CA1274214A - Substrates coated with metal, simi-metal or carbon by plasma vapor - Google Patents

Abstract

SUBSTRATES COATED WITH METAL, SEMI-METAL, OR CARBON BY PLASMA VAPOR DEPOSITION

ABSTRACT

Radio frequency conductive substrates comprising, e.g., plates or fibers of carbon or the like and a thin, uniform firmly adherent film comprising at least one metal, semi-metal or carbon deposited by plasma assisted chemical vapor deposition onto the radio frequency excited substrate, and apparatus for their pro-duction. Composites comprising the coated substrates and a continuous matrix of a ceramic or an organic polymer are also disclosed.

Description

~27~

FIELD OF THE INVENTION

The present invention relates to subjecting an electrically conductive substrat~, for example, carbon fibers, filaments, fibrils, films, ribbons, sheets, : 20 plates, and the like to plasm~ enhanced chemical vapor deposition usin~ capacitively coup}ed plasma in which the substrate is one of the radiofrequency electrodes.
The substrates thus treated, or post-treated, for example, by gas phase graftlng, exhibit considerably altered or 25 modified 6urface characteristics. Th`e invention also :~ relate~ to composite articles comprised of the substra~es which have been subjected to the aforesaid treatment, assembled in heterogeneous combination with a ceramic or :~ an organic polymeric material, the articles exhibiting 30 various improved physical propertles such as enhanced mechanical ~trength.

~35 T

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BACKGROUND OF THE INVENTIO~
_ _ Composite article~ comprising ceramics or plastics reinforced with materials of diverse origins, such a~ gla88, carbo~, synthetic fiber~, silicon carbide, boron, and the like, find wide-~pread use in replacing components made of either heavier or lower strenyth conventional materials such as aluminum, steel, ti~anium, vinyl polymers, nylons, polyesters, etc., in aircraft, automobiles, office equipment, sporting goods, and in many other fields. The composites comprise two or more compone~ts, at least one of which defineR a continuous phase, or "matrix", and at least one other defining a "reinforcement" for the assembly.
A common problem in the use of reinforcements in such composites is a seeming lack of ability to translate their properties to the material, e.g., ceramic or heat curable polymer, to which ultimate and intimate contact is to be made. This leads to a loss in properties due to the lack of adhesion between the matrix component and the reinforcing means comprising the composite. The prior art is replete with attempts to improve on the :: adhesion between matrix and substrate by performing a variety of surface treatments on the reinforcement, and these include various chemical, electrochemical, mechanical, and other treatments.
. For example, carbon substrates are often given a post-manufaaturing surfa~e treatment which is a light oxidation and this improves interlaminar shear strength in composite materials. In addition, many such substrates are also provided with a sizing in the form of a polymer compatible with epoxy or polyimide matrix resins.
Although such techniques are relatively simple and low cost, they have a limited range o~ ~tility. Other ~35 techniques have al30 been propo~ed, ~uch as acid treat-~2~

. - - 3 o ment, ammonia treatment, carbide coatinl~, carbon dioxide treatment, electrolytic treatment, irradiation, isocyanate trea~me~t, metal halide trea~ment, organometallic treat-ment, whiskerization, and the like. Ion plating treat-S ments, including those which are pla~ma as~isted, aredescrib~d in numerou~ patents and p~blications. For example, S.C. Sanday, Proceeding~ Fifth Metal ~atrix Composite~ Technology Conference, May, 1983, p. 27-1 to 27-11, deals with ion plating on ibers, in which the plating i~ ultimately converted to the continuous matrix phaæe of the composite. Aisenberg, U.S. 3,904,505 and 3,961,103, uses an externally generated plasma to accelerate ion plating, and in this in~tance, the sub-strate is radio frequency excited. Inductive plasma assisted vapor deposition is disclosed in three papers by K. R. Linger, Compsitec (G.B.) Vol. 8, No. 3, pp.
139-44, July, 1977; Vorabdrucke Plan~ee Semin, 9th, 1977, 2, D12/1-D12/4 and Proc. Conf. Ion-Plating Allied Tech. 1977, 223-9. Other such ~reatment~ are disclosed 20 in Toho Beslon Co~ Japanese Patent Publication 58,120,876 (1983) (C.A. 100:8~06r), ion bombardment and ion plating;
Japanese Patent Publication 79,163,790 (1979~ (C.A. 92:
202375 m), ion plating; Japanese Patent Publication - 79,162,690 (1979) (C.A. 92:202376n), also ion plating;
25 Japane~a Patent Publication 78,34,083 (197e~ (C.A. 90:
75547a), plas~a etch and ion plating; Japanese Patent-Publication 78,66,831 (1976) (C.A. 90:11032w), plasma etch and ion plating; Japane~e Patent Publication 78,38,793 (1978) (C.A. 89:91997s), ion plating; Japanese 30 Patent Publication 78,38,791 (1978) (C.A. 89:202717n), ion plating, Laminating and hot pres~ing; and Japanese Paten~ Publication 77,27,826 (1977) (C.A. 87:43143~), plasma ~tch and ion plati~g. Al&o known ar~ pla~ma ~prayed coatiny techniques, e.g., C.A. 96:56379e, in which the metal comes out a~ fine par~icleæ which are 7~2~.~

