What is nitric passivation?


What is nitric passivation?

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.

How do you passivate with nitric acid?

Nitric acid passivation is most useful in enhancing the corrosion resistance of freshly machined surfaces. The standard nitric acid passivating solution is made up and used as follows: 10 to 15 percent by volume of nitric acid (HNO3) in water.

Is passivation the same as electroplating?

Passivation is a chemical process designed to remove free iron and other contaminants from the part surface. Electropolishing is an electro-chemical process that removes surface metal which improves micro finish, provides deburring and adds to the aesthetics of your part.

What is the purpose 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.

How do you passivate stainless steel with nitric acid?

Passivating stainless steel is typically accomplished in industry by dipping the part in a bath of nitric acid. Nitric acid dissolves any free iron or other contaminants from the surface, which cleans the metal, and it re-oxidizes the chromium; all in about 20 minutes.

What is difference between plating and passivation?

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.

Is passivation necessary?

Passivation is necessary to remove these embedded contaminants and return the part to its original corrosion specifications. Though passivation can improve the corrosion resistance of certain stainless steel alloys, it does not eliminate imperfections like micro cracks, burrs, heat tint and oxide scale.

Is nitric acid harmful to stainless steel?

Nitric acid is strongly oxidising and attacks most metals, but due to its powerful oxidising nature, it promotes the resistance of stainless steel to corrosion. Generally stainless steels are resistant to corrosion in nitric acid over a wide range of concentration and temperature.

Does nitric acid react with stainless steel?

Generally stainless steels are resistant to corrosion in nitric acid. Nitric acid is used in the chemical ‘passivation’ of stainless steels. (Higher concentrations obtained by removing water, which can involve the use of sulphuric acid, which has a high affinity for water.)

Is passivation considered plating?

Passivation is commonly used in zinc or zinc-alloy plating as part of the post-treatment process to prevent the onset of white rust, which is a rapidly spreading localized rust area that is prevalent with zinc.

What material is resistant to nitric acid?

Niobium and tantalum are among the most corrosion resistant metals to nitric acid. They exhibit resistance in the acid at all concentrations to temperatures as high as 250 ° C.

Will nitric acid dissolve steel?

Steel can be dissolved with a diluted solution of nitric acid and water. The chemical make up of nitric acid reacts to the iron in steel, producing iron nitrate and hydrogen gas. As this chemical reaction takes place, the steel begins to dissolve.

What metals do not dissolve in nitric acid?

Some precious metals, such as pure gold and platinum-group metals do not react with nitric acid, though pure gold does react with aqua regia, a mixture of concentrated nitric acid and hydrochloric acid.