[0001] The present invention relates to continuous yarns and tows comprising high strength
bundles of composite fibers comprising conductive semi-metallic cores coated with
thin adherent layers of metals, to methods for their production, and to articles made
from such yarns.
BACKGROUND OF THE INVENTION
[0002] Bundles of high strength fibers of non-metals and semi-metals, such as carbon, boron,
silicon carbide, and the like, in the form of filaments, mats, cloths and chopped
strands are known to be useful in reinforcing metals and organic polymeric materials.
Articles comprising metals or plastics reinforced with such fibers find wide-spread
use in replacing heavier components made of lower strength conventional materials
such as aluminum, steel, titanium, vinyl polymers, nylons, polyesters, etc., in aircraft,
automobiles, office equipment, sporting goods, and in many other fields.
[0003] A common problem in the use of such fibers, and also glass, asbestos, and others,
is a seeming lack of ability to translate the properties of the high strength fibers
to the material to which ultimate and intimate contact is to be made.
[0004] The problem is manifested in a variety of ways: for example, if a length of high
strength carbon fiber yarn is enclosed lengthwise in the center of a rod formed from
solidified molten lead, and the rod is pulled until broken, the breaking strength
will be less than expected from the rule of mixtures, and greater than that of a rod
formed from lead alone, due to the mechanical entrapment of the fibers. The lack of
reinforcement is entirely due to poor translation of strength between the carbon fibers
and the lead. The same thing happens if an incompatible high strength fiber is mixed
with a plastic material. If some types of carbon fibers, boron fibers, silicon carbide
fibers, and the like in the forms of strands, chopped strands, non-woven mats, felts,
papers, etc. or woven fabrics are mixed with organic polymeric substances, such as
phenolics, styrenics, epoxy resins, polycarbonates, and the like, or mixed into molten
metals, such as lead, aluminum, titanium, etc., they merely fill them without providing
any reinforcement, and in many cases even cause physical properties to deteriorate.
[0005] All of these problems are generally recognized now, after years of research, to result
from the need to insure adequate bonding between the high strength fiber and the so-called
matrix material, the metal or plastic sought to be reinforced. It is also known that
bonding can be improved with careful attention to the surface layer on each macro-micro
filament or fibril in the material selected for use. Glass filaments, for example,
are flame cleaned and then sized with a plastic-compatible organosilane to produce
reinforcements uniquely suitable for plastics.
[0006] Such techniques do not work well with other fibrous materials and, for obvious reasons,
are not suitable for carbon fibers, which would not surface texture, and which have
different boundary layers.
[0007] High stength carbon fibers are made by heating polymeric fiber, e.g., acrylonitrile
polymers or copolymers, in two stages, one to remove volatiles and carbonize and another
to convert amorphous carbon into crystalline carbon. During such procedure, it is
known that the carbon changes from amorphous to single crystal then orients into fibrils.
If the fibers are stretched during the graphitization, then high strength fibers are
formed. This is critical to the formation of the boundary layer, because as the crystals
grow, there are formed high surface energies, as exemplified by incomplete bonds,
edge-to-edge stresses, differences in morphology, and the like. It is also known that
the new carbon fibrils in this form can scavenge nascent oxygen from the air, and
even organic materials, to produce non- carbon surface layers which are firmly and
chemically bonded thereto, although some can be removed by solvent treating, and there
are some gaps or open spaces in the boundary layers. Not unlike the contaminants on
uncleaned, unsized glass filaments, these boundary layers on carbon fibers are mainly
responsible for failure to achieve reinforcement with plastics and metals.
[0008] Numerous unsuccessful attempts have been reported to provide such filaments, especially
carbon filaments, in a form uniquely suitable for reinforcing metals and plastics.
Most have involved depositing layers of metals, especially nickel and copper as thin
surface layers on the filaments. Such a composite fiber was then to be used in a plastic
or metal matrix. The.metals in the prior art procedures have been vacuum deposited,
electrolessly deposited, and electrolytically deposited, but the resulting composites
were not suitable.
