DEVELOPMENT OF CHROMATE-FREE PASSIVATION PROCESSES FOR GALVANIZED STEEL

In recent years, nano-sized cerium and silicon-containing coatings have been increasingly used as alternatives to chromate layers on galvanized steel. The present work is devoted to the development of the technology for obtaining these coatings. The processes of applying cerium and silicon-containing coatings to galvanized steel have been developed. The solution for the application of cerium-containing coatings contains in its composition: 10-25 g/I Ce(NO3)center dot 3.6H20; 15-25 m1/I H2O2, 0.5-2 g/I PEG 1500.Solution for the deposition of silicon-containing coatings contains: 25-35 g/I Na2SiO3.5H2O; 20-30 m1/I H2O2, 0.2-0.5 g/I oxyethylenediphosphonic acid (OEDP). It is established that the developed passivation coatings applied on galvanized steel parts for corrosion resistance and protective ability are comparable with chromate coatings. It has been revealed that cerium-containing coatings, like chromate coatings, have the ability to self-heal. It was revealed that, unlike chromate coatings, the developed cerium and silicon-containing coatings withstand the thermal shock without degrading of characteristics. It was established that the thickness of cerium containing coatings is about 65 nm, and that of silicon-containing coatings is about 50 nm. It should be specially noted that the thickness of these coatings is noticeably less than the thickness of the chromate layers (200-1000 nm).