HOLLOW CYLINDRICAL CARBON FIBRE CONSTRUCTION

Abstract

A hollow cylindrical carbon fiber construction, including a carbon fiber nonwoven, which is continuous between the inner lateral surface and the outer lateral surface of the carbon fiber construction all around. The hollow cylindrical carbon fiber construction can be obtained by a method in which a hollow cylindrical starting fiber construction, which includes a nonwoven that is continuous between the inner lateral surface and the outer lateral surface of the starting fiber construction all around, is subjected to a pyrolysis process.

Claims

1-16. (canceled)

17. Hollow cylindrical carbon fibre construction, comprising a carbon fibre nonwoven, which is continuous between the inner lateral surface and the outer lateral surface of the carbon fibre construction all around.

18. The carbon fibre construction according to claim 17, wherein the proportion of carbon fibres in the carbon fibre nonwoven is at least 50% by weight.

19. The carbon fibre construction according to claim 17, wherein the carbon fibre nonwoven has a mean density in a range of 0.04 to 0.4 g/cm.sup.3.

20. The carbon fibre construction according to claim 17, wherein the carbon fibre nonwoven, which is continuous all around, has a tensile strength of at least 0.01 MPa.

21. The carbon fibre construction according to claim 17, wherein the density of the carbon fibre nonwoven in a region facing the inner lateral surface is higher than the density of the carbon fibre nonwoven in a region facing the outer lateral surface.

22. The carbon fibre construction according to claim 17, wherein the carbon content of the carbon fibres is at least 92% by weight.

23. The carbon fibre construction according to claim 17, wherein the carbon fibres have a BET surface area of 1 to 1500 m.sup.2/g.

24. A method for producing a carbon fibre construction according to claim 17, wherein a hollow cylindrical starting fibre construction, which comprises a nonwoven that is continuous between the inner lateral surface and the outer lateral surface of the starting fibre construction all around, is subjected to a pyrolysis process.

25. The method according to claim 24, wherein the pyrolysis process comprises a first temperature treatment at 500 to 1,600° C.

26. The method according to claim 25, wherein the pyrolysis process comprises a second temperature treatment at 1,600 to 3,000° C.

27. The method according to claim 24, wherein the starting fibre construction is drawn onto a cylindrical shaping body and is shrunk onto the cylindrical shaping body during the pyrolysis process.

28. The method according to claim 26, wherein the first temperature treatment takes place after the starting fibre construction has been drawn onto the shaping body, the carbon fibre construction obtained is pulled off the shaping body and the carbon fibre construction pulled off the shaping body is subjected to the second temperature treatment.

29. The method according to claim 24, wherein the BET surface area of the carbon fibres of the carbon fibre construction present after the first or second temperature treatment is increased by gas activation.

30. The method according to claim 24, wherein the fibres of the hollow cylindrical starting fibre construction comprise polyacrylonitrile-based fibres, viscose fibres and/or pitch-based fibres.

31. Carbon fibre construction obtainable according to the methods of claim 24.

32. A device comprising the carbon fibre construction according to claim 17, wherein the carbon fibre construction is an element selected from the group consisting of a high-temperature insulating cylinder, a filter material in a filter candle, a carrier material for filter media, a droplet separator or demister, an electrode material, a resistance-heating element and a catalyst carrier.

Description

[0088] The invention is illustrated by means of the following drawings and embodiment, without being restricted thereto.

[0089] FIGS. 1A and 1B are sections through carbon fibre nonwovens not according to the invention FIG. 2 is a section through a hollow cylindrical carbon fibre construction according to the invention

[0090] FIGS. 1A and 1B illustrate known possible ways of applying carbon fibre nonwovens that are not continuous all around. For the sake of simplicity, the application on the lateral surface of a cylinder is illustrated.

[0091] The section shown in FIG. 1A represents a cut surface through a carbon fibre nonwoven 2 and a cylinder 10. The carbon fibre nonwoven 2 is applied to the lateral surface of the cylinder 10 by conventional winding without an overlap region. The cut surfaces 3, 4 of both ends of the wound layer run approximately parallel to one another and close to one another. This creates a gap region that runs substantially orthogonally to the outer and inner surface of the carbon fibre nonwoven. The gap region is covered with carbonisable binder 5. The carbon fibre nonwoven does not join together in the gap region because all the fibres are cut off at the cut surfaces 3, 4 and do not extend out from one cut surface 3 into the other cut surface 4. The gap region should have exactly the same width everywhere, which width is as narrow as possible; this can only be achieved with great effort.

[0092] The section shown in FIG. 1B represents a cut surface through a carbon fibre nonwoven 2 that is applied by conventional winding with an overlap region 6 to the cylinder 10. In the overlap region 6, the carbon fibre nonwoven is applied in multiple layers. A small overlap region 6 is shown by way of example. The carbon fibre nonwoven 2 can, however, also be longer and wound up in multiple layers all around. Regardless of the size of the overlap region 6, the carbon fibre nonwoven 2 is connected in a spiral all around because the fibres run within the spirally wound carbon fibre nonwoven 2. The fibres do not run from one layer into the next layer located further outside or further inside.

[0093] FIG. 2 is a section through a self-supporting hollow cylindrical carbon fibre construction 1, comprising a carbon fibre nonwoven 2, which is continuous between the inner lateral surface 7 and the outer lateral surface 8 of the carbon fibre construction 1 all around.