[0009] Vacuum deposition, e.g., of nickel, U.S. 4,132,828, made what appears to be a continuous
coating, but really isn't because the vacuum deposited metal first touches the fibrils
through spaces in the boundary layer, then grows outwardly like a mushroom, then joins
away from the surface, as observed under a scanning electron microscope as nodular
nucleation. If the fiber is twisted, such a coating will fall off. The low density
non-crystalline deposit limits use.
[0010] Electroless nickel baths have also been employed to plate such fibers but again there
is the same problem, the initial nickel or other electroless metal seeds only small
spots through holes in the boundary layer, then new metal grows up like a mushroom
and joins into what looks like a continuous coating, but it too will fall off when
the fiber is twisted. The intermetallic compound is very locally nucleated and this,
too, limits use. In the case of both vacuum deposition and electroless deposition,
the strength of the metal-to-core bond is always substantially less than one-tenth
that of the tensile strength of the metal deposit itself.
[0011] Finally, electroplating with nickel and other metals is also featured in reported
attempts to provide carbon finers with a metal layer to make compatible with metals
and plastics, e.g., R.V. Sara, U.S. 3,622,283. Short lengths of carbon fibers were
clamped in a battery clip, immersed in an electrolyte, and electroplated with nickel.
When the plated fibers were put into a tin metal matrix, the fibers did not translate
their strength to the matrix to the extent expected from the rule or mixtures. When
fibers produced by such a process are sharply bent, on the compression side of the
bend there appear a number of transverse cracks and on the tension side of the bend
the metal breaks and flakes off. If the metal coating is mechanically stripped, and
the reverse side is examined under a high-power microscope, there is either no replica
or at best only an incomplete replica of the fibril, the replica defined to the 40
angstrom resolution of the scanning electron microscope. The latter two observations
are strongly suggestive that failure to reinforce the aluminum matrix was due to poor
bonding between the carbon and the nickel plating. In these cases, the metal to core
bond strength is no greater than one-half of the tensile strength on at most 10% of
the fibers, and substantially less than one-tenth on the remaining 90%.
[0012] It has now been discovered that if electroplating is selected, and if a very high
order of external voltage is applied, much higher than was thought to be achievable
in the prior art, uniform, continuous adherent, thin metal coatings can be provided
to reinforcing fibrils, especially carbon fibrils. The voltage must be high enough
to provide energy sufficient to push the metal ions through the boundary layer to
provide uniform nucleation with the fibrils directly. Composites of yarns or tows
comprising the thin metal coatings on fibers, woven cloth, yarns, and the like, according
to this invention can be knotted and folded without the metal flaking off. The composites
are distinguishable from any of the prior art because they can be sharply bent without
the fibrils slipping through a tube of the metal, as observed with electroless metal
or vacuum deposited composites and sharply bending them, especially with nickel, produces
neither transverse cracking ("alligatoring") on the compression side of the bend nor
breaking and flaking when the elastic limit of the metal is exceeded on the tension
side of the bend. In other words, the composites of the present invention are distinguishable
from those of the prior art because (i) they are continuous, (ii) the majority of
the composite fibers are uniformly metal coated; and (iii) the bond strength (metal-to-core)
on the majority of fibers is at least about 10 percent of the tensile strength of
the metal deposit, preferably not substantially less than about 25 percent, especially
preferably not substantially less than about 50 percent. In the most preferred embodiments,
the metal-to-core bond strength will be not substantially less than about 90 percent
of the tensile strength of the metal deposit. Highest properties will be achieved
with yarns or tows of composite fibers in which the metal-to-core bond strength approaches
about 99 percent of the tensile strength of the metal, and special mention is made
of these.
[0013] Articles made by adding the yarns or tows of the present invention to a matrix forming
material also distinguish from the prior art because they are strongly reinforced.
In addition, the articles possess other advantages, for example, they dissipate electrical
charges and if certain innocuous metals are used in the coatings, e.g., gold and platinum,
they will not be rejected when implanted into the body.
BRIEF DESCRIPTION OF THE DRAWINGS
[0014] The invention may be more readily understood by reference to the accompanying drawings
in which:
Fig. 1 is a transverse cross sectional view of a metal coated fiber of this invention.
Fig. la is a longitudinal cross sectional view of a metal fiber according to this
invention.
