Mechanisms of Microwave Absorption in Carbon Compounds from Shungite

Abstract

According to SEM, X-ray phase analysis, Raman scattering data features of nanostructural changes in shungite carbon structure were found when processing shungite in 52 % hydrofluoric acid. It is found that conductivity increases up to the values of electrical graphite and absorption of microwave radiation also increases at frequencies up to 40 GHz, which, along with dielectric losses, is due to intense processes of both scattering at laminar carbon structures and absorption of electromagnetic energy.

Full text

JOURNAL OF NANO- AND ELECTRONIC PHYSICS ЖУРНАЛ НАНО- ТА ЕЛЕКТРОННОЇ ФІЗИКИ
Vol. 5 No 4, 04023(3pp) (2013) Том 5 № 4, 04023(3cc) (2013)
The article was reported at the International Conference «Physics and Technology of Nanomaterials and Structures», Kursk, 21-22 November, 2013
2077-6772/2013/5(4)04023(3) 04023-1  2013 Sumy State University
Short Communication
Mechanisms of Microwave Absorption in Carbon Compounds from Shungite
S. Emelyanov1, A. Kuzmenko1, V. Rodionov1, M. Dobromyslov2
1 Southwest State University, 94, 50 Let Oktyabrya Str., 305040 Kursk, Russia
2 Pacific National University, 136, Tihookeanskaya Str., 680035 Khabarovsk, Russia
(Received 24 October 2013; published online 10 December 2013)
According to SEM, X-ray phase analysis, Raman scattering data features of nanostructural changes in
shungite carbon structure were found when processing shungite in 52 % hydrofluoric acid. It is found that
conductivity increases up to the values of electrical graphite and absorption of microwave radiation also
increases at frequencies up to 40 GHz, which, along with dielectric losses, is due to intense processes of
both scattering at laminar carbon structures and absorption of electromagnetic energy.
Keywords: Scanning electron microscopy, X-ray diffraction, Small-angle X-ray scattering, Raman
scattering spectroscopy, Mapping of Raman shift distributions, Microwave absorption, Shungite.
PACS numbers: 07.78. + s, 07.85.Fv, 42.65.Dr, 07.57. – c
1. INTRODUCTION
Micro- and nanostructural features of naturally-
doped minerals-shungites that have particles not
greater than 100 nm in size and coherent scattering
areas of several nanometers are of interest for studying
the attenuation mechanisms in microwave range [1, 2].
So mechanically and chemically disintegrated
shungites from Sazhogin deposits have been studied
according to the procedure described in [3] with the
chemical processing 6HF + SiO2 → H2[SiF6] + 2H2O.
2. EXPERIMENTAL SECTION
Element distribution in cleavages of chosen
samples (JEOL JSM6610LV, EDX Oxford
Instruments) was typical and is given in Fig. 1a-d
with mapping data with a resolution of 1 m. After
chemical processing the structure turned
delaminated, and the particles became oval with an
average diameter of up to 100 m (Fig 2a). The
carbon content, according to increase by 6 %. The
increase in content of metals occurs and the silicon
content dropped off ten-fold.
Fig. 1 – SEM-images of shungite (a) with a resolution of 1 m with elemental contrast: b – C, c- Si, d- O
a
b
c
d

S.EMELYANOV, A. KUZMENKO, V. RODIONOV, ET AL. J. NANO- ELECTRON. PHYS. 5, 04023 (2013)
04023-2
Fig. 2 – SEM of HF processed shungite powder (top).
Eelemental composition (%) before (black) and after
processing (grey) (bottom)
Fig. 3 – X-ray patterns of shungite before and after processing
Analysis of shungite phase composition (GBC
ЕMMA, CuK) before and after processing is given in
Fig. 3. It is found that it belongs to shungites of the
1 type (reflection in the neighborhood of 2

 80[2]).
The reflections of all modifications of quartz and
carbon structures typical of shungite were observed.
Using diffraction patterns before and after processing
the sizes of carbon nanostructures have been
calculated (the coherent scattering areas (L) of X-ray
radiation) from the Scherer equation: L  k/(Bcos

