Galvanization of Metal

A material that has undergone the galvanization process—a corrosion prevention method for iron or steel in which zinc is applied to the base to stop it from rusting—is referred to as galvanized metal. Typically, it’s done to enhance the durability of metallic parts.

Galvanization of Metal
Galvanization of Metal

Iron or steel is coated with zinc during the galvanizing process to increase the base material’s resistance to corrosion. Because of its adaptability, this metal coating can be used in a variety of industries, such as solar, electronics, construction, and automotive.

History of Galvanization

  • The renowned Indian medical book, the Charaka Samhita, published approximately in 500 BC, talks about a metal that, when oxidized, produces pushpanjan, also known as ‘philosopher’s wool’, that is believed to be zinc oxide.
  • The Discovery of 2,500-year-old ornaments composed of alloys with 80% zinc content has hinted towards the galvanization in past.
  • The first known specimen of galvanized iron was found on 17th-century Indian armor in the Royal Armories’ Museum collection in the United Kingdom.
  • In 1837, France and England discovered the technology of galvanizing sheet iron at the same time.
  • The technique of galvanization is named after Luigi Galvani, an Italian physician, physicist, biologist, and philosopher.

Galvanized Metal

  • To create a protective layer of zinc which is metallurgically attached to the surface of iron or steel, clean, oxide-free iron or steel must be submerged in molten zinc during the galvanization process.
  • After that, the coating forms a metallurgical bond with the metal’s surface, serving as a sacrificial anode. Thus, the coating gives the metal endurance and resilience.

Types of Galvanization

Different methods can be employed to galvanize the metals. They are discussed here:

Hot-Dip Galvanizing

  • The machine operators have to chemically or manually, clean the base metal before galvanizing.
  • Afterward, the base metal is dipped into a molten zinc 460°C (860°F) bath to carry out this process.
  • After being dipped in molten zinc, the base metal creates a metallurgical bond.
  • When the metal is extracted from the bath, it interacts with oxygen to produce zinc oxide.
  • Furthermore, carbon dioxide combines with zinc oxide, generating zinc carbonate, which serves as the last protective layer.
  • The technique of galvanizing creates an excellent, dense coating of zinc on the surface of the substrate metal, making it more resistant to corrosion.
  • This technique makes the galvanization quicker and more importantly economic.
  • Hot dip galvanization can be carried out with both simple and complex sheet metal designs.
  • Hot-dipping generally preserves the metal’s structural integrity, although hydrogen embrittlement is possible in certain extremely high-strength steels.

Electro-Galvanizing

  • Using this technique, an electrolyte solution is first heated to an electrical current prior its application to the steel material. The zinc ions are transferred onto the metal substrate by the electric current.
  • The metal is submerged in an electrolyte solution, usually made of zinc sulfate or zinc cyanide. After that, the zinc will bond to the substrate metal and create a layer of protection.
  • Electro-galvanizing is employed on lengthy rolls of metal sheets during the early stages of product development.
  • This method provides a precise and consistent coating thickness to the material.
  • But this approach produces a thinner coating, unlike hot-dip galvanization.
  • For the metal’s smooth zinc coats, grain refiners are added.

Sherardizing

  • Sherardizing is a solid dispersion method that involves heating items in the presence of zinc dust and an inert substance, such as sand.
  • The operation is usually carried out inside of a slowly spinning sealed container at temperatures around 320 ºC – 500 ºC.
  • The zinc/iron amalgamated layer thereafter gets zinc phosphate, producing a clean-coated finish.
  • The protective layer precisely matches the curves of the base material, and consistent coatings emerge on all products, even the ones with irregular shapes.
  • Sherardize coatings possess a mat-gray appearance and can develop scratches from regular exposure with other adhesives. Because of the coating’s hardness, such scrapes are minor and have no impact on its corrosion resistance.
  • Sherardizing coatings produce a tougher, smoother surface finish than hot dip galvanizing, as well as greater control over coating thickness.
  • Because this galvanizing procedure does not require hydrogen, hydrogen embrittlement is prevented.
  • This process is commonly used to apply a zinc coating on iron or copper items.
  • It was developed by metallurgist Sherard Osborn Cooper-Coles.

Zinc Spray Galvanizing

  • Zinc spray galvanizing is the technique used to apply a protective coating to a steel surfaces using fragmented particles of molten zinc.
  • This procedure is appropriate for structures that are too massive to be submerged in a zinc bath, as well as objects that would deform during hot-dip galvanizing.
  • The process begins with surface prep, which requires removing rust, and undesirable exterior coatings such as paint, oil, and other impurities.
  • The cleaning process involves applying high-pressure abrasive blasting, which further affects the surface.
  • The atomized metal fragments then get sprayed over the rough surface, where they begin to adhere and solidify.
  • Multiple layers are put on to increase the coating’s thickness, with typical values spanning from 80 and 300 microns, however, thicknesses of 50 to 500 microns can also be achievable.

