DE20221582U1 - High-temperature-resistant adhesive based on water glass comprises boron nitride as an additive - Google Patents

Abstract

High-temperature-resistant adhesive based on water glass comprises boron nitride as an additive. Independent claims are also included for the following: (1) Process for gluing flat metal substrates using the above adhesive; and (2) Fuel cell consisting of several metal layers glued together. Preferred Features: The adhesive contains 1-40 wt. %,, preferably 7-25 wt.% boron nitride referred to the dry weight. The boron nitride is present in particle form with a mean particle size of 1-10 Micro.

Description

The The invention relates to a high temperature-resistant adhesive based on water glass.

On Waterglass-based adhesives are, for example, as high-temperature-resistant cold adhesives known, inter alia, for bonding materials on the Base of calcium and alumina silicates, fibrous cements or Ceramics are used.

From These adhesives are known to have high temperature resistance and also against many chemicals, especially acids, organic solvents, oil and gasoline resistant are.

adversely in the known high temperature-resistant adhesives based on water glass is that these in their use for bonding metallic Substrates, especially at high temperatures, i. in the temperature range above 700 ° C, for outgassing and foaming tend to weaken the adhesive bond and in particular to a reduced Tightness of the same opposite liquids and gases.

In the past, for bonding of metallic substrates, for example, with glass solders have been obtained, as for example in the EP 0907 215 A1 in the application of high temperature fuel cells are described in detail.

High temperature Adhesives for Metal substrates are especially in the production of this kind of fuel cells of importance in which a large variety of flat Metal substrates stacked on top of each other are arranged and gas-tight at predetermined areas and in particular electrically insulating to connect.

glass solders have here first adequate gas tightness as well as sufficient electrical Isolation property proved and are also among the required Temperatures> 700 ° C temperature stable.

adversely with the Glasloten is that these only with a relatively large expenditure applied to the splices and then the adhesive bond can be produced. Are the glass solders in operation temperature cycles subjected as usual Use of high temperature fuel cells is the case this for the formation of cracks and the glued joints formed from glass solder lose their gas tightness.

task The present invention is a high temperature adhesive to propose, which in particular also for the bonding of Metal substrates suitable and which also at high operating temperatures its gas tightness and electrical insulator properties are not loses.

These Task is inventively characterized solved, that a high temperature-resistant adhesive based on water glass Boron nitride is added as an additive.

Amazingly, let yourself by adding boron nitride to the water glass based adhesive its tendency to foam sufficiently suppress at high operating temperatures.

In order to can be very thin Bonded connections produce, nevertheless, a sufficient gastightness have and also at high temperatures their good insulator properties maintained and when passing through temperature cycles not to cracking tend.

Furthermore the adhesives of the invention are suitable also for bonding metal and ceramic as well as two ceramic elements together.

The Effect of oppression or pushing back the Aufschäumneigung high-temperature waterglass-based adhesives are already possible reach with low levels of boron nitride, e.g. with a Proportion of 1 wt .-% based on the dry matter. The shares that The adhesives may have boron nitride are on a large scale variable and can adapted to the respective requirements of the splices. Preferably, an upper limit for the proportion of boron nitride adhered to the dry mass of the adhesive of 40 wt .-%.

Often finds you have very good adhesive properties, especially a very good Gas tightness of the splice and good insulator properties of the Bonding point when boron nitride is added to the adhesive in the range from 7 to 25 wt .-% based on the dry weight of the adhesive.

The Boron nitride is called particulate Aggregate processed to the adhesive, and recommends this it is to use boron nitride with an average particle size of 1 .mu.m to 10 .mu.m.

Particularly suitable products have a specific surface area of the boron nitride in the range from 2 to 20 m ² / g.

A The preferred modification of BN is hexagonal, graphite analog BN.

The water glass component itself, which is a composition of the formula Me ₂ O.SiO ₂ is preferably used with a molar ratio of SiO ₂ : Me ₂ O of ≥ 2: 1, in particular> 3, wherein Me preferably represents Na and / or K. The waterglass component may also be included in lithium waterglass or formed entirely of lithium waterglass.

critical for one good high-temperature strength of the splice is that the waterglass component a high melting point, in particular a melting point in the range from 1100 to 1150 ° C or more.

the Adhesives can if necessary, one or more mineral fillers be added here, it should be noted that the filler so selected he must be able to reach a temperature of 1100 ° C or more is non-gasrous.

