DE10135235A1 - Production of a gas-tight, high temperature resistant joint between a metallic and a ceramic component used for a high temperature fuel cell comprises welding a gap between the ceramic and metallic components using a laser - Google Patents

Abstract

Production of a gas-tight, high temperature resistant joint between a metallic and a ceramic component comprises welding a gap between the ceramic and metallic components using a laser. Preferred Features: A focused laser is used. The laser leaves the gap between the ceramic and metallic components so that the components are welded and joined in a single step. The laser used is a carbon dioxide laser or an excimer laser. An additional material, preferably glass, ceramic, metal or metal composite, is applied between the metallic and ceramic components.

Description

The invention relates to a method for producing a gastight connection between a metallic and a ceramic substrate, especially for gas-tight Connections in connection with corresponding components of a High temperature fuel cell (SOFC) or one Carbonate melt fuel cell (MCFC).

State of the art

To achieve large electrical outputs, the Usually several individual fuel cells by connecting Elements, so-called bipolar plates or also Interconnectors called, electrically and mechanically to each other connected to a fuel cell stack.

Different types of fuel cells are known. To belong to the alkaline fuel cells (ABZ) that Polymer membrane fuel cells (PEM-BZ), the direct methanol Fuel cells (DMBZ), the oxide ceramic fuel cells (OKBZ) or the carbonate melt fuel cells (KSBZ).

The oxide ceramic fuel cells are among the High temperature fuel cells (SOFC) because of their operating temperature up to 1000 ° C, while the polymer membrane Fuel cells with a working temperature of 70 to 90 ° C are low-temperature fuel cells.

When stacking the individual fuel cells pay particular attention to the two electrode spaces gas-tightly separated on the anode and cathode sides are. The seal must be on the cells themselves, as well as at the corresponding gas inlet and outlet elements.

When making a Up to now, high-temperature fuel cell stacks have been used for joining techniques allow using metallic and ceramic components to connect a glass solder.

For this purpose, glass solder is placed between the components to be connected introduced, and the components to temperatures up to approx. 900 ° C heated. The glass solder melts at these temperatures on. When cooling specifically, the glass solder crystallizes a glass ceramic and so regularly forms one gastight connection between the components.

Can only be disadvantageous for the fuel cell itself Materials are used that can withstand these high temperatures survive a puncture (this is the maximum permissible temperature when using bipolar plates approx. 1000 ° C). In addition, an adjustment of the glass plummet, as Paste or as a molded part, to the geometry of the connecting components required.

Task and solution

The object of the invention is a compared to the prior art Technically improved process for producing a gastight connection of metals and / or ceramics for the To create high temperature use. Furthermore, it is the Object of the invention, a generated by this method High temperature fuel cell with gas-tight connections to create between ceramic and / or metal parts.

The object is achieved by a method according to Main claim, as well as a high temperature fuel cell according to ancillary claim. Further advantageous configurations of the process and the fuel cell can be found in the subclaims referring to them in each case.

Subject of the invention

The method according to the invention for producing a gas-tight and high-temperature resistant connection between a metallic and a ceramic component for a high-temperature fuel cell is characterized in that a gap located between the ceramic and the metallic component is welded with the aid of a laser. This creates a gas-tight and temperature-resistant joint connection in one step. No other joining material, such as e.g. B. glass solder, necessary for the connection. Another advantage of this method is that the entire component does not have to be subjected to a heating process. Only the area in the immediate vicinity of the joining seam is thermally stressed. The laser, in particular a focused laser, advantageously only heats the components locally and briefly in the joining area. A particularly suitable laser is a CO ₂ - or an excimer laser.

This method is particularly advantageous when the thermal expansion coefficients of the components to be connected differ by less than 1 × 10 ^-6 1 / K.

The thermal expansion coefficients are further apart, additional advantages are advantageous in the method Joining material between the components to be connected provided. This additional material has in particular one thermal expansion coefficient between those of the components to be connected, so a gradual one Transition in thermal expansion between the To create components. Suitable materials, their thermal expansion coefficient by a specialist in can be adapted to a certain extent for example glass materials, especially silicate, boratic, phosphatic or mixed bound. Farther are suitable as additional joining materials multi-phase ceramics, also metallic or ceramic May contain fibers or whiskers. Even metals or Metal / ceramic composites are additional joining materials to call.

