FIELD OF THE INVENTION
The present invention relates to a method to prepare electrically conducting
fiber and yarn of CNT-metal composite. More particularly, the invention
relates to a process of preparing interconnected multi-walled carbon
nanotubes fiber with metal particles with a continuous electrical path for but
not restricted to current carrying and EMI shielding applications.
BACKGROUND OF THE INVENTION
Since pioneering work by Iijima in 1991 [1], carbon nanotubes (CNTs) have
attracted interest of scientists. Initially, researchers focused on preparation
and study of properties of CNTs. With more understating of CNTs properties,
research focus has now shifted towards the application of nanotubes. In
general, CNTs have been applied in two types of systems; first is microscopic
systems such as microsensors, microchips and molecular electronics while
other is macroscopic systems such as composites, bucky papers as well as
continuous fibers.
Composites are materials made from two or more constituent materials with
significantly different physical or chemical properties which remain separate
and distinct at the macroscopic or microscopic scale within the finished
structure. The composites can be categorized by the matrix materials as a
polymer matrix, metal matrix and ceramic matrix composites. Because of its
high aspect ratio and exceptional physical properties, CNTs are considered as
the "ultimate filler" in composites [2]. Development in the low-cost
manufacturing technology for robust carbon nanotube (CNT) composite
based conductors can bring a revolutionary change in energy transmission. In
addition to energy transmission CNT base conductors will find its applications
in EMI shielding, motor windings and light weight cabling [3-4].

The process of growth of nanotube is very sensitive to a variety of factors,
such as carbon source, catalyst, temperature, carrying gas, pressure and
reaction time. A slight deviation in any of these factors during the process of
growth could result in variations in CNT products [5-6]. Nanotubes from most
suppliers, even those from the same batch, are diverse by length, diameter,
wall numbers, and chirality. The diversity causes difficulties in the composite
processing. Therefore, it was required to develop a method for growing
uniform CNTs and process it to make a composite.
Many inventors have invented methods to prepare nanotube yarn, CNT-metal
composites, its processing and improve its electrical conductivity. Some of the
most relevant disclosures related to present invention are mentioned here.
Invention US8602765B2 by Kai-Li Jiang et al. relates to method to prepare a
CNT yarn. The yarn was prepared by pulling CNTs from an array grown on a
substrate.
Invention US20090282802A1 discloses the method to prepare nanofiber yarn
by twisting and spinning CNTs from an array of substantially parallel
nanofibers.
Starkovich et al. in inventions US 2013/0183439 A1 and WO 2013/109442 A1
discloses the methods to improve the electrical conductivity of CNT yarn by
chemical doping by bromine, iodine, chloroauric acid, hydrochloric acid,
hydroiodic acid, nitric acid, and potassium tetrabromoaurate.
Pulickel. M. Ajayan et al. in invention WO 2012118836 A1 discloses methods
to prepare multiwalled CNT yarn and doping it to improve its electrical
conductivity.

The current carbon nanotube fibers have limitations in conductivity,
resistivity, thermal stability, and current carrying capacity. Even though
preparation of CNT yarn and methods to improve its conductivity including
doping have been reported, the reported processes mainly doping involves
highly corroding materials and are not suitable for an up-scalable
manufacturing process. Further reported methods reduce mechanical
strength while improving electrical conductivity. In the present disclosure, a
method to prepare yarn of CNT-metal composite with enhanced electrical
conductivity has been disclosed.
OBJECTS OF THE INVENTION
It is therefore an object of the invention to propose a method to prepare
CNT- metal composite with inter-connected metal particles in the form of a
yarn.
Another object of the invention is to propose a method to prepare CNT- metal
composite with inter-connected metal particles in the form of a yarn, wherein
aligned interconnected multi-walled carbon nanotubes are grown and
reinforced by CNT wetting metal particles.
SUMMARY OF THE INVENTION
The present invention discloses a method to prepare a yarn of CNTs
reinforced with metal particles to form a composite of CNT and metal. The
metal particles are interconnected within the matrix of CNTs to enhance the
electric conductivity of yarn. The metal particles including but not limited to
nickel and tungsten used for making composite have the ability to wet multi-
walled CNTs. The synthesis process for fabrication of highly aligned
interconnected multi-walled carbon nanotubes fiber includes but not
restricted to dry spinning using low-pressure chemical vapor deposition and

