JP4808526B2 - Composite structure, method for producing composite structure, membrane oxygen separator, and membrane reactor - Google Patents

Description

  The present invention relates to a composite structure in which a mixed conductive solid electrolyte ceramic having both oxygen ion conductivity and electronic conductivity and a metal member are joined, and a method for manufacturing the same. This composite structure is suitable for application to membrane oxygen separation and membrane reactors.

  Typical examples of using mixed conductive solid electrolyte ceramics having both oxygen ion conductivity and electron conductivity include membrane oxygen separation and membrane reactors.

  Membrane oxygen separation utilizes a phenomenon in which oxygen ions move in a solid electrolyte using a difference in oxygen partial pressure as a driving force. For example, high-pressure oxygen-containing gas (air or the like) can be supplied to one side of the solid electrolyte, and normal-pressure oxygen can be obtained from the opposite side. In this case, mixed conductive ceramics are used, and electrons move simultaneously with the movement of oxygen ions to achieve charge balance, eliminating the need for an external circuit.

  The membrane reactor supplies a hydrocarbon gas and an oxygen-containing gas (for example, air) with a solid electrolyte interposed therebetween, and partially oxidizes the hydrocarbon gas to convert it into hydrogen or the like. In this case as well, since mixed conductive ceramics are used, electrons move simultaneously with the movement of oxygen ions to achieve a charge balance.

  In any case, the structure is such that different gas species are isolated by solid electrolyte ceramics, and the apparatus main body is made of metal, so that the solid electrolyte ceramics is surely joined to a metal member somewhere. In addition, if there is a gas leak at the junction, the separation of different gases becomes incomplete, leading to a decrease in the purity of the separated oxygen in the membrane oxygen separation and a decrease in the conversion efficiency in the membrane reactor. Therefore, it is necessary to provide a sufficient gas sealing property as well as a high bonding strength at the bonding site between the solid electrolyte ceramic and the metal member. In addition, since the high temperature of 700 ° C. or higher is necessary for oxygen ions to move within the solid electrolyte ceramics at a level that can be industrially used, the above-described gas sealing property must be realized at a high temperature.

  In addition, since such a bonded body is exposed to a wide temperature range from room temperature to high temperature, stress generation based on the difference in thermal expansion concentrates on the bonded portion, fragile ceramics are destroyed, and the interface between the ceramic and metal bonding material In this case, it is necessary to solve the problem that peeling occurs and gas sealing performance is impaired. Furthermore, considering long-term use at high temperatures, diffusion between solids occurs easily, so the problem of deterioration in reliability due to structural changes at the bonding interface must be solved.

  While high-level joining techniques for solving many problems are required in this way, many techniques using glass as a sealing material have been reported in the past (for example, see Patent Documents 1 to 3). These make use of the property of glass that softens in a high temperature region close to the operating temperature, and realizes high temperature sealing performance based on a concept similar to a liquid seal. However, the thermal expansion coefficient of silica, which is the main component of glass, is extremely low compared to that of solid electrolyte ceramics, and it is sufficient in terms of reliability, such as the sealing performance being impaired by the addition of thermal history. Absent. Further, it has not been sufficient for the problem that the solid electrolyte is deteriorated due to the reaction between silica and the solid electrolyte caused by the operation at a high temperature for a long time.

  Attempts have been reported to increase the reliability by bringing the thermal expansion coefficient closer to that of the solid electrolyte. For example, Patent Documents 4 and 5 disclose a technique using a composite of glass and ceramics as a sealing material. However, even in this case, it was not sufficient to prevent the deterioration of the solid electrolyte due to the reaction with silica.

  In addition, by using aluminum as a sealing material, only the surface is oxidized to realize the bonding strength with ceramics, and the stress generation based on the difference in thermal expansion is suppressed by utilizing the softening phenomenon of aluminum as a base material at a high temperature. Is disclosed in Patent Document 6. However, there has been a problem in terms of reliability when used for a long time at a temperature exceeding 660 ° C., which is the melting point of aluminum.

JP 2004-119161 A JP 2004-227848 A JP-A-5-29010 JP 2001-135327 A Japanese Patent Laid-Open No. 10-32244 Japanese Patent Laid-Open No. 9-231987

  As described above, the conventional technique has not realized sufficiently reliable bonding. This is because when dissimilar materials such as ceramics and metal members are joined and they are to be used at high temperatures, it is difficult to avoid stress generation due to thermal expansion differences over a wide temperature range from room temperature to high temperature regions. This is because the above-mentioned situation has a background, and accompanying this, problems such as destruction of ceramics in the vicinity of the bonding interface, occurrence of peeling at the bonding interface, and deterioration of gas sealing performance have occurred.

