<P> Galvanic corrosion (also called bimetallic corrosion) is an electrochemical process in which one metal corrodes preferentially when it is in electrical contact with another, in the presence of an electrolyte . A similar galvanic reaction is exploited in primary cells to generate a useful electrical voltage to power portable devices . </P> <P> Dissimilar metals and alloys have different electrode potentials, and when two or more come into contact in an electrolyte, one metal acts as anode and the other as cathode . If the electrolyte contains only metal ions that are not easily reduced (such as Na, Ca, K, Mg, or Zn), the cathode reaction is reduction of dissolved H to H or O to OH . The electropotential difference between the reactions at the two electrodes is the driving force for an accelerated attack on the anode metal, which dissolves into the electrolyte . This leads to the metal at the anode corroding more quickly than it otherwise would and corrosion at the cathode being inhibited . The presence of an electrolyte and an electrical conducting path between the metals is essential for galvanic corrosion to occur . The electrolyte provides a means for ion migration whereby ions move to prevent charge build - up that would otherwise stop the reaction . </P> <P> In some cases, this type of reaction is intentionally encouraged . For example, low - cost household batteries typically contain carbon - zinc cells . As part of a closed circuit (the electron pathway), the zinc within the cell will corrode preferentially (the ion pathway) as an essential part of the battery producing electricity . Another example is the cathodic protection of buried or submerged structures as well as hot water storage tanks . In this case, sacrificial anodes work as part of a galvanic couple, promoting corrosion of the anode, while protecting the cathode metal . </P>

Where does corrosion occur in a galvanic cell