Field of the Invention
The present invention relates to a process for developing a coating of reduced
graphene oxide on the surface of a large metal sheet and glass. This process
comprises coating of seedlac and Ni-seedlac solution on the metal surface
followed by heating under controlled atmosphere.
Background of the Invention
Graphene is an allotrope of carbon, which contains a single atomic sp2 carbon
arranged in honeycomb fashion making a two-dimensional sheet. This material
exhibits various unusual properties such high electron mobility (2 x 105 cm2 V-1 s-
1) at room temperature, thermal conductivity ( 5 x 105 Wm-1K-1) and high
Young's modulus (~lTPa) [Science, 306, 666, 2004; Nature, 438, 197, 2005;
Phys. Rev. Lett., 100, 016602, 2008; Science, 321 , 385, 2008 ]. Besides,
coating of graphene over the surface of metal improves the corrosion resistance
of metal [ACS Nano, 6, 1102, 2012]. Moreover, the properties of graphene have
been tailored by substituting heteroatom like oxygen on the graphene sheet.
Such graphene with the heteroatom has been coined as a "reduced graphene
oxide" in the literature (Angew Chem. Int. Ed. 49, 9336, 2010). Several methods
have been reported in the literature for the deposition of graphene on metal
surface, which includes chemical vapor deposition (CVD) method. However, CVD
process is expensive and is incapable of a large scale production.
Several methodologies have been patented on coating of graphene or reduced
graphene oxide on the surface of metals sheets. US 20130143067 Al discusses
about coating of graphene on metal plates such as steel, aluminum, copper and

its wire by using chemical vapor deposition and spray technique. The spray
technique uses polymer mixed reduced graphene oxide, which is to be a
composite instead of pure reduced graphene oxide. Therefore, the metal sheet
coated with the composite will have different properties than the metal coated
with the pure reduced graphene oxide. Reference may also be made to a patent
US 20090110627 Al, wherein the synthesis of graphene sheet is made from
different carbon sources, which includes carbon monoxide, alcohols and
polycydic aromatic compounds. US 20110104442 Al, also describes deposition
of graphene by CVD method directly on substrates using carbon sources other
than graphite. US 20100021708 Al discloses the deposition of graphene on a
SiO2 / Si substrate. However, the deposition process is very slow because it
involves several coating and chemical etching steps.
Sun et al. reported the growth of graphene from Poly(methyl methacrylate
(PMMA) and sucrose on Cu substrate [Nature 468, 549, 2010]. WO 2012064102
A3 disclosed the coating of graphene on steel using acetylene gas as a carbon
source. Reference may also be made to a patent US13704054 Al, which claimed
coating of graphene on steel surface for corrosion resistance. This method
comprises the synthesis of reduced graphene oxide from graphite powder by
oxidation-reduction process followed by mixing with polyimide. Subsequently, the
reduced graphene oxide-polyimide composite was coated on the steel surface.
However, process is time consuming and polyimide has poor adherence to steel
surface. In light of the above discussed references, it is evident that graphene
coating has been disclosed and developed using various carbon sources and CVD
technique however, the large scale production remain a challenge.

On the other hand, coating of graphene by solution method is well established
[Int. J. Chem. Eng. App., 3, 453, 2012] and is capable of a large scale
production. The solution method follows the following procedure; (a) graphite
powder needs to be oxidized to minimize the vander Walls forces between, the
two graphitic layers, (b) the prepared graphite oxide is dispersed in water by
sonication, (c) the dispersed graphite oxide solution is reduced using the
reducing agents such as hydrazine, HI acid, NaBH4, citric acid etc. (d) the
reduced product is dispersed in a suitable organic solvent and is used for
coating. But, this method involves several disadvantages that limit the process to
be used at industrial scale for the following reason; the conversion of graphite
powder to graphite oxide involves several steps which is time consuming and
uses some harmful acids likeHNO3 and H2SO4. Further, reducing agents are also
toxic, handling them in large scale is a problem and the reduced product has a
very low dispersity in organic solvent and hence, requires sonication for a long
time. Also, the adherence of the graphene sheets with the metal surface is very
low. Besides, the graphite used for the carbon source is expensive.
Some reports show that natural carbon source like flower petal can be used to
produce graphene in a large scale at low cost [Carbon 50, 4123, 2012].
However, graphene produced from natural sources finds difficulty to integrate on
the metal/alloy surfaces, therefore, finds limited application in the area of
graphene coated metal sheets.
Hence, there is need of an invention that can synthesize graphene at large scale
using available carbon sources. Further, process should be cost effective and
commercially viable.

