pasivace

Pasivace, in materials science often called passivation, is a chemical or electrochemical treatment that creates a stable, protective oxide or inert surface layer on a metal or semiconductor. The goal is to reduce surface reactivity, increase corrosion resistance, and promote long-term stability in harsh environments. Passivation is not a traditional coating; the protective layer is ultrathin and becomes part of the metal surface.

In metals, passivation is commonly applied to stainless steels and nickel alloys, where a chromium-rich oxide film (often Cr2O3) forms to limit active sites for corrosion. Aluminum and titanium form their own native oxide films, alumina (Al2O3) and titanium dioxide (TiO2), which contribute to passivity. The resulting protection depends on alloy composition, surface condition, temperature, and the chemicals used during treatment.

Typical procedures involve an initial cleaning to remove oils and contaminants, followed by immersion or spraying with acidic solutions. Nitric acid baths are commonly used for stainless steel, with citric acid as a milder alternative. Temperature ranges are usually from room temperature to moderately elevated temperatures for short times. For aluminum, citric or phosphoric acid formulations are common. After treatment, thorough rinsing and drying are essential. Standards such as ASTM A967/A967M and ASTM A380 cover chemical passivation and related cleaning for stainless steel parts and assemblies.

Benefits of passivation include improved corrosion resistance, a more uniform surface, and reduced staining. Limitations include the fact that passivation is not a mechanical barrier and the thin oxide layer can be damaged by abrasion. Environmental and waste-management considerations are important due to acid baths. In semiconductor technology, passivation also refers to insulating or protective layers that reduce surface recombination, illustrating variations of the term.