FIELD OF THE INVENTION
The present invention relates to a nickel coated carbon fiber reinforced
polymer composites and a method for the preparation thereof.
BACKGROUND OF THE INVENTION
Carbon fibers are classified into two main groups. These are pitch and pan
based carbon fibers. As compared to PAN-based carbon fibers, the pitch-based carbon
fibers have a relatively high tensile modulus but a relatively low tensile strength and a
relatively low compressive strength. The structure, crystalline morphology that
provides for the high tensile modulus also allows for the brittle failure of these fibers
caused by the propagation of even minute flaws. In order to reduce the tendency of
carbon fibers to fail through flaw propagation as described above, a variety of prior
art patents i.e., methods for producing such fibers with a less ordered, more random
microstructure are known. To date, these efforts have focused on the method by
which the fiber is extruded, including modification of the geometry of the die through
which the fiber is extruded, rather than on composition modification.
Honjo and Shindo (K. Honjo and A. Shindo, "Influence of carbide formation
on the strength of carbon fibers on which silicone and titanium have been
deposited", J. Materials Science (1986), 21(6), 2043-2048) applied a coating of
titanium carbide on carbon fibers using a flow of gaseous mixtures of titanium
chloride, hydrogen and argon at a temperature from 800 to 1000°C to improve the
mechanical performance of fibers. However, the strength of coated fibers decreases
with increasing thickness of titanium carbide layer. To improve its performance in
another experiment they applied a silicone carbide layer (K. Honjo and A. Shindo,
"Interfacial behaviour of aluminium matrix composites reinforced with ceramics
coated carbon fibers", Proceedings of the First International Conference on
Composite Interfaces, North-Holland, New York (1986), 101-107) with a uniform
thickness, about 0.5 urn, by heating carbon fibers in a flow of gas mixture of
monomethyl trichloro silane, methane, hydrogen and argon, at a certain hydrogen
concentration, at a temperature of about 1200°C. Again 40% decreased in tensile
strength is observed in silicone coated carbon fiber. Again in another experiment, they
(K. Honjo and A. Shindo, "Interfacial behaviour of aluminium matrix composites
reinforced with ceramics coated carbon fibers", Proceedings of the First
International Conference on Composite Interfaces, North-Holland, New York (1986),
101-107) coated with a carbon layer and then with a ceramic layer such as titanium
carbide, silicone carbide, or titanium nitride. The double layer coated fiber exhibited a
lower strength than that of the fiber coated with the ceramic layer alone. Kamioka (N.
Kamioka, "Metal-coated carbon-fiber friction materials" Japan, 62275185, 30th
November 1987) applied a coating of aluminium and/or iron on carbon fiber by
vapour deposition or electroplating followed by hot press forming. The material thus
formed was sintered in a reducing atmosphere to get a carbon fiber friction material.
Samejima et al. (S. Samejima, S. Suzuki and YNakahara, "Manufacture of metal
coated carbon fibers for electromagnetic shields, by guiding carbon fiber bundles
with specified degree of circularity into an electroplating bath using a roller
electrode and coating the bundles with metals", Japan, 2005097776, 14th April
2005) applied metal coating on carbon fiber for electromagnetic shields by
electroplating techniques.
Composite materials containing carbon fibers/fabrics are, widely used in
application ranging from aerospace to sports equipments for its light weight and very
good mechanical properties. In spite of its good mechanical properties, trial is being
made to improve its performance by adding nanoparticles in the matrix material. But
the uniform distribution of nanomaterials in the matrix is a major problem due to its
light or heavy density/viscosity with respect to the matrix material. Such matrix
materials can be plastic, ceramic, 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. During fabrication of such
high performance composites matrix and/or reinforcing materials create defect and
initiate failure. In addition, they limit the efficiency with which the reinforcing fibers
carry load. This limitation has been illustrated explicitly in both polymer and ceramic
matrix composites.
OBJECTS OF THE EVVNETION
An object of the present invention is to propose a nickel coated carbon fiber
reinforced polymer composites and a method for the preparation thereof which results
in a high performance composite with improved thermal and mechanical properties
for structural application through the use of nickel coated carbon fibers/fabrics which
overcome the disadvantages in existing composites like microcracking of matrix,
breaking of fibers, delamination, debonding, etc.
Another object of this invention is to propose a process for the uniform
coating of nickel on long fibers which is a continuous process.
Further object of the present invention is to propose a nickel coated carbon
fiber and a method for the preparation thereof which avoids complicated operations
such as sputtering or evaporation through e-beam or magnetic field using costly
equipment or by electrodeposition technique.
Still further object of the present invention is to propose a nickel coated
carbon fiber reinforced polymer composites and a method for the preparation thereof
wherein the thickness of nickel coating is uniform through out the surface.
Yet further object of the present invention is to propose a nickel coated
carbon fiber reinforced polymer composites and a method for the preparation thereof
which enables to coat uniformly carbon fiber with nickel in the range of thickness
from 10 to 10,000nm.
Still further object of the present invention is to propose a nickel coated
carbon fiber reinforced polymer composites and a method for the preparation thereof
which results in high performance composite wherein change occurs in the density of
nickel on the surface of carbon fiber in the range of 10 to 90% (by weight).
Still further object of the present invention is to propose a nickel coated
carbon fiber reinforced polymer composites and a method for the preparation thereof
which results in the improvement of thermal stability of nickel coated carbon fiber,
4.5% weight loss when the carbon fiber is coated with nickel in the temperature range
of 25 to 900°C in nitrogen atmosphere where as weight loss is 15% in the uncoated
(as-received) carbon fiber.
