DE9421895U1 - Device for chemical deposition on fibers - Google Patents

Description

Ol/U-10/DE

Device for chemical deposition on fibres

The invention relates to a device for the chemical deposition of carbon, ceramics, such as silicon carbide, or other inorganic substances, such as metals or metal alloys, on a single fiber or individual fibers in a fiber bundle, hereinafter also referred to simply as a fiber, according to the preamble of claim 1.

Chemical deposition, also often referred to as CVD (chemical vapor deposition), refers to all processes in which layers are deposited on a substrate from the gas or vapor phase by adding activation energy. Both individual gases or vapors and mixtures of gases and vapors can be used.

The fibers to be coated can be individual fibers or fiber bundles, so-called rovings, which are later woven into a fabric, for example. The fibers can also consist of different materials. However, the fibers must be sufficiently resistant to the heat stress during CVD. Rovings usually consist of 500 to 12,000 individual fibers with a diameter of 6 to 12μπα.

Of particular importance is the coating of rovings made of carbon fibers or SiC and Al ₂ O ₃ fibers, which have proven themselves in the production of high-strength polymer, ceramic and metal matrix composite materials. Such materials were initially used in aerospace and are increasingly gaining importance in the entire industrial production of highly stressed parts.

The coating of the fibres is necessary so that the fibres, especially the individual fibres of rovings, can form such a bond with the

Matrix material that ensures the technically and technologically desired macroscopic properties of the composite materials.

According to the state of the art, the coating of the fibers is generally carried out by means of chemical deposition from the gas or vapor phase.

The gaseous or vaporous starting materials required for the layer deposition via a chemical reaction are brought to the substrate surface in a reactor, where they react or decompose to form the corresponding layer-forming compounds after the activation energy is added. The processes are carried out in such a way that solid components are deposited on the substrate as a result of the chemical reaction. Any gaseous, often toxic exhaust gases that may be produced must be removed from the process zone. The temperatures required for such processes are well over 1000 ⁰ C.

The problem with coating rovings is that the manufacturer often coats the rovings with a plastic that makes them easier to handle, a so-called sizing agent. This sizing agent must be removed as soon as possible before the fibers are coated.

In H. Plänitz, G. Bochmann, W. Wagner, M. Seidler and E. Wolf: CVD coating of carbon fibers in batch operation and in a continuous process, In: Wiss. Z. d. TU Karl Marx Stadt No. 32(1990) p.218 and E.Than, A. Hofmann, H.Podlesak, H. Plänitz, A. Schulze. E. Kieselstein, G. Leonhardt: The interface behavior of SiC and its application in fiber-reinforced aluminum, In: Material Science and Materials Technology No. 23(1992) p.267, the coating of fiber bundles is described, in which the activation energy is supplied from the outside by radiant heating in a CVD reactor under atmospheric pressure conditions (hot wall reactor).

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In these CVD hot-wall reactors, the roving is fed into and out of a quartz glass tube through lock systems. Fine control valves are used to create a defined atmosphere in the quartz glass tube with regard to the gas composition and gas flow rate. The quartz glass tube is heated from the outside by radiant heating.

In the state of the art, DE OS 19 54 480 describes a pyrolitic process for depositing boron on a single carbon wire. The carbon wire between 12.7 and 50.8 μπα is heated to a temperature between 1,100 and 1,300 ⁰ C by electrical resistance. The coating is carried out in a tubular reactor with a gas atmosphere of boron halide, through whose two metal end plugs the carbon wire is passed. Mercury is used as a conductive sealing agent.

The object of the invention is to provide a device for the continuous coating of fibers, in particular fiber bundles, by chemical deposition, which enables the homogeneous and gap-free coating of the fibers, in particular the individual fibers of rovings, on all sides with relatively little technical effort. The layers should be adhesive and the individual fibers should not stick together. Furthermore, the mechanical properties of the fibers should not be changed by the coating. Toxic exhaust gases should be detectable in closed circuits.

The invention solves the problem by the features mentioned in the characterizing part of claim 1. Further developments of the invention are characterized in the subclaims.

The essential element of the invention is that the device according to the invention for chemically depositing layers on fibers takes place exclusively in a narrowly confined space within a reaction tube,

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·· ·· ··· ··· »· ·» which in turn is arranged in a vacuum chamber.

