Reaction of graphite with sulfuric acid in the presence of KMnO4

Article abstract of DOI:10.1007/s11176-005-0191-4

The reaction of graphite with sulfuric acid in the presence of KMnO ₄ (oxidant : graphite ratio 0.027-0.55) involves consecutive and concurrent reactions: graphite intercalation and direct oxidation of the carbon matrix. The properties of graph

Full text of DOI:10.1007/s11176-005-0191-4

Russian Journal of General Chemistry, Vol. 75, No. 2, 2005, pp. 162 168. Translated from Zhurnal Obshchei Khimii, Vol. 75, No. 2, 2005,
pp. 184 191.
Original Russian Text Copyright
2005 by Sorokina, Khaskov, Avdeev, Nikol’skaya.
Reaction of Graphite with Sulfuric Acid
in the Presence of KMnO4
N. E. Sorokina, M. A. Khaskov, V. V. Avdeev, and I. V. Nikol’skaya
Lomonosov Moscow State University, Moscow, Russia
Received May 12, 2003
Abstract The reaction of graphite with sulfuric acid in the presence of KMnO (oxidant:graphite ratio
4
0
.027 0.55) involves consecutive and concurrent reactions : graphite intercalation and direct oxidation of the
carbon matrix. The properties of graphite bisulfate and its reaction products are determined by the stage
number of the intercalation compound; the decomposition enthalpies of the stage I IV graphite bisulfate cor-
relate with the enthalpies of graphite intercalation with sulfuric acid.
Chemical reactions involving graphite form the
basic synthetic route to an abundant and original class
of compounds, viz. graphite intercalation compounds
KMnO is scarce. In this connection of mention are
4
the works of Inagaki et al. [4] and Avdeev et al. [5],
who established that the potential of a graphite sample
stepwise grows in the course of intercalation with
H SO in the presence of such strong oxidants as
(
GICs). These reactions are peculiar in that they leave
the graphite structure almost intact, and simply
increase the distance between graphite layers as a
result of intercalation of various chemical reagents
between graphite grids. The interest in GICs is
primarily explained by such their features as regular
lamellar structure, highly anisotropic properties, as
well as unusual mode of bonding between intercalated
compounds and the graphite grid. Special place
among GICs belongs to graphite bisulfate, the product
of graphite reaction with sulfuric acid, that, on the one
hand, is a model compound for development of the
classical stage structural model and, on the other,
serves as the starting material for the production of
oxidized graphite and a unique low-density material,
foam graphite.
2
4
KMnO , HNO , or K Cr O . The plot of potential vs.
4
3
2
2
7
time is stepwise and is similar to that characteristic of
anodic oxidation of graphite. From this observable we
can conclude that both chemical and electrochemical
oxidants act in a similar way. The effect of conditions
of chemical treatment of graphite in the H SO
2
4
KMnO system on the properties of the reaction
4
products have not been considered in detail.
It the present work we have studied the reaction of
graphite with sulfuric acid in the presence of KMnO4
at a widely varied KMnO :graphite weight ratio. By
4
varying reactant ratio and treatment time one can
control oxidation conditions and study the effect of
these factors on the structure and properties of both
GICs and oxidized graphite and foam graphite.
The intercalation of graphite with sulfuric acid can
only be accomplished in the presence of an oxidant
Synthesis of graphite bisulfate. The reaction of
graphite with sulfuric acid in the presence of KMnO4
was assumed to occur by scheme (1).
(
chemical or electrochemical); in both cases, irrespec-
tive of the nature of the oxidant, graphite bisulfate is
formed [1]. Depending on the nature of the oxidant
and the concentration of the acid, graphite bisulfate
of various composition C +2 HSO 2H SO can be
5
2
C24s + KMnO4 + 17H SO4
4s
4
2
4
s
5
C HSO4 2H SO + MnSO + KHSO + 4H O. (1)
formed (s is the stage number equal to the number of
graphite grids between two closest layers of the inter-
calate [1]) [2]. Later it was established that whether
one or another stage forms also depends on the redox
potential of the oxidizing solution [3]. Graphite reac-
tions in C H SO [O] systems ([O] = K Cr O or
24 2 4 4 4 2
Here s is the stage number of the GIC.
