In the present investigation, exfoliated graphite sheets were obtained from the thermo-chemical treatment
of natural graphite flakes. In this process, the graphite expands almost 300-350 times of its original volume
and takes the shape of worms. These worms can be pressed or rolled into any desired shape without any
binder. The exfoliated graphite sheets show excellent electrical properties i.e. high dielectric constant
(ε = 6.374 ×107) and comparatively low dielectric loss (tanδ = 138) across the frequency in the range 50 Hz to
30 MHz and temperature in the range 40-300 °C. The products developed from exfoliated graphite can have
very good sealing applications in industrial areas, especially for gaskets in the automobile industries

Deshmukh, Kalim

Jain, P.K.

Joshi, Girish M.

English

SocioEconomic Challenges Journal (Sumy State University)

JOURNAL OF NANO- AND ELECTRONIC PHYSICS ЖУРНАЛ НАНО- ТА ЕЛЕКТРОННОЇ ФІЗИКИ 
Vol. 8 No 1, 01022(3pp) (2016) Том 8 № 1, 01022(3cc) (2016) 
 
 
2077-6772/2016/8(1)01022(3) 01022-1  2016 Sumy State University 
Fabrication and Excellent Dielectric Performance of Exfoliated Graphite Sheets 
 
Girish M. Joshi1,*, Kalim Deshmukh1, P.K. Jain2 
 
1 Polymer Nanocomposite Laboratory, Material Physics Division, School of Advanced Sciences,  
VIT University, Vellore-632014, TN, India 
2 Center for Carbon Materials, International Advanced Research Center for Powder Metallurgy and New Materials, 
Autonomous Center of Department of Science and Technology, P. O. Balapur, Hydrabad-500 005, India. 
 
(Received 04 December 2015; published online 15 March 2016) 
 
In the present investigation, exfoliated graphite sheets were obtained from the thermo-chemical treat-
ment of natural graphite flakes. In this process, the graphite expands almost 300-350 times of its original vol-
ume and takes the shape of worms. These worms can be pressed or rolled into any desired shape without any 
binder. The exfoliated graphite sheets show excellent electrical properties i.e. high dielectric constant 
(ε  6.374  107) and comparatively low dielectric loss (tanδ  138) across the frequency in the range 50 Hz to 
30 MHz and temperature in the range 40-300 C. The products developed from exfoliated graphite can have 
very good sealing applications in industrial areas, especially for gaskets in the automobile industries. 
 
Keywords: Carbon materials, Dielectrics, Electrical properties, Electron microscopy. 
 
 PACS numbers: 81.05.ue, 72.80.Vp 
 
 
                                                                
* varadgm@gmail.com 
1. INTRODUCTION 
 
The Single layer graphene has attracted much atten-
tion in the past several years because of its exceptional 
properties such as high surface area, high mechanical 
strength and high elasticity [1, 2]. Obtaining graphene 
in the form of nanoribbon sheets is of technological im-
portance and can be utilized as a compatible medium [3]. 
The graphene nanoribbon sheets with an optimum size 
of 40 nm produced by chemical treatment method has 
been used widely for several technological applications. 
The shaping and yielding of the graphite is one of the 
key interest to explore the possibility to use this materi-
al for electrical circuits, field effect transistors and gra-
phene based integrated circuits. It is also most suitable 
for several industries such as chemical, biomedical as 
machined and processed nano entity [4, 5]. Numerous 
studies have been under taken to exfoliate graphene 
sheets by soincation [6], chemical route [7], photo-
catalytic process [8], ion based electro-chemical route [9], 
modular shear loading and mechanical drilling [10-12]. 
Herein, we developed exfoliated graphite sheets by 
thermo-chemical treatment of graphite flakes. The 
microstructure of these exfoliated graphite sheets were 
studied by SEM. The impedance analyzer was used to 
study the electrical properties of the exfoliated graphite 
sheets as a function of frequency in the range 50 Hz-
30 MHz  and temperature in the range 40-300 oC. 
Preparation exist, and submitted manuscript should 
be ready for publication. Simultaneously with the content 
reviewing, any manuscript is checked for compliance to 
the stated formatting requirements. If the checking is 
failed, the manuscript is returned to authors for revision. 
 
2. EXPERIMENTAL AND MATERIALS 
 
2.1 Materials 
 
Natural Graphite flakes were supplied by Carbotech 
Engineers PVT, Ltd, Jaipur, India. Sulphuric acid 
(H2SO4) and nitric acid (HNO3) was purchased from 
Sisco Research Laboratories, PVT, Ltd., India. 
 
2.2 Protocol to Obtain Exfoliated Graphite Sheets 
 
Graphite was chemically treated before its exfolia-
tion. There are many oxidants, which can be used for 
intercalation like Nitric acid (HNO3), Hydrogen peroxide 
(H2O2), Potassium di-Chromate (K2Cr2O7) etc. In the 
present study, the mixture of Sulphuric acid (H2SO4) 
and Nitric acids (HNO3) in a 3 : 1 ratio was used for 
graphite intercalation. Once the graphite flakes were 
intercalated, they were subjected to thermal shock at 
1000 C in a specially designed furnace. The thermal 
shock results into a very high expansion of these graph-
ite flakes, almost 300 to 350 times the original volume of 
graphite flakes, depending on the process parameters. 
The surface area of exfoliated graphite sheets has 
been obtained using (11-2370) Gemini, Micromeritics, 
USA, surface area analyzer at a regeneration tempera-
ture of 200 °C for 2 h with N2 purging. 
 
