CHROMATE-FREE COMPOSITION BASED ON CERIUM AND LANTHANUM COMPOUNDS FOR PASSIVATION OF ZINC SURFACES Russian patent published in 2021 - IPC C23C22/06 C23C22/53 

FIELD: car industry; shipbuilding; agriculture; petrochemical industry.

SUBSTANCE: invention relates to passivation of the surface of protective metal coatings; it can be used to increase the corrosion resistance of galvanized steel in the car, shipbuilding, agricultural, petrochemical and other industries. A composition for chromate-free passivation of galvanized steel surface contains: cerium nitrate hexahydrate 5.5-7 g/l; lanthanum nitrate hexahydrate 2.3-4 g/l; boric acid 1.0-1.5 g/l; hydrogen peroxide 5-10 ml/l; potassium pyrophosphate 0.02-0.03 g/l; water up to 1 l. The developed composition is applied to a galvanized steel surface at a temperature of 40-50°C, pH 2.5-3.0.

EFFECT: combined introduction of cerium and lanthanum compounds into the solution reduces porosity from 4 to 0 units/100 mcm², increases the protective capability of formed coatings, reduces the total concentration of ions of rare earth metal in the composition, and the introduction of potassium pyrophosphate increases the stability of the working solution.

1 cl, 7 ex