Still further object of the present invention is to propose a nickel coated
carbon fiber reinforced polymer composites and a method for the preparation thereof
which results in the improvement in storage modulus of high performance
composites prepared by nickel coated carbon fiber and polyester resin at room
temperature, i.e., 25°C by 40% with respect to the uncoated carbon fiber.
Still further object of the present invention is to propose a nickel coated
carbon fiber reinforced polymer composites and a method for the preparation thereof
which results in the improvement in storage modulus of high performance
composites by 75% with respect to the uncoated carbon fiber's composites at high
temperature, i.e., 50°C.
Still further object of the present invention is to propose a nickel coated carbon
fiber reinforced polymer composites and a method for the preparation thereof wherein
relative storage modulus of high performance composites increases with increasing
temperatures upto 70°C unlike in the conventional method.
Still further object of the present invention is to propose a nickel coated carbon
fiber reinforced polymer composites and a method for the preparation thereof which
results in 35% improvement of loss modulus in high performance composites.
Still further object of the present invention is to propose a nickel coated carbon
fiber reinforced polymer composites and a method for the preparation thereof which
results in 30% improvement in damping is observed in high performance composites
when the carbon fiber is coated with nickel.
Still further object of the present invention is to propose a nickel coated
carbon fiber reinforced polymer composites and a method for the preparation thereof
wherein the glass temperature of hybrid nanocomposites is shifted to the high
temperature, ie., from 65 to 105°C when the carbon fiber is coated with nickel and the
change in glass transition temperature is ~ 40°C which is exceptional.
STATEMENT OF THE INVENTION
According to this invention there is provided a nickel coated carbon fiber reinforced
polymer composites comprising of long carbon fiber, coated with nickel (Ni) and a
thermoset polymer matrix.
Further according to this invention there is provided there is provided a
process for preparation of a nickel coated carbon fiber reinforced composites
comprising the steps of:
-heating the carbon fibers/fabrics at a temperature of 100-700°C for 0.1 -2
hours in air,
-coating of nickel on carbon fibers/fabrics in the temperature range of 25 to
90°C for 1 to 120 minutes by dipcoating/sol-gel method/wet spray,
-heating the nickel coated fibers/fabrics in the temperature range of 50 to
150°C for a period of 0.1 to 2 hours to obtain nickel coated carbon fibers/fabrics,
-dipping the nickel coated carbon fibers/fabrics in the mixture of resin,
hardner and catalyst followed by moulding and curing.
BRIEF DESCRIPTION OF THE ACCOMPANY 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 coating unit, coating of nickel on carbon
fibers/fabrics
Figure 2 shows a XRD pattern of nickel coated carbon fiber. The coating was done
using different compositions of catalyst (The number within the parenthesis
indicates the serial number of coating experiment. Few selective compositions are
described in Table 1.
Figure 3 shows a XRD pattern of nickel coated carbon fiber. The temperature of
coating solution was varied from 25 to 90°C.
Figure 4 shows a XRD patterns of nickel coated carbon fibers for different coating
times 0 (as-received), 2, 5, 10 and 15 minutes using various catalysts.
Figure 5 shows a SEM micrograph for as-received carbon fiber at a magnification of
10000X.
Figure 6 shows a SEM micrograph of nickel coated carbon fiber for coating time of 2
minutes.
Figure 7 shows a SEM micrograph of nickel coated carbon fiber for coating time of 5
minutes.
Figure 8 shows a SEM micrograph of nickel coated carbon fiber for coating time of
10 minutes.
Figure 9 shows a SEM micrograph of nickel coated carbon fiber for coating time of
30 minutes.
Figure 10 shows ED AX data of as-received carbon fibers.
Figure 11 shows ED AX data of nickel coated carbon fibers for coating time of 2
minutes.
Figure 12 shows ED AX data of 5 minutes nickel coated carbon fibers.
Figure 13 shows ED AX data of nickel coated carbon fibers for coating time of 10
minutes.
Figure 14 shows EDAX data of nickel coated carbon fibers for coating time of 30
minutes.
Figure 15 shows TGA curves (13: 0 minute coating time; A: 2 minutes coating time;
and V: 5 minutes coating time) of nickel coated carbon fibers in nitrogen
atmosphere at a heating rate of 10°C/ minute.
Figure 16 shows derivative (% wt. loss/minutes.) curves (ISI: 0 minute coating time;
and A: 2 minutes coating time) of nickel coated carbon fibers in nitrogen
atmosphere at a heating rate of 10°C/ minute.
Figure 17 shows heat flow curves (EJ: 0 minute coating time; A: 2 minutes coating
time; a: 5 minutes coating time; J3: 10 minutes coating time; and if: 15 minutes
coating time) of nickel coated carbon fibers in nitrogen atmosphere at a heating rate
of 10°C/ minute.
Figure 18 shows weight loss curves (El: 0 minute coating time; A: 2 minutes coating
time; a: 5 minutes coating time; J3: 10 minutes coating time; and •&•; 15 minutes
coating time) of nickel coated carbon fibers in oxygen atmosphere at a heating rate
of 10°C/minute.
Figure 19 shows derivative (%weight loss/ minutes) for curves (El: 0 minute coating
time; A: 2 minutes coating time; o: 5 minutes coating time; J3: 10 minutes coating
time; and if: 15 minutes coating time) of nickel coated carbon fibers in oxygen
atmosphere at a heating rate of 10°C/ minute.
Figure 20 shows heat flow curves for (El: 0 minute coating time; A: 2 minutes
coating time; O: 5 minutes coating time; J3: 10 minutes coating time; and V :15
minutes coating time) of nickel coated carbon fibers in oxygen atmosphere at a
heating rate of 10°C/ minute.
Figure 21 shows heat flow vs. time curves (El: 0 minute coating time; A: 2 minutes
coating time; V: 5 minutes coating time; I 3 : 10 minutes coating time; and ir: 15
minutes coating time) of nickel coated carbon fibers in oxygen atmosphere at a
heating rate of 10°C/ minute.
