FIELD OF THE INVENTION
The present invention relates to the process of forming a composite of carbon
nanotube and metal (copper/nickel/silver) nanowire fibers/wires with
enhanced electrical conductivity and mechanical strength. The invention
further relates to a carbon nanotube yarn and metal nanowire composite.
BACKGROUND OF THE INVENTION
For real-world current conductor applications in electrical, aerospace and
defense industry, conversion of nanostructured carbon nanotubes (CNTs) into
a macro fiber (yarn/wires) and sheets (mats) form is essential. The primary
driving force for the conversion of CNTs into macro form is the lightweight
(1/5th of copper), inert and non-corrosive, less thermal build up and no
fatigue failure nature of the CNT wires and mats. Several strategies have
been developed to prepare CNT fiber and mats. The fiber preparation method
includes dry and wet spinning. In the dry spinning process, carbon nanotube
arrays grown on a substrate is converted into a wire. In wet spinning process
nanotubes solution is converted to a wire. The only method which is capable
of preparing the wire and mat is the gas phase pyrolysis (floating catalyst)
method. It holds high promise for large-scale commercialization of CNT wire
and mat. In the gas phase pyrolysis method CNT sock or aerogel is generated
and converted to either wire or mat. However, mere conversion of CNT into
wire and mat does not guarantee the electrical conductivity comparable to a
standard copper conductor.

Several inventors have disclosed methods to improve the electrical and
mechanical properties of as-prepared CNT wire and mats. The disclosures on
electrical property improvement of CNT wire are novel and are capable of
enhancing electrical conductivity. However, most of the processes involve
corrosive gasses and acids including iodine, hydrochloric acid, hydroiodic acid,
nitric acid, etc. The destructive nature of the gasses and acids pose an
environmental hazard. The resultant effect being the acceptability for
upscaling is narrow. Some of the most relevant disclosures related to the
present invention are US 2013/0183439 A1 and WO 2013/109442 A1 which
disclose the methods to improve the electrical conductivity of CNT wire by
chemical doping by bromine, iodine, chloroauric acid, hydrochloric acid,
hydroiodic acid, nitric acid, etc. Invention WO 2012118836 A1 discloses
methods to improve the electrical conductivity of CNT wire by doping.
Invention US 2012/0100203A1 discloses a method to prepare a composite
with nanopowders or nanofibers compatible with the dry spinning process.
The research conducted on these materials for achieving high conductivity
(~107 S/m) is primarily limited to smaller samples. Hence, the need for
scaling up the process to manufacture CNT lightweight conducting wires and
mats is essential.
OBJECTS OF THE INVENTION
It is, therefore, an object of the invention to propose a process for forming
carbon nanotube metal nanowire/Yarn composite with enhanced electrical
conductivity and mechanical strength.
A further object of the invention is to propose a carbon nanotube yarn and
metal nanowire composite.

SUMMARY OF THE INVENTION
According to the present invention, there is provided a process for forming
carbon nanotube metal nanowire/Yarn composite with enhanced electrical
conductivity and mechanical strength in which the metal nanowire infiltration
into CNT wire is conducted by dispersing of metal nanowire into carbon
nanotubes (CNT) wetting liquid with 10-80% volume percentage having a
metal nanowire dimensions of length of 10-50 microns and diameter of 10-20
nm. The nanowire dispersed CNT wire is laser processed and annealed under
high temperature (200-1000 ◦C) and high vacuum (10-6 to 10-7 Torr). The
invention is also directed to a CNT metal nanowire composite with enhanced
electrical conductivity and mechanical strength.
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS
Figure 1. Schematic showing the preparation of carbon nanotube-metal
nanowire (Copper/ Silver/ Nickel) composite, where CNT is synthesized by
gas phase pyrolysis.
Figure 2. Schematic showing the preparation of carbon nanotube-metal
nanowire (Copper/ Silver/ Nickel) composite, where CNT is synthesized by
LPCVD on catalyst coated substrate.
Figure 3. Scanning electron microscopic (SEM) image of the bare carbon
nanotube wire/fiber and carbon nanotube wire/fiber-metal nanowire (Silver)
composite.

