Chemistry Reference
In-Depth Information
Table 2. (Continued)
Average
particle
size (
BET
surface area
(
A
BET
)
m
2
g
-1
surface area
(
BET
constant
(
C
BET
)
CB
S
aggregate
)
Sample name
A
CB
av
d
)
.
m
2
g
-1
nm
#51-CB
260
18.5
――
160
#3845-1-CB
1600
54.4
――
50
#3845-2-CB
1900
49.2
――
55
LGC2102-CB
1300
69.4
9±1
39
――――
Carbotrap-F-B
(before step)
5200
(after step)
5900
6.79
4±2
408
This difference between
n
m
(before)
and
n
m
(after)
is calculated to be 6.2 %, which
suggests that the packing density of adsorbed N
2
molecules increases 6.2 % by a
transition of liquid state to solid state.
Table 2 clearly shows that all
n
m
values are in excellent agreement with
n
PointB
-values, and that
C
BET
of graphitized CB samples (#3845-CB, LGC2102-
CB, Carbotrap-F-CB) is notably larger than that of nongraphitized CB sample
(#51-CB).
Furthermore, we tried to re-calculate
C
BET
-values using the other N
2
isotherms (standard
data) reported by Kaneko et al. [15] and Kruk et al. [16].
All
C
BET
values including ours indicate that the
C
BET
-values of nongraphitized
CB adsorbents having heterogeneous carbon surface are in the vicinity of 260, while
those of graphitized CB samples varies from values of1300-1900 forsamples#3845-
CB and LGC2102-CB having partially heterogeneous surface to a very high value
of 6000 for Carbotrap-F-CB of highly uniform surface.
Magnitude of
C
BET
is, therefore, closely related to the extent of surface
homogeneity of CB particle; in other words, increase of surface homogeneity
brings about remarkable increase in
C
BET
. On the homogeneous surface of a
highly graphitized carbon black, the first and the second layers of N
2
are formed
at distinctly different
p/p
o
regions, respectively. This results in sharpening of knee
in the monolayer region of the isotherm.
The BET surface areas (
A
BET
) of the present carbon black adsorbents were
calculated from
n
m
by assuming the adsorbed area of a N
2
molecule (
) to be
0.162 nm
2
for the CB adsorbents without step. When there is a small step, the
2
