Galvanized iron is iron ore that has been refined, molded and coated with zinc plating. The zinc provides the galvanization, as zinc resists corrosion typical of ungalvanized wrought or cast iron. Galvanized iron is manufactured and used for wide variety of purposes but its primary use is for sheet metal roofing and other building materials, such as metal framing studs, metal roof shingles and fencing. Other uses include wire mesh, pipes, roof ornaments and other decorative exterior architectural products, gutters, flashing, metal buckets and connectors, such as screws and nails. The material resists rust and is therefore a very common material for outdoor projects.
The term galvanized originates from Luigi Galvani, an 18th century Italian physician and physicist who experimented in bioelectricity and electrochemistry. His experiments and research, centered around the chemical and electric reactions, did not directly lead to galvanized iron, but they did spark research into the chemical reactions between metals. Zinc-covered iron, it was later discovered, resists oxidation that turns bare iron into red dust in a matter of years. Galvanized iron revolutionized metalworking and spawned the modern galvanized iron industry.
Iron is galvanized by several different processes. The most common is electrogalvanization, the process of immersing the molded iron product into an electrolyte solution of zinc sulfate. Hot-dip galvanization, another common process, is iron dipped into molten zinc or zinc alloys. In sherardization, the iron is placed in an airtight vault and heavily dusted with powdered zinc particles. The fourth process, less effective than the others, is painting or spraying molten zinc or zinc pigments onto the metal.
The types of iron galvanization differ for various uses. For example, sheet metal roofing exposed to the harshest outdoor elements year round, is usually hot-dipped or electroplated. Inferior roofing is painted with zinc. Gutters and pipes may be painted or sprayed.
Galvanized iron is not completely corrosion-resistant. Products that are exposed to concrete, acid rain, tannic acids from certain trees and excessive moisture will rust over time. Abrasions or the creeping and twisting of the iron can split open the zinc coating, allowing moisture into the cracks and rusting the iron beneath. Despite its vulnerabilities, galavanized iron products are extremely strong and remain as the only corrosion-resistant metal products available.