What does passivation do to metal?

Passivation is a widely-used metal finishing process to prevent corrosion. In stainless steel, the passivation process uses nitric acid or citric acid to remove free iron from the surface. The chemical treatment leads to a protective oxide layer that is less likely to chemically react with air and cause corrosion.

What is the process of passivation?

The passivation process is a method of improving the corrosion resistance of stainless steel parts by removing ferrous contaminants like free iron from their surface, restoring them to their original corrosion specifications.

Can steel be passivated?

Stainless steel and aluminum are both self-passivating materials, but they are not impervious to corrosion. Irregularities in grain, created by manufacture or heat treatments, can create weakness. Surface deposits of oil or other chemicals also may interrupt the passive film.

What causes passivation?

Passivation is the process of treating or coating a metal in order to reduce the chemical reactivity of its surface. This corrosion-resistant surface can be damaged through mechanical means or heat or chemical damage. When that happens, iron is exposed and the item is once again subject to rusting.

Does passivation remove rust?

In general, passivation does not discharge existing stains or rust. That requires other methods, such as light abrasion, bead blasting, tumbling and sometimes sanding. Passivation also does not remove weld scale, black oxides and burn marks from welding.

Can stainless steel rust?

Stainless steel remains stainless, or does not rust, because of the interaction between its alloying elements and the environment. These elements react with oxygen from water and air to form a very thin, stable film that consists of such corrosion products as metal oxides and hydroxides.

What is the difference between passivation and plating?

Passivation is the process of treating a metal surface to reduce the impact of environmental factors such as water or air. With regard to plating, a common practice is to coat a surface with a metal oxide to slow down the oxidation process, thus providing greater corrosion resistance.

What metals can be passivated?

Chromate conversion is a common way of passivating not only aluminium, but also zinc, cadmium, copper, silver, magnesium, and tin alloys. Anodizing is an electrolytic process that forms a thicker oxide layer. The anodic coating consists of hydrated aluminium oxide and is considered resistant to corrosion and abrasion.

What chemical is used for passivation?

Most Common Method – Nitric Acid The most commonly used chemical method to passivate a stainless steel surface is to apply nitric acid. Nitric is a strong mineral acid so it can quickly dissolve all iron compounds and other trace metals that are on the surface.