  What makes it difficult to solve the problem is that these two problems are related to each other. For example, in order to avoid peeling at the interface, if the adhesiveness of the sealing material for bonding represented by silver brazing is improved to the ceramic, the sealing material is likely to react with the ceramic, and the ceramic is destroyed near the bonding interface. Is likely to occur. On the other hand, in order to avoid destruction of ceramics in the vicinity of the bonding interface, in the case of silver brazing, it is effective to reduce the amount of components other than silver in the brazing material. As a result, the reaction of the sealing material with the ceramic is reduced, the invasion of the sealing material into the ceramic is not observed, and the ceramic is not destroyed. On the other hand, however, the adhesion of the sealing material to the ceramic is lowered, and this time, the joining interface is liable to peel off. Thus, the solution to the two problems of the prior art was in a dilemma.

  SUMMARY OF THE INVENTION In view of the above-described problems, an object of the present invention is to provide a sufficiently reliable composite structure and a method for manufacturing the same, even when stress is generated based on a difference in thermal expansion that is considered inevitable.

The composite structure of the present invention is as follows.
(1) A composite structure in which solid electrolyte ceramics and a metal member are joined by silver brazing, and after forming a metal plating layer on at least a surface of the solid electrolyte ceramics to be joined by silver brazing, the metal plating A metal paste coating layer containing silver and copper is formed on the surface of the layer, and further, the solid electrolyte ceramic and the metal member are joined by silver brazing via the metal paste coating layer. A composite structure.
(2) The composite according to (1), wherein the metal plating layer includes a plurality of metal plating layers, and at least one of the metal plating layers is gold or an alloy plating layer containing gold. Structure.
(3) The composite according to (1), wherein the metal plating layer includes a plurality of metal plating layers, and at least one of the metal plating layers is silver or an alloy plating layer containing silver. Structure.
(4) The metal plating layer includes a plurality of metal plating layers, and the first plating layer in contact with the solid electrolyte ceramics includes one or a combination of two or more selected from the group consisting of nickel, cobalt, and chromium. The composite structure according to any one of (1) to (3), wherein
(5) The composite structure according to any one of (1) to (4), wherein the entire thickness of the metal plating layer is 0.02 μm or more and 5 μm or less.
(6) Copper contained in the metal paste coating layer is added to the metal paste as one or both of metal copper powder and silver copper alloy powder, and the copper content is the metal paste coating layer. It is 0.1 mass% or more and 20 mass% or less with respect to silver in the inside, The composite structure as described in (1) characterized by the above-mentioned.
(7) The coating amount of the metal paste coating layer is 0.001 g / cm ² or more and 0.1 g / cm ² or less per unit area in terms of the mass of silver in the metal paste coating layer (1) Or a composite structure according to (6).
(8) The composite structure according to (1), wherein the silver solder contains 90% by mass or more of silver as a metal component.
(9) The composite structure according to (1), wherein the silver solder contains only silver as a metal component.

The membrane oxygen separator of the present invention is as follows.
(10) A membrane-type oxygen separator comprising the composite structure according to any one of (1) to (9).

The membrane reactor of the present invention is as follows.
(11) A membrane reactor comprising the composite structure according to any one of (1) to (9).

The manufacturing method of the composite structure of the present invention is as follows.
(12) The method for manufacturing a composite structure according to any one of (1) to (9), wherein a metal paste coating layer is formed in advance on a joining surface of a solid electrolyte ceramic, and then the metal paste A composite structure characterized in that a silver brazing member is disposed between the coating layer portion and the metal member, and the solid electrolyte ceramic and the metal member are joined by silver brazing by heating above the melting point of the silver brazing. Body manufacturing method.
(13) The method for producing a composite structure according to any one of (1) to (9), wherein one or more metal plating layers are formed on a joining surface of a solid electrolyte ceramic, and the metal After forming a metal paste coating layer on the surface of the plating layer, a silver brazing member is disposed between the metal paste coating layer portion and the metal member, and heated to the melting point of the silver brazing or above, the solid electrolyte A method for manufacturing a composite structure, comprising: bonding a ceramic and the metal member by silver brazing.

  According to the present invention, it is possible to suppress the destruction of ceramics in the vicinity of the joint interface, which has been a problem in the past, and to prevent peeling at the interface between the ceramic and the sealing material. It is possible to improve the properties, and to bring about remarkable effects such as improvement of oxygen purity and reliability in membrane oxygen separation, and improvement of conversion efficiency and reliability in membrane reactors.