deposited as such on the fiber~. Other. plasma treat ments are known, e.g., the pla~ma gener.ated heat-treated surface modifications on c~rborl described in Boom, I) . S .
3,723,289; 3,824,398; and 3,780,255t arld ill Hou, U.S.
3, 762, 941 and 3, 767, 774, and the superi.is~ial c:athode sputtering modifications in Masotti, et: alO, U.S.
3,813,282. A polyphenylene polymer i5 deposited from a plasma a~ a coating on carbon as described in EIou, U . S .
3,745,104 and 3,853,600. Fujimori, et al., Japanese Patent Publication No. 70,770, 1983, vaguely describes the use of a plasma assisted chemical vapor depo~ition of silicon carbide onto 20 micron carbon fiber to enhance the tensile strength, but no data are given in respect to beneficially affecting composites. Of intere~t in thi~ connection also are the ion plating with sputtering, pla~ma assisted, techniyues describPd in Sumitomo Electric Ind. Japanese Patent Publication 8070-769 (1983) (C.A.
99:14622W), Japanese Patent Publication 8060063 (1983) (C.A. 99:144596), and Mitsubishi Electric Corp., Japanese Patent Publication 81,140,021 (1981~ (C.A. 96:71290n), silane and methane deposit silico ~ arbon in an inductive plasma. Sung, Dagli and Ying, describe sur~ace modification of graphite substrates, both blocks and fiber~, via plasma treatment in 37th Annual Conference, 25 Reinforced Plastics/Composite~ Institut~, The Society of the Plastics Industry, Inc., January }1-15, 1982, Session 23-B, Page 1-6. The technique employed was to use an ~ inductively coupled pla ma, in which the substrate is : not excited. It is also di~closed that gas pha~e grafting can be achieved. Composite3 made from fibers modified by this techn~que had lower flexural strength, but better (but "not phenomenal") interlaminar ~hear strength than tho~e made from untreated fibers. Also of interest is Toray Industries , Inc ., Japanese Patent Publication 72,24,979 (1972) (C.A. 78:31295q) which disclo&es acrylic ~7~Z~4 o vapor inductive plasma treatment of carbon fibers. Such techniques also do not give good unifonn coatings if yarns or tow~ of fibers are to be treated because of rather poor penetration into the innermo~t ~ibers. Goan describes methods u~ing an inductively coupled pla6ma (U.S. 3,776,829, ammonia, and U.S. 3,634,220, oxygen) to produce functionalized carbon fibers which beneficially enhance flexural strength, modulus and ~hear strength parallel to the line of fiber-q in epoxy resin composites.
No beneficial ef~ect on interlaminar shear streng~h ig disclosed.
Unfortunately, the results which have bee~
attained to date can be deemed to be generally inadeyuate, otherwise deficient, and/or are not readily reproducible.
It is believed that a primary shortcoming is Lack of uniform film deposition or incomplete fiber penetration.
In addition, especially with ion plating methods, there are produced rough surface coatings which do not impart good handleability to ~ubstrates comprising yarn or tows. The coating~ produced without fiber bias when ion plated in bundles of 2-3, are also rough and brittle, and the fiber~ fu~e together. A need therefore exists for improving the physical properties of the composites to align these properties more clo~ely to the theoretical.

: 30 .