DETAILED DESCRIPTION OF THE INVENTION
The present invention relates to a process of preparing a carbon nanotube
and metal (copper/nickel/silver) nanowire fibers/wires (4) with enhanced
electrical conductivity and mechanical strength. The process includes a
nanowire infiltration into carbon nanotube yarn before densification by
twisting during spinning method and condensing in gas phase pyrolysis
(floating catalyst) method. Preferably the metal nanowire dispersed liquids
are made of Cu/Ni/Si nanowire with dimensions of length 10-50 microns and
diameter 10-20 nm. More preferably the metal nanowire dispersions are
prepared from and not limited to silver, copper, and nickel in liquids that have
good wettability with CNT. Preferably the wetting liquid is selected based on
the wettability tendency of the liquid with CNT. Ideally, the liquids can be and
not limited to isopropyl alcohol, ethanol, acetone, ethylene glycol. Infiltration
by CNT wetting liquid is an efficient method to improve mechanical strength
by densifying CNT wire/fiber prepared by spinning from an aligned array of
CNT or by gas phase method. Infiltration of the metal nanowire into the CNT
volume improves interfacial connectivity between the adjacent CNT and
further incorporating metal nanowires at CNT junctions will enhance electrical
conductivity and mechanical stability. The tensile strength of yarns prepared
by spinning or gas phase pyrolysis is limited to the Van der Waals forces and
weak interfacial interactions among the CNT. However, the yarn specific
strength is higher due to the tube alignment and entanglement generated in
the spinning or condensing process. Whereas the limitation, i.e., tensile
strength beyond particular value resides in weak inter tube shear interactions.
Hence increasing strength is necessary for various applications. And the
inclusion of metal nanowires into CNT wires/fibers can benefit in connecting
the adjacent CNT and help in load transfer and in enhancing mechanical
strength. Further electrical conductivity can also be enhanced due to the
presence of conducting nanowires, where the probability of inter-connectivity

between metal nanowires across the matrix is high. Hence the disclosed
process can result in improving the electrical conductivity and mechanical
strength.
In the spinning process where CNT array is converted to wire/fiber, metal
nanowire dispersed CNT wetting liquid is impinged on to the CNT web just
before spinning. The metal nanowire is dispersed in CNT wetting liquid either
by mechanical-agitation/sonication/ultra-sonication. After metal nanowire
infiltration, the CNT is spun with appropriate speed. The spinning leads to the
formation of entangled and densified CNT-metal nanowire composite. The
metal nanowire infiltrated and densified CNT thus formed, is processed to
achieve compaction and reduction of voids formed during spinning. For CNT
wire prepared by gas pyrolysis method, the CNT elastic smoke is condensed
in a CNT wetting liquid with metal nanowires sprayed (1) on to the CNT
elastic smoke. During the condensation, the metal nanowires get trapped
across the volume of CNT wire/fiber/ribbon. The composite is later densified
by passing through pressurized rollers several times.
For enhancement of the electrical conductivity and mechanical strength
improved interfacial connectivity between the CNT and metal nanowires is
essential which requires thermal processing like heating in a controlled
atmosphere. Preferably the heating is performed with a laser in a vacuum
atmosphere or the presence of inert gas. Processing in high vacuum (>10-6
Torr) prevents oxidation of CNT and also aids in the removal of any de-
absorbed species during laser heating. The laser is scanned across the length
of CNT-metal nanowire composite. The high thermal conductivity of the
nanotubes results in uniform heating, melting/welding of metal nanowires
and connecting the adjacent nanotubes and benefit in load transfer and in
enhancing mechanical strength. The reduction of voids and formation of
conducting layer path across the volume of the CNT combined with the

