Chemistry Reference
In-Depth Information
adsorption apparatus makes it possible to measure the N
2
adsorption isotherms at
77.4 K in a very wide pressure range from
p/p
o
=10
-8
to
p/p
o
=0.999 [6-9]. In
addition, liquid argon of high purity (99.995%) (b.p.: 87.3 K) is readily available,
which makes it easy to measure the precise N
2
isotherms at 87.3 K up to
p/p
o
=10
-8
.
In our previous works [8,9], the N
2
isotherms at these two temperatures have been
applied to investigations of surface characters of nonporous carbon blacks or
microporosities of activated carbons fibers, where our attention was mainly
focused on the isotherms at low relative pressures.
In the present work, characters of several nonporous CB adsorbents will be
investigated using the N
2
isotherms at the three relative pressure ranges;
i.e
., (1)
p/p
o
=10
-7
-10
-2
(low relative pressure ranges), (2)
p/p
o
=10
-4
-0.50 (medium relative
pressure ranges), and (3)
p/p
o
=0.900-0.998 (high relative pressure ranges). First,
the N
2
isotherms (77.4 K) at
p/p
o
=10
-4
-0.50 (medium relative pressure ranges) by
nongraphitized and graphitized CB adsorbents will be analyzed by the BET
method [10-12]. As pointed out by Sing and coworkers [12], it is very important
to select the appropriate relative pressure ranges for BET plots in order to obtain
the reliable surface areas and the BET constant values. According to the method
recommended by Sing and coworkers [12], we tried the BET plots for the N
2
isotherms by nongraphitized and graphitized CB adsorbents. The BET surface
areas (
A
BET
) and constants (
C
BET
) of the CB adsorbents will be used in estimation
of particle size of primary CB particles, and consideration of surface
homogeneity/heterogeneity of CB particles, respectively. Second, the N
2
isotherms (77.4 K) at
p/p
o
=0.900-0.998 (high relative pressure ranges) will be
used in estimation of macroporosity of CB aggregates. The distinct adsorption
hysteresis in the N
2
isotherms (77.4 K) was detected at very high
p/p
o
ranges,
usually at
p/p
o
=0.950-0.998 (
e.g.
Figure 7(a)). Because of experimental difficulty,
thus far little attention has been paid to the N
2
isotherms in such high relative
pressure ranges (
p/p
o
=0.950-0.998). However, they give the important
information about macroporosity of CB aggregates. In this work, the pore size
distribution (PSD) of macropore ranges (pore width
＞
50 nm) will be calculated
by means of BJH method [13]. On the basis of the PSD and particle size of the
CB adsorbents, the macroporous textures will be considered. Furthermore, we
tried the evaluation of particles size of the CB aggregates. For this purpose, it is
necessary to carry out the
plots at very high relative pressure ranges
(
p/p
o
=0.970-
0.998). From such
plots, the approximate size of CB aggregates
(secondary particle) may be determined. Third, the N
2
isotherms (77.4 and 87.3
K) by graphitized CB adsorbent (Carbotrap-F-CB) with highly homogeneous
surface were measured in a very wide pressure range of
p/p
o
=210
-7
-10
-2
. The
