FIELD OF THE INVENTION:
The present invention relates to a carbon nanotube coated long carbon fiber/fabric and a
process for preparation thereof.
BACKGROUND OF THE INVENTION!
Reference may be made to the patent application no. 1813/Del/2005. Composite
materials containing carbon fibers are, already widely used in applications ranging from
aerospace to sports equipments. In such materials the matrix can be plastic, epoxy, metal
or carbon. The incorporation of carbon fiber into matrix not only confers strength and
elasticity to the material but also greatly enhances toughness that is its ability to resist
cracking. Carbon nanotubes have outstanding mechanical properties i.e., average
Young's modulus -1.25 TPa, and average tensile strength -lOOGPa. In this context the
carbon nanotubes are an ideal candidate for further improvement of mechanical
properties in high performance composite structures. But the ability to disperse nanotubes
into polymer is a major problem for controlling the properties. Nanotubes that are in
clumps or agglomerated with other carbonaceous materials create defect and initiate
failure. In addition, they limit the efficiency with which nanotubes carry load. This
limitation has been illustrated explicitly in both polymer and ceramic matrix composites.
Conventional carbon nanotubes polymer composites are prepared by two ways.
One root is the addition of carbon nanotubes in the polymer matrix using costly mixer, if
the matrix is available in the solid form. Otherwise it is done by sonication if the matrix
material is available in liquid form. In both cases the uniform dispersion of carbon
nanotubes is a major problem. Researchers did not find any substantial improvement in
mechanical properties, thermal stability, electrical resistivity, magnetic
properties using this technique. Other root is the mixing of carbon nanotubes in the
precursor of fibers, i.e., pitch in the case of pitch based carbon fiber then extruding the
fiber through a spinneret. Researchers have made composites using this fiber and
polymer matrix. Again they did not find any substantial improvement in all these
properties, i.e., mechanical, thermal stability, electrical resistivity, magnetic, etc due to
the uneven distribution of carbon nanotubes.
Carbon nanotubes have an outstanding tensile strength of-37-100 GPa, stiffness
of -640-800 GPa, Young's modulus of - 2.8-3.6 TPa, specific gravity of - 1.30,
electrical conductivity of - 106 S/m, thermal conductivity of - 2000 W/mK, specific
surface area of 1350 m2/g, etc. It is synthesized by arc-discharge technique, pyrolitic
method, vapor phase growth, laser ablation method, chemical vapor deposition, plasma
enhanced chemical vapor deposition, etc.
The arc discharge technique: In this method [ T. Mukai and Y. Nishi, "Production of
carbon nanotubes by arc discharge", Japan (2004), 2004161576, 10th June 2004; Y.
Ando, and X.-L Zhao, "Method to produce carbon nanotube filament", Japan (2005),
2005100757, 14th April 2005; and Y. Agawa, S. Horiuchi, and G.-H. Chen,
"Manufacture of carbon nanotube by vacuum arc deposition", Japan (2004),
2004307241, 4th November 2004.] two graphite rods are used as cathode and anode,
between which, arcing occurs when DC voltage is supplied. A large quantity of electrons
moves to the anode and collide into the anodic rod. Carbon clusters from the anodic
graphite rod caused by the collision are cooled to low temperature and condensed on the
surface of the cathodic graphite rod in an argon-filled vessel (100 Torr). The carbon
needles, ranging from 4 to 30 nm in diameter, up to 100 um in length and 2 to 50 in
number called multiwall are grown on the negative end of the carbon electrode. Now to
produce single wall carbon nanotubes by this method the graphite rods are bored and
filled with appropriately proportional composites of graphite powder and catalytic Co,
Ni, Fe, and Y powder.
Pyrolytic method: In this method [T. S. Lee, "Mass synthesis equipment of carbon
nanotubes using pyrolysis", Repub. Korean (2002), 2002025101, 3rd April 2002; and T.
Oshima, M. Yumura, H. Ago, T. Morita, and H. Inoue, "Method and apparatus for
producing carbon nanotubes", Japan (2003) 3404543, 12th May 2003.] benzene vapor
and hydrogen are introduced into a ceramic reaction tube in which a central graphite rod
is positioned to act as a substrate. The temperature is raised to 1000°C and held at this
level for almost 1 hr before cooling to room temperature and flushing with argon gas. The
deposited material is then scrapped from the substrate and subjected to a heat treatment at
2500-3000°C in order to graphatize for 10 minutes. The resulting materials under TEM
show the presence carbon nanotube.
Vapor phase growth: Most synthesis methods of carbon nanotubes are carried out by
deposition of catalytic metals on a substrate and using conventional gas, such as C^2,
CHt, C2H4 or C2He etc. They [ E.H. Hong, D.H. Kim, G.H. Lee, C.M. Yoo, and J.H.
