Environmental factors affecting the corrosion behavior of reinforcing steel Ⅱ. Role of some anions in the initiation and inhibition of pitting corrosion of steel in Ca(OH)_2 solutions

摘要

Potential-time curves are constructed for the steel electrode in naturally aerated Ca(OH)_2 solutions simulating the corrosion behavior in concrete. Cl~- and SO_4~(2-) ions cause the destruction of passivity and initiation of pitting corrosion. The rate of oxide film growth by Ca(OH)_2 and oxide film destruction by Cl~- and SO_4~(2-) ions follows a direct logarithmic law as evident from the linear relationships between the open-circuit potential and the logarithm of immersion time. Chromate, phosphate, nitrite, tungstate and molybdate ions inhibit the pitting corrosion of steel. The rate of oxide film healing and thickening increases with their concentrations. In presence of constant inhibitor concentration, the efficiency of pitting inhibition increases in the order: (weak) CrO_4~(2-) < HPO_4~(2-) < NO_2~- < WO_4~(2-) < MoO_4~(4-) (strong).