| dc.description.abstract | Cables are a key part of electrical and electronics systems, responsible for carrying
electricity and signals over long distances. Ensuring their safety and reliability is essential to ensure
electricity and signals are delivered without interruptions. Silver-plated copper cables are widely
utilized in various high-performance applications by NASA, DOE and DOD due to better electrical
and thermal conductivity, higher corrosion resistance, solderability, crimp ability, flexibility and
durability compared to pure copper. However, silver-plated copper cables are highly susceptible
to a specific kind of corrosion called red plague which significantly affects its mechanical and
electrical properties including strength, ductility, fatigue life and electrical conductivity.
Addressing red plague is a significant challenge for many NASA, DOE, and DOD systems.
Thus far, all experimental studies concerning red plague have been conducted exclusively
on cable samples without electrical current applied. However, in real-world applications—ranging
from industrial environments to advanced systems used by NASA and the DOD—these cables are
typically connected via solder joints, routinely carry electrical current, and operate for extended
periods under varying atmospheric conditions. As regards the current direction in-plane to the
copper-silver interface, it is well understood that the current itself will not affect the corrosion.
Therefore, by best knowledge, there is no scientific finding/report on the corrosion in cables
carrying DC current and the impact of current on corrosion. This approach aligns with current
scientific knowledge, which suggests that the rate of corrosion growth should not be affected by
the electrical current itself in the cables. As a result, investigating the specific impact of direct
current (DC) on corrosion in silver-copper cables under real-world conditions is both urgent and
essential.
Currently, corrosion detection and monitoring techniques for corrosion under coating and
insulation such as red plague are mainly destructive which involves peeling of the insulation layer
for visual inspection of cables resulting in material damage, cable wastage, and significant
corrosion-related costs. This is because detecting red plague, which occurs specifically in silver
plated copper cables, presents unique challenges as the corrosion develops internally at the
interface between the silver plating and the copper core, making it difficult to identify using
conventional non-destructive testing methods. Therefore, it is important to develop a non
destructive corrosion detection and monitoring technology to minimize catastrophic system
failures and reduce the high costs associated with corrosion.
In this work, red plague in silver-plated copper cables with and without DC current was
experimentally studied and characterized under 90oF and 90% relative humidity atmospheric
condition using optical microscopy (OM), scanning electron microscopy (SEM), energy dispersive
x-ray spectroscopy (EDS) and nano x-ray CT techniques.
Firstly, the corrosion rates/depth in cables with and without DC current including
longitudinal and transversal was experimentally determined. The atmospheric spread/depth of
corrosion for long term periods was predicted using corrosion models. The influence of DC current
on the corrosion growth in cables was also experimentally exploited. The study revealed that DC
current significantly accelerates corrosion, causing red plague to occur earlier, grow faster, and
cover a larger area. Corrosion was also observed to spread along the cables in the direction of DC
current. In addition, corrosion at the current input end (positive) was also found to be more severe
than output end (negative) of the cables. Corrosion also initiates earlier and progresses faster in
cables carrying higher current values or subjected to higher current densities.
Furthermore, this research determined that the corrosion acceleration observed in cables
with DC can be attributed to self-hall effect phenomenon. In silver-plated copper cables with DC
current, the self-hall effect is believed to cause the electrons to drift away from the cable surface
under the influence of Lorentz force, creating localized regions of electron depletion promoting
anodic reactions and making the regions more susceptible to corrosion. Moreover, the Hall effect
phenomenon in copper conductors was experimentally verified in this study, further supporting
these findings.
Finally, a novel time-dependent s-parameter-based non-destructive and in-situ technology
was developed to evaluate the corrosion status in the silver-plated copper cables. Two techniques
were developed to effectively represent the corrosion status in the cables, namely the loss function
and peak analysis method. The loss function approach involves utilizing loss function formulas,
specifically mean squared value, to compute the numerical difference differences of the s
parameter readings at various time points. The peak analysis method involves using a Fast Fourier
Transform smoothing and counting zero crossing using softwares for counting the number of peaks
within specific frequency ranges.
Ultimately, this dual approach – integrating experimental study and non-destructive
technology – will not only provide a way to assess the operational readiness of the system in which
silver-plated copper cables are used but would facilitate a substantial reduction in system failures
and associated costs due to corrosion. | en_US |