Yum, "Method of preparing carbon nanotubes under vapour phase condition",
Repb. Korean (2002), 2002020282, 15th March 2002; and H. Oshima, and S. Maruyama,
"Method and apparatus for production of carbon nanotubes", Japan (2005),
2005029436, 3rd February 2005] have reported the vapor phase growth of carbon
nanotubes on patterned substrate by directly supplying metal-organic catalyst (ferrocine)
in the chamber. The catalytic metals vaporizes from powder are atomic, they are formed
as fine particles down to several to tens of nm in the chamber. The fine catalytic particles
in presence of carbons form carbon nanotubes.
Laser ablation method: A laser [Y.K. Chang, "Manufacture of carbon nanotubes and
laser target for manufacturing carbon nanotube", Japan (2001), 2001089117, 3rd
April 2001] is used to vaporize a graphite target in helium or argon filled oven at a
temperature of 1200°C and pressure of 500 Torr. Carbon clusters from the graphite target
are cooled, adsorbed, and condensed on the Cu collector at a low temperature. The
condensates are mixture of carbon nanotubes and nanoparticles. MWNTs are produced in
the case of pure graphite, but uniform SWNT are synthesized when a mixture of graphite
and any of Co, Ni, Fe, or Y is used instead of pure graphite.
Chemical vapor deposition (CVD): This process [A. Grill, D. Neumayer, and D. Singh,
"Control of carbon nanotube diameter using CVD or plasma-enhanced CVD
growth", USA (2005), 2005089467, 28th April 2005; and M. Ishida, T. Ichihashi, Y.
Ochiai, and J. Fujita, "Method for preparation of carbon nanotube and carbon
nanotube structure", PCT Int. (2005), 2005033006, 14th April 2005] includes catalystassisted
decomposition of hydrocarbons, usually ethylene or acetylene, in a tube reactor
at 550-750°C and growth of carbon nanotubes over the catalyst. Best results are obtained
with Fe, Ni or Co as catalyst.
Plasma enhanced chemical vapor deposition (PECVD): PECVD [A. Grill, D.
Neumayer, and D. Singh, "Control of carbon nanotube diameter using CVD or
plasma-enhanced CVD growth", USA (2005), 2005089467, 28th April 2005; and G. S.
Kim, and H.J. Ryu, 'Carbon nanotube synthesis using modified inductively coupled
plasma chemical vapour deposition (ICP CVD) process, Rep. Korean (2003),
2003052637, 27th June 2003] has an advantage of low temperature synthesis over thermal
CVD. It generates glow discharge in a chamber or a reaction furnace by a high frequency
applied to both electrodes. A substrate is placed on the grounded electrode. Typical
hydrocarbon sources include methane, ethylene and acetylene. The pure hydrocarbon is
desirable to dilute with argon, hydrogen or ammonia. The pressure in the reactor typically
ranges from 1 to 20 Torr with a hydrocarbon fraction of up to 20%.
Researchers are trying to utilize the outstanding properties of carbon nanotubes
through several roots i.e., by mixing of carbon nanotubes in the polymer matrix in
presence of carbon fibers [S. Eto, T. Akira, and H. Tanisugi "Manufacture of
electrically conductive carbon nanotube-containing carbon fiber reinforced
thermoplastic resins and their shaped articles", Japan (2003), 2003286350, 10th
October 2003; Y. Takebe, M. Honma, and S. Ishibashi, "Production method of carbon
fibers for fiber reinforced resin compositions with good electrical conductivity",
Japan (2003), 2003239171, 27th August 2003; and M. Honma, Y. Takebe, and S.
Ishibashi, "Carbon fiber reinforced resin compositions with good electrical
conductivity and mechanical properties for molded articles", Japan (2003),
2003238816, 27th August 2003]. Another group of researchers [ A. A. Ogale, D.D. Edie
and A.M. Rao, "Mesophase pitch based carbon fibers with carbon nanotube
reinforcements", USA (2004), 20040096388, 20th May 2004] mixed carbon nanotubes
into the precursor of fiber or polymer and then extrude into fiber for further improvement
in dispersion of carbon nanotubes into matrix material and to get the best mechanical
properties. The distribution of carbon nanotubes in the matrix material is not uniform due
to its light weight.
Disadvantages of the existing Processes;
(1) It is not possible to synthesis carbon nanotubes on the surface using arc-discharge
technique, pyrolytic method, and laser ablation method.
(2) It is possible to synthesis on carbon nanotubes on the substrate using vapor phase
growth, chemical vapor deposition and plasma enhanced chemical vapor deposition. But
the size of substrate is limited to few millimetres. It is not useful for structural
application. This process is batch process.
