Alkali-resistant adhesion promoters

Phosphate pre-treatments may be either zinc phosphate (from zinc dihydrogen phosphate solutions) or an iron phosphate (fi om alkali phosphate solutions) (see Conversion coating and Pre-treatment of steel). The conversion reactions are promoted by accelerators (depolarizers), for example, bromates or molybdates in alkali phosphate baths or chlorates in zinc phosphate baths (with Ca or Ni grain-refining additions). Iron phosphate pre-treatment coatings are often described as amorphous . In practice, however, they are usually crystalline deposits of iron oxides and iron phosphate. Zinc phosphate pre-treatment coatings are always crystalline. A fine, dense crystal pattern of zinc phosphate on the metal surface is the ideal, as it improves both paint adhesion and corrosion resistance most effectively. 

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