EP1827670A1

EP1827670A1 - Ceramic-metal or metal alloy junction assembly

Info

Publication number: EP1827670A1
Application number: EP05825170A
Authority: EP
Inventors: Pascal Del Gallo; Nicolas Richet; Christophe Chaput; Laetitia Trebuchaire
Original assignee: Air Liquide SA; LAir Liquide SA pour lEtude et lExploitation des Procedes Georges Claude
Current assignee: Air Liquide SA; LAir Liquide SA pour lEtude et lExploitation des Procedes Georges Claude
Priority date: 2004-12-17
Filing date: 2005-12-13
Publication date: 2007-09-05
Also published as: WO2006064160A1; JP2008524099A; FR2879594A1; CN101080265A; FR2879594B1

Abstract

The invention concerns a junction assembly (5) comprising: a ceramic tube (3) with axis (X'X), defining an inner zone (ZC) and an outer zone (ZM); a metal socket (2) with cylindrical junction zone (2b) of axis (X'X) enclosing said tube (3) through a gap (4); the sealing between said tube (3) and the socket (2) is provided by a junction element (1), made of a gas-tight material, and having a thermal expansion coefficient higher than 9. 10-6/ °C; said ceramic having a thermal expansion coefficient higher than that of the metal; said zone (2b) having, perpendicular to (X'X) a small dimension (1). The invention also concerns a reactor (6) comprising such an assembly (5), in particular for gas production and/or for gas separation.

Description

CERAMIC JUNCTION ASSEMBLY - METAL OR METAL ALLOY

The invention relates to a ceramic-metal junction assembly comprising a ceramic part, a piece of metal or metal alloy and a ceramic - metal or metal alloy junction element which provides a junction between the two parts, as well as a reactor having such a junction assembly.

In the context of the use of ceramic membrane metal reactors, such as a CMR (membrane catalytic reactor), for example for the production or separation of gases, it is essential to form a junction between the ceramic and the metal. or metal alloy which constitutes a wall of said reactor. Indeed, such reactors generally comprise within them a ceramic part or membrane, which is usually in the form of a substantially hollow tube closed at one of its ends and open at the other end, which partially envelops an inner zone. which has an atmosphere that is usually gaseous, and which defines an area outside itself, inside said reactor, which comprises another atmosphere that is often gaseous. The two atmospheres are thus present in said reactor, do not communicate directly with each other and are separated by the ceramic part. At least one exchange, which is often gaseous, selective, takes place between the two atmospheres via and through the ceramic part, and may give rise to at least one reaction on one side or the other of said ceramic piece. The tube is most often held in place in the reactor via a piece of metal or metal alloy, generally of the same metal or metal alloy as said wall of the reactor. said piece may belong to said wall or may simply be attached to said wall.

However, it is technically difficult to design and produce a junction assembly between a ceramic and a metal or a metal alloy that is gas-tight under oxidizing atmosphere conditions on one side of the junction and reducing atmosphere of the other side of the junction, and pressure difference between said two atmospheres between 0 and 30 bar (0 and 0.3 MPa). In addition, in the case of the use of a CMR, the conditions of implementation of such a junction are even more severe, because said atmospheres are likely to contain water vapor and the junction assembly must work in a temperature range of about 20 ^° C. (room temperature) to 900 ^° C. or more. All these constraints therefore require the use of materials, whether it is a ceramic, a metal or metal alloy or a joining material, chemically inert with respect to each other, and having suitable physical properties, in particular a CET (coefficient of thermal expansion) adapted.

Research into a suitable junction assembly has so far focused on two different points, namely the formulation of the junction material and the shape (the "design") of the element. junction.

As regards the formulation of the joining material, many problems arise because of the evolution, over time and at high temperature (600 to 900 ^° C.), of the parameters of this material.

Among these parameters, the most critical parameters are the coefficient of thermal expansion (CET) and the chemical and physical stability of the material. Indeed, in a temperature range from room temperature to a high temperature, it is essential to take into account factors such as the possible evaporation of component (s) of said material, the evolution of the TEC and / or the eventual crystallization of component ( s) of said material. In this respect, partially or fully crystallized materials offer more extensive possibilities, especially in terms of the evolution of the thermal expansion coefficient as a function of the temperature, and of the high temperature stability time.

A first approach consisted in crystallizing glass to better adapt its properties, which led to the development of specific glasses of the Lithium AluminoSilicate or LAS type (US4921738), Barium AluminoSilicate or BAS (US6430966) or Barium calcium AluminoSilicate or BCAS . These compositions have a good refractoriness and a CET greater than those of conventional uncrystallized compositions. Unfortunately, they have too much chemical reactivity with ceramics.

A second approach has been to add a crystallized phase in a glass in order to increase the CET or to use a crystallizable glass, for example in the form of powder or preform (US5725218, US6402156). However, the multiplication of the interfaces created by the presence of several phases in the joining material increases the possibilities of leaks and therefore loss of sealing of the junction assembly.