Fig. 2 and 2a are transverse cross sectional views of, respectively, a multinodal
core and a "cracked" core fiber coated with metal according to this invention.
Fig. 3 shows a longitudinal cross section of sharply bent metal coated fiber according
to this invention; and Fig. 3a shows a longitudinal cross section of a sharply bent metal coated composite
prepared according to the prior art;
Fig. 4 is a partial sectional view of a metal coated composite fiber-reinforced polymer
obtained by using this invention; and
Fig. 5 is a view showing an apparatus for carrying out the process of the present
invention.
[0015] All the drawings represent models of the articles described.
SUMMARY OF THE INVENTION
[0016] According to the present invention, continuous tows or yarns of high strength composite
fibers are provided, the majority of which fibers comprise a core and at least one
thin, uniform, firmly adherent, electrically conductive layer of at least one electrodepositable
metal, the bond strength of said layer to said core being not substantially less than
about 10 percent of the tensile strength of the metal. The bond strength in each fiber
is at least sufficient to provide that when the fiber is bent sharply -enough to break
the coating on the tension side of the bend because its elastic limit is exceeded,
the coating on the compression side of the bend will remain bonded to the core and
will not crack circumferentially.
[0017] In preferred features the core comprises carbon, boron or silicon carbide, especially
carbon fibrils.
[0018] The most preferred yarns of composite fibers will be those in which, when the coating
is removed by mechanical means and examined, there will be a replica of the fiber
or fibril surface on the innermost surface of the removed coating, as examined under
a scanning electron microscope of a definition of 40 angstroms or better.
[0019] Among the features of the invention are knottable tows or yarns of the new composite
fibers, fabrics woven from such yarns, non-woven sheets, mats and papers laid up from
such fibers, chopped strands of such fibers and articles comprising such fibers uniformly
dispersed in a matrix comprising a metal or an organic polymeric material. In preferred
embodiments, coating metals will be nickel, silver, zinc, copper, lead, arsenic, codmium,
tin, cobalt, gold, indium, iridium, iron, palladium, platinum, tellurium, tungsten
or a mixture of any of the foregoing, without limitation, preferably in crystalline
form.
[0020] In another principal aspect the present invention contemplates a process for the
production of continuous tows or yarns of high strength composite fibers, said process
comprising:
(a) providing a continuous length of a plurality of electrically conductive semi-metallic
core fibers,
(b) immersing at least a portion of the length of said fibers in a bath capable of
electrolytically depositing at least one metal,
(c) applying an external voltage between the fibers and the bath in excess of that
is' sufficient to (i) dissociate the particular metal and (ii) to uniformly nucleate
the dissociated metal through any barrier layer onto the surface of said fibers; and
(d) maintaining said voltage for a time sufficient to produce a thin, uniform, firmly
adherent, electrically conductive layer of electrolytically deposited metal on said
core, the bond strength of said layer to said core being not substantially less than
about 10 percent of the tensile strength of the metal.
[0021] In preferred features, the process will use core fibers of carbon, boron or silicon
carbide, especially preferably carbon fibrils.
[0022] In one preferred embodiment the plurality of core fibers comprise a tow of carbon
fibers and the product of the process is a tow of composite fibers which can be knotted
without separation of the layer of metal or portions thereof from the core fibers.
[0023] Other preferred features comprise the steps of weaving or knitting yarns produced
by the process into a fabric, laying them up into a non-woven sheet, or chopping them
into shortened lengths.
[0024] Other preferred features include carrying out the process in an electrolytic bath
which is recycled into contact with the fibers immediately prior to immersion in the
bath so as to provide increased current carrying capacity to the fibers and replenishment
of the electrolyte on the surface of the fibers.
DETAILED DESCRIPTION OF THE INVENTION
[0025] Referring to Figs. 1 and la continuous yarns and tows for use in the core 2 according
to the present invention are available from a number of sources commercially. For
example, suitable carbon fiber yarns are available from Hercules Company, Hitco, Great
Lakes Carbon Company, AVCO Company and similar sources in the United States, and overseas.
