Chemistry of inorganic compounds – Carbon or compound thereof – Elemental carbon
Patent
1986-01-09
1988-09-13
Doll, John
Chemistry of inorganic compounds
Carbon or compound thereof
Elemental carbon
4234475, 423453, 423458, 423461, 502183, 502185, D01F 912, D01F 914
Patent
active
047708670
DESCRIPTION:
BRIEF SUMMARY
The invention concerns a process for the production of carbon fibres which are vapour-deposited from methane.
At the present time, carbon fibres are produced virtually entirely by pyrolysis of polyacrylonitrile fibres (referred to as P.A.N. fibres). That method is relatively easy to carry out and it affords the advantage of producing fibres which are as long as may by desired. On the other hand, the diameter of the fibres produced is governed by that of the initial P.A.N. fibre and in most cases it is around 7 to 10 .mu.m.
Two other processes have been the subject of investigation: one is referred to as "ex-mesophase fibres", which comprises starting from pitch which is run out into thread form, then oxidised, carbonised and graphitised, being described for example in French patent No. 2 512 076 (MITSUI) and EP-A-No. 27739 (Union Carbide), the other being referred to as the process "by vapour-deposition"; the vapour-deposition process ccmprises producing fibres by thermal decomposition of a hydrocarbon on a substrate on which catalyst particles have been deposited.
The principles of that process were described by L. Meyer, Zeit.Krist. 109 (1957), pages 61 and 67, Hillert and Lange, Zeit. Krist. 111 (1958), pages 24-34, and then by Endo (Doctorate thesis, Orleans, 1975) and J. Cryst.Growth 32, 335 (1976) who showed that those fibres could be produced in a controlled and economic fashion, and explained the mechanism thereof, which splits up into a catalytic effect followed by a pyrolitic effect. It is for that reason that reference is sometimes made to "CC" fibres (catalytic carbon fibres) to denote those products.
The process developed by Endo to produce fibres in large amounts and of substantial lengths comprises passing a hydrogen-benzene mixture without preheating into a cylindrical reactor containing a substrate (a tube of graphite, ceramic . . . ), the surface of which has been activated by the deposit of metal particles. The reactor is in a tubular furnace which subjects it to a temperature gradient from 950.degree. C. to 1100.degree. C. The size of the fibres is highly sensitive to the heating gradient, the total flow rate, the composition of the gases and the geometry of the reactor. Depending on the conditions under which the preparation operation is carried out, the diameter of the fibres varies from a few thousands of Angstroms to a few tens of microns, while the length varies from a few centimeters to a few tens of centimeters. The fibres produced in that way have a breaking stress of 1 to 3 GPa, a Young's modulus of 200 to 300 GPa and an electrical resistivity of 10.sup.-3 .OMEGA..cm.
Japanese patent application (KOKAI-No. 51/33210 Showa-Denko) describes a process for the preparation of carbon fibres by vapour-deposition from a mixture of hydrogen and a cyclic hydrocarbon (benzene, toluene) or an aliphatic hydrocarbon (ethane or octane) in a quartz reactor at a temperature of from 1030.degree. to 1300.degree. C.
Germination is effected for a period of 10 to 30 seconds with a gas velocity of S.times.(100 to 1500) cm per minute, wherein S is the cross sectional area of the tube in square centimeters; the growth of the fibres occurs with a gas velocity of 10 to 30 centimeters per minute, in from 30 to 180 minutes. That process makes it possible to produce fibres which are from 7 to 50 .mu.m in diameter and from 30 to 180 mm in length. That patent does not refer to the presence of a catalyst.
Japanese patent application KOKAI No. 57/ll7662 (published on July 22, 1982) in the name of SHOWA-DENKO describes a method which is similar to that referred to above, with a catalyst selected from refractory materials in groups 4A, 5A, 6A and 8 and more particularly: Ti, Zr, V, Nb, Cr, Mo and Mn.
The same catalysts had already been claimed in a previous Japanese patent application in the name of SHOWA-DENKO (KOKAI No. 52/103528 published on 30 th August 1977) with a preference for Fe, Co, Ni, V, Nb and Ta, the hydrocarbon being selected from benzene, toluene, methane, ethane, propane, butane, propylene and cyc
REFERENCES:
patent: 4391787 (1983-07-01), Tibbetts
patent: 4565684 (1986-01-01), Tibbetts et al.
Tamai et al., Carbon Deposition on Iron and Nickel Sheets From Light Hydrocarbons, Carbon, 1968, vol. 6, pp. 593-602.
Koyama et al., Carbon Fibers Obtained by Thermal Decomposition of Vaporized Hydrocarbons, Japanese Journal of Applied Physics, vol. 11, No. 4, 4/72, 445-9.
Bonnetain Lucien
Coulon Michel
Kandani Najib
Maire Jacques
Doll John
Kunemund Robert M.
Le Carbone-Lorraine
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