The main differences between black passivation and blue-white passivation are their composition, properties and application scenarios.
Author: Anna
The main differences between black passivation and blue-white passivation are their composition, properties and application scenarios.
Composition and properties
Black passivation: Black passivation is usually obtained by adding metal ions such as copper, silver, iron, nickel, etc. as blackening agents in a passivation solution with a pH of 2-4. This kind of passivation film formation speed, but the film layer arrangement structure is relatively loose, so the salt spray resistance is relatively low, the black passivation film without closed treatment in the neutral salt spray test generally can only be maintained for about 36 hours.
Blue-white passivation: Blue-white passivation solution mainly consists of trivalent chromium salt, sulfuric acid, nitric acid and hydrofluoric acid and other components, and sometimes add nickel salts, cobalt salts, rare earth metal salts and sol-gel type sealer. Due to the lack of hexavalent chromium components, the corrosion resistance of the blue and white passivation film is poor, and the neutral salt spray test can generally only reach 48-72 hours.
Application Scenarios
Black Passivation: Commonly used for metal finishes that require a black appearance, such as certain mechanical parts or decorative items. Due to its low cost and obvious appearance, black passivation is more common in industrial applications.
Blue-White Passivation: is mainly used where there is a need to improve the corrosion resistance of metal surfaces, especially in wet or corrosive environments. The corrosion resistance of blue and white passivated films is not as good as that of colored passivation, but it is still used in some less demanding environments.
Cost and maintenance
Black passivation: due to its relatively simple composition, it is low cost and suitable for mass production.
Blue and white passivation: although slightly more costly, its corrosion resistance is still economical in some environments.
In summary, black passivation and blue-white passivation differ in composition, performance and application scenarios, and users can choose the appropriate passivation method according to their specific needs.