).
The reflection width was considered by the level 0.5
(B), θ is the Bragg angle,

 0.154178 nm for CuK,
k is a constant equal to 0.9 for reflections to the plane
(002) and 1.84 to the plane (10) according to [2]. For
the plane (100) we adopted k  1.4. The predicted
sizes of L are shown in Table 1 in comparison both
with sizes in [2] and those according to small-angle
X-ray scattering data (SAXSees mc2, CuK).
Table 1 – Predicted sizes of carbon nanostructures
Samples
B,
degree
2

,
degree
L100, nм
Initial
4.5
26
3.6
After HF
8.0
26
5.5
According
to [2]
3.9
–
5.4
SAXSess
–
–
5.1
Raman scattering spectra on samples before and
after processing shungite were examined with a
resolution of 500 nm with a spectral resolution of up
to 0.8 сm – 1 (OmegaScope, SmartSPM) and are
shown in Fig.4. I this case excited were lines D – A1g
(1354 сm – 1) – vibration of the whole carbon
structure and G – E2g (1593 сm – 1) – antisymmetric
vibration of carbon structures and the second order
lines 2D – 2688 and 2G – 2916 сm – 1. The
amorphization level K by the variation of ID – A1g и
IG – E2g: K  (ID + IG)/(ID – IG) in shungite before and
after processing was  5 и  8, respectively. The lines
of fullerenes 450 and 190 сm – 1 with their content of
up to 2 % were found in Raman spectra by mapping
the cleavage surfaces of shungite (scans of
900 spectra 60  60 m).
Conductivity of shungite samples in the form of
pressed tablets (220 аtm, 1  10  20 mm) examined
with the LCR-meter Instek LCR-819 is characterized
by an order of magnitude increase, up to the value for
ordinary graphite. Nonlinear increase is observed to
600 K and a succeeding saturation in the range
measured to 800 K. All samples are characterized by
high absorbing capacity (Fig. 5a, b) of microwave
radiation (PNA-L Agilent N5230A, 12.6 – 40 GHz).
Fig. 4 – Raman spectra of shungite before ( ) and
after HF processing ( ). One of 900 scans of
Raman scattering with lines С60 ( )
3. RESULTS AND DISCUSSION
The transmission coefficient within the range
19.6 and 21.7 GHz was equal on average to – 21 dB,
and on 29.1 GHz – 39 dB. The shungite transmission
coefficient S21 is probably due to multiple reflections
and absorptions within laminar carbon structures
(Fig. 2). This fact is also indicated by the observed
decrease in S21 for the sample from – 9.5 dB to –
44.5 dB at 13.6 GHz and 38.5 GHz, respectively,
С – 15.3
С60 – 40.3
SiO2 - 26.6
С – 25.8
С60 – 30.8

MECHANISMS OF MICROWAVE ABSORPTION IN CARBON COMPOUNDS… J. NANO- ELECTRON. PHYS. 5, 04023 (2013)
04023-3
Fig. 5 – Amplitude-frequency characteristic of S21 before
(top) and after HF processing (bottom) of shungite
that is more than 4.5-fold. The depth of skin layer for
microwave radiation:   (

f

)-1/2 (f is frequency of
electromagnetic radiation,



0

 is suppressor
penetrability,

0 is permeability of vacuum,

is
electroconductivity) turns out to be much greater
than the sizes of nanocarbon laminar structures,
which adds to multiple reflections. Also, as shown in
Fig. 5, the surface eddy currents grow. When
RC  RMе, the Joule heat loss increases.
4. CONCLUSIONS
Thus, the increase of microwave radiation
absorption in derivatives from shungite carbon
structures, in addition to dielectric losses, is due to
intense processes of both scattering and absorption of
electromagnetic energy.
REFERENCES
1. F. Qin, C. Brosseau, J. App. Phys. 111, 061301 (2012).
2. V.V. Kovalevski, P.R. Buseck, J.M. Cowley, Carbon 39,
243 (2001).
3. A.P. Kuzmenko, V.M. Emelianov, V.E. Dreizin, S.A. Efanov,
V.V. Rodionov, Proceedings of the Southwest State
University 2 (2012).