碳钢在NaHCO3+NaCl溶液中的亚稳态孔蚀特征

用动电位极化和恒电位极化法研究了A3碳钢在不同浓度NaCl的0.5mol/LNaHCO₃溶液中亚稳态孔蚀行为。实验发现亚稳态电流波动峰具有快速上升、缓慢下降的特点。亚稳孔出现电位E_m 服从正态分布,随着Cl^-浓度的提高,E_m 值向负方向移动。亚稳孔的峰频变化规律与电位关系不大。恒电位极化时,当电位高于E_m而大大低于孔蚀电位E_b 时,电流波动保持一定时间后会最终消失,并产生直径为微米级的小蚀孔。当电位接近孔蚀电位时,一段时间的电流波动后电流往往迅速上升,最终转变为稳定蚀孔.

Feature of metastable pitting of carbon steel in NaHCO3+NaCl solutions

The metastable pitting behavior of A3 carbon steel in 0.5mol/L NaHCO^₃ solutions containing different concentrations of NaCl were studied with the potentiodynamic and potentiostatic polarization methods. It is found that the current fluctuations of the metastable pitting occurred with a characteristic of quick increase and slow decrease. The occuring potential of the metastable pits E_m obeys a normal distribution, and decreases with the increase of the chloride concentration. Potential has no appar effect on the frequency of fluctuations. In potentiostatic test, when the potential is above E_m and far below the pitting breakdown potential E_b, the current fluctuations remain for a period then disappear, resulting in the pits with a diameter of microns. When potential is close to E_b, the current may finally rise continuously after a certain time of fluctuations, and the metastable pitting is replaced by a stable piting.