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Corrosion generally implies a harmful deterioration of a metal; of course this can be due to oxidation (the metal rusting), but it can also be due to many other things. American chemistry teacher get that right: "The corrosion process is usually electrochemical in nature, having the essential features of a battery. Corrosion is a natural process that commonly occurs because unstable materials, such as refined metals want to return to a more stable compound. For example, some metals, such as gold and silver, can be found in the earth in their natural, metallic state and they have little tendency to corrode. Corrosion involve two chemical processes…oxidation and reduction. Oxidation is the process of stripping electrons from an atom and reduction occurs when an electron is added to an atom. The oxidation process takes place at an area known as the anode. At the anode, positively charged atoms leave the solid surface and enter into an electrolyte as ions. The ions leave their corresponding negative charge in the form of electrons in the metal which travel to the location of the cathode through a conductive path. At the cathode, the corresponding reduction reaction takes place and consumes the free electrons. The electrical balance of the circuit is restored at the cathode when the electrons react with neutralizing positive ions, such as hydrogen ions, in the electrolyte. From this description, it can be seen that there are four essential components that are needed for a corrosion reaction to proceed. These components are an anode, a cathode, an electrolyte with oxidizing species, and some direct electrical connection between the anode and cathode. Although atmospheric air is the most common environmental electrolyte, natural waters, such as seawater rain, as well as man-made solutions, are the environments most frequently associated with corrosion problems."