The required quantities of the oxidant were calcu-
lated by this equation. The reaction results are given
in Table 1 and Fig. 1. The experimental data provide
evidence for the validity of Eq. (1) for the stage I IV
graphite bisulfate. The identity periods of the syn-
thesized graphite bisulfate samples fit known values
[2].
2
4
2
2
7
HNO ) are the most thoroughly studied. The latter
3
oxidants are widely used in the production of various-
purpose foam graphite. At the same time, the informa-
tion on graphite bisulfate formation in the presence of
1
070-3632/05/7502-0162 2005 Pleiades Publishing, Inc.

REACTION OF GRAPHITE WITH SULFURIC ACID
163
Table 1. Effect of graphite intercalation conditions on the
Probably, in the graphite H SO KMnO system
2
4
4
stage number of graphite bisulfate
we deal with processes characteristic of anodic oxida-
tion of graphite [6]: oxidation of the graphite matrix
to macrocation Cn with subsequent intercalation
+
Graphite bisulfate
KMnO4 :
graphite
weight ratio
Identity
period
Synthesis
time
stage no.
between the polyarene grids of sulfate anions and
sulfuric acid molecules; oxidation of peripheral carbon
atoms at plane edges and in defects to oxygen-contain-
ing functional groups (COH, C=O, COOH); and
chemical dispersion of graphite particles to soluble
compounds, such as benzenepolycarboxylic and
mellitic acid, as well as wet burning of carbon to
gaseous oxides [reaction (2)].
I ,
C
expected experiment
0
0
0
0
0
0
0
0
0
.110
.055
.036
.027
.165
.165
.550
.550
.550
15 min
30 min
40 min
50 min
24 h
I
II
III
IV
I
I
I
I
I
I
7.98
11.33
14.70
18.07
7.96
II
III
IV
I
a
a
5C + 4KMnO + 8H SO
4
72 h
24 h
I
7.99
4
2
a
5
CO + 4MnSO + 6H O + 4KHSO . (2)
2 4 2 4
a
170 h
10 h
b
a
In this system, KMnO acts as an oxidant that
4
favors graphite intercalation. Decreased oxidant
a
b
Overoxidized I stage.
At 80 C.
concentration decreased the amount of KMnO dif-
4
fusing to the graphite matrix per unit time; therefore,
the time of synthesis of graphite bisulfate with a stoi-
chiometric amount of the oxidant increases with in-
creasing stage number. It can also be proposed that
with increasing amount and, as a result, concentration
9
00
(
a)
6
3
00
00
of such a strong oxidant as KMnO , the contribution
4
of direct oxidation of the graphite matrix increases.
To assess the effect of oxidant concentration, a series
of experiments was performed, in which the amount
1
1
00000
of KMnO was increased compared with stoichio-
(
b)
4
8
6
4
2
000
000
000
000
metric for the first stage by 50 and 500%, and the
synthesis time and temperature were, too, much in-
creased. Figures 1b and 1c show the X-ray diffraction
patterns of the graphite bisulfate samples synthesized
with the stoichiometric amount of KMnO . As seen
4
00000
from the figures, the intensity of reflections decreases
with decreasing graphite bisulfate stage number. This
observation can be explained in terms of the decreas-
ing size of crystallites that effect coherent X-ray scat-
tering. Treatment of graphite with an oxidizing mix-
(
c)
8
6
4
2
000
000
000
000
ture containing excess KMnO provides a strongly
4
1
00000
amorphized stage I graphite bisulfate, as evidenced by
further decrease in the intensity of reflections and
their broadening.
(
d)
8
6
4
2
000
000
000
The structure amorphization is favored by that the
reaction is performed in the presence of such a strong
000
0
oxidant as KMnO whose potential in 96% sulfuric
4
acid is higher, as we found in [3], than that of forma-
tion of the stage I graphite bisulfate.
2
0
30
40
50
60
2
, deg
We also found in [3] that the increased potential
will probably favor side reactions forming surface
oxygen-containing groups. Moreover, in [5] we
showed that the enthalpy of intercalation of sulfuric
acid into a graphite matrix in the presence of KMnO4
is much dependent on the amount of the latter (4
Fig. 1. X-ray diffraction patterns of sulfuric acid
graphite intercalation compounds obtained at graphite:
KMnO ratios of (a) 0.55, (b) 0.11, and (c) 0.055 0.027
4
and (d) starting graphite (d
3.35 ) (2 is the reflec-
02
0
tion angle and I, reflection intensity; the same for Fig. 3).
