TECHNICAL FIELD OF THE INVENTION
The present invention relates to nitrogen modified graphene. More particularly, the
invention relates to a nano-lubricant composition comprising the nitrogen modified
graphene having improved lubricating properties. The invention also 5 relates to process
of preparing the nitrogen modified graphene.
BACKGROUND AND PRIOR ART
Lubrication of the industry components is done by oil which is the base fluid. This
10 reduces the friction and temperature resulting in an increase of the lifetime of the
components. Nano-lubricants can provide better lubrication effects due to the
considerable decrease in the friction and temperature, which depends on the base oil and
the nanomaterials used. The flexible carbon based nanomaterials have the ability to
convert the thermal energy generated, into the lattice oscillations thereby reducing the
15 increase in the temperature and friction, which reduces the wear properties. Besides, the
flexible carbon based nanomaterials dispersed in oils can be used to increase the thermal
conductivity, reduce the friction and enhance the heat transfer coefficients.
Nano-lubricants are nanoparticle dispersions in base fluids which find potential
20 applications in the fields of cooling and lubrication. The flow properties and dynamic
viscosity can be tuned by proper selection of flexible carbon based nanomaterial
nanoparticles. These flexible carbon based nanomaterials with low volume
concentration and high aspect ratio are more efficient when dispersed in base oils.
Carbon nanomaterials such as graphene are endowed with high aspect ratio and good
25 thermal conductivity and hence graphene can be dispersed in coolant for better cooling
purposes.
US 8575335 B2 forms N-graphene as a metal-free oxygen reduction catalyst not
containing metal such as platinum for a H2/O2 fuel cell. The method comprises of
30 reacting an organic material having amino groups with graphite in a reaction medium
containing polyphosphoric acid and phosphorus pentoxide, thereby the graphite being
3
exfoliated with the functional group of the organic material grafted to the graphite to
prepare organic material-grafted graphene and then heat treating at a temperature of 300
to 1,200° C in an atmosphere of gas selected from the group consisting of methane,
hydrogen, nitrogen, helium, neon, argon and the combination thereof.
5
US 8664439 B2 teaches Graphene, comprising of a structure of carbon (C) atoms
partially substituted with boron (B) atoms and nitrogen (N) atoms, wherein the graphene
has a band gap of is about 0.05 eV to about 0.3 eV and its use in transistors. The
graphene is fabricated by performing a chemical vapor deposition (CVD) method using
10 borazine or ammonia borane as a boron nitride (B—N) precursor.
US 8222190 B2 teaches a lubricant composition having improved lubricant properties,
comprising of a lubricating fluid and nano-graphene platelets (NGPs) dispersed in said
fluid, wherein said nano-graphene platelets have a proportion of 0.001% to 75% by
15 weight based on the total weight of the fluid and the graphene platelets combined. These
suspension use additives like dispersing agent and surfactant, followed by ultrasonication
treatment. It teaches the formation of graphite oxide from graphite and later
exfoliation. It demonstrates that lubricant composition with NGPs exhibit an improved
friction, viscosity, thermal conductivity and stability. This prior art does not mention N20
doping but it talks about `Graphite oxide inserted into a quartz tube at a temperature of
1,050° C. for 60 seconds under a flowing nitrogen condition to obtain exfoliated
graphite oxide. Flow of nitrogen will not incorporate nitrogen in the nano-graphene
platelets (NGPs).
25 Nano-graphene platelets are different that graphene (nano-graphene platelets contain
more number of layers compared to graphene).
WO 2015031841 teaches the use of activated expanded graphite oxide comprising at
least one dopant in capacitors. Two types of nitrogen dopants are used pyridinic
30 nitrogen (N6) and pyrrolic nitrogen (N5).
4
CN 103359708 A provides nitrogen doped graphene for use in capacitors, batteries and
as electrodes. The process, by Hummer’s method converts graphite to graphene oxide.
Later, graphene oxide reacts with polymer (Pluronic F-127) in the presence of gas
atmosphere of ammonia gas and an inert gas like argon to obtain nitrogen doped
graphene. However, use of gases like ammonia 5 is hazardous.
Thus, the flexible carbon material has varied applications because of its high surface
area and excellent electronic and thermal conductivity however the products are not
having high yield and stability. Thus, there is a need to provide a better product in high
10 yield and which is more stable and can be used for multiple applications.
