Corrosion Protection - There are two corrosion phases to consider when specifying a Zinc finish.

The first phase is the time taken for the deposited Zinc layer to show the first sign of corrosion, often called ''WHITE RUST''. When Zinc oxidises, in its pure form it is white, but, in practice, the colour of the oxide salt can range from grey to black. At this stage, whilst the finish may be unattractive, the component is still protected by the Zinc.

The second phase is the time it takes for the steel itself to start to corrode with evidence of familiar ''RED RUST''. The structure of the component is being degraded from this point.

EXTENDING THE TIME TO WHITE RUST

The subsequent application of chromate conversion coatings over Zinc plating, as well as top coat sealants and lacquers, give additional protection particularly under humidity and moisture conditions. The process colours the deposit and the resultant colour is often used to specify the correct film, e.g. the clear or yellow passivite. Chromate films are very thin and add no measurable thickness to the overall coating. Most passivated parts retain their electrical conductivity to varying degrees.

The degree of corrosion prevention is therefore directly proportional to the thickness of the Zinc layer deposited and the type of passivate applied. Dependent upon customer requirements, a Zinc layer of 5 to 25 microns in thickness can be applied.

The following table shows a possible range of corrosion protection tested in 5% neutral salt spray in accordance with ASTM B117.

Corrosion Protection
	White-h	Red-h
Clear Passivate	20-24	96
Yellow Passivate	72-96	150-200
Hexavalent Chrome Free Thick Film	120	360

We offer a specially formulated Zinc finish with trivalent passivate to withstand 500 hours to 'Red Rust'.