The differences between chemical and electrochemical corrosion are:
First, the electronic gains and losses are different
The two methods of reacting to gain and loss of electrons are different. Chemically corroded metals and oxidants gain and lose electrons directly. Electrochemical corrosion uses the principle of primary cells to gain and lose electrons. In the electrochemical corrosion reaction, the metal loses electrons and is oxidized. The reaction process is called the negative electrode reaction process, and the substance in the medium gets electrons from the metal surface and is reduced. The reaction process is called the positive electrode reaction process.
With or without current
The two kinds of reactions are different in the presence or absence of current. The chemical corrosion reaction is not accompanied by the generation of current, and the electrochemical corrosion reaction is accompanied by the generation of current. In the process of electrochemical corrosion, the metal and the electrolyte form two electrodes, which form a corrosive galvanic cell, so that an electric current passes.
Third, the oxidized substance is different
The two kinds of materials that are oxidized during the two different corrosion processes are different. Chemically corroded metals are oxidized. For example, oxidizing gases such as high-temperature furnace gases cause iron oxides on the steel surface and decarburization on the surface; electrochemically active metals are oxidized. The iron and a small amount of carbon in the steel just happens to form countless tiny galvanic cells to corrode.
Fourth, the response is different
The nature of the two reactions is different. Electrochemical corrosion is the transfer of electrons during corrosion, while chemical corrosion is a pure chemical reaction. Chemical corrosion occurs a redox reaction due to the contact of a metal with an external medium. Electrochemical corrosion is metal corrosion that occurs during electron transfer.