With regard to the shape of the joining element, a first approach consisted in compressing a joining element consisting of a deformable junction material, said element being pressed against the metal or metal alloy part and on the ceramic piece. The junction material is generally a fluid phase such as for example glass. It then adapts to the shape of said parts. It can then undergo compression forces that allow it to ensure good contact with said parts at its interfaces with them.

However, the stresses exerted on the ceramic part then pose a significant problem. Indeed, such stresses can cause the ceramic piece to crack, and at worst to split. Moreover, in most cases, the presence in the joining element of an additional component is necessary to complete the gastightness, especially if the surface conditions of the interfaces of the connecting element with the parts mentioned above are very irregular. This type of embodiment requires having the closest possible thermal expansion coefficients for the metal or metal alloy part and the ceramic part, because of the intimate contact between each of the two parts and the joining element. The possible deformations of the metal part or metal alloy necessarily exert constraints on the ceramic part. In most cases, repeated thermal cycles and / or thermal shocks lead to cracking of the ceramic part.

A second approach has been to modify the shape of the joining element, to limit the effect of stresses that may be exerted on the ceramic part. Thus, EP-A-1 067 320 discloses a junction element formed of at least one metal toroidal ring, said ring being able to deform. Such a joining element therefore makes it possible to maintain a pressure at the interfaces between the connecting element and the metal or alloy part. metal and the aforementioned ceramic part. Such a joining element makes it possible above all to limit the radial stresses which are exerted on the ceramic part during thermal cycles, since the ring is formed by a metal sheet whose thickness is much smaller than the width of the ring. . By cons, as said ring is metal, surface roughness problems can arise very quickly for the surfaces forming the interfaces, which can lead to leakage. This is why, in an embodiment with at least two rings, a fluid phase (in particular glass) is generally trapped between two neighboring rings. This fluid phase poses a problem of stiffening the junction at temperatures where said phase is not fluid, in particular at temperatures ranging from room temperature (approximately 20 ^° C.) to the softening temperature of said phase.

The junction assembly according to the invention overcomes the problems described above, and to provide other advantages. One of the objects of the invention is to propose a junction assembly which makes it possible to limit the stresses exerted on the ceramic part, in particular during thermal cycles varying between the ambient temperature and a high temperature. Thus, the invention relates to a ceramic-metal junction assembly, said assembly comprising: 1) at least one ceramic piece in the form of a hollow tube and substantially cylindrical axis (X'X), closed to one of its ends and open at the other end, defining an inner zone called ceramic zone and an outer zone called metal zone, said ceramic and metallic zones not communicating with each other and being separated at least partially by the ceramic part, at least partially sheathed by

2) at least one sleeve of metal or metal alloy having a part hereinafter called "junction zone" substantially cylindrical and hollow axis (X'X) at least partially enveloping said tube, a substantially annular axis space ( X'X) being provided between said tube and said junction zone,

3) the seal between said tube and said sleeve being provided by at least one ceramic-metal junction element which is in contact with the tube and with said junction zone of the socket, the junction element being at least partially present in said annular space occupying a subspace (4a) and preferably in the form of a substantially annular piece,

said ceramic having a coefficient of thermal expansion (CET) greater than or equal to the coefficient of thermal expansion (TEC) of the metal or metal alloy, said metal alloy comprising at least 10% by weight of nickel and at least 15% by weight of chromium,

* Said connecting element comprising at least one joining material, preferably consisting of said joining material, ensuring gas tightness of 20-900 ⁰ C, preferably being solid at a temperature of 650 to 900 ⁰ C, and having a coefficient of thermal expansion (CET) of the ambient temperature at 900 ^° C. greater than or equal to 9.times.10.sup.- ⁶ / ° C., preferably from 9 to 15.times.10.sup.- ⁶ / ^0.degree. C., said joining assembly being such that said zone junction has a small dimension, along any axis (Y'Y) passing through said junction area and perpendicular to the axis (X'X). In a preferred embodiment of the invention, the dimension ratio along the axis (X'X) of the junction zone to the subspace is at least equal to 2/1, and is preferably in the range of 2/1 to 100/1. The ratio of dimensions along the axis (X'X) of the junction zone to the subspace is the ratio of the mean dimension along the axis (X'X) of the junction zone to the average dimension according to the axis (X'X) of the subspace. In the case that will be illustrated below where the shapes of the subspace and the junction zone are both annular axis (X'X), said dimension is the height of the ring.

Advantageously according to the invention, the combination of the properties of the joining material and the possibilities of deformation of the socket makes it possible to have a junction assembly which provides improvements over the junction assemblies of the prior art. These improvements are mainly expressed in terms of the chemical and physical stability of the junction assembly, the limitation of the stresses exerted on the ceramic tube, the achievement of a gaseous seal from ambient temperature to high temperature, and improvement of the resistance of the junction assembly to thermal cycles ranging from ambient temperature to high temperature. Indeed, the presence of a junction zone of small size of the sleeve advantageously provides according to the invention possibilities of deformation of said sleeve. Such deformations limit the stresses exerted on the ceramic tube, in particular in the temperature range from ambient temperature (about 20 ^° C.) to high temperature.

