Pintapassatointi

Pintapassatointi, or surface passivation, is a range of treatments that form or enhance a protective, chemically inactive surface layer to reduce reactivity and improve stability. It is used in metals, semiconductors, and coatings.

Common methods are chemical, electrochemical, and thermal passivation. Chemical passivation uses oxidizing solutions to create oxide layers; for example stainless steel is treated in nitric or citric acid to remove loose iron and promote a chromium-rich film. Electrochemical passivation, such as anodizing, forms controlled oxides by applying voltage. Thermal passivation heats the material to stabilize surface films without altering bulk properties.

Materials and mechanisms: stainless steel, aluminum, and titanium form protective oxides (Cr2O3, Al2O3). In silicon-based devices, passivation can involve silicon dioxide, silicon nitride, or hydrogen termination to reduce surface states and recombination. Organic coatings can also act as passive barriers.

Applications: corrosion resistance in architecture, chemical processing, and marine environments; semiconductor devices, solar cells, and MEMS; medical implants and packaged electronics.

Advantages include reduced corrosion rates, improved wear and chemical resistance, and more stable surface properties. Limitations include potential damage from mechanical wear, environmental incompatibilities, and the need for careful process control. Standards such as ASTM A967 provide guidance for stainless-steel passivation practices.