~35 SUMMARY OF THE INVENTIO~I

Aceordingly, a primary object of this invention iR to provide ~n Lmproved surface trea~flent for reinforc-S ing means intended for ultimate use in otherwi~e conven-tional composite asse~blies.
Another object of ~his invention i~ to provide an apparatus for conducting ~uch surface ~reatment.
Another object of this invention is to provide an improved compo~ite afisembly, the phy~ical properti.es of which are enhanced or improved with respect to the prior art.
Still another ob~ect of the in~ention i5 to provide a ~ubstrate having enhanced surface character-iStiC8 such that it i3 eminently suitable ~or thefabrication of composites there:from by rea~o~ of its great compatibility with great adhesiveness to various n~atrix components therefor.
~ In attaining the~e object~, one feature of this invention re~ides in subjecting a substrate, e.g., an electrically conductive sub~trate, such as carbon, silicon, ~ilicon carbide, and the like, for example, in the form of fibers, filaments, fibrils, films, ribbons, sheet~, plates, blocks, and the likP to capacitively coupled pla~ma enhanced chemical vapor deposition while the substrate is in a radio frequency excited state.
This dif~ers from the prior art in that the plasma is : capacitatively coupled and the substrate it9elf i~ radio frequency biased. This leads to more efficient and more uniform surface coating, even on the innermost fibers of a yarn or tow comprising bundle~, e~gO, of from 3,000 to l~,OOU fibers. In addition, in preferred features, the radio ~requency power can be varied to produce a wide range of predetermined modulus to mateh the properties to the matrix employed. Another feature o~ the invention ~7~

resides in pos-t-treatment steps, including grafting with another monomer. Still another feature of this invention resides in the fabrication of various composite assemblies utilizing the thus treated substrates as the reinforcing means therefor and which composites exhibit enhanced and improved physical and/or mechanical properties such as tensile and/or bending strength, etc.
Accordingly, the invention herein comprises a coated substrate comprising a radio frequency conductive core and at least one thin, uniform, firmly adherent, elemental film comprising at least one metal, semi-metal or carbon deposited on said core by plasma enhanced chemical vapor deposition while said core was radio frequency excited.
Other objects, features and advantages of the inven-tion will be apparent to those skilled in the art from the detailed description of the invention which follows.
BRIEF DESCRIPTION OF THE DRAWINGS
The invention may be more readily understood by reference to the accompanying drawings in which:
FIGURE 1 is a transverse cross sectional view of a film-coated fiber of this invention.
FIGU~E la is a longitudinal cross sectional view of a film-coated fiber according to this invention.
FIGURE 2 is a view showing an apparatus for carrying out a process of the present invention.
FIGURES 2a, 2b and 2c are views of electrode configurations suitable for use in the apparatus shown in FIGURE 2 for carrying out the process of the present invention.

i i ' 74~

7a 61109-7373 FIGURE 3 is a schematic view o:E an apparatus for continuously carrying out the plasma assisted chemical vapor deposition process of the present invention.
FIGURE 4 is a partial sectional view of a film-coated fiber-reinforced matrix composite of the present invention.

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DETAILED DESC~IPTION OF T~IE INVE~TION

Plasma enhanced chemical ~apor deposition iR a very well known technique, as ill~strat~d by ~ome of ~he . 5 reerences mentioned above, being ba~d on the equally well known phenomenon of plasma pol~er:ization of.mono-meric ga3es which generats highly cro~-linked, thin films ~ca 1000 Angstroms in thickne~s) on the ~urface an~, depending on the chemical nature of the substrates, coatings may also be grafted to the substrate. For plasma treatment, a radio frequen~y generator can be coupled to an impedence matching box and the output fed ~o a reactor. Typically, a power input of 10 to 100 watts will be used, preferably at a pressure not ~ub-s~antially in excess of about 5000 microns of mercury,most preferably in the range of 20 to 500 microns. The frequency of the power generator can vary widely, but it is usually in the range of from about 0~5 kHz to about 2500 MHz. Standard commercial units, which yenerate 13.6 M~z are convenient. The process can be carried out batchwise or continuously.
In the present invention, it is critical to the process to feed energy to the substra~e to insure radio frequency excitation. In distinction with most 25 processes of the prior art, in the present invention, the plasma i~ capacitatively coupled~ Such features of this invention provide uniform and even film coating, ev~n a~ the innermost fibers if multifilament fibers and tows are to be coated. While not critical, it is also 30 very much preferred to operat~:at pressures sub~tantially below atmospheric pressure an~, e~pecially preferably, below about 5000 micron of mercury. As mentioned, even : more preferable is to operate in the range of 10 to 500 micron~ of mercury, and optimum re~ults are achieved in ~35 the range of 10 to 100 microns of ~ercury.