Figure 22 shows storage modulus vs. temperature curves for nickel coated carbon
fiber reinforced polymer composites (El: as-received carbon fiber; O: nickel coated
carbon fiber, coating time 5 minutes).
Figure 23 shows relative storage modulus vs. temperature curves for nickel coated
carbon fiber reinforced polymer composites (El: as-received carbon fiber; and O:
nickel coated carbon fiber, coating time 5 minutes).
igure 24 shows loss modulus vs. temperature for curves for nickel coated carbon
fiber reinforced polymer composites (El: as-received carbon fiber; and O: nickel
coated carbon fiber, coating time 5 minutes).
Figure 25 shows relative loss modulus vs. temperature curves for nickel coated
carbon fiber reinforced polymer composites (El: as-received carbon fiber; and O:
nickel coated carbon fiber, coating time 5 minutes).
Figure 26 shows tan delta vs. temperature curves for nickel coated carbon fiber
reinforced polymer composites (El: as-received carbon fiber; and O: nickel coated
carbon fiber, coating time 5 minutes).
Table 1: Compositions of coating solution for nickel.
Table 2: Thickness of nickel layer for different coating times.
Table 3: Elemental analysis of nickel coated carbon fiber coated for different time.
Table 4: Degradation temperatures corresponding to peak for as-received carbon
fibers and nickel coated carbon fibers in nitrogen atmosphere.
Table 5: Degradation temperature corresponding to peak for as-received carbon fibers
and nickel coated carbon fibers in oxygen environment.
Table 6: Glass transition temperature (Tg) of nickel coated carbon fiber reinforced
polymer composites.
DETAILED DESCRIPTION OF THE INVENTION WITH REFERENCE TO
ACCOMPANYING DRAWINGS;
(1) Coating of nickel on the surface of carbon fiber/fabric
The carbon fibers/fabrics are heated at a temperature of 100-700°C for 0.1-2 hours in
air. The carbon fibers/fabrics are coated with nickel in the temperature range of 25-
90°C for 1 to 20 minutes by dipcoating/sol-gel method/wet spray method using an
acidic bath shown in figure 1.
Few selective compositions of the bath are given in Table 1. The
bath is prepared by first dissolving the required amount of oxidizing
agent in de-ionized water in the ratio of 0.001:1-3.5:1 (GM/CC) at
. 25°C and subsequently other chemicals are added in the solution. The
mixture is continuously stirred for -30 minutes to ensure the proper mixing
of all chemicals. This colored solution is used in the dip-coating set-up, Figure 1 to
deposit nickel on the surface of carbon fibers/fabrics. The coating is produced by the
controlled chemical reduction of metallic ions onto a carbon fiber/fabric surface. The
deposit/coating itself is catalyst to the reduction reaction and the reaction continues as
long as the surface remains in contact with the bath solution or the solution gets
depleted of solute metallic ions. As for an example the acidic bath for coating of
nickel contains nickel sulphate, sodium hypophosphite, sodium succinate and succinic
acid. Nickel sulphate acts as a source of nickel ions while sodium hypophosphite acts
a reducing agent. Sodium succinate performs the role of a complexing or chelating
agent and succinic acid is used to keep the pH value of solution within the range of 5-
6. The coating of nickel on carbon fibers/fabrics is done by dipping of carbon
fibers/fabrics for different times. Few selective experimental conditions are also
indicated in Table 1. After dipping the carbon fibers/fabrics in the bath it is placed in
an oven over a range of temperature from 50 to 150°C for 0.1 to 2 hours. The
advantage of this technique is that it is much more economical and easy as compared
to other coating techniques and also it does not require any external energy source
other than heating to make deposition of nickel on the substrate. The coating is
uniform throughout the contours of the substrate because no electric current is used.
Therefore, all parts of the surface area of substrate, which are equally immersed in the
bath, have equal probability of getting ions deposited. The nickel coated carbon fiber
is 10-90% by weight and the coating comprises from about 10 to about 10,000 nm by
thickness.
For wet spraying/sol gel processes, 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 1:2-1:10 (gm:ml). When metal nitrate is fully dissolved in water,
an equal amount of metal carbonate is added in the solution. The resulting colored
solution was stirred continuously till it turned into a semi solid mass/gel. This
semisolid mass/gel is kept in an oven in the temperature range of 75 to 150°C for
example-12 hrs to vaporize 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 is done by spraying the solution of colored
powder. The solution is prepared by mixing for example -10 g of powder in for
example 500 ml of methyl alcohol which is stirred at room temperature for -30 min.
After spraying this solution on carbon fiber, the fiber is placed in an oven at a
temperature of 50 to 500°C for -0.1 to 2 hours.
The coating of nickel is illustrated by the following equations as example
without restricting the scope of the invention to the same.
In atomic hydrogen mechanism where atomic hydrogen is released as the result of the
catalytic dehydrogenation of hypophosphite molecule adsorbed at the surface. The
reaction-taking place is illustrated below:
The adsorbed active hydrogen then reduces nickel at the surface of substrate.
Simultaneously, some of the absorbed hydrogen reduces a small amount of the
hypophosphite at the catalytic surface to water, hydroxyl ion and phosphorus, (eq. 7).
Most of the hypophosphite present is catalytic, which is oxidized to orthophosphite
and gaseous hydrogen, (eq. 8), causing low efficiency of electroless nickel solutions
for alloy coating while the deposition of nickel and phosphorus continues.
