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FIG. 1. When electrical contact is made between electrodes A and B, electrode B acts as an electron sink, thus upsetting the equilibrium and causing continued dissolution of A.

FIG. 1. When electrical contact is made between electrodes A and B, electrode B acts as an electron sink, thus upsetting the equilibrium and causing continued dissolution of A.

plants. It is not necessary for the components to be macroscopic, monolithic electrodes for this to happen, and the same effect can be seen when there are different microstructurai features within one alloy. In practice, it is the regional variations in electrode potential over an alloy surface that are responsible for much of the generalized surface corrosion that takes place in metallic components.

Many of the commonly used surgical alloys contain highly reactive metals (i.e., with high negative electrode potentials), such as titanium, aluminum, and chromium. Because of this high reactivity, they will adsorb oxygen upon initial exposure to the atmosphere. This initial oxidation stage leaves an impervious oxide layer firmly adherent to the metal surface; thus all other forms of corrosion may then be stifled because the oxide layer acts as a protective barrier, passivating the metal. It should also be noted that it is possible to enhance the oxide layer artificially to provide better corrosion resistance.

In summary, the basic principles of corrosion determine that:

1. In theory, corrosion resistance can be predicted from standard electrode potentials. This explains the nobility of some metals and the considerable reactivity of others, but is not useful for predicting the occurrence of corrosion of most alloy systems in practice.

2. Irrespective of standard electrode potentials, the corro

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