Biomedical Engineering Reference
In-Depth Information
adsorption values
m
. The calculated trend of the adsorption heat vs.
a
the
values is shown in Fig. 4.9.
The curve of Fig. 4.9 is in satisfactory agreement with the
results of other measurements [37, 44-46], with
m
a
q
approaching
st
the value of vaporization (condensation) heat
increases.
The other adsorbent characteristics, calculated by the BET theory
for the adsorption of nitrogen and oxygen at 77 K, are listed in
Table 4.1.
Table 4.1
q
when
m
L
a
Sorption parameters calculated by the BET theory
Activated
carbon AG-3
Fullerene
Astralen
O
2
N
2
O
2
N
2
O
2
N
2
C
4.02
13.66
6.57
10.76
11.34
24.02
BET
n
,
mol/g
7.75
× 10
-5
5.39
× 10
-5
2.84
× 10
-3
6.53
× 10
-3
2.38
× 10
-4
3.9 ×
10
-4
m
Q
*
0.333 0.213
0.281 0.234
0.229
0.169
ABET,
m
2
/g
5.66
6.44
244.462 637.09 20.55
38.3
The
C
value is related to the surface fraction occupied by a
BET
monolayer (
θ
), to the free surface fraction (
θ
) and to the relative
1
0
pressure
P/P
by the simple equation [21].
C
0
=
(
θ
/
θ
)(
P
/
P
)
BET
1
0
0
On the other hand, this value can be calculated from the energy
characteristics of adsorption using the equation [20]
C
≈
exp(
q
/
RT
)
BET
0
The data presented in Table 4.1 very satisfactorily agree with
the results reported in Ref. [22], but noticeably deviate from those
obtained in Ref. [37, 44]. These deviations may be connected to
different crystalline structures of the adsorbents and methods for
their preparation, as underlined by the authors of [44].
The values of
specific surface area given in Table 4.1 can be
used to compare the experimental adsorption isotherms obtained
for three different adsorbents by constructing the so-called standard
isotherms [20, 21]. The corresponding nitrogen and oxygen
adsorption isotherms at 77 K are shown in Fig. 4.10. It may be noted
A
BET