OBJECT OF THE INVENTION
It is therefore an object of the present invention to provide a cost-effective Nanolubricant
composition that exhibits reduced co-efficient of friction(COF) and surface
15 temperature.
It is another object of the present invention is to provide a Nano-lubricant composition
which is stable while demonstrating the properties of reduced co-efficient of friction and
surface temperature.
20
It is yet another object of the present invention to provide a Nano-lubricant composition
that exhibits a better combination of friction, wear, and heat transfer properties while
maintaining the viscosity of the composition.
25 Still another object of the present invention is to provide a method for preparation of
lubricant composition with nitrogen doped graphene.
SUMMARY OF THE INVENTION
According to one aspect of the present invention, there is provided a nano-lubricant
30 composition having improved lubricant properties, comprising: (a) a lubricating fluid;
5
and (b) N-doped graphene (NTEG) dispersed in said fluid, wherein said the N-doped
graphene is 0.125mg/40ml to 5mg/40mlof oil.
According to another aspect of present invention, there is provided a method of
preparing Nano-lubricant composition comprising the 5 following steps:
i. converting the natural graphite to graphite oxide;
ii. thermal exfoliation of graphite oxide prepared from step (i) to
form TEG (thermal exfoliated-reduced graphene);
iii. negatively charging the TEG of step (ii) with anionic
10 polyelectrolyte;
iv. dispersion of TEG obtained from step (iii);
v. chemical polymerization of the product of step (iv) with
polypyrrole;
vi. annealing at 800ºC in inert gas atmosphere and thereby reducing
15 the graphite oxide to N-TEG (nitrogen doped graphene), and
vii. dispersing the N-TEG in lubricating oil using probe sonication to
form nano-lubricant.
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS
20 The accompanying figures, which are incorporated in and constitute a part of this
specification, illustrate several aspects and together with the description serve to explain
the principles of the invention.
FIGURE 1& 2 shows the FESEM image of synthesized TEG.
FIGURE 3 & 4 shows the transmission electron micrograph of nitrogen doped
25 thermally exfoliated reduced graphene (N-TEG).
FIGURE 4 shows the XRD pattern of graphite (Gr), graphite oxide (GO) and thermally
exfoliated graphene (TEG).
FIGURE 5shows the Raman spectra of graphite (Gr), graphite oxide (GO) and
thermally exfoliated graphene (TEG).
30 FIGURE 6 & 7 shows the stability results of nano-lubricants with TEG and N-doped
graphene.
6
FIGURE 8 shows the effect on coefficient of friction with N-TEG.
FIGURE 9 shows the comparative effect on surface temperature of base oil and N-TEG
–oil.
FIGURE 10 shows the stability result after 4 months.
5
DETAILED DESCRIPTION OF THE PRESENT INVENTION
The present invention provides a lubricant composition having a lubricating fluid and
N-doped graphene (NTEG) dispersed in the lubricating fluid. N-Teg is present in the
composition in a range from 0.125mg/40ml to 5mg/40ml, preferably from
10 0.125mg/40ml to 0.25mg/40ml and more preferably 0.125mg/40ml.
A preferred group of lubricating fluids according to present invention includes organic
substances containing primarily carbon, hydrogen and oxygen, e. g., oils from
petroleum consisting essentially of complex mixtures of hydrocarbon molecules. More
15 specifically, lubricating oil or “lube oil” refers to a selected fraction of refined mineral
oil used for lubrication of moving surfaces, usually metallic surfaces, which cover from
small precision machinery to the heaviest equipment. Lubricating oils usually contain
additives to impart desired properties such as viscosity and detergency. The petroleum
liquid medium can be any petroleum distillates or synthetic petroleum oils.
20 Representative petroleum lubricating oils used in this invention include lubes used to
lubricate automobiles, gears, automatic transmissions, turbines, aviation engines, and
refrigeration equipment. This invention is best used for ID Fan lube oil servoprime 68
brand (Indian Oil) used in NTPC which is ISO VG 68 grade but applicable to other
brands like Shell, IBP, HPCL base fluids of same grade. The preferred lubricating fluid
25 for the present invention is mineral oil>99% (trade name Servoprime 68) also known as
ID Fan lube oil of. NTPC
In this invention, it has been demonstrated that the nitrogen modified graphene as
provided in present invention as additive for fan lube oil lubricant, the friction
30 coefficient is decreased by ~25% compared to the base oil. This decrease in frictional
coefficient of N-TEG-oil nano-lubricants can be attributed to the layered structure of
7
graphite and due to its self-lubrication. There is an increase in temperature while
incorporating the ID fan oil and use of nano-lubricant reduces the increase in
temperature by 15°C. The stability of the nano-lubricant keeps the operating
temperature low and increases the machine life. This also reduces the electrical power
required to run the ID Fan machine, due to reduction in friction coefficient 5 and hence
results in power savings.
