Let’s discuss the issue of metal coatings and cladding as measures for preventing metal corrosion
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A thin layer of a more corrosion-resistant metal (such as chromium, nickel, lead, etc.) can be used to protect the underlying steel layer. The common method is electroplating, usually 2 to 3 layers are applied, each with a thickness of only a few dozen micrometers; as a result, micro-pores are inevitably present. The solution can penetrate these pores, thereby creating corrosion cells within the coating–substrate layer. When the coating is made of precious metals (such as gold and silver) or metals that are prone to passivation (such as chromium and titanium), as well as nickel and lead, their higher potential compared to iron causes them to act as cathodes, thereby accelerating the corrosion of the underlying iron. Therefore, such coatings are not suitable for highly corrosive environments (such as acids), but can be used in environments like the atmosphere and water; the slowly formed corrosion products can block the micropores, increasing resistance and thus providing a certain lifespan. If base metals such as zinc and cadmium are used as the coating, the polarity of the corrosion cell is reversed; the exposed steel inside the pores acts as the cathode, while the zinc or cadmium coating acts as the anode. Zinc and cadmium are used as sacrificial anodes to provide cathodic protection for steel; in a mild corrosion environment, zinc corrodes slowly and can thus maintain a long service life. Tin-plated iron (tinplate) is widely used in food cans. Tin has a higher standard potential than iron, but in food organic acids its potential is lower than that of iron, allowing it to act as a sacrificial anode. In addition to electroplating, hot-dip plating (melting immersion plating), flame spraying, vapor deposition, and full-metal sheet cladding are also commonly used. The latter has no micropores, offers better corrosion resistance and a longer lifespan, but is more expensive.
Among metal corrosion prevention measures, the use of metal coatings and cladding is a common approach. By coating the surface of steel with a metal that has greater corrosion resistance, such as chromium, nickel, or lead, it is possible to effectively protect the underlying steel from erosion. However, the plating layer is often only a few dozen micrometers thick, and it may contain pores that allow corrosive agents to penetrate, thereby creating a corrosion cell between the plating layer and the underlying layer. Especially when the coating is a precious metal or a metal prone to passivation, this battery effect leads to accelerated corrosion of the underlying iron. If base metals such as zinc and cadmium are used as the coating, these metals act as sacrificial anodes to protect the underlying iron, which serves as the cathode, from corrosion; this method is effective in mild corrosive environments. Furthermore, although tin in tinplate (tin-plated iron) has a higher potential than iron, it can also act as a sacrificial anode under certain conditions, such as in the environment of organic acids in food cans. In addition to electroplating, methods such as hot-dip plating, flame spraying, vapor deposition, and full-metal sheet cladding can be used to provide a more uniform and dense protective layer. These methods typically have no pores, offer better corrosion resistance and a longer lifespan, but they are relatively more expensive. .