At is the particle size of the mineral filler little critical. In view of the often desired layer thicknesses 10 to 100 microns are used particle sizes, on average about 0.5 to 30 microns, preferably 1 to 20 microns be. For platelet-shaped fillers, such as. Mica, are also larger dimensions in the platelet level possible, since these are at least partially applied to the surface of the Align applied substrate.

The Amount of mineral filler in the adhesive leaves vary within wide limits. This gives the opportunity additive of mineral filler such that the thermal expansion coefficient similar to the dried adhesive that of the metallic substrate to be bonded, in particular steel is.

Often as Cheap Found proportions of the mineral filler in the adhesive (turn based on the dry mass of the adhesive) are from 1 to 40 Wt .-%, more preferably 4 to 20 wt .-%.

The fillers can as well as a means for modifying the viscosity of the adhesive may be used, so that may be a thickener can be omitted.

preferred mineral fillers are kaolin, mica and talc. Other mineral fillers can be selected according to the previously given rule that the mineral filler at a temperature of up to 1100 ° C released no gas fractions may.

It has been found to be adhesive with mineral fillers have particularly good properties when kaolin is the main constituent the filler content forms or as a sole filler is used. Kaolin leaves but also successful in mixtures with talc and mica deploy.

In the adhesive, the waterglass component is preferably with a Solid glass content of 30 to 40 wt .-% processed. Will be a relative high content of boron nitride, it is recommended that the water content to increase the overall mix slightly.

Further it may be appropriate to add a dispersing agent to the adhesive, being here often Proportions in the range of 0.1 to 5 wt .-%, more preferably 0.4 to 1.5% by weight, based in each case on the dry mass of the adhesive, are generally sufficient in particular mineral fillers dispersed in the adhesive of the invention to stabilize.

Become low levels of fillers used or dropped these fillers Completely away, it is recommended to add a thickener to the adhesive, especially in the form of silica and in an amount of up to 10 wt .-% (based on the dry matter of the adhesive).

The The invention further relates to the use of an adhesive such as it has been described above for bonding flat metal substrates, in particular for bonding sheet steel layers.

When area Metal substrates are particularly suitable here elements from which Fuel cells are produced. Here are the special advantages the high temperature resistant according to the invention Adhesive to advantage, because here is a high temperature resistant Splice needed, the above In addition, has a high gas-tightness and also good Isolatoreigenschaften shows. All three requirements are ideally met by the adhesive of the invention Fulfills. Beyond that are the adhesive layers remain flexible even after drying and curing, i.e. slight elastic deformations of the metallic substrates do not result Cracks in the adhesive portions and not to their chipping.

Such Type bonded metal substrates allow operating temperatures up to 850 ° C or sometimes even a bit more, without their adhesive properties, in particular also their gas tightness and insulator properties underneath Suffer.

The invention further relates to a method for bonding flat metal substrates, this being characterized in that an adhesive of the type according to the invention described above is used and applied to at least one of the surfaces to be bonded together (usually at room temperature) that the metal substrates to be bonded then at least in the Be contacted area of the splices and that then the adhesive is dried and cured at elevated temperature.

The adhesives according to the invention allows application of the adhesive at room temperature and this simplifies the handling of the adhesive according to the invention considerably. For example, the adhesives of the invention can be screen-printed Instruct. Compared with the first after applying At least to be melted glass solders arise here considerable Advantages.

The Drying of the adhesive is preferably carried out at a higher temperature, especially at temperatures of 70 ° C or higher, more preferably in Range from 70 to 80 ° C.

The Invention finally relates a fuel cell with several metal layers glued together, wherein the bonding of the metal layers by means of an adhesive according to the invention, as described above.

The Invention will be described below with reference to the drawings and examples even closer explained. They show in detail:

1 High-temperature fuel cells in exploded view; and

2 a high temperature fuel cell block in sectional view in assembled condition.

1 contains an exploded perspective view of two along the stacking direction 112 successive fuel cell units 114 , Each of the fuel cell units 114 comprises a substantially plate-shaped cathode-anode-electrolyte unit 116 (hereinafter referred to briefly as KAE unit), between a contact plate 118 and a fluid guide frame 120 is held.

The KAE unit 116 comprises a gas-permeable, electrically conductive substrate, which may be formed, for example, as a metal wire mesh, metal wire fleece, metal wire mesh, metal wire mesh, or as a porous body made of sintered or pressed metal particles, whereby a fuel gas may pass through a substrate from a fuel gas space adjacent to the substrate.

Further, the KAE unit includes 116 an arranged on the substrate plate-shaped anode made of an electrically conductive ceramic material, such as Ni-ZrO ₂ cermet (ceramic-metal mixture) and a parallel thereto arranged plate-shaped cathode, which consists of an electrically conductive ceramic material, for example of LaMnO ₃ formed is.