In present inventionnitrogen containing graphene is obtained by using polymer
polypyrrole (PPy) starting with the monomer pyrrole. This coating is essential to modify
10 the carbon hexagonal with maximum nitrogen content. Besides, the present method
does not use any additives, surfactants for the dispersion of nitrogen doped graphene
and this is achieved by the modification of the carbon hexagonal by nitrogen containing
polymer polypyrrole.
15 To obtain a high yield of graphene sheets for various applications, graphene sheets are
synthesized by chemical reduction of graphite oxide. The number of layers of N-TEG as
obtained will be around 8-10 layers and the size of the particle will be 3 nm to 5 nm.
The nano-lubricant composition according to present invention is having coefficient of
20 friction ranging from 0.17 to 0.21 and viscosity ranging from 0.071 Pa.s. to 0.076 Pa.s.
In accordance with the present invention, a method of preparing Nano-lubricant
composition is provided comprising of nitrogen-doped graphene, comprising the
following steps:
25 i. converting the natural graphite to graphite oxide using Hummers’
method;
ii. thermal exfoliation of graphite oxide prepared from step (i) to form TEG
(thermal exfoliated-reduced graphene);
iii. negatively charging the TEG of step (ii) with anionic polyelectrolyte;
30 iv. dispersion of TEG obtained from step (iii);
v. chemical polymerization of the product of step (iv) with polypyrrole;
8
vi. annealing at 800ºC in inert gas atmosphere and thereby reducing the
graphite oxide to N-TEG (nitrogen doped graphene); and
vii. dispersing the N-TEG in lubricating oil using probe sonication to form
nano-lubricant.
In the method of manufacturing of the nitrogen incorporated graphene, 5 the incorporated
nitrogen replaces the carbon thereby induces the wrinkles in the surface of the graphene.
The present invention thus provides a better method of nitrogen doping of two
dimensional carbon nano structure compared to the existing hazardous methods, which
is simple, non-hazardous, gives a better control over nitrogen content. The present
10 method is free from hazardous material like ammonia for doping graphene. The anionic
polyelectrolyte is PSS (poly(sodium 4-styrenesulfonate)) of molecular weight of 70,000.
The sonication treatment is done for 30min with 20 KHz frequency and power of 500W.
Inert gas as used herein can be Argon. The thermal exfoliation step is conducted for 30s
15 at 1000˚C.
In the method of dispersing nitrogen incorporated graphene in lubricant oil, the solute
nitrogen incorporated graphene disperses uniformly in the lubricant oil i.e. ID Fan Lube
Oil of NTPC (Trade name-Servoprime 68). The present N- TEG as compared to the
20 conventional lubricant provides the following advantageous features:
 Performance enhancement of about 25% in reducing the coefficient of friction.
 Performance enhancement of 15˚C in reducing the temperature due to the
decrease in the friction.
 Decrease of 5% in the viscosity of the base lubricant.
25  Highly stable under the atmospheric conditions.
The invention is now illustrated by way of non-limiting examples.
Example 1
Preparation of TEG
9
Step a: Graphite oxide (GO) was prepared from natural graphite using Hummers’
method. In a typical synthesis, graphite powder (2 g) was added to concentrated H2SO4
(46 mL) while continuously stirring in an ice bath.
Step b: NaNO3 (1 g) and KMnO4 (6 g) were added gradually and successively.
Step c: The suspension was further removed from the ice bath and was 5 allowed to cool
to room temperature.
Step d: Next, water (92 mL) was added to the above mixture. After 15 min, warm water
(280 mL) was added to dilute the mixture.
Step e: Following this, H2O2 (3%) was added until the solution turns bright yellow.
10 Step f: The suspension was then filtered and repeatedly washed with warm water.
Step g: The residue was diluted using water and the resulting suspension was
centrifuged.
Step h: The final product was dried under vacuum at 60°C and stored in vacuum
desiccators until further use.
