Evaluation of Corrosion Protective Properties of Polymer Films Coated on Steel after a Chemical Conversion Treatment by AC Impedance Measurement and Scanning Vibrating Electrode Technique

Abstract

The corrosion protective properties of polymer resins coated on steel after chemical conversion treatment in molybdate-phosphate systems were evaluated by AC impedance measurement and scanning vibrating electrode technique (SVET). The steel was chemically treated with Na2MoO4 and a phosphate, such as Na6P4O13, Na5P3010, C2H8P207 (HEDP), H3PO 3 or H3PO4, and was coated with epoxy resin (EP), poly (vinyl chloride) resin (VC) and fluoro resin (F). The most efficient solution for the chemical conversion treatment was found to be a O.5 M Na2MoO4-10% Na6P4013 aqueous solution of pH 10, and the most efficient immersion time was 6 hours. The corrosion protective property of specimen coated with F resin paint on the chemically treated steel plate was excellent compared with that on the non-treated or the Na2CrO4 (0.5 M) -treated steel plate. The film resistance (Rf) from AC impedance measurement and the current density (i) from SVET were correlated with each other. It was found that the corrosion protective property of paint film could be evaluated by SVET.