RUSSIAN JOURNAL OF GENERAL CHEMISTRY Vol. 75 No. 2 2005

164
SOROKINA et al.
Table 2. Thermal properties of graphite bisulfatea
Graphite bisulfate
H ,
H ,
d
kJ mol
H, kJ mol 1
C
d
T T ,
C
Tmax, C
m, %
i
f
kJ mol 1 H SO
1
stage no.
C
2
4
I
II
III
IV
202 326
181 308
205 319
192 322
193 315
283
256
266
268
258
156
137
85
106
89
31.2
27.9
19.8
18.6
114.6
30
46
58
69
3.0
2.2
1.6
1.8
H SO + graphite
2
4
a
(
(
T and T ) Initial and final temperatures of the endo effect, respectively; (T
m) weight loss with respect to the graphite weight; and ( H) enthalpy change.
) maximum temperature of the endo effect;
i
f
max
1
4
0 kJ mol ). On this basis we suggested in the cited
Thermal analysis of graphite bisulfate. A typical
thermoanalytical curve in the 30 350 C [thermogravi-
metry (TG) and differential scanning calorimetry
(DSC)] of the stage II graphite bisulfate is given in
Fig. 2a. At 350 C, the graphite bisulfate decomposes
completely to graphite with the interplanar spacing
work that the use of KMnO in the synthesis of gra-
4
phite bisulfate would induce side reactions. The
experimental data obtained in the present work pro-
vide conclusive evidence for this suggestion.
(
a)
d002 of 3.36
.
2
55.7 C
0
.5
.0
12
The DSC curves contain a number of broad endo
peaks. The weak effect at 50 180 C is accompanied
by an inconsiderable weight loss. The strongest heat
effect is observed at 180 325 C, and it is a superposi-
tion of two unresolved endo effects, the first being
much stronger than the second. The strongest endo
effect is accompanied by a one-stage and large weight
loss. The resulting data are represented in Table 2.
1
8
6
0
0
1
1
80.5 C
1
.5
4
2
307 .7 C
2
2
.0
.5
2
753 mJ
100 150 200 250 300 350
b)
257.6 C
0
5
0
The DSC curves for the I IV stages have similar
shapes. Moreover, the decomposition onset tempera-
ture is almost independent on the stage number of the
starting GIC, while Matzui et al. [7] reported the
tendency of the decomposition onset temperature to
increase with increasing stage number. The similar
DSC curves and almost equal specific decomposition
enthalpies of graphite bisulfate suggest that processes
(
16
14
0
.5
0
1
1
2
0
1
1
.0
.5
8
1
92.8 C
2
2
.0
.5
6
4
2
2991 mJ
associated with H SO4 deintercalation from the
2
5
0
100 150 200 250 300 350
graphite matrix contribute little compared with
another, more energetic process. The case in point is
that the graphite bisulfate samples prepared on the
graphite powder by the proposed procedure contain
much acid on the surface. Figure 2b presents the
behavior of sulfuric acid on the surface of the starting
graphite under heating. As seen, the DSC pattern is
similar to the above pattern for graphite bisulfate,
implying that the enthalpy is mostly contributed by
boiling and decomposition of sulfuric acid on the
surface of the graphite sample. This is a probable
reason why in our case, unlike what is observed in
(
c)
0
2
.5
2
66.5 C
47.0 C
11 C
4
0
0
0
0
0
.1 96.4 C
2.0
1.5
5
.2
.3
4
11 C
139.9 C
1.0
.4
.5
0.5
0
1
72.0 C
288.0 C
4
01.3mJ
415 mJ
1
00
200
300 400 500 600
T, C
[
7], the decomposition onset temperature of graphite
Fig. 2. Thermoanalytical curves (DSC and TG) for the
a) stage II graphite bisulfate (m 3.67 mg), (b) H SO
bisulfate does not increase with increasing stage
number.
(
2
4
on the starting graphite support (m 2.85 mg) and
c) oxidized graphite obtained from the stage III graphite
bisulfate (m 4.79 mg).
