Method of obtaining a carbon fiber fabric by continuously carbonizing a cellulose fiber fabric
The carbonization of cellulose fiber fabric comprises an initial stage of heat treatment up to 250° C. to 350° C., with a relatively high mean temperature rise speed of 10° C./min to 60° C./min, an intermediate stage up to 350° C. to 500° C. with a lower mean temperature rise speed of 2° C./min to 10° C./min, and a final stage up to 500° C. to 750° C. with a mean temperature rise speed that is again raised to 5° C./min to 40° C./min.
1. A method of obtaining a carbon fiber fabric by carbonizing a cellulose fiber fabric, the method comprising:
(a) admitting a cellulose fiber fabric having warp and weft yarns to be carbonized through an inlet to a carbonization chamber;
(b) causing the cellulose fiber fabric to be subjected to a heat treatment by travelling continuously through the carbonization chamber between said inlet and an outlet of the carbonization chamber, wherein a method of said heat treatment comprises:
(i) entering an initial chamber stage at said inlet of the carbonization chamber for bringing the temperature of the cellulose fiber fabric entering the carbonization chamber to a value lying in the range 250° C. to 350° C., the initial stage comprising temperature rise at a first mean speed lying in the range 10° C./min to 60° C./min;
(ii) exiting the initial chamber stage and entering an intermediate stage for raising the temperature of the fabric to a value lying in the range 350° C. to 500° C., the intermediate stage comprising temperature rising at a second mean speed lower than the first and lying in the range 2° C./min to 10° C./min; and
(iii) departing the intermediate chamber stage and entering a final stage for raising the temperature of the fabric to a value lying in the range 500° C. to 750° C., the final stage comprising temperature rising at a third mean speed greater than the second and lying in the range 5° C./min to 40° C./min; and
(c) retrieving a carbon fiber fabric resulting from carbonization of said cellulose fiber fabric at the outlet of the carbonization chamber.
2. A method according to claim 1 , characterized in that the transit time of the fabric through the chamber lies in the range 20 min to 2 h.
3. A method according to claim 1 , characterized in that, prior to carbonization, the fabric is subjected to relaxation treatment at a temperature lying in the range 100° C. to 250° C.
4. A method according to claim 3 , characterized in that the relaxation treatment is performed in air.
5. A method according to claim 3 , characterized in that the relaxation treatment is performed for a duration lying in the range 15 min to 3 h.
6. A method according to claim 1 , characterized in that the carbonized fabric is subjected to high temperature heat treatment lying in the range 1000° C. to 2800° C. after it has passed through the carbonization chamber.
7. A method according to claim 6 , characterized in that the high temperature heat treatment is performed for a duration lying in the range 1 min to 10 min.
8. A method according to claim 1 , characterized in that the carbonized fabric is subjected to activation treatment.
9. A method according to claim 4 , characterized in that the relaxation treatment is performed for a duration lying in the range 15 min to 3 h.