'> ~ A

According to the invention, and referrin~ to FIGURE 2, the ba~ic plasma coating apparatus consists of radio frequency (RE) generator 2 (13.56 MHz, ~aterials Research Corp.), impedence matching network 4, and gas S Lmpervious container 6 (a bell jar). :~mpedence matching networX 4 permits optimum RF power tran~fer to the plasma. Ma~s flow monitor 8 (Matheson) measures gas flow into reactor 6. Monomer liquid i~ held in container 10. Inert gas, e.gO, argon i~ held in tank 12. Dry nitrogen is stored in tank 14. Vacuum pump 16 is connected to the apparatus through cold trap 18, which is cooled, for example, with liquid nitrogen. Any of a number of electrode configurations can be u~ed, for example, those shown in FIGURES 2a, 2b and 2c, respec-lS tively, wherein the substrate 20 is an electrode and i~
RF biased. The other electrode 22 is grounded. In allcases a configurati~n must be selected 80 as to provide uniform, non-directionally biased film deposition.
Illustratively, if the electrode comprises the ~ubstrate and is a 10 inch length or 6,000 or 12,000 carbon fiber tow ~e.g., CELION 6X and 12k, Celane~e Corp.), and the RF power input is in the range of 10-100 watts at a pres~ure of 30 to 400 microns of mercury, uniform coating~ in the range of 50 to 10,000 Angstroms, pre-ferably 200 to 5,000 Angstroms, are readily produced with the innnermost ~ibers also being coated.
Feed and take up apparatus are readily con-structed so that continuous tows can also be conveyed through the pla~ma and coated in accordance with the ~oregoing principles, and continuous methods are pre-ferred features of the invention. A suitable apparatus is 6hown in FIGURE 3. Here, container 24 for the reaction zone comprises a quartz reaction tube. RF Generator and impedence matching network 26, are a~ described in FIGURE 2. The yarns or tows o graphite fiber 28 are *Trade Mark ~7~

excited by pas~ing over conductive roller~ 30a and 30b before going through ~acuum introduction bu~hing 32 into container tube 24. The other electrode co~prise3 RF
grounded screen 34. Ga3 is fed to reactor 24 through port~ 36a and 36b, and mean~ to pull a vacuum on the sy~tem co~pri~e~ port 38 connect~d to a vacuum pump tnot ~hown). To maintain ga~ tightness, the coated tow i8 removed through e~it tube 38, which also i~ connected to vacuum. Support plates 40a and 40b hold the apparatu~
1~ together and provide a grounding means for grounded screen electrode 34. Feed roll 42 and take up roll 44 are used to supply fiber and collect coated fiber, Optionally, as shown by D.C. unit 3 in FIG. 2 means for rendering the Rub~trate D.C. conductive, comprising a battery, etc., can be interposed. ~his renders conduc-tive sub~trate 20 capable of attracting charged ions and provides enhanced film properties in ~ome instances.
As will be illu~trated by the example~, the materials fed to the respective reactors, either elements, compounds, or mixture~ thereof, will produce films by chemical vapor deposition, enhanced by plasma, of almost any type ~esired. The procedure in one aspect can coat _~-element~, of at least one metal, ~emi-metal or non-metal, e.g., antimony, tungsten, titanium, silicon and alpha-car~on on the substrates. In another a~pect, i~ will be ~hown that inorganic materials can be uniformly coated, such as Si C , Al O , CaO, AlPO , etc., as well as ~ilicon/nitrogen, sllicon/carbon, silicon/carbonloxygen, ~ilicon/carbo~/oxygen/nitrogen and ~imilar coatings.
Such refractory coating will enhance molten metal wetting and Lmpregnati~n of fiber bundles. ~or example, AlPO
o~ carbon will enhance wetting by aluminum; U.S.
4,008,299. Such coatings are al80 u~eful in the fahri-cation of ceramic composite~ becau~e they impart oxida-~35 tion resistance and control the bonding to the ceramic ~ ~74~