All are made, in general, by procedures described in U.S. 3,677,705. The fibers can
be long and continuous or they can be short, e.g., 1 to 15 cm. in length. As mentioned
above, all such carbon fibers will contain a thin, imperfect boundary layer (not shown)
of chemically bonded oxygen and chemically or mechanically bonded other materials,
such as organics.
[0026] Metal layer 4 will be of any electrodepositable metal, and it will be electrically
continuous. Two layers, or even more, of metal can be applied and metal can be the
same or different, as will be shown in the working examples. In any case, the innermost
layer will be so firmly bonded to core 2 that sharp bending will neck the metal down
as shown in Fig. 3, snapping the fiber core and breaking the metal on the tension
side of the bend when its elastic limit is exceeded. This is accomplished without
causing the metal to flake off when broken (Fig. 3a), which is a problem in fibers
metal coated according to the prior art. As a further distinction from the prior art,
the metal layer of the present invention fills interstices and "cracks" in fibers,
uniformly and completely, as illustrated in Figs. 2 and 2a.
[0027] The high strength metal coated fibers of this invention can be assembled by conventional
means into composites represented in Fig. 5 in which matrix 6 is a plastic, e.g.,
epoxy resin, or a metal, e.g., lead, the matrix being reinforced by virtue of the
presence of high strength fibrous cores 2.
[0028] Formation of the metal coating layer by the electrodeposition process of this invention
can be carried out in a number of ways. For example, a plurality of core fibers can
be immersed in an electrolytic bath and through suitable electrical connections the
required high external voltage can be applied. In one manner of proceeding, a high
order of voltage is applied for a short period of time. A pulse generator, for example,
will send a surge of voltage through the electrolyte, sufficient to push or force
the metal ion through the boundary layer into contact with the carbon or other fiber
comprising the cathode. The short time elapsing in the pulse will prevent heat from
building up in the fiber and burning it up or out. Because the fibers are so small,
e.g., 5 to 10 microns in diameter, and because the innermost fibers are usually surrounded
by hundreds or even thousands of others, even though only 0.5 to 2.6 volts are needed
to dissociate the electrolytic metal ion, e.g., nickel, gold, silver, copper, depending
on the salt used, massive amounts of external voltage are needed, of the order of
5 times the dissociation values, to uniformly nucleate the ions through the bundle
of fibers into the innermost fibril and then through the boundary layer. Minimum external
voltages of e.g., 10 to 50, or even more, volts are necessary.
[0029] Although pulsing as described above is suitable for small scale operations, for example,
to metallize pieces of woven fabrics, and small lengths of carbon fiber yarns or tows,
it is preferred to carry out the procedure in a continuous fashion on a moving tow
of fibers. To overcome the problem of fiber burnout because of the high voltages,
to keep them cool enough outside the bath, one can separate the fibers and pour water
on them, for example, but it is preferred to operate in an apparatus shown schematically
in Fig. 5. Electrolytic bath solution 8 is maintained in tank 10. Also included are
anode baskets 12 and idler rolls 14 near the bottom of tank 10., Two electrical contact
rollers 16 are located above the tank. Tow 24 is pulled by means not shown off feed
roll 26, over first contact roller 16 down into the bath under idler rolls 14, up
through the bath, over second contact roller 16 and into take up roller 28. By way
of illustration, the immersed tow length is about 6 feet. Optional, but very much
preferred, is a simple loop comprising pump 18, conduit 20, and feed head 22. This
permits recirculating the plating solution at a large flow rate, e.g., 2-3 gallons/min.
and pumping it onto contact rolls 16. Discharged just above the rolls, the sections
of tow 24 and leaving the solution are totally bathed, thus cooling them. At the high
current carried by the tow, the 1
2R heat generated in some cases might destroy them before they reach or after they
leave the bath surface without such cooling. The flow of the electrolyte overcomes
anisotropy. Of course, more than one plating bath can be used in series, and the fibers
can be rinsed free of electrolyte solution, treated with other conventional materials
and dried, chopped, woven into fabric, all in accordance with conventional procedures.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0030] The following Examples illustrates the present invention, but are not intended to
limit it.
