DE10135235C2 - Process for producing a gas-tight connection between a metallic and a ceramic substrate - Google Patents

Description

The invention relates to methods for producing a gastight connection between a metallic and a ceramic substrate, especially for gas-tight connections conditions in connection with corresponding components High temperature fuel cell (SOFC) or a 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 interconnects called gates, electrically and mechanically with each other connected to a fuel cell stack.

Different types of fuel cells are known. This includes ren the alkaline fuel cells (ABZ), the polymer membrane bran fuel cells (PEM-BZ) that burn direct methanol Stofzellen (DMBZ), the oxide ceramic fuel cells (OKBZ) or the carbonate melt fuel cells (KSBZ).

The oxide ceramic fuel cells are among the highest 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.

In particular, when stacking the individual fuel cells take special care that 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 producing a high temperature fuel cell stacks have been used until now, which allow metallic and ceramic components to connect using 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. It melts at these temperatures Glass solder on. When it cools down, it crystallizes Glass solder from a glass ceramic and thus forms rule moderately a gas-tight connection between the components.

Can only be disadvantageous for the fuel cell itself Materials are used that have this high tempera survive the damage-free structure (that's how it is maximum permissible temperature when using bipo larer plates approx. 1000 ° C). In addition there is a match solution of the glass solder, as a paste or as a molded part the geometry of the components to be connected is required Lich.

DE 691 25 265 T2 discloses a method of manufacture separation of a separator (bipolar plate) for a Brenn material cell. Individual layers become one Cutting device welded with a laser, at for example an anode edge plate, an intermediate connection and a cathode edge plate. These will first placed on top of each other and the environment of a Edge connected section with heat dissipating Pressed metal. During the section under pressure stands the individual layers along their  outer circumferential lines using a welding heat source welded throughout. On all three layers metallic components.

Furthermore, it is known from DE 41 19 910 C1 that a ceramic layer the size required for sintering material heat through high-energy radiation, e.g. B. in the form of a focusing laser that can. A kera is caused by laser exposure Mix material layer sintered or just ge dries. It is advantageous when using a laser practically no effect on adjacent layers brought about.

Task and solution

The object of the invention is a compared to the state Technically improved method of manufacture a gas-tight connection of metals and ceramics to create for high temperature use.

The object is achieved by methods according to the claims 1 and 2.

More beneficial Procedures can be found in the respective references Dependent claims.  

Subject of the invention

The inventive methods for producing a gas-tight and high-temperature resistant connection between a metallic and a ceramic component for a high-temperature fuel cell are characterized in that a gap between the ceramic and the metallic construction part is welded with the aid of a laser. This creates a gas-tight and temperature-resistant joint in one step. No other joining material, such as e.g. B. glass solder, necessary for the connection. Another advantage of this drive is that not all of the components 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.

Are the thermal expansion coefficients still available? each other, is advantageous in the method additional Joining material between the components to be joined hen. 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 wise glass materials, especially silicate, borati cal, phosphatic or also mixed bound. Farther are suitable as additional joining materials one or more  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 thereby the components to be connected ther be mixed too much.

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

In the manufacture of 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 passed over the cells and not also over the bipolar plates, since otherwise a short circuit is generated. This means for the seals presented here

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

For this gas-tight separation, two alternative variants of the method according to the invention are presented.
Variant 1 : Laser welding without joining compound
Variant 2 : Laser welding with joining compound

version 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-like material. 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 shape-independent, ie it can be used on the one hand for planar rectangular or round, for three-dimensional ("egg carton shape") and on the other hand for tubular and quasi-tubular systems. A permanent, non-releasable connection is formed within the fuel cell stack at the joining seams. A prerequisite for such seams is therefore that the thermal expansion coefficients α of the materials have no differences greater than 1 × 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 independent of the shape of the fuel cell, the possibility of using different materials within a fuel cell stack, which thereby, if necessary, for. B. gradual transition of the physical properties between inter-connector 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, the expansion coefficient of the surrounding material (cell and metal frame, α ~ 12 × 10 ^-6 1 / K) are adapted. These include materials based on glass materials, silicate, borate, phosphate or mixed bound; with or without ceramic or metallic fillers and 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 in the fuel connection system cell stack rigid, d. H. preferably suitable for a sta stationary application. However, it is also possible to use it a suitable seal design, see here DE 100 33 898 A1, mobile applications 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 cheaper ger.

By using a laser for joining there is no loading 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 work 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 feedthroughs can be designed in such a way that the feedthrough of the lower plate is smaller than that of the one lying on it, so that it can be "internally welded" by means of the laser (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. These can be filled with crystalline components such as MgO or ZrO ₂ or metals to improve the coefficient of expansion, or spontaneous targeted crystallization can occur during the temperature treatment.

Glasses, in particular on the basis of 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 mas % 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 speaking of 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 mode ling of temperature distribution during C = 2 laser irradiati on 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 approximately 1150 ° C., but this is in the 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 those with 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 1 ^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 with a CO ₂ laser at powers between 500 and 1300 W per 1 mm ∅ area is possible. 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 to FIGS. 1 and 2

1

Interconnector (first component)

2

Substrate (second component)

3

cathode

4

gas channel

5

gap

6

Weld

7

additional joining material

Claims (7)

1. A method for producing a gas-tight and high-temperature resistant connection between a metallic interconnector and a ceramic component of a high-temperature fuel cell, the difference in thermal expansion coefficients of the two components is not greater than 1.10 ^-6 1 / KJ, with the step by moving off to be joined with a laser, a gap located between the ceramic component and the metallic interconnector is welded by the energy input of the laser. 2. Method for producing a gas-tight and high-temperature resistant connection between a metallic interconnector and a ceramic component of a high-temperature fuel cell, the thermal expansion coefficients of which differ by more than 1.10 ^-6 1 / K.
with the steps
in the gap between the ceramic component and the
metal interconnector, a joining material is inserted,
by driving the seam to be joined with a laser, a gap located between the ceramic component and the metallic interconnector is welded by the energy input of the laser. 3. The method according to the preceding claim 2, in which as an additional material glass, ceramic, metal or a metal composite is used. 4. The method according to any one of the preceding claims 2 to 3, where an additional material is used whose thermal expansion coefficient between those of the components to be connected lies. 5. The method according to any one of the preceding claims 1 to 4, where a focusing laser is used becomes. 6. The method according to claim 5, in which a CO ₂ laser is used as the focusing laser. 7. The method of claim 6, wherein an excimer laser is used as a focusing laser.