Corrosion of Silver-Plated Copper Conductors - NEPP

Figure 6a. Section through X -X (see
Fig. 5), the superimposed numbers
referring to corroded strands. Three of
the 143 strands are corroded to some
extent (2.1%)
Figure 6b. Detail of strand no. 1 from
Figure 6a. Adjacent strands are
uncorroded, but support crystals of
cuprous oxide (x150)
Figure 6c. One strand in the centre of the
braid has been totally transformed to a
silver tube. Cuprous oxide (visible as
bright red under polarised light) is located
within the silver tube and within all the
inter-strand spaces
Figure 6d. Tunnelling corrosion along
strand no. 3 (x 150)
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Conclusions
These laboratory examinations have confirmed the existence of red-plague corrosion,
restricted to isolated areas, on the outer braid shield of three spacecraft cables. In the
most severely affected area, 3% of the strands making up the braid cross-section have
been affected. It is estimated that a maximum of 2% of the electrically conductive path
has been degraded.
The silver-plating thickness on the braids is generally good, but corrosion has
initiated at randomly spaced defects. The loose-fitting out jacket facilitates the
ingress of humidity and chloride and fluoride contaminants may possibly have an
accelerating effect on the galvanic corrosion mechanism.
The actual extent of red-plaque corrosion is markedly less than would be expected
from visual inspection alone. Corrosion has only taken place in isolated areas. These
areas contain silver and copper oxides (both of which are electrically conductive).
The evidence of liquid on the braid suggests that in the past the