EXAMPLE 1
[0031] In a continuous electroplating system, a bath is provided having the following composition:
[0032] The bath is heated to 140-160°F and has a pH of 3.8-4.2.
[0033] The anode baskets are kept filled with electrolytic nickel pellets and 4 tows (fiber
bundles) of 12,000 strands each of 7 micron carbon fibers are continuously drawn through
the bath while an external voltage of 30 volts is applied at a current adjusted to
give 10 ampere-minutes per 1000 strands total. At the same time,electrolytic solution
is recycled through a loop into contact with the entering and leaving parts of the
tow. The tow is next passed continuously through an identical bath, at a tow speed
of 5.0 ft./min. with 180 amps. current in each bath. The final product is a tow of
high strength composite fibers according to this invention comprising a 7 micron fiber
core and about 50% by weight of the composite of crystalline electrodeposited nickel
adhered firmly to the core.
[0034] If a length of the fiber is sharply bent, then examined, there is no circumferential
cracking on the metal coating in the tension side of the bend. The tow can be twisted
and knotted without causing the coating to flake or come off as a powder. If a section
of the coating is mechanically stripped from the fibrils-, there will be a perfect
reverse image (replica) on the reverse side.
EXAMPLE 2
[0035] If the procedure of Example 1 is repeated, substituting two baths of the following
compositions, in series, and using silver in the anode baskets, silver coated graphite
fibers according to this invention will be obtained.
[0036] The first bath is to be operated at room temperature and 12-36 volts; the second
at room temperature and 6-18 volts.
EXAMPLE 3
[0037] The procedure of Example 2 can be modified, by substituting nickel plated graphite
fibers as prepared in Example 1 for the feed, and the voltage in the first bath is
reduced to about 18 volts. There are obtained high strength composite fibers according
to this invention in which a silver coating surrounds a nickel coating on a graphite
fiber core.
EXAMPLE 4
[0038] The procedure of Example 1 can be modified by substituting for the nickel bath a
bath of the following composition, using zinc in the anode baskets, and zinc coated
graphite fibers according to this invention will be obtained:
[0039] The bath is run at 100°F and 18 volts are externally applied.
EXAMPLE 5
[0040] The procedure of Example 1 can be modified by substituting for the nickel bath a
bath of the following composition, using copper in the anode baskets, and copper coated
graphite fibers according to this invention will be obtained:
[0041] The bath is run at 140°F and 18 volts are externally applied. The copper plated fibers
should be washed with sodium dichromate solution immediately after plating to prevent
tarnishing. If the procedure of Example 3 is repeated, substituting the copper bath
of this example for the silver bath, there will be obtained high strength composite
fibers according to this invention in which a copper coating surrounds a nickel coating
on a graphite fiber core.
EXAMPLE 6
[0042] The procedure of Example 1 can be modified by substituting for the nickel bath two
baths of the following composition, using standard 80% cu/20% zinc anodes, and brass
coated graphite fibers according to this invention will be obtained:
[0043] Both baths are run at 110-120°F. Since one-third of the brass is plated in the first
bath, at 24 volts, and two-thirds in the second at 15 volts, the current is proportioned
accordingly. Following two water rinses, the brass plated fibers are washed with a
solution of sodium dichromate, to prevent tarnishing, and then rinsed twice again
with water.
EXAMPLE 7
[0044] The procedure of Example 1 can be modified by substituting for the nickel bath a
bath of the following composition, using solid lead bars in the anode baskets, and
lead coated graphite fibers according to this invention will be obtained:
[0045] Optionally, about 2 g./l. of &-naphthol and of gelatine are added. The pH is less
than 1, the bath is operated at 80°F and an external voltage of 12 volts is applied.
If the coating thickness exceeds 0.5 microns, there is a tendency for the lead to
bridge between individual filaments.
EXAMPLE 8
[0046] By the general procedure of Example 1, and substituting a conventional gold bath
for the nickel electroplating bath and applying sufficient external voltage, composite
high strength fibers comprising gold on graphite fibers are obtained.
EXAMPLE 9
[0047] Silicon carbide filaments and boron fibers are coated with nickel by placing them
in cathodic contact with a nickel plating bath of Example 1 and applying an external
voltage of about 30 volts.
