DE202014006209U1 - Carbon-containing composite material - Google Patents

Abstract

Carbon-containing composite material comprising a carbon body and at least one SiC layer, characterized in that the at least one SiC layer has been applied to the carbon body by an epitaxial growth process.

Description

Field of the invention

The invention relates to a carbonaceous composite comprising a carbon body and at least one SiC layer. The invention particularly relates to carbon / graphite materials, such as. Carbon fiber reinforced carbon (CFC) sealed with a gas and liquid impervious SiC layer via an epitaxial growth process.

Technical background

Carbon-based materials, which include the material CFC, are state of the art as holders and frames in the field of hardening. However, a disadvantage is the direct contact of the components to be cured with the carbon-based material, since it can lead to carburizing, contact reactions, which negatively affect the metallic components in their properties. However, carbon based materials such as CFC, due to their woven structure, exhibit a very high level of strength coupled with low weight which can increase the batch weight.

In most cases, the curing process is preceded by a cleaning process. The cleaning can be carried out on plastic carriers, with subsequent conversion to CFC carrier for curing must take place. In order to be able to use CFC also in the cleaning process, the CFC material must be gas- and liquid-tight sealed. The necessary implementation could then be eliminated, thereby enabling a more economical process.

The coating of carbon / graphite based materials is known in the art. The coating is usually carried out by vapor deposition or infiltration with Si and conversion of the near-surface layer in SiC by a thermal process. Thereafter, further protective layers of SiC must be applied in order to seal the surface gas- or liquid-tight. As an additional oxidation layer, an SiO ₂ layer can be produced. In these processes, the near-surface layers of the carbon material are converted and changed.

So describes DE 39 20 450 A1 For example, a method in which a carbon matrix in the surface region is at least partially converted into SiC, three or more layers of SiC or Si ₃ N _{4 are} deposited thereon and a top layer of vitrified SiO ₂ or a mixture SiO ₂ / Si is applied. This multi-layered structure of oxidation protection is accomplished by a method in which the surface area carbon matrix is at least partially converted to SiC by pack silicization or liquid impregnation with silicon or treatment with Si vapor and conversion of carbon to silicon carbide, deposition of three or more layers of silicon carbide or Si ₃ N ₄ by chemical vapor deposition and pyrolysis of alkylsilanes or alkylhalosilanes and subsequent application of a cover layer by chemical vapor deposition and conversion of the cover layer into vitrified SiO ₂ or a mixture of vitrified SiO ₂ / Si by annealing.

As an advantage of the conversion of carbon in the surface area in SiC is in DE 39 20 450 A1 described that the adhesion of the subsequently applied protective layers is improved on the body.

DE 101 61 218 A1 describes that the shaped body of carbon fiber reinforced carbon material used is processed close to final shape and then infiltrated at temperatures of about 1600 ° C in vacuum or under inert gas with a silicon melt or a silicon alloy melt, whereby at least a portion of the carbon of the matrix and / or fibers is converted to SiC becomes. In addition to silicon, the metals of subgroups I to VIII can also be used as further constituents of the melt, in particular Ti, Cr, Fe, Mo, B and Ni. The liquid infiltration of the CFC molded body produces a dense, solid and very hard shaped body of C / SiC material containing fibers, generally carbon fibers, with a matrix of predominantly SiC, Si and C.

Alternatively, the preparation of the matrix according to DE 101 61 218 A1 by the pyrolysis of Si-containing, preceramic polymers, such as arise for example by the pyrolysis of polymers containing one or more of the elements Si, B, C, N, P or Ti. The processing takes place at high temperatures of z. Eg 1500-1900 ° C.

A known alternative material is fiber-reinforced aluminum oxide, which, however, shows disadvantages compared to the CFC material in terms of manufacturing costs and strength.

Object of the invention

• a) ein direkter Kontakt mit einem Werkstück zu keinen chemischen Reaktionen führt,
• b) keine Flüssigkeit in den Werkstoff eindringen kann,
• c) die SiC-Schicht eine starke Haftung auf der Oberfläche des kohlenstoffbasierten Werkstoffs aufweist, und
• d) die Oberfläche des kohlenstoffbasierten Werkstoffs bei dem Aufbringungsprozeß der SiC-Beschichtung chemisch nicht verändert wird.

The object of the invention is to carbon-based materials such. B. CFC, with a ceramic layer to seal so that

• a) direct contact with a workpiece does not lead to any chemical reactions,
• b) no liquid can penetrate into the material,
• c) the SiC layer has a strong adhesion to the surface of the carbon-based material, and
• d) the surface of the carbon-based material is not chemically altered during the deposition process of the SiC coating.

These and other objects are achieved by the subject matter of the claims.

