The word “passivation” is thrown around quite a bit in the metal finishing and metal cleaning circles and as such holds different meaning for different people. The core root of the word “passivation” relates to the passivity of the metal. The passivated metal gets a protection by the passivation layer to prevent reactions with water, oxygen, chlorine and other sources of probable corruption.

In metal finishing and cleaning there are quite a few different ways in which the term passivation is used.

Equipment made from stainless steel is passivated after or during fabrication. Stainless steel itself is a naturally passivating material; it forms a protective layer spontaneously on exposure to air or water. In actual surroundings it is difficult to prevent contamination of stainless steel as it gets fabricated into tubes, tanks and other geometries that are required by clients.  The tools which are used in fabrication are very seldom corrosion resistant themselves, and they leave small amounts of corrosion behind which happens during bending, sawing, cutting and sanding. Even the tools that are meant for the fabrication of stainless steel are prone to leave deposits behind. Even the pristine stainless steel might have exposed grain boundaries that may get corroded. Passivation takes place by washing completed and ready fabrications with nitric acid.

Any process that uses nitric acid or citric acid to alter the surface properties of a work piece is also known as passivation. Cleaning is the first step of such a passivation process.  The cleaning helps to remove oil, grease and other contaminants from the surface that would otherwise not have been removed. Pre-cleaning is followed by a rinse and wash to avoid contamination of the passivation acid by the cleaning elements. There are a series of acid tanks that achieve the process of passivation. This is then touched up by water or slightly caustic rinses to counteract any remaining acids. Finally the object is dried.

Passivation has also become associated with the processes that do the normal function of metallic passivation and also removes bacteriological residues from the work pieces. Elimination of biological contaminants requires the application of heat.

As you can see, passivation means different things to different people. The expectation of any specification from a passivation process should therefore be fully understood prior to designing equipment for the process. Cleaning of the material is an important step and true passivation is not achieved unless acid is involved. If you are looking for passivation services, search for passivation services and passivation plating services.

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