gaseous growth using gaseous catalyst and precursors. The metal
reinforcement process includes an organic solvent to carry metal particles and
agitated spray process.
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS
1. Figure 1 shows the schematic diagram of the apparatus used for
preparing thread of CNT-metal composite by the disclosed method.
2. Figure 2 shows a flowchart showing different steps involved in the
disclosed method to prepare CNT-metal composite thread using a dry
spinning process for CNT growth.
3. Figure 3 shows a flowchart showing different steps involved in
disclosed method to prepare CNT-metal composite thread using
gaseous growth process for CNT growth.
4. Figure 4 shows SEM image of carbon nanotube fibers being pulled
from the edge of the substrate to form a web of nanotubes.
5. Figure 5 shows SEM image of nickel particles distributed in matrix of
carbon nanotubes.
6. Figure 6 shows SEM image of CNT-nickel composite thread showing
nickel particles entrapped between individual fibers of carbon
nanotubes.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
The embodiments of the present invention disclose a method to prepare yarn
having one or more thread of CNT-metal composite. The metal particles
(MPs) reinforced in the matrix of multi-walled including double-walled CNT. In
the present invention, the carbon nanotube fiber were grown with various
arrangements and sizes by methods including but not limited to low-pressure

chemical vapor deposition with dry spinning and/or growth of aligned CNT in
a gaseous form on gaseous catalyst. The CNTs have a tendency to
interconnect to one another by Vander Waal interactions during growth and
form continuous fibers.
In preferred embodiments, wetting with mechanically and an ultrasonically
agitated suspension was used. An organic carrier liquid with CNT wetting
property including but not limited to ethanol, isopropanol, methanol, acetone
and their combination thereof was used as a carrier fluid for transporting MPs
to the surface of CNT nanofibers. The dimensions of metal particles vary from
10 nm to 10 µm of any shape including spherical and cylindrical. The MPs
were dispersed in the carrier fluid by a method including but not limited to
mechanical stirring and ultra-sonication to form a suspension (103).
In another embodiment, the preparation of CNT yarn was carried out by a dry
spinning method. A low-pressure chemical vapor deposition process was used
to grow an array of highly aligned multi-walled including double-walled CNT
on a substrate coated with the catalyst (101). Due to high surface area and
Vander Waal interaction between CNTs, aligned CNTs tend to pull each other
to form a fiber. A thread of variable thickness from 2 nm to 1 mm could be
formed from by twisting multiple fibers into single thread. As shown in figure
1, a web of CNT fibers is formed just before the twisting locus. The MPs
containing suspension was sprayed or jetted on the web to entrap metal
particles into the CNT web (102) before twisting. Because of high surface
area of CNTs metal particles attach to individual CNT fiber and are twisted
along with the fiber to form thread as shown in figure 2. The thread was then
passed through a heating chamber with vacuum or inert atmosphere to melt
the MP and form CNT-metal composite with interconnected MP reinforced in
CNT matrix.
In some embodiments, smoke of highly aligned CNT was generated using
liquid or gaseous precursors and catalyst using a gaseous growth method.

Being in a gaseous state, long aligned nanotubes of length varying from 1 µm
to 100 µm interact with each other to form continuously connected smoke of
nanotubes. A cold suspension of MPs at a temperature of -20 °C to 40 °C was
sprayed or jetted on the CNT smoke. The smoke then condensed in the form
of ribbon and MPs got attached on to the surface of interconnected
nanotubes. The ribbon of condensed interconnected nanotubes was then
twisted to form a thread of CNT-metal composite. The thread was then
passed through a heating chamber with inert atmosphere or vacuum to melt
MPs on the surface of CNTs and form a CNT-metal composite with
interconnected MPs reinforced in CNT matrix.
The following example is presented to further illustrate the invention, but it is
not be considered as limited thereto.
Example: An array of aligned multi-walled carbon nanotubes of ~300 µm
height was grown on catalyst-coated silicon wafer of diameter 100 mm using
low-pressure chemical vapor deposition. Gaseous precursors and carrier were
passed over the surface of a catalyst under controlled temperature and
pressure conditions. As shown in figure 4, the fibers of nanotube were pulled
from one edge of the substrate such that a web of nanotubes is formed. Due
to high surface area and Vander Waal interaction between CNTs, the aligned
CNTs tend to pull each other to form a long continuous fiber. A suspension of
nickel particles with a size distribution between 10 nm and 100 nm was
prepared in ethanol. The loading of nickel particles in ethanol was maintained
between 1% and 20% (w/w). The suspension of nickel in ethanol was
agitated mechanically and ultrasonically before spraying it onto the web of
CNT fibers. The high surface energy of nanotubes resulted in attachment of
nickel nanoparticles onto the surface of individual CNT fibers. These fibers
were then twisted to form a thread with nickel particles embedded into it.
The thread was then passed through a heating chamber at 900 °C with argon

