GB2588498A

GB2588498A - Copper-carbon nanotube hybrid wire for electrical conduction and method of making same

Info

Publication number: GB2588498A
Application number: GB2011733.9A
Authority: GB
Inventors: Shenoy Gangoli Varun; Kazimierska Ewa; Jonathan Barnett Christopher; Barron Andrew
Original assignee: Swansea University
Current assignee: Swansea University
Priority date: 2019-08-05
Filing date: 2020-07-29
Publication date: 2021-04-28
Also published as: GB202011733D0

Abstract

The carbon nanotube reinforced copper nano hybrid wire is formed by the electrodeposition of copper into the interior of the nanotubes of a preformed CNT fibre or fabric. A reaction in acid or anodization is followed by electrolysis of a copper salt from aqueous solution for a chosen period of time. A longer period of time will provide electrodeposited copper on the exterior surface of the nanotubes. Carbon nanotube reinforced copper hybrids according to the invention provide wire with a lower weight than pure copper, and a specific conductivity close to that of copper.

Description

UNITED KINGDOM PATENT APPLICATION FOR:

COPPER-CARBON NANOTUBE HYBRID WIRE FOR ELECTRICAL CONDUCTION AND METHOD OF MAKING SAME

INVENTORS:

VARUN SHENOY GANGOLI

EWA F<AZIMIERSKA

CHRISTOPHER JONATHAN BARN ETT

ANDREW ROSS BARRON

DOCKET NUMBER: ESRI-004

CROSS-REFERENCE TO RELATED APPLICATIONS

10011 This application claims benefit of United States provisional patent application serial number 62/882,752, filed August 05, 2019, which is herein incorporated by reference in its entirety.

BACKGROUND

Field

10021 The present invention relates to the composition and method for making such a composition of a copper-CNTs hybrid wire in which copper is impregnated within the void space of a CNT cable, and then a composite is formed on the surface of said cable. The blended Cu-CNT composite is prepared by the electrolytic deposition of copper metal from solution into an expanded and surface activated premade CNT fiber.

Description of the Related Art

10031 The various allotropes of carbon nanomaterials include buckrninsterfullerene, graphene, and carbon nanotubes (CNTs). Single walled carbon nanotubes (SWCNTs) and multi walled carbon nanotubes (MVVCNTs) are both cylindrical entities in which the crystal lattice remains unbroken along the length of the tubes. Because of their high electrical conductivity, nanometer diameters, high aspect ratios, and high degree of flexibility, CNTs are ideal materials for the preparation of transparent conductive films and coatings. CNTs network films can be prepared on flexible or rigid substrates by various solution processing methods. Flexible transparent conductors prepared from single walled (SWCNTs) and multi-walled (MWCNTs) carbon nanotubes have been reported. SWCNTs have smaller diameters than MWNTs (approx. 1 nm versus 30 nm).

10041 Most of power distribution today is via the electrical grid, which relies on copper (or aluminum) cables within an iron sheath. Unfortunately, over 10% of the power transmitted is lost due in the main to resistive heating effects within the cables. To compensate for each 200 MW of line loss, another coal plant must be on-line. In 2011, summertime electrical generation in the US was 1,026 GW. Therefore, a 10% loss would be equivalent to ca. 200 average-sized coal power plants. Furthermore, because of limits in grid capacity, wind turbines are routinely turned off, because the excess electricity cannot be transported as needed. In addition to issues associated with power loss, the weight of any conductor has a significant impact on energy consumption, which is particularly true in the automotive and aerospace industries. Proposed long term solutions to low transmission losses of electricity involve CNTs), in particular metallic single walled carbon nanotubes (SWCNTs), or a near term solution involving the improvement in conductivity and ampacity of copper by the addition of CNTs, resulting in a Cu-CNT composite material termed ultra-conductive copper.

10051 Copper and aluminum are the industry standards for conductors and which one is used depends on the application. Where weight is an issue, aluminum provides a better solution because it is lighter than copper; however when more power density is needed the higher conductivity (and thus smaller size) of a copper cable is selected. With the increased power needs the necessity to increase current capacity is a technological challenge.

10061 Proposed long-term solutions to low transmission losses of electricity involve carbon nanotubes (CNTs), in particular metallic single walled carbon nanotubes (SWNTs). The all carbon nanotube wire in which the CNTs are all metallic in nature (as opposed to a mixture of metallic and semiconducting as used in present commercial CNT cables; however, while cables of CNTs have been manufactured the inability at present to obtain sufficiently long samples of pure metallic CNTs is a major roadblock to the all carbon wire. Thus, while we understand that eventually an all carbon wire will be needed to meet future needs, an increased performance for copper wire is an interim solution. Two advantages of "upgrading" copper are that the lifespan of existing copper cable technology is quite good, so long as it is installed per its design specifications, and the ability to create cables of desired length and diameter would meet an industry-wide demand.

10071 One approach for the improvement in conductivity and ampacity of copper has been the development of a new copper/nanocarbon composite having a better room-temperature electrical conductivity than pure copper. This new composite material, called ultraconductive copper (UCC), is a composite of <5% w/w nanocarbon dispersed in >95% w/w of pure copper. As such it has been proposed that the presence of the nanocarbon provides suitable pathways for increased conduction. UCC technology has already been claimed to have conductivities as high as ten times that of pure copper, and several other groups have claimed various achievements.

10081 An alternative approach involves assembly of a plurality of metallic strands and carbon nanotube strand (Richmond, et al. US Patent 10,109,391). As an alternative it is claimed that plurality of carbon nanotubes dispersed in the continuous metal phase can provide thermal conductivity and electrical conductivity which are generally significantly higher than the pure metal continuous phase material, mechanical strength is 2 to 3 times greater than that of the pure metal (Chen US Patent 7,651,766). A theoretical model was used to estimate the possible gains in the conductivity versus the percent fill factor of the nanotubes in a ultra-low resistivity in copper matrix, assuming: ballistic conductance over the full length of single wall carbon nanotubes (SWCNTs) with the following nominal properties: mean length of 10 pm, mean diameter of 1.2 nm, resistance at room temperature of 18 KO/tube. This translates into a room temperature resistivity of 0.35 pacm for the nanotubes in contrast to 1.67 pacm for copper and a predicted doubling of the conductivity with 30-40% of CNTs.

10091 The fabrication of Cu-CNT composites has been accomplished in a variety of different ways including electrolytic co-deposition (Chen, US Patent 7,651,766), powder metallurgy, powder injection molding, electroless plating, die-casting (Nayfeh, et al. US Patent 8,347,944), and others (White, et al. US Patent 8,354,593). Despite a large number of reports on the fabrication of strong and highly conductive composites, there appears to be little obvious correlation between the Cu-CNT performance and the concentration or identity of the CNTs (SWNTs or multi walled carbon nanotubes, MWNTs) or method of fabrication of the composite (Table 1).

Table 1. A comparison of the conductivities and ampacities of CNT-Cu composites synthesized by various methods.

Material Method CNT Load Conductivity Ampacity (x 106 S/cm) (A/cm2) SWCNT N/A 100% 11.3 (theory) 109 (theory) 1.9-0.08 107-109 (exP) (exp) Cu N/A N/A 5.8 106 Cu-SWCNT Simulation 30-40°/0 w/w 12 a N/A Cu-SWCNT Electroplating 10% v/v 6.06 N/A Cu-CNT Electroplating 45% v/v 2.1 -4.7 6 x 108 Cu- Electroplating 1.0-1.4% 0.27-0.31 N/A MWCNT w/w Cu- Electroplating -10% v/v 4.5 N/A

MWCNT

Cu- Electroplating -1 g/cm3 3.22 N/A

MWCNT

Cu- Electroless 5% v/v -4.6 N/A

MWCNT

Cu- Powder 0.1% w/w 5.8 N/A MWCNT metallurgy 10101 An alternative approach is the formation of a coaxial cable comprising: a core of CNTs and a conductive coating disposed about the CNTs (Jiang, et al. US Patent 8,247,036) or alternatively, CNTs coating a conductive core (Wei, et al. US Patent 9,193,586). Composite electric cables have been proposed by twisted together CNTs with a metal (Kamiyama, et al. US patent 9,362,022).

10111 The present invention contemplates new and improved systems and methods that resolve the above-referenced difficulties and others. Despite the disparate methods reported, it is clear that developing a consistent controlled route to blended CuCNT composites is important. The present invention provides the method for reaching this goal.

SUMMARY

10121 The present invention describes a new electrically conducting wire structure comprising of a copper metal core imbedded within a copper-CNT composite layer. In a variation of the present invention the copper-CNT composite layer can be further coated with copper. The goal of the present invention is to create a conductive wire with a lower weight than pure copper, and a specific conductivity close to, or even higher than, that of copper.

10131 Using preformed CVD grown CNT fibers as templates, copper is electrodeposited inside the void created by swelling CNT fibers, and subsequently creating a Cu-CNT hybrid by imbedding the electrodeposited copper in the CNT fiber between the individual CNTs and CNT bundles.

10141 The swelling of the CNT fiber is achieved by either acid treatment or anodization. In each case, it enables the copper salts to diffuse inside the CNT fiber structure, upon which they are reduced to copper metal. The acid treatment and anodization treatment overcome the inherent hydrophobic nature of the CNTs and facilitate transport of the aqueous electroplating solution inside the CNT fiber, providing the unique structure claimed herein.

10151 Another object of the present invention is to increase the electrical conductivity of CNT fibers through the creation of a Cu-CNT hybrid, electrically conductive, wire. A further advantage of the present invention is that the wire has a reduced weight as compared to a copper wire of comparable diameter. Furthermore, the present invention provides a route to scalable manufacture of a Cu-CNT hybrid structure that does not rely on powder metallurgy and ensures the alignment of the CNTs within the wire.

