Chemistry Reference
In-Depth Information
Table 11.2
Nickel and cobalt absorption capacity and their diffusion coefficient as a
function of precipitation-bath parameters during PAN-fibre production
Parameters
Concentration of
Temperature of
Plasticisation drawing,
B
,
NaCNS in
precipitation bath, K
% (
C
pB
=
12%,
T
=
10°C)
precipitation bath
(
C
pB
=
12%,
B
=
700%)
C
pB
, % (
B
=
700%,
T
=
10°C)
8
12
16
273
283
293
500
700
900
1100
Ni(II)
7.40
19.00
30.00
14.00
18.50
16.00
22.00
18.00
7.80
5.40
diffusion
coefficient,
D
¥
10
13
,
m
2
/s
Quantity
0.80
1.00
1.04
0.94
1.00
0.92
1.06
1.05
0.89
0.89
of sorbed
Ni(II), %
Co(II)
8.00
18.00
27.50
23.20
18.20
15.50
21.00
17.50
7.50
5.60
diffusion
coefficient
D
¥
10
13
,
m
2
/s
Quantity of
0.81
0.97
1.03
0.93
0.97
0.91
1.02
0.98
0.88
0.86
absorbed
Co(II), %
nickel is absorbed in the fibre structure as NiS. Sulphide produced by
decomposition of the reducing agent forms NiS, which is sparingly soluble
in water and precipitates. The amount of NiS in PAN and silk fibres is much
lower than in the other fibres, probably due to the presence of functional
groups in its structure. These groups are able to coordinate with the reduc-
ing agent, resulting in a more stable complex. As a consequence, this dimin-
ishes the decomposition rate of the reducing agent.
Despite the fact that the Ni content and the fractions of NiS and Ni in
silk and PAN fibres (after thermofixation) are comparable if rongalite is
used as a reducing agent, a considerable difference in specific electrical
resistance is observed. This indicates that the amount of nickel absorbed by
the fibres and by the functional groups present at the fibre structure is not
enough to explain the results. In addition, the distribution of the Ni parti-
cles is important. First, with scanning election microscope (SEM) it was
found that the distribution of Ni in silk was not uniform, while in PAN fibres
the distribution is uniform within the fibre and at the surface. The latter is
due to adsorption of nickel on the functional groups of the PAN chemical
structure. The non-uniform distribution of nickel in silk can be explained
