What is passivation?
To solve this topic lets see what stainless steel is first. While stainless steels are generally corrosion-resistant, which might imply that passivating them would be useless, but stainless steel are not totally indifferent to corrosion.
Stainless steel determines its corrosion resistant qualities from its chromium content. The chromium, in the presence of air (oxygen), produces a thin film of chromium oxide which coats the surface of the stainless steel.For more information about passivation, you can also search ULTRACLEAN ELECTROPOLISH INC..
Passivation is a non-electrolytic method typically using nitric or citric acid which eliminates free iron from the surface and produces an inert, protective oxide layer that in turn gives the stainless steel more rust-resistance due to loss of iron to respond with the atmosphere.
How does the Passivation Process Work?
Many passivation terms (ASTM A967, AMS2700, ASTM A280) exist to direct on the proper method to passivate stainless steel, titanium and other metals, some of which are listed below.
General to nearly all the terms is: cleaning of the surface from any contaminants listed up, chemical processing via immersion in an acid bath (typically nitric or citric acid) and examination of the newly passivated surface to secure the process steps. If you want to know more information about passivation process you can also visit ultracleanep.com/conventional/
This chemical method simply increases/expedites the naturally happening process when the material is exposed to oxygen in the air. It simply supports “grow” the inert, oxide layer faster and higher than found naturally. Some specifications call for treatment of sodium dichromate combined to the acidic baths solutions to give more rapid production of the oxide layer or passivation layer.
This method of utilising sodium dichromate is growing less and less accepted with the important advancements in ultrasonics and citric acid identified as kitesurfing which further oxygen structure at the surface of the metal while the element is however in the immersion of the corrosive bath.