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The purpose of this investigation is to analyze the effectiveness of phosphates as inhibiting agents for steel bars embedded in mortars. Three mix designs were selected for this study: mix A had no admixed chlorides and was used as reference; mix designs B and C were contaminated with 1% in weight of chlorides/weight of cement and mix C also incorporated 7% Na 3 PO 4 .12 H 2 O. After setting for 48 h, the samples were cured for 7 days immersed in water. Three specimens of each group were then immersed in aerated saline solutions 0.5 mol L −1 NaCl during 720 days. The corrosion potential ( Ecorr ), the polarization resistance ( Rp ) and the electrochemical impedance spectra were recorded regularly. After 720 days of immersion one set of mortars was anodically polarized and another set cathodically polarized. After that, Raman spectra of corrosion products were registered. Additional specimens were used to evaluate porosity and chloride profiles. The presence of phosphate ions as inhibitors has no effect on Ecorr values and suggests mixed-type inhibition. Mix C remains passive until 180 days of exposure, with Rt> 100 kΩ cm 2 . At longer times, Rt decreases in time but the inhibition percentage is always higher than 95% when evaluated by impedance spectra. Using Rp , inhibition stays above 70%. Anodic and cathodic polarization curves, together with corrosion potential values, suggest that phosphates behave as a mixed-type inhibitor. [ABSTRACT FROM AUTHOR]

Abstract: The influence of initial surface conditions on the subsequent corrosion behaviour of AZ31 and AZ61 magnesium alloys in 0.6M NaCl solution has been studied using electrochemical impedance spectroscopy. For obtaining the different surface conditions, some of the specimens were immersion tested with the surface in the as-received condition, while others were tested immediately after mechanical polishing, and part of the polished specimens after six months of exposure to the laboratory atmosphere. Considering the evolution of the high-frequency capacitive arc of the Nyquist diagram, whose diameter is related to the corrosion process, a clear effect of the initial surface conditions is observed only in the early stages of testing. This effect is especially significant for the freshly polished specimens. [Copyright &y& Elsevier]