OBJECTS OF THE INVENTION
An object of the present invention is to propose a carbon nanotube coated long carbon
fiber/fabric and a process for preparation thereof wherein newly developed fiber is
characterized through surface area, scanning electron microscopy, transmission electron
microscopy, I-V characteristics, magnetic properties, etc.
Another object of the present invention is to propose a carbon nanotube coated long
carbon fiber and a process for preparation thereof which enables to coat a multiple fiber
instead of single fiber at a time.
Further object of the present invention is to propose a carbon nanotube coated long
carbon fiber/fabric and a process for preparation thereof which enables to control the
growth of carbon nanotubes with respect to length, i.e., 10 nm to 20000 nm
Yet further object of the present invention is to propose a carbon nanotube coated long
carbon fiber/fabric and a process for preparation thereof which enables to change the
density of carbon nanotubes on the surface of carbon fiber in the range of 10 to 90%.
Still further object of the present invention is to propose a carbon nanotube coated long
carbon fiber/fabric and a process for preparation thereof which enables to control the
diameter of carbon nanotubes within the range of 1 to 60 nm.
Yet further object of the present invention is to propose a carbon nanotube coated long
carbon fiber/fabric and a process for preparation thereof wherein 50% carbon nanotubes
are single wall.
Still another object of the present invention is to propose a carbon nanotube coated long
carbon fiber/fabric and a process for preparation thereof which is an insitu process where
the presence of process variable is minima.
Yet another object of the present invention is to propose a carbon nanotube coated long
carbon fiber/fabric and a process for preparation thereof wherein the carbon nanotubes
grown on the surface of carbon fiber is helical in structure, not straight structure as
observed in conventional process, which helps to improve the strain at breaking point of
composite materials.
The inventive features of the present invention are depicted in the independent
claims and the advantageous features are indicated in the dependent claims.
STATEMENT OF INVENTION
According to this invention there is provided a carbon nanotube coated long carbon
fiber/fabric comprising carbon fiber coated with catalyst and nanotube.
Further according to this invention there is provided a process for preparation of a carbon
nanotube coated long carbon fiber/fabric comprising the steps of:
-heating the carbon fiber/fabric at a temperature of 100-700°C for 0.1 -2 hours
in air,
-coating of catalyst on carbon fiber/fabric at a temperature of 25 to 150°C for 1
to 120 minutes by dip coating/sol-gel method/wet spray as herein described,
-heating the catalyst coated fiber/fabric at a temperature of 50 to 500°C for 0.1
to 2 hours to form a layer of metal/metal oxide followed by cooling,
-feeding of the catalyst coated fiber/fabric into the reactor,
-connecting the reactor to a vacuum line to pump down to less than 200 mm Hg,
-incorporation of the inert gases, carbon containing gases and reducing gases
into the reactor,
-de-oxygenation of the gases followed by removal of moisture,
-heating of catalyst coated carbon fiber/fabric at a temperature of 400 to 1500°C
for 0.1 to 2 hours in mixture of carbon, inert and reducing atmosphere to obtain carbon
nanotube.
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS AND
TABLES;
Further, objects and advantages of this invention will be more apparent from the ensuing
description when read in conjunction with the accompanying drawings and wherein:
Figure 1 shows a schematic diagram of reactor for producing carbon nanotubes on
substrate.
Figure 2 shows SEM micrograph for as-received carbon fiber at a magnification of
10000X.
Figure 3 shows SEM micrograph of carbon nanotubes coated carbon fiber at a
magnification of 6528X.
Figure 4 shows another SEM micrograph of carbon nanotubes coated carbon fiber
at a magnification of 7000X.
Figure 5 shows another SEM micrograph of carbon nanotubes coated carbon fiber at a
magnification of 12000X.
Figure 6 shows another SEM micrograph of carbon nanotubes coated carbon fiber at a
magnification of 32000X.
Figure 7 shows another SEM micrograph of carbon nanotubes coated carbon fiber at a
magnification of 21000X.
Figure 8 shows another SEM micrograph of carbon nanotubes coated carbon fiber at a
magnification of 206452X.
Figure 9 shows another SEM micrograph of carbon nanotubes coated carbon fiber at a
magnification of 80364X.
Figure 10 shows another SEM micrograph of carbon nanotubes coated carbon fiber at a
magnification of 270400X.
Figure 11 shows a TEM micrograph of carbon nanotubes coated carbon fiber.
Figure 12 shows another TEM micrograph of carbon nanotubes coated carbon fiber.
Figure 13 shows a SAD pattern of carbon nanotubes coated carbon fiber.