15
Graphene is prepared by the thermal exfoliation of graphite oxide.
GO powder (about 300mg) was spread in a quartz boat and inserted for 30s in a quartz
tube kept in a furnace at1000°C. Thermal exfoliation and reduction occurs
simultaneously and the product is called TEG (thermal exfoliated-reduced
20 graphene).Fig. 1 shows the FESEM image of synthesized TEG taken by putting a small
amount of powder sample on carbon tape.
Example 2
Preparation of N-doped Graphene
25 Graphene was prepared by the thermal exfoliation of graphite oxide (GO), where GO
was prepared from natural graphite powder using Hummer’s method.
Step a: The TEG obtained from the example 1wasnegatively surface charged with the
anionic polyelectrolyte, poly(sodium 4-styrenesulfonate) (PSS, MW = 70,000, Aldrich)
as described.
30 Step b: TEG was dispersed in an aqueous solution (1 wt. %) of anionic PSS
polyelectrolyte (0.15 mg mL-1) by combination of strong stirring and sonication.
10
Step c: The solution was then stored at 50°C for 12 h.
Step d: The final solution was then filtered and washed several times with de-ionized
(DI) water to remove the excess PSS in the solution followed by drying in a vacuum
oven at 70°C for 12 h..
Step e:Polypyrrole (PPy) was coated on PSS modified TEG (5 PTEG-(poly(sodium 4-
styrenesulfonate)-TEG).) by chemical polymerization of pyrrole (0.5 ml) with ferric
chloride (FeCl3,1.2 g) in hydrochloric acid (HCl, Aldrich) solution (50 ml of 0.1 mol L-
1). This causes the negatively charged graphene to be coated with nitrogen containing
polymer polypyrrole (PPy) using the monomer pyrrole and the oxidizing agent FeCl3 in
10 a medium of 0.1M HCl.
Step f: The material was then filtered and washed with a large amount of water and
subsequently with ethanol to remove the residual oxidant.
Step g: Finally, it was washed with acetone and dried at 60ºC to obtain PPy-PTEG.
The advantage and significance of attaching negatively charged ions on TEG are to coat
15 TEG with nitrogen containing polymer polypyrrole (PPy) starting with the monomer
pyrole. This coating is essential to modify the carbon hexagonal with maximum
nitrogen content.
Step h: PPy-PTEG was heated at 800 ºC in argon atmosphere in order to remove all the
polymers from the graphene surface and incorporating nitrogen atoms in the graphene
20 network yielding N-TEG.
Step i: PPy coated graphene was annealed in argon gas atmosphere and that dopes the
nitrogen atoms into the graphene structure (Figure 3).
Example 3
25 Preparation of Nano lubricant
Nano-lubricants was prepared by dispersing a required amount N-doped Graphene in ID
Fan Lube Oil of NTPC using probe sonication. The probe sonication was done for 30
min with a 20 KHz frequency and power of 500W using probe sonicator. Different
nano-lubricants with different amounts of TEG and N-doped Graphene were prepared.
30 The stability of these nano-lubricants was checked by probing the settlement after onemonth
time.
11
Example 4- Analytical Studies:
Example 4a-FESEM (Field Emission Scanning Electron Microscopy)
Fig. 1 shows the FESEM image of synthesized TEG taken by putting 5 a small amount of
powder sample on carbon tape. The image shows a large area of transparent graphene
sheet with rough and soft wrinkled surface morphology. Transmission electron
microscopy is a powerful technique used extensively to provide definitive identification
of graphene materials. The sample preparation is done by depositing a drop of ethanol
10 dissolved TEG on Cu grid. Figure 2 clearly shows the wrinkles on the surface and
folding at the edges of TEG sheets.
Figures 3 shows the Transmission electron micrograph of nitrogen doped thermally
exfoliated reduced graphene (N-TEG).
15
Example 4b
XRD pattern
Figure 4 shows the XRD pattern of graphite (Gr), graphite oxide (GO) and thermal
exfoliated graphene (TEG). The intense crystalline peak of graphite occurs at ~26°. This
20 is the characteristic peak of hexagonal graphite with a d spacing of 0.34 nm. Upon
conversion of Gr into GO, the peak position shifts to ~10°. The interlayer spacing now
increases to 0.84 nm. This increase in d spacing is due to the intercalation of -OH
containing functional groups in between the graphene layers. After exfoliation of GO
with argon at 1050 °C, the 10° peak disappears and a broad peak appears, starting from
25 ~14° to 30°. The decrease in interlayer spacing to 0.37 nm suggests the removal of
oxygen and water from the GO interlayer during thermal exfoliation. This broad peak is
also suggestive of a loss of the long-range order in graphene.
