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What Is Passivation?

Chemical passivation plays a vital role in many industries that require corrosion-resistant metal.

Passivation is a chemical process that gives metals like stainless steel corrosion resistance while also removing imperfections from a metal’s surface. Passivation produces a result similar to electropolishing, but instead of using an electrical current, it uses an acidic solution to coat metal with a protective layer carefully.

It is a proven and economical way of protecting equipment in various situations, ensuring no part fails prematurely.

What About Aluminum?

Aluminum can be treated with Nitric or Phosphoric Acid for cleaning and De-smutting purposes, and it is beneficial, but it is not considered as a “Passivation” in the conventional sense.

How Do You Passivate?

To passivate a metal like stainless steel, you must use chemical processes to remove free iron. This creates a protective oxidative layer that is “passive”, meaning it won’t react to corrosive exposure from water or air.

This chemical process selectively removes free iron from a metal’s surface, only leaving behind oxides like chromium and nickel. In a sense, passivation uses corrosion to fight corrosion because it uses oxidation to fight other corrosive exposures.

What Is The Passivation Process?

To passivate a metal item, it must be free of chemicals and debris that can interfere with the chemical process. The metal is first inspected and cleaned before being soaked in a nitric acid solution. Citric acid can also be used in place of nitric acid, but it is not as common.

The duration and temperature of the soak will vary according to the application of the item and its composition. After contaminants, minor imperfections, and rust are removed from the material, it is rinsed and allowed to dry. Note that the passivation process can also be adjusted for projects that need to be done in-house.

What Is Device Passivation?

Passivation can mean the success or failure of a device. For example, in the medical and pharmaceutical industries, passivation plays an essential role in protecting the health of patients and consumers. Device passivation is used to protect asthmatic drugs from corrosion, surgical tools from rust, and the integrity of lifesaving equipment..

What is the difference between pickling and passivation? Passivation is less aggressive than pickling, only adding an oxidative layer that is .0000001inches thick. In some cases, pickling can also be used to prepare metal before passivation.

Although both processes are used to raise the chromium content in metal, they achieve this by different means. Passivation uses an acidic solution, while pickling uses heat. This means that pickling removes the heat-affected layer of stainless steel, while passivation only removes iron from the surface.

What Are The Types of Passivation?

The type of passivation you need will vary according to the type of metal you are using and how it will be applied. Chemical passivation can be adjusted to any of the most commonly used metals to achieve a fine finish and a layer of protection against corrosion.

What is Meant by Passivated?

A material is passive when it does not react to oxygen or water. A passivated material has been treated with a chemical process to remove iron. After the iron is removed, the metal is rinsed and allowed to dry, and the drying process creates the desired protective oxidative layer. Steel can be pickled, but we would use Muriatic / Hydrochloric Acid to do that , not Nitric or Citric Acid.

Is Passivation Necessary?

Although chemical passivation is not considered the most efficient means of finishing material, it’s not always possible to do it through electropolishing. Items that cannot be taken offsite or are too large to use an electrical current for polishing are clear examples of when chemical passivation is the best option.

If it suits your project’s needs both in economic and practical terms, then passivation may not be necessary when electropolishing is used instead. Ultimately, passivation should be paramount for metal parts or devices vulnerable to corrosion.

Can Passivation Be Removed?

The fine oxidative layer that passivation produces is very durable, but it can be removed. When a passivated metal undergoes repeated abrasion from polishing, sandblasting, or maintenance, it can expose free iron on the surface. This is why passivation is usually one of the last steps in the manufacturing process.

Is Passivation a Coating?

Passivation produces a thin but durable protective coating over metal. Passivation selectively removes free iron from its surface and leaves behind a layer of oxidative metals like chromium or nickel. This means the coating produced by passivation is formed due to the reaction that follows when the iron is removed at the surface level.

What Chemical is Used for Passivation?

Passivation uses nitric acid and, less commonly, citric acid to treat metal. Nitric acid is suitable for many grades of stainless steel, titanium, and aluminum but can also be adjusted when there is a higher risk of flash attacks.

Flash attacks describe a dull grey layer that forms after passivation instead of the intended fine finish. Sodium dichromate can be added to the nitric acid solution to reduce the risk of flash attacks and the concentration of nitric acid can also be adjusted to prevent etching.

Can Aluminum Be Passivated?

Aluminum can and should be passivated when corrosion is a concern. Aluminum doesn’t have the same inherent protective properties as stainless steel, so a passivation treatment can provide many benefits here.

Can Stainless Steel Be Passivated?

Stainless steel can be passivated using nitric acid, or less commonly, citric acid. It is common practice to use passivation on stainless steel for various applications. Passivation is a flexible process that can be applied to stainless steel of almost any size and dimension.

Is Passivation Conductive?

Passivation is conductive and has a constant electrical resistance. Passivated metal raises the content of chromium at the surface, which gives it a high affinity for oxygen. The thin oxidized layer produced by the reaction allows the metal to retain a high level of conductivity.

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