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Passivation Stainless Steel Passivation According to ASTM A380, passivation is "the removal of exogenous iron or iron compounds from the surface of stainless steel by means of a chemical dissolution, 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 also describes passivation as "the chemical treatment of stainless steel with a mild oxidant, such as a nitric acid solution, for the purpose of enhancing the spontaneous formation of the protective passive film."Passivation is performed with acid solutionsStress , to remove contaminants and promote the formation of the passive film on a freshly created surfacePassivation . Common passivation treatments include nitric acid Stainless steels solutions or pastes which will clean the steel surface of free iron contaminants. Care must be taken in selecting and using passivation treatments to ensure the selected treatment will target the contaminant. Passivation will also aid in the rapid development of the passive oxide film on the steel's surface. Passivation does not usually result in a marked change in appearance of the steel surface. Both pickling and passivation solutions can employ dangerous acids that can damage both the operator and the environment if not handled correctly. Passivation should only be performed by trained, experienced technicians familiar with the potential hazards associated with the science. Safety practices must be fully understood when handling passivation chemicals. Special boots, gloves, aprons and other safety equipment must be used. Tanks, heaters and ventilation, as well as baskets and racks must be appropriately engineered to perform the process. Stainless pickling acids are highly corrosive to carbon steel. It is essential that all acids are thoroughly removed by rinsing the component after completing the process. Residual hydrofluoric acid will initiate pitting corrosion. It may be advantageous to neutralize the acid with an alkali before the rinsing step. Passivation is recommended where the surface must be free of iron. The presence of any iron, cast iron, mild steel, carbon steel or low alloy steel particles on the surface of stainless steel will promote pitting corrosion at the cells set up between the "free" iron and stainless steel. It may even cause rouging of the otherwise stainless, stainless steel. This potentially very serious (and certainly unsightly) problem most often occurs due to contamination by scraping with carbon steel tools or fixtures, or from grinding swarf. Passivation also aids in the rapid development of the passive surface layer on the steel. The iron removal iron can be readily carried out by the procedures in the following table adapted from ASTM A380. () reference Passivation Procedures
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