Example 4c
30 Raman spectra
12
Figure 5 represents the Raman spectra of pristine Gr, GO, TEG. It is observed that the
laser induces defects and at high intensities even causes the burning of graphene. Hence,
all the measurements are done at low laser intensities. The absence of D band in
graphite suggests that graphite used is defect free. However, the overtone of the D-band,
called the 2D band, is present and occurs at about 2717 cm-1. A highly 5 intense G band,
corresponding to the optically allowed E2g phonons at the Brillouin zone center, occurs
at about 1585 cm-1. The Gband of GO is located at 1609 cm-1, while that of TEG is
shifted back to 1589 cm-1, close to the value of pristine graphite indicating the reduction
of GO during hydrogen treatment. In addition a broadening of G band is observed in
10 GO, TEG, and is attributed to an increase in the disorder. The chemical treatments are
done to obtain GO, and its exfoliation to get TEG, induces defects in the graphitic
structure. As a result a broad D-band with intensity comparable to that of the G band is
obtained in GO, TEG. Quite often the ratio between the intensities of the D and G bands
is used to predict the presence of defects in the samples and also the size of the in-plane
15 sp2 domain. The ratio of intensities of D and G-band peak, ID/IG, varies inversely with
the size of the crystalline grains (La) or inter-defect distance, ID/IG=C(λ)/La, where C(λ)
is a wavelength-dependent pre-factor and is equal to C0 + C1×λ, whereC0and C1 are
constants. The ratio of peak intensities of D and G-mode (ID/IG) for TEG is around 0.85
as compared to 0.99 for GO, thus indicating a ‘self-healing’ mechanism resulting in
20 good restoration of the p-conjugated structure.
Example 5
Stability Studies on various types of nano-lubricant:
Nano-lubricants are not stable because nanoparticles are not able to disperse into the
25 lubricants.
Stability in the present nano-lubricant compositions means that there is no sediment
formation over the time. Various experiments were conducted to compare the present
Nano-lubricant compositions having N-doped Graphene and Nano-lubricant
compositions having TEG. Stability of nano-lubricants was studied at room
30 temperature, by subjecting the nano-lubricants to centrifugation at 2,000 rpm for 5 h.
Figures 6 and 7 shows the photographs of the nano-lubricants prepared with TEG in ID
13
Fan Lube Oil of NTPC and N-doped Graphene in ID Fan Lube Oil of NTPC with
different amounts of TEG and N-doped Graphene, respectively. It was observed that
nano-lubricants with N-doped Graphene give the best stability as seen from the figure 7.
The light yellow to brown color in different nano-lubricants indicated the presence of
N-TEG in these nano-lubricants. These nano-lubricants having N-5 doped Graphene are
stable for more than 5h under centrifugation at 2,000rpm without any sedimentation.
Further, in order to optimize the concentration of additive, N-doped Graphene in Nanolubricant
compositions, various concentrations were prepared and tested for their
tribological properties using 4-ball tester under ASTM standard.
10
Table 1. Change in the COF with concentration of additive (N-TEG) at the ASTM
standard
(rotating speed of 600 rpm and constant load of ~392 N at the oil temperature of 75~C).
S.No Oil Type (with N-TEG) Co efficient of friction
(COF)
1. Base Oil 0.225
2. 0. 015625mg/40 ml 0.21
3. 0.03125mg/40 ml 0.20
4. 0.0625mg/40 ml 0.18
5. 0.125mg/40 ml 0.17
6. 0.250mg/40 ml 0.17
7. 0.5mg/40ml 0.32
8. 1mg/40 ml 0.18
9. 1.5mg/40ml 0.20
10. 2 mg/40 ml 0.24
11. 2.5mg/40ml 0.25
12. 5 mg/40 ml 0.23
15
14
Table 1 gives the change in the COF with concentration of additive (N-TEG) at the
ASTM standard (rotating speed of 600 rpm and constant load of ~392 N at the oil
temperature of 750C). Figure 8 shows the dependence of COF with N-TEG (base oil and
0.125 mg/40 ml of base oil; 2.5 mg/40 ml). It is observed that the optimum amount of
the additive (N-TEG) is 0.125mg/40ml for which the maximum 5 decrease of COF is
obtained. It is observed that at the concentration of 0.125mg/40ml and 0.250mg/40ml,
the viscosity almost remains same while the two properties of decrease in COF and
reduced temperature are achieved. So both the concentrations i.e. 0.125mg/40ml and
0.250mg/40ml are giving better results and the preferred range would be 0.125mg/40ml
10 to 0.250mg/40ml.