Figure 14 shows BET or Langmuir function for (0: as received carbon fibers; and A:
carbon nanotubes coated carbon fibers, coating time 30 minutes) carbon fibers.
Figure 15 shows isotherm curves for (1U: as received carbon fibers; and A: carbon
nanotubes coated carbon fibers, coating time 30 minutes) carbon fibers.
Figure 16 shows I-V curves for (13: as received carbon fibers; and A: carbon nanotubes coated carbon
fibers, coating time 30 minutes) carbon fiber.
Figure 17 shows M-H curve for nickel coated carbon fibers, coating time 5 minutes.
Figure 18 shows M-H curve for carbon nanotubes coated carbon fibers, coating time 30
minutes.
Table 1: BET surface area of as-received carbon fibers and carbon nanotubes coated
carbon fibers.
Table 2: Onset voltage of as-received carbon fibers and carbon nanotubes coated carbon
fibers.
Table 3: Magnetic parameters of nickel coated and carbon nanotubes coated carbon
fibers.
DETAILED DESCRIPTION OF THE INVENTION WITH REFERENCE TO
ACCOMPANYING DRAWINGS;
[1] Coating of catalyst on the surface of carbon fiber/fabric:-
The carbon fiber/fabric is heated at a temperature of 100-700°C for 0.1-2 hours in air
followed by coating of the fiber/fabric with metal/metal oxide at a temperature of 25-
150°C for 1 to 120 minutes by simple dip coating/sol-gel method/wet spraying. Wherein
the solution is prepared by mixing oxidizing agent, reducing agent, dictating agent and/or
buffer solution wherein the buffer solution is used to keep the pH value of the solution
within the range of 5-6. The reducing agent is selected from the group of metal hydride or
metal hypophosphite, the oxidizing agent is selected from the group of metal sulphide or
metal disulphide or metal sulphate or metal halide, chelating agent is selected from the
group of chelating agents consisting of water, carbohydrates, including polysaccharides,
organic acids with more than one coordination group, lipids, steroids, amino acids and
related compounds, peptides, phosphates, nucleotides, tetrapyrrols, ferrioxamines,
ionophores, such as gramicidin, monensin, valinomycin, phenolics, 2,2'-
bipyridyldimercaptopropanol, ethylenedioxy-diethylene-dinitrilo-tetraacetic acid,
ethylene-glycol-bis-(2-aminoethyl)-N,N,N', KP-tetraacetic acid, lonophores-nitrilotriacetic
acid, NTA ortho-Phenanthroline, salicylic acid, triethanolamine, sodium succinate,
sodium acetate, ethylene diamine, ethylenediaminetetraacetic acid,
diethylenetriaminepentaacetic acid, ethylenedinitrilotetraacetic acid, and mixtures
thereof and buffer solution is selected from the group week acid consisting of succinic
acid, formic acid, acetic acid, trichloroacetic acid, hydrofluoric acid, hydrocynic acid,
hydrogen sulphide, water, etc; and its salt of sodium or potassium. The ratio of oxidizing
agent to reducing agent is 1: 0.5 to 5:1. After dipping the coated carbon fiber/fabric is
placed in an oven maintained at a temperature of 50 to 500°C for a period of 0.1 to 2
hours to form a layer of metal/metal oxide followed by cooling to the room temperature.
For wet spraying/sof-get telfcnnlqiie, the coating of metal oxide is prepared by
mixing of metal nitrate and metal carbonate. Metal nitrate is dissolved in de-ionized
water in the ratio of 1:2 to 1:10 (gm:ml). When metal nitrate is folly dissolved in water,
an equal amount of metal carbonate is added in the solution. The resulting colored
solution was stirred continuously tift it turned into a semi solid/gel mass. This semisolid
mass/gel is kept in an oven in the temperature range of 75 to 150°C for example~4 to
all water. Then the resulting mass is kept in furnace in the temperature range of 300-
500°C for 1 to 8 hrs. After cooling down to room temperature the brown colored mass is
ground in an agate mortar. The coating of this mass on the surface of carbon fiber/fabric
is done by spraying the solution of colored powder. The solution is prepared by mixing
for example ~1 to 10 g of powder in for example 50 to 500 ml of methyl alcohol which is
stirred at room temperature for -10 to 30 min. After spraying this solution on carbon
fiber/fabric, the fiber/fabric is placed in an oven at a temperature of 50 to 500°C for -0.1
to 2 hours.
