The magic of zinc in corrosion control

by Ofentse Sefolo
The magic of zinc in corrosion control

Zinc is an abundant and essential element, non-toxic and safe for use, yet few people and even less engineers appreciate it as a truly magic metal that offers a multitude of applications and versatility. For people in the corrosion world, who seek to extend the life of atmospherically exposed steel, zinc is best known in terms of corrosion control.

Yet how many architects, designers and consulting engineers truly realise the magic that zinc quietly does all around us – protecting railways, bridges, concrete, power pylons and mining structures from catastrophic failure due to corrosion?

Zinc is used extensively to coat steel for the prevention of corrosion. Zinc-oxide is a unique and very useful material in modern civilisation. It is widely used in the manufacture of paints, rubber products, cosmetics, pharmaceuticals, floor coverings, plastics, printing inks, soap, storage batteries, textiles, electrical equipment and other products. Zinc-sulphide is used for making luminous dials, X-ray and television screens and fluorescent lights.

Zinc has an extraordinary capacity to protect uncoated steel structures against premature corrosion. If zinc is alloyed with aluminium to form Zincalume, and this is coated onto a thin steel sheet (continuous galvanising) and receives a resilient organic coating, then it becomes long-lasting as roof sheeting or cladding for buildings.

Critical electrical infrastructure on the coast must have zinc galvanised parts to last up to 30 years.

Hot-dip galvanising
Where zinc really comes into its own, is in the hot-dip galvanising of steel items, wire, poles, steel structures and reinforcing steel for concrete systems. Once the hot-dip galvanised item is exposed to the atmosphere and a corrosive environment, the zinc that is metallurgically bonded to the steel starts to perform its magic.

Hot-dip galvanising of steel takes place in a galvanising kettle. Once the steel is removed from the molten zinc in the kettle, it is ready either to be painted with an organic coating system to give even more corrosion protection to the steel, or it can be left unpainted and used as is and exposed to the atmosphere.

When the steel is immersed in the molten zinc in the kettle and removed for cooling, the result is a metallurgically magic system that protects the underlying steel, although in fact with time the zinc is being sacrificed to protect the steel. So, when you are next out and about, take time to see if you can spot a galvanised steel structure. You will be amazed at the prevalence of galvanised steel!

For more information, contact the International Zinc Association, Africa Desk:
Tel: +27 21 788 9980
Cell: 082 831 2924 (Simon Norton)
Email: zinc@iafrica.com
Website: www.zinc.org

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