DE19743723C2 - Process for coating reinforcement components for composite ceramics - Google Patents

Description

The invention relates to a method for manufacturing of coatings on reinforcement components for Composite ceramics, especially non-oxide Ver bundle ceramics. The different reinforcement compo fibers, mat made from them ten, fabric, short fibers or similar components, made of carbon, silicon carbide, silicon (oxy) carbide, Silicon nitride or silicon (carbo) nitride.

These can be used in the production of composite ceramics Fabrics can also be used as matrix elements. There at an embedding is to be used in each case the gain component in a pre-stage matrix, which is then pyrolytically converted into the ceramic form  becomes. Ceramic materials produced in this way then have inherently a certain porosity.

Contrary to the use of metallic or on Plastic-based matrices must be observed that the integration of the fibers or the other Ver Strengthening components are not made in solid form may. The integration should have a so-called In interface. The Inter to be used face a significantly reduced strength than the company or the matrix. With the additional use of an interface are the properties regarding Crack deflection, crack bridging and pull-out Properties (pull-out effect) improved and one composite ceramics assembled in this way has a high Strength and fracture toughness. As materials graphite is preferred for such an interface and hexagonal boron nitride because they have a Have layer structure.

For the fabrics used for the reinforcement components problems occur when it is used exposed to higher temperatures. Here, for. B. Carbon fibers already at temperatures from approx. 500 ° C degraded oxidatively and accordingly the mechanical Strength of the composite formed in the ceramic irreversibly destroyed.

Since, as already mentioned, the ceramic is porous, bie the matrix only provides limited protection against it thermal influences and the application of a corresponding  Protective layer on the reinforcement used Component is essential if the Composite ceramics even at high temperatures and in egg be used in an oxygen-containing atmosphere what with ceramic materials with great certainty is the case. So can conveniently Beschich SiC are applied to the thermal Increase resilience.

The required layer thicknesses are on the Fibers or corresponding tissues made from them, in the area between 50 and 5000 nm.

Known procedures for applying such protection layers are e.g. B. PVD and CVD processes, wherein Problems of a technological nature in particular occur that complicated geometries anyway must be coated evenly and in particular re when coating fiber mats with large difficult to access inner surface areas of the technological effort increases and not all Be stratification processes without further success. A coating process that can possibly be used Ren is the CVI process (Chemical Vapor Infiltra tion), for which very high investment and Be drive costs are required and the coating done at low speed and only very simple stoichiometries can be mastered. So can with such a CVI process, for example Layers of carbon and boron nitride as lubricants  and with SiC as internal oxidation protection be put.

A method is known from US 4,921,731 the ceramic coatings abge on substrates be divorced. About specific coating brine nothing can be seen.

Another method is from US 5,227, 199 be knows. Mixed brines are described in EP 0 374 754 A1 fenbart.

It is therefore an object of the invention to provide protective layers on reinforcement components for use in ver bundle ceramics on simple and relatively inexpensive Way to manufacture in the form that a firm adhesive, dense and even coating follows, even at temperatures above 1300 ° C is stable.

According to the invention, this object is achieved by the in claim 1 resolved characteristics. Favorable off design forms and developments of the invention result when using the in the subordinate Features mentioned claims.

In the method according to the invention is so ge works that precursors come in the form of stable brine and then in a liquid process, such as B. a sol-gel process, by dipping, spraying hen, brushes, squeegees or in the form of the coating  of individual continuous fibers in a continuous Process, be applied and then a thermal treatment is carried out with the applied sol is converted into an oxidic layer becomes.

This will make it a suitable one Stoichiometry possible that good wettability and liability on the Ver strengthening component is achieved. The so made The layer is non-porous, coherent and adheres firmly after the thermal treatment is carried out has been.

In a simple way, the viscosity of the Sols are set and use that each time de order process then determines the necessary for this viscosity of the sol.

In contrast, in the method according to the invention to known wet coating processes of fibers or fabrics are not polymers, but brine and as target compounds oxides or oxide mixtures received. This can, in addition to the improved Protection against oxidation also the pull-out behavior of the company with a single composition be sert as z. B. with alkaline earth aluminates becomes possible.

The coating of the reinforcement components with egg nem liquid process is much cheaper  and easier to control than with the known ones CVD process is possible and can also automati be settled.

Use the viscosity and surface tension of the ten Sols may vary depending on the order process used be set and thereby a gore-free Order, with a coherent layer, too with very small radii of curvature of the company used sern, can be achieved.

With the invention it is possible to use layers provide, in addition to the interface effect also a Ensure adequate protection against oxidation, what up was only possible through multiple coating. There by not only can the effort for manufacturing of composite ceramics, but also theirs Quality can be improved. The procedure can be both used in fibers, fiber mats and ceramics be, with very firmly adhering, dense oxidic Protective layers with a thickness of 40 to 20,000 nm can be generated, with a layer thickness between between 100 and 1000 nm is particularly favorable. Depending on Composition of the protective layer produced can the composite ceramics produced in this way then at Tempe temperatures up to at least 1300 ° C but also at 1800 ° C can be used easily.

According to the invention, a sol is made from an aluminum Compound and a strontium alcoholate or acylate used.  

These mixtures of alcoholates or acylates are by adding water to brine that is stable in storage leads, but the addition also in the form of air moisture can occur. In addition to the Sta bilization of the mixtures complexing agents, such as Ace contain tylacetone, ethylenediamine or maleic acid.

