Chemistry Reference
In-Depth Information
The present work has showed that analysis of
plots at very high relative
pressures (
p/p
o
=0.970-0.999) makes it possible to evaluate the CB aggregate size.
However, as is seen from Figure 12, there is large fluctuation in the
plots.
a
d
from N
2
adsorption data. In future, we will try to improve the automatic adsorption
apparatus so as to decease fluctuation in the
CB
aggregate
The present work is the first step of evaluating
plots at the extremely high
relative pressures of
p/p
o
=0.970 - 0.999.
3. Low Relative Pressure Ranges (P/P
o
=10
-7
-10
-2
); Surface Homogeneity
or Heterogeneity of CB Particles
3.1. Henry's Law and Deviation from Its Law at Very Low Relative Pressures
In the section (1), the effect of graphitization on the surface homogeneity of
CB particles has been considered. The
C
BET
values, which are evaluated from the
BET plot (
p/p
o
=0.001-0.20), depend remarkably on surface homogeneity. It has
been pointed out that increase in surface homogeneity brings about the remarkable
increase in the
C
BET
value. In the present section, effect of the surface
homogeneity on the N
2
isotherms at 77.4 K will be examined in detail at the very
low relative pressures.
The reduced adsorption isotherms of N
2
at 77.4 K by nongraphitized CB
(#51-CB) and graphitized CB (#3845-2-CB, LGC2102-CB, and Carbotrap-F-CB)
are shown in Figure 13, where
n
is an adsorbed amount at
p/p
o
=0.400 and
n
an adsorbed amount at arbitrary relative pressure.
Here, the reduced adsorption isotherms are expressed as
log
(
n
/
n
)
vs
.
10
0
o
10
pp
. From Figure 13, it is found that the reduced isotherms by the
present CB adsorbents are classified into three groups below
p/p
o
=210
-5
. From
this experimental fact, it has been suggested that the surface characters
(homogeneity/heterogeneity) of CB particles are characterized by the N
2
adsorption isotherms in very low relative pressure ranges.
The three groups of reduced isotherms can be expressed as the following
experimental formulas. For Carbotrap-F-CB of our work and Carbopack-F-CB by
Kruk et al. [16].
log
(
/
)
n
p
(
p/p
o
=10
-6
-210
-5
)
(3.1)
log
1
00
log
3
00
o
n
p
0