By "gas-tightness of 20 to 900 ^° C." is meant according to the invention that no leakage (s) of gas from 20 to 900 ° C. occurs. By "solid at a temperature of 600 to 900 ^° C." is meant according to the invention that the viscosity is greater than ¹² mPa.s for a glass and that said temperature is below the melting temperature for a crystal. In general and preferably, said joining material is solid at the temperature (s) of use of said assembly.

The "coefficient of thermal expansion (CET)" is a standard data for the skilled person. By "small dimension" is meant according to the invention that the dimension is small and is in a range of size that can be easily found by the skilled person, depending on the given parameters such as the CET of the material of junction, and the shape of the socket. The minimum dimension is given by the machinability of the metal or metal alloy. An example of a small dimension will be given below in the examples. Typically, said small dimension is about 20 to 500 μm, preferably about 50 to 400 μm, more preferably about 200 to 300 μm.

The ceramic tube is generally a ceramic membrane present inside a reactor. The bushing is generally such that it can be mechanically and tightly bonded, typically by screwing, welding or any other method of tight assembly known to those skilled in the art, generally in a manner, fixed or removable, to a such reactor, preferably a wall of a reactor.

According to the invention, the ceramic is generally an ionic conductor, preferably an ionic and electronic conductor, said ceramic more preferably comprising at least one crystalline lattice comprising at least one oxygen deficiency, said ceramic being, even more preferably chosen from ceramics of perovskite crystal structure and cerium oxides. For example, the ceramic is composed of a porous layer (located on the ZM side) and a dense layer (located on the ZC side) of respective Lao compositions, ₅ Sr ₀ ^ Fe _O , ₉ Ti ₀ , iθ ₃ - _δ. Lao βSro, 4Feo, GGAO, iθ3-δ.

The coefficient of thermal expansion (TEC) of the ceramic generally depends on its formulation. In general, it is from 9 to 20.10 ^{^"6/0} C.

Preferably, said metal or metal alloy comprises on one part of, preferably on all, the surface of said junction zone, at least one layer of at least one oxide typically of thickness greater than or equal to approximately 1 μm and preferably thickness less than or equal to about 10 μm. Advantageously, the presence of such an oxide layer makes it possible to protect the metal or metal alloy during the manufacture of the junction assembly and, above all, ensures an adhesion function between the joining material and the metal or metal alloy. If this layer is too thin (typically less than or equal to about 1 micron), the adhesion of the junction between the joining material and the metal or metal alloy is difficult to achieve. If this layer is too thick (typically greater than or equal to about 10 microns), it may flake during said manufacture, and therefore not to ensure adhesion role. For each case, the skilled person is able to establish a range of thicknesses and / or an optimum thickness of the layer according to the data available.

The metal may be, for example, nickel or platinum. The metal alloy generally has the following properties: resistance to oxidation under an oxidizing atmosphere up to 1200 ^° C., resistance to reduction under a reducing atmosphere up to 1200 ^° C., resistance to creep up to 1200 ^° C., a melting point greater than or equal to 1200 ^° C., and a thermal expansion coefficient (TEC) of 20 ^° C. at 900 ^° C. of 8 ° to

25. 10 ^{^"6/0} C, preferably from 10 to ^{18.10" ^6/0} C. The alloy is generally selected from stainless steels which are for example commercial alloys such as Haynes 230® alloy, the alloy 800HT ® and Inconel 686®.

Preferably, said joining material is glass, which has a coefficient of thermal expansion (TEC) greater than the coefficient of thermal expansion (TEC) of the metal or metal alloy and lower than the coefficient of thermal expansion (CET ) ceramic, resistance to a pressure difference between the ceramic zone and the metal zone of between 0 and 3 MPa, chemical stability with respect to the ceramic, chemical stability with respect to the metal or of the metal alloy, resistance to reduction under a reducing atmosphere up to 1200 ^° C., resistance to oxidation under an oxidizing atmosphere up to 1200 ^° C., adhesion to the metal or metal alloy and adhesion to the metal. ceramic.

The ceramic tube is generally closed at one end by any shape such as square or hemispherical or any intermediate shape. In addition, the open end of the ceramic tube may be of a shape facilitating anchoring on / in the socket.