conduction channels of CNT can result in an enhancement of electrical
conductivity. Further, during evaporation of the liquids (while laser
processing) a sizeable capillary force may be generated to draw adjacent
nanotubes together. Preferably resulting in enhancement of mechanical and
electrical properties. The laser processed CNT wire/fiber is further heat
treated in high vacuum (>10-6 Torr) and high temperature (800-1000°C)
environment. The heating is performed to anneal the material and minimize
the stress. Depending on the requirement, the annealing may also be
performed in the presence of H2, Ar, etc. Laser heating and annealing lead to
the formation of metal nanowire CNT junctions with enhanced electrical
conductivity and mechanical stability. The following examples are presented
to illustrate the invention further, but it is not being considered as limited to
it.
EXAMPLE 1
Process for preparing a CNT-metal (copper/nickel/silver) composite is
described. CNT are synthesized either on catalyst coated substrate in low-
pressure chemical vapor deposition (LPCVD) system or by gas pyrolysis
method in a horizontal atmospheric chemical vapor deposition system. The
substrate containing aligned CNT array (5) grown by LPCVD is transferred to
a spinner, and spinning (7) is performed. In this example the metal nanowire
used for preparing the CNT-metal composite wire/fiber is silver. The silver
(nickel/copper) nanowires are dispersed in ethanol as per required
volume/weight percentage by mechanical-agitation/sonication/ultra-
sonication. The silver nanowire dispersed in ethanol (1) is sprayed in the form
a jet with controlled velocity. The metal nanowire-dispersed solution is
sprayed on to the CNT web just before the web (6) is twisted. This assures
the distribution of metal nanowires across the volume of the CNT
yarn/wire/fiber (8), thus forming a CNT-metal wire/fiber composite (10).

Insertion/inclusion of the metal nanowires before spinning ensures the
presence of metal nanowires between the sidewall–sidewall contact of
adjoining CNTs. Similarly, in the gas phase pyrolysis method the elastic CNT
smoke (2) exiting the horizontal CVD is sprayed with silver nanowire
dispersed ethanol from three directions, and condensed CNT-silver nanowire
composite is collected on a spindle (3). Optimization of silver nanowire
infusion into CNT is performed by varying the silver nanowire content
(volume/weight percentage) in ethanol. Optimal value of silver nanowire
content is determined by the measuring electrical conductivity of the CNT-
metal nanowire composite. CNT wire infused with metal nanowire is collected
on an alumina cylinder (3,8), which is later transferred into a vacuum
chamber for laser processing. The CNT-metal nanowire composite is prepared
by heating the CNT yarn/fiber/wire infused with silver nanowire with a diode
laser (beam size ~20-50 µm) in a vacuum. Depending on the diameter of the
wire to be heated the laser beam spot size is selected. The power of the laser
is varied from 100-400 W. Laser processing is done in a high vacuum of 10-6
Torr and also in the presence of Argon. Argon gas of ~500 sccm is used
during the laser processing. Further, the outlet of the vacuum chamber is
connected to a vacuum pump which evacuates the Argon gas continuously.
EXAMPLE 2
In addition to the laser processing explained in example 1 in this example the
heating of the CNT-silver nanowire composite is performed in high
temperature (800-1000◦C) and high vacuum (>10-6 Torr) or in the presence
of Ar, H2 or N2 atmosphere. The alumina or quartz cylinder CNT- silver
nanowire composite laser processed in the previous example is placed inside
a three zone tube furnace and heating is performed in steps either in a
vacuum or in Ar, H2 or N2 atmosphere for ~8-10 Hrs. The heating/annealing
of the composite is performed to further enhance the interface between

metal nanowire CNT junctions resulting in enhanced mechanical strength and
electrical conductivity.
Although various embodiments of this invention have been shown and
described, it should be understood that various modifications and
substitutions, as well arrangements and combinations of the preceding
embodiments can be made by those skilled in the art, without departing from
novel spirit and scope of the invention.


b) NON - PATENT LITERATURE
1. Chaffee. J., Lashmore. D., Lewis. D., Mann. J., Schaeur, and White. B,
Direct synthesis of CNT yarns and Sheets, NSTI-nanotech, 3, 118-121
(2008).
2. Agnieszka. L. R., Lukasz. K., Peng. X., Krzysztof. K., Towards the
development of carbon nanotube based wires, Carbon, 68, 597-609
(2014).
3. Feng. C., Liu. K., Wu. S. J., Liu. L., Cheng. J. S., Zhang. Y., Sun. Y., Li.
Q., Fan. S., and Jiang. K., Flexible, Stretchable, Transparent
Conducting Films Made from Superaligned Carbon Nanotubes, Adv.
Funct. Mater., 20, 885–891 (2010).