Hereinafter, the present invention will be specifically described.
FIG. 1 is an example of the present invention and shows a cross section of a typical structure. The solid electrolyte ceramics 2 has a thin film structure formed on the porous support 1, and the whole is in the shape of a cylindrical tube sealed on one side and attached to a metal flange (metal member) 4. Yes.

  A metal paste comprising silver and copper on the surface of the solid electrolyte ceramics 2 in which a silver solder 3 is arranged in a groove formed by the solid electrolyte ceramics 2 and a metal flange (metal member) 4 and in contact with the silver solder 3 A coating layer 5 is formed. The solid electrolyte ceramics 2 and the silver solder 3 are bonded by gas sealing at a portion where the metal paste coating layer 5 is formed. On the other hand, the gas seal joining of the silver solder 3 and the metal member 4 is relatively easy.

  Therefore, a composite structure in which the solid electrolyte ceramics 2 and the metal member 4 are gas-sealed and joined via the silver solder 3 is configured. The metal paste coating layer 5 may be applied over a wider area than the portion in contact with the silver solder 3 on the surface of the solid electrolyte ceramic 2, or more than the portion in contact with the silver solder 3. You may apply | coat to a narrow range.

  In another embodiment of the present invention, after a metal plating layer is formed on the surface of the solid electrolyte ceramic 2, a metal paste coating layer 5 is formed on the surface of the plating layer, and this metal paste coating layer 5 is further formed. There is a composite structure of the solid electrolyte ceramics 2 and the metal member 4 which is silver brazed to the metal member 4 and gas tight.

  Although FIG. 1 illustrates a cylindrical tube shape with one side sealed as an example, a flat plate shape may be used as long as the combination configuration of materials in the joint is the same. In addition, the structure of the metal member 4 exemplifies a flange having a tray structure that does not flow out when the silver solder 3 is melted, but if a joining method and conditions are selected so that the silver solder 3 does not flow out, The tray structure is not necessarily required, and may be a flat structure.

  The metal paste used in the present invention contains a metal component, and initially has fluidity and can be applied to an object to be joined, and a fixed coating layer can be formed by drying after coating. Moreover, in this invention, it is essential to contain silver and copper as a component of a metal paste. This is to ensure wettability between the ceramic and the silver solder.

  The copper contained in the metal paste coating layer of the present invention is preferably 0.1% by mass or more and 20% by mass or less with respect to silver in the metal paste coating layer. When the copper content exceeds this range, there arises a problem that the solid electrolyte ceramics in the vicinity of the joined portion are easily broken after joining. On the other hand, if the content is less than this range, the wettability between the ceramic and the silver solder becomes unstable, and a problem of causing a leak at the joint interface is likely to occur.

  Moreover, when copper is added in an oxide state, the effect is not sufficiently obtained, and it is desirable to add copper in the form of a metal powder such as a copper alloy containing copper and / or silver. In addition to these, noble metals such as gold, platinum, and palladium may be included in the metal paste. Furthermore, even if some impurities are mixed in the metal paste coating layer, no problem occurs. The allowable range of this impurity is about 1% by mass or less with respect to silver in the paste coating layer.

  Moreover, in order to ensure the soundness of the coating layer after drying, the metal paste coating layer may contain an organic binder or the like. However, in order to keep the metal paste coating layer sound even after the heat treatment for bonding, the ratio of the organic binder to the whole nonvolatile components of the metal paste is preferably about 1% by mass or more and 35% by mass or less. If the amount of the organic binder increases outside this range, the strength of the coating layer after heat treatment becomes too low. Further, if the content is less than this range, the effect of addition hardly appears.

The coating amount of the metal paste coating layer on the ceramic surface is preferably 0.001 g / cm ² or more and 0.1 g / cm ² or less per unit area in terms of the mass of silver in the metal paste coating layer. If the coating amount exceeds this range, problems such as peeling of the coating layer at the time of heat treatment for bonding and breakage of ceramics in the vicinity of the bonding portion are likely to occur. If the coating amount is less than this range, the effect of the coating layer is difficult to obtain.

  The method for forming the metal paste coating layer in the present invention may be any method, but may be applied with a brush or the like, may be coated with a coater, or may be dip coated by dip coating.

  In the present invention, the use of silver brazing, that is, pure silver or a silver alloy, as the sealing material for bonding is due to the chemical characteristics of silver. That is, since silver is more stable in a metal state even at a high temperature than in an oxide state, good sealing performance can be realized by maintaining a softened state at a high temperature.

  In the present invention, the silver solder may contain copper, indium, tin, and the like, which are additive elements for improving wettability, but the silver solder preferably contains 90% by mass or more of silver as a metal component. This is because the presence of the additive element can improve the wettability of the silver brazing ceramics, but the ceramics are easily destroyed as a side effect.