EMBODIMENT 1

[0094] A method based on BELTEX technology was selected from the known methods for the production of mechanically strengthened nonwovens by means of circular needling, and a hollow cylindrical starting fibre construction was thus produced by circular needling of an uncompacted web of fibres. 100% viscose fibres were used to produce the web (3.0 dtex, cut length 65 mm). The hollow cylindrical starting fibre construction obtained had a length of 830 mm, an inside diameter of 600 mm, an outside diameter of 740 mm and thus a wall thickness of 70 mm. The weight of the starting fibre construction was 27 kg. This results in a volume of the starting fibre construction of 122,289 cm.sup.3 and a density calculated from this of 0.22 g/cm.sup.3.

[0095] This starting fibre construction was subjected to a first high-temperature treatment. For this purpose, it was placed on a cylindrical metal shaping body having a diameter of 430 mm and subjected to a first temperature treatment (carbonisation) in a combustion container in a furnace at 900° C. under a protective gas atmosphere. After this temperature treatment, cooling took place and the hollow cylindrical carbon fibre construction obtained was then pulled off the shaping body. The carbon fibre construction had a length of 580 mm, an inside diameter of 448 mm, an outside diameter of 548 mm and thus a wall thickness of 50 mm. The weight of the carbon fibre construction was 7 kg. This results in a volume of 45,370 cm.sup.3 and a density calculated from this of 0.15 g/cm.sup.3. The carbon fibre construction was then additionally subjected to a second high-temperature treatment (graphitisation), no shaping body and combustion container being used. The carbon fibre construction was graphitised at 2,200° C. in a furnace under a protective gas atmosphere. After this high-temperature treatment, the hollow cylindrical carbon fibre construction obtained had a length of 580 mm, an inside diameter of 450 mm, an outside diameter of 550 mm and thus a wall thickness of 50 mm. The weight of the construction was 6.4 kg. This results in a volume of 45,552 cm.sup.3 and a density calculated from this of 0.14 g/cm.sup.3.

[0096] To determine the high-temperature thermal conductivity (according to DIN 51936), a sample was taken of the graphitised carbon fibre construction from both the inner lateral surface and the outer lateral surface. The dimensions of the samples were selected in accordance with the specifications in DIN 51936. A diameter of 20 mm and a length of 3 mm were selected. By weighing the sample, a bulk density according to DIN 51918 of 0.16 g/cm.sup.3 could then be determined for the inner lateral surface and a bulk density of 0.15 g/cm.sup.3 could be determined for the outer lateral surface.

[0097] The roundness of the inside diameter of the carbon fibre construction obtained after the first high-temperature treatment was determined by optical 3D technology (scan) of the hollow cylinder using a COMET® system from Zeiss.

[0098] The roundness was determined by recording the largest and smallest measurable inside diameter. The roundness can then be calculated from the difference. A value of ±4 mm was obtained for the carbon fibre construction.

EMBODIMENT 2

[0099] A method based on RONTEX technology was selected from the methods for the production of mechanically strengthened nonwovens by means of circular needling described in the prior art, and a hollow cylindrical starting fibre construction was thus produced by circular needling of an uncompacted web of fibres. 100% oxidised polyacrylonitrile (SGL—PANOX®; available under the designation C63-1.7/1.39-A110) was used to produce the uncompacted web of fibres. The starting fibre construction obtained had a length of 170 mm, an inside diameter of 145 mm, an outside diameter of 170 mm and thus a wall thickness of 12.5 mm. The weight of the construction was 215 g. This resulted in a volume of 1,050 cm.sup.3 and a density calculated from this of 0.20 g/cm.sup.3.

[0100] The starting fibre construction was subjected to a first high-temperature treatment (carbonisation). For this purpose, the construction was placed on a cylindrical shaping body made of metal having a diameter of 130 mm and carbonised in a combustion container in a furnace at 900° C. under a protective gas atmosphere. After this temperature treatment, the mixture was cooled and the hollow cylindrical carbon fibre construction obtained was then pulled off the shaping body. After this high-temperature treatment, the hollow cylindrical carbon fibre construction obtained had a length of 150 mm, an inside diameter of 130 mm, an outside diameter of 152 mm and thus a wall thickness of 11 mm. The weight of the construction was 113 g. This resulted in a volume of the construction of 731 cm.sup.3 and a density calculated from this of 0.16 g/cm.sup.3.

[0101] This carbon fibre construction was then additionally subjected to a second high-temperature treatment (graphitisation), no shaping body and combustion container being used. The construction was graphitised in a furnace at 2,200° C. under a protective gas atmosphere. After this high-temperature treatment, the hollow cylindrical carbon fibre construction obtained had a length of 150 mm, an inside diameter of 131 mm, an outside diameter of 152 mm and thus a wall thickness of 10.5 mm. The weight of the construction was 100 g. This resulted in a volume of 700 cm.sup.3 and a density calculated from this of 0.14 g/cm.sup.3.

[0102] In both embodiments, all of the hollow cylindrical constructions (the starting fibre constructions and the constructions obtained after carbonisation and after graphitisation) were self-supporting. As explained above, they could therefore also be referred to as hollow cylindrical fibre bodies.

LIST OF REFERENCE NUMERALS

[0103] carbon fibre construction 1 [0104] carbon fibre nonwoven 2 [0105] cut surface 3 [0106] cut surface 4 [0107] binder 5 [0108] overlap region 6 [0109] inner lateral surface 7 [0110] outer lateral surface 8 [0111] cylinder 10