What is Passivation
Passivation is “the removal of exogenous iron or iron com-pounds from the surface of a stainless steel by means of a chemicaldissolution, most typically by a treatment with an acid solution that will remove the surface contamination but will not significantly affect the stainless steel itself.”In addition, it alsodescribes passivation as “the chemical treatment of a stainless steel with a mild oxidant, such as a nitric acid solution, for the purpose of enhancing the spontaneous formation of the protective passivefilm.”
In layman’s terms, the passivation process removes “free iron”contamination left behind on the surface of the stainless steel as a result of machining and fabricating processes.
Thesecontaminants are potential corrosion sites which, if not removed, result in premature corrosion and ultimately result in deterioration of the component.In addition, the passivation process facilitates theformation of a very thin, transparent oxide film, which protects the stainless steel from “selective”oxidation (corrosion).
How is the Passivation Process Performed?
The process typically begins with athorough cleaning cycle.It is intended to remove oils, greases, forming compounds, lubricants, coolants, cutting fluids, and other undesirable organic and metallic residue left behind as a result offabrication and machining processes.General degreasing and cleaning can be accomplished by a variety of commonly accepted methods, including vapor degreasing, solvent cleaning, and alkaline soaking.After removal of the organic and metallic residues, the parts are placed into the appropriate passivation solution.Although there are many variations of passivating solutions, the overwhelming choice isstill the nitric acid based solutions.
Recently, there has been substantial research performed to develop alternative processes and solutions that are more “environmentally friendly,”yet equally...