  The point of the present invention is that, even if an additive element for improving the wettability is not contained in the silver brazing, a wettability improving component represented by copper is necessary at this interface, which is most important in the joining of the ceramic and the silver brazing. New knowledge that sufficient wettability can be ensured if a limited amount is present and that adverse effects on ceramics can be removed, and formation of a metal paste coating layer has been found as a suitable method for carrying out this. That is.

  That is, in the present invention, the presence of the metal paste coating layer can sufficiently secure the wettability of the ceramic and the silver brazing, so that the necessity of the silver brazing containing the additive is reduced. For this reason, in a more preferred embodiment of the present invention, the silver solder is pure silver with no additives. However, no problem arises even if some impurities are mixed in the silver solder at this time. The allowable range of this impurity is about 1% by mass or less with respect to silver.

  The metal plating layer, in part, has the effect of a barrier layer that avoids deterioration of the solid electrolyte, and therefore, when used together with the metal paste coating layer, it helps to further improve the reliability of the composite material. For this reason, it is important to use a chemically stable metal as the metal plating layer in order to further improve the reliability.

  Moreover, in order to suppress gas leak to the minimum, the material of metal plating is preferably used that has excellent adhesion to the solid electrolyte ceramics and the metal paste layer. Examples of metal plating materials that satisfy these requirements include Au, Pt, Pd, Ni, Cr, Co, and alloys containing these metals, but particularly include gold or alloy plating layers containing gold. Metal plating is suitable as the barrier layer. This is due to the chemical nature of gold. Therefore, it is of course possible to use gold or an alloy plating layer containing gold as a whole, but multilayer plating can also be suitably used from the viewpoint of reducing material costs.

  In the case of multilayer plating, it is more preferable that at least one layer is gold or an alloy plating layer containing gold. Examples of this alloy plating include gold and silver alloys. For the same reason, metal plating including silver or an alloy plating layer containing silver can be cited as another metal plating layer suitable as another barrier layer.

  On the other hand, for the purpose of minimizing gas leakage, the first plating layer in contact with the solid electrolyte ceramic is preferably one or a combination of two or more in the group consisting of nickel, cobalt, and chromium. This is because these elements hardly react with the solid electrolyte and can be formed with good adhesion.

  Although the thickness of the entire metal plating layer is appropriately determined in consideration of the operating temperature and atmosphere, if it is made too thin, the effect of improving the barrier effect and wettability by metal plating will not come out much, and conversely it will be too thick. Therefore, the effective plating thickness for the present invention is generally in the range of 0.02 μm to 5 μm. Within this range, the thickness of the gold or gold-containing alloy plating layer, the thickness of silver or the alloy plating layer containing silver, and the thickness of the first plating layer made of nickel, cobalt, or chromium are also appropriately determined.

  As a method for forming the plating, a vapor phase plating method such as a vapor deposition method or a sputtering method may be used, but a method of electroless plating by dipping in a plating bath is the simplest method. Note that some impurities may be mixed in the plating layer. For example, in electroless Ni plating using hypophosphorous acid or the like, phosphorus may be mixed into the Ni plating layer. Further, when a metal plating layer is formed by sputtering, argon is mixed, but in any case, even if such impurities are mixed, there is no problem.

Mixed conductive solid electrolyte ceramics used in membrane oxygen separators and membrane reactors are mixed conductive materials centered on perovskite-type oxides and oxide ion conductivity of 0.1 S / m or more at 850 ° C. An oxide having an oxide or a composite material of an oxide and a metal is preferably used. Examples of well-known perovskite oxide materials include (La, Sr) (Co, Fe) _Ox , (Ba, Sr) (Co, Fe) _Ox , (Ba, Sr) (Co, Nb) _Ox type (where x is a value determined so as to satisfy the charge neutrality condition). In addition, in the membrane reactor, a material having a reduced Co content compared to the material used in the membrane oxygen separation is more preferable so that the oxide does not decompose even in a highly reducing atmosphere such as hydrocarbon gas such as methane. preferable.

