Formation of Metal Passivation and Thickness of Passivation Film

Passivation is defined as the formation of a very thin protective layer on the surface of a metal material under oxidizing conditions, achieved by strong anodic polarization, to inhibit corrosion. Some metals or alloys develop a simple inhibiting layer at the activation potential or under weak anodic polarization, thereby reducing the corrosion rate. According to the definition of passivation, this situation does not fall under passivation.

The structure of the passivation film is extremely thin, with a thickness measurement ranging from 1 to 10 nanometers. Detection of hydrogen in the passivation thin film indicates that the passivation film may be a hydroxide or hydrate. Iron (Fe) is difficult to form a passivation film under normal corrosion conditions; it only occurs in highly oxidizing environments and under anodic polarization to high potentials. In contrast, chromium (Cr) can form a very stable, dense, and protective passivation film even in mildly oxidizing environments. In iron-based alloys containing chromium, when the chromium content exceeds 12%, it is called stainless steel. Stainless steel can maintain a passivated state in most aqueous solutions containing trace amounts of air. Nickel (Ni), compared to iron, not only has better mechanical properties (including high-temperature strength) but also exhibits excellent corrosion resistance in both non-oxidizing

Formation of Metal Passivation and Thickness of Passivation Film

Passivation is defined as the formation of a very thin protective layer on the surface of a metal material under oxidizing conditions, achieved by strong anodic polarization, to inhibit corrosion. Some metals or alloys develop a simple inhibiting layer at the activation potential or under weak anodic polarization, thereby reducing the corrosion rate. According to the definition of passivation, this situation does not fall under passivation.

The structure of the passivation film is extremely thin, with a thickness measurement ranging from 1 to 10 nanometers. Detection of hydrogen in the passivation thin film indicates that the passivation film may be a hydroxide or hydrate. Iron (Fe) is difficult to form a passivation film under normal corrosion conditions; it only occurs in highly oxidizing environments and under anodic polarization to high potentials. In contrast, chromium (Cr) can form a very stable, dense, and protective passivation film even in mildly oxidizing environments. In iron-based alloys containing chromium, when the chromium content exceeds 12%, it is called stainless steel. Stainless steel can maintain a passivated state in most aqueous solutions containing trace amounts of air. Nickel (Ni), compared to iron, not only has better mechanical properties (including high-temperature strength) but also exhibits excellent corrosion resistance in both non-oxidizing and oxidizing environments. When the nickel content in iron exceeds 8%, it stabilizes the face-centered cubic structure of austenite, further enhancing passivation capability and improving corrosion protection. Therefore, chromium and nickel are crucial alloying elements in steel.and oxidizing environments. When the nickel content in iron exceeds 8%, it stabilizes the face-centered cubic structure of austenite, further enhancing passivation capability and improving corrosion protection. Therefore, chromium and nickel are crucial alloying elements in steel.