Objects of the Invention
An object of the present invention is to provide a process for the coating of
reduced graphene oxide on a metal substrate.
Another object of the invention is to synthesize reduced graphene oxide at large
scale using a commercially viable method.
Another object of the invention is to develop a process of synthesizing reduced
graphene oxide using chemicals that are not hazardous in nature.
One more object of the invention is to synthesize reduced graphene oxide using
naturally available carbon resources.
Still another object of the invention is to develop a reduced graphene oxide
formulation that can be applied using simple coating techniques such as dip
coating.
BRIEF DESCIPTION OF THE DRAWINGS
Fig. 1 depicts chemical structure of seedlac.
Fig.2 is a XPS spectrum of seedlac.
Fig. 3 is a Raman spectrum of reduced graphene oxide coated steel.
Fig.4 XPS spectrum of reduced graphene oxide coated steel.
Fig.5 Backscattered image with EDX analysis of reduced graphene oxide coated
steel.
Fig.6 Raman spectrum of reduced graphene oxide coated on oxidized steel.
Fig.7 Raman spectrum of reduced graphene oxide coated Cu.

Fig.8 XPS spectrum of reduced graphene oxide coated Cu.
Fig.9 Backscattered image of reduced graphene oxide coated Cu with EDX
analysis.
Fig. 10 Raman spectrum of reduced graphene oxide coated steel. The coating is
developed using Seedlac and NiCI2 solution.
Fig. 11 Backscattered and secondary images of reduced graphene oxide coated
Nickel sheet with EDX analysis.
Fig. 12 XPS data of reduced graphene oxide coated glass.
Fig. 13 Backscattered image of reduced graphene oxide coated glass with EDX
analysis.
Fig. 14 TEM micrograph of the reduced graphene oxide sheet with SAED pattern.
Summary of the Invention
The present invention provides a process for developing a reduced graphene
oxide coating on a metallic substrate such as steel, copper, zinc, nickel,
aluminum and alloys thereof. The coating can be further developed on a glass
substrate as well. The current process comprises dip coating of the substrate in
seedlac or seedlac-Nickel chloride (NiCI2) solution followed by heating in the
range under controlled atmosphere. The seedlac or seedlac-NiCI2 solution is
prepared in a C1-C4 alcohol such as methanol, ethanol, isopropanol or tert-butyl
alcohol. Preferably, a C2-C4 alcohol is used. The substrate is dipped in to the
seedlac or seedlac-Nickel chloride (NiCI2) solution one or more times and then
dried in air. The dried substrate is then heated under controlled atmosphere of
Ar / N2 / Ar-H2 / N2- H2 at a different flow rate ranging from 100 to 500 sccm for
a period of 10 to 120 minutes

Description of the Invention
Graphene with some oxygen content was termed as reduced graphene oxide.
Graphene variant as per the current invention also contains oxygen content and
hence, has been termed reduced graphene oxide throughout the invention.
Seedlac is a natural adhesive gum and is also known as natural varnish. Seedlac
contains cyclic six and five membered carbon rings with a long aliphatic chain
attached hydroxyl and acetate functional groups as depicted in figure 1 & 2.
Current invention makes use of seedlac as carbon source for synthesis of
reduced graphene oxide. Seedlac can be transformed to reduced graphene oxide
under optimized experimental conditions, as the bond rearrangement occurs
through removal of hydroxyl functional groups on heating. This process
overcomes some of the above problems associated with the large area coating of
graphene on metal surface.
In an embodiment of the present invention, the process for coating of reduced
graphene oxide on a substrate comprises:
(i) Preparation of seedlac solution in an alcohol. In an embodiment of the
invention, alcohol is selected from ethanol, isopropanol, tert-butyl
alcohol and a mixture thereof. Methanol can also be used however, it
is toxic compared to C2-C4 alcohols. The concentration of seedlac
solution varies in the range of 10 - 100 gram / liter of the alcohol. The
seedlac solution is prepared by heating seedlac in the C2-C4 alcohal at
a temperature ranging between 60 to 90°C for a period of 10 to 60
minutes to prepare a homogeneous solution.

