Metallurgy: Oil from the Medicine Cabinet

Titanium and stainless steel rank high among the glamour metals of modern technology. Because they retain their great strength even when heated to high temperatures, they have countless uses in such space-age products as Gemini capsules and jet engines. They would have countless other applications were it not for one exasperating characteristic: they cannot be used for moving parts that rub against other hunks of titanium or stainless steel. When they are, the pieces simply stick together.

Every oil known to science has failed. As soon as the metals rub themselves clean, molecules begin moving in both directions across the interface, the area of contact between the two metals. The “seizure” that results is as effective as a weld. Even machining is difficult. When a steel cutting tool is used on stainless steel or titanium, it sticks to the piece it is shaping and cuts out rough chunks instead of smooth chips.

The difficulty seemed insurmountable until General Electric scientists went, in effect, to the medicine chest. Iodine, they discovered, is the answer. Dissolved in benzine and mixed with oil, the element reacts immediately with clean titanium and steel, forming a thin film of metallic diiodide that is strong enough to hold two pieces apart. The layers of microscopic diiodide crystals also slide against each other like cards in a deck, allowing the surfaces to move freely.