Between Anode and cathode, an electrolyte is arranged, which is preferably formed as a solid electrolyte and, for example, yttrium-stabilized Zirconia is formed.

The contact plates 118 serve to dissipate the released during the reaction at the anode electrons from the anode via the substrate or to supply the required for the reaction at the cathode electrons of the cathode.

For this purpose, each of the contact plates 118 of a highly electrically conductive metal sheet having a plurality in the longitudinal direction of the contact plate 118 extending parallel ribs, which is a contact area 134 form. This contact area 134 points upward and thus to the anode of the same fuel cell unit 114 associated KAE unit 116 projecting anode-side ribs and from the contact area 134 down and thus to the cathode of an adjacent fuel cell unit 114 associated KAE unit 116 projecting cathode-side ribs on.

The cathode-side ribs of the contact area 134 each stand with the cathode of an adjacent fuel cell unit 114 associated KAE unit 116 in electrically conductive surface contact, so that electrons from the contact plate 118 can get to the cathode. In this way, the contact plates allow 118 the charge balance between the anodes and the cathodes along the stacking direction 112 successive KAE units 116 ,

The at the ends of a fuel cell block composite 106 (see. 2 ) arranged contact plates 118 are (not shown in the drawing way) connected to an external power circuit to those at these terminal contact plates 118 to give up arising electric charges.

In a side area of each contact plate 118 are a plurality, for example two, substantially circular fuel gas passage openings 142 educated. Each of the fuel gas passage openings 142 is of an annular downwardly offset edge region 144 surround.

A side area with respect to the contact surface 134 opposite side area of each contact plate 118 is with a plurality, for example, three, substantially circular exhaust gas passage openings 152 Mistake. Each of the exhaust gas passage openings 152 is of an annular downwardly offset edge region 154 surround.

The exhaust gas passage openings 152 the contact plate 118 allow the passage of from the fuel cell units 114 exhaust gas to be discharged through the contact plate 118 containing excess fuel gas and products of combustion, especially water.

Each of the fluid guide frames 120 has a substantially rectangular, central passage opening 176 for the passage of the KAE unit 116 same fuel cell unit 114 on.

In a side area of the fluid guide frame 120 are a plurality, for example two, substantially circular Brenngasdurchgasöffnungen 182 formed, which the passage of fuel gas through the fluid guide frame 120 enable.

In a side area with respect to the passage opening 176 opposite side region are a plurality, for example three, substantially circular exhaust gas passage openings 184 formed, which the passage of from the fuel cell units 114 exhaust gas to be discharged through the fluid guide frame 120 enable.

In each case a fluid guide frame 120 and a contact plate 118 together form a housing of a fuel cell unit 114 , The fluid guide frame 120 and the contact plate 118 such a housing of a fuel cell unit 114 at their connecting flanges 192 fixed to each other and sealed gas-tight against each other by means of an adhesive layer of the high-temperature resistant adhesive according to the invention.

In the area of the exhaust gas passage openings 152 . 184 are annular support elements 200 arranged, which with its underside each at the top of an exhaust passage opening 152 surrounding border area 154 a contact plate 118 and with their upper side respectively at the bottom of the exhaust passage opening 184 in the fluid guide frame 120 surrounding area.

Similar, only in their dimensions of the support elements 200 at the exhaust gas passage openings 152 . 184 distinctive support elements 200 are between the contact plate 118 and the fluid guide frame 120 in the area of the fuel gas passage openings 142 . 182 arranged.

The support elements 200 serve to the contact plate 118 and the fluid guide frame 120 a housing of a fuel cell unit 114 Keep at a distance from each other and so a compression of the housing by the during assembly of the fuel cell block assembly 106 (see. 2 ) to prevent clamping force acting on the housing.

The support elements 200 can be solid with radially extending gas passage channels, but it can also support elements 200 are used, which are formed as porous, gas-permeable sintered elements of a ceramic and / or a metallic material.

How best 1 can be seen, limit those in the stacking direction 112 successive contact plates 118 and fluid guide frame 120 with the respectively arranged therebetween support elements 200 several, for example three, exhaust ducts 240 into which exhaust gas from the fuel gas chambers of the fuel cell units 114 through the gas passageways in the support elements 200 can enter and sealed by adhesive gaskets from the oxidant spaces of the fuel cell units 114 are separated.