10161 The abovementioned and other purposes of the present invention, characteristics and advantages will be obvious and clear after referring to the detailed description, preferred embodiment and the attached figures.

BRIEF DESCRIPTION OF THE DRAWINGS

10171 By way of illustration and not limitation, the invention is described in detail hereinafter on the basis of the embodiments represented in the accompanying figures.

10181 Figure 1 shows a schematic representation of the cross section of a Cu-CNT hybrid fiber, comprising of a CNT fiber core (1) coated with copper (2) by electrodeposition.

10191 Figure 2 shows a schematic representation of the cross section of a Cu-CNT composite fiber, comprising of a CNT fibril core infiltrated with copper (3) coated with copper (2) by electrodeposition.

10201 Figure 3 shows a schematic representation of the cross section of a Cu-CNT hybrid fiber in the present invention, comprising of a CNT fiber that has been expanded by acid treatment or anodization and both filled with copper by electrodeposition to create a core (4) and infiltrated with copper (3) by electrodeposition.

10211 Figure 4 shows a schematic representation of the cross section of a Cu-CNT hybrid fiber in the present invention, comprising of a CNT fiber that has been expanded by acid treatment or anodization, filled with copper by electrodeposition to create a core (4), infiltrated with copper (3) by electrodeposition and coated with additional copper (2) by electrodeposition.

10221 Figure 5 shows a representation of the formation of the Cu-CNT hybrid wire of the invention. In which the (A) commercial CNT fiber (5) is (B) swelled by either acid treatment or anodization such that water (6) and the copper electrolysis solution (7) can diffuse inside the swollen fiber (5). Upon the application of a constant current (D) electrodeposition of copper (8) occurs selectively inside the CNT fiber (5). One the electrodeposited copper fill the CNT fiber, electrodeposition infiltrates the CNT fiber bundles (E) to create a Cu-CNT matrix (3). Subsequent electrodeposition (F) results in the growth of a copper coating (2).

10231 Figure 6 shows a schematic representation of a possible continuous process for creating the Cu-CNT hybrid (7) of the present invention. The CNT fiber (6) is spooled across a series of rollers (5, 10, and 13) through one or more chemical baths. Rollers (10) are insulating, while roller (5) is conductive, and roller (13) is chosen depending on the identity of bath (8). In one embodiment of the invention the first bath (8) will contain acid to activate and swell the fiber, while the second bath contains the copper electrodeposition solution (9). In a second embodiment of the invention the first bath (8) will contain electrolyte solution to activate and swell the fiber under a constant voltage between the cathode roller (13) and the anode (12). For the electrodeposition the roller (5) acts as the cathode while an additional anode (11) is employed. The fiber direction of travel is indicated (14), and an optional eighted roller (15) is added to enable densification of the Cu-CNT hybrid (7).

10241 Figure 7. WAXS images for a single strand of the Nanocomp fiber showing the diffraction pattern indicating the presence of SWCNTs, MWCNT wall spacing, or graphite (002) planes and consistent with a preferential alignment of the CNTs along the cylindrical axis of the fiber.

10251 Figure 8. A series of images taken from a video recording of two CNT fiber expanding when in a 3 mM H2SO4 solution in water and connected as electrodes while being fed 14 V DC. The CNT fibers expand and drift towards each other, and are contained inside electrically insulating holders to prevent a short circuit.

10261 Figure 9. A photographic image of a length of CNT fiber in a strong acidic solution such as Piranha solution showing the swelling and expanding that occurs.

10271 Figure 10 shows typical Raman spectra for un-modified (no-treatment) and Piranha treated CNT fibers. The relative ratio of D and G bands shows that there is minimal damage or chemical modification to the CNT fibers.

10281 Figure 11 shows a photographic image of an example of three electrodes used in the Examples: CNT fiber working cathode connected to a Cu slug for better electrical contact with the power supply (left), Ag/AgCI reference electrode (center) and Pt counter electrode (right), all mounted in a custom-made lid. Both ends of the CNT fiber can be connected to two Cu slugs if working in a smaller-sized cell.

10291 Figure 12 shows a photographic image of a typical electroplating cell. The electrodes are connected to the power supply and held in place using a stand.

10301 Figure 13 shows a photographic image of the top of a typical electroplating cell.

10311 Figure 14 shows a photographic image of a typical electroplating cell with the electrodes connected to the power supply, which in turn is separately connected to a laptop and control software allowing real-time monitoring.

10321 Figure 15 shows a photographic image of the CNT fiber swelling and expanding when exposed to the electrolyte solution at a constant voltage of 2.5 V for 60 seconds. The fiber is less dense than before and floats to the top of the cell.

10331 Figure 16 shows a photographic image of the CNT fiber with reduced Cu on the inside forming the Cu-CNT hybrid in a constant current mode at 0.25 A for 1000 seconds.

10341 Figure 17 shows a photographic image of the CNT fiber with reduced Cu on the inside and more Cu on the outside in a constant current mode at 0.4 A for 2000 seconds. A section of the fiber is pulled out over time to allow for uniform current density between the working electrodes and consistent electrodeposition of Cu.

10351 Figure 18 shows a photographic image of a 1-foot long Cu-CNT hybrid wire prepared by the method of the present invention.

10361 Figure 19 shows an SEM image of the cross section of Cu-CNT hybrid wire.

10371 Figure 20 shows the EDX map for the cross section of Cu-CNT hybrid wire as well as EDX Cu, C and 0 layered elemental maps for the cross section of copper-carbon nanotube hybrid wire.

10381 Figure 21 shows one possible flowchart of a typical process used to create the Cu-CNT hybrid wire.

10391 Figure 22 shows the real-time charting of the CNT fiber electrode conductance (in the system, and not by itself) as a function of time. The point of highest conductance is where all the Cu inside the fiber is reduced completely.

10401 Figure 23 shows a SEM image of the opened sock nature of the CNT fiber as Roving material out of the synthesis reactor. The diameter ranges from about 300600 pm.

10411 Figure 24 shows an SEM image of the twisted sock nature of two CNT fibers available as a retail product. The diameter ranges from about 150-200 pm.

10421 Figure 25 shows a photographic image of the CNT fiber as-is on the left, a section of the same fiber after swelling and expanding when voltage is passed through it as a working electrode inside the electrolyte bath in the center, and another section of the eventual Cu-CNT hybrid wire formed with reduced Cu on the inside and some Cu on the outside.

10431 Figure 26 shows an optical microscope image of the Cu-CNT hybrid wire.

10441 Figure 27 shows an optical microscope image of the Cu-CNT hybrid wire.

10451 Figure 28 shows an optical microscope image of the Cu-CNT hybrid wire.

10461 Figure 29 shows a photographic image of Cu electroplated on an untreated section of CNT fiber with no swelling or Cu infiltration.

10471 Figure 30 shows a photographic image of a section of CNT fiber breaking apart under a pressure of 3000 PSI.

10481 Figure 31 shows a photographic image demonstrating that the Cu-CNT hybrid wire retains its structural integrity after being pressed to 6000 PSI 10491 Figure 32 shows a photographic image of a section of CNT fiber swelling when used as a working electrode in a 10% aqueous solution of H2SO4 for 30 seconds.

10501 Figure 33 shows a photographic image of a section of CNT fiber treated in a mixture of sulfuric acid and nitric acid (3:1 v/v) at 70 °C for 3 hours. The fiber does not retain structural integrity under these conditions.

10511 Figure 34 shows a photographic image of a section of CNT fiber with a shorter anodization time of 10 seconds which causes swelling and Cu ion absorption only at the extremities. Cu is thus deposited only on the ends and not uniformly through the length of the fiber.

10521 Figure 35 shows a photographic image of an example Cu-carbon nanotube hybrid wire after thermogravimetric analysis in air to 800 'C. The composite nature of the material meant that it disintegrated into strands where the carbon was before, and shows how the copper and carbon form a continuous hybrid material.

10531 Figure 36 shows an example of a thermogravimetric.: analysis (TGA) for purified CNT fiber in air to 1000 C. The purification process results in a --99% pure CNT fiber with no impurities, as compared to a starting fiber with 20-25 wt% impurities.

10541 Figure 37 shows an example thermogravimetric analysis for a Cu-CNT hybrid wire prepared using purified CNT fiber. The TGA was done in air to 800 CC at which point ail the CNTs oxidized. Note: irregular spikes in the data are due to errors in data recording. This sample had 12-15 wt% CNTs compared to the 99% it started with, with the rest being copper as copper oxide after the TGA oxidation. An approximation can be made based on literature to help say this sample had a coppercarbon mass ratio of between 6.1 and 6.5:1.

10551 Figure 38 shows a photographic image of a 1-foot long section of a Cu-carbon nanotube hybrid wire heated to 150 00 in air and tested for electrical conductivity. The setup involves calibration to account for contact resistances, as well as thermocouples for temperature readout and configuration in addition to precise digital multimeters to read out the current passing through the fiber.

10561 Figure 39 shows a photographic image of an Omicron Nanotechnology digital power supply used to feed voltage through a test sample for electrical conductivity measurements.

10571 Figure 40 compares the electrical resistance of copper and an example Cu-CNT hybrid wire of equivalent diameters at 25 and 150 10581 Figure 41 shows the electrical resistance per unit length (0/pm) as measured at 25 DC using the Nanoprobe: sample A is purified YE-A10 anodized and electroplated in separate electroplating bath; sample B is the same as sample A, but crimped using commercial electrical connectors; sample C is YE-A10 anodized and electroplated in single process; sample D is purified YE-A10 anodized and electroplated in a single process; sample E is purified roving anodized and electroplated in single process; sample F is YE-MO electroplated with no infiltration, control.

DETAILED DESCRIPTION

10591 The present invention is differentiated from the prior art in that it allows for large diameter CNT fibers to be infiltrated with copper as well as copper core to be created within the void space in the CNT fiber.