Generally 1 gm of sodium hypophosphite is required to reduce 0.02 gm of nickel, for
an average efficiency of 37%. The coefficient of utilization of hypophosphite varies a
little with the nature of buffer additive. The highest degree of utilization of the
hypophosphite is the solution containing sodium acetate, and the lowest is that with
sodium citrate. The main characteristic of the process is the change in the composition
of the solution. The concentration of nickel salt and hypophosphite is decreased and
the concentration of acid is increased during the progress of deposition.
The temperature of electroless nickel solutions is one of the important factors
affecting the rate of deposition. The rate of deposition is low at temperatures below
65°C, and increases with an increase in temperature. This is true for almost all the
systems. Above 75°C, the bath becomes unstable. One of the difficulties of this
process is the maintenance of the bath composition. As the reaction proceeds,
continuous lowering of the rate of reduction of metal occurs. The solutions cannot be
replenished due to the formation of nickel phosphite. If nickel phosphite is
precipitated in the bath, the surface quality of coating deteriorates resulting in rough
and dark coatings. Moreover, the nickel concentration in the solution also decreases
and the bath goes to the verge of total decomposition. Sodium succinate reduces the
formation of nickel phosphite and reduces the rate of deposition and acts as a
complexing agent.
(2) Fabrication of nickel coated carbon fiber reinforced polymer cocomposite:
The carbon fabric is cut in right shape using template from nickel coated carbon
fabrics. The matrix used to prepare the composite is for example polyester resin. The
weight ratio of polyester resin:catalyst:hardner is 100:0.5:0.5 tolOO:5:5. Total number
of layers used to prepare the hybrid nanocomposites is 3. The composite is prepared
by conventional hand lay up technique. The preform is loaded in hydraulic press. The
pressure cycle is varied from 1 to 10 MPa. The preform is allowed to cure in the
temperature range of 50 to 150°C for 1 to 16 hours. The volume fraction of fiber is
varied from 30 to -70%. After curing, the composites are removed from hydraulic
press, and used for the characterization of volume fraction of fibers, storage modulus,
loss modulus, glass transition temperature, etc.
The preform comprises structural reinforcement formed from carbon
fibers/fabrics coated with nickel and non-structural thermosetting matrix.
The polymer curing agent/hardner and accelerator/catalyst are temperature
activatable and cured below the degradation temperature of the polymers in the
temperature range of 50 to 150°C, pressure of 1 to 10 MPa and time of 1 to 16 hours.
The solution for accelerator/catalyst comprising 20 to 99% w/w of solvent (s),
and 1 to 80% w/w of cobalt-containing salt (s), and optionally 0.1-8%w/w of
stabilizer (s), up to a total of 100% w/w.
The as-received carbon fibers, nickel coated carbon fibers and its composites
were characterized through thermogravimetric analysis over a range of temperature,
environment (i.e. oxygen and nitrogen) and heating rate; dynamic mechanical
analysis; scanning electron microscopy; and x-ray diffraction studies to find out
optimum condition of nickel coating on the surface of carbon fiber and its
performance in the structural applications.
The compositions of coating solution used in the dip coating are the key
parameter affecting in the coating process of nickel; however, in addition to this, other
parameters like pH, temperature, bath loading factor, and the surface area of the
substrate also affect the thickness of coating on the substrate. Various compositions of
coating solution for nickel are given in Table 1. The carbon fibers/fabrics coated with
different compositions of coating solution for the constant period of time 5 minutes,
and bath temperature of 65°C, were analyzed through XRD analysis. Figure 2 shows
the XRD pattern of nickel coated carbon fibers with different bath compositions along
with the as-received carbon fibers (without coating). The peak, around 20- 26° is the
characteristic peak of carbon fiber due to its graphitic structure. The location and
broadness of this peak indicate that the carbon fibers have a coke like character. The
peak around 29~34° shows nickel on the surface of carbon fiber. Because, nickel
sulphate and sodium hypophosphite were used as an oxidizing and reducing agent
respectively, the presence and absence of this peak indicates the ability of bath i.e.
whether the bath can be used for nickel coating or not. A little bit shifting of this peak
is also observed in the XRD patterns. It is clear from Figure 2 that for the given
conditions, solution (3) gives the best coating because the intensity of peak
corresponding to nickel for this solution is maximum at the same coating time, while
there is no peak observed for the compositions (1) and (2). From this it is clear that
the coating is possible for the compositions of 3 and 4 at a temperature of 65°C for a
period of 5 minutes while in others (1 and 2) the coating was not possible. This
behavior for different compositions may be attributed to the amount of reducing agent
present in the bath. Although the increase in hypophosphite concentrations improves
the rate of reduction of catalyst, extra amounts of reducing agents may cause
reduction reaction in the bulk of solution, which in turn may lead to no coating or
poor coating of nickel on the surface of carbon fiber. The appropriate amount of
hypophosphite can be adjusted by observing the bath condition during the course of
reaction. This fact is also clear from the ratio of oxidizing agent to the reducing agent
in all compositions. The ratio varies from 1:0.5 to 5:1. The ratios for selective
compositions 1, 2, 3 and 4 are: 1.33, 1.67, 2.00 and 2.50 respectively. In first two
cases since the ratio is less than the critical value so coating was not observed on the
surface of carbon fiber while in third and fourth case as the ratio is greater than that
value (as compared to one and two) the coating was observed. In fourth case it is too
high, which leads to a poor quality of coating on the surface of carbon fiber. From the
XRD analysis (Figure 2), it is concluded that the optimum ratio of oxidizing agent to
reducing agent is 2.0 at a temperature of 65°C for a coating time of 5 minutes.
