kromoxidfilm

Kromoxidfilm, or chromium oxide film, is a thin, protective layer that forms on the surface of chromium-containing metals, most commonly stainless steels and other chromium-rich alloys. The film is primarily composed of chromium(III) oxide (Cr2O3) and acts as a passive barrier that reduces further oxidation of the underlying metal.

Formation and characteristics: The chromium oxide film forms spontaneously when the metal is exposed to oxygen, air, and mildly oxidizing environments. It can also be enhanced or thickened by chemical or electrochemical treatments, such as passivation or mild anodizing. Typical spontaneous film thickness on stainless steel is only a few nanometers, though treatments can increase thickness to several tens of nanometers. The film is dense, adherent, and self-healing: if the surface is locally damaged, chromium ions can migrate to the defect and reform Cr2O3.

Properties and function: The chromiuм oxide film provides excellent corrosion resistance by acting as a barrier to the diffusion of oxygen, water, and aggressive ions (such as chlorides). Its presence is a key reason why stainless steels resist rusting in many environments. The film is electrically insulating and chemically stable under ambient to moderately oxidizing conditions. Its optical appearance can vary with thickness, sometimes giving subtle color tints.

Applications and limitations: The film is fundamental to the corrosion resistance of stainless steel and chromium-containing alloys used in architectural, automotive, kitchenware, and chemical-processing equipment. In some applications, the film is deliberately enhanced through passivation or chromate conversion coatings. It can be degraded by strong reducing chemicals, highly aggressive fluorides, or severe mechanical wear, after which reformation requires exposure to oxidizing conditions.