10601 Based upon prior theoretical model there are three requirements to successfully prepare a Cu-CNT composite: 1. the CNTs need to be well dispersed; 2. the CNTs should preferably be aligned; 3. the CNTs should be well contacted within the matrix.

[061] In addition, it is known that functionalization of CNTs results in a decrease of their electrical conduction. Thus, a further requirement is that the CNTs should be as pristine as possible. Unlike the prior art, the present invention meets these requirements.

10621 There are a number of general methods for creating a Cu-CNT composites

that have been reported in the prior art:

a. blend CNTs into copper powder; b. coating individual CNTs or CNT bundles with copper; c. coating copper with CNTs.

10631 Given that the alignment of the CNTs is considered important one alternative to these routes is to infiltrate copper into a premade CNT fiber. Such CNT fibers may be produced by a range of methods that include spinning a CNT dispersion liquid containing a plurality of CNTs including one or more CNT having at least partially collapsed structures, a dispersant, and a solvent by extruding the CNT dispersion liquid into a coagulant liquid (Smalley, et al. US Patent 6,936,233). Chemical vapor deposition (CVD) is the current standard route to high-volume carbon nanotubes (CNTs) production (Shaffer, et al. US Patent 8,173,211). Commercial CNT fibers prepared by CVD growth show a preferential alignment along length of the fiber.

[64] Electrolysis of copper is a well-known process and involves plating metallic copper onto a substrate that acts as the cathode in an electrochemical cell. Electrodes are an electrical conductor (usually a metal) that is connected to something that is not a metal. The cathode type of electrode delivers electrons (negative charge) and the anode collects electrons (has the positive charge).

[65] CNT fiber prepared by CVD takes the form of a woven hollow sock-like structure that is collapsed and twisted into a fiber. Electrochemical deposition of copper on a CNT fiber from a copper sulfate sulfuric/acid bath results in coating of the outside of the fiber (Figure 1). The reason is that the CNTs are highly hydrophobic, and as a result the copper elecytrolyte does not diffuse inside the gaps between CNTs in a pristine fiber structure. This issue can potentially be overcome by the use of a surfactant or the use of small diameter fibrils with a diameter of between 5 and 30 pm (Hannula et al., 2016). In this work, the fibril is of sufficiently small diameter that copper is formed within the fibril; however, the resulting Cu-CNT wire has a diameter of 10 to 50 pm, which is a smaller diameter than 40 gauge wire. Unfortunately, wiring for home, automotive, aerospace and shipboard applications will be of a larger diameter. For example, household wiring is ordinarily 12 or 14 gauge (2 mm and 1.6 mm, respectively). Thus, it is important to be able to create larger diameter Cu-CNT composite wire than disclosed in the prior art in which the copper is infiltrated within the CNT fiber.

10661 Since the CNTs are hydrophobic it is necessary to create a hydrophilic surface to allow for the wetting of the CNT fiber by an electrolyte solution. Treatment of individual CNTs in strong acids such as Piranha solution result in the surface functionalization of the CNTs making them less hydrophobic, i.e., more hydrophilic (Jafry, et al., 2007). Piranha solution a mixture of sulfuric acid (H2SO4) and hydrogen peroxide (H202). Treatment of CVD produced CNT fibers with strong acid solution (such as Piranha solution) results in the fibers swelling (Figure 8 and Figure 9) consistent with the sock-like structure being expanded and solution infiltrating inside the sock structure. Upon removal of the swollen CNT fiber from solution water may be squeezed out of it showing that solution can diffuse inside the fiber sock-like structure. The acid treatment is preferably performed for between about 60 seconds and 120 minutes.

10671 If the acid treatment is combined with electrodeposition of copper from a CuSO4/H2SO4 solution at a pH of about 1, the Cu2+ ions diffuse inside the CNT fiber structure prior to reduction. The acid treated CNT fiber is placed in a CuSO4/H2SO4 solution at a pH of about 1, as the cathode. In a typical system a platinum anode may be used along with an Ag AgCI reference electrode.

10681 It should be understood that the acid treatment and electrodeposition can be performed in the same container or in two separate containers.

10691 Reduction of the aqueous Cu2+ ions to metallic copper (Cu°) occurs by exposing the CNT fiber cathode to a constant current of between about 0.01 A and 0.1 A for between about 60 seconds and about 120 minutes. Under these conditions metallic copper is initially formed inside the CNT fiber sock structure (Figure 25). With longer electrolysis time, and/or a higher current, the copper deposition continues until the void space inside the CNT fiber sock structure is filled and then copper infiltrates the CNT fibers. The resulting Cu-CNT structure is shown in Figure 25. Photographs of the resulting Cu-CNT hybrid wire are shown in Figures 26 -28.

10701 The diameter of the resulting Cu-CNT hybrid wire is 0.5 -1.5 mm, which is comparable to the CNT sock as expanded by the acid. Furthermore, as may be seen by comparing the images in Figure 26 and Figure 27, the morphology of the surface of the Cu-CNT hybrid wire replicates that of the CNT fiber.

10711 If electrodeposition is continued past creating a completely filled and infiltrated Cu-CNT hybrid wire then an additional layer of copper is deposited on the outside, creating a new structure shown in Figure 4 and Figure 18.

10721 The conditions for electrodeposition of copper are chosen such that there is the potential for hydrogen to be generated at the cathode. This is to minimize oxidation of the resulting copper. However, if desired it is possible to reduce any copper oxide by heating the final Cu-CNT composite under a hydrogen containing gas flow at a temperature of between about 400 °C and about 500 °C. Hydrogen concentration of the gas may be, but are not limited to, 5-10% H2 in either nitrogen or argon. The composition of the reducing gas and the temperature are chosen to ensure reduction of any oxide, and potentially to remove any impurities on the CNTs (Gangoli, et al., US Patent Application).

10731 Cross section microscopic images show that the void inside the CNT fiber sock structure is filled with copper and the copper is imbedded into the CNT fiber.

10741 One possible method of determining the extent of the electrodeposition reaction is to monitor the electrical conduction (or resistance) of the CNT fiber electrode in the system during the electrodeposition process. As shown in Figure 22, upon initiation of electrodeposition the electrical conduction decreases (electrical resistance increases). As copper is electrodeposited inside the CNT fiber structure the electrical conduction increases (electrical resistance decreases). The point of maximum electrical conduction (minimum electrical resistance) appears to coincide with the complete filling and infiltration of the CNT fiber structure, i.e., Figure 3. With continued copper deposition the electrical conduction decreases (electrical resistance increases) again.

10751 As an alternative to acid treatment of the CNTs, the CNT fiber may be expanded to allow for infiltration by the electrolysis solution by exposing the CNT fiber to a constant voltage. The resulting surface charge causes the CNT fiber to swell. Although it is understood that the exact voltage and time of exposure will be defined by the choice of CNT fiber, a value of about 2 V to about 3 V for between 50 seconds to 300 seconds have been found to be sufficient. Subsequent electrodeposition of copper occurs at constant current in a similar manner to the method involving the acid treated CNT fiber.

10761 It is understood that both acid treatment and anodization methods allows for simple continuous processing. A suggested apparatus for continuous processing is shown in Figure 6.

10771 It is understood that upon swelling of the CNT fiber provides sufficient porosity between the individual CNTs or bundles of CNTs that comprise the fiber to allow the copper salts to diffuses inside. Upon exposure to the constant current, the copper ions inside the expanded CNT fiber would be expected to be selectively reduced, causing the copper deposition to occur inside the fiber rather than coating the outside of the fiber.

10781 Once the CNT fiber is filled with copper, continued electrolysis will occur to impregnate the CNT fiber bundles within the fiber, and finally coat the outside of the entire Cu-CNT fiber.

10791 One advantage of the present invention over the prior art is that the Cu-CNTs hybrid wire is highly uniform along the length. In prior art it is noted that some parts of the fiber surface were more active for copper deposition, which indicates that the activation energy is not constant along the fiber length (Hannula, et al., 2016).

10801 The Cu-CNT hybrid wire produced by the present invention is a unique structure as an electrically conducting material comprising of a copper metal core imbedded within a copper-CNT composite layer (Figure 3). In a variation of the present invention the copper-CNT composite layer can be further coated with copper (Figure 4). The goal of the present invention is to create a conductive wire with a lower weight than pure copper, and a specific conductivity close to that of copper.

EXAMPLES

10811 The carbon nanotube fiber yarns (Roving, and single-ply YE-A10) were purchased from Nanocomp Technologies, Inc. Other chemicals are: copper(II) sulphate pentahydrate, 99+% (Acros, Organic), sulphuric acid 95-97% (Sigma Aldrich), sodium chloride (Sigma Aldrich), hydrogen peroxide100 volumes >30% w/v (Fisher Chemical). Millitrack purified water is used to prepare all solutions. Chlorine gas (>99.9% pure), argon gas (>99.998% pure), hydrogen gas (>99.8% pure), and two composite gas mixtures (5 vol% hydrogen/95 vol% nitrogen; 10 vol% hydrogen/90 vol% nitrogen) were purchased from Matheson Tr-Gas, Inc. The fibers, and roving in particular, were characterized using energy-dispersive X-ray spectroscopy (EDS), wavelength-dispersive X-ray spectroscopy (VVDS), thermogravimetric analysis (TGA) in air, and resonant Raman spectroscopy. Careful analysis revealed that the fibers had an average residual iron content of -15 wt% (in the form of -21 wt% iron oxide). In addition, the fibers had a significant amount of amorphous (non-graphitic) carbon and YE-A10 also had -1 wt% calcium introduced presumably via internal processing using hard water at Nanocomp Technologies, Inc. Approximately 25% of the residual iron was present as iron sulfide or iron oxide, with the oxidized Fe2+ form not easily removed relative to Fe°.

