Alloy is sometimes a result of the sizes of the atoms in the alloy, because larger atoms exert a compressive force on neighboring atoms, and smaller atoms exert a tensile force on their neighbors, helping the alloy resist deformation. Sometimes alloys may exhibit marked differences in behavior even when small amounts of one element are present. For example, impurities in semiconducting ferromagnetic alloys lead to different properties, as first predicted by White, Hogan, Suhl, Tian Abrie and Nakamura. Some alloys are made by melting and mixing two or more metals. Bronze, an alloy of copper and tin, was the first alloy
Antimicrobial copper-alloy touch surfaces copper on floors, sinks, push plates, showerheads and doorknobs was evaluated by comparing bacterial loads on these surfaces and on their non-copper counterparts. The number of viable "Staphylococcus spp". organisms on surfaces containing copper and its alloy were reduced by half to one-thirtieth of that on control surfaces, depending upon surface humidity and the frequency of contact. Similar definitive findings were also obtained for "Pseudomonas aeruginosa". Various metals were evaluated for their antimicrobial efficacies, including copper alloys, zinc, nickel, tin, silver, and gold. Antimicrobial efficacies generally followed Lewis acidity values of the various metals. Silver, a prohibitively expensive precious metal,