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Active TRL 3 (started at 2, targeting 3)
Project Objective
The primary goal of this project is to complete the experimental study for the determination of the corrosion process and rate of cables under different environmental and operational conditions.
Project Description
This project aims to prevent the possible failures caused by the corrosion of silver-plated copper cables widely used in current NASA systems. The primary goals of this project are: to complete the experimental study for the determination of the corrosion process and rate of cables under different environmental and operational conditions; and to monitor the corrosion status in cables, further validating the nondestructive methods developed by this team in a previous project.
In this proposed project, four objectives are to:
1) Continue experiments to determine the corrosion rate up to a time period of two years and determine the chemical reaction(s) and products generated by the corrosion and study the chemical mechanism of these reactions. The results will establish a solid database to
estimate the corrosion status of a cable, which can help NASA to guide the future practices;
2) Search a commercially available solder so that bonding cables with the solder will minimize/eliminate the increase in the corrosion rate caused by the solder. The selected solder will be recommended to NASA for future fabrication of circuits, which would increase the reliability of the systems, in which silver-plated copper wires/cables are used;
3) Test the corrosion rate of cables under different electrical currents to determine whether there is a threshold of the current, meaning the corrosion acceleration due to the current is very weak when the current is lower than the threshold. If, yes, the threshold current will be experimentally determined for each cable. Based on the results, a recommendation about limit of electrical current to pass through a cable will be made; and
4) Further develop the nondestructive methodology for in-situ monitoring the status of corrosion in a cable. The S-signal of cables will be determined at frequencies from 100 kHz to 3 GHz for the cables treated at different conditions with different times. All four parameters of four signals (i.e., S11, S12, S21, and S22) will be used for the study. At the end, a simple parameter with a well-defined frequency range will be selected to represent the corrosion status of a cable. The patent application about the technology will be updated.
Project Results and Conclusions
General results are listed below.
•All cables suffer significant red plague.
•For cables (Ag/Cu) bonded with solder (Pb/Sn), the corrosion starts at the junction and then spreads along the cable into areas under insulation and penetrates deeper into the copper core.
•It was experimentally observed that solders with less elements show a slower corrosion.
For cables without DC current:
•Under 90° F and 90% relative humidity, the corrosion progresses along the cable direction (longitudinal) to about 1 inch in the first year while the average corrosion depth across the radius direction (transversal) is about 5.43 microns in the first year for a strand of 230μm-radius.
•Under 70°F and 40% RH, after 1 year, no cables suffered red plague corrosion yet. Therefore, more time is needed.
•With corrosion induced manually in the cables, the longitudinal corrosion spreads is about
3 inches in the first year in cables without solder joints, and about 4 inches in the first year in cables bonded with solder joints.
•The atmospheric depth of corrosion for long-term periods was predicted using the power function and power linear model.
For cables with DC current:
•Red plague is severe, occurs faster, and covers a larger area than without DC current. The current causes expansion of silver cover cracks in the cables which further enhanced the transfer of oxygen and corrosion products, thereby accelerating corrosion of copper.
•Corrosion (longitudinal) spreads much faster along the cables in the direction of DC current.
•Under 90° F and 90% Relative Humidity, the corrosion (longitudinal) progresses about 10 inches in the first year while it (transversal) is about 23.18 microns in the first year for a strand of 230μm-radius.
•Under 70° F and 40% RH, the corrosion (longitudinal) spreads along the cable direction to about 0.4 inches in the first year.
•The atmospheric spread/depth of corrosion for long term periods was predicted using the power function and power linear model.
Benefits include: 1) Establishing a solid database to predict the corrosion status of cables with different history so that possible failures in aerospace systems due to the cables will be prevented; 2) Training students to tackle the future challenges in NASA systems; and 3) Developing new knowledge and technology related to corrosion of cables through publications and patent application, which also can be used by manufacturers to improve the quality of their products.
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