(2) Coating of Carbon Nanotubes (CNTs) on the Surface of Carbon Fiber/Fiber
The coating of carbon nanotubes is conducted in a tubular reactor placed horizontally,
and the schematic diagram of the experimental setup is shown in Figure 1. This reactor
has a quartz tube of for example 84 cm length with outer diameter of for example 49 mm
and inside diameter of for example 45 mm. It is constructed in such a way that the carbon
fiber/fabric can be easily inserted and removed from the reactor. The reactor is heated in
a three zone tubular furnace. A proportional temperature controller controls the furnace
temperature in each zone. The temperature is kept around 700 to 900°C in the mid zone
of furnace to facilitate the decomposition of precursor gases. The inlet and outlet
temperatures are maintained at 300-600°C. Nitrogen, helium, argon, chlorine, hydrogen,
methane, ethane, propane, carbon dioxide, ethylene, acetylene and mixtures of it are used
as precursor gases. Each gas has its own function.
Acetylene/methane/ethylene/propane/carbon dioxide/ethane acts as a source of carbon,
hydrogen/chlorine acts as a reducing gas and nitrogen/helium/argon acts as a carrier gas
and also provides the inert atmosphere inside the reactor. The catalyst coated carbon
fiber/fabric is incorporated in the middle zone of the reactor through molten
metal/nonmetal to make an oxygen free atmosphere. The reactor is connected to a
vacuum line and then pumped down to less than 200 mm Hg. The gases enter in the
reactor through three different nonreturn valves. The flow rates of gases4ffe measured
rotometers, as shewn in Ngiwe 1. Gases are first-deoxygenated by passmg them through
an alkaline pyrogaflel seJutiaa-and subsequently moisture is removed by gassing them
through a silica gel bed. The gases are mixed before entering into the reactor. The water
circulation arrangement is made at inlet and exit of the reactors tube to keep the
temperature at desired level. Water is also used as a coolant in the condenser. Any
condensable in the reactor effluent is collected in a liquid collector where as
noncondensables are sent to the exit flow, which is recorded by the pressure indicator dial
and then vented to the atmosphere. The different conditions are used in each run to grow
carbon nanotubes.
The fabric/fiber is incorporated in a reactor through molten metal/ nonmetal
shown in Figure 1. As the reactor is connected to a vacuum line the gas of reactor is
pumped down to less than 200 mm Hg to remove oxygen from the reactor, i.e., to make
an inert atmosphere. Thereafter again inert gas is inserted in the reactor. When it comes
to the atmospheric pressure again it is pumped down to less than 200 mm Hg. This
process is continued atleast 10 times till free of oxygen. In the next step the temperature
of reactor is increased in between 400 to 600°C in an inert atmosphere. The rate of inert
gas flow is kept constant at for example 120 ml/min. After 5 to 10 minutes reducing gas
is allowed to flow at the rate of 5 to 25 ml/min for 10 to 30 minutes. After this the reactor
temperature is raised in between 400 to 1500°C in the same atmosphere. When the
temperature becomes constant at the desired temperature, carbon containing gas is
allowed to flow at the rate of 5 to 25 ml/min along with the flow of other gas. The
reaction is carried out at this temperature for 0.1 to 2 hours. After this the fiber/fabric is
allowed to cool to room temperature and taken for characterization of carbon nanotubes.
The carbon fiber/fabric (as-received carbon fiber/fabric) and carbon nanotubes
coated carbon fiber/fabric were characterized through scanning electron microscopy,
transmission electron microscopy, EDAX analysis, JiET surface area, .J-V characteristics,
and magnetic properties to evaluate its performance in high tech applications.
Surface morphology and elemental analysis of as-received carbon fiber/fabric and
carbon nanotubes coated carbon fiber/fabric have been analyzed through scanning
electron microscopy (SEM), transmission electron microscopy (TEM) and EDAX
analysis. The micrograph of as-received carbon fiber is shown in Figure 2. The fiber
surface is very smooth and there is no pit mark on the surface of carbon fiber. The
diameter of carbon fiber is calculated from this micrograph. It is seen that the diameter of
fibers is varied from 4 to 6 urn, SEM micrographs of carbon fiber coated with carbon
nanotubes have been shown in Figures 3 and 4 at a magnification of 6528X and 7000X
respectively. The micrograph shows a good and uniform coating of carbon fiber surface
by carbon nanotubes. The micrographs of carbon nanotubes synthesized on carbon fiber
using mixed catalysts are shown in Figures 5 and 6. It is observed that the density of
carbon nanotubes on the surface of carbon fiber is higher in micrograph shown in
Figures 3, 4 and 6 as compared to the micrograph shown in Figure 5. To calculate the
length and diameter of carbon nanotubes, a single strand of carbon nanotubes is carefully
chosen from Figures 3, 4, and 6 and shown in Figures 7, 8, 9, and 10 at a magnification
21000X, 80364X, 206452X and 270400X respectively. The maximum length and
diameter of the carbon nanotubes, measured from these micrographs is -20000 nm and
-40 nm respectively. These observations are further supported by TEM analysis, which
will be discussed in the next section. The closer look at the micrographs shown in
Figures 7, 8, 9 and 10 reveals the carbon nanotubes are in coiled structure, helical
structure. This coil morphology comes from the anisotropic properties of catalyst
particles.
