Hot dip galvanizing is a process of coating steel and iron with a layer of zinc to prevent corrosion. The process involves fluxing in molten or aqueous zinc ammonium chloride before bonding the zinc layer. The history dates back to the 1700s, and the modern process involves an aqueous solution or molten ammonium chloride. The finished piece has a pure outer layer of zinc, followed by a layer of a zinc-iron alloy, and then a substrate of iron or steel. The buildup of zinc oxide and zinc carbonate prevents rust and extends the life of the item.
Hot dip galvanizing is a process of coating metals such as steel and iron with a thin layer of zinc. Because zinc interacts more easily with oxygen than iron or steel, it will tend to corrode first and protect the underlying metal. Hot-dip galvanizing is typically a multi-step process that requires a piece of metal to be fluxed in molten or aqueous zinc ammonium chloride before a layer of zinc is bonded to it. The pure zinc layer then transforms to zinc oxide when exposed to oxygen and finally to zinc carbonate after exposure to carbon dioxide. Another similar process is electroplating, which is an electroplating method that deposits a thinner layer of zinc.
The history of hot dip galvanizing dates back to the 1700s when the process was first described. It was later perfected in the 1800s when the modern flushing procedure was first introduced. This early hot-dip galvanizing process involved cleaning the piece of iron with sulfuric acid and then using ammonium chloride as a fluxing agent, a method which has remained to this day.
Modern hot dip galvanizing uses an aqueous solution or a molten layer of ammonium chloride to perform the fluxing step. This is needed to prepare the iron or steel piece for galvanizing. When an aqueous solution is used, it is typically stored in a separate flush tank. However, molten ammonium chloride is typically suspended over a bath of pure zinc, so that the fluxing process occurs when a workpiece is placed in the bath for galvanizing.
The hot-dip galvanizing process effectively bonds a layer of zinc to the surface of an iron or steel workpiece. Each finished piece may vary slightly in physical composition, although it typically has a pure outer layer of zinc, followed by a layer of a zinc-iron alloy, and then a substrate consisting of iron or steel. The pure zinc layer will typically turn to zinc oxide after being exposed to oxygen, after which it will be exposed to carbon dioxide to create zinc carbonate.
Iron and steel are both subject to corrosion in the presence of oxygen, a process that leads to the formation of rust. This can be prevented by coating an item with zinc, as zinc is a little more reactive to oxygen than iron or steel. The buildup of zinc oxide and zinc carbonate on the outside of a metal piece typically changes the color to a dull gray, but the underlying metal is not damaged. Items treated with hot-dip galvanization tend to last longer when exposed to the elements, and they can even be welded if you pay close attention to the presence of the resulting zinc fumes.
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