The selection of suitable additional joining materials is not on low-melting materials as before limited. Due to the local heating, this Process also use higher melting materials come without the components to be connected are too thermally stressed.

Laser welding can also be used for complicated geometries the seams to be formed can be used without any problems. The Joining seam is regularly gastight and extremely stable.

Special description part

• a) daß die Zellen derart ausgestaltet sein müssen, daß sich nach dem Laserschweißen kein direkter Kontakt zwischen Anode und Kathode ausbildet und
• b) daß die Fügung an den Gaseinlass- und -auslasselementen immer isolierend ausgestaltet wird.

When producing a fuel cell, several individual cells are combined to form a fuel cell stack. When stacking the cells, ensure that the two combustion chambers are gas-tight on the anode and cathode sides. The sealing must take place both on the cells and on the gas inlet and outlet elements (see FIG. 1). An important prerequisite for the seal is that the electrical current is only conducted via the cells and not also via the bipolar plates, since otherwise a short circuit is generated. This means for the seals presented here

• a) that the cells must be designed in such a way that no direct contact between anode and cathode is formed after laser welding and
• b) that the joining of the gas inlet and outlet elements is always designed to be insulating.

Two alternative variants of the method according to the invention are presented for this gas-tight separation.

Variant 1: Laser welding without joining compound
Variant 2: Laser welding with joining compound

Variant 1 ( Fig. 1)

In variant 1, the metallic interconnector (IK) and the substrate are welded together in such a way that the gap between the IK and the substrate is closed with the IK of the same type. This is done by introducing energy with the help of a focused laser. After the laser has been shut down on all sides, the gas channels between the anode and cathode sides are separated from one another in a gas-tight manner. The advantage of this method is that no additional native or foreign material has to be used for gas-tight joining. The variant is independent of shape, ie it can be used for planar rectangular or round, for three-dimensional ("egg carton shape") and for tubular and quasi-tubular systems. A permanent, irreversible connection is formed within the fuel cell stack at the seams. A prerequisite for such joining seams is therefore that the thermal expansion coefficients α of the materials have no differences greater than l × 10 ^-6 1 / K.

Variant 2 ( Fig. 2)

In contrast to variant 1, additional material for welding must be available for this variant. Advantages of this variant are a weldability that is independent of the shape of the fuel cell, the possibility of using different materials within a fuel cell stack, which, if necessary, results in a. B. gradual transition of the physical properties between interconnector and cell can form, the independence of the cell from the surrounding interconnector and a higher tolerance to manufacturing processes (see Fig. 2).

For this technology, for example, some materials can be used, which are adapted to the surrounding material (cell and metal frame, α ~ 12 × 10 ^-6 1 / K) in the expansion coefficient. These include materials based on glass materials, silicate, borate, phosphate or mixed bound; with or without ceramic or metallic fillers, as well as ceramics, single or multi-phase, filled or unfilled with metallic or ceramic fibers or whiskers, as well as metals or metal / ceramic composites (for cell sealing).

Both variants are one in the connection system Fuel cell stack rigid, d. H. preferably suitable for one stationary application. However, it is also possible through Use of a suitable seal design, see the German patent application DE 100 33 898.4-45, mobile Make applications of the fuel cell.

The materials are either as pasty materials, as Powder or as a semi-finished product on the areas to be joined applied and fixed by laser with the cell and the Welded metal frame. A separate heating phase like z. B. omitted when using glass solders and makes thereby making the manufacturing process easier and cost-effective.

By using a laser for joining there is none Restriction to low-melting glass solders, glass ceramic solders or composite glass solders, but it can melt on higher Glasses, crystallizing glasses, ceramics or Metal materials are used because only the mass to be joined (to be welded) is heated locally and the Environment remains comparatively "cold".

The joints of the gas bushings can be such be designed so that the implementation of the lower plate is smaller than that of those lying on it, so that by means of the laser can be "internally welded" (variant 2).