EXAMPLE 10
[0048] A composition is prepared by chopping the composite fibers of Example 1 into short
lengths, 1/8" to 1" long, then thoroughly mixing with thermoplastic nylon polyamide
in an extruder, and chopping the extrudate into molding pellets in accordance with
conventional procedures. The pellets are injection molded into plaques 4" x 8" x 1/8"
in size. The plaque is reinforced by the composite fibers. By virtue of the metal
content, it also does not build up static charge, and it can act as an electrical
shield in electronic assemblies.
EXAMPLE 11
[0049] Bundles of nickel plated graphite fibers of about one inch in length prepared according
to the procedure of Example 1 are mixed 1:9 with uncoated graphite fibers and laid
up into a non woven mat, at 1 oz./l sq. yard. The mat has a metal content of about
5% by weight of nickel and can be impregnated with thermosetting resin varnishes and
consolided under heat and pressure into reinforced laminates having high strength
and excellent electrical dissipation properties.
EXAMPLE 12
[0050] Long, nickel coated graphite yarns prepared by the general procedure of Example 1
are pultruded at a high rate with molten lead in an apparatus from which a 1/8" diameter
rod issues in solidified form, down through the center of which runs the nickel coated
graphite fibers. The lead is alloyed to the nickel without complete solvency of the
nickel and the nickel is well bonded to the graphite fibrils. This results in a translation
of the physical strength of the graphite fibers through the nickel plating, nickel/lead
interpose to the lead matrix. A section of the rod is pulled in an apparatus to measure
breaking strength. In comparison with a lead rod of the same diameter, the breaking
strength nickel coated graphite fibers of this invention is very much higher.
[0051] The foregoing patents and publications are incorporated herein by reference. Many
variations of the present invention will suggest themselves to those skilled in this
art in light of the above, detailed description. For example, aluminum can be deposited
from ethereal solutions. Metals, e.g., tungsten, can be deposited from molten salt
solutions, e.g., sodium tungstenate. The tow can be treated to remove metal from sections
thereof, and thereby segmented structures are provided which have utility, for example,
as electrical resistors. All such variations are within the full intended scope of
the invention as defined in the appended claims.
1. A continuous yarn or tow comprising high strength composite fibers, the majority
of which have an electrically conductive semi-metallic core and at least one thin,
uniform, firmly adherent, electrically conductive layer of at least one electrodeposited
metal on said core, the bond strength of said layer to said core being not substantially
less than about 10 percent of the tensile strength of the metal.
2. A continuous tow or yarn as defined in Claim 1 wherein the bond strength of said
layer to said core in the majority of said fibers is at least sufficient to provide
that when the composite fiber is bent sharply enough to break the coating on the tension
side of the bend because its elastic limit is exceeded, the coating on the compression
side of the bend will remain bonded to the core and will not crack circumferentially.
3. A continuous yarn or tow is defined in Claim 1 wherein said bond strength is not
substantially less than about 25 percent of said tensile strength.
4. A continuous yarn or tow as defined in Claim 1 wherein said bond strength is not
substantially less than about 50 percent of said tensile strength.
5. A continuous yarn or tow as defined in Claim 1 wherein said bond strength is not
substantially less than about 90 percent of said tensile strength.
6. A continuous yarn or tow as defined in Claim 1 wherein said bond strength is not
substantially less than about 99 percent of said tensile strength.
7. A continuous yarn or tow as described in Claim 1 wherein said metal is crystalline.
8. A fiber as defined in Claim 1 wherein said core comprises carbon, boron or silicon
carbide.
9. A fiber as defined in Claim 2 wherein said core comprises carbon fibrils.
10. A fiber as defined in Claim 9 wherein removal of the coating by mechanical means
provides a replica of the fibril surface on the inner surface of the removed coating.
11. A tow or yarn as defined in Claim 1 which can be knotted without substantial separation
and loss of said metal coating.
12. A fabric woven or knitted from yarns as defined in Claim 1, alone, or in combination
with yarns which are of different material.
13. A non-woven sheet laid up from lengths of yarns as defined in Claim 1, alone,
or in combination with yarns of different material.