The invention also relates to a method of manufacturing an assembly as described above, said method comprising the following successive steps: 1. At least partial preoxidation of a surface of a junction zone of a metal sleeve or metal alloy or a precursor thereof, so as to form at least partially at least one layer of at least one metal oxide on said surface;

2. assembly of a junction material or a precursor thereof, the sleeve of step 1, and a ceramic piece or precursor thereof, said assembly generally comprising a wedging by maintaining the connecting element at the junction area of the socket, then

3. heat treatment of the assembly of step 2, under an inert gas such as nitrogen, under partial pressure of oxygen of between 0 and 22%, and at a temperature of 650 to 1200 ^° C. for a period of 5 minutes. mn to 10 hours, comprising a rise in temperature from room temperature to a treatment temperature, at least one temperature step at the treatment temperature, at least one temperature decrease to a stabilization temperature, at least a stabilization plateau at the stabilization temperature, and at least one final descent to a treatment end temperature which is most often ambient temperature, said heat treatment leading to the formation of the connecting element within the junction assembly.

By "temperature plateau" is meant according to the invention that said temperature is generally maintained for a period of a few minutes to a few hours depending on the materials used.

The treatment temperature can be fixed or vary within the indicated range. Said method may further comprise an additional step, which is performed between the preceding steps 1 and 2 or preceding the preceding step 1, said additional step being the following step: Manufacturing a junction material preform, in the form of a substantially cylindrical and hollow tube open at at least one of its ends, said manufacture comprising at least one pressing and a densification, or at least one sintering, or at least one minus a melting and pouring in a mold, at a temperature of 600 to

1200 ^° C. for 10 to 40 minutes, said preform serving to form the joining material assembled in step 2.

Finally, the invention relates to a reactor, said reactor comprising at least a majority of said junction assembly according to the invention or manufactured according to a process according to the invention, said reactor surrounding the ZM zone, the metal sleeve or metal alloy of the junction assembly being mechanically connected to said reactor, and the axis (X'X) being disposed substantially vertically, said reactor comprising at least one fluid inlet in the zone ZM and at least one fluid outlet of the zone ZM, said reactor further comprising at least one fluid inlet in the zone ZC and at least one fluid outlet of the zone ZC.

The reactor generally must withstand a pressure of from 1 to 30 bars (0.1 to 3 M.Pa), and at a temperature from room temperature to at least 900 ⁰ C or even to 1200 ⁰ C. In addition, it must consist of at least one metal or metal alloy that is resistant to a generally reducing atmosphere.

Most often, a selective passage of fluid within said reactor is possible between the zone ZC and the zone ZM through the ceramic tube, preferably from the zone ZC to the zone ZM.

Preferably, the junction assembly is linked mechanically to a wall of said reactor.

Generally, said fluid is gaseous and comprises at least one gaseous component.

Such a reactor is generally such that at least one of its walls is metallic, most often of the same metal or metal alloy as said sleeve, or of a metal or metal alloy that is chemically compatible with the metal or metal alloy. of the socket.

The invention finally relates to a method of using said reactor for the production of gas and / or the separation of gas, at a use temperature of 400 ^° C. to 900 ^° C., said joining assembly being such that the junction is solid at the temperature to which it is subjected during said use. Typically, the use temperature is less than or equal to the softening temperature of the glass when the joining material is glass. For example, said reactor can be used for the production of synthesis gas from methane and oxygen. The operating temperature may vary or be fixed in the range indicated above. Inside the reactor, the temperature can be distributed unevenly.

The invention will be better understood and other features and advantages will appear on reading the following description, given by way of non-limiting example, with reference to FIGS. 1 to 3.

FIG. 1 schematically represents a partial view of a reactor comprising, for the most part, within it a junction assembly according to the invention. FIG. 2 schematically represents a partial view of the junction assembly according to the invention of FIG. 1.

FIG. 3 represents, in a particular example, the thermal cycle to which a junction assembly according to the invention is subjected during its manufacture.

FIG. 1 schematically represents a partial view of a reactor 6 comprising, for the most part, a junction assembly 5 according to the invention. Said junction assembly 5 has been welded to the rim of an orifice 10 of a wall of said reactor 6. Said reactor 6 comprises a piece or socket made of metal or metal alloy 2, a ceramic part or tube 3, and a junction element 1 of substantially annular shape and installed in a substantially annular space 4 occupying a substantially annular subspace (4a) formed between the parts 2 and 3. Said junction assembly 5 and each of the parts 2, 3 and 1 which compose it are all substantially coaxial axis (X'X) substantially vertical. The inside of the reactor 6 is divided by the device into two zones ZM and ZC, which are physically separated mainly by the ceramic tube 3. The junction assembly delineates the zone ZC. The reactor 6 and the junction assembly delimit the zone ZM. The reactor 6 comprises a fluid inlet 7 in the zone ZM and a fluid outlet 8 of the zone ZM.

