ELECTROCHEMICAL QUARTZ-CRYSTAL MICROBALANCE IN MODERN CORROSION RESEARCH - STUDY OF THE PRETREATMENT OF GALVANIZED STEEL

The electrochemical quartz crystal microbalance (EQCM) is applied in o rder to study the technical pretreatment processes of galvanized steel such as alkaline cleaning, chromating End phosphating in modern trica tion solutions. The mass change associated with these reactions is mon itored in situ under conditions which are very similar to those of a c oil-coating line. It is shown that cleaning of the zinc surface in an alkaline cleaning solution is a two-step process: removal of the zinc oxide layer by a chemical dissolution followed by electrochemical diss olution of zinc, the rate of which is controlled by the diffusion of z incate ions into the electrolyte. During phosphating of the sample, th ree subsequent steps are observed: zinc dissolution during the first s econds followed by precipitation of a phosphate layer and then cementa tion of Ni, which leads again to increasing dissolution of the base ma terial.