1. Origin and evolution

Pickling a steel surface with a dilute, hot phosphoric acid solution leads to the formation of iron phosphate, which provides passivation and improves the corrosion resistance of paint coatings. This has long been known as Pickling, or also the Duplex Footner process [1] , when phosphoric passivation follows sulfuric acid pickling.

Phosphating metals with iron phosphate in aqueous solution dates back to 1906 with Thomas Coslett's English patent, registered in France in 1907, and the first applications appeared in 1908 (Coslettisation). By 1910, Coslett was already using solutions based on phosphoric acid and zinc phosphate.

Parkerization – deep manganese phosphating (treatment time 1 h 30 min) – for anticorrosion purposes...