used to produce porous ceramics with interconnected pores.

FIG. 1 is a diagram schematically showing the porous ceramic sintered body of the present invention; Flowchart showing steps for manufacturing the porous ceramic sintered body of the present invention A 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. SEM images of fracture surfaces of molded articles of Examples 16, 19, 23 and 27 Figures showing SEM images of fracture surfaces of sintered bodies of various examples Figures showing SEM images of fracture surfaces of sintered bodies of various other examples A diagram showing a SEM image of a fracture surface of a sintered body of yet another example Diagram showing the relationship between water content in dispersion medium and open porosity and relative density Diagram showing the relationship between firing temperature and open porosity

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, embodiments of the present invention will be described with reference to the drawings. In addition, the same number is given to the same element, and the description is omitted.

(Embodiment 1)
Embodiment 1 describes a porous ceramic sintered body and a method for producing the same according to the present invention.

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

The porous ceramic sintered body 100 of the present invention comprises an oxide ion/electron mixed conductor 110 . The oxide ion-electron mixed conductor 110 may be any mixed conductor, but perovskite mixed conductors, fluorite mixed conductors, cermet mixed conductors, spinel 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), 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, gallium 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/electron mixed conductors and are readily available as raw materials for producing the porous ceramic sintered body of the present invention. Although it is selected depending on the application, for example, when the porous ceramic sintered body of the present invention is used as an oxygen permeable membrane or an air electrode of a fuel cell, BSCF having excellent oxygen permeability is preferable. Among them, Ba _0.5 Sr _0.5 Co _0.8 Fe _0.2 O _3-δ (δ is a numerical value indicating electrical neutrality, and 0.2<δ<0.6) is preferable.

The porous ceramic sintered body 100 of the present invention has communicating pores 120 (also called a communicating pore structure). By having the pore communicating structure 120, breathability can be improved. The continuous pore structure 120 is confirmed by microscopic observation using a scanning electron microscope or the like. For example, the continuous pore structure 120 is observed as pores penetrating the inside of the porous ceramics or pores formed by connecting spherical pores to each other in a beaded pattern.

The porous ceramic sintered body 100 of the present invention has the above-described pore communicating structure 120, and furthermore, the open porosity satisfying the range of 19% or more and 81% or less (when the external volume of the sintered body is 1) The percentage of the volume of the open pore portion occupied therein). A porous ceramic sintered body having a desired open porosity can be provided by controlling the conditions in the manufacturing method described below. The open porosity is measured by the Archimedes method, the gravimetric porosity method, the mercury porosity method, or the like.

The porous ceramic sintered body 100 of the present invention has a relative density within the range of 19% or more and 80% or less. If the relative density is within this range, the porous ceramic sintered body will not be brittle and break, and will be excellent in handling. The relative density is calculated from the ratio of 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-described continuous pore structure 120, and 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 means the length of the communicating pores 120 in the lateral direction, and the pore diameter distribution may be obtained from the adsorption/desorption isotherm. Approximately 100 pore sizes may be calculated from the image obtained by and averaged. If the pore diameter is within this range, the air permeability is excellent.

Since the porous ceramic sintered body 100 of the present invention is obtained by the manufacturing method described later, ice crystals such as sodium ions, potassium ions, magnesium ions, calcium ions, hydroxide ions, carbonate ions, etc. described in Patent Document 2 The pore size 130 described above can be controlled without the use of coarsening inhibitors. As a result, it is possible to provide a porous ceramic sintered body that does not contain unnecessary ions, and to exhibit the inherent properties of the oxide ion/electron mixed conductor 110 .

The porous ceramic sintered body 100 of the present invention preferably has an open porosity satisfying the range of 50% or more and 75% or less, and has a relative density satisfying the range of 23% or more and 50% or less. It has a pore size that satisfies the range of 5 μm or more and 20 μm or less. This makes it more breathable and easier to handle.

The porous ceramic sintered body 100 of the present invention preferably has a closed porosity satisfying the range of 0.05% or more and 4.0% or less. As a result, the pore-communicating structure is ensured, and the air permeability is particularly excellent. The closed porosity is measured by the Archimedes method, the X-ray CT method, or the like.

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

Next, a method for manufacturing the above-described porous ceramic sintered body 100 of the present invention will be described with reference to FIGS. 2 and 3. FIG. The inventors focused on the use of starch as a pore-forming agent, and in particular, succeeded in forming an open pore structure by utilizing the gelatinization/aging phenomenon of starch. I will explain in detail.

