from the conferences organized by TANGER Ltd.
The work is devoted to the study of the process of passivation of zinc and its alloys in ecologically safe molybdate-containing solutions in order to replace highly toxic solutions of black chromate passivation.The concentration range of the solution components was determined, in which black coatings are deposited, corresponding to a point of 10 on a ten-point color scale. It was found that the optimal pH values of the solution are in the range from 4.8 to 5.2 units. At lower pH values, adhesion deteriorates and the black color of coatings degrades, at higher pH values, coatings do not form at all. High-quality deep black coatings (10 points) are formed at temperatures of 45-85 oС.The color of the coatings changes from rainbow to black depending on the duration of their formation; the coatings of deep black color are formed with a process duration of at least 5 minutes. It was found that the coatings contain molybdenum oxides (IV, V, VI) and zinc oxides.Has been developed the technological process of passivation of zinc surfaces in a solution containing (g/l): 14-20 (NH4)6Mo7O24; 10-18 CH3COONa; 1-5 NiSO4·6H2O, which allows the formation of black molybdenum-containing coatings at t = 45-85 oС and = 7-10 min, comparable in protective and optical characteristics with black chromate coatings.
Keywords: Corrosion protection, molybdenum-containing coatings, chromate-free passivation of zink plated steel, black decorative coatings, black light absorbing coatings© This is an open access article distributed under the Creative Commons Attribution License which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.