COF decreases from 0.225 to 0.170 for base oil to 0.125mg/40ml of N-TEG, which is
about 25% reduction in the COF. This decrease in frictional coefficient of N-TEG-oil
nano-lubricants can be attributed to the layered structure of graphite and due to its self15
lubrication. Since, the present graphene consists of 1-2 nm layers as single flakes, it can
act as nano-bearing between moving parts and can reduce the friction. Flake size may
be 1-2 nm layers during running of ID fan due to wear and rotation. Further
experiments were conducted to compare the temperature of engine oil and N-TEG-oil as
a function of increase in the load. Figure 9 depicts the same. The load capacity is
20 determined by increasing the load at regular intervals of 10 min with an increment of
200N. It has been observed that in case of base engine oil, temperature increases to
63°C at 1400 N load, but in NTEG-oil (0.125 mg/40mL), the temperature increases up
to around 48°C at 1400 N load. The temperature thus decreases by 15°C.
25 From the combined observations of table 1, Figure 8 and Figure 9, it is observed that
maximum decrease in COF is observed at the concentration of 0.125mg/40ml and
0.250mg/40ml. Further at a concentration of 0.125mg/40ml, the temperature increase is
much less than base oil. This is because of the presence of the additive N-TEG, due to
which the friction coefficient decreases and hence the temperature increase is small with
30 Nano-lubricant compositions. On the other hand, in the case of base engine oil, the
frictional force on time was increased and hence, the temperature increases rapidly.
15
Thus the nano-lubricant composition of present invention is having a reduced COF and
reduced temperature. Reduced COF and reduced operating temperature decreases the
wear and tear of parts of machines and thereby increases the life of the machine. This
also results in electrical power saving and reduce operating costs of the machine.
Further, it is also desirable to maintain the viscosity of the Nano-lubricant 5 composition
of the present invention while maintaining the properties of reduced COF and reduced
temperature. Viscosity increase changes other properties of the oil such as flow rate etc.
and therefore the viscosity of the nano-lubricant should be the same as the base
lubricant “ID Fan lube oil of NTPC”)Thus experiments were performed to observe the
10 viscosity change of the Nano-lubricant composition with various amount of N-TEG.
The results are provided in Table 2:
Table 2. Change in viscosity with increasing concentration of additive N-TEG.
S.No Oil Type (with NTEG)
Viscosity (in
Pa·s)
1. Base Oil (ID Fan lube oil of NTPC(Servoprime 68))
0.079
N-TEG concentration
2. 0.015625 mg/40 ml 0.076
3. 0.03125 mg/40 ml 0.077
4. 0.0625mg/40 ml 0.079
5. 0.125mg/40 ml 0.072
6. 0.250mg/40 ml 0.071
7. 0.5Mg/40ml 0.072
8. 1mg/40 ml 0.072
9. 1.5mg/40ml 0.074
10. 2 mg/40 ml 0.074
11. 2.5mg/40ml 0.074
12. 5 mg/40 ml 0.074
16
 Parameters 1. 100 Shear Rate (in 1/s) 2. 500 Seconds 3. Room Temperature
It is observed that at the concentration of 0.125mg/40ml and 0.250mg/40ml, the
viscosity almost remains same. It is thus observed that at the concentration of
0.125mg/40ml the viscosity of the Nano-lubricant composition is maintained 5 while the
two properties of decrease in COF and reduced temperature are achieved. It has been
observed that in case of base engine oil, temperature increases to 63°C at 1400 N load,
but in NTEG-oil (0.125 mg/40mL), the temperature increases up to around 48°C at
1400 N load. The temperature thus decreases by 15°C. (Figure 9)
10
It is evident from the above that both the concentrations i.e. 0.125mg/40ml and
0.250mg/40ml are giving better results.
