JP6442366B2 - Oxygen permeable membrane - Google Patents

Description

  The present invention relates to an oxygen permeable membrane and a method for producing the oxygen permeable membrane.

  2. Description of the Related Art Conventionally, oxygen permeable membranes in which an oxide that exhibits oxygen ion (oxide ion) conductivity and an oxide that exhibits electronic conductivity are mixed are known as oxygen permeable membranes that selectively transmit oxygen. As an example of such an oxygen permeable membrane, for example, an oxygen permeable membrane using stabilized zirconia as an oxide exhibiting oxygen ion conductivity and a lanthanum chromite complex oxide as an oxide exhibiting electron conductivity is proposed. (For example, refer to Patent Document 1).

International Publication No. 2014/038186 Pamphlet

An oxygen permeable membrane composed of a complex oxide is generally produced by a production method involving a firing step. However, when the oxygen permeable membrane contains a lanthanum chromite complex oxide as described above, If the firing is carried out, the denseness of the oxygen permeable film may be insufficient. Therefore, in order to ensure the denseness of the oxygen permeable film containing the lanthanum chromite-based composite oxide, it is desirable to perform firing in a nitrogen atmosphere or the like. However, when the firing is performed in a nitrogen atmosphere or the like, the denseness of the oxygen permeable membrane can be secured, but oxygen deficiency occurs in the crystal of the lanthanum chromite complex oxide in the oxygen permeable membrane, so that the performance of the oxygen permeable membrane is improved. May be reduced. As a method for recovering the above-described oxygen deficiency, a method of introducing oxygen into the crystal of the lanthanum chromite complex oxide by heating the oxygen-permeable film after firing in the presence of oxygen (such as in the atmosphere) is also conceivable. When the oxygen permeable film is heated in the presence of oxygen, La ₂ Zr ₂ O ₇ that is a high resistance phase may be generated on the surface of the oxygen permeable film. This is presumably because the lanthanum (La) element in the lanthanum chromite complex oxide is liberated as La ₂ O ₃ and reacts with zirconium oxide (ZrO ₂ ) by heating in the presence of oxygen. When the above-described high resistance phase is formed on the surface of the oxygen permeable membrane, the oxygen permeable performance of the oxygen permeable membrane may be lowered.

The present invention has been made to solve the above-described problems, and can be realized as the following forms.
One aspect of the present invention is an oxygen permeable membrane comprising a mixed conductive layer comprising an oxygen ion conductor made of stabilized zirconia and an electronic conductor made of a lanthanum chromite complex oxide; The oxide has a composition formula La _1-x M _x CrO _3-z (wherein M is calcium (Ca) or strontium (Sr), 0 <x ≦ 0.3, and z <3). There oxide represented by); said oxygen permeable membrane further comprises a support; the mixed conductive layer, the formed on a support Rutotomoni, relative density be 95% or more; the mixed conducting layer In the X-ray diffraction pattern using CuKα as the radiation source for the surface on the side where the support is disposed in FIG. ₂ , the integration of the main peak of La ₂ Zr ₂ O ₇ with respect to the main peak of the stabilized zirconia An oxygen permeable membrane having an intensity ratio of 2% or less.
In such a form, the oxygen permeation film can be ensured to be dense and the oxygen permeation performance can be prevented from being lowered due to the high resistance phase containing La ₂ Zr ₂ O _7. It becomes possible to improve the performance of the membrane. In addition, since the mixed conductive layer can be made thinner by providing the support, the oxygen permeation performance of the oxygen permeable membrane can be further improved.
In addition, the present invention can be realized in the following forms.

(1) According to an aspect of the present invention, there is provided an oxygen permeable membrane including a mixed conductive layer including an oxygen ion conductor made of stabilized zirconia and an electron conductor made of a lanthanum chromite complex oxide. . In the oxygen permeable membrane, the lanthanum chromite complex oxide is an element selected from an alkaline earth metal excluding magnesium (Mg), wherein the composition formula is La _1-x M _x CrO _3-z. Yes, 0 ≦ x ≦ 0.3, z is arbitrary) and / or composition formula LaCr _1-x Mg _x O _3-z (where 0 ≦ x ≦ 0.3, z is arbitrary) It is an oxide represented by. In this oxygen permeable membrane, the integrated intensity of the main peak of La ₂ Zr ₂ O ₇ with respect to the main peak of stabilized zirconia in an X-ray diffraction pattern using CuKα as a radiation source for at least one surface of the mixed conductive layer The ratio is 2% or less.

According to the oxygen permeable membrane of this form, both the securing of the denseness of the oxygen permeable membrane and the suppression of the decrease in oxygen permeability due to the high resistance phase containing La ₂ Zr ₂ O ₇ are achieved, The performance of the oxygen permeable membrane can be improved.

(2) The oxygen permeable membrane of the above aspect may further include a support, and the mixed conductive layer may be formed on the support.
According to this form of the oxygen permeable membrane, the mixed conductive layer can be made thinner by providing the support, and therefore the oxygen permeable performance of the oxygen permeable membrane can be further improved.

(3) In the oxygen permeable membrane of the above aspect, the support is made of magnesium (Mg), calcium (Ca), aluminum (Al), zirconium (Zr), hafnium (Hf), titanium (Ti), yttrium (Y). And an oxide of a selected element that is one or more elements selected from the group consisting of scandium (Sc) and chromium (Cr), and 50 masses of metal elements contained in the oxide constituting the support % Or more may be the selected element.
According to this form of the oxygen permeable membrane, the support provided in the oxygen permeable membrane contains an element that is difficult to change in valence. Therefore, even when the oxygen permeable membrane is applied to a reformer that undergoes a partial oxidation reaction, the stability of the support provided in the oxygen permeable membrane can be ensured.

(4) The oxygen permeable membrane of the said form is good also as being formed on the said support body which does not contain a magnesium (Mg) element substantially.
According to this form of the oxygen permeable membrane, it is possible to suppress a decrease in oxygen permeation performance caused by the reaction of the lanthanum chromite complex oxide included in the mixed conductive layer with the constituent material of the support.

(5) In the oxygen permeable membrane according to the above aspect, the support includes stabilized zirconia and / or partially stabilized zirconia, and the stabilized zirconia and / or partially stabilized zirconia included in the support includes. The agent may be a stabilizer different from magnesium oxide (MgO).
According to this form of the oxygen permeable membrane, it is possible to suppress degradation of the performance of the oxygen permeable membrane due to the stabilized zirconia and / or magnesium (Mg) in the partially stabilized zirconia contained in the support.

(6) In the oxygen permeable membrane of the above aspect, the stabilizer contained in the stabilized zirconia and / or partially stabilized zirconia included in the support is calcium oxide (CaO), yttrium oxide (Y ₂ O ₃ ), It may be at least one stabilizer selected from scandium oxide (Sc ₂ O ₃ ).
According to this form of the oxygen permeable membrane, the difference in thermal expansion coefficient between the mixed conductive layer and the support can be easily approximated.

(7) The oxygen permeable membrane of the above aspect further includes a catalyst layer having an activity of promoting a reaction of ionizing oxygen molecules or a reaction of generating oxygen molecules from oxygen ions, and the oxygen permeable membrane is interposed via the catalyst layer. It may be formed on the support.
According to this form of the oxygen permeable membrane, the oxygen permeable performance of the oxygen permeable membrane can be further enhanced. In addition, the mixed conductive layer can be made thin.

(8) In the oxygen permeable membrane of the above aspect, the support may have an activity of promoting a reaction of ionizing oxygen molecules or a reaction of generating oxygen molecules from oxygen ions.
According to this form of the oxygen permeable membrane, the configuration of the oxygen permeable membrane and the method for producing the oxygen permeable membrane can be simplified as compared with the case where a separate catalyst layer is provided between the mixed conductive layer and the support.

(9) According to another aspect of the present invention, a method for producing an oxygen permeable membrane comprising a mixed conductive layer comprising an oxygen ion conductor made of stabilized zirconia and an electron conductor made of a lanthanum chromite complex oxide Is provided. In this production method, the lanthanum chromite-based composite oxide is a composition formula La _1-x M _x CrO _3-z (wherein M is an element selected from alkaline earth metals excluding magnesium (Mg)). 0 ≦ x ≦ 0.3, z is arbitrary) and / or composition formula LaCr _1-x Mg _x O _3-z (where 0 ≦ x ≦ 0.3, z is optional) It is an oxide represented by The manufacturing method includes: a first step of mixing the oxygen ion conductor and the electron conductor to form the mixed conductive layer; a second step of firing the mixed conductive layer in an inert atmosphere; After the second step, a third step of heat-treating the mixed conductive layer under a temperature condition of 1000 ° C. or higher in the presence of chromium (Cr) element and oxygen.

According to the method for manufacturing an oxygen permeable membrane of this embodiment, after the mixed conductive layer is fired in an inert atmosphere to ensure the denseness of the mixed conductive layer, heat treatment is performed in the presence of chromium (Cr) element and oxygen. Is doing. Therefore, even if oxygen deficiency occurs in the crystal of the lanthanum chromite complex oxide in the oxygen permeable film in the baking process, the above heat treatment suppresses generation of a high resistance phase containing La ₂ Zr ₂ O _7. Thus, the oxygen permeation performance of the oxygen permeable membrane can be improved.

  The present invention can be realized in various forms other than those described above. For example, the present invention can be realized in the form of a reformer provided with an oxygen permeable membrane or a pure oxygen production device provided with an oxygen permeable membrane.

It is a cross-sectional schematic diagram which shows schematic structure of the oxygen permeable film of 1st Embodiment. It is process drawing which shows the manufacturing method of the oxygen permeable film of embodiment. It is explanatory drawing showing the mode of heat processing. It is explanatory drawing showing the mode of heat processing. It is explanatory drawing showing the mode of heat processing. It is a cross-sectional schematic diagram which shows schematic structure of the oxygen permeable film of 2nd Embodiment. It is explanatory drawing which shows the result of having investigated the performance of the oxygen permeable film in the table | surface. It is explanatory drawing which shows the result of having investigated the performance of the oxygen permeable film in the table | surface. It is explanatory drawing which shows the result of having investigated the performance of the oxygen permeable film in the table | surface. It is explanatory drawing showing schematic structure of the measuring apparatus used in order to measure an oxygen permeation | transmission characteristic. It is explanatory drawing which shows the X-ray-diffraction pattern of the sample 11. 3 is an explanatory diagram showing an X-ray diffraction pattern of Sample 1. FIG. It is explanatory drawing which shows the analysis result about the samples 17, 18, and 21. FIG.

