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 in April 2011 analyzed the effectiveness of copper-alloy furnishings to lessen the microbial load on various frequently touched surfaces such as door handles, toilet seats, and railings. Of the 14 surfaces tested 8 had statistically significant decreases in the number of microbes found on them while the other 6 had a decrease in the number of microbes as well, but not in a statistically significant amount. Additionally certain microbes in particular were found in far less quantities on the copper-alloy surfaces than on the normal ones, these being Vancomycin-resistant "Enterococcus", "Staphylococcus aureus", and Coliform bacteria. The study concluded that copper