The protective properties of various phosphate coatings on steel

Abstract

Coatings of iron, manganese and zinc phosphates formed on steel by representative industrial immersion processes are compared, with special reference to their value in the prevention of rasting. The results are examined in the light of the thickness, composition and wear resistance of the coatings. Protective properties are relatively well developed in manganese phosphate coatings, but, since phosphating in practice normally constitutes only a part of a protective system involving organic coatings, iron and zinc phosphates can give adequate results in appropriate systems. A recent spot‐test of Russian origin, although at present not sufficiently well developed for inspection purposes, is likely to provide a useful additional tool for examining coatings. Variations in the coatings, in particular those that occur in the working range of a plain manganese phosphate process, have been examined and one untoward effect was identified, that due to adventitious copper contamination of the bath.

Analysis of the corrosion behavior of steel reinforcement protected by phosphate coatings

“…Coatings obtained from solutions of phosphates of several metals, such as primary iron and manganese phosphates or manganese and zinc, have the highest anticorrosive properties [15]. Films formed in a solution of manganese containing iron and zinc compounds have the best corrosion resistance [16]. When properly processed, the phosphate layer is a light gray 3-8 μm thick film with a fine crystalline structure and high adhesive and protective properties [9,17].…”