A. Configuration of the oxygen permeable membrane of the first embodiment:
FIG. 1 is a schematic cross-sectional view showing a schematic configuration of an oxygen permeable membrane 10 and a device 20 including the oxygen permeable membrane 10 as a first embodiment of the present invention. First, the configuration of the oxygen permeable membrane 10 will be described. The oxygen permeable membrane 10 is composed of a mixture of an oxide exhibiting oxygen ion conductivity (hereinafter also referred to as an oxygen ion conductor) and an oxide exhibiting electronic conductivity (hereinafter also referred to as an electron conductor). Yes. Thereby, the oxygen permeable film 10 exhibits oxygen ion conductivity and electron conductivity.

Stabilized zirconia can be used as the oxygen ion conductor contained in the oxygen permeable membrane 10. Stabilized zirconia is zirconia stabilized by dissolving one or more dopants that are oxides into zirconium oxide (ZrO ₂ ). Examples of the oxide that can be used as the dopant include yttrium oxide (Y ₂ O ₃ ), scandium oxide (Sc ₂ O ₃ ), and ytterbium oxide (Yb ₂ O ₃ ), which are rare earth oxides. Calcium oxide (CaO) or magnesium oxide (MgO) can also be used as a dopant. In zirconia, by replacing the tetravalent and stable zirconium (Zr) site with a divalent or trivalent and stable element contained in the dopant, oxygen vacancies are formed in the structure and oxygen ion conductivity is increased. As it is expressed, the crystal structure is stabilized. From the viewpoint of oxygen ion conductivity and stability, the stabilized zirconia is preferably selected from yttria stabilized zirconia (hereinafter also referred to as YSZ) and scandia stabilized zirconia (hereinafter also referred to as ScSZ).

  In stabilized zirconia, oxygen ion conductivity improves as the amount of dopant added increases. Generally, when the amount of dopant added is near the minimum amount necessary to obtain fully stabilized zirconia, The ionic conductivity is maximum. If the dopant is added excessively beyond such a value, the oxygen ion conductivity tends to decrease. Therefore, in order to ensure the oxygen ion conductivity and to obtain the effect of increasing the stability of the entire oxygen permeable membrane 10, the additive amount of the dopant in the stabilized zirconia is desirably 3 to 12 mol%. In particular, when using yttria-stabilized zirconia as the stabilized zirconia, the amount of dopant added is preferably 3 to 8 mol%. When using scandia-stabilized zirconia as the stabilized zirconia, the amount of dopant added is preferably It is preferable to set it as 7-11 mol%.

  The electron conductor contained in the oxygen permeable membrane 10 is at least one electron selected from an electron conductor represented by the following formula (1) and an electron conductor represented by the following formula (2). A conductor can be used.

_{La 1-x M x CrO 3} -z ... (1)
(In the formula, M is an element selected from an alkaline earth metal excluding magnesium (Mg), and 0 ≦ x ≦ 0.3. Also, z is the ratio of the metal element in the formula and the environment. (This value indicates that the amount of oxygen atoms varies depending on the temperature and atmosphere.)

_{LaCr 1-x Mg x O 3} -z ... (2)
(In the formula, 0 ≦ x ≦ 0.3. Further, z is a value indicating that the amount of oxygen atoms varies depending on the ratio of the metal element in the formula, the environmental temperature, and the atmosphere. )

  An electron conductor, which is a lanthanum chromite complex oxide, can improve the stability of the oxygen permeable membrane when combined with stabilized zirconia. That is, it is possible to suppress the reaction between the oxygen ion conductor and the electron conductor in the oxygen permeable membrane. Therefore, x = 0 may be sufficient in the said Formula (1) and / or (2) Formula. However, as shown in the above formula (1), an element selected from alkaline earth metals excluding magnesium (Mg) is added to the lanthanum (La) site, or as shown in the above formula (2). By adding a magnesium (Mg) element to a chromium (Cr) site, the electron conductivity of the oxygen permeable film 10 can be further increased. In the formula (1), M which is an alkaline earth metal is particularly preferably strontium (Sr) or calcium (Ca).

  In the above formulas (1) and (2), the larger the value of x, the higher the electron conductivity of the electron conductor of this embodiment. However, as the value of x is increased (the amount of substitution is increased), the crystal structure becomes unstable and the reactivity with other elements increases. Specifically, when the value of x exceeds 0.3, for example, in the firing step for manufacturing the oxygen permeable membrane 10 by mixing the electron conductor of this embodiment and the oxygen ion conductor, the electron conductor In addition, the amount of heterogeneous phase having a composition different from that of the oxygen ion conductor is increased. Therefore, in this embodiment, the range of x in the composition formula (1) is 0 ≦ x ≦ 0.3. In order to further suppress the generation of the heterogeneous phase, it is desirable that the range of x is x ≦ 0.2. In order to improve the oxygen permeation performance of the oxygen permeable membrane 10, it is desirable that the range of x is 0.1 ≦ x. As described above, the value of z in the composition formulas (1) and (2) depends on the ratio of the metal elements constituting the electron conductors of the formulas (1) and (2), the environmental temperature, It is a value indicating that the amount of oxygen atoms varies depending on the atmosphere, and can take a numerical value in the range of 0 to 0.2, for example.

The oxygen permeable membrane 10 of this embodiment includes a mixed conductive layer obtained by mixing the oxygen ion conductor and the electronic conductor as described above. FIG. 1 shows a state in which the oxygen permeable membrane 10 is a self-supporting membrane constituted only by a mixed conductive layer without having a support. In the oxygen permeable membrane 10 of this embodiment, in the X-ray diffraction pattern using CuKα as the radiation source for at least one surface of the mixed conductive layer, the main peak of La ₂ Zr ₂ O ₇ is compared with the main peak of stabilized zirconia. The integrated intensity ratio is 2% or less. That is, La ₂ Zr ₂ O ₇ , which is a compound containing a zirconium element (Zr) derived from stabilized zirconia that is an oxygen ion conductor and a lanthanum element (La) derived from a lanthanum chromite complex oxide that is an electronic conductor. This is characterized in that the abundance on the surface of the mixed conductive layer is extremely small. Since the abundance of La ₂ Zr ₂ O _{7 on} the surface of the mixed conductive layer is small, the oxygen permeable membrane 10 of this embodiment can realize a good oxygen transmission rate.

In this embodiment, when an X-ray diffraction pattern using CuKα as a radiation source for the surface of the mixed conductive layer included in the oxygen permeable membrane 10 is obtained, it is the strongest among the peaks existing in the vicinity of 2θ = 28 ° to 29 °. The peak was defined as the main peak of La ₂ Zr ₂ O ₇ . Therefore, in the present embodiment, the La ₂ Zr ₂ O ₇ showing the main peak may include a case where a small amount of Sr or Cr is dissolved in the La site or Zr site. In order to secure the performance of the oxygen permeable membrane 10 more sufficiently, the main peak of La ₂ Zr ₂ O _{7 and} the main peak of stabilized zirconia described above are formed on both sides of the mixed conductive layer constituting the oxygen permeable membrane 10. It is preferable that the requirement relating to the integral intensity ratio between is established.

  Further, since the oxygen permeable membrane 10 is desired to be a gas impermeable dense membrane, the relative density of the oxygen permeable membrane 10 is desirably 90% or more, more desirably 93% or more, and 95 % Or more is more desirable. Here, the relative density represents the ratio of the actually measured density of the sample to the theoretical density of the sample. The theoretical density can be determined from the atomic weight of elements contained per unit cell of the sample and the lattice constant. The lattice constant of the sample can be obtained by an X-ray diffraction method (XRD measurement). The actual measurement of the density of the sample can be performed by the Archimedes method.

  Such a relative density value can be easily realized by firing in an inert atmosphere when the oxygen permeable conductor is produced by mixing the oxygen ion conductor and the electron conductor and then firing. A method for manufacturing the oxygen permeable membrane 10 will be described later. Note that the relative density of the oxygen permeable membrane 10 is affected by the firing temperature in the firing step during the production of the oxygen permeable membrane and the mixing ratio of the oxygen ion conductor and the electron conductor. Therefore, the firing temperature and the mixing ratio may be appropriately set in consideration of the desirable relative density of the oxygen permeable membrane 10 and the like.

B. Production method of oxygen permeable membrane:
FIG. 2 is a process diagram showing a method for manufacturing the oxygen permeable membrane 10 of the present embodiment. When manufacturing the oxygen permeable membrane 10, first, an oxygen ion conductor and an electron conductor as raw materials for the oxygen permeable membrane 10 are prepared (step S100).

  Each of the oxygen ion conductor and the electron conductor can be formed by, for example, a solid phase reaction method. The solid phase reaction method is a measurement of a powder raw material such as oxide, carbonate, or nitrate so that the metal element in the powder raw material is in a predetermined ratio according to the composition of the oxide to be produced. This is a well-known method for synthesizing a desired oxide by performing heat treatment (firing) after mixing. Each of the production methods of the oxygen ion conductor and the electron conductor may be a method other than the solid phase reaction method. For example, various methods capable of producing a composite oxide such as a coprecipitation method, a pechini method, or a sol-gel method. The method can be adopted. The pechini method is a method in which a precursor is prepared by an esterification reaction between a chelate compound of a metal ion and citric acid and a polyalcohol such as ethylene glycol, and oxide particles are obtained by heat treatment. In step S100, the oxygen ion conductor and the electron conductor can be prepared in a powder state, for example.

  After step S100, the oxygen ion conductor and the electron conductor are mixed and molded to form a mixed conductive layer (step S110). This step S110 corresponds to the first step described in the means for solving the problem. In order to form a mixed conductive layer, for example, an oxygen ion conductor powder and an electron conductor powder are used, and the oxygen ion conductor and the electron conductor are sufficiently mixed in a sufficiently small particle size. Then, it may be molded. In order to sufficiently mix the oxygen ion conductor and the electron conductor with a sufficiently small particle diameter, for example, a ball mill may be used. The mixing ratio of the oxygen ion conductor and the electron conductor is appropriately determined in consideration of the oxygen permeation performance of the oxygen permeable membrane 10 obtained as a result of the balance between oxygen ion conductivity and electron conductivity realized by each oxide. You just have to decide. The mixing ratio of the electron conductor in the oxygen permeable membrane 10 which is a mixture of the oxygen ion conductor and the electron conductor is preferably 5 mol% or more, for example. The mixing ratio is preferably 50 mol% or less, more preferably 40 mol% or less, and still more preferably 30 mol% or less. The mixture of the oxygen ion conductor and the electron conductor may be formed by press molding, for example.

