Chemistry Reference
In-Depth Information
Table 11.7
Changes of A and B as a function of PAN-fibre quantity in solution
for an initial rongalite/Ni(II) concentration ratio of 1.5/0.5 at 313 K for 20 min
PAN-fibre A 10
2
B 10
2
K
V
¥
10
4
,
mol l
-
1
min
-
1
quantity
(g l
-
1
)
Fibre
Model
Fibre
Model
Fibre
Model
Fibre
Model
4.6
-
0.155
-
0.164
-
0.084
-
0.097
0.999
0.999
18.2
18.3
20.0
-
0.166
-
0.175
0.083
0.106
0.999
0.999
19.5
19.1
29.6
-
0.177
-
0.180
0.081
0.096
0.999
0.999
21.1
21.2
pared with the use of PAN precursors, particularly if the concentration
of functional groups in solution is low.
Finally, a difference in reduction, absorption and adsorption rate of Ni(II)
can be observed between freshly formed and thermofixated PAN fibre.
Proof was not found for this effect, but probably the absorption capacity of
the thermofixated fibre is reduced, resulting in a decrease in the absorption
of Ni(II) in the PAN-fibre structure.
In a second experiment, the kinetics of Ni(II) decrease was followed as
a function of time in solutions containing different amounts of freshly
formed PAN fibre. The experimental results were also calculated using
Equations 11.7 and 11.8, and an acceptable correlation was found between
both methods (Table 11.7). Note also from Table 11.7 that the amount of
fibre present in the solution does not affect B; only A is dependent on the
amount of fibre in solution. Figure 11.4 shows the experimental data and
the data from the modelling. It can be seen that the kinetics increase when
more PAN fibre is present in solution. This is very clear, because more PAN
fibre means a higher capacity to ad- and absorb Ni(II), and also the con-
centration of rongalite drops faster because more catalytic decomposition
occurs through interaction with Ni-cyanide complexes.
Several cables of PAN fibres, obtained through an optimised wet-spin-
ning process followed by chemical metallisation in a pH = 5.5 solution at
333 K and containing 1.5 mol l
-1
of rongalite and 0.5 mol l
-1
NiCl
2
, resulted
in fibre with a specific electrical resistance of 2.5 ¥ 10
-4
W m. These fibres
contain about 5.5% Ni, consist of about 40 000 elementary fibres and have
a weight of 15.3 g m
-1
.The specific electrical resistance of these fibres is still
much higher than for a metallic conductor. However, because of the adsorp-
tion capacity of PAN fibres for Ni(II), through its cyanide and carboxylic
acid groups, a relatively large fraction of Ni is present at the surface of the
fibres. These Ni centres form a sort of 'seed' layer that can be used as a sub-
strate layer for growing a Ni layer using an electrodeposition method in a