TEM study gives detailed information about the nanostructure of carbon
nanotubes. Micrographs have been taken for all samples of carbon nanetubes synthesized
using various catalysts i.e., i.e., iron (Fe), cobalt (Co), nickel (Ni), ruthenium (Ru),
rhodium (Rh), palladium (Pd), iridium (Ir), platinum (Pt) chromium (Cr), molybdenum
(Mo), etc. Figure 11 shows a TEM micrograph of carbon nanotubes coated carbon fiber.
It shows a rough surface as compared to the as-received carbon fiber because of the
presence of carbon nanotubes on the surface of carbon fiber. The TEM micrograph of
carbon nanotubes grown on the surface of carbon fiber using mixed catalysts is shown in
Figure 12. It shows the bundles of carbon nanotubes. The kinks in the structure of carbon
nanotubes are also clearly visible in the micrograph. These kinks are may be due to the
coiled structure, helical structure or presence of pentagon/heptagon bonds in the structure
of carbon nanotubes. The corresponding selective area diffraction (SAD) pattern is also
shown in Figure 13. It shows the crystalline nature of carbon nanotubes. The ring
patterns show that the carbon fibers are not only crystalline but are also somewhat
graphitic. The brightest ring corresponds to the (002) reflection of hexagonal graphite.
The next continuous ring seen in the diffraction pattern corresponds to the (110)
reflection of hexagonal graphite. There is no difference in the intensity for this particular
diffracted ring, which suggests that there is no preferred orientation along the a*- or b
axes. The maximum diameter and length of carbon nanotubes measured from these
micrographs and comes out to be -40 nm and -20000 nm respectively. This confirms the
previous measurements done with the help of SEM micrographs (Figures 9 and 10). The
rope like structure of bundles of carbon nanotubes can also be observed from these
micrographs.
BET surface area measurements were performed for as-received carbon
fiber/fabric and carbon nanotubes coated carbon fibers to observe the effects of carbon
nanotubes. Figure 14 shows the variation of BET function with relative pressure for asreceived
carbon fiber/fabric and carbon nanotubes coated carbon fiber/fabric. The BET
function increases with increase in relative pressure for all samples, but for as-received
carbon fiber/fabric it becomes constant after the relative pressure value of 0.15, while for
carbon nanotubes coated carbon fiber/fabric it follows a linear relationship with relative
pressure. It goes on increasing through out the range of relative pressure. This is due to
the presence of carbon nanotubes, which are known to have a very large aspect ratio. The
standard isotherms for as-received carbon fiber/fabric and carbon nanotubes coated
carbon fiber/fabric are also measured and the nature of these isotherms is shown in
Figure 15. The volume adsorbed increases very rapidly after a certain value of relative
pressure (PJP0= 0.9) for both fibers. This trend is most prominent in the case of carbon
nanotubes coated carbon fibers/fabrics. This is may be due to the larger capillary action
because of presence of carbon nanotubes on the surface of carbon fibers. Initially the
pressure is not high enough to provide sufficient infiltration force but after P/Po = 0.9, it
is large enough to initiate the infiltration of nitrogen inside the carbon nanotubes present
on the surface of carbon fibers. This causes a steep increase in the volume adsorbed on
the surface of carbon nanotubes coated carbon fiber. The value of BET surface area for
different samples is listed in Table 1. Three times increment in the value of BET surface
area is observed for carbon nanotubes coated fiber/fabric as compared with as-received
carbon fiber/fabric. This increase in the value of BET surface area is expected because of
the presence of carbon nanotubes. The three fold increase in the value of BET surface
area of carbon nanotubes coated carbon fiber and sudden increase in volume adsorbed of
nitrogen at same relative pressure confirms the growth of carbon nanotubes on the
surface of carbon fiber because carbon nanotubes have very high value of aspect ratio
which causes an increase in the surface area of carbon fibers.
An attempt was made to get an I-V characteristic curve for these fibers/fabrics.