After forming the mixed conductive layer in step S110, the mixed conductive layer is baked in an inert atmosphere (step S120). This step S120 corresponds to the second step described in the means for solving the problem. Here, under an inert atmosphere means in an inert gas containing no oxygen or under vacuum. Examples of the inert gas to be used include nitrogen (N ₂ ), argon (Ar), helium (He), and neon (Ne), and particularly from nitrogen (N ₂ ) and argon (Ar). It is desirable to bake in at least one selected inert gas. The step of firing the mixed conductive layer is a step for densifying the mixed conductive layer. When the oxygen permeable film contains a lanthanum chromite complex oxide like the oxygen permeable film 10 of the present embodiment, the denseness of the oxygen permeable film may be insufficient when firing is performed in the presence of oxygen. In this embodiment, the denseness of the mixed conductive layer is ensured by firing the mixed conductive layer under an inert atmosphere.

  The firing temperature in step S120 is, for example, preferably 1200 ° C. or higher, and more preferably 1300 ° C. or higher, in order to make the mixed conductive layer a sufficiently dense sintered body. Further, the firing temperature of the mixed conductive layer is preferably 1700 ° C. or lower, more preferably 1600 ° C. or lower, for example, from the viewpoint of suppressing the reaction between the oxygen ion conductor and the electron conductor in the firing step, and 1500 ° C. The following is more preferable.

  After step S120, the fired mixed conductive layer is heat-treated (annealed) in the presence of chromium (Cr) element and oxygen (step S130) to complete the oxygen permeable membrane 10. This step S130 corresponds to the third step described in the means for solving the problem. In step S120 described above, when the mixed conductive layer is baked in an inert atmosphere, the mixed conductive layer is densified, but oxygen vacancies may occur in the crystals of the lanthanum chromite complex oxide in the mixed conductive layer. Such oxygen deficiency in the lanthanum chromite complex oxide causes a decrease in oxygen permeation performance in the oxygen permeable membrane 10. In step S130, the mixed conductive layer is heat-treated in the presence of oxygen, whereby oxygen is introduced into the crystal of the lanthanum chromite complex oxide to recover the oxygen deficiency.

However, when heat treatment is performed in the presence of oxygen in this manner, a high resistance compound, specifically La ₂ Zr ₂ O _7, may be generated on the surface of the mixed conductive layer. The reason is that the lanthanum (La) element in the lanthanum chromite complex oxide contained in the mixed conductive layer is liberated as La ₂ O _{3 in the} presence of oxygen, and zirconium oxide (ZrO ₂ ) contained in the mixed conductive layer. It is thought that it reacts with. For example, when the lanthanum chromite complex oxide contained in the mixed conductive layer is LaCrO ₃ , the reaction shown in the following formula (3) proceeds. In addition, as shown in the above-described formulas (1) and (2), even when the lanthanum chromite complex oxide contained in the mixed conductive layer further contains an alkaline earth metal, La ₂ O ₃ and chromium oxide are produced.
2LaCrO ₃ → La ₂ O ₃ + Cr ₂ O ₃ (3)

As described above, when the compound La ₂ Zr ₂ O ₇ having high resistance is generated on the surface of the mixed conductive layer, the oxygen permeation performance of the oxygen permeable membrane may be deteriorated. In the present embodiment, the above-described high-resistance compound is suppressed from being generated on the surface of the mixed conductive layer by performing heat treatment under the condition where chromium (Cr) element is present together with oxygen. The reason why the formation of a high resistance compound can be suppressed by heat treatment under the condition where chromium (Cr) element is present together with oxygen is considered as follows. That is, by performing heat treatment under the condition where chromium (Cr) element is present together with oxygen, chromium oxide (mainly chromium trioxide: CrO ₃ ) is diffused as a gas in the atmosphere, and the chromium oxide concentration in the atmosphere is reduced. Rise. Since the reaction of the above formula (3) is an equilibrium reaction, the reverse reaction of the arrow of the formula (3) easily proceeds due to the increase of the chromium oxide concentration in the atmosphere, and the production of La ₂ O ₃ is suppressed. As a result, it is considered that the production of La ₂ Zr ₂ O ₇ due to the reaction between La ₂ O ₃ and zirconium oxide (ZrO ₂ ) is suppressed.

Note that “in the presence of chromium (Cr) element” in step S130 means that chromium oxide is present in the atmosphere (the activity of CrO _{3 in} the atmosphere is increased) and suppresses the reaction of formula (3). Any state that can be used. That is, “in the presence of chromium (Cr) element” means that the substance contains a chromium (Cr) element. More specifically, it means that there is a substance further containing a chromium (Cr) element in addition to the chromium compound contained in the mixed conductive layer. For example, in addition to the presence of an oxide containing chromium (Cr), the presence of metallic chromium or a chromium-containing alloy is included. When chromium trioxide (CrO ₃ ) is used as the substance containing chromium (Cr), the activity of CrO _{3 in} the atmosphere can be increased by volatilizing a small amount of chromium trioxide (CrO ₃ ). It is done. Further, in the case of using another substance containing chromium (Cr), it is considered that chromium trioxide (CrO ₃ ) generated by oxidizing the chromium (Cr) element diffuses into the atmosphere. It is sufficient that chromium trioxide (CrO ₃ ) exists in the atmosphere during the heat treatment. These substances containing chromium (Cr) may be coexisted with the mixed conductive layer in the state of powder, for example, during the heat treatment. As the substance containing chromium (Cr), it is particularly desirable to use Cr ₂ O ₃ and / or lanthanum chromite complex oxide.

  3-5 is explanatory drawing which shows the specific aspect for making it "in presence of chromium (Cr) element" at the time of the heat processing of step S130. As an example, FIGS. 3 to 5 show a state in which the mixed conductive layer 12 is heat-treated in a container made of a crucible 40 (for example, made of alumina) having a lid 42 (for example, made of alumina).

  FIG. 3 shows how the mixed conductive layer 12 is buried in a powder 46 containing a chromium (Cr) element in a crucible 40. FIG. 4 shows a state in which the mixed conductive layer 12 is placed on the mesh 44 in the crucible 40 and is arranged in a state of being separated from the powder 46 containing the chromium (Cr) element. That is, the mixed conductive layer 12 coexists with a substance containing a chromium (Cr) element in a non-contact manner. FIG. 5 shows that in a crucible 40, a powder 46 containing chromium (Cr) element, a powder 48 not containing chromium (Cr) element, and the mixed conductive layer 12 are arranged in this order, and chromium (Cr ) The mixed conductive layer 12 is separated from the powder 46 containing the element.

3 to 5, as described above, the powder 46 is a powder of an oxide containing chromium (Cr) such as lanthanum chromite complex oxide or Cr ₂ O ₃ , or metal chromium or a chromium-containing alloy. It can be a powder. Further, the powder 46 may be mixed with a powder made of a material not containing a chromium (Cr) element in addition to a powder made of a material containing a chromium (Cr) element.

When the mixed conductive layer 12 is embedded in the powder 46 as shown in FIG. 3, the powder 46 does not substantially react with the mixed conductive layer 12, or the influence by reacting with the mixed conductive layer 12 is within an allowable range. It is sufficient to use a powder made of the substance. For example, the lanthanum chromite complex oxide represented by the formula (1) or (2) described above can be used. Alternatively, LaCrO ₃ in which an alkaline earth metal is not doped in lanthanum or chrome sites may be used. When using a lanthanum chromite complex oxide, it is particularly desirable to use a powder made of the same kind of compound as the lanthanum chromite complex oxide contained in the mixed conductive layer 12 as an electron conductor. In this way, even if the powder 46 remains on the surface of the mixed conductive layer 12 after the heat treatment, changes in the performance of the mixed conductive layer 12 can be suppressed.

  The powder 46 may further contain a stabilized zirconia, for example, a stabilized zirconia selected from scandia stabilized zirconia (ScSZ), yttria stabilized zirconia (YSZ) and scandia stabilized zirconia (ScSZ). In this case, the same kind as the stabilized zirconia contained in the mixed conductive layer 12 is desirable. In FIG. 3, if a powder in which the same kind of substance as lanthanum chromite complex oxide and stabilized zirconia included in the mixed conductive layer 12 is used as the powder 46, the powder is formed on the surface of the mixed conductive layer 12 after the heat treatment. Even if 46 remains, it is possible to achieve high oxygen permeation performance by suppressing variation in performance of the mixed conductive layer 12.

When using a powder in which lanthanum chromite complex oxide and stabilized zirconia are mixed as the powder 46, the ratio of the lanthanum chromite complex oxide is desirably 10 mol% or more. Note that after the heat treatment, the mixed conductive layer 12 may be washed or the surface of the mixed conductive layer 12 may be polished to remove the powder 46 attached to the surface of the mixed conductive layer 12. When using a powder 46 containing a material different from the constituent material of the mixed conductive layer, such as Cr ₂ O ₃ , in particular, a material that can affect the performance of the oxygen permeable membrane 10, the mixed conductive layer is used after the heat treatment. It is desirable to remove the powder 46 adhering to the 12 surfaces.

  4 and 5, when the mixed conductive layer 12 and the powder 46 are separated from each other, it is necessary to consider the influence of the powder 46 remaining on the surface of the mixed conductive layer 12 after the heat treatment. Absent. The mesh 44 used in FIG. 4 is desirably formed of a material having low reactivity with the mixed conductive layer 12, and may be formed of a noble metal such as platinum, for example. In FIG. 5, the powder 48 disposed between the powder 46 and the mixed conductive layer 12 has low reactivity with the mixed conductive layer 12, and even if it remains on the surface of the mixed conductive layer 12 after the heat treatment, It is desirable to select a powder that has an acceptable impact on performance. As the powder 48, for example, stabilized zirconia powder can be used.

In any case, the container may be heat-treated in the presence of oxygen. The presence of oxygen can be, for example, in the atmosphere, and it is only necessary that chromium oxide (CrO ₃ ) derived from the chromium (Cr) element in the substance constituting the powder 46 is generated in the atmosphere. Therefore, the conditions in the presence of oxygen may be appropriately selected from conditions in the range of 1 to 100% oxygen concentration. The lid body 42 is used to ensure the concentration of chromium oxide (CrO ₃ ) volatilized from the powder 46 in the crucible 40, and the inside of the crucible 40 is not sealed, and the inside and outside of the crucible 40 communicate with each other. Thus, oxygen is supplied into the crucible 40.