Advantages of Galvanized Metals

There are several advantages of galvanizing the metals. Some of the major advantages are discussed here:

Economic Initial Cost

Choosing galvanized steel may appear to be more expensive at first, but it is a terrific long-term investment. It has a cheaper initial cost than several other routinely specified protective paints for steel. The cost of applying labor-intensive coatings such as painting has risen far higher than the cost of industrial galvanizing. So it is cheaper when compared to other coatings.

Low Maintenance Cost

Steel without a protective covering requires additional maintenance to preserve its physical appearance and structural integrity. Even if galvanizing is more expensive than other coatings initially, it’s often cheaper in the long haul. Maintenance is a challenge and increases expenses when structures are placed in remote places, as well as when a plant closure or stoppage of production occurs.

Time-Saving

Galvanizing is a quick and simple process. A complete protective layer can be applied in a matter of minutes. For larger applications, galvanized steel components are ready to use. When the structure is fully assembled, it is immediately available for use or the next step of construction.

Durability

Galvanized coatings on conventional structural parts have an average life expectancy of well over 50 years in most rural situations, and 20 to 25 years or even longer under intensive urban and coastal exposure. A steel structure can be preserved for more than a century with an average 85 micron thick covering—the same thickness as an A4 sheet of paper.

Complete Protection

Every square inch of the galvanized material is protected from damage, including sharp edges and difficult-to-access areas. No other coating applied to a structure or manufacturing after completion provides the same level of protection as galvanization.

Reliable

There are several reasons why galvanizing steel is the most effective kind of prevention of corrosion. To begin, galvanizing is a spontaneous metallurgical process that occurs when cleansed steel is placed in the molten zinc at a specific temperature. Compared to a paint coating, the metallurgical bond established by galvanizing is an everlasting component of the steel rather than a chemical or mechanical one.

Drawbacks of Galvanization

Although there are a lot of advantages of galvanization there are some drawbacks to it. Some of the drawbacks are discussed here:

Expensive

The galvanization process is occasionally costly, particularly for large-scale operations. Galvanizing steel is often more expensive than other corrosion-prevention procedures, such as painting or applying sealant. This may not be practicable for some projects when the budget is a significant determining factor.

Toxic

Galvanizing steel uses zinc, a substance that can be harmful to human health if inhaled or swallowed. Zinc can also release toxic poisons into the environment as it corrodes.

Corrosion

Galvanizing steel is the process of coating the metal with a layer of zinc to prevent corrosion. Galvanized steel, while resistant to red rust, can develop white rust over time if exposed to moisture.

Poor Appearance

The zinc coating on the metal might make it appear dull, which some people dislike. Furthermore, with time, the zinc coating may begin to flake off, creating an uneven and ugly surface.

Applications of Galvanized Metals

Galvanized metal has a wide range of applications, some of which are briefly covered here.

Automobile Industry

Zinc-coated automobile bodywork has become common in automobile manufacturing, while the maker previously restricted them to high-end models. The “body-in-white,” built entirely of galvanized steel, accounts for approximately 80% of a car’s body. Galvanized steel’s ability to resist corrosion makes it a helpful tool for automobile development since it enables manufacturers to provide consumers with “anti-rust assurances.”

Construction

Galvanized steel has been the construction industry standard for almost a century, regardless of residential or business purposes. Along with to its endurance, it is utilized in the building because of its aesthetic value. People also utilize it for minor structural components such as fencing, rails, gutters, tubes, poles, and others.

Wind-Mills and Solar-Panel

Solar panels and windmills must function constantly for an extended period, therefore interruptions for repairs and maintenance would increase costs. Galvanized steel is employed in solar energy installations because of its corrosion resistance. Even in tough climates, hot dip galvanized steel can provide long-lasting protection.

Tele-Communication Sector

Because of the high towers and distant locations, phone connections and towers are challenging to repair regularly. They must be protected if they are to operate uninterrupted. Wires of phone and equipment boxes are made of galvanized steel. As so, it reduces the risk of harm and does not require any maintenance.

Video Reference

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Other References

  • https://www.indexfix.com/frequently-asked-questions/sherardizing-coating
  • https://eoncoat.com/what-is-metal-galvanization-and-what-are-the-dangers/
  • https://www.sciencedirect.com/topics/materials-science/galvanized-metal
  • https://tampasteel.com/what-is-galvanized-metal/
  • https://waykenrm.com/blogs/galvanized-metal/
  • https://www.corrosionpedia.com/definition/1421/zinc-spray-galvanizing
  • https://moduloc.ca/blog/pre-galvanized-vs-hot-dip-galvanized-steel-which-is-better/
  • https://galvanizing.org.uk/galvanise-steel/

About Author

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Jyoti Bashyal

Jyoti Bashyal, a graduate of the Central Department of Chemistry, is an avid explorer of the molecular realm. Fueled by her fascination with chemical reactions and natural compounds, she navigates her field's complexities with precision and passion. Outside the lab, Jyoti is dedicated to making science accessible to all. She aspires to deepen audiences' understanding of the wonders of various scientific subjects and their impact on the world by sharing them with a wide range of readers through her writing.

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