Sodium Molybdate as a Corrosion Inhibitor of Mild Steel in Natural Waters Part 1: Flow Rate Effects Available to Purchase

Sodium molybdate (Na₂MoO₄) has been proposed as a possible replacement for chromate-based corrosion inhibitors for steel. Although Na₂MoO₄ is used in industry, little characterization of its behavior in low-conductivity natural waters or under flowing conditions has been performed. Effects of flow rate and water treatment on ASTM A36 carbon steel (UNS K02600) in natural lake water has been examined by electrochemical impedance spectroscopy (EIS) using the rotating cylinder electrode technique. The corrosion behavior of A36 steel was found to be highly dependent upon flow rate in untreated natural water, but only moderately dependent upon flow rate in waters treated with Na₂MoO₄, as determined by alternating and direct current methods. The electrochemical impedance spectra of steel in natural water were corrupted by artifacts at frequencies of 100 Hz and above. These artifacts were exacerbated by the low conductivity of the natural water. The solution and polarization resistances were isolated in the spectra in a series of experiments using solutions of different conductivities.