Biomedical Engineering Reference
In-Depth Information
activation of hydrogen molecules in these regions,
Q
= 120 ± 2 kJ
II
−1
mol
) [51, 54, 61, 62].
The mass action law for reaction (2.13) can be written as
(H
2
X
/
X
K
II
IIm
,
(2.14)
(13)II
0
(
P
/
P
)(1 -
X
/
X
)
H
H
II
IIm
2
2
which corresponds to the Henry-Langmuir isotherm, i.e., the
Langmuir nondissociative adsorption isotherm (i.e., the Fermi-
Dirac-like distribution), which at small pressures (
0
K
(
P
/
P
)
(13)II
H 2
H
2
<< 1) corresponds to the Henry isotherm
0
K
(
P
/
P
)
P
X
(13)II
H
H
H
.
II
K
2
2
2
(2.14a)
0
(13)II
0
X
(1 +
K
(
P
/
P
)
P
IIm
(13)II
H
H
H
2
2
2
The equilibrium constant for reaction (2.13) is described by the
formula
 
D
D
S
H
(13)II
(13)II
 
K
exp
exp
,
(2.15)
(13)II
R
 
RT
D
H
D
H
D
H
D
H
(13)II
(10)II
(11)II
(12)II
D D
H
H
,
(2.16)
dis
(12)II
def
where
of adsorbed
hydrogen molecules in the intergranular or defective regions of the
carbon material (C
X
is the equilibrium concentration (H
/C
)
II
2
II
def
) at the pressure of
P
(Pa) and temperature
H
2
T
) molecules to the number of
carbon atoms in the intergranular or defective regions of the material
(C
(K), i.e., the ratio of adsorbate (H
2
def
def
≥ C
), which may be close to the number of sorption centers
ch
def
C
≤0.5 is the maximum (carbohydride) local
concentration of the adsorbate, ∆
,
X
= (H
/C
def
)
IIm
2
IIm
ch
S
is the standard entropy for
(13)II
reaction (2.13), ∆
(2H) is the experimental
value of the molar enthalpy of the chemical bond formation that links
two hydrogen atoms to a carbon center in a zigzag edge position
(Fig. 2.8, model H) localized in the intergranular or defective (surface)
regions of the carbon material.
Using the model for the diffusion of hydrogen molecules in
graphite lattice, accompanied by reversible dissociation, and
duffusant capture on carbon chemisorption centers, we express
the effective diffusivity (
H
= -560 ± 10 kJ mol
−1
(12)II
D
) and the effective diffusion-activation
II
enthalpy (
Q
) as
II
 
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