The effect of temperature on the thickness of nickel coating on the surface of
carbon fiber is also discussed. The composition of bath for this experiment has been
taken corresponding to the composition (3) given in Table 1, as this composition
shows the best performance in the previous experiment i.e. variation of bath
composition at a temperature of 65°C for a coating time of 5 minutes. The
temperature of bath was varied from 25 to 90°C. Figure 3 shows the XRD patterns of
nickel coated carbon fibers coated for different bath temperatures. It shows that there
is a nickel peak for the bath temperature of 70°C. On the other hand no peak is
observed for other bath temperatures i.e., 25 to 65 and 75 to 90°C. It is conclude that
the temperature has a considerable influence on the rate of coating process. The rate
of deposition process increases with an increase in temperature and attains a
maximum at a particular temperature. Beyond this temperature it is not possible.
Because after this temperature it becomes difficult to maintain the pH of the solution
and, therefore, the quality of the coating deteriorates. So it could be concluded from
this XRD studies that the optimum coating temperature for this composition is in the
range of 65 to 75°C.
To see the effect of coating time of nickel on the surface of carbon fiber, the
carbon fibers have been coated for different times with a bath composition similar to
the solution number 3. The coating time was varied from 1 to 120 minutes.
Representative plots of intensity vs. angle for 2, 5, 10 and 15 minutes coating time of
nickel on the surface of carbon fiber are shown in Figure 4. It shows an increase in
the intensity of peak corresponding to nickel with increasing coating time. This
increase in intensity is due to the increase in thickness of nickel layer. This could be
further confirmed by the SEM and EDAX analysis of nickel coated carbon fiber
discussed in the next section. Figure 4 also shows that the carbon basal planes of the
carbon structure are not changed by nickel coating, because, their is no change in the
nature of peak corresponding to 2q ~ 26°.
Surface morphology and elemental analysis of as-received carbon fibers and
nickel coated carbon fibers have been analyzed through scanning electron microscope
(SEM) and EDAX analysis. The micrograph of as-received carbon fiber is shown in
Figure 5. The fiber surface is very smooth and there is no pit mark on the surface of
carbon fiber. The diameter of carbon fibers is calculated from this micrograph. It is
seen that the diameter of fibers at a magnification of 10000 X is ~5 um. The
micrographs of carbon fiber coated with nickel are also taken at different
magnifications and an attempt was made to calculate the thickness of nickel coating.
The EDAX analyses of these samples are also performed to see the percentage of
nickel present on the surface of carbon fiber;. Figures 6, .7, 8, and 9 show the
micrographs of nickel coated carbon fiber for coating times of 2, 5, 10 and 30 minuses
respectively. Figures ^Q, 11,12,13, aijd 14 shew the EDAX analysis of nickel coated
carbon fibers for coating times of 0, 2, 5, 10 and 30 minute respectively. The
thickness of nickel layer corresponding to the different coating times is given in
Table 2. The thickness of nickel layer is found to be increasing with an increase in
coating time and varies from -150 nm for 2 minutes to -1800 nm for 30 minutes
coating time. The elemental analysis of these samples is given in Table 3. From
Table 3 it is observed that the percentage of nickel present on the surface of carbon
fibers also increases with an increase in coating time and vary from 0.9 wt% for 2
minutes to 60 wt% for 30 minutes coating time. In this Table 3 the amount of carbon
and nickel is presented, the rest amount is due to the presence of other elements,
which act as an impurity during the coating of nickel. So it is essential to find an
optimum coating condition. Now to find out the optimum coating time thermo
gravimetric analysis (TGA) for nickel coated and as-received carbon fibers was
carried out and will be discussed in the next section.
TGA analysis of as-received carbon fibers and nickel coated carbon fibers is
essential to know the degradation behaviour, i.e., thermal stability of these fibers with
respect to the temperatures and environments. The thermal analysis was carried out
under nitrogen and oxygen environments over a temperature range of 50-900°C and
discussed in the next section.
The TGA analysis of as-received carbon fibers was carried out in the nitrogen
atmosphere and shown in Figure 15. The weight loss of as-received carbon fibers
during entire temperature range is -15%. This weight loss is may be due to the loss of
polymer sizing present on the carbon fibers. To confirm this the as-received carbon
fiber was heated in the temperature range of 100 to 700°C for a period of 0.1 to 2
hours in the air atmosphere. This heated fiber was used for TGA study. The 15%
weight loss is not observed in the TGA analysis for the heated fiber. The total weight
loss for heated carbon fiber sample is observed to be -9%. This is either due to the
degradation of carbon fiber or the presence of small amount polymer sizing on the
heated carbon fiber. Figure 15 also shows that the degradation rate for as-received
carbon fibers is very slow up to a temperature of 250°C and then suddenly increases at
~300°C. After 450°C the degradation rate again decreases and weight remains almost
constant to 900°C. On the other hand, for the heated carbon fiber the weight
continuously decreases from 300°C to 900°C without sudden weight loss as observed
in as-received carbon fiber before heat treatment. To find out the degradation
temperature where the rate of degradation is maxima, a derivative curve (%
weight/minute) is constructed against temperature and shown in Figure 16. The peak
corresponding to as-received carbon fibers occurs at a temperature of ~360°C which is
corresponding to the maximum slope of weight loss curve for as-received carbon
fibers. Now to understand the thermal stability of nickel coated carbon fiber, TGA
analysis is also carried out on the nickel coated carbon fibers in the nitrogen
atmosphere over a range of temperature from 50-900°C. The thermal behavior of
nickel coated carbon fibers is also included in the same Figure 15. It shows that the
weight loss is less for nickel coated carbon fiber as compared to the as-received
carbon fiber for the given temperature range and environment. Again to understand
the effect of thickness of nickel coating on the thermal stability of carbon fiber,
thermogravimetric analysis is also carried out on the nickel coated carbon fibers
having a coating time of 2 and 5 minutes. These plots are also included in the same
Figure 15. The total Weight loss for nickel coated carbon fibers is same for 2 minutes
and 5 minutes coating time. Since the difference in weight loss for 2 minutes and 5
minutes coating is very less while the amount of nickel present is more for 5 minutes
coating time (as observed from ED AX analysis), so 5 minutes coating time is chosen
as optimum coating time for further study and has been used for making a nickel
coated carbon fiber reinforced composite. The derivative of weight loss
(%weight/minute) for nickel coated carbon fiber coated for different coating times are
also shown in the same Figure 16. The peaks for as-received and heated carbon fibers
are more intense than nickel coated carbon fibers, which is due to the higher weight
loss of these samples as compared to the nickel coated carbon fibers. The derivative
curves for nickel coated carbon fibers with different coating times are almost a
straight line because of low weight loss for these samples under given conditions.
