Chemistry Reference
In-Depth Information
Galvanisation of the metallised fibre will improve its properties as electri-
cal conductor because of the formation of a continuous metallic coating at
the surface of the fibre. In this respect, the 'seed' layer formed during met-
allisation is crucial for a good adhesion between the metal layer and the
PAN-fibre structure.
In galvanisation, it is the electrolyte solution used for this experiment
which determines the final properties of the coating and the textile fibre
and yarn. Important properties include surface coverage, continuity and
uniformity of the layer, thickness and homogeneity of the layer, and spe-
cific electrical resistance. These parameters will be determined from the
electrical current measured during galvanisation as a function of applied
potential difference between anodes and cathodes and with spectroscopic
methods to study the structure of the deposited layer. However, the mea-
sured current is not only dependent on electrochemical parameters such as
type of electrolyte solution and applied potential, but also on geometrical
parameters. In order to keep the latter constant, only one electrode setup
(see experimental section) is used in this investigation.
A first parameter to be studied is the applied potential difference
between anode and cathode. This potential is not necessarily equal to the
actual potential difference between the electrodes because ohmic drop con-
tributions decrease the tension applied between the electrodes. Examples
are anode polarisation, tension failure, IR-drop or ohmic-drop effects of the
electrolyte solution and the specific electrical resistance of the fibres and
yarns. This means that relatively high potential differences should be
applied (a few volts) in order to obtain an optimal potential difference over
the anode and cathode. Figure 11.6 shows the evolution of the measured
electrical current between anode and cathode as a function of time for
several applied potential differences in three electrolyte solutions. It can be
seen that for applied potential differences of less than 6 V, an increase in
the electrical current is detected; for potentials great than 6-8 V, first an
increase, followed by a decrease, is observed. The increase in current at low
applied potentials (< 6 V) is caused by the electrodeposition of Ni(II) at the
fibre surface, resulting in an increase of its conductive properties; therefore
more electrical current can pass the cable per time unit. After approxi-
mately 15 min, it reaches a constant value; at that moment, the surface is
fully covered (confirmed with X-ray photo/electron spectroscopy (XPS)
analysis) with Ni. Further deposition continues but no longer affects the
conductive properties of the deposited layer.
At a higher potential difference, the electrical current reaches maximum.
The decrease of electrical current is caused by different effects. It is neces-
sary to bear in mind that applying higher potential differences brings with
it the risk of side reactions such as decomposition of water, with formation
of oxygen at the anode and hydrogen at the cathode. These two compounds