10821 All electrochemical experiments are carried out on IviumStat potentiostat.

Three-electrode cell is used throughout all experiments. CNT fiber acts as working electrode (cathode), platinum mesh electrode is used as counter electrode and silver/silver chloride electrode is used as reference electrode. They are fitted through the three openings in the house made lid of glass vial, which serves as a reactor (Figure 11). Ivium software is used to set the process parameters.

10831 Before the copper deposition is carried out, CNT fiber is electro-oxidized in 10% aqueous solution of H2SO4 for 30 s. As a result, CNT fiber swells increasing its volume (Figure 32).

10841 To overcome hydrophobic nature of CNTs the fibers undergo treatment in Piranha solution, mixture of sulfuric acid (H2SO4) and hydrogen peroxide (H202) (4:1 v/v) for a time between 60 and 120 min. This results in the fiber swelling (Figure 9). Piranha treated fibers are washed with copious amount of water and left to dry in air.

10851 To improve interaction between copper and CNT fibers the latter ones are treated in a mixture of sulfuric acid and nitric acid (3:1 v/v) at temperature 70 °C for 3 hours. This process is too strong and compromised the fiber's integrity (Figure 33).

10861 Three types of CNT fibers: as received, electro-oxidized and Piranha etched fibers are plated with copper. The solution from which copper is electrodeposited on CNT fiber cathode to form copper-carbon nanotube hybrid wire is 0.6 M CuSO4 and 0.09 mM NaCI dissolved in aqueous solution of H2SO4, to a solution pH = 1.

10871 Copper-carbon nanotube hybrid wires are annealed using a tabletop horizontal tube reactor (Nanotech Innovations SSP-354), which consists of two distinct temperature zones. The central parts of each copper-carbon nanotube hybrid wires are reeved around copper rod and placed within the reactor. 5% Hydrogen and 95% Argon gas mixture is used to create a chamber of reducing gases within the quartz tube. The rate of gas flow within the quartz tube is controlled. The two zones are heated to 400 °C for 90 min. After this time the reactor is cooled, and the gas flow is halted. Once the reactor is cool, the fibers were removed.

10881 As received and Piranha etched CNT fibers are characterized using Raman spectroscopy to determine the level of functionalization (Figure 10). Scanning electron microcopy (SEM) was used to see the surface coverage and cross section of copper-carbon nanotube hybrid wires and it shows that copper ions are reduced inside the previously expanded CNT fibers (Figure 19). Energy dispersive X-ray (EDX) analysis was used to provide elemental identification and quantitative composition of the copperCNT fibers. EDX provided evidence that copper ions infiltrate the expanded CNT fiber and are reduced within (Figure 20).

10891 Example 1: A 1' long section of Nanocomp YE-Al 0 was purified to remove impurities and allow more space inside for Cu to get in between the individual CNTs. Measure -1.25 fiber (excess over 1' to account for fiber not affected by the process) and wrap both ends around copper target. Then insert the fiber middle section through the small opening of the chosen vial top, and have the platinum electrode and reference Ag electrode through the other openings. Insert the combination inside a container with the electrolytic bath (0.6 M CuSO4 in water along with some H2SO4 and NaCI) and connect the electrodes to the power supply as seen below. Use lvium to set the process parameters. The first step involves anodization to get the CuSO4 aqueous solution to infiltrate the fiber. Use chronoamperometry at 2.5 V for 60 seconds, making sure the fiber does not hit the platinum electrode. If successful, the fiber will swell up and float upwards due to the increased volume and lower density than before. Now switch over to chronopotentiornetry at -0.025 A for 1000 seconds, you will notice nothing initially as the Cu deposited on the platinum electrode goes out into the bath and soon there will be H2 evolution which will help reduce CuSO4 inside the fiber to Cu° and push out the water/sulfate. At the end of 1000 seconds, the fiber will be dense enough to be pushed downwards in a single file as opposed to the fat, conjoined loop at the beginning. Turn off the power supply, carefully disconnect the electrodes, and pull out the looped fiber. Pry apart the two ends, and remove one of the Cu targets to now have a single line of the fiber with one Cu target at an end. Slowly insert this into the bath such that the fiber is now occupying the height of the container and is ready for more uniform Cu deposition. Position the platinum electrode to be close to the top of the fiber that is inside the bath such that Cu is deposited uniformly along the first -1/4th of the fiber length from the top. Use chronopotentiometry again, this time at -0.04 A and the time based on what is optimal for the fiber of your choosing. For chlorinated YE-A10, -1200 seconds is best. After 1/4 of the time is done, slowly pull out the first 1/4 of the fiber such that the second 1/4 is now closer to the electrode and getting a higher rate of deposition. Continue until the entire fiber is processed to your desire. Depending on how close to the electrode and the plating parameters, you may end up with a thick, flat sheet with Cu infiltrated and coming inside-out, or a more cylindrical fiber with Cu inside and outside but compressed from the Cu plating pushing out any remaining moisture/unreduced Cu.

10901 Example 2: A 15 cm long section of Nanocomp YE-Al 0 are measured and cut. Each fiber is folded half and copper foil is wrapped around the middle section to provide better contact between CNT fiber and crocodile clip. The two free ends of the fiber are inserted through the small opening of the customized vial lid and immersed in the electrochemical cell. The first step involves anodization (electro-oxidation) in 10% H2SO4 to introduce oxygen-containing functional groups at the CNT material surface. These functional groups reduce the charge-transfer resistance of the CNT. Anodization in 10% H2SO4 at 2.5 V versus Ag/AgCI also causes the CNT material to open up and allow in next step the CuSO4 aqueous solution to infiltrate the fiber. Make sure the fiber does not touch the platinum electrode. If successful, the fiber will swell up and float upwards due to the increased volume and lower density than before. The expanded CNT fiber is removed from the sulfuric acid, rinsed with distilled water and left on filter paper to remove water but not to complete dry. For copper electrodeposition the washed and drained fiber is immersed in electroplating bath (0.6 M CuSO4, 0.09 mM NaCI dissolved in aqueous solution of H2SO4, pH1) and constant current of -0.1 A is applied for 120 seconds. At this current copper deposition can be observed after few seconds. The potential value increases due to the nucleation and growth of the copper electrodeposit. There is also hydrogen gas produced on the platinum anode. In aqueous acidic solutions, the reduction of protons to hydrogen is a common competitive reaction during copper electrodeposition. While the electrodeposition progresses the Cu-CNT composite fiber becomes dense enough to be pushed downwards. At the end of 120 seconds turn off the power supply, carefully disconnect the electrodes, and pull out the fiber. Rinse it thoroughly by dipping in and out in distilled water and air-dry.

10911 Example 3: The procedure explained in Example 2 was followed except that constant current of -0.025 A is applied for 120 seconds. Visible deposition of copper was noticed on the CNT fiber sample.

10921 Example 4: The procedure explained in Example 2 was followed except that 5 cm long section of Nanocomp YE-A10 was used. The anodization time was reduced to 10 s and the functionalized fiber was not allowed to drain the water absorbed in washing step. Coper deposited on the anodized CNT fiber formed large lumps on both ends (Figure 34).

10931 Example 5: The procedure explained in Example 2 was followed except that the CNT fiber was used without electrochemical anodization or Piranha treatment. Copper was electrodeposited uniformly on the outside only (Figure 29).

10941 Example 6: The procedure explained in Example 2 was followed except that Piranha treated CNT 15 cm long fibers were used directly for electrodeposition of copper. Electroplating solution containing copper ions did not infiltrate the fiber and copper deposited only on the surface of the fiber.

10951 Example 7: A 15 cm long section of Nanocomp YE-Al 0 are measured and cut. For the Piranha treatment each fiber is folded half and immobilized within the cuts of cardboard holder in the way that two ends can freely reach the etching mixture in glass Petri dish. The result of this step is that oxygen-containing functional groups are introduces at the CNT material surface. These functional groups the hydrophobicity of CNT fibers. Etching also causes the CNT material to open up and expose larger are for copper seeds deposition. Piranha treated fibers are washed with copious amount of water and left to dry in air. For the synthesis of pyridine functionalized CNT fibers, Piranha treated fibers are folded half and wrapped around paper clip to assure only the ends to be immersed in reacting solution. DCC (269 mg), 4-hydroxypyridine (126 mg), and 4-dimethylaminopyridine (DMAP, 12 mg) are dissolved in methanol (10 mL).

Piranha-etched CNT fibers in 80 mL of methanol are hanged above the solution allowing only the free ends to be wetted and the mix is gently stirred at 50 °C for 48 h. After that time CNT fibers are removed and washed thoroughly with methanol and dried in air. In the next step these pyridine-modified CNT fibers (py-CNT fiber) are further functionalized by copper seeds. Again, py-CNT fibers are folded half and wrapped around the paper clip to allow only the ends to be seeded. CuSO4. 5H20 (62 mg), and ethylenediaminetetraacetic acid (EDTA, 47 mg) are bath sonicated for 10 min before pyCNT fibers in 42 mL of purified water are mixed in. Then hydrazine (78%, 0.15 mL) is added dropwise. Stirred mixture is allowed to react in covered beaker for 90min before copper seeded CNT fibers are removed, rinsed with purified water by dipping in and out and allowed to dry in air. Dried Cu-CNT fibers are characterized by SEM. At the magnification of 10K only few Cu seeds are observed.

10961 Example 8: The procedure explained in Example 7 was followed except that the seeding time was increased to 180 min. 10971 Example 9: The procedure explained in Example 7 was followed except that the seeding time was increased to 5 hours.

10981 Example 10: The procedure explained in Example 7 was followed except that the seeding time was increased to 24h. SEM images show that after 24 h of Cu seeding the fibers are uniformly covered with disconnected copper nanoparticles (Figure 19).