The treatment temperature of the heat treatment in step S130 may be any temperature that can recover the oxygen vacancies described above and can suppress the formation of the high-resistance compound described above. Specifically, the temperature may be any temperature at which chromium oxide (CrO ₃ ) can diffuse and exist in the atmosphere when the above-described substances containing chromium (Cr) element coexist. The heat treatment may be performed at a temperature condition of 1000 ° C. or higher, for example. Moreover, it is desirable that the heating temperature be equal to or lower than the firing temperature in step S120. By performing the heat treatment below the firing temperature, it is possible to suppress the reaction between the oxygen ion conductor and the electron conductor in the mixed conductive layer.

C. Configuration of device 20:
Returning to FIG. 1, the apparatus 20 including the oxygen permeable membrane 10 made of the mixed conductive layer manufactured as described above may be a reformer, for example. Hereinafter, the apparatus 20 as a reformer will be described.

  The apparatus 20 includes the oxygen permeable membrane 10 described above, and a reforming material channel 16 through which a fluid as a reforming material flows is formed on one surface side of the oxygen permeable membrane 10. Further, an air flow path 18 through which air as an oxygen-containing gas flows is formed on the other surface side of the oxygen permeable membrane 10. The oxygen permeable membrane 10 has oxygen ion permeability, and has a property of specifically transferring oxygen from a side having a high oxygen partial pressure to a side having a low oxygen partial pressure. Therefore, in the apparatus 20, oxygen in the air channel 18 permeates to the reforming raw material channel 16 side through the oxygen permeable membrane 10. In the apparatus 20 of the present embodiment, the partial oxidation reaction of the reforming material proceeds on the surface of the oxygen permeable membrane 10 on the side of the reforming material channel 16 using oxygen that has permeated the oxygen permeable membrane 10. .

In FIG. 1, the oxygen partial pressure (PO ₂ ) on the air flow path 18 side is higher than the oxygen partial pressure (P′O ₂ ) on the reforming raw material flow path 16 side, and between the both surfaces of the oxygen permeable membrane 10. A state in which the oxygen partial pressure gradient is generated is conceptually shown by a broken line. In the oxygen permeable membrane 10, oxygen permeates from the high oxygen partial pressure side (air flow path 18) to the low oxygen partial pressure side (reforming raw material flow path 16) using such an oxygen partial pressure difference between both surfaces as a driving force. . At this time, oxygen molecules in the air channel 18 are ionized on the surface of the oxygen permeable membrane 10 on the air channel 18 side, and the generated oxygen ions pass through the oxygen permeable membrane 10 having oxygen ion conductivity in the reforming raw material. It moves to the flow path 16 side. Since the oxygen permeable membrane 10 of this embodiment has electron conductivity as well as oxygen ion conductivity, when oxygen ions move as described above, electrons move in the opposite direction to the oxygen ions. Therefore, oxygen can be permeated without applying an external voltage to the oxygen permeable membrane 10. The electron conductivity in the oxygen permeable membrane 10 may be both electron conduction and hole conduction, or may be either one. In the present embodiment, the oxygen permeable membrane 10 having the electron conductivity includes both the electron conduction and the hole conduction.

  When oxygen is transported to the reforming material channel 16 side as described above, the reforming material is reformed by a partial oxidation reaction on the reforming material channel 16 side of the oxygen permeable membrane 10, and hydrogen and Carbon monoxide is produced. Various gaseous fuels or liquid fuels can be used as the reforming raw material. As the gaseous fuel, for example, hydrocarbon fuel such as methane or natural gas mainly composed of methane can be used. As the liquid fuel, for example, liquid hydrocarbon, alcohol such as methanol, or ether can be used. Such an apparatus 20 can be used, for example, to obtain hydrogen supplied as fuel gas to the fuel cell. Alternatively, the obtained hydrogen and carbon monoxide may be used for further hydrocarbon conversion to produce a liquid hydrocarbon fuel, that is, for GTL (Gas To Liquid) technology.

  In addition, you may apply the oxygen permeable film 10 of this embodiment to apparatuses other than a modifier. For example, a pure oxygen production apparatus may be manufactured using the oxygen permeable membrane 10 and the oxygen permeable membrane 10 may be used to obtain a highly pure oxygen gas from the oxygen-containing gas.

Moreover, the oxygen permeable membrane 10 of this embodiment does not consist only of a mixed conductive layer, but may provide a catalyst layer on at least one surface of the mixed conductive layer. The catalyst layer is a reaction that proceeds on the surface of the oxygen permeable membrane 10 (surface exchange reaction), that is, a reaction in which oxygen ions are generated from oxygen molecules on one side (high oxygen partial pressure side) (1 / 2O ₂ + 2e ⁻ → O ²⁻ ), or a layer that promotes a reaction (O ²⁻ → 1 / 2O ₂ + 2e ⁻ ) in which oxygen molecules are generated from oxygen ions on the other surface (low oxygen partial pressure side). When the apparatus 20 is a reformer, the catalyst layer disposed on the low oxygen partial pressure side can be a layer that promotes the above-described reforming reaction.

Such a catalyst layer can be formed of, for example, a noble metal such as platinum (Pt), a metal such as nickel (Ni), or a metal oxide such as nickel oxide (NiO). In addition, the catalyst layer can be formed using a perovskite complex oxide such as a lanthanum-iron complex oxide or a lanthanum-chromium complex oxide. Examples of the lanthanum-chromium composite oxide catalyst include compounds represented by the following formula (4). In the formula, the value of x can be set to 0.8, for example. In the formula, 0 <y <0.2 may be satisfied. z is a value indicating that the amount of oxygen atoms varies depending on the ratio of the metal element in the formula, the environmental temperature, and the atmosphere.
_{La x Sr 1-x Cr y} Ni 1-y O 3-z ... (4)

According to the oxygen permeable membrane 10 of the present embodiment configured as described above, an electronic conductor composed of an oxide represented by formula (1) and / or an oxide represented by formula (2), and stabilized zirconia And a stabilized zirconia of a main peak of La ₂ Zr ₂ O ₇ in an X-ray diffraction pattern using CuKα as a radiation source for at least one surface of the mixed conductive layer. The integrated intensity ratio with respect to the main peak is 2% or less. Therefore, in the oxygen permeable membrane, the oxygen permeable membrane is compatible with suppressing the decrease in oxygen permeable performance due to the high resistance phase containing La ₂ Zr ₂ O ₇ and ensuring the denseness of the oxygen permeable membrane. It becomes possible to improve the performance.

In particular, in the manufacturing method of the oxygen permeable membrane 10 of the present embodiment, the mixed conductive layer is fired in an inert atmosphere to ensure the denseness of the mixed conductive layer, and then in the presence of chromium (Cr) element and oxygen. Heat treatment is performed. Therefore, even if oxygen deficiency occurs in the crystal of the lanthanum chromite complex oxide in the oxygen permeable film in the baking process, the above heat treatment suppresses generation of a high resistance phase containing La ₂ Zr ₂ O _7. Thus, the oxygen permeation performance of the oxygen permeable membrane can be improved. As a result, the integrated intensity ratio of the main peak of La ₂ Zr ₂ O _{7 to} the main peak of stabilized zirconia is 2% in the X-ray diffraction pattern using CuKα as the radiation source for at least one surface of the mixed conductive layer. The following oxygen permeable membrane 10 can be obtained easily.

Note that when the oxygen deficiency is recovered by performing heat treatment in the absence of chromium (Cr) element after the firing step in an inert atmosphere, La ₂ Zr ₂ O ₇ is included on the surface of the mixed conductive layer. When a high resistance phase is formed, a measure for removing the high resistance phase by polishing or the like after the heat treatment is also conceivable. However, according to the present embodiment, oxygen permeation performance can be ensured while recovering oxygen vacancies in the mixed conductive layer by a simple process without requiring a further process of removing the high resistance phase.

D. Second embodiment:
FIG. 6 is a schematic cross-sectional view showing a schematic configuration of the oxygen permeable membrane 110 of the second embodiment. The oxygen permeable membrane 110 can be applied to the same device 20 as the oxygen permeable membrane 10 of the first embodiment. The oxygen permeable membrane 110 includes a mixed conductive layer 22 having the same configuration as that of the mixed conductive layer constituting the oxygen permeable membrane 10. That is, a mixed conductive layer 22 including an electron conductor made of an oxide represented by the formula (1) and / or an oxide represented by the formula (2) and an oxygen ion conductor made of stabilized zirconia is provided, and mixed conduction is provided. In the X-ray diffraction pattern using CuKα as the radiation source for at least one surface of the layer 22, the integrated intensity ratio of the main peak of La ₂ Zr ₂ O _{7 to} the main peak of stabilized zirconia is 2% or less. Yes. The oxygen permeable membrane 110 further includes a support 24 made of a porous body, and the mixed conductive layer 22 is formed on the support 24.

  The support 24 may be formed of a material that is stable in the firing step in an inert gas atmosphere and does not cause reduction or melting. For example, the support 24 can be formed of a ceramic material. When the support is formed of a ceramic material, when mixing the ceramic raw material powder, for example, a porous material such as an acrylic resin and a binder are added and mixed. The support 24 can be obtained. It is desirable that the pore former is easily removed in the firing step. It should be noted that the porosity and pore diameter of the support to be produced may be appropriately adjusted according to the particle size of the pore former used and the mixing ratio of the ceramic material powder.

  Examples of the ceramic material constituting the support 24 include, for example, magnesium (Mg), calcium (Ca), aluminum (Al), zirconium (Zr), hafnium (Hf), titanium (Ti), yttrium (Y), An oxide containing as a main component one or more elements selected from the group consisting of scandium (Sc) and chromium (Cr) can be given. The oxide constituting the support 24 is mainly composed of one or more elements selected from the above group, specifically, an element excluding oxygen in the oxide constituting the support 24, That is, it means that the total proportion of the elements included in the above group occupies 50% by mass or more of the metal elements. Among the elements excluding oxygen in the oxide constituting the support 24, the content (content ratio) of the elements included in the above group is measured by semi-quantitative analysis (fundamental parameter method) of fluorescent X-ray analysis. be able to. In addition, the 1 or more types of element selected from the said group is corresponded to the selection element described in the means for solving a subject.