In a similar way are also between the border areas 144 the fuel gas passage openings 142 every contact plate 118 and the fluid guide frame 120 one in the stacking direction 112 under the relevant contact plate 118 arranged fuel cell unit 114 Adhesive seals arranged which the fuel gas passage openings 142 and 182 in the contact plate 118 or in the fluid guide frame 120 enclose annular, so that in the stacking direction 112 successive contact plates 118 and fluid guide frame 120 together with the respective intermediate supporting elements 200 and adhesive gaskets multiple, for example, two, fuel gas channels 260 form, which are along the stacking direction 112 extend from which fuel gas through the gas passageways in the support elements 200 in the fuel gas chambers of the fuel cell units 114 can emerge and wel che through the adhesive seals gas-tight from the oxidant spaces of the fuel cell units 114 are separated.

According to the invention, the adhesive gaskets are each made of a gas-tight, electrically insulating coating from a high formed temperature-resistant adhesive according to the invention, which as a paste by screen printing or by roll coating or via a nozzle in the form of a bead on the surface of the contact plate 118 or on the surface of the fluid guide frame 120 is applied.

Further, the fuel gas space of each fuel cell unit becomes 114 from the oxidant space one in the stacking direction 112 above arranged fuel cell unit 114 gas-tight separated by a fuel gas space seal, which can also be formed from the high temperature resistant adhesive according to the invention.

The fuel cell units 114 of the fuel cell block assembly 106 from 2 are along the stacking direction 112 stacked so that the cathode-side ribs of each contact plate 118 to the cathode of the KAE unit 116 the underlying fuel cell unit 114 extend and abut in the electrically conductive contact on the same.

The fuel gas passage openings are aligned 142 . 182 and the exhaust passage openings 152 . 184 along the stacking direction 112 successive fuel cell units 114 with each other, so the fuel gas channels 260 or the exhaust ducts 240 to build.

How out 2 can be seen, flows at the lower end of each fuel gas channel 260 in the same a Brenngaszuführöffnung 234 which is a lower end plate 108 of the fuel cell block assembly 106 coaxial with the respective fuel gas channel 260 interspersed.

At the the respective fuel gas channel 260 opposite end of Brenngaszuführöffnung 234 is a fuel gas branch line 236 connected, which leads to a (not shown) fuel gas supply.

The exhaust ducts 240 of the fuel cell block assembly 106 open at their upper ends in each case to a respective exhaust duct 240 coaxial exhaust discharge opening 262 which the lateral upper end plate 111 interspersed and at her the respective exhaust duct 240 opposite end to a respective exhaust branch line 242 connected.

These exhaust branch lines 242 open into an exhaust treatment unit (not shown).

During operation of the fuel cell device 106 the fuel gas flows through the fuel gas branch lines 236 and the fuel gas supply ports 234 in the two fuel gas channels 260 and distributed from there through the gas passageways in the fuel gas channel side support elements 200 on the fuel gas chambers of the fuel cell units 114 , which respectively through the contact plate 118 , the fluid guide frame 120 and the KAE unit 116 the fuel cell unit concerned 114 are enclosed.

The fuel gas is at least partially at the respective fuel gas space limiting anode of the respective KAE unit 116 oxidized.

The oxidation product (water) arrives together with excess fuel gas from the fuel gas chambers of the fuel cell units 114 through the gas passage channels in the abgaskanalseitigen supporting elements 200 into the three exhaust channels 240 from which it is supplied to the (not shown) exhaust treatment unit.

To the along the stacking direction 112 successive fuel cell units 114 to fix each other by external tension, are several connecting screws 250 (please refer 2 ), which through holes 252 in the middle upper end plate 110 of the fuel cell block assembly 106 enforce and at her the respective screw head 254 opposite end with an external thread 256 are provided, which in each case a threaded hole 258 in the lower end plate 108 of the fuel cell network 106 is screwed in, so that the middle upper end plate 110 and the lower end plate 108 through the connecting screws 250 be braced against each other and a desired pressing force on the end plates 108 . 110 on the middle, the contact fields 134 comprehensive area of the stack of fuel cell units 114 is transferable (see 2 ).

By the use of the high temperature resistant according to the invention Klebemittels can be the fuel cell units with greater efficiency finished and the splices remain even at high operating temperatures the cells of 850 ° C and more gas-tight and have a flexibility even in the dry state, the is sufficient for the occurring during assembly of the cell block assembly personnel and resist deformation easily. Also when starting the cell blocks, at which the cell blocks first brought to operating temperature makes the property by the adhesive according to the invention formed high temperature resistant sealing points positively noticeable. Here, too, remain any elastic deformations of the metal layers without adverse consequences for the gas-tightness of the connection of the supporting elements with the metal layers or the metal layers with each other.

