INVESTIGADORES
YOHAI DEL CERRO lucia
congresos y reuniones científicas
Título:
Testing inorganic ions as "green" corrosion inhibitors for construction steel
Autor/es:
FRANCISCO MONTES ; L. YOHAI; M. VÁZQUEZ; M.B. VALCARCE
Lugar:
Split
Reunión:
Simposio; 7th Regional Symposium on Electrochemistry of South-East Europe; 2019
Institución organizadora:
Association of South-East European Electrochemists
Resumen:
Reinforced concrete is a reliable building material due to many excellent properties such as stregth and durability. Marine environments and chloride-contaminated aggregates accelerate deterioration and failure[1]. Inhibitors are frequently considered to mitigate steel corrosion [2]. Nitrite ions are effective corrosion inhibitors but there are environmental concerns associated to their use[3]. Sodium phosphate (Na3PO4)[4] and sodium silicate (Na2SiO3) are tested as alternatives of interest. The evaluation is carried out in a solution that simulates the composition of the pores in chloride-contaminated concrete. The inhibitor concentration is 0.3 mol/L and the pH of the synthetic medium that simulates contaminated concrete is 13 (PSS), while the inhibitor/chloride ratio is 1.Anodic polarization curves and weight-loss test are complemented with micro-Raman spectroscopy to evaluate the surface film compostion in different corrosion stages. The electrodes were stabilized for 24 h at open circuit potential (OCP). It is well-known that chloride contamination promotes active corrosion. When phosphate ions are incorporated, pitting is inhibited even if the OCP moves toward slightly more negative values. The composition of the surface layer changes when phosphates are present. Raman spectra show a broad band, centered in 982 cm-1, suggesting that phosphates incorporate to the passive film. Even after 90 days at open circuit potential weight loss is minimal. Phosphates are also present in the corrosion products.The presence of silicate ion inhibits the localized corrosion, even polarizing to potentials close 0.6 VMOE. The passive current decreases markedly when compared to the uninhibited solution. As for phosphates, long term exposures show minimal weight loss when silicates are present. Silicate ions are not readily detectable by Raman spectroscopy, since the bands appear superimposed with others originated in the passive film.Relevant parameters associated to pitting corrosion are shown in table 1.It can be concluded that phosphate and silicate ions are good candidates to be used as green corrosion inhibitors for steel in chloride-contaminated concrete. Table 1: Comparison of electrochemical parameters whne phosphate or silicate ions are present. Potetial values are evaluated with Hg/HgO/KOH 1 mol L-1 as reference electrode (MOE, E = 0.123 V vs. SHE)OCP/mVMOEEPIT /mVMOEEPIT-OCP/mViPAS/μA cm-2PSS + Cl-−237 ± 30−263 ± 34182 ± 815.4 ± 2.6PSS + [PO43-]/[Cl-]=1−263 ± 34No pitting0.3 ± 0.12PSS + [SiO32-]/[Cl-]=1-328 ± 59No pitting1.3 ± 0.7