METHOD OF PRODUCING A CARBON-CERAMIC SHAPED BODY

Abstract

The invention relates to a method of producing a carbon-ceramic shaped body comprising a carbon fibre-reinforced carbon matrix and a content of silicon carbide and silicon, characterised in that a carbonisable shaped body having an organic matrix based on cellulose and reinforced with carbonisable textile structures has been carbonised to form a porous shaped body and the porous carbonised shaped body is then subjected to a liquid silicisation to give the carbon-ceramic shaped body, This method is performable in an economically advantageously manner without losing the beneficial properties achievable according to the prior art.

Claims

1. A method of producing a carbon-ceramic shaped body comprising a carbon fibre-reinforced carbon matrix and a content of silicon carbide and silicon, characterised in that a carbonisable shaped body having an organic matrix based on cellulose and reinforced with carbonisable textile structures, which are carbonisable synthetic fibres of modified natural substances of plant origin and which are present in the form of endless fibres, yarns and/or planar textile structures, has been carbonised to form an open pore porous shaped body with an open porosity of from 15 to 60% and the open-pore porous carbonised shaped body is then subjected to a liquid silicisation to give the carbon-ceramic shaped body.

2. The method according to claim 1, characterised in that the cellulose is of natural origin or is used in the form of a carbonisable dissolving pulp or carbonisable paper pulp.

3. The method according to claim 1, characterised in that the degree of polymerisation of the cellulose is between approximately 108 and 5500.

4. The method according to claim 1, characterised in that the synthetic fibres are cuprammonium rayon fibres, viscose fibres, modal fibres or artificial silk fibres.

5. The method according to claim 1, characterised in that the carbonisable planar textile structures are present in the form of woven fabric, warp knitted fabric, weft knitted fabric, braiding, laid scrim, winding or nonwoven fabric.

6. (canceled)

7. (canceled)

8. (canceled)

9. The method according to claim 1, characterised in that the proportion of the carbonisable textile structure is between 10 and 90 wt. %.

10. The method according to claim 1, characterised in that the carbonisable shaped body is planar.

11. The method according to claim 10, characterised in that a plurality of planar shaped bodies are pressed together.

12. The method according claim 1, characterised in that the carbonisation is controlled such that an open porosity of from 20 to 55% is established in the porous carbonised shaped body.

13. The method according to claim 1, characterised in that the open-pore porous carbonised shaped body is placed in a container filled with silicon powder and/or granular silicon material and is heated in a vacuum and/or protective gas to a temperature above the silicon melting point, the open-pore porous carbonised shaped body being infiltrated with the liquid silicon via capillary forces and the silicon reacting with the matrix carbon of the open-pore carbonised shaped body.

14. The method according to claim 13, characterised in that, following the reaction of the silicon with the carbon of the open-pore porous carbonised shaped body, the shaped body is cooled under application of a vacuum.

15. The method according to claim 1, characterised in that the open-pore porous carbonised shaped body is infiltrated with liquid silicon to such an extent that the carbon-ceramic shaped body, as compared to the precursor in the form of the open-pore porous carbonised shaped body, has a weight increase of from approximately 30 to 140 wt. %.

16. The method according to claim 13, characterized in that the container comprises a graphite crucible.

Description

[0024] The invention is further explained with reference to the following examples.

Example 1

[0025] The method according to the invention is started with the product obtainable by the method of WO 2013098203 A2. More specifically: A cellulose fibre (more detailed definition: commercially available tyre cord fibre from the company Glanzstoff, 1k filaments, 1840 dtex) is previously wetted by a 6% solution of cellulose in ethyl methylimidazolium acetate (EMIM acetate), wet-wound onto a metal mould measuring 18×18×0.1 cm.sup.3 in such a way that, after four layers, the metal mould is rotated by 90°. The metal mould is rotated six times so that a 24-layer shaped body is produced overall. This 24-layer shaped body is annealed at 70° C. for 45 min. The ionic liquid (EMIM acetate) serving as solvent is washed out three times in an aqueous coagulation bath. The shaped body is then dried in a heating press under a pressure of 6 N/cm.sup.2 and at a temperature of 80° C. for 1 h. The carbonisation is carried out in a protective gas atmosphere in five steps: at the beginning, the shaped body is heated to 120° C. at a rate of 10 K/min. After a holding time of 30 min, heating up to 200° C. takes place at a rate of 5 K/min. A further reduction of the heating rate to 1 K/min up to 260° C. counteracts the shrinkage behaviour. The last temperature increase to 1650° C. is achieved with a heating rate of 5 K/min. After cooling, a carbonised shaped body with a carbon yield of 24% is provided. This carbonised shaped body is then silicised. This is combined with seven times the amount of ultra-pure silicon in powder form. The silicisation takes place in a vacuum at 1650° C. The subsequent cooling also takes place in a vacuum. The subsequent cooling also takes place in a vacuum up to a temperature of 150° C.

[0026] The result is a stable carbon-ceramic shaped body with a silicon absorption of 72% based on the carbonised shaped body. The carbon-ceramic shaped body according to the invention has an open porosity of 6%, a flexural modulus of 4.7 MPa, a fracture strength of 20.1 MPa and an apparent interlaminar shear strength of 2.7 MPa.

Example 2

[0027] Following Example 1, a cellulose fibre is previously wetted by a solution consisting of an 8% solution of cellulose in EMIM acetate and is wet-wound onto a metal mould measuring 18×18×0.1 cm.sup.3 in such a way that a 24-layer shaped body is produced. The subsequent method steps (washing, drying and carbonisation) are carried out as in Example 1 and result in a carbonised shaped body with a carbon yield of 22%. This is then silicised (see Example 1) to obtain a carbon-ceramic shaped body according to the invention.

[0028] The result is a stable carbon-ceramic shaped body with a silicon absorption of 104%, based on the carbonised shaped body. The obtained fibre-reinforced carbon-ceramic shaped body has an open porosity of 11%, a flexural modulus of 8.1 MPa, a fracture strength of 18.2 MPa and an apparent interlaminar shear strength of 1.1 MPa.

Example 3

[0029] A 24-layer shaped body wound from cellulose is produced as described in Example 1. The ionic liquid (EMIM acetate) serving as solvent is washed out three times in a coagulation bath consisting of an aqueous 0.4 M ADHP solution (ADHP: ammonium dihydrogen phosphate), while at the same time the shaped body is supplemented with ADHP. The subsequent method steps (drying and carbonisation) are carried out as in Example 1 and result in a carbonised shaped body with a carbon yield of 31%. Subsequently, silicisation is carried out according to the procedure in Example 1 to obtain the carbon-ceramic shaped body according to the invention.

[0030] The result is a stable carbon-ceramic shaped body with a silicon absorption of 59%, based on the carbonised shaped body. The obtained fibre-reinforced carbon-ceramic shaped body has an open porosity of 6%, a flexural modulus of 11 MPa, a fracture strength of 45.1 MPa and an apparent interlaminar shear strength of 2.5 MPa.