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

S210: Ceramic particles 310, which are oxide ion/electron 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/electron mixed conductor described above with reference to FIG. Starch 320 is a carbohydrate represented by (C ₆ H ₁₀ O ₅ ) _n (where 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 in the later-described gelatinization, making it easier to control aging. As the starch 320, those containing amylose and amylopectin in any ratio can be employed, but among them, those satisfying amylose:amylopectin=5:95 to 40:60 are preferable because they promote the gelatinization/aging phenomenon described later. . More preferably, one satisfying amylose:amylopectin=15:85 to 25:75 is adopted. Specifically, rice starch, corn, wheat, or the like can be used as the starch 320 .

In addition, a binder may be added in order to maintain the molded body to be described later. Such a binder is preferably an organic binder that burns off during sintering, which will be described later, and examples thereof include polyvinyl alcohol (PVA), methyl cellulose, acrylic resin, and the like. Such an organic binder is effective for binding the ceramic particles 310 when mixed in the range of 0.1 to 0.3 parts by weight with respect to 100 parts by weight of the ceramic particles 310 . Also, the organic binder may be used by dissolving it in a dispersion medium.

In addition, if the ceramic particles 310 and the starch 320 are set so that the size of the ceramic particles 310 is smaller than that of the starch 320, the starch 320 is surrounded by the ceramic particles 310 due to electrostatic interaction, and the ceramic particles 310 and starch 320 become dispersed with each other (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 more than 1 μm and 50 μm or less. This promotes good dispersion without the ceramic particles 310 and the starch 320 aggregating.

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. Dispersion medium 330 preferably contains alcohol instead of water alone in order to suppress the gelatinization phenomenon and control the texture and open porosity. Alcohols include, but are not 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 obtained porous ceramic sintered body can be controlled only by controlling the content of water.

When the dispersion medium 330 contains alcohol and water, the alcohol and water are preferably mixed in mass % so as to satisfy alcohol:water = 0:100 to 70:30 (here, 0 :100 implies 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, the gelatinization/aging phenomenon is not sufficiently accelerated, and the compact before sintering cannot be maintained. More preferably, alcohol and water are mixed so as to satisfy an alcohol:water ratio of 5:95 to 60:40 by mass. Within this range, a porous ceramic sintered body having strength can be obtained while maintaining a high open porosity. More preferably, the alcohol and water are mixed so as to satisfy an alcohol:water ratio of 20:80 to 40:60 by mass.

Furthermore, in step S210, the ceramic particles 310 and the starch 320 are mixed so that the starch 320 in the range of 20 parts by weight to 75 parts by weight is filled with 100 parts by weight of the ceramic particles 310 . If the amount of starch 320 is less than 20 parts by weight, the oxygen permeability may not be expected because the open pore structure is not sufficiently formed. If the starch 320 exceeds 75 parts by weight, the amount of the pore-forming agent is too large, and the compact 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 is added to 100 parts by weight of the ceramic particles 310 . Within this range, a porous ceramic sintered body having the above-described open porosity and relative density can be obtained. More preferably, the ceramic particles 310 and the starch 320 are mixed so that 30 parts by weight or more and 35 parts by weight or less of the starch 320 is added to 100 parts by weight of the ceramic particles 310 . As a result, the porous ceramic sintered body 310 containing more ceramic particles 310 is obtained, so that the reaction field can be particularly increased.

Furthermore, in step S210, ceramic particles 310 and starch 320 are mixed so that the concentration of ceramic particles 310 and starch 320 in dispersion medium 330 is 0.2 g/mL or more and 0.6 g/mL or less. Within this range, the ceramic particles 310 and the starch 320 are dispersed in the dispersion medium 330, so that the gelatinization phenomenon, which will be described later, can be promoted. More preferably, the concentrations of ceramic particles 310 and starch 320 satisfy 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 . A gelatinized starch 350 is shown in FIG. If the temperature is less than 50°C, gelatinization of the starch 320 may not progress. If the temperature exceeds 150° C., gelatinization of the starch 320 proceeds rapidly, and a good open pore structure may not be obtained.