This allows the fiber and in particular the roving to be degassed in an advantageous manner before coating and the pressure conditions can be advantageously regulated and controlled. In particular, toxic exhaust gases can be discharged in a controlled manner. In contrast to state-of-the-art solutions, the process is isolated from the surrounding atmosphere and the process cannot be influenced by the atmosphere, nor can the atmosphere be contaminated by the process gases.

With the relatively low working pressure within the vacuum chamber, an increased partial pressure of this gas advantageously occurs in the reaction tube, i.e. in the immediate vicinity of the substrate or on the fiber or roving. The pressure conditions lead to good diffusion conditions, especially in the reaction tube when laminar gas flow conditions still exist. This essentially results in an advantageous all-round and homogeneous coating of the individual fibers of a roving. Another advantageous effect, which is probably caused by an electrostatic charge in the reaction tube, causes the fiber bundle of a roving to expand in the area in which the chemical deposition reaction takes place. The activation energy required for chemical deposition can be supplied in any way. Resistance heating can advantageously be used for conductive fibers, e.g. carbon fibers. However, any other heating devices can also be used.

e.g. radiant heating.

Advantageously, the use of a plasma source inside and/or outside the reaction tube can be provided. The plasma source can advantageously be used to support the coating process.

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The plasma source is used to generate a plasma within the reaction tube, which is maintained parallel to the coating process so that the coating is carried out using plasma.

It is also possible to reduce the temperature load on the fibers in some cases, as part of the activation energy required for chemical deposition is supplied by the plasma. On the other hand, the plasma source can be used to generate a plasma outside the reaction tube and subject the fibers to a plasma treatment immediately before coating, which advantageously removes both existing sizing and other contaminants. At the same time, the fibers are heated up, which reduces the energy supply required within the reaction tube to heat the fibers to the reaction temperature and increases the throughput speed.

The plasma source can use various principles to generate plasma. To generate a plasma in the reaction tube, a microwave or high-frequency plasma can be used to advantage, which is coupled into the reaction tube.

The advantage of plasma-assisted coating lies in particular in a possible reduction in the temperature load on the fibers and in a significantly higher coating rate, which enables a higher throughput speed of the fibers through the reaction tube.

The supply and/or take-up spools are advantageously arranged in the vacuum chamber. However, these spools can also be located outside the vacuum chamber and only the fibers can be guided into or out of the vacuum chamber via locks.

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The device according to the invention can be equipped with a reaction tube, but it is also advantageously possible to arrange several reaction tubes and the associated supply and/or take-up spools in parallel. As a rule, one reaction tube is used per fiber. However, several fibers or rovings can also be guided through one reaction tube.

The main advantage of the device according to the invention is that fibers or rovings can be provided with a high-quality, homogeneous and adhesive coating in a closed work space by means of chemical deposition from the gas phase, without causing any environmental pollution.

The invention will be explained in more detail below using two exemplary embodiments.

The drawing shows in Figure 1 an embodiment of a device according to the invention for coating a carbon roving in a schematic section. Figure 2 shows an embodiment of a device according to the invention for coating several carbon rovings.

The device according to the invention according to Figure 1 consists of a vacuum chamber 1 with a vacuum pump connection 2 to the vacuum pump unit and an adjustable process gas inlet 3. A reaction tube 4 made of quartz glass is located horizontally in the vacuum chamber 1 and has a central process gas connection 5, which is connected to the process gas inlet 3. On both sides of the reaction tube 4 there are guide elements in the form of guide rollers 6 and The roving 8 made of carbon fibers, which is to be coated, is guided over these and guided self-supporting through the reaction tube 4. The uncoated roving 8 is located on the supply reel 9 and the coated roving 8 is wound onto the take-up reel 10.

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wound up. In the exemplary embodiment, the two guide rollers 6 and 7 are both connected to a common circuit with the power source 11 and a switch 12, whereby the circuit between the guide rollers 6 and 7 is closed by the conductive roving 8 made of carbon fibers. A microwave plasma source 13 is arranged parallel to the reaction tube 4, which can couple a plasma into the reaction tube 4. A radiant heat source 14 is arranged between the supply coil 9 and the guide roller 6. The energy is supplied via the power source 15 and the switch 16.

The use of the device according to the invention is described in more detail below.

