Learn about the classification of corrosion

Thread Content

Based on the pattern of corrosion, it can be divided into two types: uniform (general) corrosion and local corrosion, with local corrosion further being subdivided into several subtypes. Based on the mechanism of corrosion, it can be divided into chemical corrosion and electrochemical corrosion. The difference between the two is that when electrochemical corrosion occurs, there are separate cathodes and anodes on the metal surface, with a small electric current flowing between them; whereas in simple chemical corrosion, no microcells are formed. It was previously believed that high-temperature gas corrosion (such as high-temperature oxidation) falls under chemical corrosion, but modern concepts indicate that there are also separated anode and cathode regions in high-temperature corrosion, as well as the flow of electrons and ions. Based on this, another classification emerged: dry corrosion and wet corrosion. Wet corrosion refers to the corrosion of metals in aqueous solutions and is a typical form of electrochemical corrosion, while dry corrosion refers to corrosion in dry gases (usually at high temperatures) or non-aqueous solutions. Pure physical corrosion is rare in metals, while in non-metals it is mostly pure chemical or physical corrosion; sometimes both effects occur simultaneously.