(ii) Coating of the viscous seeldlac solution on the substrate. In an
embodiment of the current invention, the substrate is selected from
steel, copper, nickel and alloys thereof. In another embodiment of the
invention, the substrate is glass. The coating thickness of seedlac
solution on the substrate surface is controlled by varying the number
of dipping of the substrate in the seedlac solution. In an embodiment
of the current invention, the substrate is dipped in the seedlac solution
in the range of 1 to 20 times. The substrate is dried in air atmosphere
for a period of 1 to 10 minutes after each dipping.
(iii) Heating the seedlac coated substrate in the temperature range of 400
to 1200°C under controlled atmosphere of Ar / N2 / Ar-H2 / N2- H2 at a
different flow rate ranging from 100 to 500 sccm for a period of 10 to
120 minutes. In an embodiment of the current invention, substrate can
be heated using an electro-heating furnace.
In an embodiment of the current invention, Nickel chloride (NiCI2) is added to the
seedlac solution in the weight ranging from O.OOlg to O.lg per volume of 100 to
1000 ml seedlac solution. Coating thickness of reduced graphene oxide on the
substrate was observed in the range of 2-100 nm.
The following examples are given by way of illustration of the working of the
invention in actual practice and therefore should not be construed to limit the
scope of the present invention.
Example-1
Seedlac solution was made by adding 2g of seedlac in isopropanol solvent of
volume in the range of 100 to 500 ml at a temperature ranging between 60 to
90°C. The seedlac solution was coated over the surface of steel, copper, zinc,
nickel, aluminum and their alloys by dip coating followed by air drying at room

temperature. The thickness of coating layer was varied by the number of
clippings. The coated metal sheets and glass were heated using an electro-
heating furnace in the temperature range of 400 to 1200°C under controlled
atmosphere of Ar / N2 / Ar-H2 / N2- H2 at the flow rate of 100 to 500 sccm for a
period of 10 to 120 minutes. The heated surface of steel, copper, zinc, nickel,
aluminum and alloys was characterized using Raman spectroscopy, X-ray
photoelectron spectroscopy and electron microscopy (Fig.3 -9).
Example 2
Seedlac solution was prepared adding 2g of seedlac in isopropanol solvent of
volume in the range of 100 to 500 ml at a temperature ranging between 60 to
90°C. NiCI2-seedlac solution was made by adding NiCI2 of weight ranging from
O.OOlg to O.lg in seedlac solution of a volume between 100 to 1000 ml. The
resulting solution was coated over the surface of steel, copper, zinc, nickel,
aluminum, alloys and glass by dip coating followed by air drying at room
temperature. The coated metal sheets and glass were heated using an electro-
heating furnace in the temperature range of 400 to 1200°C under controlled
atmosphere of Ar / N2 / Ar-H2 / N2- H2 at the flow rate of 100 to 500 sccm for a
period of 10 to 120 minutes. The heated metal sheets and glass were
characterized using Raman spectroscopy and X-ray photoelectron spectroscopy
(Fig. 10 & 11).
Example 3
Seedlac solution was made by adding 2g of seedlac in isopropanol solvent of
volume in the range of 100 to 500 ml at a temperature ranging between 60 to
90°C. The seedlac solution was coated over the glass surface by dip coating
followed by air drying at room temperature. The thickness of coating layer was
varied by the number of dipping. The coated metal sheets and glass were heated
using an electro-heating furnace in the temperature range of 400 to 1200°C

under controlled atmosphere of Ar / N2 / Ar-H2 / N2- H2 at the flow rate of 100 to
500 sccm for a period of 10 to 120 minutes. The heated surface of steel, copper,
zinc, nickel, aluminum, alloys and glass was characterized using X-ray
photoelectron spectroscopy and electron microscopy (Fig. 12 -14).
(i) The XPS data of the coated reduced graphene oxide exhibits the carbon
to oxygen (C / O) ratio of better than 39:1 and the full width half
maxima of Cls is less than 1.4 eV.
(ii) The Raman data of the coated reduced graphene oxide exhibits the ID /
IG value of less than 0.8.
(iii) The observed number of layers in reduced graphene oxide is around 10
from TEM and Raman data (Nature Nanotech., 8, 235 (2013).
(iv) The sheet resistance of the reduced graphene oxide over glass is less
than 3 kOhm.
The current process of synthesizing reduced graphene oxide coating on a
substrate has a number of advantages. The process uses seedlac as a natural
carbon source for direct coating of reduced graphene oxide on a metal surface.
The process of coating is very simple and can be easily adapted to coat steel
surfaces or any other metallic surface. Further, the process does not make use of
any hazardous chemicals and hence, is an environmentally process. It was
further tested and validated that current process can be used to coat reduced
graphene oxide even on oxidized steel surface.
Although exemplary embodiments of the present invention have been described
in detail hereinabove, it should be clearly understood that many variations and
modifications of the basic inventive concepts herein taught which may appear to
those skilled in the present art will still fall within the spirit and scope of the
present invention, as defined in the appended claims.

