Phosphate ions as effective inhibitors for carbon Steel in carbonated solutions contaminated with chloride ions

L. YOHAI; W. SCHREINER; M. VÁZQUEZ; M.B. VALCARCE

ELECTROCHIMICA ACTA

PERGAMON-ELSEVIER SCIENCE LTD

Lugar: Amsterdam; Año: 2016 vol. 202 p. 231 - 242

0013-4686

This investigation focuses on sodium biphosphate (Na2HPO4) as corrosion inhibitor forconstruction steel. All the tests are carried out in a solution that simulates the compositionof the pores in chloride-contaminated carbonated concrete. The carbonated solution (CS)contained Na2CO3 (0.0015 mol L-1), NaHCO3 (0.03 mol L-1) and NaCl (0.1 mol L-1),resulting in [Cl-]/[OH-]=10000. Inhibited solutions (IS20, IS60 and IS100) incorporated 20,60, and100mmol L-1Na2HPO4 respectively. These were labeled IS20, IS60 and IS100respectively and result in [HPO42-]/[Cl-] = 0.2, 0.6, and 1. Cyclic voltammograms andanodic polarization curves were complemented with micro-Raman spectroscopy and XPS,to evaluate the surface film composition. The results show that chloride contaminationpromotes active corrosion. When phosphate ions are incorporated, steel becomes passivewith a more positive corrosion potential (Ecorr), and pitting presents as the predominantform of localized corrosion. Raman spectra show a broad band, centred in 982 cm-1,suggesting that phosphates incorporate to the passive film. Phosphates are also present inthe corrosion products. The surface film becomes more protective to pitting for the highestbiphosphate content. However, after pitting no repassivation was detected. After over onemonth in immersion, steel remains passive in the condition IS100, with inhibitionefficiency higher than 99%. In contrast, in the case of IS60 and IS20, pitting was detected.It can be concluded that phosphate ions are good candidates to be used as corrosioninhibitors for steel in chloride-contaminated concrete.