In the example, Roving 8 consists of 6,000 individual carbon fibers with an individual fiber diameter of 8 μπα, with Roving 8 coated with a sizing agent. The individual fibers of Roving 8 are to be coated on all sides with a 600 nm thick carbon layer.

After the supply reel 9 and the take-up reel 10 have been inserted into the vacuum chamber 1, the roving 8 to be coated is guided from the supply reel 9 via the guide rollers 6 and 7 to the take-up reel 10. The vacuum chamber 1 is then evacuated to a vacuum of 10' ² mbar. In the process, the atmospheric gases or vapors that are harmful to the coating process, in particular O ₂ and H ₂ O, are pumped out of the vacuum chamber 1 and the supply reel 9, the roving 8 to be coated and the take-up reel 10 are degassed.

While the vacuum generation is maintained, the process gas inlet 3 is opened for the purpose of coating, so that a pressure of about 0.6 mbar is established within the reaction tube 4. In the example, acetylene (C ₂ H ₂ ) is used as the process gas.

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The radiant heat source 14 and the microwave plasma source 13 are then put into operation and the roving is moved through the reaction tube 4 by means of the guide rollers 6 and 7 at a speed of about 55 m/h. In parallel, the circuit with the power source 11 is closed via the guide rollers 6 and 7 and the roving 8 with the switch 12.

In the process, the roving 8 is first heated in the radiant heat source 14, whereby the plastic sizing on the fibers of the roving 8 is removed.

The roving 8 then enters the reaction area within the reaction tube 4. This reaction area is determined on the one hand by the area between the guide rollers 6 and 7, in which the roving 8 is heated by means of electrical resistance, and is located in particular within the effective range of the discharge of the microwave plasma source 13.

The roving 8 is heated between the guide rollers 6 and 7 to a temperature of about 950 ⁰ C by the electrical resistance and the effect of the microwave plasma source 13. The layer deposition process then takes place automatically in the reaction tube 4 under the effect of acetylene as the process gas. With the specified process parameters, a carbon layer with a largely homogeneous layer thickness of 600 nm is deposited on the individual fibers of the roving 8. The particularly homogeneous layer deposition is achieved by the special device according to the invention and the resulting effect of the vacuum.

Figure 2 shows a schematic representation of the structure of a device according to the invention with several rovings 8, which are individually guided from the supply reels 9 through the reaction tubes 4 to the winding reels 10. The process steps when using the device are equivalent to those in the example according to Figure 1.

Claims (8)

01/U-lO/DE Protection claims 1. Device for the chemical deposition of carbon, ceramics or other inorganic substances on a single fiber or individual fibers in a fiber bundle with a reaction tube through which the process gases and/or vapors required for chemical deposition flow and through which the fiber to be coated is guided, characterized in that the reaction tube (4) is arranged within a vacuum chamber (1), that guide elements are provided which guide the fiber to be coated axially through the reaction tube (4) and that a device is provided which supplies the activation energy required for chemical deposition into the reaction tube (4). 2. Device according to claim 1, characterized in that a supply spool (9) for the uncoated fiber and/or a take-up spool (10) for the coated fiber are arranged within the vacuum chamber (1). 3. Device according to claim 1 or 2, characterized in that the device for supplying the activation energy is a resistance heating device, such that electrically conductive sliding guides and/or guide rollers (6 and 7) are arranged as guide elements before and after the reaction tube (4), over which the electrically conductive fiber to be coated is guided, and that the guide elements are connected to a common circuit. 4. Device according to claim 1 or 2, characterized in that the device for supplying the activation energy is a radiant heat source. 01/U-lO/DE 5. Device according to one of the preceding claims, characterized in that a plasma source is present within the vacuum chamber (1), which generates a plasma, e.g. a microwave or a high-frequency plasma, inside and/or outside the reaction tube (4). 6. Device according to one of the preceding claims, characterized in that within the vacuum chamber (1) in front of the reaction tube (4) there is a heat source which encloses the fiber to be coated and can be operated with an energy at which existing sizes and impurities can be evaporated from the uncoated fiber. 7. Device according to one of the preceding claims, characterized in that several reaction tubes (4) and associated guide elements and/or devices for supplying the activation energy and/or supply and/or take-up reels (9 and 10) are present within the vacuum chamber. 8. Device according to one of the preceding claims, characterized in that guide elements are provided on a reaction tube (4) which guide several fibers through this reaction tube (4).