(
The total heat effect of decomposition of the stage
1
I IV graphite bisulfate ( H 130 kJ mol H SO )
2
4
RUSSIAN JOURNAL OF GENERAL CHEMISTRY Vol. 75 No. 2 2005

REACTION OF GRAPHITE WITH SULFURIC ACID
165
presumably comprises the heat of H SO deintercala-
Table 3. Properties of oxidized graphite
2
4
tion from the graphite matrix ( H ) and the enthalpy
d
changes associated with the behavior of H SO on the
Weight gain
2
4
Sulfur
content of
oxidized
surface of the graphite sample [ H(H SO )
Graphite
bisulfate
stage no.
with account
for finely
dispersed
2
4
1
Weight gain
1
15 kJ mol H SO ]. Knowing the weight loss (m )
2 4 l
m, %
we can estimate the heat of evaporation and desorp-
tion of the given amount of the acid from the surface
of the graphite sample [ H = H(H SO )*m ]. The
graphite, %
residue, %
2
4
l
difference between Hexp and H is the enthalpy of
Stoichiometric amount of oxidant
H SO deintercalation from the graphite matrix. From
I
II
III
IV
45.8
11.5
10.3
5.6
49.3
12.8
11.5
6.0
4.6
3.1
3.0
1.9
2
4
+
the composition of graphite bisulfate C24sHSO4
H SO [2] we can calculate the weight of sulfuric
2
2
4
acid deintercalated on decomposition of graphite bi-
sulfate. The experimental results and calculated de-
Oxidant excess
intercalation heats per mole intercalated acid [ H ,
I
I
19.6
17.6
9.2
23.6
23.0
24.1
20.0
18.6
4.3
3.9
2.8
2.6
3.0
d
1
kJ mol
H SO ] and per mole graphite [ H ,
2 4 d
kJ mol 1 C] are given in Table 2.
5
2
.0
.8
The H values per mole intercalated acid vary
d
linearly with stage number. This result can be ex-
plained by the fact that decreasing stage number of
GIC results in decrease in the stage number of the
be expected, oxidative dispersion and wet burning of
the graphite matrix are favored by excess oxidant and
increased temperature.
latter and increase in H per mole graphite. It should
d
be noted that the resulting values are small ( Hd
.5 3.0 kJ mol 1 C) and compare with the enthalpies
1
of H SO intercalation into graphite [5].
2
4
As shown by X-ray phase analysis (Fig. 3), the
hydrolysis product is a many-phase mixture compris-
ing higher stage GIC and defective graphite; there-
with, the graphite phase (d002 3.35 A) is present only
in the oxidized graphite firmed by hydrolysis of the
stage IV graphite bisulfate. The X-ray patterns of the
Hydrolysis of graphite bisulfate. Graphite bisulfate
samples were hydrolyzed using the decantation te-
chnique. As known hydrolysis results in destruction
of GIC, deintercalation of sulfuric acid, and formation
of oxidized graphite that contains bound water,
various surface functional groups, and residual acid
[
8]. Since on treatment of graphite with a mixture of
sulfuric acid and the oxidant we observe, along with
the intercalation of H SO into the graphite matrix,
(
a)
5
000
2
4
3000
side processes that result in sample amorphization and
chemical dispersion, increase in the amount of the
oxidant in the system increases the fraction of micro-
particles that do not drop on decantation and exist in
the suspended state. Consequently, as the stage
number decreases, the fraction of finely dispersed
residue increases. Thus, for the IV stage this fraction
is 0.3 0.5%, for the I stage it is 3.5 4.1%, and with
a 5-fold oxidant excess it attains 14.5 15.5%. As seen
from Table 3, the oxidized graphite synthesized with
a stoichiometric amount of the oxidant gains weight
by 6 to 50% as the stage number of the starting gra-
phite bisulfate decreases. The sulfur content, too,
depends on GIC stage and increases from 1.9 to 4.6%
in going from the IV to I stage.
1
7
000
000
(b)
(c)
40
5
3
1
000
000
000
1
0000
8
6
4000
000
000
2000
0
10
20
30
50
2
60
, deg
The weight gain for the oxidized graphite samples
obtained with excess KMnO is 20 24%, which is
Fig. 3. X-ray diffraction patterns of oxidized graphite
prepared from the stage (a) I, (b) II, and (c) III graphite
bisulfate.
