Effect of triethanolamine and sodium hexametaphosphate on formation, growth and breakdown of passive layer in concrete pore solution

Abstract

In present study, 0.1 (M) triethanolamine (C6H15NO3: TEA) and 0.01 (M) sodium hexametaphosphate [(NaPO3)6: SHMP] have been dissolved in deionized water to synthesize the TS inhibitor solution. Different amounts such as 0.01, 0.10 and 0.25% of TS inhibitor have been taken to study the corrosion performance of steel rebar in 0.6 (M) NaCl contaminated concrete pore (CPNC) solution. The corrosion mechanism and kinetics of the steel rebars in presence of inhibitor have been studied by open circuit potential (OCP), electrochemical impedance spectroscopy (EIS) and potentiodynamic polarization (PDP) with exposure periods while the morphology and nature of passive film formed on rebar surface have been examined by scanning electron microscopy (SEM), atomic force microscopy (AFM) and X-ray photoelectron spectroscopy (XPS), after 192 h of immersion. The steel rebar immersed in without inhibitor solution (CPNC) has exhibited lowest film resistance (Rf) and charge transfer resistance (Rct) with pits formation in passive film. Alternatively, the steel rebars exposed to inhibitor added CPNC solutions show higher in Rf, Rct values, lowest corrosion current density (icorr), nobler OCP and cluster like morphology of the passive films. It is attributed to the adsorption of TEA molecules on the rebar surface by donating lone pair of electrons from N atom while PO3 4 ions (from SHMP) transform the Fe(OH)2 into FePO4. The corrosion inhibition efficiency of the inhibitor containing samples are increased with exposure periods and the maximum is found to be 97.57% by 0.10% TS after 192 h of exposure.