Sticky Vacuum

The two pieces of copper clung together as if welded--but there was no adhesive between them. As they explained how they turned the trick, scientists of the National Research Corp. gave U.S. technology a practical and powerful boost into space.

Metallurgists have long known why metals do not bond themselves together when they come in contact in the earth's atmosphere. Exposed to air, they have already become covered with oxide films or a thin layer of gas that keeps the metals from actually touching. National Research scientists were interested in what happens when metals touch in the hard vacuum high above the earth's atmosphere. In their space simulation chamber they created an almost perfect vacuum (10 torr--), the same as spacecraft encounter 500 miles above the earth. In that ultra emptiness, surface gases evaporated; oxide films, once cleaned off, did not return.

And pieces of bare metals that touched together "grew" together as if welded.

National Research scientists have made pieces of metal grab each other in a vacuum until sometimes the "cold-weld"' that formed had 95% of the strength of solid metal. Steel grabs strongly, and the scientists suspect that many other metals will do the same.

One lesson already learned is that moving parts of a space vehicle designed to work in a vacuum for long periods should not have simple metal-to-metal bearings.

They are likely to jam in cold-welds. This may well have happened already; the phenomenon would explain the misbehavior of such moving parts as electrical relays in complicated satellites. Ordinary greasy lubricants do little good; they evaporate too quickly. National Research scientists have found a few solid materials that can keep metals from sticking together, but they are not yet satisfied. They are still looking for a reliable way to make a long-lasting space bearing.

The potential problems of metals in space are numerous and annoying. But the tendency of metals to grab each other may have advantages too. When space vehicles are assembled in orbit, say National Research scientists, their joints may well be made of metals that cold-weld firmly as soon as they touch.

-- Scientists measure high vacuum in torrs. One torr (named after Italian Scientist Evangelista Torricelli, 1608-47, inventor of the mercury barometer) is the pressure that will support a column of mercury one millimeter high.

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