10991 Example 11: A 35 cm long section of Nanocomp YE-A10 was measured and cut. The two ends were attached to copper slugs and the middle section of the fiber was passed through one of the smaller holes in a custom-made lid for a conical flask-based electrolyte cell. The Ag/AgCI and Pt electrodes were passed through the other openings and held in place. The flask was filled with an electrolyte solution of 0.6 M CuSO4 in an aqueous solution of 10 vol% H2504 and NaCI and the electrodes connected to a power supply with Ivium software to control and monitor the process. A constant current of 0.1 A was supplied to the system for 5 min and the fiber taken out for characterization. There was minimal Cu electroplating through the length of the fiber, with some copper near the top closest to the power supply connection.

101001 Example 12: A 35 cm long section of Nanocomp YE-A10 was measured and cut. The two ends were attached to copper slugs and the middle section of the fiber was passed through one of the smaller holes in a custom-made lid for a conical flask-based electrolyte cell. The Ag/AgCI and Pt electrodes were passed through the other openings and held in place. The flask was filled with an electrolyte solution of 0.6 M CuSat in an aqueous solution of 10 vol% H2SO4 and NaCI and the electrodes connected to a power supply with Ivium software to control and monitor the process. A constant current of 0.1 A was supplied to the system for 15 min and the fiber taken out for characterization. There was minimal Cu electroplating through the length of the fiber, with some copper near the top closest to the power supply connection.

101011 Example 13: A 35 cm long section of Nanocomp YE-A10 was measured and cut. The two ends were attached to copper slugs and the middle section of the fiber was passed through one of the smaller holes in a custom-made lid for a conical flask-based electrolyte cell. The Ag/AgCI and Pt electrodes were passed through the other openings and held in place. The flask was filled with an electrolyte solution of 0.6 M CuSO4 in an aqueous solution of 10 vol% H2SO4 and NaCI and the electrodes connected to a power supply with Ivium software to control and monitor the process. A constant current of 0.2 A was supplied to the system for 15 min and the fiber taken out for characterization. There was more Cu electroplating through the length of the fiber, especially on the top half closest to the power supply connection.

101021 Example 14: A 35 cm long section of Nanocomp YE-A10 was measured and cut. The two ends were attached to copper slugs and the middle section of the fiber was passed through one of the smaller holes in a custom-made lid for a conical flask-based electrolyte cell. The Ag/AgCI and Pt electrodes were passed through the other openings and held in place. The flask was filled with an electrolyte solution of 0.6 M CuSat in an aqueous solution of 10 vol% H2SO4 and NaCI and the electrodes connected to a power supply with Ivium software to control and monitor the process. A constant current of 0.2 A was supplied to the system for 30 min and the fiber taken out for characterization. There was more Cu electroplating through the length of the fiber, especially on the top half closest to the power supply connection, compared to example 13.

101031 Example 15: A 35 cm long section of Nanocomp YE-A10 was measured and cut. The two ends were attached to copper slugs and the middle section of the fiber was passed through one of the smaller holes in a custom-made lid for a conical flask-based electrolyte cell. The Ag/AgCI and Pt electrodes were passed through the other openings and held in place. The flask was filled with an electrolyte solution of 0.6 M CuSO4 in an aqueous solution of 10 vol% H2SO4 and NaCI and the electrodes connected to a power supply with Ivium software to control and monitor the process. A constant current of 0.25 A was supplied to the system for 30 min and the fiber taken out for characterization. There was more Cu electroplating through the length of the fiber, especially on the top half closest to the power supply connection, but with less uniform consistency.

101041 Example 16: A 35 cm long section of Nanocomp YE-A10 was measured and cut. The two ends were attached to copper slugs and the middle section of the fiber was passed through one of the smaller holes in a custom-made lid for a conical flask-based electrolyte cell. The Ag/AgCI and Pt electrodes were passed through the other openings and held in place. The flask was filled with an electrolyte solution of 0.6 M CuSO4 in an aqueous solution of 10 vol% H2SO4 and NaCI and the electrodes connected to a power supply with Ivium software to control and monitor the process. A constant current of 0.25 A was supplied to the system for 2000 seconds with a quarter length of the fiber slowly removed out every 500 seconds or when the maximum conductance was reached as read by Ivium. This resulted in more uniform Cu electroplating on the surface of the fiber, but no infiltration as with the samples prepared in examples 11-15.

101051 Example 17: A 35 cm long section of Nanocomp YE-A10 was measured and cut. The two ends were attached to copper slugs and the middle section of the fiber was passed through one of the smaller holes in a custom-made lid for a conical flask-based electrolyte cell. The Ag/AgCI and Pt electrodes were passed through the other openings and held in place. The flask was filled with an electrolyte solution of 0.6 M CuSat in an aqueous solution of 10 vol% H2SO4 and NaCI and the electrodes connected to a power supply with Ivium software to control and monitor the process. A constant voltage of 0.1 V was supplied to the system for 60 seconds, which caused part of the fiber to swell and expand-especially the top section closest to the power supply. A constant current of 0.25 A was then supplied to the system for 2000 seconds with a quarter length of the fiber slowly removed out every 500 seconds or when the maximum conductance was reached as read by Ivium. The uneven anodization and swelling resulted in non-uniform copper deposition, but there was some infiltration of copper inside the fiber as seen by SEM.

101061 Example 18: A 35 cm long section of Nanocomp YE-A10 was measured and cut. The fiber was treated with Piranha solution for 120 seconds, which caused the fiber to swell and expand. The two ends of the fiber were attached to copper slugs and the middle section of the fiber was passed through one of the larger holes in a custom-made lid for a conical flask-based electrolyte cell. The Ag/AgCI and Pt electrodes were passed through the other openings and held in place. The flask was filled with an electrolyte solution of 0.6 M CuSO4 in an aqueous solution of 10 vol% H2SO4 and NaCI and the electrodes connected to a power supply with Ivium software to control and monitor the process. A constant current of 0.25 A was then supplied to the system for 2000 seconds with a quarter length of the fiber slowly removed out every 500 seconds or when the maximum conductance was reached as read by Ivium. SEM and optical imaging showed there was some infiltration of copper inside the fiber but to a smaller, and less uniform extent, compared to the sample prepared in example 17.

101071 Example 19: A 35 cm long section of Nanocomp YE-A10 was measured and cut. The fiber was treated with Piranha solution for 120 seconds, which caused the fiber to swell and expand. The two ends of the fiber were attached to copper slugs and the middle section of the fiber was passed through one of the larger holes in a custom-made lid for a conical flask-based electrolyte cell. The Ag/AgCI and Pt electrodes were passed through the other openings and held in place. The flask was filled with an electrolyte solution of 0.6 M CuSO4 in an aqueous solution of 10 vol% H2SO4 and NaCI and the electrodes connected to a power supply with Ivium software to control and monitor the process. A constant current of 0.25 A was then supplied to the system for 2000 seconds with a quarter length of the fiber slowly removed out every 500 seconds or when the maximum conductance was reached as read by Ivium. SEM and optical imaging showed there was some infiltration of copper inside the fiber but to a smaller, and less uniform extent, compared to the sample prepared in example 17.

101081 Example 20: A 35 cm long section of Nanocomp YE-A10 was measured and cut. The fiber was treated with Piranha solution for 120 seconds, which caused the fiber to swell and expand. The two ends of the fiber were attached to copper slugs and the middle section of the fiber was passed through one of the larger holes in a custom-made lid for a conical flask-based electrolyte cell. The Ag/AgCI and Pt electrodes were passed through the other openings and held in place. The flask was filled with an electrolyte solution of 0.6 M CuSO4 in an aqueous solution of 10 vol% H2SO4 and NaCI and the electrodes connected to a power supply with Ivium software to control and monitor the process. A constant current of 0.4 A was then supplied to the system for 2000 seconds with a quarter length of the fiber slowly removed out every 500 seconds or when the maximum conductance was reached as read by Ivium. SEM and optical imaging showed there was some infiltration of copper inside the fiber but to a smaller, and less uniform extent, compared to the sample prepared in example 17. There were also sections where copper was electroplated on the surface more than the others, causing for inconsistency inside and outside.

101091 Example 21: A 35 cm long section of Nanocomp YE-A10 was measured and cut. The fiber was treated with Piranha solution for 180 seconds, which caused the fiber to swell and expand. The two ends of the fiber were attached to copper slugs and the middle section of the fiber was passed through one of the larger holes in a custom-made lid for a conical flask-based electrolyte cell. The Ag/AgCI and Pt electrodes were passed through the other openings and held in place. The flask was filled with an electrolyte solution of 0.6 M CuSO4 in an aqueous solution of 10 vol% H2SO4 and NaCI and the electrodes connected to a power supply with Ivium software to control and monitor the process. A constant current of 0.25 A was then supplied to the system for 2000 seconds with a quarter length of the fiber slowly removed out every 500 seconds or when the maximum conductance was reached as read by Ivium. SEM and optical imaging showed there was some infiltration of copper inside the fiber but to a smaller, and less uniform extent, compared to the sample prepared in example 17.

101101 Example 22: A 35 cm long section of Nanocomp YE-A10 was measured and cut. The two ends were attached to copper slugs and the middle section of the fiber was passed through one of the smaller holes in a custom-made lid for a conical flask-based electrolyte cell. The Ag/AgCI and Pt electrodes were passed through the other openings and held in place. The flask was filled with an electrolyte solution of 0.6 M CuSO4 in an aqueous solution of 10 vol% H2SO4 and NaCI and the electrodes connected to a power supply with Ivium software to control and monitor the process. A constant voltage of 0.1 V was supplied to the system for 60 seconds, which caused part of the fiber to swell and expand-especially the top section closest to the power supply. A constant current of 0.25 A was then supplied to the system for 2000 seconds with a quarter length of the fiber slowly removed out every 500 seconds or when the maximum conductance was reached as read by Ivium. The uneven anodization and swelling resulted in non-uniform copper deposition, but there was some infiltration of copper inside the fiber as seen by SEM.