In the event that this is necessary to a ge suitable viscosity for coating by spray hen, diving, squeegees or the other known Ver stop driving, it can be cheap inert Ver add thickener.

The subsequent thermal treatment should be favorable sometimes in several stages, at different temperatures repairs are carried out. With a thermal treatment at least temporarily in an inert atmosphere also has a favorable effect and thereby the burn-up of carbon fibers can be prevented.

Possible examples with which the invention Approach to be made clearer will be followed described as follows:

example 1

0.00508 mol of strontium metal are dissolved in 10 g of propionic acid with simultaneous stirring. The strontium propionate solution thus prepared is then added dropwise in 0.068 mol of an aluminum sec-butylate propionate. The aluminum propinate solution is prepared as follows. In pre-laid 0.1 mol of Al (OBu ^s ) ₃ , 0.1 mol of isopropoxyethanol is added dropwise and then, with simultaneous cooling, 0.5 mol of propionic acid is also slowly added. This mixture is then diluted 1: 1 with isopropanol. At the end of the hydrolysis, a clear, colorless and highly viscous sol is formed with a solids content of 3.73% by mass. This sol is then also stable over a period of more than three months.

Example 2

Carbon fiber mats (commercially available from Toray) are immersed in a sol of the composition SrAl ₁₂ O ₁₉ with a solids content of 1.23% by mass without removing the size. After immersion, they are then pulled uniformly out of the sol at a constant speed of 10 cm / min and dried at room temperature for a period of up to 16 h and then at 110 ° C. for a period of 4 h. In order to largely oxidize the organic residues, the correspondingly coated mats are further subjected to a thermal treatment. The heating is carried out in stages of 100 ° / h in air up to a total of 450 ° C and the mats are finished at a temperature of 450 ° C. A final thermal treatment is then carried out at 1200 ° C., preferably under a nitrogen atmosphere.

Example 3

For the investigation of the pull-out behavior (pull- out) were instead of composite ceramics or fiber matted fiber bundles embedded in the model test rated.

A fiber bundle with a length of approx. 20 cm Carbon fibers (from Toray under the designation T 800 commercially available), were in the Mold coated with crystalline strontium aluminate. The correspondingly pretreated fibers are then in a silicon nitride / silicon carbonitride matrix been bedded. 50 g of polysilazane SLM 465012, 50 g silicon nitride with one particle through knives from 1 to 5 µm, 20 ml toluene and 1 g n-butyl ammonium chloride mixed over a period of 1 h and a slip using a ball mill manufactured. (Polymer and silicon nitride are more common specifically at Wacker-Chemie GmbH, Munich, he available).

The carbon fibers were then coated by Immerse in the brine from the precursor mixtures. After immersion, the coated coal fa in a stick at a temperature of 80 ° C Dried atmosphere. Following that the carbon fiber bundles also under an inert gas condition in steps of 150 ° C / h  Heated 350 ° C and then ge at this temperature for 1 h hold. As a result, the polymer crosslinks to insoluble ones and infusible products. For pyrolysis of the sili Organocium compound was at a speed from 30 ° C / h to 800 ° C and then again heated faster to 1200 ° C at 150 ° C / h. At the The final temperature was the coated carbon fiber held for 2 hours and then in Steps cooled from 150 ° C / h to room temperature.

The carbon fiber bundles coated in this way were then ge broken and the break points light-optically in incident light and also examined in a scanning electron microscope. There at showed a very pronounced pull-out fect (pull-out effect) that protrude on the far the fibers were recognizable.

In the experiments carried out according to the invention, it was found that mullite and SrAl ₁₂ O ₁₉ -coated carbon fiber filaments are substantially more resistant to oxidation than uncoated carbon fiber filaments. In comparative investigations, it was found that the tear-off temperatures in air with a tensile load of 5 MPa result in clear differences and for uncoated carbon fiber filaments at temperatures between 635 and 645 ° C, in contrast to the simply coated carbon fiber filaments, higher tear-off temperatures could be measured , the latter only cracking at temperatures of 795 ° C for mullite layers and at 925 ° C for a SrAl ₁₂ O ₁₉ layer.

Claims (7)

1. A method for coating reinforcement components for composite ceramics, in which fibers, fabrics or mats are coated with a sol using a liquid process, characterized in that the sol consists of an aluminum compound and a strontium alcoholate or acylate. 2. The method according to claim 1, characterized in that the materials of the Reinforcement components made of carbon, silicon um (oxy) carbides, silicon nitrides or silici um (carbo) nitrides by dipping, spraying, pin selneln, doctor blades or by coating individual Continuous fibers in the bundles, mats and felts be coated. 3. The method according to claim 1 or 2, characterized in that the mixture Kom plexing agents such as acetylacetone, ethylenediamine or maleic acid can be added. 4. The method according to any one of claims 1 to 3, characterized in that the sol to Ein position of viscosity and surface tension  additionally water or inert thickeners be added. 5. The method according to any one of claims 1 to 4, characterized in that a sol with atomic ver ratio Al: Sr from 4: 1 to 12: 1 becomes. 6. The method according to any one of claims 1 to 5, characterized in that after the order of the Sols on the reinforcement components the thermi treatment in several temperature levels is carried out. 7. The method according to any one of claims 1 to 6, characterized in that the thermal loading action in an inert protective gas atmosphere, is carried out at least partially.