Any of the above-described selected elements is an element that hardly changes its valence. Therefore, the oxide of the selective element constituting the support 24 has high stability in the environment of the manufacturing process of the oxygen permeable membrane 110 and in the environment at the time of use. The stability of the oxides constituting the support 24 under the firing conditions in an inert gas atmosphere can be determined from, for example, the Ellingham diagram. The Ellingham diagram is a graph plotting the standard reaction Gibbs energy at each temperature for various oxides, with the horizontal axis representing temperature and the vertical axis representing standard reaction Gibbs energy (ΔG ⁰ ). The stability of various oxides can be confirmed. In the Ellingham diagram, the substance located at the lower side of the diagram indicates that the oxide is more stable. Based on the Ellingham diagram, the oxide of each element included in the above group depends on the inert gas used in step S120. It can be confirmed that the oxygen partial pressure of about 10 ⁻⁵ atm considered to be formed is stable even at a high temperature of 1700 ° C. By configuring the support 24 with the oxide, the oxygen permeable membrane is damaged due to reduction and melting of the oxide due to high temperature and low oxygen partial pressure even in the firing step (step S120) in an inert atmosphere. Can be suppressed. Furthermore, by configuring the support 24 with the oxide, the stability of the support 24 can be ensured even when the oxygen permeable membrane 110 is applied to the device 20 that is the reformer described above. Can do.

  In addition, the support 24 is preferably formed of a substance that has a sufficiently small degree of reaction that proceeds with the mixed conductive layer in a manufacturing process including firing. Specific examples of such a ceramic material constituting the support 24 include, for example, stabilized zirconia. When stabilized zirconia is used as the material of the support 24, the stabilized zirconia is the same as the stabilized zirconia contained in the mixed conductive layer 22 as an oxygen ion conductor (the same kind and amount of stabilizer is used). May be different. When the support 24 is composed of stabilized zirconia, a reaction between the mixed conductive layer 22 and the support 24 (an oxygen ion conductor or an electronic conductor included in the mixed conductive layer 22 and a constituent material of the support 24 This is desirable because the reaction between the two is difficult to proceed. From the viewpoint of suppressing the reaction between the support 24 and the mixed conductive layer 22, the support 24 and the mixed conductive layer 22 are made of the same kind (the same type of stabilizer used) of stabilized zirconia. It is more desirable to configure. Further, when the support 24 is constituted by stabilized zirconia, the difference in the thermal expansion coefficient between the support 24 and the mixed conductive layer 22 can be reduced, so that the oxygen permeation caused by the difference in the thermal expansion coefficient can be reduced. The membrane damage can be suppressed and the durability of the oxygen permeable membrane can be improved. From the viewpoint of improving the strength of the support 24, a configuration using partially stabilized zirconia as the stabilized zirconia is also suitable.

  In order to form the mixed conductive layer 22 on the support 24, for example, in step S110 of FIG. 2, a paste is prepared by adding a solvent to the powder of the oxygen ion conductor and the powder of the electron conductor, and the prepared paste is used. What is necessary is just to apply | coat on the said support body. And what is necessary is just to perform the baking process of step S120, and the process of the heat processing of step S130 on the conditions mentioned already.

  Even with such a configuration, the same effects as those of the first embodiment can be obtained. Further, according to the second embodiment, by using the support 24, the mixed conductive layer 22 can be formed thinner, and the oxygen permeation performance of the oxygen permeable membrane 110 can be improved.

  When the mixed conductive layer 22 is provided on the support 24 as in the present embodiment, the mixed conductive layer 22 is formed on the support 24, and the firing process (step S120) and the heat treatment process (step S130). Will be performed. Therefore, when the heat treatment for recovering oxygen vacancies described above is performed in the absence of chromium (Cr) element, unlike the present embodiment, the above-described heat treatment is performed at the interface between the support 24 and the mixed conductive layer 22. High resistance phase can be formed. In such a case, it is impossible to remove the high resistance phase formed at the interface between the support 24 and the mixed conductive layer 22 by polishing or the like. In the present embodiment, since the heat treatment in step S130 is performed in the presence of the chromium (Cr) element, the formation of a high resistance phase at the interface between the support 24 and the mixed conductive layer 22 can be suppressed. Therefore, the method for producing the oxygen permeable membrane 10 of the present embodiment involving the heat treatment in the presence of chromium (Cr) element is particularly a method for producing an oxygen permeable membrane in which the mixed conductive layer 22 is formed on the support 24. Are better.

  In the second embodiment, the above-described catalyst layer may be provided on at least one surface of the mixed conductive layer 22. That is, a catalyst layer may be provided at the interface where the mixed conductive layer 22 is in contact with the support 24, or a catalyst layer may be provided on the surface of the mixed conductive layer 22 on the side away from the support 24. When the catalyst layer is provided at the interface where the mixed conductive layer 22 is in contact with the support 24, for example, a paste containing the material of the catalyst layer is prepared and applied onto the support 24 and baked. A catalyst layer may be formed. Thereafter, a paste containing the material of the mixed conductive layer may be applied on the formed catalyst layer, and the firing process (step S120) and the heat treatment process (step S130) described above may be performed. When the catalyst layer is provided on the surface of the mixed conductive layer 22 on the side away from the support 24, the step of applying the paste containing the material of the catalyst layer on the mixed conductive layer is the above-described firing step (step S120). Either before or after, or before or after the heat treatment step (step S130). The catalyst layer may be porous to such an extent that oxygen can be supplied to one surface of the mixed conductive layer 22 or oxygen that has passed through the mixed conductive layer 22 can pass.

It is desirable that the support 24 provided in the oxygen permeable membrane 110 does not substantially contain a magnesium (Mg) element. Even if the support 24 contains a magnesium (Mg) element, the effect of suppressing the formation of a high resistance phase (La ₂ Zr ₂ O ₇ ) on the surface of the mixed conductive layer 22 is obtained. However, the oxygen permeation performance of the oxygen permeable membrane 110 can be further enhanced by containing substantially no magnesium (Mg) element. When the support 24 contains a magnesium (Mg) element, the magnesium (Mg) in the support 24 is doped into the B site in the perovskite type (ABO ₃ ) electronic conductor contained in the mixed conductive layer 22, and the B site. Excessive conditions can occur. When the B site is excessive, the electron conduction performance of the electron conductor is reduced (the resistance of the mixed conductive layer 22 is increased), and the oxygen transmission rate in the oxygen permeable film 110 can be reduced.

  Specifically, the support 24 provided in the oxygen permeable membrane 110 does not substantially contain a magnesium (Mg) element. Specifically, the content of the magnesium (Mg) element in the support 24 is 0.1% by mass or less. It is desirable to be. The content of the magnesium (Mg) element in the support 24 can be measured by semi-quantitative analysis (fundamental parameter method) of fluorescent X-ray analysis.

When the support 24 is constituted by using stabilized zirconia, it is desirable that the stabilizer to be dissolved in the stabilized zirconia is a stabilizer different from magnesium oxide (MgO). Specifically, the stabilizer to be dissolved in the stabilized zirconia is at least one kind of stabilizer selected from calcium oxide (CaO), yttrium oxide (Y ₂ O ₃ ), and scandium oxide (Sc ₂ O ₃ ). It is desirable to be an agent. From the viewpoint of suppressing the doping of Mg into the B site of the perovskite type electron conductor contained in the mixed conductive layer 22 described above, the stabilizer in the stabilized zirconia contained in the mixed conductive layer 22 is also magnesium oxide ( Desirably, the stabilizer is different from (MgO).

E. Third embodiment:
In the oxygen permeable membrane 110 shown in FIG. 6, the support 24 may further have catalytic activity. That is, the support 24 has an activity of promoting a reaction (1 / 2O ₂ + 2e ⁻ → O ²⁻ ) that generates oxygen ions from oxygen molecules, and a reaction (O ²⁻ → 1 / 2O ₂ + 2e) that generates oxygen molecules from oxygen ions. ^- ), Or when the apparatus 20 including the oxygen permeable membrane 110 is a reformer, it may have the activity of promoting the above-described reforming reaction. Such a configuration will be described below as a third embodiment.

The support 24 according to the third embodiment can be produced by further mixing a substance having catalytic activity with the same ceramic material as the support 24 according to the second embodiment. As the ceramic material, it is desirable to use stabilized zirconia. In particular, at least one selected from calcium oxide (CaO), yttrium oxide (Y ₂ O ₃ ), and scandium oxide (Sc ₂ O ₃ ) is stabilized. It is desirable to use stabilized zirconia contained as an agent. As the substance having catalytic activity, the substances constituting the catalyst layer described above can be used, and in particular, perovskite-type composite oxides such as lanthanum-iron-based composite oxides and lanthanum-chromium-based composite oxides are used. It is desirable.

  The support 24 of the third embodiment can be produced in the same manner as the support 24 of the second embodiment. For example, when mixing the ceramic raw material powder and the powder of the above-mentioned substance having catalytic activity, a pore-forming agent such as an acrylic resin and a binder may be added, mixed, and fired after molding. The mixing ratio of the ceramic raw material powder and the powder of the substance having catalytic activity may be appropriately set between 1: 9 and 9: 1 by volume ratio.

  Even with such a configuration, the same effects as those of the first embodiment and the second embodiment can be obtained. In addition, according to the third embodiment, the configuration of the oxygen permeable membrane and the method for producing the oxygen permeable membrane can be simplified as compared with the case where a separate catalyst layer is provided between the mixed conductive layer 22 and the support 24. Can do.

F. Variation:
In each of the above embodiments, in order to manufacture an oxygen permeable membrane, an oxygen ion conductor and an electron conductor are mixed to form a mixed conductive layer (first step), and the formed mixed conductive layer is fired ( (2nd process) Then, it heat-processes on the temperature conditions of 1000 degreeC or more in presence of chromium (Cr) element and oxygen (3rd process). On the other hand, you may manufacture an oxygen permeable film by the method which does not accompany a baking process. An example of a method for producing an oxygen permeable film without firing includes a method of forming a mixed conductive layer in which an oxygen ion conductor and an electron conductor are mixed, for example, by thermal spraying. When forming the mixed conductive layer, thermal spraying may be performed in an inert atmosphere. Thereafter, if heat treatment is performed at a temperature of 1000 ° C. or higher in the presence of chromium (Cr) element and oxygen, oxygen deficiency generated in the lanthanum chromite complex oxide in the thermal spraying process is recovered, Similar mixed conductive layers can be obtained. That is, in the X-ray diffraction pattern using CuKα as a radiation source for at least one surface, the integrated intensity ratio of the main peak of La ₂ Zr ₂ O _{7 to} the main peak of stabilized zirconia is 2% or less. A layer can be obtained.

