Chromating of zinc plating coatings / Thick layer passivation

Pragokor Zn 27 K is a chromating agent, without six-valence chromium content, for thick-layered passivation of zinc electroplated coatings being deposited from weak acid and alkaline non-cyanide as well as cyanide baths. At application, a bright iridescent layer of bluish-to-blue and green or blue and violet colour which substantially boosts corrosion durability of zinc coatings. Moreover, the passivation may be formed on zinc alloyed coatings of the ZnFe and ZnCo types. Besided the zinc plated coatings, the passivation of other zinc coatings is feasible as well, but with an inferior appearance. The final character of the chromating layer, i.e. hardness and durability against touch, are being stabilized after both drying out and ripening for about 24 hours. The surface weight of the passivation layer varies from 0,6 to 1,6 g/m2 according to the running conditions of the bath, especially bath temperature and operation time, the thickness within 100 – 300 nm being low enough to allow routine non-destructive ways of its measurement. Unlike the common chromates containing passivation baths, the thick-layered passivation is less susceptible to drying temperature and can even withstand temperatures above 120 °C.