4
almost half the weight gain of the oxidized graphite
obtained from the stage I graphite bisulfate. As would
RUSSIAN JOURNAL OF GENERAL CHEMISTRY Vol. 75 No. 2 2005

1
66
Table 4. Thermal analysis of oxidized graphite
Effect Parameter Graphite bisulfate stage no.
II III IV
SOROKINA et al.
stages 2 3 times. The content of associated water
in the oxidized graphite prepared from the stage I
graphite bisulfate is 2 3 times higher that the respec-
tive contents for the other stages. This result is
probably explained by a change in the hydrolysis
mechanism in going from the stage II to stage I
I
1
T T ,
C
C
38 173 36 165 35 172 30 198 graphite bisulfate [9].
i
f
Tmax
,
116
97
0.9
96
1.1
101
The enthalpies of the second effect and the weight
loss decrease (from 2.5 to 0.6 kJ mol 1 C and from
H,
2.8
1.0
kJ mol 1
C
1
5.2 to 3.7%, respectively) with increasing stage
m, %
12.3
173 305 165 283 172 288 198 296
255 253 267 276
2.5 0.9 1.2 0.6
5.5
6.3
3.7
number. We suggest liberation of sulfuric acid in this
2
T T ,
C
C
i
f
temperature range, since the H of the second effect
Tmax
,
is 137 kJ mol 1 H SO , which compares with the ex-
2
4
H,
perimental decomposition enthalpy of graphite bi-
kJ mol 1
H, kJ g
m, %
C
sulfate ( Hexp 130 kJ mol 1 H SO ). The fact that the
1
2
4
1.4
15.2
1.4
5.5
1.5
6.3
1.4
3.7
specific enthalpies (per 1 g of evolved substance) are
equal to each other suggest that the decomposition
processes are similar in nature. It should be noted that
the weight loss associated with the second endo effect
correspond to the residual H SO (sulfur) content in
3
T T ,
C
C
305 500 402 500 411 511 398 495
438 443 447 443
1.0 0.3 0.4 0.2
i
f
Tmax
,
H,
kJ mol 1
2
4
C
the oxidized graphite samples.
1
H, kJ g
m, %
1.6
5.2
0.6
4.3
0.9
3.5
0.5
2.5
As the amount of the oxidant used in the synthesis
of graphite bisulfate is increased, the content of
surface functional groups increases, as seen from the
weight losses for the third endo effect. As judged
from the enthalpy of the third endo effect, the qualita-
tive composition of surface functional groups changes.
For example, in the oxidized graphite samples syn-
thesized from the stage I graphite bisulfate, surface
functional groups begin to decompose already at
oxidized graphite are impossible to assign unambi-
guously: Reflections can be assigned to the VII and
higher stages. Residual stages cannot be completely
hydrolyzed and removed only by additional washing
in more severe conditions [T(H O) 95 C], while the
sulfur content therewith decreases about 1.5-fold.
2
3
20 C, whereas in those prepared from the stage II IV
Thermal analysis of oxidized graphite. Oxidized
graphite samples were subjected to complex thermal
analysis. A typical thermoanalytical curve (oxidized
graphite prepared from the stage III graphite bisulfate)
is given in Fig. 2c. It should be noted that, irrespec-
tive of stage number, the DSC curves have similar
patterns. The curves show three endo effects at 30
graphite bisulfates, at 400 C only.
The oxidized graphite samples were subjected to
thermal treatment under conditions of thermal shock.
Analysis of the X-ray patterns of the foam graphite
samples prepared from the stage I IV graphite bisul-
fites shows that the major phase is a graphite with the
interplanar spacing d002 of 3.36 3.37 . In going
from higher to lower stages, the intensity of diffrac-
5
10 C: The first endo effect is in the range 30 175 C,
the second, at 175 305 C, and the third, at 305
5
10 C. Once 550 C has been attained, full decomposi- tion reflections of foam graphite changes appreciably.
tion of the oxidized graphite to graphite (d002 3.36 ).
The resulting data are listed in Table 4. It can be sug-
gested that the first endo effect corresponds to loss of
associated water. The temperature range of the
second endo effect coincides with the range of
It is interesting to note that such a regularity in
intensity changes is already observed in the stage of
graphite bisulfate and oxidized graphite formation.