The The following examples are recipes, as they successfully with high-temperature fuel cells used to form the sealing regions as described above can be.

Example 1:

73 parts by weight of sodium water glass having a SiO ₂ : Me ₂ O ratio of 3.3 and a glass content of about 35 wt.% Be with 8 parts by weight of kaolin, 3 parts by weight of mica and 16 parts by weight of boron nitride (alpha-BN, hexagonal graphite-analogous BN, average particle size 4 μm).

The so obtained adhesive is about a nozzle as a bead on the metal or ceramic surfaces to be bonded Component of a high-temperature fuel cell applied. The individual components of the fuel cell are joined together and the Fuel cell block dried at a temperature of 70 to 80 ° C. A curing The splice is carried out at the first heating of the block to operating temperature. The splices prove to be gas-tight and keep the operating conditions at 850 ° C in the endurance test without problems. Also the electrical resistance values at operating temperature are sufficiently high. In particular, observed you do not foaming at Heating up to the operating temperature of the cells. The splices have no after passing through several temperature cycles Cracking up.

ever after selected Ordering may be desired its the viscosity to increase the adhesive mass. This can be known per se viscosity-modifying agents such highly dispersed silicic acid without impairment the properties of the adhesive bonds in the above Use recipe. The proportions of fumed silica on the Total formulation is preferably 0.2 to 5 wt.% Which one wide Has leeway in adjusting the viscosity.

Becomes a lower viscosity for the elected Application process needed, let yourself to achieve this simply by adding water.

Example 2:

To 68 parts by weight of water glass, 20 parts by weight of kaolin and 12 parts by weight Boron nitride given (specifications as above). Also this recipe for the adhesives according to the invention results in the test comparable results as the recipe of example 1.

Example 3:

To 79 parts by weight of water glass are 7 parts by weight of kaolin, 4 parts by weight Talc and 10 parts by weight BN added (specifications as before). Again, comparably satisfactory results are achieved in the test as in Example 1.

Example 4:

Out a commercially available Waterglass-based cold glue, namely Canol 460 from Segliwa GmbH, Wiesbaden, Germany becomes an adhesive mixture with the addition of BN manufactured, which contains 17 wt.% BN.

Also leaves this mixture successfully used as an adhesive in high temperature fuel cells deploy.

Claims (14)

High temperature-resistant adhesive based on water glass, characterized in that the adhesive comprises boron nitride as an additive. Adhesive according to claim 1, characterized in that that boron nitride has a dry matter content of From 1% to 40% by weight, preferably 7 to 25 wt .-%, is contained in the adhesive. Adhesive according to Claim 1 or 2, characterized that the boron nitride is in particle form with a middle Particle size from 1 μm to 10 μm. Adhesive according to one of Claims 1 to 3, characterized that the boron nitride in the form of hexagonal, graphite-like Modification is contained in the adhesive. Adhesive according to one of claims 1 to 4, characterized in that the waterglass component is a composition of the formula Me ₂ O.SiO ₂ has a molar ratio SiO ₂ : Me ₂ O of> 3, wherein Me preferably represents Li, Na and / or K. Adhesive according to one of claims 1 to 5, characterized the water glass component has a melting point in the range of 1100 to 1150 ° C having. Adhesive according to one of the preceding claims, characterized in that the adhesive further comprises a mineral filler, which is non-gasifying up to a temperature of 1100 ° C or more. Adhesive according to claim 7, characterized in that that the mineral filler included in an amount in the adhesive is that the coefficient of thermal expansion similar to the dried adhesive that is steel. Adhesive according to claim 6 or 7, characterized that the proportion of the mineral filler in the adhesive (relative to the dry mass) 1 wt.% to 40 wt.%, preferably 4 to 20 wt. is. Adhesive according to one of claims 7 to 9, characterized that the mineral filler selected is kaolin, mica and / or talc. Adhesive according to one of Claims 1 to 10, characterized the waterglass component has a glass content of 20 to 50% by weight, preferably 30 to 40 wt .-%, having. Adhesive according to one of Claims 1 to 11, characterized that it also a dispersant, preferably with a proportion from 0.2 to 5 wt .-%, more preferably 0.4 to 1.5 wt .-% (relative on the dry mass). Adhesive according to one of Claims 1 to 12, characterized the adhesive further comprises a thickening agent, in particular in the form of silica in an amount of up to 10% by weight. Fuel cell with several, glued together Metal layers, characterized in that the bonding means an adhesive according to a the claims 1 to 13 is made.