As one desirable embodiment of the present invention, the metal member is made of aluminum bronze containing 8% or more of aluminum, and the solid electrolyte ceramic is a porous body having a porosity of 10% or more. And a method of selecting a material of 21 to 29 ppm / ° C. between 100 and 850 ° C. As an example of such a solid electrolyte ceramic, the one whose composition is represented by the following (formula 1) can be given.
_{{Ln a Ba b A 1-} ab} {B 1-x B 'x} αO (3- δ) ··· ( Equation 1)
(Here, Ln is a combination of one or more elements selected from Y or lanthanoid elements. A is a combination of one or two elements selected from Sr or Ca. B is Co, Fe. , A combination of one or more elements selected from the group consisting of Cr and Ga, including Fe or Co, and the sum of the number of moles of Cr and Ga is the number of moles of all B elements (1-x) 0% or more and 20% or less, B ′ is a combination of one or two or more elements selected from Nb, Ta, Ti, or Zr that must contain Nb or Ta, and has a mole number of Ti and Zr. The sum is 0% or more and 20% or less with respect to the number of moles x of all B ′ elements, provided that 0 ≦ a ≦ 0.2, 0.1 ≦ b ≦ 0.2, 0.07 <x ≦ 0.5, 0 .9 ≦ α ≦ 1.2, δ is a value determined to satisfy the charge neutrality condition.)

  The membrane oxygen separation apparatus and membrane reactor having the composite structure of the present invention can simultaneously suppress destruction of ceramics, separation at the joint interface, and generation of gas leaks in the vicinity of the joint interface between the ceramic and the metal member. it can. For this reason, it is possible to realize a highly reliable apparatus that does not cause a problem of deterioration in gas sealability at the joint even if the joint is repeatedly subjected to thermal stress as the apparatus is started, stopped, etc. Become.

  A membrane type oxygen separation apparatus using a composite structure having this structure has, for example, a composite structure for oxygen separation shown in FIG. 1, and supplies high-temperature and high-pressure air to the outside of the structure. Collect the permeated oxygen inside. Since the movement of oxygen ions in the solid electrolyte occurs from the higher oxygen partial pressure to the lower one, oxygen is also separated by setting the outer raw material air side to high temperature normal pressure and reducing the inner separated oxygen side. be able to. The oxygen separation structure has a structure in which a thin film of mixed conductive solid electrolyte having both oxygen ion conductivity and electron conductivity is formed on a porous support, and electrons move along with the movement of oxygen ions. Since it moves in the opposite direction, the charge neutral condition is satisfied in the solid electrolyte, so that no external wiring is required and the structure is simple.

  In this membrane oxygen separator, the mixed conductive solid electrolyte is made thin, so that the movement of oxygen ions is performed efficiently. The thickness of the thin film is generally in the range of 1 to 100 μm. On the other hand, the porous support is used for ensuring mechanical strength while having good air permeability. Therefore, the porosity of the porous support is adjusted within a range in which both (breathability and mechanical strength) are satisfied, but generally the porosity (= 100-relative density (%) with respect to the dense body) ) In the range of 20 to 60%. The thickness of the porous support is also determined in consideration of both characteristics, but is generally selected from the range of 1 to 50 mm.

On the other hand, the membrane reactor is one in which a hydrocarbon gas such as methane is partially oxidized by a catalyst to obtain a synthesis gas (mixed gas of hydrogen and carbon monoxide). Syngas is a gas with high industrial value that is a raw material for clean fuel, such as methanol, Fischer-Tropsch synthetic oil, and dimethyl ether. Moreover, it is also promising as a raw material for hydrogen production by combining hydrogen production by a water gas shift reaction of carbon monoxide (CO + H ₂ O → H ₂ + CO ₂ ).

  Structurally, the apparatus has the composite structure illustrated in FIG. 1 similar to a membrane oxygen separator, and two kinds of gases, hydrocarbon gas and air (a source of oxygen for partial oxidation), are solid. Since it is efficient to supply the electrolyte so as to face each other, a structure for inserting a gas introduction pipe inside the reaction tube is provided. A system in which hydrocarbon gas such as methane is supplied to the outside of the reaction tube and air is supplied to the inside may be adopted, or the opposite supply method may be used. However, a reforming catalyst is held on the hydrocarbon-side solid electrolyte surface.

Next, the manufacturing method of the composite structure of this invention is described.
First, a metal paste coating layer is formed on the surface of the solid electrolyte ceramic. The metal paste can be prepared by mixing metal component powder, an organic binder, a solvent, and the like, and kneading using a three-roll. Moreover, you may mix and mix a commercially available metal paste and the metal powder of an additive so that it may become a predetermined composition. The paste thus prepared is applied and dried to form a paste application layer. As the paste application layer, a conventionally known technique can be used as long as it is a method capable of forming a uniform and sound application layer, such as application with a brush as described above.