The reactor 6 also comprises a fluid inlet 9 in the zone ZC, which serves both at the inlet and at the fluid outlet 9 of the zone ZC. The arrows indicate the flow direction of the fluids, which are usually gases. In an example of use of the reactor 6 for the production of synthesis gas (mixture of hydrogen gas H ₂ and carbon monoxide CO) at high temperature, typically at an operating temperature of 700 to 900 ^° C., the air enters the zone ZC through the inlet 9, while methane gas supplies the zone ZM through the inlet 7. The zone ZM is under a pressure of 30 bar (3 MPa). In use, the joining member 1 being sealed, O ₂ oxygen passes through the junction assembly 5 through the wall of the ceramic tube 3. This passage is in the form of O ₂ ^" ions, which pass through the ceramic by the O ₂ vacancies present in its crystal lattice.In the ZM zone, the reaction CH4 + O ₂ -> H ₂ + CO can then take place, which leads to the production of a synthesis gas mixture which is discharged through the outlet 8. The hydrogen gas H ₂ and carbon monoxide CO can be easily separated from each other by If necessary, the nitrogen gas N ₂ remaining in zone ZC emerges via inlet 9. Thus, it has been possible to selectively separate air in oxygen gas O ₂ and nitrogen N ₂ , and conducting in the ZM zone of reactor 6 a gaseous reaction with oxygen as a reagent.

FIG. 2 schematically represents a partial view of the junction assembly according to the invention as represented in FIG. 1.

The ceramic piece 3 is a cylindrical tube plugged at one end. It also delimits a ceramic zone ZC inside said tube 3 and an outer zone called metal zone ZM. The closed end 3b of the tube 3 has a hemispherical shape and is opposite the sleeve 2. This side is defined as the high side in the following description. The other end 3a of the tube 3 is open and is located inside the socket 2. This side is defined as the low side in the following description. The metal zone ZM and the ceramic zone ZC do not communicate directly with each other, but only through the wall of the ceramic tube 3.

The sleeve 2 is substantially hollow. One can distinguish, in radial section, three main parts on the sleeve 2, from bottom to top: a lower part 2d provided with a bore, then from a shoulder 2c, a middle part 2f corresponding to a first chambering, then finally from a second shoulder 2a, an upper part corresponding to a second chamber, wider than the first. The outer diameter of the sleeve 2 is on this constant embodiment for the lower 2d and median 2f.

On the other hand, we can distinguish two different configurations on the upper part. Still in section, it is observed that the outside diameter tapers in right bevel angle 45 °, 2e, then on a length L, the outside diameter is again constant. This last part is the junction zone, 2b. The thickness 1 of the junction zone 2b is the small dimension 1 according to the invention.

As shown in Figure 2, the ceramic tube 3 is adjusted to the first recess and its lower portion 3a rests on the shoulder 2c. The wedging of the tube 3 on the sleeve 2 is performed through the shoulder 2a.

For any axis (Y'Y) perpendicular to the axis (X'X) which passes through the junction zone 2b of the sleeve 2, said junction zone 2b is of small dimension 1 along the axis (Y'Y).

The joining element 1 is annular. On this realization, it occupies only a subspace 4a annular of the annular space 4. The height of the joining element 1 is less than the height L of the junction zone 2b. The insertion depth of the joining element 1 in the sleeve 2 is such that its upper part is substantially at the same level as the upper end of the sleeve 2.

Figure 3 is explained below in Example 1.

EXAMPLES

The examples which follow illustrate the invention without limiting its scope. Example 1

The junction assembly 5 of the example is as shown in Figure 2. The dimensions of the different parts are as follows:

• Width 1 of the junction area 2b: 0.25 mm

• Length L of the junction area 2b: 5 mm

• Internal diameter of the junction area 2b: 12 mm

• Outside diameter of the 2nd part: from 12.25 to 16 mm

• Inside diameter of the 2nd part: 12 mm

• Height of the 2nd part (according to (X'X)): 5 mm • Outside diameter of parts 2f and 2d: 16 mm

• Inside diameter of part 2f: 10 mm

• Height of part 2f: 10 mm

• Inner diameter of the lower part 2d: 7 mm • Total height of the sleeve 2 (depending on the axis (X'X)): 50 mm The sleeve 2 thus defined is a part (or ring) made of an alloy which is Haynes 230®. Haynes 230® alloy is a good refractory material, which has been chosen for its refractoriness, resistance to high temperature oxidation and its TEC of 15.2.10 ^{~ 6} / ° C between room temperature and 800 ⁰ C. Its composition is as follows (% by weight): Ni 57%, Cr 22%, Mo 2%, W 14%, Fe 3%, C 0.1%, Al 0.3%.

The ceramic piece 3 is a ceramic tube 3 which is closed at one end 3b and which is composed on its entire wall with a porous layer (located on the

ZM) and a dense layer (located on the ZC side) of respective compositions Lao, 5So, 5Feo, 9TiO, i0 ₃ -s and La ₀ , 6Sr _O ^ Fe ₀ , 9Ga ₀ , iO ₃ - _δ .