We claim:
1. A process for synthesizing reduced graphene oxide from seedlac on a
substrate, the process comprising:
preparing the seedlac solution in a C2-C4 alcohol;
dipping the substrate in to the seedlac solution one or more times;
and
heating the substrate in the temperature range of 400°C to 1200°C
under controlled atmosphere of Ar / N2 / Ar-H2 / N2- H2 at the flow
rate of 100 to 500 sccm for a period of 10 to 120 minutes.
2. The process as claimed in claim 1, wherein the substrate is a metallic
sheet.
3. The process as claimed in claim 1, wherein the substrate is a glass
sheet.
4. The process as claimed in claim 2, wherein the metallic sheet is made
of a material selected from the group consisting of steel, copper,
zinc, nickel, aluminium and the alloys thereof.
5. The process as claimed in claim 1, wherein the C2-C4 alcohol
comprises ethanol, isopropanol and mixture thereof.
6. The process as claimed in claim 1, wherein the substrate is an
oxidized steel surface.

7. The process as claimed in claim 1 further comprising the step of
drying the substrate after each dipping in to the seedlac solution by
keeping the substrate in air atmosphere for a period of 1 to 10
minutes.
8. The process as claimed in claim 1, wherein the seedlac solution is
prepared by heating seedlac in the C2-C4 alcohol at a temperature
ranging between 60°C to 90°C for a period of 10 to 60 minutes.
9. The process as claimed in claim 1 further comprising the step of
adding Nickel Chloride to the seedlac solution in the C2-C4 alcohol.
10. The process as claimed in claim 1, wherein the concentration of
seedlac is in the range of 10 -100 gram / liter of the C2-C4 alcohol.
11. The process as claimed in claim 1, wherein the substrate is heated
using an electro-heating furnace.
12. A process for coating a substrate with reduced graphene oxide, the
process comprising:
preparing a seedlac solution in a C2-C4 alcohol;
dipping the substrate in to the seedlac solution one or more times;
and

heating the substrate in the temperature range of 400°C to 1200°C
under controlled atmosphere of Ar / N2 / Ar-H2 / N2- H2 at the flow
rate of 100 to 500 sccm for a period of 10 to 120 minutes.
13. The process as claimed in claim 12, wherein the substrate is a
metallic sheet.
14. The process as claimed in claim 12, wherein the substrate is a glass
sheet.
15. The process as claimed in claim 13, wherein the metallic sheet is
made of a material selected from the group consisting of steel,
copper, zinc, nickel, aluminium and the alloys thereof.
16.The process as claimed in claim 12, wherein the C2-C4 alcohol
comprises ethanol, isopropanol and mixture thereof.
17.The process as claimed in claim 12, wherein the substrate is an
oxidized steel surface.
18.The process as claimed in claim 12 further comprising the step of
drying the substrate after each dipping in to the seedlac solution by
keeping the substrate in air atmosphere for a period of 1 to 10
minutes.
19.The process as claimed in claim 12, wherein coating thickness of
reduced graphene oxide is in the range of 2-100 nm.

20.The process as claimed in claim 12 further comprising the step of
adding Nickel Chloride to the seedlac solution in the C2-C4 alcohol.
21.The process as claimed in claim 12, wherein the seedlac solution is
prepared by heating seedlac in C2-C4 alcohol at a temperature
ranging between 60°C to 90°C for a period of 10 to 60 minutes.
22. The process as claimed in claim 12, wherein the substrate is heated
using an electro-heating furnace.
23.The process as claimed in claim 12, wherein the concentration of
seedlac is in the range of 10 - 100 gram / liter of C2-C4 alcohol.

ABSTRACT

The present invention relates to synthesizing reduced graphene oxide on the
surface of a metal sheet and glass. The invention particularly relates to a process
for coating a substrate with reduced graphene oxide using seedlac as a carbon
source. As per the process of the current invention, a solution of seedlac is
prepared in an alcohol and the substrate is dipped in to the solution for one or
more time. The substrate is then dried in air for 1-10 minutes and thereafter,
heated to a temperature range of 400 to 1200°C under controlled atmosphere of
Ar / N2 / Ar-H2 / N2- H2 at a different flow rate ranging from 100 to 500 sccm for
a period of 10 to 120 minutes.