Preferably, the mixture 340 is heated in the temperature range of 100° C. to 130° C. for 30 minutes to 2 hours while being stirred. As a result, the gelatinization phenomenon of the starch 320 progresses uniformly throughout, resulting in a pore-communicating structure whose shape is controlled. It should be noted that the progress of the gelatinization phenomenon can be confirmed by visually confirming the presence of viscosity. The product thus obtained is called gelatinized body 360 .

Stirring may be performed manually, or a stirrer using a magnetic stirrer or the like may be used. Stirring is preferably performed at a rotation speed of 700 rpm to 1200 rpm. As a result, uniformly gelatinized starch is positioned 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 held under a second condition that satisfies a temperature range of −10° C. or lower. to retrograde the starch 350. Holding at the first condition dehydrates the water from the starch. Holding at the second condition accelerates starch retrogradation and results in recrystallized starch 370 . The water 380 dehydrated from the starch freezes. The product thus obtained is called aged body 390 .

In step S230, the first condition is preferably to keep the gelatinized product 360 in the temperature range of −2° C. or higher and 5° C. or lower for 30 minutes or longer and 2.5 hours or shorter. Within this range, the dehydration of water from the starch can be accelerated and aging can be induced.

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

Step S240: Dry the aged body 390 obtained in step S230 to remove the dispersion medium. Here, drying removes the frozen dispersion medium (water or both water and alcohol) to obtain a compact 391 composed of recrystallized starch 370 and ceramic particles 310 .

Drying may be carried out by either atmospheric pressure drying or vacuum freeze-drying. In the case of atmospheric pressure drying, the drying may be carried out at room temperature, but since it takes a long time, it is preferably carried out at a temperature in the range of 40°C or higher and 100°C or lower. If the temperature exceeds 100° C., the dispersion medium is abruptly removed, and the compact 391 may collapse. More preferably, drying may be performed at a temperature in the range of 40° C. or higher and 60° C. or lower for 1 hour or longer and 3 hours or shorter. Within this range, a compact 391 in which cracks and warpage are suppressed can be obtained.

Vacuum freeze-drying preferably involves drying at a pressure of 1×10 ⁻³ atm or less for a time of greater than 24 hours and less than or equal to 72 hours. The dispersion medium may not be sufficiently removed within 24 hours. 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. Although the lower limit is not particularly limited, there is no problem if it is 1×10 ⁻⁶ atm or more.

In step S240, drying is preferably performed until the compact 391 has an open porosity in the range of 40% to 90%. As a result, a sintered body that is firmly adhered can be obtained by subsequent firing without breaking the molded body 391 .

Step S250: The compact 391 obtained in step S240 is fired. As a result, the recrystallized starch 370 is removed and interconnected pores (continuous pore structure) 392 are formed to obtain the porous ceramic sintered body 100 of the present invention. The firing conditions are not particularly limited as long as the firing temperature is equal to or higher than the burn-out temperature of starch and the temperature allows the ceramic particles 310 to adhere and form a neck. More than 24 hours or less. The firing atmosphere depends on the type of ceramic particles, but if it is an oxide, it may be in the air.

In addition, drying and removal of starch may be performed prior to baking. That is, by controlling the temperature profile up to the firing temperature, the starch can be dried, removed, and finally sintered. For example, the starch in the molded article can be dried by holding the molded article at a temperature of 150° C. to 450° C. for 1 hour to 6 hours. The starch can then be removed from the compact by holding at 450° C. to 600° C. for 30 minutes to 3 hours. The drying of the starch may also be carried out in two steps, 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. As a result, the starch can be reliably dried while maintaining the compact.

(Embodiment 2)
Embodiment 2 describes applications using the porous ceramic sintered body of the present invention.
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 comprises a support 410 and an oxygen separation active layer 420 located on the support 410 . Here, since the support 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 The oxygen separation active layer 420 located thereon will not be destroyed even by the . In addition, 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 capacity can be achieved.

In addition, 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, no interfacial reaction phase is generated.

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

The operation of the oxygen permeable membrane 400 will be described. When air containing oxygen passes through the pore communication structure 120 in the porous ceramic sintered body 100 constituting the support 410 and reaches the oxygen separation active layer 420, the oxygen receives electrons, and O ₂ +4e ⁻ →2O The reaction of ^2- results in an oxide ion. The generated oxide ions diffuse in the oxygen separation active layer 420, bond with each other on the opposite surface of the layer 420, and become oxygen by the reaction of O ²⁻ +O ²⁻ →O ₂ +4e ⁻ to form oxygen content. The oxygen is released to the side of the oxygen separation active layer 420 with a lower pressure facing the support 410 . Pure oxygen can be separated from air in this way. 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 as the support 410 is positioned on the support 410. 420 can be suppressed from being destroyed.

