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Why is Passivation used? |
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In iron or zinc phophate coating, passivation application must be done at the last stage. There are two types of passivation as chromium and non-chromium. The surfaces obtained after phosphate baths are not in homogeneous form. The property of the passivation to homogenize the phosphated surfaces reduces the air diffusion between paint and surface. Especially the chromium passivations are effective in paint adhesion by replacing ion groups such as Ca Mg on metal surfaces which cause roughness of water and which are caused by rinsing and chromium passivations provide extra resistance against corrosion. In chromium passivation baths, waiting time must be paid attention to. Chromic acid can have corrosive effect on the coating when applied long time. Passivation baths can be applied at room temperature. It is recommended to use the bath at 40-50 ºC to increase the drying performance and not to have drying problems. |
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