Tech Briefs

Electrically Conductive Anodized Aluminum Surfaces

These coatings are highly adherent, transparent, and relatively inexpensive.

Anodized aluminum components can be treated to make them sufficiently electrically conductive to suppress discharges of static electricity. The treatment was conceived as a means of preventing static electric discharges on exterior satin-anodized aluminum (SAA) surfaces of spacecraft without adversely affecting the thermal-control/optical properties of the SAA and without need to apply electrically conductive paints, which eventually peel off in the harsh environment of outer space. The treatment can also be used to impart electrical conductivity to anodized housings of computers, medical electronic instruments, telephone-exchange equipment, and other terrestrial electronic equipment vulnerable to electrostatic discharge.

The electrical resistivity of a typical anodized aluminum surface layer lies between 1011 and 1013 Ω.cm. To suppress electrostatic discharge, it is necessary to reduce the electrical resistivity significantly . preferably to<=109 Ω.cm. The present treatment does this. The treatment is a direct electrodeposition process in which the outer anodized surface becomes covered and the pores in the surface filled with a transparent, electrically conductive metal oxide nanocomposite. Filling the pores with the nanocomposite reduces the transverse electrical resistivity and, in the original intended outer-space application, the exterior covering portion of the nanocomposite would afford the requisite electrical contact with the outer-space plasma.

The electrical resistivity of the nanocomposite can be tailored to a value between 107 and 1012 Ω.cm. Unlike electrically conductive paint, the nanocomposite becomes an integral part of the anodized aluminum substrate, without need for adhesive bonding material and without risk of subsequent peeling. The electrodeposition process is compatible with commercial anodizing production lines.

At present, the electronics industry uses expensive, exotic, electrostatic-discharge-suppressing finishes: examples include silver impregnated anodized, black electroless nickel, black chrome, and black copper. In comparison with these competing finishes, the present nanocomposite finishes are expected to cost 50 to 20 percent less and to last longer.

This work was done by Trung Hung Nguyen of EIC Laboratories for Marshall Space Flight Center. For further information, access the Technical Support Package (TSP) free on-line at www.techbriefs.com/tsp under the Materials category. MFS-32092-1

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