The Corrosion Behaviour of Electrochemical Zn Coated with Conversion Chromate and Phosphate Films in Concrete

The corrosion behaviour of electrochemical Zn coatings with and without chromate (VI, III) and phosphate (amorphous and crystalline) films in aerated 0.1 M NaOH + 0.1 M NaCl solution and concrete, immersed into water has been studied. The estimated corrosion rate in 0.1 M NaOH + 0.1 M NaCl solution is minimal cf. Zn chromatised in Cr³⁺ solution. The value of j_cor of Zn chromatised in Cr⁶⁺ solution is 1.5 times as high as that in Cr³⁺. The experiments carried out in concrete immersed into water (pH 12.5) have shown that all the chromate films studied do not extend the operating time of the sample. The best corrosion protection is provided by crystalline phosphate film.