Figure 4a shows the plot of the bulk density of foam
graphite ( fg vs. stage number of the starting GIC).
H SO4 deintercalation from the graphite bisulfate
2
matrix; therefore, we assign this effect to deintercala-
tion and evaporation of residual sulfuric acid. The last
endo effect is probably associated with decomposition
of surface groups and CO, CO , and H O evolution.
At a stoichiometric oxidant amount, the bulk
density of foam graphite decreases with decreasing
stage number, in agreement with the data in [10]. Ase
the foaming degree increases with decreasing stage
2
2
Table 4 lists the enthalpies of the three endo effects. number, the stronger burn-out of the graphite matrix
As seen, the H of the first endo effect is the highest
for the I stage, and it is higher than those for the II IV
enhanced, as evidenced by the fact that the yield by
carbon depends on the stage number of the starting GIC
RUSSIAN JOURNAL OF GENERAL CHEMISTRY Vol. 75 No. 2 2005

REACTION OF GRAPHITE WITH SULFURIC ACID
167
(
a)
(b)
9
9
9
6.5
6.0
5.5
95.0
4.0
3.5
3.0
7
6
5
9
9
9
4
3
2
1
2
3
4
1
2
3
4
Starting bisulfate stage no.
c)
Starting bisulfate stage no.
(
1.0
(d)
1
00
9
0
0
0
0
0
0
0
.8
.6
8
7
6
5
4
3
0.4
0
.2
0
0
0
0
0.1 0.2 0.3 0.4 0.5 0.6
KMnO :graphite weight ratio
0.1 0.2 0.3 0.4 0.5 0.6
KMnO4:graphite weight ratio
4
Fig. 4. Properties of foam graphite vs. conditions of synthesis of starting graphite bisulfate: (a) bulk density ( ) vs. stage
fg
number; (b) yield by carbon vs. stage number; (c) specific surface area (S ) vs. KMnO :graphite weight ratio; and (d) sulfur
sp
4
content of foam graphite vs. KMnO :graphite weight ratio.
4
(
Fig. 4b). The strongest burn-out of the graphite
oxidizing solution was removed, and the product was
subjected to X-ray phase and thermal analyses. The
X-ray phase analysis was performed on a URD dif-
fractometer (CuK radiation, Ni filter) in the angle
range 5 80 under an X-ray amorphous film. The
complex thermal analysis was performed on a Netzsch
Jupiter STA-449C analyzer at 30 600 C under argon,
heating rate 10 deg/min. Hydrolysis and washing of
matrix is observed with the samples obtained with a
-fold oxidant excess: The yield by carbon decreases
to 82 85%. The trend in the specific surface area [S
5
sp
2
1
4
0 90 m g (Table 5)] with increasing KMnO4 :
graphite ratio is opposite (Fig. 4c).
The dependence of the sulfur content of foam
graphite on the oxidant amount is shown in Fig. 4d.
The sulfur content of foam graphite regularly in-
creases with decreasing stage number of the starting
GIC, which agrees with the data in [11]. It should be
noted that the sulfur content increases with increasing
oxidant amount. Under the assumption that sulfuric
acid is harder to remove from defects, this fact
provides one more evidence to show that increased
oxidant amount in the system enhances imperfectness
of the graphite matrix.
Table 5. Properties of foam graphite
Yield by
Starting
graphite
bisulfate
stage no.
carbon
with account S ,
for finely m g
dispersed
Sulfur
content of
oxidized
Bulk
sp
density
2
1
, g l 1
fg
graphite, %
residue, %
Stoichiometric amount of oxidant
EXPERIMENTAL
I
II
III
IV
2.7
4.8
5.2
6.8
93.3
94.0
95.3
65.2
45.2
42.5
43.1
0.34
0.19
0.15
0.10
Natural large-flake graphite (ash content <0.04%,
particle size 315 400 m, interplanar spacing d0
02
3
96.3
3
.35 ) and chemical grade H SO (
1.83 g cm )
2
4
22
Oxidant excess
94.6
and KMnO were used as starting reagents.