 
 
Fig. 1 – Process flow chart of exfoliated graphite product 
 GIRISH M. JOSHI, KALIM DESHMUKH, P.K. JAIN J. NANO- ELECTRON. PHYS. 8, 01022 (2016) 
 
 
01022-2 
2.3 Characterizations 
 
The surface morphology of the sample was analyzed 
using Phillips XL 30 Series field emission scanning 
electron microscope operating at an accession voltage of 
25 kV under vacuum (10 – 5 mbar). 
The dielectric properties of exfoliated graphite 
sheets were measured using a Newton’s 4th Impedance 
Analyzer (PSM1735, N-4L,UK) as a function of fre-
quency in the range 50 Hz to 30 MHz and temperature 
in the range 40-300 C. 
 
3. RESULTS AND DISCUSSION 
 
The exfoliated graphite sheet was produced from 
unique thermo-chemical treatment of natural graphite 
flakes.  The process flow chart for exfoliation of graph-
ite is shown in Fig. 1. In this process, the graphite 
expands almost 300-350 times of its original volume 
and takes the shape of worms. These worms can be 
pressed or rolled into any desired shape without any 
binder. The compression or rolling of exfoliated graph-
ite particles give a flexible sheet which is usually 
named as flexible graphite foil. The sheet is having an 
excellent salient features such as impermeable to gases 
and fluids and can be used from – 200 to + 500 °C in 
the oxidizing atmospheres and up to 2500 °C in the 
non-oxidizing atmosphere or vacuum. It cannot be 
wetted with molten glass, metals etc. It offers high 
anisotropy in electrical and thermal conductivities. It 
exhibits excellent temperature shock resistance. It does 
not age or creep. It is self-lubricating and can be easily 
cut and punched. It is resistant to radiation doses of 
any magnitude occurring in nuclear power stations. 
The obtained graphite worms are pressed and rolled 
into graphite sheets and tapes as shown in Fig. 2. 
 
 
 
Fig. 2 – Flexible Graphite tapes and foils 
 
 
 
Fig. 3 – Micrographs of (a) Graphite Flakes (b, c) Exfoliated 
Graphite Worms 
It was interesting to know the surface area of the 
graphite worms produced by graphite flakes. The sur-
face area and the degree of exfoliation of graphite pow-
ders is given in Table 1. 
 
Table 1 – Surface area and degree of exfoliation of Graphite 
powders 
 
Sample Degree of Exfo-
liation  
Active Surface 
area (m2/gm) 
Graphite Flakes 
(+40) 
– 1.5 
Exfoliated 
Graphite 
350 45.5 
 
It can be seen that the surface area of exfoliated 
graphite sheet was increased upon exfoliation. The 
SEM micrographs of worms shows graphite expansion 
in c-direction only and in a-direction there was no 
change. At higher magnifications of graphite worms 
one can observe the honeycomb structure of graphite 
layers. A very high expansion in the c-direction of 
graphite flakes, was observed through SEM images as 
shown in Fig. 3 (a-c). The microstructure of worm was 
like a honeycomb structure or Chinese accordion.  
Recently, the electrochemical impedance spectros-
copy technique was employed to distinguish between 
graphene, graphene oxide and different graphene based 
materials [13, 14]. In the present study, the dielectric 
properties of exfoliated graphite sheets were carried 
out and the results are depicted in Fig. 4. 
 
 
 
 
 
Fig. 4 – Dielectric Constant (a) and Dielectric Loss (b) of  
G-sheets as function of temperature 
 FABRICATION AND EXCELLENT DIELECTRIC PERFOMANCE… J. NANO- ELECTRON. PHYS. 8, 01022 (2016) 
 
 
01022-3 
The exfoliated graphite sheets show very high die-
lectric constant (ε  6.374  107) and comparatively low 
dielectric loss (tanδ  138) as a function of frequency in 
the range 50 Hz to 30 MHz and temperature in the 
range 40-300 C. The dielectric loss can be optimized 
further by chemically modifying the exfoliated graphite 
sheets for its implementation in industrial applica-
tions. Hence, such materials with superior dielectric 
properties can be useful in electrical and electronic 
industry for capacitors, supercapacitors and/or embed-
ded capacitors applications. 
The exfoliated graphite sheet was produced from 
unique thermo-chemical treatment of natural graphite 
flakes. In this process the graphite expands almost 300-
350 times of its original volume and takes the shape of 
worms. Therefore, the products developed from this 
process are not only retaining the excellent inherent 
properties of graphite but also complex processing free 
from carbonizations and graphitization can be avoided. 
Moreover, the products are flexible in nature unlike 
brittle as in the case of synthetic graphite. The exfoliated 
graphite sheet show excellent electrical properties such 
as high dielectric constant and comparatively low dielec-
tric loss. Hence, such materials can be useful in different 
industries such as in electronic, electrical and nuclear 
industry to prepare prototype products. 
 
ACKNOWLEDGEMENTS 
 
The authors wish to thank Naval Research Board, 
Defence Research and Development organization (NRB-
DRDO), New Delhi for providing facility for electrical 
characterization under project No 259/Mat./11-12.
 
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Fabrication and Excellent Dielectric Performance of Exfoliated Graphite Sheets

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