matrix. These coating~ are expected to provide abrasion r~si~tance also, extending their u~e to commercial weaving or braiding equipment. In ~till another aspect, the sub~trates unifor~ly coated with a ;Çilm of amorphous 5 carbon having a high population of active site~, before removal from the pla~a apparatu~ and whiLe 8till under moderate vacuum, are e~po~ed to a ga~ of a monomer or polymer that will react with the reactive ~ite, ga~
phase gra~ting the monomer or polymer molecule to the amorp~ou~ carbon surface, and thereby functionalize an organic film. Such monomer or polymer i~ 8elected to give maximum compatibility for bonding to a matrix material. For example amorphous carbon coating~ prepared in a styrene plasma can be selectively functionalized with nitrogen ~ontaining groupq ~uch ~ amides by briefly ~ -exposing the coating to an ammonia plasma before expo~ure to the ambient atmosphere. Amorphous carbon coatings can also be functionalized with ~xygen containing groups by exposing the amorphou-~ carbon coatings to ambient air. Carbon coating~ put down in acrylic acid ~apor result in free radical polymerization of acrylic acid on the fiber ~urface, and this can be verified by x-ray photo electron spectroscopy.
Referring to FIGS. 1 and la continuous bundle~
of fibers ~or u~e in the core 50 according ~o`the pre~ent invention are available from a number of sources commer-cially. For exa~ple, ~uitable carbon fiber yarns are available from Hercule~ Company, Hitco, Great La~es : Carbon Company, AVCO Company and similar sources in the United States, and over~eas. All are made, in general, by procedure~ described in U.S. 3,677,7~5. The fibers can be long and continuou~ or they can be &hort, e.g., 1 : to 15 cm. in lengt~l.
The core can al80 include a ~etal~ preferably ~3S a~ a surface layer, a~d especially preferably as an 3L~7a~
_12 _ 1109-7373 electroplated metal layer comprising nickel, copper, lead, gold, silver, mixtures of the foregoin~ and the like. These preferably are made by p~ocedures disclo ed in assignee'~ European Patent Application No. 88,884 (September 21, 1983).
Film 52 will be of any metal, ~emi-metal or non-metal, element or compound, or mixture thereof which has been deposited on the core by plasma enhanced chemical vapor deposition. Two layers, or even more, of such films can be applied and the films can be the ~ame or different, as will be shown in the working examples.
In other embodiments (not shown), the core can compri8e a plate-like subs~rate and an adhesive or coat-ing can be applied over the fiLm, and the adhesive con--tinuous phase serves as the matrix therefor. In order to demonstrate the beneficial influence of the respective films on such substrate~, the plates can be coated with thin layers of adhesives comprising, for example a thin layer of bisphenol A diepoxide and diethylenetriamine.
2a Curing the resin at 16 hours and then for 80C for 2 hours provides significant increases in bonding strength, due to the presence of the surface film of this invention.
The film coated fibers of this invention can be a~embled by conventional ~eans into composites rep-resented in FIG. 4 in which matrix 54 is a plastic, e.g., epoxy resin, a polyimide resin or a ceramic, e.g., glass, the matrix being reinforced by virtue of the presence of film-coated fibrous cores 50.
To make polymeric matrix, fiber-reinforced compo~ites, any method known in the art, such as the methods de~cribed in assignee's Canadian Patent No. 1,186,886 can be used. The polymeric material can be film coated, melt blended,~solvent blended, or the like, onto the film coated ~.~74~1~

reinforcement in the form of fibers, yarns or tows, woven, braided or knitted fabrics, non-woven sheets, chopped fibers and the like.
Suitable resins are polyesters, polyethers, polycarbonates, epoxies, phenolics, epoxynovolacs, epoxy-polyurethanes, ureatype resins, phenolformaldehyde resins, melamine resins, melamine thio-urea resins, urea-aldehyde resins, alkyd resins, polysulfide resins, vinyl organic prepolymers, multifunctional vinyl ethers, polymers of vinyl ethers, polymers of vinyl esters, polycarbonate-copolyesters, polycarbonate-copolysilicones, polyetheresters, polyimides, polyamides, polyesterimides, polyamideimides, poly-etherimides, and polyvinyl chlorides, mixtures of any of the fore-going, and the like. The polymeric material may be present alone or in combination with copolymers and polymeric blends may also be used. The polymeric material may, when combined with the coated reinforcement of this invention, be convertible by heat or light, alone or in combination with catalysts, acceLerators, cross-linking agents, etc., to form components suitable for end uses, such as airfoils, protective clothing, sporting equipment, office machinery housings, television cabinets and the like. The amount of reinforcement used will be conventional, but preferably, the reinforcement will comprise at least about 40 percent by volume of the composite.
To make ceramic matrix, reinforced composites, any method known in the art, such as the methods described in Carbon and Graphite Fibers, Ed. Marshall Sittig, Noyes Data CorpO, 1980, pp. 263-269, can be used. Film coated fibers, e.g., at least 40 percen-t by volume, can be formed into composites with ceramics, such as glass, cement and refractory compounds, such as niobium carbide or tantalum carbide. Thermal shock resistance and reduc-tion in brittleness are two properties beneficially affected byreinforcing ceramics in this way.