101111 Example 23: A 35 cm long section of Nanocomp YE-A10 was measured and cut. The two ends were attached to copper slugs and the middle section of the fiber was passed through one of the smaller holes in a custom-made lid for a conical flask-based electrolyte cell. The Ag/AgCI and Pt electrodes were passed through the other openings and held in place. The flask was filled with an electrolyte solution of 0.6 M CuSO4 in an aqueous solution of 10 vol% H2SO4 and NaCI and the electrodes connected to a power supply with Ivium software to control and monitor the process. A constant voltage of 0.1 V was supplied to the system for 60 seconds, which caused part of the fiber to swell and expand-especially the top section closest to the power supply. A constant current of 0.4 A was then supplied to the system for 2000 seconds with a quarter length of the fiber slowly removed out every 500 seconds or when the maximum conductance was reached as read by Ivium. The uneven anodization and swelling resulted in non-uniform copper deposition, but there was more infiltration of copper inside the fiber as seen by SEM compared to example 17.

101121 Example 24: A 35 cm long section of Nanocomp YE-A10 was measured and cut. The two ends were attached to copper slugs and the middle section of the fiber was passed through one of the smaller holes in a custom-made lid for a conical flask-based electrolyte cell. The Ag/AgCI and Pt electrodes were passed through the other openings and held in place. The flask was filled with an electrolyte solution of 0.6 M CuSO4 in an aqueous solution of 10 vol% H2SO4 and NaCI and the electrodes connected to a power supply with Ivium software to control and monitor the process. A constant voltage of 0.1 V was supplied to the system for 60 seconds, which caused part of the fiber to swell and expand-especially the top section closest to the power supply. A constant current of 0.4 A was then supplied to the system for 2000 seconds with a quarter length of the fiber slowly removed out every 500 seconds or when the maximum conductance was reached as read by Ivium. The uneven anodization and swelling resulted in non-uniform copper deposition, but there was more infiltration of copper inside the fiber as seen by SEM compared to example 17.

101131 Example 25: A 35 cm long section of Nanocomp YE-A10 was measured and cut. The two ends were attached to copper slugs and the middle section of the fiber was passed through one of the smaller holes in a custom-made lid for a conical flask-based electrolyte cell. The Ag/AgCI and Pt electrodes were passed through the other openings and held in place. The flask was filled with an electrolyte solution of 0.6 M CuSO4 in an aqueous solution of 10 vol% H2SO4 and NaCI and the electrodes connected to a power supply with Ivium software to control and monitor the process. A constant voltage of 0.1 V was supplied to the system for 60 seconds, which caused part of the fiber to swell and expand-especially the top section closest to the power supply. A constant current of 0.4 A was then supplied to the system for 2000 seconds with a quarter length of the fiber slowly removed out every 500 seconds or when the maximum conductance was reached as read by Ivium. The uneven anodization and swelling resulted in non-uniform copper deposition, but there was more infiltration of copper inside the fiber as seen by SEM compared to example 17.

101141 Example 26: A 35 cm long section of Nanocomp YE-A10 was measured and cut. One end was attached to a copper slug and the rest of the fiber was passed through one of the smaller holes in a custom-made lid for a conical flask-based electrolyte cell. The Ag/AgCI and Pt electrodes were passed through the other openings and held in place. The flask was filled with an electrolyte solution of 0.6 M CuSO4 in an aqueous solution of 10 vole/0 H2SO4 and NaCI and the electrodes connected to a power supply with Ivium software to control and monitor the process. A constant voltage of 0.25 V was supplied to the system for 120 seconds, which caused all of the fiber to swell and expand-especially the top section closest to the power supply. A constant current of 0.4 A was then supplied to the system for 2000 seconds with a quarter length of the fiber slowly removed out every 500 seconds or when the maximum conductance was reached as read by Ivium. There was uniform and more infiltration of copper inside the fiber as seen by SEM compared to example 17.

101151 Example 27: A 35 cm long section of Nanocomp YE-A10 was measured and cut. One end was attached to a copper slug and the rest of the fiber was passed through one of the smaller holes in a custom-made lid for a conical flask-based electrolyte cell. The Ag/AgCI and Pt electrodes were passed through the other openings and held in place. The flask was filled with an electrolyte solution of 0.6 M CuSO4 in an aqueous solution of 10 vole/0 H2SO4 and NaCI and the electrodes connected to a power supply with Ivium software to control and monitor the process. A constant voltage of 0.25 V was supplied to the system for 120 seconds, which caused all of the fiber to swell and expand-especially the top section closest to the power supply. A constant current of 0.4 A was then supplied to the system for 2000 seconds with a quarter length of the fiber slowly removed out every 500 seconds or when the maximum conductance was reached as read by Ivium. There was uniform and more infiltration of copper inside the fiber as seen by SEM compared to example 17.

101161 Example 28: A 35 cm long section of Nanocomp YE-A10 was measured and cut. One end was attached to a copper slug and the rest of the fiber was passed through one of the smaller holes in a custom-made lid for a conical flask-based electrolyte cell. The Ag/AgCI and Pt electrodes were passed through the other openings and held in place. The flask was filled with an electrolyte solution of 0.6 M CuSO4 in an aqueous solution of 10 vol% H2304 and NaCI and the electrodes connected to a power supply with Ivium software to control and monitor the process. A constant voltage of 0.25 V was supplied to the system for 120 seconds, which caused all of the fiber to swell and expand-especially the top section closest to the power supply. A constant current of 0.4 A was then supplied to the system for 2000 seconds with a quarter length of the fiber slowly removed out every 500 seconds or when the maximum conductance was reached as read by Ivium. There was uniform and more infiltration of copper inside the fiber as seen by SEM compared to example 17.

101171 Example 29: A 35 cm long section of Nanocomp YE-A10 was measured and cut. One end was attached to a copper slug and the rest of the fiber was passed through one of the smaller holes in a custom-made lid for a conical flask-based electrolyte cell. The Ag/AgCI and Pt electrodes were passed through the other openings and held in place. The flask was filled with an electrolyte solution of 0.6 M CuSO4 in an aqueous solution of 10 vol% H2SO4 and NaCI and the electrodes connected to a power supply with Ivium software to control and monitor the process. A constant voltage of 0.25 V was supplied to the system for 120 seconds, which caused all of the fiber to swell and expand-especially the top section closest to the power supply. A constant current of 0.25 A was then supplied to the system for 1000 seconds followed by a constant current of 0.4 A for 2000 seconds with a quarter length of the fiber slowly removed out every 500 seconds or when the maximum conductance was reached as read by Ivium. There was consistent Cu infiltration and deposition throughout the length of the fiber.

101181 Example 30: A 35 cm long section of Nanocomp YE-A10 was measured and cut. One end was attached to a copper slug and the rest of the fiber was passed through one of the smaller holes in a custom-made lid for a conical flask-based electrolyte cell. The Ag/AgCI and Pt electrodes were passed through the other openings and held in place. The flask was filled with an electrolyte solution of 0.6 M CuSO4 in an aqueous solution of 10 vol% H2SO4 and NaCI and the electrodes connected to a power supply with Ivium software to control and monitor the process. A constant voltage of 0.25 V was supplied to the system for 120 seconds, which caused all of the fiber to swell and expand-especially the top section closest to the power supply. A constant current of 0.25 A was then supplied to the system for 1000 seconds followed by a constant current of 0.4 A for 2000 seconds with a quarter length of the fiber slowly removed out every 500 seconds or when the maximum conductance was reached as read by Ivium. There was consistent Cu infiltration and deposition throughout the length of the fiber. A 1-foot long section of the fiber from example 30 was placed in between two flat stainless-steel plates and on a pneumatic press bed. The fiber, as seen in Figure 31, only densified at pressures even exceeding 6000 PSI.

101191 Example 31: A 35 cm long section of Nanocomp YE-A10 was measured and cut. One end was attached to a copper slug and the rest of the fiber was passed through one of the smaller holes in a custom-made lid for a conical flask-based electrolyte cell. The Ag/AgCI and Pt electrodes were passed through the other openings and held in place. The flask was filled with an electrolyte solution of 0.6 M CuSO4 in an aqueous solution of 10 vol% H2SO4 and NaCI and the electrodes connected to a power supply with Ivium software to control and monitor the process. A constant voltage of 0.25 V was supplied to the system for 120 seconds, which caused all of the fiber to swell and expand-especially the top section closest to the power supply. A constant current of 0.25 A was then supplied to the system for 1000 seconds followed by a constant current of 0.4 A for 2000 seconds with a quarter length of the fiber slowly removed out every 500 seconds or when the maximum conductance was reached as read by Ivium. There was consistent Cu infiltration and deposition throughout the length of the fiber.

101201 Example 32: A 35 cm long section of purified Nanocomp YE-A10 was measured and cut. One end was attached to a copper slug and the rest of the fiber was passed through one of the smaller holes in a custom-made lid for a conical flask-based electrolyte cell. The Ag/AgCI and Pt electrodes were passed through the other openings and held in place. The flask was filled with an electrolyte solution of 0.6 M Cu504 in an aqueous solution of 10 vol% H2504 and NaCI and the electrodes connected to a power supply with Ivium software to control and monitor the process. A constant voltage of 0.25 V was supplied to the system for 120 seconds, which caused all of the fiber to swell and expand-especially the top section closest to the power supply. A constant current of 0.25 A was then supplied to the system for 1000 seconds followed by a constant current of 0.4 A for 2000 seconds with a quarter length of the fiber slowly removed out every 500 seconds or when the maximum conductance was reached as read by Ivium. There was consistent Cu infiltration and deposition throughout the length of the fiber, with an increased amount of copper in this sample compared to example 30 as measured by a microbalance before and after.