The DTA analysis is also performed on as-received carbon fibers, heated
carbon fibers and nickel coated carbon fibers to get an idea about the degradation
reaction and phase transition if any, occurring in these samples. Figure 17 shows the
DTA curves for these samples in the nitrogen atmosphere. The nature of heat flow
curve follows the same pattern for both samples, which suggests the type of
degradation reaction is same for all samples. The heat flow increases with an increase
in temperature up to ~400°C and after this it starts decreasing with the increase in
temperature for as-received carbon fibers. For nickel coated carbon fibers for different
coating times, the change in heat flow with temperature occurs in a similar fashion. It
increases up to a temperature of ~370°C and starts decreasing with an increase in
temperature after this. The peaks corresponding to this behavior of heat flow for asreceived
and nickel coated carbon fibers coated for different coating times can be
observed from Figure 17. The nature of peaks for all samples suggests that the
degradation is an endothermic reaction. The temperature corresponding to these peaks
are measured and have been tabulated in Table 4.
The TGA analysis of as-received carbon fibers and nickel coated carbon fibers
are also done in the oxygen atmosphere to observe the effect of oxygen on the thermal
stability of all these carbon fibers. The weight loss behavior of all these fibers with
respect to the temperature in oxygen atmosphere is shown in Figure 18. 100% weight
loss is observed for as-received and heated carbon fiber where as the weight loss for
nickel coated carbon fiber is within the range of 90-98%. The minimum weight loss is
observed for the nickel coated carbon fiber, which is again for the coating time of 15
minutes. This is may be because of the higher amount of nickel present for 15 minutes
coating time. The degradation of as-received carbon fibers starts slowly from ~300°C
and at ~350°C the weight loss increases rapidly up to a temperature of ~630°C and
after this the weight of samples remains almost constant up to 800°C. There is no
further weight loss is observed after 630°C. Similarly the derivative curve i.e. weight
loss with respect to the time was measured against temperature and shown in Figure
19. The peak at 570°C corresponds to the maximum weight loss i.e., degradation
temperature for as-received carbon fiber. Where as for nickel coated carbon fibers the
weight loss increases rapidly after 650°C and after ~720°C there is no weight loss
observed for these samples. The maximum degradation temperature for nickel coated
carbon fiber appears at a temperature of 670°C in oxygen atmosphere. The starting
degradation temperature for as-received and heated carbon fibers is ~350°C while for
nickel coated carbon fibers the degradation starts at ~650°C which indicates that the
thermal stability of carbon fibers has been increased after nickel coating. A very
strange phenomenon in weight loss curves is observed in all samples under oxygen
atmosphere (Figure 18). There is a sudden fluctuation in temperature at ~610°C for
as-received fibers and at ~700°C for nickel coated carbon fibers. This phenomenon is
also observed when the temperature is measured against time. The as-received and
heated carbon fibers show a peak at a time of 50 minutes. This peak is shifted to the
higher time of 60 minutes when the fibers are coated with nickel, which again
indicates the higher thermal stability of nickel coated carbon fibers as compared to the
as-received and heated carbon fibers. The one reason behind this phenomenon is may
be due to the change in micro structure of carbon fibers. This fluctuation is observed
only in the sample temperature not in programme temperature, when the sample
temperature and programme temperature are measured against time.
The DTA analysis for as-received carbon fibers and nickel coated carbon
fibers is performed in order to understand the heat flow behavior and nature of
degradation reaction in oxygen atmosphere. The nature of DTA curve is shown in
Figure 20. It shows the heat flow increases slowly with an increase in temperature but
at a temperature of ~620°C it increases very rapidly and again decreases with
increasing temperature in case of as-received and heated carbon fibers. It becomes
almost constant after ~650°C for these samples. For nickel coated carbon fibers for
different coating times the heat flow increases slowly with an increase in temperature
and at ~ 720°C, it increases very rapidly and again decreases on further increasing the
temperature and becomes almost constant after ~750°C. The endothermic nature of
degradation reaction as observed in the nitrogen atmosphere is also shown in the
oxygen atmosphere. But the peaks are very sharp here unlike in nitrogen environment
where the peaks were broader. These sharp peaks suggest a sudden degradation of
samples, which is observed in weight loss curves shown in Figure 18. All the weight
loss occurs in a narrow temperature range in the case of oxygen atmosphere while in
the nitrogen atmosphere the weight loss occurs over a broad range of temperature.
The temperature corresponding to these endothermic peaks are measured and listed in
Table 5. Figure 21 presents the heat flow vs. time for as-received, heated and nickel
coated carbon fibers in the oxygen atmosphere. The peak shows the time of maximum
degradation of samples. For as-received carbon fiber the peak is present at -48
minutes while for the nickel coated carbon fibers the peak has been shifted towards
the higher time and occurs at a time of -58 minutes, which indicates that the
degradation of nickel coated carbon fibers has started after the degradation of asreceived
and heated carbon fibers. So it can be inferred that the nickel coated carbon
fibers are more thermally stable as compared to the as-received and heated carbon
fibers. The presence of small peaks in all these curves can be observed from Figure
21. These peaks occur at the time, corresponding to the time of fluctuation of
temperature. The nature of these peaks indicates an exothermic reaction. This is again
due to the change in microstructure.
