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Vacant Electron Spaces in Atoms Make Metals Resistant to Rusting ACANT spaCC1' ill tht: atoms of nickel arc respo1l5ible for its resistance to corrosion or "rusting," according to Dr. Herbert H. Uhlig, Metallurgist of the General Electric Research Laboratory. In earlier researches, he found that the stainlessness of stainless steel is not due primarily to the formatioll on the surface of a film of oxide, as formerly supposed. Instead it results from the electronic arrangement in the atoms of the alloy. Now he finds that the same thing is true for corrosion-resistant alloys such as that of copper and nickel (Monel). An atom may be thought of as a nucleus around which revolve, somewhat in the manner of planets around the sun, from 1 to 92 electrons_ These move in from one to seven different orbits or shells. Ordinarily aile shell is filled with electrons before the
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next aile begins, though in the case of certain ;'transition" elements there are vacancies in the shell next to the outer one. 'In nickel, for example, there are only 8 electrons in the third shell, instead of the 10 it could hold, despite the fact that there are two electrons in the fourth and outermost shell. With inner· shells completely filled, a metal is more subject to corrosion. Because of the vacancies nickel is very resistant to corrosion, but it is too expensive for many applications, and so it is alloyed with copper which is lower in cost. The atom of copper has one more electron than that of nickel. In the alloy these extra electrons go to fill the vacancies in tbe nickel atom. However, as long as any vacancies remain ill the nickel the alloy still resists corrosion as well as pure nickel. Finally, when the proportion of 60 per cent copper and 40 per cent nickel is reached all the nickel vacancies have been filled. Further increasing tbe proportion of copper makes the alloy less resistant until pure copper is reached. whicb corrodes much more than pure nickel.