WE CLAIM :
1. A process for forming carbon nanotube metal nanowire/yarn
composite with enhanced electrical conductivity and mechanical
strength, the process comprising: -
i) preparing carbon nanotubes (CNT) on catalyst coated substrate in low
pressure chemical vapor deposition (LPCVD) system, wherein the
substrate containing aligned array having double-walled, thin-multi-
walled, and multi-walled carbon nanotubes; and
ii) preparing carbon nanotubes (CNT) by gas phase pyrolysis (floating
catalyst) method including double-walled, thin-multi-walled and multi-
walled carbon nanotubes; and
iii) conducting infiltration of CNT yarn/wire with metal nanowire dispersed
liquid.
2. The process as claimed in claim 1, wherein the metal nanowires are
and not limited to copper, nickel, and silver.
3. The process as claimed in claim 1, wherein the nanowire dimensions is
having length 10-50 microns and diameter 10-20 nm.
4. The process as claimed in claim 1, wherein the volume (weight)
percentage of metal nanowire is 10-80% in liquid.

5. The process as claimed in claim 1, wherein the metal nanowires are
dispersed in CNT wetting liquid including and not limited to isopropyl
alcohol, acetone, ethanol, ethylene glycol.
6. The process as claimed in claim 1, wherein the metal nanowires are
dispersed in CNT wetting liquid by mechanical-
agitation/sonication/ultra-sonication.
7. The process as claimed in claim 1, wherein the metal nanowire
dispersed liquid is infiltrated before the yarn is twisted.
8. The process as claimed in claim 1, wherein the metal nanowire
sprayed liquid is infiltrated before the yarn is condensed.
9. The process as claimed in claim 1, wherein the width of the metal
nanowire dispersed liquid jet is defined by the width of the CNT web.
10. The metal nanowire infiltration of CNT of claim 1, wherein the location
the metal nanowire dispersed liquid jet is defined by distance of the
CNT web and the twister head.
11. The process as claimed in claim 1, wherein the carbon nanotubes
(CNT) is formed by gas phase pyrolysis method.

12. The process as claimed in claim 11, wherein the width the metal
nanowire dispersed spray is defined by the width of the CNT elastic
smoke.
13. The process as claimed in any of claims 1 to 10, wherein the location
the metal nanowire dispersed spray is dependent on the distance
between CVD exit and collector spindle distance.
14. The process as claimed in claim 13, wherein the velocity/speed of the
metal nanowire dispersed liquid jet on to CNT web is dependent on
the speed of collector spindle.
15. The process as claimed in claim 13 or claim 14, wherein the spray rate
of the metal nanowire dispersed spray jet on to CNT elastic smoke is
dependent on the speed of collector spindle.
16. The process as claimed in claim 1, comprising laser processing of the
CNT metal nanowire including annealing under high temperature and
high vacuum annealing.
17. The process as claimed in claim 16, wherein the CNT metal nanowire
infiltrated CNT is processed with a laser of varying power dependent
on the diameter of CNT metal nanowire composite.

18. The process as claimed in claim 17, wherein the laser can be and not
limited to CO2, diode laser.
19. The process as claimed in claim 17, wherein the laser processing is
either performed in high vacuum (>10-6Torr) or in the presence of
gasses including and not limited to Ar, H2, O2, N2 and wherein the
laser scan speed can be and not limited to 1-10 mm/sec.
20. The process as claimed in claim 17, wherein the metal nanowire
infiltrated CNT is processed at high temperature (800-10000C) and
high vacuum (>10-6Torr) in the presence of gasses including and not
limited to Ar, H2, O2, N2.