The variations of current with applied voltage for all these samples are shown in
16. The electrical resistivity of all these samples was measured from I-V curve data. The
trend observed from these curves shows good information about the use of these
materials. The onset value is higher for as-received carbon fiber/fabric as compared with
carbon nanotubes coated fiber/fabric. There is a decrease of -47% in onset voltage of
carbon fibers after the growth of carbon nanotubes on the surface of carbon fiber, which
could be useful for future application of these carbon nanotubes coated carbon fibers. The
reduction in onset voltage after growth of carbon nanotubes may be attributed to the
presence of carbon nanotubes, which have a very low value of resistivity (-10"4 Q.cm)
and very high value of current density (~1013 A/m2). These carbon nanotubes might be
participating in electrical conductance as a conducting coating on the surface of carbon
fiber, which give rise in electrical conductivity of carbon fiber. The onset voltage for both
fibers is tabulated in
The effect of carbon nanotubes on the saturation magnetization of carbon
fiber/fabric has been studied with the help of vibrating sample magnetometer. The
saturation magnetization gives very useful information about the possible use of any
material under magnetic field. It is known that carbon is a weak magnetic material, which
could be also observed from the hysteresis loop of carbon fiber (not shown here). Since
the area enclosed by the loop is very small consequently the magnetic hysteresis loss is
also very small. The M-H curve for nickel catalyst coated carbon fiber is shown in
Figure 17. The saturation magnetization measured from this curve is 4.27 e.m.u. The
saturation magnetization curve for carbon nanotubes coated carbon fibers is shown in
Figure 18. The area enclosed in this curve i.e. magnetic hysteresis loss is also very small
for carbon nanotubes coated carbon fibers. The saturation magnetization measured from
this curve is -3.55 e.m.u. The saturation magnetization for catalyst coated carbon fiber is
higher that the CNT coated carbon fibers, which is due to presence of ferromagnetic Ni
coating on the surface of carbon fiber. The value of saturation magnetization, coercivity
and retentivity of nickel coated- and carbon nanotubes coated carbon fibers are given in
disperse the nanomaterials in the matrix. If it is carbon nanotubes again it is difficult
due to its lightweight. However, the present invention proposes a process where
distribution of carbon nanotubes is uniform through out the surface of carbon fiber
and/or matrix. Now in composite material, no addition of carbon nanotubes in the
matrix separately is required. This carbon nanotubes coated carbon fiber can be used to
make any composite materials for structural application.
ADVANTAGE 3: A uniform coating of carbon nanotubes on the surface of individual long
carbon fiber in the density range of 1 to 90%.
ADVANTAGE 4: The length of carbon nanotubes on the surface of long carbon fiber can
be varied within the range of 10 to 20000 nm.
ADVANTAGE 5: The diameter of carbon nanotubes on the surface of long carbon fiber is
within the range of 1 to 60 nm.
ADVANTAGE 6: The carbon nanotubes grown on the surface of carbon fiber is helical in
structure, which helps to improve the strain at breaking point of composite materials.
ADVANTAGE 7: IMPROVEMENT IN the surface area of carbon fiber by three times with
respect to the conventional carbon fiber.
ADVANTAGE 8: 50% decrease in onset voltage when the carbon fiber is coated with
carbon nanotubes.
ADVANTAGE 9: The magnetic hysteresis loss is ~ zero when the carbon fiber is coated
with carbon nanotubes.
ADVANTAGE 10: As it is insitu process for coating of carbon nanotubes on carbon fiber,
this technique does not require any mixer for addition of carbon nanotubes in the matrix
during fabrication of composite structures, which is very costly equipment in
conventional process.
ADVANTAGE 11: Less processing cost for coating of carbon nanotubes on long carbon
fiber as it does not require plasma enhanced chemical vapour deposition unit.
ADVANTAGE 12: GREAT POTENTIAL OF the carbon nanotubes coated carbon fiber in the
manufacture of fiber reinforced composites for high tech applications, i.e., aerospace,
automobile, etc.
EXPECTED OUTCOME 1: The carbon nanotubes coated carbon fiber can be used to make a
high performance composite. These composites can replace various existing
components of spacecraft. Few of these Interior components are wall and floor
panels, pack boards, instrument panels, dividers and bulkheads, EMI-shielded panels,
racks and enclosures, ducting, decorative panels and trim, etc. In addition to these
components, few airframe components are leading edges, radomes, fairings, inlets,
guide vanes, ducts, shrouds, housing, etc; existing components of BOEING-777
commercial aircraft, i.e., aft fairings, elevator, engine cowlings, fin torque box, flap
track fairing, flaperon, floor beams, inboard flap, inboard spoilers, leading edge panels,
main landing gear doors, nose radome, nose gear doors, outboard aileron, outboard flap,
outboard spoilers, rudder, stabilizer torque box, strut forward, trailing edge panels,
wing fixed leading edge, wing to body fairing, etc; existing components of AIRBUSA340
commercial aircraft, i.e., are ailerons, apron, aft pylon fairings, belly fairing skin,
CLG doors, elevator, fin box attachment, , fin TE panels, fin LE tip, fin fairing,
fuselage fairing, flap track fairing, HTP outer boxes, HTP LE, HTP LE panels, MLG
door, MLG bay top panel, MLG leg fairings, nacelle, NLG doors, outer flaps, pylon
fairing, radome, rudder, spoilers, wing LE fillet, wing LE upper panels, wing LE lower
panels, wing tip fence, etc.; automobile industries, i.e., leaf spring, shaft, outer body,
etc.; conventional sport materials like tennis racket, golf shaft, etc.