4
I
I
4.6
5.4
4.5
2.9
6.0
68.9
79.4
93.9
0.41
0.40
0.99
1.00
0.80
Graphite powder was added to a freshly prepared
solution of KMnO in conc. H SO , and the mixture
94.0
87.0
82.0
84.6
4
2
4
was intermittently stirred for some time. The amount
of KMnO and reaction time were varied over a wide
4
range. When the synthesis had been complete, excess
RUSSIAN JOURNAL OF GENERAL CHEMISTRY Vol. 75 No. 2 2005

168
SOROKINA et al.
graphite bisulfate were performed at a graphite:distil-
led water weight ratio of 1:20. During hydrolysis, the
graphite suspension was stirred, after which the pre-
cipitate was let to settle, and the most part of the solu-
tion was decanted (the operation was repeated). The
oxidized graphite was filtered off, dried at 90 C, and
weighed. The weight gain m was calculated by the
following formula.
REFERENCES
1
2
. Herold, A., NATO ASY, Ser. B, 1987, vol. 172, p. 3.
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1
938, vol. 234, no. 1, p. 1.
3
4
. Avdeev, V.V., Monyakina, L.A., Nikol’skaya, I.V.,
Sorokina, N.E., and Semenenko, K.N., Carbon, 1992,
vol. 30, no. 6, p. 819.
. Inagaki, M., Iwashita, N., and Kouro, E., Carbon,
1
990, vol. 28, no. 1, p. 49.
m(%) = (m /m ) 100.
5. Avdeev, V.V., Monyakina, L.A., Nikol’skaya, I.V.,
Sorokina, N.E., Semenenko, K.N., and Finaenov, A.I.,
Carbon, 1992, vol. 30, no. 6, p. 825.
og sg
Here mog is the weight of the oxidized graphite after
drying and msg is the weight of the starting graphite.
The weight of the finely dispersed fraction in the
decanted solution was determined by the same proce-
dure. Thermal treatment of the oxidized graphite was
performed in a muffle oven (900 C) using a graduated
6
. Shapranov, V.V. and Yaroshenko, A.P., Khimiya i
fizika uglya (Chemistry and Physics of Coal), Kiev:
Naukova Dumka, 1991, p. 56.
7
. Matzui, L., Vovchenko, L., Ovsienko, I., and Khar-
kov, E., Mol. Cryst. Liq. Cryst., 2000, vol. 340,
p. 197.
quartz glass. The bulk density of foam graphite ( fg
and the yield by carbon were calculated by the follow-
ing formulas.
)
8. Sorokina, N.E., Geodakyan, K.V., and Bondaren-
ko, G.N., Abstracts of Papers, I Vsesouznaya konfe-
rentsiya Khimiya i fizika soedinenii vnedreniya
(
I Union Conf. Chemistry and Physics of Intercala-
tion Compounds ), Rostov-on-Don, 1990, p. 44.
. Besenhard, J.O., Minderer, P., and Bindl, M., Synth.
Metals, 1989, vol. 34, no. 2, p. 133.
=
m /V .
fg fg
fg
9
Here m and V are the weight and volume of foam
fg
fg
10. Nikol’skaya, I.V., Fadeeva, N.E., Semenenko, K.N.,
Avdeev, V.V., and Monyakina, L.A., Zh. Obshch.
Khim., 1989, vol. 59, no. 12, p. 2653.
graphite, respectively.
Yield by carbon (%) = m(%)(m /mog) 100.
11. Mandrea, A.G., Geodakyan, K.V., and Sorokina, N.E.,
Abstracts of papers, I Vsesouznaya konferentsiya
Khimiya i fizika soedinenii vnedreniya (I Union
Conf. Chemistry and Physics of Intercalation
Compounds ), Rostov-on-Don, 1990, p. 54.
fg
Here mog is the weight of foamed oxidized graphite
and m , weight of resulting foam graphite [6].
fg
1
2. Eksperimental’nie metody v adsorbtsii i molekulyarnoi
khromatografii (Experimental Methods in Adsorption
and Molecular Chromatography), Nikitina, Yu.S. and
Petrova, R.S., Eds., Moscow: Mosk. Gos. Univ.,
1990.
The H SO contents were determined using an AC-
932 express sulfur analyzer, and the specific
surface areas were estimated by the method of nitro-
gen thermodesorption [12].
2
4
7
RUSSIAN JOURNAL OF GENERAL CHEMISTRY Vol. 75 No. 2 2005