Their CET, measured between 25 and 1000 ⁰ C, are identical and equal to 14, 8.10 ^{~ 6} / ° C, their densities are respectively

6 g / cm ³ and 6.2 g / cm ³ . The porous layer is thick

0.9 mm and the dense layer is 0.1 mm thick. The dimensions of the tube are:

¹ Length: 252 mm "Inner radius: 0.8 mm, and: ¹ Thickness: 1 mm.

The joining material is glass and forms a joining element 1 in the form of a substantially annular piece or cord 1. This cord 1 is completely inserted in the space 4, occupying a subspace (4a) , the top of the cord (1) being located at the height of the junction zone 2b. Two different glasses were tested as a joining material. The dimensions of the joining element 1 are:

• Height: 2.5 mm

• Inner radius: 0.9 mm, and:

• Thickness: 1.4 mm. The dimension ratio along the axis (X'X) of the junction zone 2b to the annular subspace 4a is equal to 5 / 2.5 or 2.

The junction assembly 5 as defined above is produced according to the invention to ensure a gas-tight connection between the ceramic tube 3, and the sleeve 2 of metal or metal alloy, of cylindrical axis symmetry (X'X), and having a particular shape (a "design"), using a glass which is the joining material. A pressure differential between 0 and 30 bar is applied between the inside and the outside of the ceramic tube 3 and therefore between the two zones ZM and ZC on each side of the junction, the pressure being higher on the ZM side. The two atmospheres present respectively in the zones ZC and ZM thus separated are respectively one oxidizing and the other reducing. The maximum working temperature is here between 700 and 900 ^° C., but the tightness must be ensured between the ambient temperature (approximately 20 ^° C.) and the said maximum temperature of use.

The first PVl tested glass is as described in US6430966; it crystallizes easily to form a phase of thermal expansion coefficient close to

13.10 ^{~ 6} / ° C and a glass transition temperature of

702 ⁰ C. The second PV2 tested glass is a commercial glass

(Schott 8350) which has a coefficient of thermal expansion of 11.7 × 10 ^-6 / ° C. and a glass transition temperature of 52 ^° C. The composition of these two glasses is shown in Table 1 below, and their properties particularly interesting for a use in a junction assembly 5 according to the invention are shown in Table 2 below.

Table 1: composition of PV1 and PV2 glasses (% by weight)

Table 2: properties of PVl and PV2 glasses

In the context of this example, it is described below the realization of the junction (or sealing).

Preparation of a Haynes 230® alloy socket 2

The sleeve 2 Haynes 230® alloy is machined from a cylinder to obtain the sleeve 2 as shown in Figure 2 and as described above. This cylinder is characterized by a chamber constituting a junction zone (thickness), at and inside which is installed the glass bead 1 which is the connecting element 1. The deformation of the metal or of the metal alloy in this part advantageously makes it possible to limit the thermal stresses likely to be exerted on the ceramic, mainly because of the differences in coefficients of thermal expansion between the materials. The free space between the shoulder 2a and the glass bead 1 is preferably substantially completely filled with a filler material (not shown here) to hold the glass preform in position during the junction heat treatment.

• Degreasing

The machined bushing 2 first undergoes a cleaning and degreasing step to eliminate machining residues. For this, the piece is immersed in a saponifying solution, the preparation protocol is as explained in Table 3, for 1 hour, with action of ultra sounds.

Table 3: protocol for the preparation of the saponifying solution

Sandblasting Then, the junction zone 2b of said sleeve 2 is sandblasted with corundum (Al2O ₃ ) to develop the surface roughness promoting mechanical adhesion by penetration of the glass in the asperities. The measured roughness has an Ra of the order of 2.5 μm. Preoxidation The adhesion is further improved by the formation of an oxide layer on the surface of the alloy, in this case by exposure to air at 900 ^° C. for 30 min. By partial dissolution of these oxides in the glass, a chemical continuity will be ensured at the glass / alloy interface.

The thickness of the oxide layer must be large enough not to attack the socket 2 during the manufacturing process of the junction assembly, but not too important not to lead to its peeling.

Thermogravimetric analysis made it possible to determine the optimal thermal cycle for the formation of such an oxide layer.

1 glass cord

The objective is to obtain a cord 1 of dense glass between the tube 3 and the sleeve 2.

PVl glass PVl glass is in the form of crushed pieces which are pressed by uniaxial pressing and baking under air at 700 ^° C. for 30 min and then densified in air at ^{0 °} C. for 15 minutes The compactness obtained is approximately 98% of the theoretical density.

PV2 glass PV2 glass is in the form of powder Direct use in this form poses the following difficulties: volume decrease between packed powder and molten glass, fast flow of molten glass These two problems can be solved by using a densified glass preform The shaping is carried out by uniaxial pressing of said powder and cooking in air at 700 ⁰ C for 30 min. The preform corresponds to a section of inner diameter tube close to the outside diameter of the tube 3 and outside diameter close to the inside diameter of the sleeve 2. The compactness obtained after densification is about 98% of the theoretical density.