14. A three-dimensional article of manufacture produced by weaving, knitting or laying
up a mat comprised of yarns as defined in Claim 1, alone, or in combination with yarns
of different material.
15. A composition of matter comprising chopped yarns or tows as defined in Claim 1.
16. A composition of matter comprising yarns or tows as defined in Claim 1, disposed
in a matrix comprising metal or an organic polymeric material.
17. A yarn or tow as defined in Claim 1 wherein said metal comprises nickel, silver,
zinc, copper, lead, arsenic, cadmium, tin, cobalt, gold, indium, iridium, iron, palladium,
platinum, tellurium, tungsten, or a mixture of any of the foregoing.
18. A process for the production of continuous or tows of high strength composite
fibers, said process comprising:
(a) providing a continuous length of a plurality of electrically conductive semi-metallic
core fibers,
(b) continuously immersing at least a portion of the length of said fibers in a bath
capable of electrolytically depositing at least one metal,
(c) applying an external voltage between the fibers and the bath in excess of that
sufficient to (i) dissociate the particular metal at the innermost of said fibers
and (ii) to uniformly nucleate the dissociated metal through any barrier layer on
the surface of said fibers; and
(d) maintaining said voltage and resulting current for a time sufficient to produce
a thin, uniform, firmly adherent, electrically conductive layer of electrolytically
deposited metal on said core, the bond strength of said layer to said core being not
substantially less than about 10 percent of the tensile strength of the metal.
19. A process as defined in Claim 18 wherein the bond strength of said layer to said
core in the majority of said fibers is at least sufficient to provide that when the
composite fiber is bent sharply enough to break the coating on the tension side of
the bend because its elastic limit is exceeded, the coating on the compression side
of the bend will remain bonded to the core and will not crack circumferentially.
20. A process as defined in Claim 18 wherein said bond strength is not substantially
less than about 25 percent of said tensile strength.
21. A process as defined in Claim 18 wherein said bond strength is not substantially
less than about 50 percent of said tensile strength.
22. A process as defined in Claim 18 wherein said bond strength is not substantially
less than about 90 percent of said tensile strength.
23. A process as defined in Claim 18 wherein said bond strength is not substantially
less than about 99 percent of said tensile strength.
24. A process as defined in Claim 18 wherein said metal is crystalline.
25. A process as defined in Claim 18 wherein said core fibers comprise.carbon, boron
or silicon carbide.
26. A process as defined in Claim 18 wherein said core fibers comprise carbon fibrils.
27. A process as defined in Claim 18 wherein the product of the process is a tow or
yarn of composite fibers which can be knotted without separation of the layer of metal
or portions thereof from the core fibers.
28. A process as defined in Claim 18 including the step of weaving or knitting yarns
produced by the process alone, or in combination with yarns of a different material
into a fabric.
29. A process as defined in Claim 18 including the step of laying up the yarns produced
by the process alone, or in combination with yarns or a different material into a
non-woven sheet.
30. A process as defined in either of Claims 28 or 29 including weaving, knitting
or laying up the material into a three-dimensional article of manufacture.
31. A process as defined in Claim 18 including the step of chopping the yarns produced
by the process into shortened lengths.
32. A process as defined in any of Claims 28, 29 or 30 including the step of forming
a reinforced composite by intimately contacting a metal or an organic polymeric material
with at least a reinforcing amount of said yarn, sheet or chopped fibers.
33. A process as defined in Claim 18 including recycling the bath into contact with
the yarns or tows immediately prior to immersion therein so as to provide increased
current carrying capacity to the yarns or tows and replenishment of the electrolyte
on the surface of the fibers therein.
34. Yarns or tows of high strength composite fibers produced by the process of Claim
18.
35. Yarns or tows of high strength composite fibers produced by the process of Claim
33.
36. A reinforced composite prepared by the process of Claim 32.
37. A reinforced composite prepared by the process of Claim 32 wherein the amount
of yarn, sheet or chopped fibers is at least sufficient to provide an electrostatically
shielded reinforced composite.
38. A single fiber recovered from a continuous yarn or tow as defined in Claim 1.