  FIGS. 7 to 9 are explanatory diagrams showing the results of producing 21 types of oxygen permeable membranes of samples 1 to 21 and examining their performances. Below, the structure and manufacturing method of each sample, and the result of having evaluated performance are demonstrated. In FIGS. 7 and 8, the determination for the sample for which good results were obtained for all evaluation items was “◯”.

<Production of each sample>
[Sample 1]
Sample 1 contains scandia-stabilized zirconia (ScSZ) containing scandium (Sc) and cerium (Ce) as an oxygen ion conductor. Also, sample 1, as an electron _conductor, containing _{La 0.8 Sr 0.2 CrO 3-z} . Sample 1 was manufactured according to the manufacturing method of FIG.

As the ScSZ, 10Sc1CeSZ manufactured by Daiichi Rare Element Chemical Industry was used. _{La 0.8 Sr 0.2 CrO 3-z} (LSC) was prepared as follows. As the raw material powder, lanthanum oxide (La ₂ O ₃ , Wako Pure Chemical Industries, purity 99.9%), strontium carbonate (SrCO ₃ , high purity chemical research laboratory, purity 99.9%), and chromium oxide ( Cr ₂ O ₃ , manufactured by High Purity Chemical Laboratory, purity 99.99%) was used. These raw material powders were weighed so that the ratio of the metal element was the composition ratio of the composition formula described above. Then, using a ZrO ₂ ball and a resin pot, wet mixing and grinding were performed for 15 hours on these raw material powders together with ethanol. Thereafter, the bath is dried in a hot bath to remove ethanol, and the resulting mixed powder is heated to 1500 ° C. at a temperature rising rate of 15 ° C./min, calcined at 1500 ° C. for 24 hours, and calcined LSC Of powder was obtained.

Further, a dispersant and a binder were added to the calcined powder, and wet mixed pulverization was performed under the same conditions as described above using ethanol, followed by drying to obtain a powder containing the calcined powder. Thereafter, the powder containing the calcined powder was mixed with ScSZ so that the mixing ratio of LSC in the mixture of ScSZ and LSC was 20 mol%, thereby obtaining a mixed powder of ScSZ and LSC. The mixed powder was compacted at 50 MPa with a hydraulic press and fired at 1500 ° C. for 24 hours in nitrogen (N ₂ ) as an inert atmosphere (step S120). After firing, the obtained sintered body was polished to a thickness of 0.6 mm and subjected to heat treatment.

The heat treatment (step S130) employs the method shown in FIG. Specifically, using an alumina crucible, the above sintered body is embedded in a powder (mixed powder of ScSz and LSC) having the same composition as the mixed conductive layer of the oxygen permeable membrane to be produced, and in the atmosphere at 1500 ° C. for 12 hours. Heat treatment was performed to obtain an oxygen permeable membrane of Sample 1. In FIG. 7, as a heat treatment method, a method of burying a sintered body in a powder having the same composition as that of the mixed conductive layer of the oxygen permeable membrane is described as “oxygen permeable membrane burying”. When obtaining the above-mentioned mixed powder, it is assumed that La _0.8 Sr _0.2 CrO _3-z is formed at 100% efficiency in the calcined powder, and the amount of powder including the calcined powder is mixed. It was set. Further, no further polishing is performed after the heat treatment.

[Samples 2 to 5]
Samples 2 to 5 contain the same ScSZ as the sample 1 as an oxygen ion conductor and the same LSC as the sample 1 as an electron conductor. Samples 2 to 5 were produced according to the production method of FIG.

The manufacturing methods of Samples 2 to 5 are different from the manufacturing method of Sample 1 in terms of the firing conditions in Step S120 or the heat treatment (annealing) conditions in Step S130. Sample 2 differs in that the heat treatment conditions were 24 hours at 1400 ° C. Sample 3 differs in that the heat treatment conditions were 48 hours at 1300 ° C. Sample 4 differs in that the firing was performed in argon (Ar) rather than in nitrogen (N ₂ ). Sample 5 is different in that, in the heat treatment, the sintered body was buried in the LSC powder, and the heat treatment was performed at 1400 ° C. for 24 hours. Oxygen permeable membranes of Samples 2 to 5 were obtained by these methods.

[Samples 6 and 7]
Samples 6 and 7 contain the same ScSZ as the sample 1 as an oxygen ion conductor and the same LSC as the sample 1 as an electron conductor. Samples 6 and 7 differ from sample 1 in the heat treatment method.

In the manufacturing methods of Samples 6 and 7, the process until the production of the sintered body to be subjected to the heat treatment was the same as Sample 1. When samples 6 and 7 were manufactured, the method shown in FIG. 4 was used for the heat treatment. Specifically, at the time of producing the sample 6, a powder of chromium (III) (Cr ₂ O ₃ ) is disposed as a powder 46 containing chromium (Cr) element in an alumina crucible, and platinum (Pt) is disposed thereon. ) Made mesh 44, the sintered body (mixed conductive layer 12) was placed on the mesh 44, and the sintered body and the powder 46 were separated. Then, a heat treatment was performed in the atmosphere at 1400 ° C. for 24 hours to obtain an oxygen permeable film of Sample 6. Sample 7 was produced in the same manner as Sample 6, except that LSC powder was used as powder 46. In FIG. 7, the heating method using the method shown in FIG. 4 and using Cr ₂ O ₃ powder as the powder 46 is described as “Cr ₂ O ₃ non-contact”, and the method shown in FIG. The heating method using LSC powder is described as “LSC non-contact”.

[Sample 8]
Sample 8 contains the same ScSZ as sample 1 as an oxygen ion conductor, and La _0.8 Ca _0.2 CrO _3-z as an electron conductor.

_{La 0.8 Ca 0.2 CrO 3-z} (LCC) is the raw material powder as a calcium carbonate (CaCO _3, manufactured by Kojundo Chemical Laboratory, 99.9% purity), strontium carbonate (SrCO _3, high purity Chemistry The powder was calcined under the same conditions as those of the LSC described above, using a powder of a laboratory product, purity 99.9%), and chromium oxide (Cr ₂ O ₃ , manufactured by High Purity Chemical Laboratory, purity 99.99%). As produced. Using such a calcined powder, a sintered body to be subjected to heat treatment was produced by the same method as Sample 1. The heat treatment was performed using the method shown in FIG. 4 under the same conditions as in sample 6, and an oxygen permeable membrane of sample 8 was obtained.

[Sample 9]
Sample 9 contains yttria-stabilized zirconia (YSZ) as an oxygen ion conductor and contains LSC similar to sample 1 as an electron conductor.

As YSZ, a sintered body to be subjected to heat treatment was produced by the same method as Sample 1 using TZ-8Y powder (Y ₂ O ₃ : 8 mol%) manufactured by Tosoh Corporation. In sample 9, after the firing in step S120, the obtained sintered body was polished to a thickness of 0.2 mm, which is one third of sample 1, and subjected to heat treatment. This is intended to suppress the influence that the oxygen permeation performance of the oxygen permeable membrane deteriorates due to the constituent material because the ionic conductivity of YSZ is about one third of the ionic conductivity of ScSZ. . The heat treatment was performed using the method shown in FIG. 4 under the same conditions as in sample 6, and an oxygen permeable membrane of sample 9 was obtained.

[Sample 10]
Sample 10 contains the same YSZ as sample 9 as an oxygen ion conductor, and the same LCC as sample 8 as an electron conductor. Sample 10 was produced in the same manner as Sample 2, except that the types of oxygen ion conductor and electron conductor used were different and that the thickness of the sintered body was 0.2 mm by polishing after firing. . Thereby, an oxygen permeable membrane of Sample 10 was obtained.

[Sample 11]
Sample 11 contains ScSZ similar to sample 1 as an oxygen ion conductor, and LSC similar to sample 1 as an electron conductor. Sample 11 was manufactured by the same method as Sample 1 except that heat treatment was performed in the air without the presence of a substance containing chromium (Cr) element. As a result, an oxygen permeable membrane of Sample 11 was obtained.

[Sample 12]
Sample 12 contains the same ScSZ as sample 1 as an oxygen ion conductor and the same LSC as sample 1 as an electron conductor. The manufacturing method of sample 12 is different from the manufacturing method of sample 1 in that the heat treatment after firing (step S130) was not performed. As a result, an oxygen permeable membrane of Sample 12 was obtained.

[Sample 13]
Sample 13 contains ScSZ similar to Sample 1 as an oxygen ion conductor, and LSC similar to Sample 1 as an electron conductor. The method for producing Sample 13 is different from the method for producing Sample 1 in that the firing (Step S120) was performed in the air and the heat treatment after the firing (Step S130) was not performed. As a result, an oxygen permeable membrane of Sample 13 was obtained.

[Sample 14]
Sample 14 contains the same ScSZ as sample 1 as an oxygen ion conductor and the same LSC as sample 1 as an electron conductor. Sample 14 has the configuration shown in FIG. 6 and is different from sample 1 in that a mixed conductive layer is formed on a support. The support provided in sample 14 was formed of calcia stabilized zirconia (CSZ).

  The support provided in the sample 14 was produced as follows. A CSZ powder (CaO: 8 mol%) manufactured by Daiichi Rare Element Chemical Co., Ltd. is used as the CSZ, and an acrylic resin pore-forming agent and an ethyl cellulose binder are added and mixed, and the molding pressure is 50 MPa. Compacted into pellets. The pellets were heated at a heating rate of 2 ° C./min and degreased at 400 ° C. for 1 hour. Thereafter, the temperature was raised at a rate of 5 ° C./min and calcined at 1300 ° C. for 24 hours to obtain a porous body having a thickness of 1 mm and a porosity of 45%. This porous body was adjusted to a thickness of 0.4 mm by polishing and used as a support.

The mixed conductive layer was formed on the support as follows. First, a solvent (mixture of butyl diglycol and ethyl cellulose) was added to the same ScSZ powder and LSC powder as used in Sample 1 to prepare a mixed conductive layer paste. Further, a platinum (Pt) paste was applied to the above support by 100 μm using a screen mask, heated at a heating rate of 5 ° C./min and baked at 1000 ° C. for 1 hour to form a catalyst layer. Thereafter, the above mixed conductive layer paste was printed on the catalyst layer to a thickness of 100 μm using a screen mask. In the same manner as Sample 1, it was calcined for 24 hours at 1500 ° C. in a nitrogen _{(N 2)} in (step S120). After firing, 100 μm of platinum (Pt) paste was applied onto the mixed conductive layer using a screen mask and fired at 1000 ° C. for 1 hour to form a catalyst layer. Thus, the laminated body provided in order of a support body, a catalyst layer, a mixed conduction layer, and a catalyst layer is heat-processed by the same method (oxygen permeable membrane substrate embedding) as the sample 1 (step S130), and a sample 14 oxygen permeable membranes were obtained.