Assembly of elements

After the development of the various elements of the junction, these elements are assembled and held in place during the junction heat treatment. The glass preform when present must particularly remain at the junction zone 2b of the sleeve 2.

The space 4 remained free, between the tube 3 and the sleeve 2, is first filled with a chemically inert powder vis-à-vis the ceramic and the alloy. This filling makes it possible subsequently to maintain a glass preform in the junction zone 2b of the sleeve 2. It is also used for this purpose a Nextel® type fiber (alumina), wrapped around the tube 3 to wedge it in the socket 2. The materials used for filling are typically MgO which is perfectly chemically inert and / or corundum and / or ceramic powder of the same ceramic as that constituting the tube 3, and / or Nextel® fiber. Junction heat treatment

The objective of this heat treatment is to create the ceramic / glass and alloy / glass interfaces. This step must be carried out under an inert atmosphere such as a nitrogen (N ₂ ) atmosphere, or under partial pressure of oxygen, in order not to modify the composition of the ceramic. The temperature and the dwell time must be perfectly controlled to prevent collapse of the glass. On cooling, the solidification of the glass can exert constraints. It is necessary to carry out a very slow descent, above the stabilization temperature (or temperature of tension). Below, the glass being solid and the constraints related to phase change and solidification being completely relaxed, the cooling rate can be faster.

• PVl glass PVl glass crystallizes easily in a CET structure close to 13.10 ^"6 / C The aim is to take advantage of its fluidity to set it up and create the interfaces, before crystallizing it to increase its CET (limitation of thermal stresses) and improve its stability at high temperature The study of the crystallization of PVl has shown that after 4 hours at 85O ⁰ C, the CET reaches a value of 12.8 × 10 ^-6 / ° C. An ATD analysis carried out under air and under N ₂ shows the presence of two crystallization peaks, the first being at 875 ^° C. and the second being at 1000 ^° C.

The heat treatment cycle therefore consists of a plateau at 115 ^° C. for 15 minutes and then a plateau at 85O ⁰ C for 4 hours to crystallize the glass, followed by a descent to room temperature, at 2 ° C / min between 85O ⁰ C and 700 ⁰ C, 1 ° C / min between 700 ° C and 45O ⁰ C then 20 ° C / min to 20 ^° C. • PV2 glass

The approach is slightly different from that of PVl glass. The goal is to get the glass spread to create the ceramic / glass and alloy / glass interfaces. The viscosity curve of PV2 glass is known. Its softening temperature is at 715 ⁰ C and its stabilization temperature (or annealing) is at 53O ⁰ C.

The thermal cycle is as shown in Figure 3 which is a curve giving the temperature T ( ⁰ C) as a function of time t (hours). This cycle is therefore composed of a rise in temperature at 2 ° / min, a spreading step of 10 min at 75 ^° C., a rapid descent of approximately up to a stabilization temperature (53 ^° C.), d a stabilizing bearing, and a slow cooling then a faster cooling to room temperature.

Claims

1. Ceramic-metal junction assembly (5), said assembly (5) comprising:

1) at least one ceramic part (3) in the form of a hollow and substantially cylindrical tube with an axis (X'X), closed at one of its ends (3b) and open at the other end ( 3a), defining an interior zone called ceramic zone (ZC) and an exterior zone called metal zone (ZM), said ceramic (ZC) and metal (ZM) zones not communicating with each other and being separated at least partially by the part ( 3) made of ceramic, at least partially sheathed by 2) at least one socket (2) made of metal or metal alloy comprising a part (2b) hereinafter called "junction zone" substantially cylindrical and hollow with axis (X'X ) at least partially enveloping said tube (3), a substantially annular space (4) with axis (X'X) being provided between said tube (3) and said junction zone (2b),

3) the seal between said tube (3) and said socket (2) being ensured by at least one ceramic-metal junction element (1) which is in contact with the tube (3) and with said junction zone (2b ) of the socket (2), the junction element (1) being at least partially present in said annular space (4) by occupying a subspace (4a) and preferably being in the form of a piece substantially annular (1),

* said ceramic having a thermal expansion coefficient (CET) strictly greater than the thermal expansion coefficient (CET) of the metal or metal alloy, * said metal alloy comprising at least 10% by weight of nickel and at least 15% by weight of chromium,

* the junction element (1) comprising at least one junction material, preferably consisting of said junction material, ensuring gas tightness from 20 to 900 ⁰ C, being preferably solid at a temperature of 650 to 900 ⁰ C , and having a thermal expansion coefficient (CET) from ambient temperature to 900 ⁰ C greater than or equal to 9.10 ^"6 /°C, preferably from 9 to 15.10 ^"6 / ⁰ C, said assembly (5) junction being such that said junction zone (2b) has a small dimension (1), along any axis (Y'Y) crossing said junction zone (2b) and perpendicular to the axis (X'X).

