b'FOGHORNFOCUS: OPERATIONSZinc Protects ShipsBy Martin Gagn, ZELIXIR Inc.S hip owners are all aware of the power of sacrificial anodes to protect steel from corrosion. When two different metals are in elec-trical contact, and bridged by an elec-trolyte, current flows from the anodic or baser metal to protect the cathodic or nobler metal. This is the basis of galvanic corrosion protection. In the case of steel and zinc, the zinc anodeABCwill sacrifice itself to protect the moreCross sections through zinc coatings. A) Thermal spray zinc. B) Hot-dip galvanized. C) Zinc rich paint. Source: M. Gagnnoble steel. The galvanic, or sacrificial, pro- coatings, such as zinc-rich primersin the dry film after curing. The binding tection properties of zinc anodes areand paints, as well as by solid metallicsystem of the paint provides physical widely known and used to protect thecoatings applied by hot-dip galvaniz- barrier protection while the metallic hulls of steel ships from corrosion. Zincing or thermal spray. zinc particles provide abrasion resis-can also be applied directly as a coatingZinc-rich paints contain fine disper- tance to the paint and cathodic protec-on a steel ship to provide galvanic pro- sions of very small solid zinc particlestion for the underlying steel. Zinc-rich tection over every square centimeter ofencapsulated in the paint film. To bepaint coatings can be applied by brush surface above and below the waterline.most effective, zinc-rich paints shouldor spray in the shop or in the field. Zinc can be applied to steel in liquidcontain at least 92 percent metallic zincLiquid-applied zinc-rich coatings are primarily used as primers support-ing various types of top-coats. Zinc-rich primer coatings are typically covered with a multi-layer paint system, such as an epoxy based mid-layer for barrier protection with a polyurethane top-coat for UV resistance. These addi-tional top-coat layers may also contain zinc oxide, which is not only a white colouring pigment but also provides mildew protection, UV protection, hiding power and neutralizes acid formation during paint oxidation.An alternative to liquid-applied zinc-rich paint coatings are solid metallic zinc coatings applied by hot-dip galvanizing or thermal spray. Metallic zinc coatings are in direct contact with the steel and provide the best galvanic protection. Hot-dip galvanizing produces a zinc coating by completely immersing the steel in a kettle of molten zinc. While immersed in the galvanizing kettle the steel reacts metallurgically with the zinc to form a distinct coating structure, which consists of a series of iron-zinc layers next to the steel with a top surface layer of pure zinc. The metallurgical reaction tightly bonds the 18JUNE 2020FOGHORN'