environment and collected over a spool. Figure 5 and figure 6 show the SEM
image of CNT-nickel composite thread collected over spool.
The present invention can be modified, and its variations can be devised by
those who are skilled in the art without departing from the spirit and scope of
the invention. The present invention, accordingly, includes all such variations
and modifications to the claims given below:
LITERATURE REFERENCES
1. S. Iijima and others, Helical microtubules of graphitic carbon, Nature,
354, 6348, pp. 56-58 (1991)
2. J. N. Coleman, U. Khan, andY. K. Gun'ko, Mechanical reinforcement of
polymers using nanotubes, Advanced materials, vol. 18, no. 6, pp.
689-706 (2006)
3. Kwan-Woo Kim, Woong Han, Byoung-Suhk Kim, Byung-Joo Kim, Kay-
Hyeok An, A study on EMI shielding enhancement behaviors of Ni-
plated CFs-reinforced polymer matrix composites by post heat
treatment, Applied Surface Science 415 55–60 (2017)
4. Byung-Joo Kim, Kyong-Min Bae, Young Sil Lee, Kay-Hyeok An, Soo-Jin
Park, EMI shielding behaviors of Ni-coated MWCNTs-filled epoxy matrix
nanocomposites, Surface & Coatings Technology 242, 125–131 (2014)
5. Agnieszka. L. R., Lukasz. K., Peng. X., Krzysztof. K., Towards the
development of carbon nanotube based wires, Carbon, 68, 597-609
(2014)
6. Wei Xu, Yun Chen, Hang Zhan, Jian Nong Wang, High-Strength Carbon
Nanotube Film from Improving Alignment and Densification, Nano
Letters, 16 (2), 946–952 (2016)

WE CLAIM :
1. A method of prepare CNT metal composite thread using dry spinning
process for CNT growth, comprising the steps of :
i) growing an array of highly aligned CNT on catalyst coated wafer using
LPCVD process;
ii) pulling CNT fibers from aligned CNT array to form a web;
iii) dispersing metal particles of dimension 10mm to 1000mm of shape
including but not limited to sphere and wires in CNT wetting organic
carrier liquid;
iv) mixing the solution of carrier liquid and metal nanoparticles to form
suspension;
v) spraying of jetting the agitated suspension on the CNT web out of
array;
vi) twisting the web to form a thread with entrapped metal particles;
vii) annealing the thread in inert atmosphere or vacuum to melt and
interconnect metal particles;
viii) collecting the thread over spool;
2. A method to prepare CNT-metal composite thread using gaseous
growth process for CNT growth, comprising the steps of :
i) generating smoke of highly aligned CNT using liquids/gaseous
precursors/catalyst;

ii) dispersing metal particles of dimension 10mm to 1000mm of shape
including but not limited to sphere and wires in CNT wetting organic
carrier liquid;
iii) mixing the solution of carrier liquid and metal nanoparticles to form
suspension and cooling it;
iv) spraying or jetting the cold suspension on the CNT smoke to condense
the suspension;
v) twisting the smoke to form a thread with entrapped metal particles;
vi) annealing the thread in inert atmosphere or vacuum to melt and
interconnect metal particles;
vii) collect the thread over spool;
3. The method as claimed in claim 1 or claim 2, wherein carbon
nanotubes comprise of multi-walled and double-walled carbon
nanotubes.
4. The method as claimed in claim 1, wherein carbon nanotube yarn is
prepared by the dry spinning of aligned carbon nanotube array of
height 100 ųm to 600 ųm or aligned carbon nanotube.
5. The method as claimed in claim 2, wherein carbon nanotube yard is
prepared on aligned carbon nanotube array in the gaseous state;
6. The method as claimed in claim 1 or claim 2, wherein organic liquid is
including, but not limited to methanol, ethanol, isopropanol, acetone,
hexane and their combinations is used as carrier for transporting metal
particles.

7. The method as claimed in claim 1 or claim 2, wherein metal particles
possesses property of carbon nanotube wetting and include but not
limited to nickel and tungsten.
8. The method as claimed in claim 1 or claim 2, wherein dimensions of
metal particles vary from 10 nm to 10 ųm of shapes including but not
limited to spherical and cylindrical.
9. The method as claimed in claim 1, or claim 2, wherein metal particles
are attached to individual fibres before twisting one or many fibres
together.
10. The method as claimed in claim 1, or claim 2, wherein thickness of
thread can be varied by changing the number of nanofibres with
attached metal particles twisted together.
11. The method as claimed in claim 1, wherein twisted thread is heated to
temperature of 3000C to 14000C.
12. The method as claimed in claim 1, wherein heating is carried out in an
atmosphere of inert gas or vacuum.