Passivation is the process by which a material becomes ‘passive,’ meaning it is less affected by environmental factors such as corrosion. It involves the spontaneous formation of a very thin, non-reactive surface film that acts as a barrier, shielding the bulk material from further attack. This film is typically an oxide or nitride layer, a few nanometers thick.
Passivation
- Christian Friedrich Schönbein
The mechanism of passivation is electrochemical. When a reactive metal like chromium, aluminum, or titane is exposed to an oxidizing environment (like air or certain acids), its surface rapidly oxidizes. If the resulting metal oxide is stable, dense, non-porous, and well-adhered to the metal surface, it forms a protective passive layer. This layer is extremely thin, often only 1-3 nanometers, but it is sufficient to dramatically slow down the rate of corrosion by preventing direct contact between the metal and the corrosive environment.
The stability of this passive film is dependent on the environment, particularly pH and the presence of certain ions like chlorides. For example, the chromium oxide ([latex]Cr_2O_3[/latex]) layer on stainless steel is highly effective in many environments but can be locally broken down by chloride ions, leading to pitting corrosion. The breakdown and reformation of this passive layer is a dynamic process. If the film is mechanically scratched or damaged, the exposed metal will often repassivate almost instantly, a property known as self-healing.
Passivation can be a natural process or can be enhanced artificially through chemical treatments, such as dipping stainless steel in nitric or citric acid to remove free iron from the surface and encourage the formation of a more robust chromium-rich oxide layer. This process is distinct from applying a revêtement, as the passive layer is formed from the base metal itself.
Type
Disruption
Utilisation
Precursors
- Discovery of reactive metals like chromium and aluminum
- Early observations of metals resisting corrosion in specific acids
- Development of electrochemical theories
Applications
- stainless steel’s résistance à la corrosion (chromium oxide layer)
- titanium’s biocompatibility in medical implants (titanium dioxide layer)
- anodizing of aluminum for protection and color
- protecting silicon wafers in microelectronics
Brevets :
Potential Innovations Ideas
!niveaux !!! Adhésion obligatoire
Vous devez être membre de l'association pour accéder à ce contenu.
DISPONIBLE POUR DE NOUVEAUX DÉFIS
Ingénieur mécanique, chef de projet ou de R&D
Disponible pour un nouveau défi dans un court délai.
Contactez-moi sur LinkedIn
Intégration électronique métal-plastique, Conception à coût réduit, BPF, Ergonomie, Appareils et consommables de volume moyen à élevé, Secteurs réglementés, CE et FDA, CAO, Solidworks, Lean Sigma Black Belt, ISO 13485 médical
Nous recherchons un nouveau sponsor
Votre entreprise ou institution est dans le domaine de la technique, de la science ou de la recherche ?
> envoyez-nous un message <
Recevez tous les nouveaux articles
Gratuit, pas de spam, email non distribué ni revendu
ou vous pouvez obtenir votre adhésion complète - gratuitement - pour accéder à tout le contenu restreint >ici<
Historical Context
Passivation
(if date is unknown or not relevant, e.g. "fluid mechanics", a rounded estimation of its notable emergence is provided)
Related Invention, Innovation & Technical Principles