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

The present invention will now 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 Laboratory Co., Ltd., average particle size: 0.5 to 1 .0 μm), and rice starch (amylose:amylopectin=20:80 (mass ratio), particle size: 2.0-8.0 μm, manufactured by Sigma-Aldrich) was used as starch. Distilled water and, if necessary, ethanol were used as a dispersion medium. These were mixed so as 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 so as to be 0.2 parts by weight with respect to BSCF (100 parts by weight) of mixtures 1-7. Moreover, the mixture was dispersed with 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 the 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). Then, it was held in a freezer and dried at atmospheric pressure using a drying oven and vacuum freeze-dried using a vacuum freeze dryer to obtain a compact (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. In condition D of Table 2, only freezing and drying as in condition C were performed without refrigeration or freezing. Condition E means that neither heating, refrigeration, freezing nor drying is performed.

[Firing]
Next, the molded body after the treatment was fired under various conditions shown in Table 3 to obtain a sintered body (step S250 in FIG. 2). Drying and removal of starch was performed prior to calcination. Specifically, the starch was held at 200°C (heating rate: 0.2°C/min) for 2 hours, and the starch was further dried at 350°C (heating rate: 0.25°C/min). ) for 2 hours and then at 500° C. (heating rate: 0.5° C./min) for 1 hour to burn off the starch. In addition, condition d means that it is not sintered.

[Examples 1 to 33]
According to the sample conditions in Table 4, samples 1 to 33 of compacts or sintered bodies were produced. The sample conditions in Table 4 will be explained. For example, the sample of Example 1 indicates that it was made according to sample condition 1-Aa. Specifically, "1" represents mixture composition 1 of Table 1, "A" represents heating, refrigerating, freezing and drying conditions A of Table 2, and "a" represents the firing conditions of Table 3. and the sample of Example 1 is a sample obtained by a combination of these conditions.

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

FIG. 5 is a diagram showing SEM images of fracture surfaces of molded articles of Examples 16, 19, 23 and 27. FIG.

According to FIGS. 5(A)-(C), the starch used as the raw material no longer had a granular shape, but was in a state of being connected to each other. On the other hand, according to FIG. 5(D), the starch used as the raw material maintained its granular form. Therefore, by heating, refrigerating, and freezing the starch under the conditions shown in Table 2, the starch used as the raw material changes from a granular form to a mutually connected form, and the gelatinization and aging phenomena appropriately occur. was shown.

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

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

6 (A) to (H) in which gelatinization and retrogradation of starch were performed under the first and second conditions described with reference to FIG. 2, and only in the second condition without performing the first condition 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 were compared to the sintered bodies of Examples 24 to 26. In comparison, it showed more interconnected pores. When compared for each sintering temperature, the open porosity of the sintered bodies of Examples 13-15, 17, 18, and 20-22 is generally higher than that of the sintered bodies of Examples 24-26. It was shown that the introduction of the process under the condition of 1 was effective for starch gelatinization and retrogradation.

Also, when comparing FIGS. 6A to 6C with FIGS. Compared to that of the sintered bodies No. 20 to 22, it was high as a whole. This suggests that not only the starch but also the dispersion medium functioned as a pore-forming agent by performing vacuum freeze-drying when removing the dispersion medium from the molded article.

Focusing on the pore diameter, as shown in FIGS. 6(A) to 6(C), atmospheric pressure drying can provide continuous pores having uniform and small pore diameters (0.5 μm to 1 μm). Do you get it. On the other hand, as shown in FIGS. 6(F) to (H), when vacuum freeze-drying is performed, not only the starch but also the dispersion medium functions as a pore-forming agent. 5 μm) are obtained.

7A to 7C, 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. 7A and 7D, it was found that when the dispersion medium does not contain water, it does not have communicating pores. This indicates that the dispersion medium should contain at least water when utilizing the gelatinization/aging phenomenon of starch.