Example 6
Stability Studies of nano-lubricantcomposition having N-doped Graphene:
15 Nano-lubricant compositions tend to sediment over the time. Hence the stability of the
nano-lubricant compositions of the present invention is critical. Stability studies were
performed at room temperature, by subjecting the nano-lubricants to centrifugation at
2,000 rpm for 5 h. These nano-lubricants are stable for more than 5h under
centrifugation at 2,000rpm without any sedimentation. The light yellow to brown color
20 in different nano-lubricants indicates the presence of N-doped graphene in these nanolubricants.
The stability of the Nano-lubricant composition has been shown in Figure
10. The target stability is for at least 12 months. It was found that the obtained nanolubricants
having N-doped graphene were stable for more than 3 months in the
stationary state.
25 It was also observed that no sediment is formed in Nano-lubricant compositions having
N-doped Graphene in the range of 0.125mg/40ml to 5mg/40ml.This excellent stability
of the obtained nano-lubricants is due to the doping of nitrogen atoms in the graphene
sheets, which may interact with the base lubricant molecules thereby retarding the
agglomeration of N-G and hence sedimentation.

WE CLAIM:
1. A nano-lubricant composition having improved lubricant properties, comprising:
(a) a lubricating 5 fluid; and
(b) N-doped graphene (N-TEG) dispersed in said fluid, wherein said N-doped
graphene is in the range of 0.125mg/40mlto 5mg/40mlof fluid.
2. The nano-lubricant composition as claimed in claim 1, wherein said N-doped
10 graphene is present in an amount ranging from 0.125mg/40ml to 0.25mg/40ml.
3. The nano-lubricant composition as claimed in claim 2, wherein said N-doped
grapheme is present in an amount of 0.125mg/40ml.
15 4. The nano-lubricant composition as claimed in claim 1, wherein said N-doped
graphene comprises pristine graphene, graphene oxide, or a combination thereof.
5. The nano-lubricant composition as claimed in claim 1, wherein the lubricant
fluid is selected from the group consisting of petroleum distillates, synthetic
20 petroleum oils, vegetable oils, ID fan oil and combinations thereof.
6. The nano-lubricant composition as claimed in claim 5, wherein the lubricant
fluid is preferably ID Fan lube oil.
25 7. The nano-lubricant composition as claimed in claim 1, wherein said N-doped
graphene have an average particle size ranging from 3 nm to 5 nm.
8. The nano-lubricant composition as claimed in claim 1, wherein the composition
has a coefficient of friction ranging from0.17to 0.21
30
18
9. The nano-lubricant composition as claimed in claim 1, wherein the composition
has a viscosity ranging from 0.071Pa.s. to0.076 Pa.s.
.
10. A method of preparing Nano-lubricant composition of claim 1, the method
comprises of the 5 following steps:
i. converting the natural graphite to graphite oxide;
ii. thermal exfoliation of graphite oxide prepared from step (i) to
form TEG (thermal exfoliated-reduced graphene);
iii. negatively charging the TEG of step (ii) with anionic
10 polyelectrolyte;
iv. dispersion of TEG obtained from step (iii);
v. chemical polymerization of the product of step (iv) with
polypyrrole;
vi. annealing at 800ºC in inert gas atmosphere and thereby reducing
15 the graphite oxide to N-TEG (nitrogen doped graphene), and
vii. dispersing the N-TEG in lubricating oil using probe sonication to
form nano-lubricant.
11. The method of preparing Nano-lubricant composition as claimed in claim 12,
20 wherein the anionic polyelectrolyte is PSS (poly(sodium 4-styrenesulfonate)) of
molecular weight of 70,000.
12. The method of preparing Nano-lubricant composition as claimed in claim 12,
wherein the sonication treatment is done for 30min with 20 KHz frequency and
25 power of 500W.
13. The method of preparing Nano-lubricant composition as claimed in claim 12,
wherein the inert gas is argon.
19
14. The method of preparing Nano-lubricant composition as claimed in claim 12,
wherein the thermal exfoliation step is conducted for 30s at 1000˚C.
15. The method of preparing Nano-lubricant composition as claimed in claim 12,
wherein said N-doped graphene comprises of at 5 least one dopant.
16. The method of preparing Nano-lubricant composition as claimed in claim 12,
wherein the dopant is nitrogen containing polymer, polypyrrole.
10 Dated this 19th day of September 2015