Improved process for growing graphite fibres

Claim 2

A process for manufacturing graphite fibres (66) characterised in that the process comprises growing the fibres (66) on an iron-base metal surface (16) initially having an oxide layer thereon thicker than a natural oxide layer and containing predominantly iron oxide, by contacting said surface (16) with a gas containing a carbonaceous precursor at an elevated temperature and under conditions suitable to cause said fibres (66) to grow.

Claim 3

A process for manufacturing graphite fibres according to claim 1, characterised in that the process includes oxidizing an iron-base metal to form said relatively thick, predominantly iron oxide layer thereon, and employing the oxide layer to nucleate the formation of graphite fibres (66) from said carbonaceous precursor.

Claim 4

A process for manufacturing graphite fibres according to claim 1 or 2, characterised in that a gas stream comprising methane flows over a flow path comprising an upstream region (18) and a downstream surface (16), said gas stream is exposed in said upstream region (18) to a chromium-base M 7 c 3 carbide at a temperature effective to pyrolyze the methane to form said carbonaceous precursor, said gas stream is exposed to said thick, predominantly iron oxide layer on said downstream surface (16) at the elevated temperature suitable to treat the oxide layer to form a surface effective for nucleating the growth of fibres thereon, and the precursor is deposited onto the treated downstream surface (16) to form said graphite fibres (66) thereon.

Claim 5

A process for manufacturing graphite fibres according to claim 1 or 2, characterised in that said fibres (66) formed have a scroll-like cross section and are 5 to 100 microns in diameter and up to several centimeters long, said process comprising flowing a stream of gas containing predominantly methane gas firstly over a surface (18) of a chromium-containing iron-base alloy initally bearing a relatively thin oxide layer of a type that naturally forms when exposed to air at ambient temperatures and thereafter over said surface (16) initially bearing said relatively thick, predominantly iron oxide, formed by heating said alloy while exposed to air, and heating said gas stream and said surfaces (16,18), while continuing said flow, at an elevated temperature and for a time sufficient to grow said graphite fibres (66) on the downstream surface (16).

Claim 6

A process for manufacturing graphite fibres according to claim 1 or 2, in which said fibres (66)formed have a scroll-like cross section and are 5 to lOO microns in diameter and up to several centimeters long, said process comprising flowing a stream of gas containing predominantly methane gas over a flow path comprising an upstream surface (18) formed of a chromium-containing iron base alloy and initially bearing a relatively thin oxide layer of the type that naturally forms upon ambient air exposure, and a downstream surface (16) formed of said iron-base metal and initially bearing a predominantly iron oxide layer greater than 1 micron thick, heating the gas stream in contact with the surfaces (16,18) to carburize the upstream surface C18) to produce thereon a chromium-containing M 7 c 3 carbide suitable for catalyzing methane pyrolysis to form carbonaceous globules and to produce on the downstream surface (16) metallic particles suitable for nucleating fibre growth from said globules, and continuing said gas stream flow and heating for a time sufficient to form carbonaceous globules at the upstream surface (18) that enter the stream and are carried to the downstream surface (16) and to cause said globules to interact with the metallic particles on the downstream surface (16) to grow the graphite fibres (66).

Claim 7

A process for manufacturing graphite fibres according to claim 1 or 2, characterised in that said fibres (66) formed have a scroll-like cross section and are 5 to 100 microns in diameter and up to several centimeters long, said process comprising flowing a natural gas stream over one side of a stainless steel wall containing at least 1 weight percent chromium so that the stream flows sequentially over an upstream surface (18) and a downstream surface (16) thereof, said upstream surface (18) initially bearing a relatively thin oxide layer of a type that naturally forms on stainless steel exposed to air at about room temperature, said downstream surface (16) initially bearing a relatively thick oxide layer of the order of 5 microns thick formed by heating stainless steel in air, heating said wall and gas stream at a temperature sufficient to pyrolyze methane in said natural gas, and continuing said heating and gas flow for a time sufficient to grow the graphite fibres(66) on the downstream surface (16).

Claim 8

A process for manufacturing graphite fibres according to claim 6, characterised in that the process includes contacting a side (20,22) of the stainless steel wall opposite the upstream and downstream surfaces (16, 18) of said one side with hydrogen gas containing water,and the wall and gases are heated to a temperature between 970°C and 1000°C.