To see the effect of nickel coating on the carbon fiber with respect to the
mechanical behavior of composite structures, the dynamic mechanical analysis was
carried out on these composites made by polyester resin and as-received carbon
fibers/fabrics and nickel coated carbon fibers/fabrics. The analysis was done within a
temperature range of 30-170°C and at a frequency of 1 Hz under bending mode. The
variation of storage modulus with respect to the temperature for all these composites
is shown in Figure 22. A significant improvement is observed in storage modulus for
the nickel coated carbon fiber composites as compared to the as-received carbon fiber
composites. The storage modulus for nickel coated carbon fiber composites is higher
than the as-received carbon fiber composites by -40% at a temperature of 25°C,
whereas the improvement is -75% at a temperature of 50°C. The storage modulus for
these composites decreases with an increase in temperature but at any temperature the
storage modulus is higher for the nickel coated carbon fiber composites as compared
to the as-received carbon fiber composites. Now the improvement in storage modulus
is explained with respect to the relative storage modulus. This relative storage
modulus is defined as the modulus ratio of nickel coated to the as-received carbon
fiber. Figure 23 shows the relative storage modulus of nickel coated carbon fiber
composites with respect to the as-received carbon fiber. The relative storage modulus
for nickel coated carbon fiber composites increases with increasing temperature
through out the temperature range of 70 and 90°C. Then it decreases with an increase
in temperature. The increase in modulus can be explained by the increase in kinetic
energy (G = v k T) where G, v, k and T are modulus, cross link density, Boltzmann's
constant and temperature respectively. But, the decrease in modulus with respect to
temperature is due to the decrease in intermolecular force of attraction in the
composite materials. In addition to this the decrease of coefficient of friction between
molecules decreases the modulus value at higher temperatures.
The variation of loss modulus and relative loss modulus with increasing
temperature is shown in Figures 24 and 25 respectively. The loss modulus of nickel
coated carbon fiber composites is higher than the as-received carbon fiber composites
in the temperature range of 35 to 105°C. It is also observed that the loss modulus
reduces with increasing temperature for as-received carbon fiber composites. Whereas
for nickel coated carbon fiber composites the loss modulus first increases up to a
temperature of 60°C and then decreases on further increasing the temperature. The
same nature is also observed in relative loss modulus data for all these composites
(Figure 25)
Figure 26 shows the variation of Tan 8 with respect to the temperature for asreceived
carbon fiber composites and nickel coated carbon fiber composites. The
value of Tan 8 first increases with an increase in temperature and then decreases on
further increasing the temperature. JFor as-received carbon fiber the Tan 8 increases up
to a temperature of ~80°C and then starts decreasing as the temperature is further
increased. Whereas, for nickel coated carbon fiber composites a broad peak is
observed. The peak temperature is known as glass transition temperatures (Tg). The
glass transition temperature for nickel coated carbon fiber composites is not well
defined. It has spread over a range of temperature. The glass transition temperature of
all these composites has been listed in Table 6. It is observed from the Table 6 that
the glass transition temperature for nickel coated carbon fiber composite is not well
defined.
Advantages of the Invention;
ADVANTAGE 1: Generally coating is done either by sputtering or evaporation through
e-beam or magnetic field using costly equipments or by electrodeposition technique.
In case of electrodeposition technique it is very tough/difficult to get a uniform
coating on the surface of substrate, whereas the present invention proposes an
electroless process for uniform coating through out the surface of carbon fiber,
which is very simple and cheep.
ADVANTAGE 2: A uniform coating of nickel on the surface of long carbon
fibers/fabrics can be obtained which is not possible for long fibers/fabrics even
through sputtering or evaporation techniques. The thickness of uniform coating
could be varied from 10 nm to 10,000 nm.
ADVANTAGE 3: SIGNIFICANT IMPROVEMENT IN the thermal stability of nickel coated
carbon fiber. 4.5% weight loss is observed when the carbon fiber is coated with
nickel in the temperature range of 25 to 900°C in nitrogen atmosphere where as
15% weight loss is observed for the uncoated (as-received) carbon fiber.
ADVANTAGE 4: IMPROVEMENT IN the storage modulus of nickel coated carbon fiber
reinforced polymer composite at room temperature, i.e., 25°C by 40% with respect
to the uncoated carbon fiber. Where as at high temperature, i.e., 50°C the
improvement is 75% with respect to the uncoated/as-received carbon fiber's
composites.
ADVANTAGE 5: Generally storage modulus decreases with increasing temperature.
This is a conventional fact in case of all composite materials. But, when the carbon
fiber is coated with nickel, the relative storage modulus of nickel coated carbon
fiber reinforced polymer composites increases with increasing temperatures upto
70°C.
ADVANTAGE 6: 35% improvement in loss modulus at a temperature of 55°C in nickel
coated carbon fiber reinforced polymer composites when the carbon fiber is coated
with nickel.
ADVANTAGE 7: 30% improvement in damping at a temperature of 105°C in nickelcoated
carbon fiber reinforced polymer composites when the carbon fiber is coated
with nickel.
ADVANTAGE 8: SHIFTING OF the glass temperature of nickel coated carbon fiber
reinforced polymer composites to the high temperature, ie., from 65 to 105°C when
the carbon fiber is coated with nickel.
ADVANTAGE 9: LESS processing cost as it does not require any costly equipment like
sputtering or e-beam evaporation units.
