Introduction to Passivation

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Definition and Function

Passivation is a chemical surface treatment process in which metals—typically stainless steel or corrosion-resistant alloys—are immersed in a specific acidic solution to form a thin, dense, and stable oxide film on the surface.
This protective layer removes free iron and surface contaminants, preventing further oxidation and corrosion, thus significantly enhancing the corrosion resistance and service life of the component.
The process does not alter the part’s dimensions or mechanical properties and is widely used in precision components, medical instruments, electronic housings, and food processing equipment.

Colors

Gold

The passivated surface generally retains its metallic appearance—bright, clean, and uniform—with no visible coating.

Depending on the material and process conditions, a slight silvery or light gray hue may appear.

Example of a bead-milled + anodized colored part

Technical Properties

Corrosion Resistance	Film Thickness	Appearance	Coating Compatibility	Stability
Greatly improved, compliant with ASTM A967 and ISO 16048 standards	Approximately 0.01–0.1 μm, transparent and colorless	Smooth, clean, and residue-free surface	Does not interfere with subsequent painting, plating, or marking	The passive layer remains stable over time, preventing re-oxidation

Applicable Materials

Metals: Stainless Steel

Process Characteristics

Conducted by chemical immersion with no effect on dimensional accuracy.

Effectively removes free iron, welding residues, and contaminants.

Forms a dense and uniform oxide film that stabilizes the metal surface.

Can be applied after machining, polishing, bead blasting, or cleaning.

Environmentally friendly citric-based passivation processes are available to replace nitric acid systems.