[Sample 15]
Sample 15 contains ScSZ similar to Sample 1 as an oxygen ion conductor, and LSC similar to Sample 1 as an electron conductor. Sample 15 has the configuration shown in FIG. 6 as with sample 14, and was prepared in the same manner as sample 14 except that the configuration of the support was different.

The support provided in the sample 15 contains La _0.8 Sr _0.2 Cr _0.85 Ni _0.15 O ₃ having catalytic activity in addition to CSZ. Such a support is prepared by mixing La _0.8 Sr _0.2 Cr _0.85 Ni _0.15 O ₃ powder in a volume ratio of 50% with respect to CSZ powder, and forming pores of acrylic resin. An agent and an ethyl cellulose binder were further added and mixed, and the same procedure as for the sample 14 support was performed. Then, in the same manner as the sample 14, the process up to the heat treatment step of step S130 is performed, and the oxygen permeable membrane of the sample 15 which is a laminated body provided in the order of the support, the catalyst layer, the mixed conductive layer, and the catalyst layer is obtained. It was.

[Sample 16]
Sample 16 contains the same ScSZ as sample 1 as an oxygen ion conductor and the same LSC as sample 1 as an electron conductor. Sample 16 was manufactured in the same manner as Sample 14 except that the heat treatment process of Step S130 was performed in the air without the presence of a substance containing chromium (Cr) element.

[Sample 17]
Sample 17 contains ScSZ similar to sample 1 as an oxygen ion conductor, and LSC similar to sample 1 as an electron conductor. Sample 17 was manufactured in the same manner as Sample 1 except that the thickness of the sintered body was 0.1 mm by polishing after firing. As a result, an oxygen permeable membrane of Sample 17 was obtained.

[Sample 18]
Sample 18 contains ScSZ similar to sample 1 as an oxygen ion conductor, and LSC similar to sample 1 as an electron conductor. The sample 18 has the configuration shown in FIG. 6, and a mixed conductive layer is formed on a support. The support provided in the sample 18 was formed of magnesium oxide (MgO).

  The support provided for the sample 18 was prepared in the same manner as the support for the sample 14 by using magnesium oxide (MgO) powder (lightly burned magnesium oxide manufactured by Tateho Chemical Industries) instead of the CSZ powder. Moreover, it produced similarly to the oxygen permeable film of the sample 14 except the point which did not provide the catalyst layer between the support body and the mixed conductive layer. As a result, an oxygen permeable membrane of Sample 18 which is a laminate provided in the order of the support, the mixed conductive layer, and the catalyst layer was obtained.

[Samples 19 to 21]
Samples 19 to 21 contain the same ScSZ as the sample 1 as an oxygen ion conductor and the same LSC as the sample 1 as an electron conductor. Samples 19 to 21 have the configuration shown in FIG. 6, and a mixed conductive layer is formed on a support. The support provided for the sample 19 was formed by CSZ, the support provided for the sample 20 was formed by YSZ, and the support provided by the sample 21 was formed by ScSZ.

The support provided for the sample 19 was produced in the same manner as the support provided for the sample 14. The support provided in the sample 20 is the same as the support of the sample 14 by using TZ-8Y powder (Y ₂ O ₃ : 8 mol%) manufactured by Tosoh Corporation, which is YSZ powder, instead of CSZ powder. Produced. In addition, the support provided in the sample 21 was prepared in the same manner as the support of the sample 14 by using 10Sc1CeSZ manufactured by 1st Rare Element Chemical Industry, which is ScSZ powder, instead of CSZ powder. The oxygen permeable membranes of Samples 19 to 21 were prepared in the same manner as the oxygen permeable membrane of Sample 14 except that the catalyst layer was not provided between the support and the mixed conductive layer. This obtained the oxygen permeable film of the samples 19-21 which are the laminated bodies provided in order of the support body, the mixed conductive layer, and the catalyst layer.

<Measurement of oxygen transmission rate>
FIG. 10 is an explanatory diagram showing a schematic configuration of the measurement apparatus 30 used for measuring the oxygen permeation characteristics of each sample. The measuring device 30 includes two transparent quartz tubes 31 and 32, alumina tubes 33 and 34, an electric furnace 35, and a thermocouple 36. Two transparent quartz tubes 31 and 32 are arranged one above the other and each sample is sandwiched between them to perform measurement. When the transparent quartz tube 31 and the sample S are joined, a gold thin film ring having an inner diameter of 10 mm is placed on the sample S, the transparent quartz tube 31 is pressed on the gold ring, and the temperature is raised to 1050 ° C. to raise the gold. Was softened to ensure gas sealability. Alumina tubes 33 and 34 are disposed inside the transparent quartz tubes 31 and 32. In the measurement of the oxygen permeation characteristics, a 99.9% hydrogen-containing gas was passed through the alumina tube 33 and air was passed through the alumina tube 34. The transparent quartz tubes 31 and 32 are arranged in the electric furnace 35, and the sample S sandwiched between the transparent quartz tubes 31 and 32 is arranged in a soaking portion in the electric furnace 35. Further, a thermocouple 36 was disposed in the alumina tube 34 so as to reach the vicinity of the sample S in order to measure the sample temperature. When measuring the oxygen permeation characteristics, heating with the electric furnace 35 was performed so that the sample temperature was maintained at 1000 ° C. When each sample is arranged in the measuring apparatus 30, air is supplied to the surface on the side having no support, and 99.9% on the surface on the side having the support. Each sample was placed so that a hydrogen-containing gas was supplied.

In each sample arranged in the measurement apparatus 30 described above, when oxygen passes through the sample from the air side (transparent quartz tube 32 side) to the 99.9% hydrogen-containing gas side (transparent quartz tube 31 side), On the hydrogen-containing gas side, water (water vapor) is generated using the permeated oxygen. Since all the water vapor in the hydrogen-containing gas discharged from the measuring device 30 is considered to be derived from permeated oxygen, the water vapor concentration in the discharged hydrogen-containing gas is determined using a specular dew point meter (manufactured by Toyo Technica). The amount of oxygen that was measured and permeated was calculated. Based on the amount of permeated oxygen calculated in this way and the permeation area of the sample, the oxygen permeation flow velocity density j (0 ₂ ) was calculated. At this time, the 99.9% hydrogen-containing gas amount supplied through the alumina tube 33 was 200 mL / min, and the air amount supplied through the alumina tube 34 was 300 mL / min using a mass flow controller.

  When measuring the oxygen permeation rate for Samples 1 to 13, platinum (Pt) paste was applied to both surfaces of each sample and baked at 1000 ° C. in the air for 1 hour to form a catalyst layer, and then the measurement was performed. It was.

<Measurement of relative density>
As described above, the relative density represents the ratio of the actually measured density of the sample to the theoretical density of the sample. The actual density of each sample was measured by the Archimedes method. Specifically, water is used as the liquid, each sample is weighed in water and in air using an electronic balance (manufactured by Shimadzu Corporation, AW220), and the specific gravity of water at the temperature at the time of measurement is used. The density of each sample was calculated. In addition, the measurement of the relative density was measured about the samples 1-13 which do not have a support body. Prior to the measurement of the relative density, each sample was washed with pure water, and the powder adhering to the surface of each sample was removed in the heat treatment step.

<Evaluation of presence or absence of high resistance phase generation>
The evaluation of the presence or absence of the production of La ₂ Zr ₂ O ₇ , which is a high resistance phase in each sample, was performed using an X-ray diffraction method (CuKα) on the sample surface before the oxygen transmission rate evaluation using MINIFlex manufactured by Rigaku Corporation. Was analyzed.

FIG. 11 shows an X-ray diffraction pattern of Sample 11 as an example, and FIG. 12 shows an X-ray diffraction pattern of Sample 1 as an example. When La ₂ O ₃ is liberated and reacts with zirconia (Zr) in the heat treatment step (step S130), it occurs in the X-ray diffraction pattern in addition to the peaks corresponding to the oxygen ion conductor and the electron conductor. A peak corresponding to the material La ₂ Zr ₂ O ₇ occurs. Therefore, based on the X-ray diffraction pattern, the integral intensity ratio of the X-ray diffraction peak of La ₂ Zr ₂ O ₇ generated by the reaction between the oxygen ion conductor and the electron conductor was determined. The integrated intensity ratio (hereinafter also simply referred to as the integrated intensity ratio) of the X-ray diffraction peak of the substance generated by the above reaction is given by the following equation (5).

Integral intensity ratio = b1 / a1 (5)

Here, a1 is the integrated intensity of the X-ray diffraction peak derived from stabilized zirconia, and b1 is the integrated intensity of the X-ray diffraction peak derived from La ₂ Zr ₂ O ₇ . The X-ray diffraction peak derived from each compound appears for each crystal plane of each compound, and the integrated intensity of the X-ray diffraction peak of each compound was determined for the strongest peak among the peaks derived from each compound. . As described above, the strongest peak among the peaks existing in the vicinity of 2θ = 28 to 29 ° by X-ray diffraction was defined as the main peak of La ₂ Zr ₂ O ₇ .

The evaluation of the product the presence of _La 2 _Zr 2 _{O 7} for samples 1-13 and 17, was carried out prior to the measurement of the oxygen transmission rate with formation of the catalyst layer. For samples 14 to 16 and 18 to 21 provided with a support and a catalyst layer, the support and the catalyst layer were removed after the measurement of the oxygen transmission rate to expose the surface of the mixed conductive layer. The presence or absence of production of La ₂ Zr ₂ O ₇ was evaluated. 7 to 9, “None” for the generation of La ₂ Zr ₂ O ₇ means that the integrated intensity ratio given by the above-described equation (5) is 2% or less, and La ₂ Zr ₂ O “Presence” of the generation of ₇ means that the integrated intensity ratio exceeds 2%.

  The method for exposing the surface of the mixed conductive layer is as follows. First, the support portion was removed by polishing. Thereafter, the catalyst layer was lightly polished and removed so as not to remove the interface with the mixed conductive layer. The catalyst layer component (Pt) remaining on the surface of the mixed conductive layer was dissolved and removed using aqua regia.

