Discuss metal corrosion prevention measures: metal coatings and cladding
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This post was last edited by Wang Wei2 on 2024-10-8 at 10:03. A thin layer of more corrosion-resistant metal (such as chromium, nickel, lead, etc.) can be used to protect the underlying steel surface. The common method is electroplating, typically 2 to 3 layers are applied, each only a few dozen micrometers thick; as a result, pores are inevitably present, and the solution can penetrate these pores, creating corrosion cells within the coating–substrate layer. When the coating is made of precious metals (gold, silver, etc.), easily passivated metals (chromium, titanium), or metals such as nickel and lead, it has a higher potential than iron; thus, it acts as a cathode and accelerates 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 electrical resistance and thus granting them a certain lifespan. When base metals such as zinc and cadmium are used as coatings, 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 (fusion plating), flame spraying, vapor deposition, and full-metal sheet cladding are also commonly used. The latter has no micropores, exhibits strong corrosion resistance, and has a longer lifespan; however, it is more expensive.
Metal coatings and claddings are commonly used anti-corrosion measures. Protection can be provided by coating the surface of steel with a metal that has greater corrosion resistance, such as chromium, nickel, or lead. Electroplating is a common method; usually 2 to 3 layers are applied, with a thickness of only a few dozen micrometers. These coatings may contain micropores, through which the solution can penetrate, thereby forming corrosion cells. If precious metals or metals prone to passivation are used as coatings, although their higher electrode potentials may accelerate the corrosion of the underlying iron, in atmospheric or aqueous environments, the corrosion products can clog the micropores, thereby prolonging the service life. When base metals such as zinc and cadmium are used as coatings, the coating acts as a sacrificial anode to protect the underlying steel from corrosion. In addition, there are methods such as hot-dip coating and flame spraying. The fully metal sheet cladding has no pores, offering better corrosion resistance and a longer lifespan, but at a higher cost. .
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