Salt water threat to planes and cars.

Certain carbon fiber composite materials used in fighter jets, automobiles, and other vehicles could fall apart if they frequently are exposed to salt water, cautions Chuk Leung, research and development director, PolyComp Technologies, Del Mar, Calif. Planes on an aircraft carrier or cars splashed with water and road salt that is used to melt snow and ice might be affected.

Composite degradation could have significant financial and safety impact. "When you have a degrading structure in airplanes and you have to maneuver, then strength is not there," Leung warns. In addition, "More and more automobiles are being made of composites to reduce weight."

Composites are made up of fibers held together by a plastic polymer matrix. The class of composites Leung is studying, in which the fibers are graphite and the matrix is a polyamide, is used in the skin and wings of the military's next-generation aircraft. If the composite is in contact with metal and is in a salt water environment, an electrochemical reaction somewhat like that in a battery begins to occur. That...