<Evaluation of reactivity between support and mixed conductive layer>
For samples 18 to 21, the reactivity between the oxide used as the support and the mixed conductive layer was evaluated. A specific method is as follows. In order to evaluate the reactivity between the support and the mixed conductive layer, each sample is composed of the constituent material of each support separately from the oxygen permeable membrane described above in which the mixed conductive layer is formed on the support. The powder and the powder made of the constituent material of the mixed conductive layer were mixed by 50 wt% and pressed to form pellets (mixed pellets). And these mixed pellets were baked on the conditions of the baking process (step S120) about each sample mentioned above. The obtained sintered body was pulverized using an agate mortar and analyzed by a powder X-ray diffraction method (CuKα). As described above, by using the mixed pellets, the constituent material of the support and the constituent material of the mixed conductive layer were sufficiently brought into contact with each other and baked, thereby making it easy to detect the reactivity of both.

  FIG. 13 shows the analysis results for samples 17, 18, and 21 as an example. In FIG. 13, the upper part shows the analysis result of the sample 18, the middle part shows the sample 21, and the lower part shows the analysis result of the sample 17. In FIG. 13, the state in which the peak of the LSC contained in the mixed conductive layer in Sample 18 is shifted is indicated by an arrow. Such peak shift (shift to the lower angle side of the peak) is caused by excessive doping of elements in the Cr site (the lanthanum chromite complex oxide contained in the mixed conductive layer reacts with the constituent material of the support). ), Indicating that the grid is getting larger. Therefore, the reactivity between the support and the mixed conductive layer was evaluated based on the presence or absence of a peak shift toward the low angle side of LSC.

<Measurement of thermal expansion coefficient>
In relation to Samples 17 to 21, a comparison was made between the thermal expansion coefficient of the mixed conductive layer and the thermal expansion coefficient of each support. That is, the thermal expansion coefficient of the mixed conductive layer containing ScSz and LSC in Samples 17 to 21 and the thermal expansion coefficients of MgO, CSZ, YSZ, and ScSZ used as the support were measured. In FIG. 9, the measurement result of the thermal expansion coefficient of the mixed conductive layer is shown in the column of the sample 17 having no support, and the thermal expansion coefficients of MgO, CSZ, YSZ, and ScSZ are sequentially shown in the columns of the samples 18 to 21, respectively. The measurement results were shown.

  Each thermal expansion coefficient was measured as follows. In order to measure the thermal expansion coefficient of the mixed conductive layer corresponding to Sample 17, pellets were obtained by press molding using a mixed powder having the same composition (ScSZ + LSC) as the mixed conductive layer of Sample 17. Further, corresponding to each of samples 18 to 21, pellets were obtained by press molding using the same oxide (MgO, CSZ, YSZ, ScSZ) powder as the constituent material of the support of each sample. These pellets were fired at 1500 ° C. and then molded into a 5 mm × 5 mm × 20 mm cuboid by polishing. Each rectangular parallelepiped sample was heated to 1350 ° C. at a temperature increase rate of 5 ° C./min. At that time, the thermal expansion coefficient was calculated by measuring the expansion and contraction of the rectangular parallelepiped sample while raising the temperature.

The linear thermal expansion coefficient α (unit: [1 / K]) is obtained by the following equation (6).
α = ΔL / (L0 · ΔT) (6)
L0: Sample length at room temperature (30 ° C) (value entered during measurement)
ΔL: Elongation between temperatures to be obtained (Here, since α of 30 ° C.-1000 ° C. was obtained on the basis of 30 ° C., ΔL = (L at 1000 ° C.) − (L at 30 ° C.))
ΔT: temperature difference between temperatures to be obtained (ΔT = 1000 ° C.-30 ° C.)

From FIG. 7, it was found that all samples fired in an inert atmosphere such as N ₂ or Ar had a relative density of 95% or more, and a dense mixed conductive layer was obtained. This is because the oxygen is not coexist in the firing atmosphere, mixed conducting layer does not generated lanthanum chromite-based composite oxide from volatile CrO ₃ which comprises, as an electron conductor, as a result, inhibition of sintering by CrO ₃ This is probably because it did not happen. On the other hand, the sample 13 fired at 1500 ° C. in the atmosphere had a relative density of 90% or less, and a sufficiently high relative density was not obtained. From the above, it was confirmed that firing in an inert atmosphere is effective in order to obtain a high firing density. Sample 13 with insufficient relative density had a low oxygen permeation rate due to the fact that cross leak was observed and the oxygen partial pressure difference between both surfaces of the oxygen permeable membrane was reduced. .

Further, as shown in FIG. 7, sample 11 was performed in the atmosphere heat treatment step S130, the integrated intensity ratio exceeds the _{2% (La 2 Zr 2 O} 7 was produced). In such sample 11, the oxygen transmission rate was below the detection limit. On the other hand, samples 1 to 10 all had an integrated intensity ratio of 2% or less, indicating a high oxygen transmission rate. Moreover, in the sample 12 which was not heat-treated after baking in the inert atmosphere (N2), the oxygen transmission rate was significantly low. This is considered to be due to oxygen deficiency generated during firing in the lanthanum chromite complex oxide in the mixed conductive layer.

  From the above, firing in an inert atmosphere is important to obtain a dense mixed conductive layer, and oxygen deficiency generated in the lanthanum chromite complex oxide is recovered by firing in an inert atmosphere. Further, it was confirmed that heat treatment in the presence of a chromium (Cr) element and oxygen is important for suppressing the formation of a high resistance phase.

As shown in FIG. 8, the same result was obtained when the mixed conductive layer was formed on the support. That is, in the sample 16 subjected to the heat treatment in the atmosphere, La ₂ Zr ₂ O ₇ was generated between the catalyst layer and any side of the mixed conductive layer. As a result, in Sample 16, the oxygen transmission rate was below the detection limit. In contrast, Samples 14 and 15 that were heat-treated in the presence of chromium (Cr) element and oxygen did not generate La ₂ Zr ₂ O _{7 on} the surface of the mixed conductive layer, and showed a high value as the oxygen transmission rate. It was. Samples 14 and 15 were superior in oxygen permeation rate even when compared with Samples 1 to 10 in FIG. 7 because it was possible to reduce the thickness of the mixed conductive layer by forming the mixed conductive layer on the support. .

As shown in FIG. 9, similar results were obtained even when the support was formed using an oxide other than CSZ. That is, by performing the heat treatment in the presence of the chromium (Cr) element and oxygen, the generation of the high resistance phase La ₂ Zr ₂ O ₇ due to the heat treatment could be suppressed. In Sample 18 using the support containing MgO, a peak shift toward the low-angle side of LSC was observed. From the viewpoint of the reactivity between the support and the mixed conductive layer, the support was Mg. It has been confirmed that it is desirable not to contain substantially. Further, as shown in FIG. 9, the thermal expansion coefficients of CSZ, YSZ, and ScSZ were closer to the thermal expansion coefficient of the mixed conductive layer than the thermal expansion coefficient of MgO. Therefore, it has been confirmed that in the case where the support is constituted by stabilized zirconia, it is possible to suppress inconvenience due to the difference in thermal expansion coefficient between the support and the mixed conductive layer.

  The present invention is not limited to the above-described embodiments, examples, and modifications, and can be realized with various configurations without departing from the spirit thereof. For example, the technical features in the embodiments, examples, and modifications corresponding to the technical features in each embodiment described in the summary section of the invention are to solve some or all of the above-described problems, or In order to achieve part or all of the above effects, replacement or combination can be performed as appropriate. Further, if the technical feature is not described as essential in the present specification, it can be deleted as appropriate.

DESCRIPTION OF SYMBOLS 10,110 ... Oxygen permeable film 12 ... Mixed conductive layer 16 ... Reformation raw material flow path 18 ... Air flow path 20 ... Apparatus 22 ... Mixed conductive layer 24 ... Support body 30 ... Measuring apparatus 31, 32 ... Transparent quartz tube 33, 34 ... Alumina tube 35 ... Electric furnace 36 ... Thermocouple 42 ... Cover body 44 ... Mesh 46 ... Powder 48 ... Powder

Claims (7)

An oxygen permeable membrane comprising a mixed conductive layer comprising an oxygen ion conductor composed of stabilized zirconia and an electronic conductor composed of a lanthanum chromite complex oxide,
The lanthanum chromite complex oxide has a composition formula La _1-x M _x CrO _3-z (wherein M is calcium (Ca) or strontium (Sr), and 0 <x ≦ 0.3). z <3)),
The oxygen permeable membrane further comprises a support,
The mixed conductive layer Rutotomoni formed on the support, and a relative density of 95% or more,
The integrated intensity of the main peak of La ₂ Zr ₂ O ₇ with respect to the main peak of the stabilized zirconia in the X-ray diffraction pattern using CuKα as the radiation source on the surface of the mixed conductive layer on which the support is disposed An oxygen permeable membrane characterized in that the ratio is 2% or less. The oxygen permeable membrane according to claim 1,
The support is made of magnesium (Mg), calcium (Ca), aluminum (Al), zirconium (Zr), hafnium (Hf), titanium (Ti), yttrium (Y), scandium (Sc), and chromium (Cr). An oxide of a selected element that is one or more elements selected from the group consisting of:
50% by mass or more of the metal element contained in the oxide constituting the support is the selective element. The oxygen permeable membrane according to claim 1,
The oxygen permeable membrane is formed on the support having a magnesium (Mg) element content of 0.1% by mass or less. The oxygen permeable membrane according to any one of claims 1 to 3,
The support comprises stabilized zirconia and / or partially stabilized zirconia;
The oxygen permeable membrane, wherein the stabilizer contained in the stabilized zirconia and / or partially stabilized zirconia included in the support is a stabilizer different from magnesium oxide (MgO). The oxygen permeable membrane according to claim 4,
The stabilizer contained in the stabilized zirconia and / or partially stabilized zirconia included in the support is selected from calcium oxide (CaO), yttrium oxide (Y ₂ O ₃ ), and scandium oxide (Sc ₂ O ₃ ). An oxygen permeable membrane characterized by being at least one stabilizer. The oxygen permeable membrane according to any one of claims 1 to 5, further comprising:
A catalyst layer having an activity of promoting a reaction of ionizing oxygen molecules or a reaction of generating oxygen molecules from oxygen ions;
The oxygen permeable membrane is formed on the support through the catalyst layer. The oxygen permeable membrane according to any one of claims 1 to 6,
The oxygen-permeable membrane, wherein the support has an activity of promoting a reaction of ionizing oxygen molecules or a reaction of generating oxygen molecules from oxygen ions.

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