  After applying a metal paste to the joining surface of the solid electrolyte ceramics, the metal paste is abutted against the metal member, and a silver brazing member is disposed at the joining portion to perform heat treatment. The heat treatment conditions are determined in consideration of the melting point of the silver brazing, but the optimum conditions are determined, but the composite structure is soundly produced above the melting point of the silver brazing so that the melting of the silver brazing is not insufficient and the gas sealability is not impaired. Heated to a temperature where it can. The heat treatment atmosphere is generally sufficient even in an air atmosphere.

  Moreover, when metal plating is first performed on the surface of the solid electrolyte ceramics, the metal plating may be immersed in a commercially available plating bath in addition to the vapor phase plating method. In the case of vapor phase plating, in order to form a plating layer only on the bonding surface, masking is performed so that the plating layer does not deposit on other surfaces. In the case of plating on a curved surface such as a cylindrical tube, a plating layer is usually formed while rotating the sample in order to achieve a uniform thickness.

  On the other hand, the method of precipitating by dipping in a plating bath has the advantage that a plating layer can be formed using a simple jig, but it tends to be inferior to vapor phase plating in terms of adhesion to solid electrolyte ceramics. Therefore, as necessary, as a pretreatment for ensuring adhesion, an acid etching process is performed on the bonding surface of the solid electrolyte ceramics. As mentioned above, although the metal plating construction method was specifically described, conventionally known techniques can be used as long as the method can ensure adhesion between the metal plating and the solid electrolyte ceramics.

  After metal plating is applied to the joining surface of the solid electrolyte ceramic, a metal paste coating layer is formed. After this paste application, the same method as described above can be used. In this case, the optimum heat treatment conditions are determined in consideration of the melting point of the plated metal material and the silver brazing used. However, the plating layer is completely melted by the heat treatment or, conversely, the dissolution of the silver brazing is insufficient. In order not to impair the sealing performance, it is heated to a temperature not lower than the melting point of the silver solder and not higher than the melting point of the metal plating layer. Moreover, although the heat treatment atmosphere depends on the oxidation characteristics of the plating material, it is generally sufficient even in an air atmosphere. However, when oxidation proceeds extremely, it is performed in a non-oxidizing atmosphere.

  The present invention will be described below with reference to examples and comparative examples.

Example 1
BaCO ₃ , SrCO ₃ , Co ₃ O ₄ , Nb ₂ O ₅ powder mixed to have a composition of Ba _0.2 Sr _0.8 Co _0.9 Nb _0.1 O _x (where x is a value determined to satisfy the charge neutrality condition) -It grind | pulverized and calcined at 900 degreeC in the air for 4 hours. The obtained calcined powder was mixed with PVA (polyvinyl alcohol) powder as a porous material after pulverization and particle size adjustment. This was filled in a rubber mold so as to have a cylindrical tube shape, CIP (hydrostatic pressure press) molding, and then fired in air at 1100 ° C. to obtain a porous support 1. The porosity of the porous support 1 was 32%.

  Next, a slurry for forming a thin film using a powder of the same material as the porous support 1 was prepared, and the porous support 1 was dipped in the slurry, dried, and then fired at 1250 ° C. in air. Thus, a dense thin film layer of a mixed conductive solid electrolyte (solid electrolyte ceramics 2) having a thickness of 50 μm was formed only on the outer surface. The dimensions of the baked oxygen separation tube were an outer diameter of about 20 mm, an inner diameter of about 15 mm, and a length of about 800 mm.

Next, a commercially available copper powder was added to a commercially available silver paste and mixed well to prepare a metal paste for coating. The amount of copper powder added was 7% by mass relative to the silver in the paste. This metal paste is applied to the area from the open end of the oxygen separation tube prepared above to about 20 mm with a brush with a dry mass of about 0.03 g / cm ² as a guide, and then naturally dried to form a metal paste coating layer 5. did. The oxygen separation tube on which the metal paste coating layer 5 was formed was brought into contact with an aluminum bronze metal flange (metal member 4) and joined using a silver solder containing only silver. The bonding conditions were an air atmosphere, 970 ° C., and 20 minutes.

  Next, the bonded composite structure was evaluated. From the appearance, the joint part was finished beautifully. In order to evaluate the gas sealing property of the joint, 1 MPa of compressed air was introduced to the outside of the separation tube at room temperature, and the flow rate of the gas leaking inside was measured. As a result, no leakage was observed, and it was confirmed that there was no leakage at the joint.

  Therefore, an oxygen separation experiment was conducted at 900 ° C. using this composite structure. In the oxygen separation experiment, high-temperature air compressed to 1 MPa is introduced to the outside of the composite structure, and the leak rate (differential pressure 0.9 MPa) at high temperature can be evaluated from the purity of the separated oxygen. As a result, it was confirmed that the oxygen purity was 99.9999% or higher (impurity gas was below the detection limit by gas chromatography), and it was judged that there was no leakage at a high temperature at the junction.

