Zinc coatings protect steel by providing a physical barrier as well as cathodic protection for the underlying steel.Īccording to the American Galvanizers Association, more than 11 million tons of zinc are consumed annually worldwide. When left unprotected, steel will corrode in almost any environment. One of zinc’s most exceptional qualities is its natural capacity to protect steel from corrosion. (Source: American Galvanizers Association). In fact, zinc oxide blocks more UV rays than any other single ingredient used in sunscreen. Additionally, zinc is found in a number of products we use daily such as cosmetics, tires, cold remedies, baby creams to prevent diaper rash, treatments for sunburns, and sunscreens. All living things from the tiniest micro-organisms to humans require zinc to live as it helps with specific metabolic processes. Zinc is also common and essential to all life. In fact, approximately 5.8 million tons of zinc are naturally cycled through the environment annually by plant and animal life, rainfall, natural phenomena, and other activity. Most rocks and many minerals, as well as humans, plants, and animals, contain zinc in varying amounts. It naturally exists in the air, water, soil, and the biosphere. Thus, for hot-dip galvanizing, the zinc carbonate layer is the rusted or corroded zinc that protects the zinc coating protecting the steel.Zinc is the 24th most abundant element in the Earth's crust. The formation of zinc carbonate turns the zinc coating to a dull grey color. The zinc carbonate layer corrodes very slowly and protects the zinc underneath. The zinc carbonate is the stable film that adheres to the zinc surface and won't wash off. Later these products react with atmospheric carbon dioxide to form zinc carbonate. The first products of zinc corrosion are zinc oxide and zinc hydroxide. The patina layer is the products of zinc corrosion and rust. The zinc is protected by the formation of a patina layer on the surface of the coating. Hot-dipped galvanizing creates a zinc barrier and sacrificial cathodic protection to prevent corrosion of the steel itself. Related: How long does galvanized steel last? The performance of galvanized steel depends on the environment as well as the galvanization process. Also like other ferrous metals, zinc corrodes or rusts at different rates depending on its environment (8).Ĭommon environments for galvanized steel are indoor and outdoor environments, storing hundreds of different chemicals, in fresh water, sea water, soils, concrete, treated wood, or extreme temperatures. However, zinc corrodes at a rate of 1/30 of that for steel. Like all ferrous metals, zinc corrodes when exposed to air and water. Electroplate galvanized steel left outside for about a decade or two will weaken the zinc coating and eventually expose the underlying steel to corrosion and rust far sooner than hot-dipped galvanized steel.Īll zinc galvanized coatings are more corrosion resistant than bare iron or steel. If the outer layer of electroplated galvanized zinc is damaged, the underlying steel will be exposed to the environment and rust. Figure 1 below illustrates the zinc thickness of various galvanizations bonded to base steel.įigure 1: Thickness and microstructure of various zinc coatings (6 p.1)Įlectroplate galvanization to apply a zinc layer has advantages, but zinc does not form a patina layer or white rust. Long term corrosion protection of the zinc coating depends on the formation of the patina layer or the exposed rusting of the zinc coating.Įarlier we discussed zinc plated steel and zinc coatings: learning how zinc protects the underlying metal from corrosion and how the type of galvanization affects the properties of the zinc metal alloys and rate of corrosion. This thin outer layer of zinc rust is white, it protects the zinc metal underneath and it does not wash off. For hot-dipped galvanizing, when a galvanized steel coating of zinc corrodes with the atmosphere or water a "patina" layer of corrosion byproducts is created. Layers of zinc corrode differently depending on which type of galvanization method is used. Yes, zinc of galvanized steel rusts, but not in the same way as other metals.
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