Passivointikäsittelyssä

Passivointikäsittelyssä is a Finnish term that refers to the passivation treatment of metals. Passivation is a chemical process that increases the resistance of a metal or alloy to corrosion by forming a thin, inert layer on its surface. This layer is typically an oxide or hydroxide film, which protects the underlying metal from reacting with its environment.

The most common metals that undergo passivation treatments are stainless steels, aluminum, titanium, and copper alloys. Stainless steel, for example, is naturally corrosion-resistant due to the presence of chromium, which forms a passive chromium oxide layer. However, during manufacturing processes like welding or machining, this protective layer can be damaged or contaminated, leading to potential rust or corrosion. Passivation treatment for stainless steel aims to restore and enhance this passive layer, removing free iron and other contaminants that could initiate corrosion.

The passivation process typically involves cleaning the metal surface to remove oils, greases, and other impurities, followed by immersion in a chemical bath. For stainless steel, this bath often contains nitric acid, although citric acid is also used as a more environmentally friendly alternative. The acid selectively removes free iron and other less noble metals, allowing the chromium to re-form a robust passive oxide layer. For other metals, different acid solutions or electrochemical methods might be employed.

The resulting passive layer is extremely thin, often only a few nanometers thick, and does not significantly alter the dimensions or appearance of the metal part. However, it drastically improves the material's durability and lifespan in corrosive environments, making passivation a crucial step in the manufacturing of many industrial components, medical devices, and food processing equipment.