~;~7'~4 DESCRIPTION OF T13~E: PREFERRED EMBODI~ENTS
_ _ The following non-limiting examples illustrate the pre~ent invention.
The ba~ic plasma coating apparatus is repre-sentea ~chematically in FIGURE 2. The components com-prised a radio ~requency (RF) generator (13.56 MHz, Materiala R~earch Corp.), an -~ ~ ce matching network an~ a container comprising a bell jar or a tubular reactor (FIG. 3). The -~m~é~e~e ma~ching networX pe.rmits optimum RF power tran~fer to the plasma. Ga~ flow into the reactor wa3 measured by a Matheson ma~s flow monitor.
The electrode configuration~ employed are shown in FIGS.
2a-c, with the actual configuration specified in the respective exa~ple. The RF power input to the reactor lS typically was in the range of 10 to 100 watt~ at pre~sures of 30 to 400 micron~ of mercury. Most examples were performed on 10 inch lengths of Celion 6k, 6000 carbon fiber tows. However, for continuous processing, a feed and take up apparatu~ was constructed to continuously 20 convey the tow through the plasma with a total capacity of 10 meters.
The surface effects of the plasma assisted chemical vapor deposition (CVD) were characterized using : x-ray photo~lectron spectroscopy (XPS) and scanning 25 electron microscopy on both treated and untreated fiber samples~
E ~ PLE 1 Antimony (Sb) Deposition from SbCl5_~E~
The apparatu~ of FIG. 2 was used with an elec~rode con-30 figu~ration ~hown. The RF power was 20 watts, the total ~: pressure was 40 mTorr (40 microns) of SbCl vapor. The reac~or background pre~sure was 10 mTorr. After 15 minutes of expo6ure, a metallic looXing coating ca 1000 Ang~rom~ ~hick of antL~ony was obtained uniformly on 35 each ~iber in the bundle. There was no non-uniform ~7a~ L4 o directionally bia~ed film deposition.

Titanium (Ti) DeE~ition from TiCl Va~r and Hydrogen. - The apparatu o FIG. 2 wa~ used with an electrode configuration ~hown. ~he ~F power was 10 wat~s, and the total pressure was 100 mTorr. The reactor background pressure was 10 mTorr. After 15 minu~es of e~po~ure, fibers were obtained evenly coated with a t:hin ~ilm of titanium, ca 5000 AngstromR thicX.

Tun~ten (W) Deposition from WF and Hydroyen.
The apparatus of FIG. 2 was used with an electrode con-figuration shown. The RF power:was 20 watts, and thetotal pressure was 100 mTorr. The reactor background pressure was 10 mTorr. The reactor pres~ure was increased ; to 20 mTorr with WF . The reactor was then pre-~surized : from 20 mTorr to 100 mTorr with H . After 10 minutes, a coating of tung~ten wa~ deposited, _ 5000 Angstromq thick.

_i icon (Si) Deposition from SiH and Argon. -: The appara~us of;FIG. 2 wa~ used with an electrode con-;~ :::~ : figuration ~hown. The RF power was ~5 watts. The total prec-~ure was 40 mTorr (SiH ~ Ar~. The system background pressure was 10 mTorr. T~e reactor pre3sure was rai6ed 30 to 30 mTorr with Ar then i~crea~ed to 40 mTorr with SlH . After 5 minutes, an even coating of Si about 1 : micron ~10,000 Ang~troms) thic~ w~s deposited on the fibexs.

~7~4 - _ 16 -O

Al~ha-Carbon ~C) De~pDsited from Styrene Vapor.
The apparatus of FIG. 2 wa~ u~ed with an electrode con-figuration show~. The RF power wa3 S0 watt~. ~he total presqure was 60 mTorr. The background E~res~ure was 10 mTorr. The reactor pre~sure wa~ increa~ed to 60 m~orr with styrene vapor. After 3 minute~, a thin, uni~orm film o alpha-carbon ca 1000 Angstrom~ thick wa~ deposi~ed on the fibers.

Carbon-Silicon (Si C ) Deposition frorn SiH , x i-x 4 CH and Ar~on. - The apparatus of FIG. 2 was u~ed with an electrode configuration shown. The RF power was 20 watts, and the total pres~ure was about 56-58 mTorr.
The CH flow rate w~s 1.7 ~tandard cubic centimeters per minute (SCCM). The SiH flow rate was 1.7 SCCM. ~he Ar flow rate was 21.2 SCCM. After 1 hour, a ~hin carbon-silicon film ca 1500 Angstroms was evenly coated on the fi~ers.

Carbon-Silicon (Si C ) Deposition from SiH
x i-x 4 and C H . - The apparatus of FIG. 2 wa~ used with an 25 el~ctrode configuration ~hown. The RF power wa~ 40 watts, ~nd the total pre~ure was 26 mTorr. The SiH
flow rate was 1.8 SCCM. The C H flow rate was 1.75 SCCM. After 1 hour, a carbon-silicon film about 1 micron thick was evenly coated on the fibers.
~XAMPLE 8 Si~icon-Nitrc~en (Si N ) ~e~osition from X~r - -~
SiC14, MH3 and N . - The apparatus of FIG~ 2 was used with an electrode configuration shown. The ~F power was 35 20 watt~, and the total pres~ure was about 40 mTorr.