2. Assembly according to the preceding claim such that the dimension ratio along the axis (X'X) of the junction zone (2b) to the subspace (4a) is at least equal to 2/1, and is preferably in the range of 2/1 to 100/1.

3. Assembly according to one of claims 1 or 2 such that said small dimension (1) is approximately 20 to 500 μm, preferably approximately 50 to 400 μm, even more preferably approximately 200 to 300 μm .

4. Assembly according to any one of the preceding claims such that said ceramic is an ionic conductor, preferably an ionic and electronic conductor, said ceramic more preferably comprising at least one crystal lattice comprising at least one oxygen vacancy, said ceramic being, even more preferably, chosen from ceramics of perovskite crystal structure and cerium oxides.

5. Assembly according to any one of the preceding claims such that said metal or metal alloy comprises on a part of, preferably over the entire, surface of said junction zone (2b), at least one layer of at least one oxide of thickness greater than or equal to approximately lμm and preferably of thickness less than or equal to approximately lOμm.

6. Assembly according to any one of the preceding claims such that said metal or metal alloy has resistance to oxidation under an oxidizing atmosphere up to 1200 ⁰ C, resistance to reduction under a reducing atmosphere up to 1200 ⁰ C, creep resistance up to 1200 ⁰ C, a melting temperature greater than or equal to 1200 ⁰ C, and a thermal expansion coefficient of 2O ⁰ C at 900°C (CET) of 8 to 25. 10 ^"6 / ⁰ C, preferably 10 to 18.10 ^"6 / ⁰ C.

7. Assembly according to any one of the preceding claims such that said junction material is glass, which has a thermal expansion coefficient

(CET) greater than the coefficient of thermal expansion (CET) of the metal or metal alloy and less than the coefficient of thermal expansion (CET) of the ceramic, a resistance to a pressure difference between the ceramic zone and the zone metal between 0 and 3 MPa, chemical stability with respect to ceramic, chemical stability with respect to metal or metal alloy, resistance to reduction under a reducing atmosphere up to 1200 ⁰ C, resistance to oxidation under an oxidizing atmosphere up to 1200 ⁰ C, adhesion on the metal or metal alloy and adhesion to the ceramic, and preferably having a softening temperature at least equal to 65O ⁰ C.

8. Assembly according to one of the preceding claims such that the sleeve (2) comprises at least one shoulder (2c) for supporting the tube (3) and/or at least one shoulder (2a) for wedging the tube (3).

9. Method for manufacturing an assembly (5) according to any one of claims 1 to 8, said method comprising the following successive steps:

1. at least partial pre-oxidation of a surface of a junction zone (2b) of a socket (2) made of metal or metal alloy or a precursor thereof, so as to at least partially form at least one layer of at least one metal oxide on said surface;

2. assembly of a junction material or a precursor thereof, of the socket (2) of step

1, and a part (3) made of ceramic or a precursor thereof, said assembly generally comprising wedging by maintaining the junction material at the level of the junction zone (2b) of the socket (2), then 3. heat treatment of the assembly from step 2, under an inert gas such as nitrogen, under partial pressure of oxygen between 0 and 22%, and at a temperature of 650 to 1200 ⁰ C for a period of 5 min to 10 hours, comprising a rise in temperature from ambient temperature to a treatment temperature, at least one temperature step at the treatment temperature, at least one drop in temperature to a stabilization temperature, at least one stabilization level at the stabilization temperature, and at least one final descent to an end of treatment temperature, said heat treatment leading to the formation of a junction element (1) within an assembly (5) junction.

10. Manufacturing method according to claim 9, further comprising an additional step, which is carried out between steps 1 and 2 of claim 9 or which precedes step 1 of claim 9, said additional step being the following step :

• manufacturing a preform of joining material, in the form of a substantially cylindrical and hollow tube open at at least one of its ends, said manufacturing comprising at least one pressing and one densification, or at least one sintering, or at least one less melting and casting in a mold, at a temperature of 600 to 1200 ⁰ C for 10 to 40 min, said preform serving as a form for the junction material assembled in step 2.

11. Reactor (6), said reactor (6) comprising within it at least mainly said junction assembly (5) according to any one of claims 1 to 8 or manufactured according to a method of any one of claims 9 or 10, said reactor (6) enveloping the zone (ZM), the sleeve (2) made of metal or metal alloy of the junction assembly (5) being mechanically linked to said reactor (6), and the axis ( X'X) being arranged substantially vertically, said reactor (6) comprising at least one fluid inlet (7) in zone ZM and at at least one fluid outlet (8) from zone ZM, said reactor further comprising at least one fluid inlet (9) in zone ZC and at least one fluid outlet (9) from zone ZC.

12. Method of using said reactor (6) for the production of gas and/or gas separation, at an operating temperature of 400 ⁰ C to 900 ⁰ C, said assembly

(5) junction being such that the junction material is solid at said operating temperature.