by Dr E. Ramanathan
MIL specification [9] classifies the types of chemical conversion phosphate coatings as M-type for manganese base and Z-type for zinc base. Besides, various combinations of chemical conversion coatings have been reported, viz., coatings based on zinc phosphate, manganese phosphate, amorphous iron phosphate, calcium modified zinc phosphate, low zinc manganese phosphate, zinc phosphate in combination with nickel and manganese, nanoparticle incorporated zinc phosphate, metal oxides such as zirconium oxide, cerium oxide, chromium oxide and yttrium oxide. Different types of processing of chemical conversion coating have also been developed such as spraying, hot immersion and cold immersion. Phosphate coatings have been reported as weight per unit surface area.