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Environmental factors affecting the corrosion behaviour of reinforcing steel. V. Role of chloride and sulphate ions in the corrosion of reinforcing steel in saturated Ca(OH)2 solutions
The corrosion behaviour of reinforcing steel in saturated naturally aerated Ca(OH)2 solutions in absence and presence of different concentrations of NaCl, NH4Cl, Na2SO4 and (NH4)2SO4 is followed by measuring of the open circuit potential complemented with SEM and EDS investigation. The rates of oxide film thickening and/or destruction in Ca(OH)2 solutions devoid of- and containing Cl(-)and SO4(2-) ions follow a direct logarithmic law as evident from the linear relationship between the open-circuit potential and the logarithm of immersion time. In presence of low concentrations of the aggressive salts, the steady-state potential, Est is approached from negative values and becomes less noble with increasing the concentration of the aggressive salt. At higher concentrations of the aggressive salts, the steady state potential, Est, is approached from noble values and becomes more active the higher the aggressive ions concentration. This is assumed to be due to the destruction of passivityand the initiation of pitting corrosion. The corrosion behaviour of the steel depends on the aggressive salts anions and cations. Sulphate ions are found to be more corrosive than chloride ions. This could be easily recognized from the pronounced shift of the steady state potential, Est, in the negative direction and the marked decrease in ΔEa in presence of sulphate salts. ΔEa of oxide film thickening in case of (NH4)2SO4 and Na2SO4 are 17.07 kJ/mol and 17.46 kJ/mol, successively, while it has the values 17.84 and 21.98 kJ/mol for NH4Cl and NaCl, successively. Ammonium salts are more corrosive than the sodium salts due to the decreased alkalinity of the medium.
Environmental factors affecting the corrosion behaviour of reinforcing steel. V. Role of chloride and sulphate ions in the corrosion of reinforcing steel in saturated Ca(OH)2 solutions
The corrosion behaviour of reinforcing steel in saturated naturally aerated Ca(OH)2 solutions in absence and presence of different concentrations of NaCl, NH4Cl, Na2SO4 and (NH4)2SO4 is followed by measuring of the open circuit potential complemented with SEM and EDS investigation. The rates of oxide film thickening and/or destruction in Ca(OH)2 solutions devoid of- and containing Cl(-)and SO4(2-) ions follow a direct logarithmic law as evident from the linear relationship between the open-circuit potential and the logarithm of immersion time. In presence of low concentrations of the aggressive salts, the steady-state potential, Est is approached from negative values and becomes less noble with increasing the concentration of the aggressive salt. At higher concentrations of the aggressive salts, the steady state potential, Est, is approached from noble values and becomes more active the higher the aggressive ions concentration. This is assumed to be due to the destruction of passivityand the initiation of pitting corrosion. The corrosion behaviour of the steel depends on the aggressive salts anions and cations. Sulphate ions are found to be more corrosive than chloride ions. This could be easily recognized from the pronounced shift of the steady state potential, Est, in the negative direction and the marked decrease in ΔEa in presence of sulphate salts. ΔEa of oxide film thickening in case of (NH4)2SO4 and Na2SO4 are 17.07 kJ/mol and 17.46 kJ/mol, successively, while it has the values 17.84 and 21.98 kJ/mol for NH4Cl and NaCl, successively. Ammonium salts are more corrosive than the sodium salts due to the decreased alkalinity of the medium.
Environmental factors affecting the corrosion behaviour of reinforcing steel. V. Role of chloride and sulphate ions in the corrosion of reinforcing steel in saturated Ca(OH)2 solutions
Einflussfaktoren der Umgebung auf das Korrosionsverhalten von armiertem Stahl. V. Die Rolle von Chlorid- und Sulfationen bei der Korrosion von armiertem Stahl in gesättigten Ca(OH)2-Lösungen
Abd El Haleem, S.M. (author) / Abd El Wanees, S. (author) / Bahgat, A. (author)
Corrosion Science ; 75 ; 1-15
2013
15 Seiten, 14 Bilder, 7 Tabellen, 72 Quellen
Article (Journal)
English
Betonstahl , bewehrter Beton , Calciumhydroxid , Chlorid , Sulfat , Korrosionsverhalten , Korrosionspotenzial , Zeitabhängigkeit , Konzentrationsabhängigkeit , Lochfraßkorrosion , Oxidschicht , energiedispersive Spektrometrie , Temperatureinfluss , Arrheniusgleichung , Aktivierungsenergie , Korrosionsmechanismus
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