  Subsequently, a thermal cycle test was conducted. The procedure is as follows: heating from normal temperature to 900 ° C. at a heating rate of 50 ° C./hour, leak evaluation test at 900 ° C. (the above-mentioned oxygen separation experiment), cooling from 900 ° C. to normal temperature at a cooling rate of −50 ° C./hour, at normal temperature This was a repeated evaluation of the leak evaluation test. As a result, it was found that even when repeated evaluations were performed up to 15 times, no room temperature / high temperature (900 ° C.) co-leakage was observed, and a highly reliable bonded body (composite structure) was obtained.

(Comparative Example 1)
An oxygen separation tube was prototyped in the same manner as in Example 1, and was directly joined to an aluminum bronze metal flange without forming a metal paste coating layer. The joining method was the same as in Example 1.

  As for the appearance of the bonding interface, compared with Example 1, the wettability of the silver solder and the solid electrolyte ceramics was poor, and leakage was observed from the interface at room temperature. Further, the high temperature sealability of this joined body was evaluated, but a large leak was confirmed even at a high temperature, and it was difficult to apply a differential pressure.

(Comparative Example 2)
An oxygen separation tube was prototyped in the same manner as in Example 1, and was directly joined to an aluminum bronze metal flange without forming a metal paste coating layer. The joining method was the same as in Example 1 except that the silver solder contained 15% by mass of copper as the copper powder.

  The appearance of the bonding interface was not inferior to that of Example 1, and the bonding site was finished fine, but leakage was already detected in the ceramic near the bonding interface at room temperature. Further, when an oxygen separation experiment of this joined body was performed, the oxygen purity was about 85%, and a decrease in oxygen purity due to leakage was observed. Further, in the subsequent thermal cycle test, the leak amount increased each time the normal temperature / high temperature was repeated, and after seven cycles, the solid electrolyte ceramics near the joint interface was damaged.

(Example 2)
An oxygen separation tube was made in the same manner as in Example 1, and then the region from the open end of the produced oxygen separation tube to about 20 mm was degreased using an alkaline solution (using a commercially available degreasing agent, 50 ° C., 3 minutes). Thereafter, etching treatment (room temperature, 3 minutes, washing with ion-exchanged water) was performed with a hydrofluoric acid solution. After applying a catalyst using a commercially available activator bath, electroless plating was performed by immersing in a commercially available Ni plating bath at 90 ° C. for 4 minutes.

  Subsequently, gold was electrolessly plated on the outermost layer by immersing in a commercially available gold plating bath at 90 ° C. for 5 minutes. As a result of cross-sectional observation, it was found that the plating layer was formed with a thickness of about 1 μm nickel and about 0.1 μm gold. Further, the adhesion between the metal plating and the surface of the oxygen separation tube was good, and it was not peeled off at all in the tape peeling test.

Next, a metal paste was prepared by the same method as in Example 1, and the dry mass was about 0.03 g / cm ^{2 in} the region from the open end of the plating layer of the oxygen separator tube prepared above to about 15 mm. It was applied and naturally dried to form a metal paste coating layer 5. The oxygen separation tube was attached to an aluminum bronze metal flange (metal member 4) and joined using a silver solder containing only silver. The joining conditions were the same as in Example 1.

  It was confirmed that the bonded portion of the bonded composite structure was finished in appearance and that there was no leakage at the bonded portion at room temperature. When an oxygen separation experiment was performed at 900 ° C., it was confirmed that the oxygen purity was 99.9999% or more (impurity gas was below the detection limit by gas chromatography), and it was judged that there was no leakage at high temperature at the junction. Furthermore, the thermal cycle test between room temperature and 900 ° C. was repeated 15 times in the same manner as in Example 1. However, no leak at room temperature / high temperature (900 ° C.) was observed at all, and a highly reliable joined body. It turned out that it became (composite structure).

(Example 3)
Various oxygen separation tubes were produced in the same manner as in Example 1. All the separation tubes were prepared so that the porosity of the porous support tube was 25 to 40% and the dense membrane thickness of the mixed conductive solid electrolyte (solid electrolyte ceramics 2) was 40 to 70 μm. The region from the open end of the obtained separation tube to about 20 mm is coated with a metal paste under different conditions, or after applying a metal plating treatment, and then applied with a metal paste. A metal flange (metal member 4) and silver containing no additive were used for the silver solder and joined.

  The reliability of the obtained composite structure was evaluated and compared. The comparison method was performed by adding two thermal histories in the temperature range from room temperature to 900 ° C. and evaluating the purity of the separated oxygen in a third oxygen separation experiment at a high temperature (900 ° C.). The results are summarized in Table 1.