Comparing FIGS. 7E and 7F, a tendency was shown that the lower the ethanol content in the dispersion medium, the higher the open porosity. The same applies to FIGS. 7B and 7C. This suggests that the open porosity can be controlled by adjusting the amounts of water and alcohol in the dispersion medium.

Comparing FIGS. 7B and 7E with FIGS. 8A and 8B, the open porosity of Examples 31 and 32, in which the amount of starch relative to the ceramic particles is increased, is lower than that of Examples 1 and 3. It showed a tendency to increase compared with that. This also indicates that a pore-forming agent utilizing the gelatinization/aging phenomenon of starch is 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 the water content in the dispersion medium, the open porosity, and the relative density.

According to FIG. 9(A), the open porosity increased as the water content in the dispersion medium increased. According to FIG. 9(B), the relative density decreased as the content of water in the dispersion medium increased. 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 the higher the water content in the dispersion medium, the higher the open porosity. From this, it was shown that a porous ceramic sintered body having an open porosity suitable for the application can be provided by appropriately selecting the sintering temperature and the content of water in the dispersion medium.

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 greater than that of the sintered bodies of Examples 26 and 30, in which the starch was not gelatinized and aged. From this, it is suggested that the use of the gelatinization/aging phenomenon of starch can promote not only the formation of interconnected pores but also the contact of ceramic particles by sintering.

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

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

Claims (13)

A method for producing a porous ceramic sintered body composed of an oxide ion/electron mixed conductor, having a pore diameter satisfying the range of 0.5 μm or more and 100 μm or less and having communicating pores,
a step of mixing the ceramic particles as the oxide ion/electron mixed conductor and starch as a pore-forming agent in a dispersion medium containing at least water;
heating the mixture obtained in the mixing step in a temperature range of 50° C. or higher and 150° C. or lower to gelatinize the starch;
The gelatinized body obtained in the heating and gelatinizing step is held under a first condition that satisfies a temperature range of −5° C. or higher and 10° C. or lower, and then held under a second condition that satisfies a temperature range of −10° C. or lower. holding at conditions to retrograde said starch;
drying the aged body obtained in the aging step to remove the dispersion medium;
and firing the compact obtained in the removing step. 2. The method according to claim 1, wherein said mixing step mixes 20 parts by weight or more and 75 parts by weight or less of said starch in said dispersion medium with respect to 100 parts by weight of said ceramic particles. 3. The method according to claim 1 or 2 , wherein the mixing step is performed so that the concentration of the ceramic particles and the starch in the dispersion medium is 0.2 g/mL or more and 0.6 g/mL or less. In the mixing step, the dispersion medium contains an alcohol,
The method according to any one of claims 1 to 3 , wherein the alcohol and the water are mixed at a ratio of 0:100 to 70:30 in mass%. The method according to any one of claims 1 to 4, wherein in the mixing step, the starch contains amylose and amylopectin, and the amylopectin contains more mass% than the amylose. 6. The method according to claim 5 , wherein the amylose and the amylopectin satisfy an amylose:amylopectin ratio of 5:95 to 40:60 in mass %. The method according to claim 6 , wherein the amylose and the amylopectin satisfy an amylose:amylopectin ratio of 15:85 to 25:75 in mass%. In the mixing step, the ceramic particles have a particle size in the range of 0.3 μm or more and 1 μm or less, and the starch has a particle size in the range of 1 μm or more and 50 μm or less. Any method described. The method according to any one of claims 1 to 8, wherein the gelatinizing step heats the mixture at a temperature in the range of 100°C to 130°C for 30 minutes to 2 hours while stirring. 10. Any one of claims 1 to 9 , wherein in the aging step, the first condition is to hold the gelatinized product in a temperature range of -2°C or higher and 5°C or lower for 30 minutes or longer and 2.5 hours or shorter. The method described in Crab. In the aging step, the second condition is that the gelatinized product is held in a temperature range of -200°C or higher and -100°C or lower for 5 seconds or longer and 10 seconds or shorter, or higher than -100°C. 11. The method according to any one of claims 1 to 10 , wherein the temperature range is -15°C or less for 1 hour or more and 24 hours or less. A method according to any preceding claim , wherein the step of removing the dispersion medium is performed by atmospheric pressure drying or vacuum freeze-drying. The method according to any one of claims 1 to 12 , wherein the step of removing the dispersion medium is carried out from the aged body until a molded body having an open porosity ranging from 40% to 90% is obtained.

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