It is to be understood that the process of the present invention is susceptible to
modification, changes, and adaptations by those skilled in the art. Such modifications,
changes adaptations are intended to be within the scope of the present invention which is
further set forth under the following claims:

WE CLAIM
1. A carbon nanotube coated long carbon fiber/fabric comprising carbon fiber/fabric
coated with catalyst and nanotube.
2. A process for preparation of a carbon nanotube coated long carbon fiber/fabric
comprising the steps of:
-heating the carbon fiber/fabric at a temperature of 100-700°C for 0.1 -2 hours
in air,
-coating of catalyst on carbon fiber/fabric at a temperature of 25 to 150°C for 1
to 120 minutes by dip coating/sol-gel method/wet spray as herein described,
-heating the catalyst coated fiber/fabric at a temperature of 50 to 500°C for 0.1
to 2 hours to form a layer of metal/metal oxide followed by cooling,
-feeding of the catalyst coated fiber/fabric into the reactor,
-connecting the reactor to a vacuum line to pump down to less than 200 mm Hg,
-incorporation of the inert gases, carbon containing gases and reducing
gases into the reactor,
-de-oxygenation of the gases followed by removal of moisture,
-heating of catalyst coated carbon fiber/fabric at a temperature of 400 to 1500°C
for 0.1 to 2 hours in mixture of carbon, inert and reducing atmosphere to obtain carbon
nanotube.
3.The composite and method as claimed in claim 1 or 2 wherein the coating of catalyst
on the surface of support material comprises cobalt oxide by cobalt chloride or cobalt
acetate or cobalt nitrate in acid or base solution; iron oxide by ferric nitrate or ferric
sulphate or ferric acetate in alcohol or acid solution; ruthenium oxide by ruthenium
nitrate solution; palladium oxide by palladium nitrate solution; molybdenum oxide by
molybdenum acetate or ammonium molybdate solution; iridium oxide by iridium acetate
solution; platinum by tetramine platinum bicarbonate or platinum acetate or platinum
nitrate solution; chromium oxide by chromium acetate solution; rhodium oxide by
rhodium acetate solution.
4. The composite and method as claimed in claim 1 or 2 wherein the catalytic particles
is/are Fe, Co, Ni, Ru, Rh, Pd, Ir, Pt, Cr, Mo, or mixtures thereof.
S.The composite and method as claimed in claim 1 or 2 wherein the support material is
selected from the group comprising of rayon based carbon fiber, pitch based carbon
fiber, polyacrylonitrile based carbon fiber; the carbon containing gas is selected from
the group consisting of saturated hydrocarbons, aliphatic hydrocarbons, oxygenated
hydrocarbons, aromatic hydrocarbons, alcohols, carbon monoxide, and mixtures
thereof; the inert atmosphere is selected from the group consisting of nitrogen, helium,
argon, and mixtures thereof, and the reducing gas is selected from the group consisting
of hydrogen, chlorine, and mixtures thereof.
6. The composite and method as claimed in claim 5 wherein the ratio of flow rate of
mixture of inert gases: reducing gas: carbon containing gas is in the ratio of 1:0:0 to
10:1:1.
7. The method as claimed in claim 2 wherein the inert gas and/or reducing gases are
substantially continuously fed into a reactor; and the substrate is continuously fed into a
reactor through a nonreactive molten material, mercury; and takeout at the exit point
continuously through a nonreactive molten material, mercury.
8. The composite and method as claimed in claim 1 or 2 wherein atleast about 40% of the
carbon nanotubes is single wall carbon nanotubes; at least 40% of the carbon nanotubes
have outer diameters less than 40 nm and at least 50% of the single-walled carbon
nanotubes have length of 9000 nm to 20000 nm.
9. The composite and method as claimed in claim 1 or 2 wherein the density of carbon
nanotubes is/are in the range of 1 to 750% (by weight).
10. A carbon nanotube coated long carbon fiber/fabric and a process for preparation
thereof substantially as herein described with reference to drawings.