  Judgment in the table indicates that there is no decrease in oxygen purity and the bonding reliability is high, and a slight decrease in oxygen purity is recognized, but a high reliability is still recognized as good, and the bonding reliability is The lower one is marked as x. As can be seen from the table, the composite structures obtained by the present invention were all judged to be good or better, and it was confirmed that they were highly reliable joint structures.

Example 4
In the same manner as in Example 1, a reaction tube for a membrane reactor in which the porous support 1 and the dense membrane of the solid electrolyte ceramics 2 were both composed of Ba _0.5 Sr _0.5 Co _0.8 Fe _0.2 O _x was produced. The porous support 1 was prepared to have a porosity of 30 to 40%, and a solid electrolyte ceramic 2 having a dense film thickness of 50 to 70 μm. A metal paste having the same composition as in Example 1 was applied by brushing to an area from the open end of the obtained reaction tube to about 20 mm, and the metal paste was applied. Further, in the same procedure as in Example 1, using a stainless steel SUS310S metal flange (metal member 4) and a silver solder containing 1% by mass of copper with respect to silver, in an air atmosphere at 970 ° C. for 20 minutes. Joined.

  It was confirmed that the joined composite structure was finished in appearance and there was no leakage at the joint. Furthermore, in order to confirm the reliability of the composite structure, the heat history was repeated up to 10 times in the temperature range from room temperature to 900 ° C., and the leak was evaluated again, but there was no leak. From this result, it was confirmed that the composite structure for a membrane reactor produced by the present invention has high reliability.

It is a cross-sectional schematic diagram which shows the typical structure of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Porous support body 2 Solid electrolyte ceramics 3 Silver solder 4 Metal member

Claims (13)

A composite structure in which a solid electrolyte ceramic and a metal member are joined by silver brazing,
After forming a metal plating layer on the surface of at least a portion of the solid electrolyte ceramic that is to be soldered with silver, a metal paste coating layer containing silver and copper is formed on the surface of the metal plating layer, and the metal paste coating is further performed. A composite structure in which the solid electrolyte ceramic and the metal member are joined by silver brazing via a layer.   The composite structure according to claim 1, wherein the metal plating layer includes a plurality of metal plating layers, and at least one of the metal plating layers is gold or an alloy plating layer containing gold.   The composite structure according to claim 1, wherein the metal plating layer includes a plurality of metal plating layers, and at least one of the metal plating layers is silver or an alloy plating layer containing silver.   The metal plating layer includes a plurality of metal plating layers, and the first plating layer in contact with the solid electrolyte ceramics includes one or a combination of two or more selected from the group consisting of nickel, cobalt, and chromium. The composite structure according to any one of claims 1 to 3.   5. The composite structure according to claim 1, wherein the entire thickness of the metal plating layer is 0.02 μm or more and 5 μm or less.   Copper contained in the metal paste coating layer is added to the metal paste as one or both of metal copper powder and silver-copper alloy powder, and the copper content is silver in the metal paste coating layer. It is 0.1 mass% or more and 20 mass% or less with respect to the composite structure of Claim 1 characterized by the above-mentioned. The coating amount of the metal paste coating layer is 0.001 g / cm ² or more and 0.1 g / cm ² or less per unit area in terms of the mass of silver in the metal paste coating layer. A composite structure according to 1.   2. The composite structure according to claim 1, wherein the silver solder contains 90% by mass or more of silver as a metal component.   The composite structure according to claim 1, wherein the silver solder contains only silver as a metal component.   A membrane oxygen separation apparatus comprising the composite structure according to any one of claims 1 to 9.   A membrane reactor comprising the composite structure according to any one of claims 1 to 9. A method for producing a composite structure according to any one of claims 1 to 9,
A metal paste coating layer is formed in advance on the joining surface of the solid electrolyte ceramics, and then a silver brazing member is disposed between the metal paste coating layer portion and the metal member, and heated above the melting point of the silver brazing. A method for producing a composite structure, wherein the solid electrolyte ceramic and the metal member are joined by silver brazing. A method for producing a composite structure according to any one of claims 1 to 9,
One or more metal plating layers are formed on the joining surface of the solid electrolyte ceramics, and the metal paste coating layer is formed on the surface of the metal plating layer, and then between the metal paste coating layer portion and the metal member. A method for producing a composite structure, comprising: arranging a silver brazing member and heating to a temperature equal to or higher than the melting point of the silver brazing so that the solid electrolyte ceramic and the metal member are joined by silver brazing.

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