Chemistry Reference
In-Depth Information
Step 1. Dry metallised fibre (0.1 g) was immersed in 50 ml of H
2
O and
10 ml of 1.5% H
2
O
2
was added. It was then boiled for 20 min. Buffer
solution (1 ml, pH = 10) was added, and the amount of Ni(II) was deter-
mined by titration with 0.01 mol l
-1
EDTA using Hg(II) as end-point
detection. Based on Equation 11.1, the amount of NiS extracted from
the fibre can be calculated with Equation 11.2:
Æ
NiS
+
H O
NiSO
+
2H
[11.1]
22
4
2
(
)
=¥
(
)
(
)
c
in %
V
58 69
.
¥
c
¥
100
1000
¥
g
[11.2]
NiS
EDTA
where
c
NiS
is the concentration of NiS,
V
is the volume of the sample,
c
EDTA
is the concentration of EDTA, and
g
is the weight of the fibre.
Step 2. Same as in step 1, but after 20 min of boiling, add 1 ml of HNO
3
and boil for another 10 min. Then proceed with the addition of the buffer
solution and the titration. The total amount of Ni + NiS is determined
by Equation 11.4 based on Equation 11.3:
Æ
(
)
+
NiS
++
Ni
2HNO
+
2H O
NiSO
+
Ni NO
3H
[11.3]
3
2
2
4
3
2
2
(
)
=¥
(
)
(
)
c
in %
V
58 69
.
¥
c
¥
100
1000
¥
g
[11.4]
Ni+NiS
EDTA
Step 3.
Finally, the amount of Ni is determined using Equation 11.5:
c
=
c
-
c
[11.5]
Ni
Ni
+
NiS
NiS
• Prior to the use of these methods, it was verified that extraction occurs
for 100%. This was done by dissolving 0.1 g of dry metallised fibre in
DMF and another 0.1 g of dry metallised fibre according to the methods
described above. In both cases, the same result for Ni or Co content was
obtained, showing that extraction occurs for 100%.
•The diffusion coefficient in Table 11.2 is determined using the Krenk
equation:
12
•
=
(
)
¥
(
)
cc
4
r
D
tp
[11.6]
t
where
c
t
and
c
•
are the concentration of absorbed metal at time t and after
equilibrium, respectively,
r
is the fibre radius, t is the time of metallisation,
and D is the diffusion coefficient.
The results of this analysis are shown in Table 11.1. It is clear that absorp-
tion of nickel in all fibres is reasonably high, but the amount of metallic
nickel is considerably higher in PAN fibres and, to a lesser extent, in natural
silk. This indicates that the structure of the fibres (pore size and perme-
ability as well as functional groups) plays an important role. Sodium
dithionite and rongalite are known as good reducing agents, but their sta-
bility is fairly limited. One of their decomposition products (particularly in
acidic solutions) is sulphide, which explains why an important fraction of
