Metal finishing processes such as Zinc Plating are described as being ‘sacrificial’ in nature, but what does this term actually refer to?
When metals such as steel, and in our case, steel springs, are exposed to the elements they will often undergo a process called Oxidation which is corrosive in nature. Iron molecules within the steel’s makeup react with the water and oxygen in the environment to form hydrated iron oxide which we commonly know as rust.
How do sacrificial coatings work?
The materials used in a Sacrificial Coating will be more reactive than the metal they are protecting. So in the example of Zinc Plating on steel, Zinc is more reactive than steel. In the electroplating process a thin layer of Zinc is added onto the steel, covering it and so it will react with the environment before the steel. As it does this, it dissolves and the electrons that are released will ‘flow’ to the metal that is being protected, in our example steel springs. This turns the surface of the steel into a cathode which prevents the corrosion of the metal.
Does it stop protecting the metal once sacrificed
All metals corrode over time, even noble ones such as gold and silver. A sacrificial coating is used to slow down this reaction, but it will not last forever. The layer of Zinc in our example is corroded in preference to the steel, but once it has been fully oxidised its protective capabilities will cease. As a general rule, a thicker coating should provide longer part life, but Zinc is popular due to its low cost so where corrosion isn’t prevalent, it may be possible to re-plate components.
This article was originally posted on Silchrome Plating.