Summary of the invention

The objects described above are achieved by a carbonaceous composite comprising a carbon body and at least one SiC layer, wherein the at least one SiC layer has been applied to the carbon body by an epitaxial growth process.

Advantages of the invention

By epitaxial growth of SiC porous structures can be gas-tight and liquid-tight sealed. The layer shows a strong adhesion with the sealed surface, which is not chemically altered by the process. The original carbon body structures, such as CFC structures, remain unchanged.

For various hardening processes, such. Vacuum curing, oil bath curing, carbonation, carbonitriding and related processes, support plates and charging racks are used. CFC charging racks are state of the art in this case, the carrier plates being made of metallic materials, with a significantly higher dead weight compared to CFC. The inventive application of the SiC protective layer, for example on CFC carrier plates, these can replace the metal carrier plates and weight can be saved.

A special case is oil bath hardening. Here, the CFC charging racks absorb oil every cycle. This oil must be burned out before the next cycle. This not only leads to an environmental impact but also to an increase in the price of the overall process. This necessary cleaning cycle leads to a shortening of the service life. By coating the components of the charging racks with the layer according to the invention, this cycle can be saved.

In the production of metal components (turning, milling, grinding, etc.) oily emulsions are usually used. These residues must be removed by a cleaning process before curing. Therefore, the necessary carrier systems must not show fluid absorption. For the reasons mentioned above, CFC is currently not usable here. As a result of the sealing according to the invention, this process is also developed for CFC materials. Another advantage lies in the fact that the components for the following curing process no longer need to be implemented.

Detailed description of the invention

The present invention relates to a carbonaceous composite comprising a carbon body and at least one SiC layer, characterized in that the at least one SiC layer has been applied to the carbon body by an epitaxial growth process.

In a preferred embodiment, the carbon body comprises carbon fiber reinforced carbon (CFC). Carbon fiber reinforced carbons are materials that are made entirely of carbon. CFC materials consist of carbon or graphite fibers of only a few 50 μm in diameter, which are embedded in a matrix of pure carbon. They give the material its high mechanical stability, while the matrix of carbon absorbs external forces and distributes them in the microstructure.

Thanks to its exceptionally high chemical and thermal resistance, CFC material is suitable for use in contact with highly corrosive, hot media. An example of this are the support grids for rectification columns for hydrofluoric acid recovery. The extremely high purity of CFC materials can also play a major role in some applications. In the semiconductor industry, for example, the supports of the crucibles in the crystal pulling process consist of CFC material.

In one embodiment, the carbonaceous composite according to the invention in the form of a support plate or a charging frame, as z. B. in oil bath hardening are used.

According to the invention, the epitaxial growth is preferably carried out by chemical vapor phase epitaxy, in particular by chemical vapor deposition. Here, the material to be grown is transported in the form of gas or gas mixtures to the carbon body and implemented there. By decomposition of silane (SiH ₄ ) or reduction of silicon chlorides with the help of hydrogen, silicon is formed on the surface of the carbon body, which grows there. Normal pressure processes require hydrogen as the carrier gas. In low pressure processes, no carrier gas is required and the amount of gas required is less.

As starting materials for the above process are preferably chlorine-containing carbosilanes having the chemical formula C _n H _{2n + 1} Si _n Cl _{2n + 1} and H ₂ can be used. Methyltrichlorosilane and H ₂ have proven to be particularly advantageous as starting materials.

The layer thickness of the SiC layer on the carbonaceous composite material according to the invention is about 20-100 microns, preferably about 60 microns.

QUOTES INCLUDE IN THE DESCRIPTION

This list of the documents listed by the applicant has been generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Cited patent literature

• DE 3920450 A1 [0005, 0006]
• DE 10161218 A1 [0007, 0008]

Claims (8)

A carbonaceous composite comprising a carbon body and at least one SiC layer, characterized in that the at least one SiC layer has been applied to the carbon body by an epitaxial growth process. The carbonaceous composite of claim 1, wherein the carbon body comprises carbon fiber reinforced carbon (CFC). The carbonaceous composite material according to claim 1 or 2, wherein the carbon body is in the form of a support plate or a charging stand. A carbonaceous composite according to one or more of the preceding claims, wherein said epitaxial growth is by chemical vapor phase epitaxy. A carbonaceous composite material according to one or more of the preceding claims, wherein the at least one SiC layer is deposited on the carbon body by chemical vapor deposition. Carbon-containing composite material according to claim 5, wherein as starting materials chlorine-containing carbosilanes having the chemical formula C _n H _{2n + 1} Si _n Cl _{2n + 1} are used. A carbonaceous composite material according to claim 6, wherein as starting materials methyltrichlorosilane and H ₂ are used. Carbon-containing composite material according to one or more of the preceding claims, wherein the layer thickness of the SiC layer 20-100 microns, preferably about 60 microns.