Suitable materials to be used are in particular:
Ceramics, in particular from natural raw materials such as quartz, feldspar, wollastonite, nepheline syenite and kaolin. Ceramics which solidify amorphously are also suitable after heat treatment. To improve the expansion coefficient, these can be filled with crystalline components such as MgO or ZrO ₂ or metals, or spontaneous targeted crystallization can occur during the temperature treatment.

Glasses, in particular based on joining glasses for aluminum oxide, Kovar, platinum or titanium, for example glasses filled with MgO or ZrO ₂ .

Metals, especially as semi-finished products or powder from the Metal frame of the same type of steel material, such as Fe-Cr steel grades with chrome contents between 16 and 26 Mass% Cr and the material numbers 1.4016, 1.4113, 1.4509, 1.4502, 1.4510, 1.4511, 1.4513, 1.4520, 1.4521, 1.4742, 1.4745, 1.4748, 1.4749 and 1.4763 or materials according to DE 196 50 704; these can also be used as Filling material for ceramics or glasses mentioned above.

embodiments Float glass (CaNaSi glass)

After applying an appropriate amount of CaNaSi glass (pasty, powdery or as a semi-finished product), the border is scanned using a focused laser (e.g. CO ₂ or excimer laser) and welded / joined in one step. This leads to an intimate, non-releasable connection between the cell and the metal frame, and due to only local heating in the jointing compound, there is no major thermal impairment of the surroundings.

Investigations by A. Helebrandt et al .: Merthamatical modeling of temperature distribution during C = 2 laser irradiation of glass, Glass Technology Vol. 34, No. 4 (1993), pp. 154-158, on a float glass showed that with a CO ₂ laser power of 142 W / cm ² the temperature on the glass surface is approx. 1150 ° C, but this at a depth of 1 mm only reached approx. 950 ° C (after a laser exposure time of 1 sec; rectangular distribution; these values shift to 1150 ° C or approx. 800 ° C when using a Gaussian intensity distribution).

This means that the high temperature (> 1000 ° C) affected zone is comparatively small.

Metal (Inconel 600 Alloy)

The basic procedure corresponds to the aforementioned example. Investigations by Kim et al .: Surface modification of Inconel 600 alloy by laser surface melting and alloying to improve its corrosion resistance; Proc. of l ^st Int. Conf. On Advanced Materials Processing 2000, pp. 237-243, on an Inconel 600, in which a surface modification should be carried out, show that laser processing is possible with a CO ₂ laser at powers between 500 and 1300 W per 1 mm ∅ area is. The layer thicknesses vary between 150 and 200 µm or between 300 and 400 µm depending on the parameters. This layer was created on a chromium-rich background layer, which had a thickness of 50-80 µm. Legend for FIGS. 1 and 2 1 interconnector (first component)
2 substrate (second component)
3 cathode
4 gas channel
5 gap
6 weld seam
7 additional joining material

Claims (9)

1. A method for producing a gas-tight and high-temperature resistant connection between a metallic and a ceramic component for a high-temperature fuel cell, characterized in that a gap located between the ceramic and the metallic component is welded with the aid of a laser. 2. The method according to the preceding claim, in which a focused laser is used. 3. The method according to any one of the preceding claims, at which the laser the gap between ceramic and metallic component and so the components in one Step welds and inserts. 4. The method according to any one of the preceding claims 1 to 3, in which a CO ₂ laser is used as a focused laser. 5. The method according to any one of the preceding claims 1 to 3, where an excimer laser as a focused laser is used. 6. The method according to any one of the preceding claims 1 to 5, where an additional material between the ceramic and the metallic component is introduced. 7. The method according to the preceding claim 6, in which as additional material glass, ceramic, metal or a Metal composite is used. 8. The method according to any one of the preceding claims 6 to 7, where an additional material is used, whose coefficient of thermal expansion between that of the components to be connected. 9. The method according to any one of the preceding claims 6 to 8, are used in the ceramic and metallic components whose thermal expansion coefficients differ by more than 1.10 ^-6 1 / K.