Alloy are relatively similar in size, the atom exchange method usually happens, where some of the atoms composing the metallic crystals are substituted with atoms of the other constituent. This is called a "substitutional alloy". Examples of substitutional alloys include bronze and brass, in which some of the copper atoms are substituted with either tin or zinc atoms respectively. In the case of the interstitial mechanism, one atom is usually much smaller than the other and can not successfully substitute for the other type of atom in the crystals of the base metal. Instead, the smaller atoms become trapped in the
Antimicrobial copper-alloy touch surfaces antimicrobial efficiency tests include: The registrations are based on studies supervised by EPA which found that copper alloys kill more than 99.9% of disease-causing bacteria within just two hours when cleaned regularly (i.e., the metals are free of dirt or grime that may impede the bacteria's contact with the copper surface). To attain the EPA registrations, the copper alloy groups had to demonstrate strong antimicrobial efficacies according to all of the following rigorous tests: The alloy groups tested and approved were C11000, C51000, C70600, C26000, C75200, and C28000. The EPA registration numbers for the six groups of alloys are as