101211 Example 33: A 35 cm long section of purified Nanocomp YE-A10 was measured and cut. One end was attached to a copper slug and the rest of the fiber was passed through one of the smaller holes in a custom-made lid for a conical flask-based electrolyte cell. The Ag/AgCI and Pt electrodes were passed through the other openings and held in place. The flask was filled with an electrolyte solution of 0.6 M CuSO4 in an aqueous solution of 10 vol% H2SO4 and NaCI and the electrodes connected to a power supply with Ivium software to control and monitor the process. A constant voltage of 0.25 V was supplied to the system for 120 seconds, which caused all of the fiber to swell and expand-especially the top section closest to the power supply. A constant current of 0.25 A was then supplied to the system for 1000 seconds followed by a constant current of 0.4 A for 2000 seconds with a quarter length of the fiber slowly removed out every 500 seconds or when the maximum conductance was reached as read by Ivium. There was consistent Cu infiltration and deposition throughout the length of the fiber, with an increased amount of copper in this sample compared to example 30 as measured by a microbalance before and after.

101221 Example 34: A 35 cm long section of purified Nanocomp Roving was measured and cut. One end was attached to a copper slug and the rest of the fiber was passed through one of the smaller holes in a custom-made lid for a conical flask-based electrolyte cell. The Ag/AgCI and Pt electrodes were passed through the other openings and held in place. The flask was filled with an electrolyte solution of 0.6 M CuSO4 in an aqueous solution of 10 vol% H2304 and NaCI and the electrodes connected to a power supply with Ivium software to control and monitor the process. A constant voltage of 0.25 V was supplied to the system for 120 seconds, which caused all of the fiber to swell and expand-especially the top section closest to the power supply. A constant current of 0.25 A was then supplied to the system for 1000 seconds followed by a constant current of 0.4 A for 2000 seconds with a quarter length of the fiber slowly removed out every 500 seconds or when the maximum conductance was reached as read by Ivium. There was consistent Cu infiltration and deposition throughout the length of the fiber, with an increased amount of copper in this sample compared to example 30 as well as example as measured by a microbalance before and after. A 35 cm long section of purified CNT fiber was characterized using thermogravimetric analysis in air, and was found to have about 99% pure carbon nanotubes with the rest being residual iron catalyst content as seen in Figure 36. This is a typical starting sample used in processing as described in Example 32. The sample from example 32 was characterized using thermogravimetric analysis in air, and was found to have about 12-15% pure carbon nanotubes with the rest being copper (as oxide after TGA in air) as seen in Figure 37. This results in an approximate Cu:C mass ratio of -6.5:1. The sample after TGA also consisted of broken strands (Figure 35), showing the composite nature of carbon and copper before which breaks apart into smaller chunks when carbon is oxidized.

101231 Example 35: A 35 cm long section of purified Nanocomp Roving was measured and cut. One end was attached to a copper slug and the rest of the fiber was passed through one of the smaller holes in a custom-made lid for a conical flask-based electrolyte cell. The Ag/AgCI and Pt electrodes were passed through the other openings and held in place. The flask was filled with an electrolyte solution of 0.6 M CuSO4 in an aqueous solution of 10 vol)/0 H2SO4 and NaCI and the electrodes connected to a power supply with Ivium software to control and monitor the process. A constant voltage of 0.25 V was supplied to the system for 120 seconds, which caused all of the fiber to swell and expand-especially the top section closest to the power supply. A constant current of 0.25 A was then supplied to the system for 1000 seconds followed by a constant current of 0.4 A for 2000 seconds with a quarter length of the fiber slowly removed out every 500 seconds or when the maximum conductance was reached as read by Ivium. There was consistent Cu infiltration and deposition throughout the length of the fiber, with an increased amount of copper in this sample compared to example 30 as well as example as measured by a microbalance before and after.

101241 Example 36: A 35 cm long section of purified Nanocomp Roving was measured and cut. One end was attached to a copper slug and the rest of the fiber was passed through one of the smaller holes in a custom-made lid for a conical flask-based electrolyte cell. The Ag/AgCI and Pt electrodes were passed through the other openings and held in place. The flask was filled with an electrolyte solution of 0.6 M CuSO4 in an aqueous solution of 10 vole/0 H2SO4 and NaCI and the electrodes connected to a power supply with lvium software to control and monitor the process. A constant voltage of 0.25 V was supplied to the system for 120 seconds, which caused all of the fiber to swell and expand-especially the top section closest to the power supply. A constant current of 0.25 A was then supplied to the system for 1000 seconds followed by a constant current of 0.4 A for 2000 seconds with a quarter length of the fiber slowly removed out every 500 seconds or when the maximum conductance was reached as read by Ivium. There was consistent Cu infiltration and deposition throughout the length of the fiber, with an increased amount of copper in this sample compared to example 30 as well as example as measured by a microbalance before and after.

101251 Example 37: A 1-foot long section of Nanocomp YE-A10 CNT fiber was tested for electrical conductivity using an Omicron Nanotechnology power supply and a custom-configuration allowing testing at 150 °C in air (as seen in Figure 38 and 39). The diameter of the fiber was measured using cross-section SEM at various points in addition to optical microscopy and a micrometer. The CNT fiber by itself is not very conductive owing to a mixture of materials including amorphous carbon, residual metal catalyst, and a mixture of carbon nanotuhes.

101261 Example 38: Three individual 1-foot long sections of Nanocomp YE-A10 CNT fiber were braided together, densified at 5000 PSI using the pneumatic press, and this sample was tested for electrical conductivity using an Omicron Nanotechnology power supply and a custom-configuration allowing testing at 150 'C in air (as seen in Figure 38 and 39). The diameter of the sample was measured using cross-section SEM at various points in addition to optical microscopy and a micrometer. The sample was again not very conductive, showing that densification aione will not help much lithe starting material is not very conductive to begin with.

101271 Example 39: Three individual 1-foot long sections of purified Nanocomp YE-A10 CNT fiber were braided together, densified at 5000 PSI using the pneumatic press, and this sample was tested for electrical conductivity using an Omicron Nanotechnology power supply and a custom-configuration allowing testing at 150 "C in air (as seen in Figure 38 and 39). The diameter of the sample was measured using cross-section SEM at various points in addition to optical microscopy and a micrometer. The sample was again not very conductive, showing that densification alone will not help much if the starting material is not very conductive to begin with, 101281 Example 40: Three individual 1-foot long sections of Cu-carbon nanotube hybrid fibers were braided together, densified at 5000 PSI using the pneumatic press, and this sample was tested for electrical conductivity using an Omicron Nanotechnology power supply and a custom-configuration allowing testing at 150 °C in air (as seen in Figure 38 and 39). The diameter of the sample was measured using cross-section SEM at various points in addition to optical microscopy and a micrometer. The sample was extremely conductive, coming up to 1/10th that of copper at 25 °C and within 1 1.5th that of copper at 150 °C as seen in Figure 40.

101291 The following examples represent attempts to replicate the present invention using alternative methods. None of these methods resulted in full infiltration of copper inside the CNT fiber.

101301 Example 41: This technique uses a tabletop horizontal tube reactor (Nanotech Innovations SSP-354), which consists of two distinct temperature zones. A quartz tube is placed within the reactor to encase the chemicals and samples being used. The reactor allows gasses to be expelled from an inlet into the outlet. The first zone (zone one) of the reactor is connected to the inlet, whereas the second zone (zone two) is connected to the outlet. Carbon nanotubes-based nanocomp yarn of length -76 cm (-80 mg) was wrapped around a glass rod and placed within zone two of the reactor. A crucible containing 10 mg of copper acetylacetonate (Sigma Aldrich, C87851-100G) and 3.7 mg of chromium hexacarbonyl (Sigma Aldrich, 241458-1OG) was placed into zone one of the reactor. The caps of the quartz tube were then fitted. To create a chamber of reducing gases within the quartz tube, 5% Hydrogen and 95% Argon gas (BOC, 5% Hydrogen/Argon 200 bar) was discharge from the the first zone through the second zone into the outlet. The tube was purged with the gas for 2 minutes at 5 liters per minutes (LPM). The rate of gas flow within the quartz tube was then controlled to 3 LPM. Firstly, zone two was heated to 400 °C to remove the amorphous carbon within the yarn. This is followed by the heating of zone one up to 250 °C to nebulize the copper and chromium precursors. The gas conveys the nebulized metals from zone one into zone two where the yarn is situated. The reaction was allowed to proceed for 14 minutes before the reactor is cooled and the gas flow is halted. Once the reactor is cool, the yarn is removed and weighed. Visible copper (bronze) coating was observed on the fiber.

101311 Example 42: The procedure explained in Example 41 was followed except that zone one of the furnace was 500 °C, while zone two of the furnace was 22.8 °C. In addition, the length of the carbon nanotubes-based nanocomp yarn was doubled with both ends of the yarn extended outside of the quartz tubes. The sections of the yarn in contact with the quartz tube were taped with masking tape to circumvent its contact with the metal cap of the reactor. Copper acetylacetonate was used in a measure of 15.5 mg. Chromium hexacarbonyl was used in a measure of 20.7 mg. The gas composition used was identical to example 1, but it had a flow rate of 1 LPM. The sample was treated at 500 °C prior to deposition. During deposition 43 Volts were applied, with a current of 0.13 A using a power supply attached to the ends of the yarn.

101321 Example 43: The procedure explained in Example 41 was followed except that zone one of the furnace was 615 °C, while zone two of the furnace was 300 °C. In addition, Copper acectylacetonate was used in a measure of 9 mg. Chromium hexacarbonyl was used in a measure of 7.4 mg. The gas composition used was identical to Example 41, but it had a flow rate of 3 LPM.

