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Metal treatment

metal treatments

Metal phosphating

Cars, refrigerators, washing machines, and other painted or enameled equipment all have a phosphated coating between the metallic surface and the paint. Purified phosphoric acid and phosphates are used in the process of phosphating metal surfaces. This operation (*) reduces the risk of metals corroding, insulates them electrically, and encourages paint to adhere to the treated surface.

(*) When a 'reactive' metal is plunged into a phosphating solution (purified phosphoric acid and/or phosphates in solution), certain elements — such as iron — are dissolved and remain at the metal-solution interface. The acidity level at the interface is reduced. The metal phosphate salts produced, combined with the cations (Ni2+, Zn2+,Mn2+) already present in the solution, precipitate on the surface of the treated metals. The resulting coating makes it easier to form the pieces of metal when cold by placing between the metal and the tool a surface that can be lubricated more easily. In addition, in the case of alkaline phosphating, solutions of sodium and potassium orthophosphates are often used on account of their buffer capacity. Moreover, when this process is carried out correctly, the metal surface, which is a natural conductor, is changed into an insulating surface offering greater resistance to corrosion when live.

Cleaning metals

These various products are also used to clean metal surfaces: before carrying out any phosphating treatment, the surfaces to be treated must be absolutely clean. This stage is vital because it ensures that there are no imperfections in the films covering the metal surfaces since any such imperfections would make them susceptible to localized corrosion. A specific product is selected to remove a specific type of impurity. For example, acidic or neutral preparations are more effective in removing limescale, while alkaline detergents perform better on grease and oily residues.

Production of electrical sheets

The electrical sheet industry also uses a particular grade of phosphate — MALP (monoaluminium phosphate) and/or purified phosphoric acid. These phosphates are used in the manufacture of magnetic grain-oriented electrical sheets, which themselves are used in the production of high quality low-loss transformers.

Treatment and polishing (electropolishing) of aluminum

Purified phosphoric acid and fluorine derivatives are used in the aluminum industry.

Fluorine derivatives are used in aluminum foundries as cast covers for baths. Purified phosphoric acid, in combination with sulfuric acid, is also used in aluminum polishing (electropolishing).

Prayon has recently developed a new range of blends containing purified phosphoric acid which is market under PraybriteTM brand.


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