~7~4 _ 17~ 61109-7373 The NH flow rate was 1.0 SCCM. The ~ flow rate was 1.5 SCCM. .The SiC1 flow rate waa 0.7 5CCM. After 45 minute~, carbon fiber~ thinly and uniforMly coated wlth a film co~prising silicon-nitrogen ca 5000 ~gstxoms i th~ck were obtained.

EXAMPL~ 9 Silicon-Carbon Oxy~en-~itrogen (SiCoN) Deposition from SiH , CH , Air and Argon. - The apparatus ~hown in FIG. 2 wa~ used with an el~ctrode configuration ~hown. The RF power was 20 watts. The total pre~ure was 60 mTorr. Ai.r compri~ed 20 mTorr. The sy~tem was brought to 60 mTorr by flowing in SiH , CH and Argon gas at the following flow rate~: SiH , l.7 SCCM ~ , 5 1.7 SCCM; and Argon 21.2 SCCM. After 1 hour a thin uniform film ca 6000-7000 Ang~troms thick wa~ deposited, having the ~ollowing elemental compo~ition: C, 22.4 ; Atomic %; 0, 44,5 Atomic %; ~, 7.4 Atomic ~; and Si, 25o8 Atomic %.

The g0neral procedure of Example 5 was repeated, ~ubstituting for the styrene pla~ma, plasmas of butane and acrylic acid vapor~. In all ca~es amorphous carbon : 25 (alpha-carbon) films were deposited.
.

~ y the procedure of Example 5, 6ub~tituting an acrylic acid plasma for a styrene plasma, and ~ubsequently exposing the amorphous alpha carbon film coated fibers to laboratory air, ~here is obtained significantly in-crea~ed amou~t~ of oxygen on the surface tby XPS), and a changed distribution of functionalitie~ (mor~ -C - O
O

~7~

group~ than on the untreated i~er ~urface. XPS ~nalysi~
of the film gave the following composit.ion: 0 , 8.81 Atomic ~; O , 2.26 Atomic ~; C , 65.58 Atomic ~;
1~3 18 C , 16.0 Atomic %; and C , 7.36 Atomic %.
1~ If the procedure i~ repeated, except thak the film i~ firBt ~XpOBe~ to acrylic acid monomer ~apor immediately after lpha carbon film depooition, and then exposed (after evacuation) to air, there i~ obtained a more ~electively functionalized surface: a ~igniicant 1~ increase in the amoun~ of C-O groups and a decrease in the amount of C = O group~.

XPS analysis of the film gave the following re6ult3: O , 11.16 Atomic %; 0 , 3.15 Atomic %, 15 C , 58.0 Atomic ~; C , 21.17 Atomic ~; and C , 6.52 19 1~3 18 Atvmic ~.

EXAMP~E5 15-17 The apparatus of FIG. 2 was u~ed with the electrode configuration shown. The RF power wa~ 25 watt~. The vacuum sy~tem wa~ initially filled to 20 micron~ pressure with Argon and then filled to 40 microns with styrene vapor. After 10 minutes, the alpha-carbon film coated fibers were expo~ed to air. The amount o 0 wa~ 5.3 ~tomic %, and C was 94.t Atomic ~. The . ls ls process was repeated but, instead of air, the alpha-carbon film was exposed i~mediately to ammonia ~as at 1000 micron~ for 15 minutes. ~he film wa~ analyzed by XPS analy~is and showed a trac~ amount of nitrogen: O
~.25 Atomic %; C , 92.~ Atomic ~ and N , 1.32 Atomic ~ When the procedure was repeated, but using a post treatment i~ an ammo~ia plasma (20 watts RF power at 2 min. at an aDmo~ia pre~ure of 50 micron~), the N/0 ratio of ~v 1 in the analyzed film indicated that the ~35 ni~rogen is present in the form of NH2 groups. The ~7~4 1109-7373 analysi3 was l 8.11 Atomic %; Cl , 83.4 Atomic %; and N , 8.44 Atomic ~. In all ca~es the coatings were about 1000 Ang~trom~ thick.

Silicon (Si) Depoqition from SiH on ~ickel Coated Carbon Fiber Substrate. - The apparatus of FIG.

