Coating processes – Coating by vapor – gas – or smoke – Carbon or carbide coating
Patent
1997-01-15
1998-08-25
King, Roy V.
Coating processes
Coating by vapor, gas, or smoke
Carbon or carbide coating
427178, 427122, 427299, C23C 1626
Patent
active
057981434
DESCRIPTION:
BRIEF SUMMARY
This is a 35 U.S.C. .sctn. 371 of PCT/GB95/01680, filed Jul. 17, 1995.
This invention relates to a method of diamond-phase carbon coating of elongate substrate material by use of chemical vapour deposition (CVD) techniques. In particular, the invention relates to use of CVD techniques to produce hollow tubes having diamond-phase carbon inner and outer walls (hollow diamond tubes).
BACKGROUND OF THE INVENTION
Diamond-phase carbon (hereinafter known as diamond) CVD is the deposition or growth of diamond on a substrate material, starting with gaseous precursors. Initial work in the field of CVD growth of diamond concentrated on growth of thin films on flat substrates. Later research has extended the field to coating of non-planar materials (e.g. P W May et al, Proc 3rd Int Symp Diamond Mater, Honolulu 1993, Proceedings Volume PV 93-17, ed. J P Dismukes and K V Ravi (Electrochem Soc Pennington, N.J.), P1036). Advances in the field include fabrication of diamond-coated metal wires (e.g. Cu, Ti and W) and formation of hollow tubes of diamond by the subsequent removal of the wire substrate by etching. However, the production of long lengths hollow tubes by etching is severely hampered by the associated difficulty in etching of lengths of fibre.
It is also known to coat SiC fibres and ceramic fibres with diamond (P W May et al ibid and P W May et al, Journal of Materials Science Letters, 13, p247-249, 1994 respectively). Such fibres are suitable for incorporation into composite materials required to be substantially non-conducting.
DESCRIPTION OF THE INVENTION
According to this invention a method of diamond coating an elongate substrate material having a surface pre-treated to establish diamond nucleation sites comprises the steps of: wherein the pitch of the helix is less than the diameter of the helix; on the elongate substrate material by chemical vapour deposition such that growth surfaces of diamond deposited upon adjacent pitches of the helix fuse such as to close the pitch of the helix and resulting in hollow diamond tubes.
Suitable elongate materials are those materials which will retain the helical geometry following preforming. Typically the materials are metals such as W, Cu, Mo, Si which are known to be substantially non-reactive within the gaseous environment of a diamond CVD chamber. However, other materials such as metals reactive to the diamond CVD gaseous precursors (e.g. steel) can be suitable for the diamond CVD process by the deposition of a inhibiting barrier layer on the surface of the reactive material prior to pretreatment for the establishing of nucleation sites. Choice of suitable elongate material will result in the elongate material acting as a reinforcing element within the hollow diamond tubes.
Preferably the CVD process takes place in a vacuum chamber having a pressure of less than 40 Torr, although atmospheric pressure CVD using combustion torch methods (e.g. plasma arc jets or oxyacetylene torches) can be used in conjunction with suitable substrate temperature control devices preventing heating of the substrate to temperatures greater than 1000.degree. C.
During the coating of the elongate material within the CVD chamber it is important that the material is immersed uniformly within the reactive gases. Typically this is achieved within a filament reactor by positioning the filament vertically and hanging the elongate material parallel to it (or passing the elongate material parallel to the filament for continuous processing) and about 5.times.10.sup.-6 m away from the filament. Within such apparatus uniformity of diamond deposition is achieved most easily for material having dimensions of less than 200.times.10.sup.-6 m in axes normal to the elongate axis of the material (e.g. diameter axis for material in the form of wire). Shadowing effects may appear on material having dimensions greater than 200.times.10.sup.-6 m and can be overcome by the positioning of the material within the inside of filament coils of the apparatus.
Typical methods of establishing nucleation sites on
REFERENCES:
Chen et al., "An investigation of diamond growth on Ferrous metals", Applications of Diamond Films and Related Materials edited by V. Tzeng et al., 1991, pp. 137-142.
Motojima et al., J. Chem Vap. Deposition, 1(2), pp. 136-156 1992.
WPI Abstract Accession No. 92-247404/30 & JP 040168264 A; (Shinku) see abstract.
Proc. 3rd Int. Symp. Diamond Matter, Honolulu, 1993, Proceedings vol. PV 93-17, pp. 1036-1041; P.W. May et al., "Preparation of CVD Diamond Wires . . . ", see especially first compleete paragraph on p. 1037.
King Roy V.
The Secretary of State for Defence in Her Britannic Majesty's Go
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