101331 Example 44: The procedure explained in Example 41 was followed except that zone 1 of the furnace was 650 °C, while zone two of the furnace was 400 °C. In addition, Copper acectylacetonate was used in a measure of 18.8 mg. Chromium (0) hexacarbonyl was used in a measure of 5.0 mg. The reaction was completed in 10 minutes. No visible deposition was noticed on the nanotube sample.

101341 Example 45: The procedure explained in Example 41 was followed except that zone 1 of the furnace was 450 °C, while zone two of the furnace was 400 °C. In addition, Copper acectylacetonate was used in a measure of 5.6 mg. Chromium hexacarbonyl was used in a measure of 4.2 mg. The reaction was completed in 17 minutes. No visible deposition was noticed on the nanotube sample.

101351 Example 46: The procedure explained in Example 41 was followed except that zone 1 of the furnace was 250 °C, while zone two of the furnace was 20 °C. In addition, Copper acectylacetonate was used in a measure of 10.2 mg. Chromium hexacarbonyl was used in a measure of 5.0 mg. The reaction was completed in 10 minutes. No visible deposition was noticed on the nanotube sample.

101361 Example 47: The procedure explained in Example 41 was followed except that zone 1 of the furnace was 250 °C, while zone two of the furnace was 600 °C. In addition, Copper acectylacetonate was used in a measure of 11.1 mg. Chromium hexacarbonyl was used in a measure of 4.9 mg. The reaction was completed in 10 minutes. No visible deposition was noticed on the nanotube sample.

101371 Example 48: The procedure explained in Example 41 was followed except that zone 1 of the furnace was 250 °C, while zone two of the furnace was 400 °C. In addition, Copper acectylacetonate was used in a measure of 19.1 mg. Chromium (0) hexacarbonyl was used in a measure of 2.7 mg. The reaction was completed in 10 minutes. Visible copper (bronze) coating was observed on the fiber.

101381 Example 49: The procedure explained in Example 41 was followed except that zone one of the furnace was 250 °C, while zone two of the furnace was 400 °C. In addition, Copper acectylacetonate was used in a measure of 11.1 mg. Chromium hexacarbonyl was used in a measure of 4.6 mg. The reaction was completed in 10 minutes. The sample was not pre-treated under high temperature. During deposition 42 Volts were applied, with a current of 0.17 A using a power supply attached to the ends of the yarn. No visible deposition was noticed on the nanotube sample.

101391 Example 50: The procedure explained in Example 41 was followed except that zone one of the furnace was 186.7 °C, while zone two of the furnace was 400 °C. In addition, the copper precursor was replaced with copper trifluoroacetylacetonate (Sigma Aldrich, 101826-50) in a measure of 10.0 mg. Chromium hexacarbonyl was used in a measure of 2.7 mg. The reaction was completed in 10 minutes. No visible deposition was noticed on the nanotube sample.

101401 Example 51: The procedure explained in Example 50 was followed except that zone one of the furnace was 196.7 °C, while zone two of the furnace was 400 °C. In addition, the copper trifluoroacetylacetonate was used in a measure of 11.0 mg. Chromium hexacarbonyl was used in a measure of 2.4 mg. The reaction was completed in 10 minutes. No visible deposition was noticed on the nanotube sample. The crucible was unoccupied by charred metal precursors.

101411 Example 52: The procedure explained in Example 41 was followed except that zone one of the furnace was 119.9 °C, while zone two of the furnace was 400 °C. In addition, the copper precursor was replaced with copper hexafluoroacetylacetonate hydrate (Sigma Aldrich, 335193-5G) in a measure of 9.8 mg. Chromium hexacarbonyl was used in a measure of 1.7 mg. The reaction was completed in 10 minutes. No visible deposition was noticed on the nanotube sample. The crucible was unoccupied by charred metal precursors.

101421 Example 53: The procedure explained in Example 52 was followed except that zone one of the furnace was 129.9 °C, while zone two of the furnace was 400 °C. In addition, copper hexafluoroacetylacetonate hydrate was used in a measure of 10.3 mg. Chromium hexacarbonyl was used in a measure of 1.0 mg. The reaction was completed in 10 minutes. No visible deposition was noticed on the nanotube sample.

101431 Example 54: The procedure explained in Example 52 was followed except that zone two of the furnace was 400 °C. The sample was not treated with metal deposition and the reaction was completed in 60 minutes.

101441 Example 55: The procedure explained in Example 41 was followed except that zone one of the furnace was 300 °C, while zone two of the furnace was 500 °C. The nanocomp yarn was replaced with YE-A10 yarn. Equal volumes of pure Nitrogen and pure hydrogen gas was used to purged the furnace. In addition, copper acectylacetonate and chromium hexacarbonyl was used. The sample was not pre-treated under high temperature. During deposition 30-40 Volts were applied using a power supply attached to the ends of the yarn. Using the SEM machine, very little chromium hexacarbonyl was observed and about 15-20% the mass of the CNT fiber of copper acectylacetonate was observed.

101451 Example 56: The procedure explained in Example 41 was followed except that no deposition of copper acectylacetonate was observed using the SEM. Using the SEM machine, very little chromium hexacarbonyl was observed.

101461 Example 57: The procedure explained in Example 41 was followed except that no deposition of chromium hexacarbonyl was observed using the SEM. About 1520% the mass of the CNT fiber of copper acectylacetonate was observed.

101471 Example 58: The procedure explained in Example 41 was followed except that the YE-A10 yarn was replaced with the Nanocomp Roving yarn. Using the SEM machine, very little chromium hexacarbonyl was observed and about 15-20% the mass of the CNT fiber of copper acectylacetonate was observed.

101481 Example 59: The procedure explained in Example 41 was followed except that the YE-A10 yarn was replaced with the YE-A10 + 3x C12 yarn. Using the SEM machine, very little chromium hexacarbonyl was observed and about 15-20% the mass of the CNT fiber of copper acectylacetonate was observed.

101491 While the forgoing is directed to embodiments of the present disclosure, other and further embodiments of the disclosure may be devised without departing from the basic scope thereof, and the scope thereof is determined by the claims that follow.

Claims

What is claimed is: 1. An electrical cable, comprising: an interior conductor core comprising electrodeposited copper and; an exterior layer enclosing the interior copper core therein, the exterior layer comprising a composite of carbon nanotubes and copper.
2. An electrical cable of claim 1, wherein additional copper is electrodeposited onto the exterior layer.
3. A method of forming copper-carbon nanotube hybrid wire, comprising: a. treating a preformed CNT fiber with acid solution; b. placing the acid treated CNT fiber in an electrolysis apparatus as the cathode; c. exposing the acid treated CNT fiber to a copper electroplating solution; d. passing a constant current through the copper electroplating solution to cause electrodeposition of metallic copper; e. removing the copper-CNT hybrid wire from the electroplating solution.
4. The method as claimed in claim 3, wherein the acid solution is Piranha solution comprising of a mixture of sulfuric acid (H2SO4) and hydrogen peroxide (H202) in a ratio of about 4:1 by volume.
5. The method as claimed in claim 3, wherein the CNT fiber is treated by acid solution for between about 60 seconds and about 120 minutes.
6. The method as claimed in claim 3; wherein the CNT fiber is positioned such that it is moveable with regard to the cathodic contact.
7. The method as claimed in claim 3; wherein the copper electroplating solution comprises of an acidic copper sulfate (CuSO4) solution, prepared by dissolution of 0.6 M CuSO4 in 10 vol% H2SO4 in DI water.
8. The method as claimed in claim 7; wherein the acidic copper sulfate (Cu804) solution has a pH of about 1.
9. The method as claimed in claim 3; wherein the current passed through the copper electroplating solution is between about 0.01 A and about 0.1 A.
10.The method as claimed in claim 9; wherein the current passed through the copper electroplating solution for a time of between about 60 seconds and about 120 minutes.
11. The method as claimed in claim 3; wherein the anode is platinum and a silver-silver chloride reference electrode is used.
12.A method of forming copper-carbon nanotube hybrid wire, comprising: a. placing a preformed CNT fiber in an electrolysis apparatus as the cathode; b. exposing the acid treated CNT fiber to a copper electroplating solution; c. applying a constant voltage to the copper electroplating solution to cause CNT fiber to swell; d. passing a constant current through the copper electroplating solution to cause electrodeposition of metallic copper; e. removing the Cu-CNT hybrid copper wire from the electroplating solution.
13. The method as claimed in claim 12; wherein constant voltage to the copper electroplating solution was between about 2 V and about 3 V.
14. The method as claimed in claim 12; wherein constant voltage to the copper electroplating solution was applied for between about 50 seconds and about 300 seconds.
15. The method as claimed in claim 12; wherein the CNT fiber is positioned such that it is moveable with regard to the cathodic contact.
16. The method as claimed in claim 12; wherein the copper electroplating solution comprises of an acidic copper sulfate (CuSO4) solution, prepared by dissolution of 0.6 M CuSO4 in 10 vol% H2SO4 in DI water.
17. The method as claimed in claim 16; wherein the acidic copper sulfate (Cu804) solution has a pH of about 1.
18. The method as claimed in claim 12; wherein the current passed through the copper electroplating solution is between about 0.01 A and about 0.1 A.
19. The method as claimed in claim 12; wherein the current passed through the copper electroplating solution for a time of between about 1000 seconds and about 2000 seconds.
20. The method as claimed in claim 12; wherein the anode is platinum and a silver-silver chloride reference electrode is used.
21. The method as claimed in claim 3, wherein the copper-carbon nanotube hybrid wire is heated in a reducing atmosphere to remove oxide.
22.The method as claimed in claim 21, wherein the gaseous atmosphere comprises about 5% to about 20% hydrogen.
23. The method as claimed in claim 12, wherein the copper-carbon nanotube hybrid wire is heated in a reducing atmosphere to remove oxide.
24.The method as claimed in claim 23, wherein the gaseous atmosphere comprises about 5% to about 20% hydrogen.