ADVANTAGE 10: GREAT POTENTIAL IN the nickel coated carbon fiber reinforced
polymer composite in the manufacture for high tech applications, i.e., aerospace,
automobile, etc.
EXPECTED OUTCOME 1: The newly developed nickel coated carbon fiber reinforced
polymer 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
EXPECTED OUTCOME 2: Again this advanced nickel coated carbon fiber reinforced
polymer composites can replace various existing components of BOEING-777
commercial aircraft. Few of these are 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
EXPECTED OUTCOME 3: This advanced nickel coated carbon fiber reinforced polymer
composites can also replace various existing components of AIRBUS-A340
commercial aircraft. Few of these 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
EXPECTED OUTCOME 4: This advanced nickel coated carbon fiber reinforced polymer
composites can be used in automobile industries. Few of these are leaf spring, shaft,
outer body, etc.
EXPECTED OUTCOME 5: These nickel coated carbon fiber reinforced polymer
composites can also be used to replace the conventional sport materials like tennis
racket, golf shaft,
It is to be understood that the process of the present invention is susceptible to
modification, changes, 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 nickel coated carbon fiber reinforced polymer composites comprising of long carbon fiber, coated with nickel (Ni) and a thermoset polymer matrix in the ratio of 100:0.5 to 100.5.
2. A process for preparation of a nickel coated carbon fiber polymer reinforced composites as claimed in claim 1 comprising the steps of:

- heating the carbon fibers/fabrics at a temperature of 100-700°C for 0.1-2 hours in air,
- coating of nickel on carbon fibers/fabrics in the temperature range of 25 to 90°C for 1 to 120 minutes by dipcoating/sol-gel method/wet spray,
- heating the nickel coated fibers/fabrics in the temperature range of 50 to 150°C for a period of 0.1 to 2 hours to obtain nickel coated carbon fibers/fabrics,
- dipping the nickel coated carbon fibers/fabrics in the mixture of resin, hardner and catalyst followed by moulding and curing.

3. A nickel coated carbon fiber reinforced composites and a method for the preparation thereof as claimed in claim 1 or 2 comprising mixing of curing agent, also known as hardner in a resin, also known as polymer in a ratio of 100:0.5 to 100:5 at a temperature of 10 to 50°C followed by mixing of accelerator, also known as catalyst with solvent in a mixture of resin and hardner in ratio of 100:0.5 to 100:5 at a temperature of 10 to 50°C.
4. A method as claimed in claim 2 wherein curing is performed at a pressure of 1 to 10 MPa, and temperature of 50 -150°C for a period of 1-16 hours after loading of perform in hydraulic press.
5. A composite and method as claimed in claim 1 or 2 wherein the carbon fiber is selected from the group comprising of rayon based carbon fiber, pitch based carbon fiber, polyacrylonitrile based carbon fiber, etc.; and the polymer material is selected from the group comprising of polyamide, polyester, polyurethane, poly sulfonamide, polycarbonate, polyurea, polyphosphonoamide,

polyarylate, polyimide, poly (amic ester), poly (ester amide), a poly (enaryloxynitrile), epoxy or mixtures thereof.
6. A composite and method as claimed in claim 5 wherein the polyester is a polyester of diacid i.e. terephthalic acid, isophthalic acid, phthalic acid, trimellitic acid, pyromellitic acid, hexahydrophthalic acid, adipic acid or sebacic acid; and diol i.e., 1, 2-ethanediol, 1,2-propanediol, trimethylolpropane, neopentyl glycol, 1,3-butanediol, 1,4,-butanediol, pentaerythritol, glycerol, tris(hydroxyethyl) isocyanurate or ethoxylated bisphenol A; which has an acid number in the range 1 to 150 mg KOH per gram; hydroxyl number less than 30 mg KOH per gram; number average molecular weight (Mn) is less than 2000; and viscosity in the range of 12000-15000 cP.
7. A composite and method as claimed in claim 1 or 2 wherein the nickel coating on the surface of support material produced by the method having a reactor cell comprising of oxidizing agent, and reducing agent, and a support material, and/or chelating agent, and/or buffer solution, and inert atmosphere comprising of nitrogen, argon, helium and mixture thereof, which is carried out at a temperature of 25 to 90°C for 1 to 120 minutes.
8. A composite and method as claimed in claim 7 wherein the oxidizing agent is selected from the group of nickel sulphide or nickel disulphide or nickel sulphate or nickel halide and the reducing agent is selected from group of nickel hydride or nickel hypophosphite.
9. A composite and method as claimed in claim 7 wherein the chelating agent is selected from the group of chelating agents comprising 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,N1, N1-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.

10. A composite and method as claimed in claim 7 wherein the
buffer solution is selected from the group of week acid comprising
of succinic acid, formic acid, acetic acid, trichloroacetic acid,
hydrofluoric acid, hydrocynic acid, hydrogen sulphide, water, etc;
and its salt of sodium or potassium and the ratio between the
oxidizing and reducing agent is 1:0.5 to 5:1.
11. A composite and method as claimed in claim 2 wherein the curing agent/hardner is selected from the group comprising of benzoyl peroxide, dicumyl peroxide, hydrogen peroxide, methyl peroxide, ethyl peroxide, methyl ethyl ketone peroxide, sulphur, and mixtures thereof; accelerator/catalyst is selected from the group of organometallic compounds which consists essentially of one or more cobalt- containing salts of cobalt octoate, cobalt 2-ethylhexanoate, and cobalt naphtenate, and one or more solvents consisting of pentane, isopentane, hexane, diethyleneglycol, dipropyleneglycol, ethyleneglycol, isobutanol, pentanol, triethylphosphate, triethylphosphite, dibutylmaleate, dibutylsuccinate, ethylacetate, and mixture thereof, and (optionally) one or more stabilizers.