Corrosion Protection

Zinc Layers

  • Sherardised layers provide active protection
  • The duration of protection depends on the layer thickness
  • Passivation and topcoats increase the protective effect significantly
  • SheraTop® is a modern duplex system

Protecting products from corrosion will preserve the value and function for a long time. Usually the replacement- or maintenancecosts are much higher than the cost of a good corrosion protection.
Zinc coatings such as Sherardizing are proven for decades and the corrosion mechanism of zinc is well known.

Since zinc is electrochemically less noble than iron, it provides an active cathodic protection. As long as enough zinc is present it will be sacrified and the base material is not attacked. In contrast to iron corrosion, zinc corrosion products adhere to the surface and protect it. Scratches are self-healing and will be filled with corrosion products to stop further attack.

The life expectancy of a zinc corrosion protection depends on the applied amount of zinc. The thicker the layer, the longer the protection. This was confirmed by numerous studies.

EN ISO 14713

In EN ISO 14713 the life expectency of zinc coatings in various corrosive environments are described. The expected life of a sherardized top layer with an average thickness of 35 microns, for an urban climate (C3) is more than twenty years.


Accelerated Corrosion Tests

In an accelerated corrosion test according to ISO 9227 all galvanized or zinc diffusion coated products corrode relatively quickly, while they are very durable in nature. During the test zinc does not have the time to build up a protective patina.

Adding a passivation or topcoat will give you an extra passive protection. In this case even thin layers of zinc will achieve excellent results in the salt spray test.

In this case the rapid test checks the unity and passivity of the top layer as well as the adhesion of the overall system.

In field application the top coat protects the active layer until it becomes faulty by cracks, scratches or other mechanical stress. In this case the active basecoat will fill the defects and reduces the corrosion attack.

A Duplex system provides therefore much better corrosion protection than the individual coatings.

The SheraTop®-System exploits the special characteristics of the sherardized base coat and is optimally adapted to the Topcats. This will achieve remarkable results in accelerated corrosion tests and application.