2 was used with an electrode coni~uration ~hown. The sub trate comprised a 6000 carbon fiber tow coated with 50 wt.~ nicXel by the electroplating proceqs de-scribed in assignee's above-mentioned European Patent Application ~o. 88j884 Example 1. The RF power was 30 watt~. The total pressure was 33 microns of mercury.
The flow rate of SiH was 3.5 SCCM. After 10 minuteR, an even coating of Si about lO,OOQ Angstroms thick wa~
deposited on the nickel coated carbon ~iber.

A pyrolytic graphite plate was placed in the apparatus of FIG. 2 and biased with RF power of 40 watts. The total pre~sure was 80 mTorr. The reactor wa~ evacuated to 4 mTorr, then backfilled to 42 mTorr with H , and further filled to 80mTorr with Al(C~ ) .
The deposition time was 30 minutes. A uniform ~ilm was deposited on the plate and comprised Al 0 H , wherein X C 2, and Y~ 3. After heat-treatment to ~ lOOO~C, the film formed stoichiometic Al 0 .

An array is made of aligned graphlte yarns coated with a selectively functionalized alpha car~on film by the procedure of Example 17. These are impreg-nated with a heat curable composition comprising an epoxy re~in and a polyamine curing aqent. The arrays ~35 are assembled into a three-dimensional shape and the q " , 2~

epoxy resin is heat cured to provide a composite in which the resin is the matrix and the film coated graphite yarns are the reinforcing phase (about 40-50% by volume). The composite exhibits improved short beam shear strength in comparison with one made with graphite yarns which are not coated in accor-dance with the present invention.

A film coated fiber tow comprising carbon and coated with a carbon-silicon film by the procedure of Example 7 is converted into a ceramic matrix composite by fusing powdered glass to the reinforcement (about 40% by volume of the reinforcement). The composite exhibits better stability after thermal cycling in an oxidative atmosphere than does one reinforced with Eibers not coated Wit}l film in accordance with the present invention.
The composite articles of the examples containing the plasma coated fibers will find use in applications where light weight, stiff components are needed, such as support beams in space structures, lightweight bridging, internal engine components on gas turl~ines and internal combustion equipment for aircraft, space vehicles, and the like.
Many variations of the present invention will suggest themselves to those skilled in this art in light of the abo~e, detailed description.
For example, composites comprising epoxy or polyimide polymeric matrixes rei.nforced with fibers coated by the procedures of Examples 1-15 and 17 can be prepared. And composites comprising other ceramics, and cement, can be prepared~ reinforced with fibers coated by the procedures o:E Examples 1-6 and 8-17. In addition, the radio frequency power can be varied to pro-duce a film with a predetermined modulus. }ligher power produces ~7~2~ ~

a higher mod~lus. Wattage~ in the range of 10 to lO0 produce film moduli in the ra~ge of 300,000 to 30,000,000 pound~ per ~quare inch. Calibration chart~ can be easily prepared to con~ert power to ultimate ~odulus.
5 All ~u~h variations are within the full intended ~cope of the lnventio~ as definea i~ the appended claims.
It is~also no~ed that this application is also closely related to applications 476,466; 476,467 and 476,471.

~35 ! / ~

Claims (10)

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. A coated substrate comprising a radio frequency con-ductive core and at least one thin, uniform, firmly adherent, elemental film comprising at least one metal, semi-metal or carbon deposited on said core by plasma enhanced chemical vapor deposi-tion while said core was radio frequency excited.

2. A coated substrate as defined in Claim 1 wherein the film was deposited on said core at a vapor pressure not substan-tially in excess of about 5,000 microns of mercury.

3. A coated substrate as defined in Claim 2 wherein the film was deposited on said core at a vapor pressure in the range of from about 20 to about 500 microns of mercury.

4. A coated substrate as defined in Claim 1 wherein the thickness of the film is in the range of from about 50 to about 10,000 Angstroms.

5. A coated substrate as defined in Claim 4 wherein the thickness of the film is in the range of from about 200 to about 5,000 Angstroms.

6. A coated substrate as defined in Claim 2 wherein the thickness of the film is in the range of from about 200 to about 5,000 Angstroms.

- 22a - 61109-7373

7. A coated substrate as described in Claim 1 wherein said film comprises antimony, tungsten, titanium, silicon or alpha-carbon.

8. A coated substrate as defined in Claim 1 wherein said core comprises a metal.

9. A coated substrate as defined in Claim 1 wherein said core comprises a plurality of radio frequency conductive fibers.

10. A coated substrate as defined in Claim 9 wherein said core comprises a yarn or tow of radio fre-quency conductive fibers.