304不锈钢在NaCl-(NH4)2SO4-NH4Cl溶液中的腐蚀行为

用电化学极化曲线和交流阻抗方法，研究了对304不锈钢（304SS）在3％NaCl和NaCl-（NH4）2SO4-NH4Cl混合溶液中的腐蚀行为．结果表明，在混合溶液中浸泡750h后，304SS仍然保持良好的钝化状态，其平均腐蚀电流密度为0．056mA／cm^2．根据交流阻抗研究结果，不锈钢在3％NaCl溶液中，主要表现出裸金属表面的点蚀和形成一定程度的钝化膜的特征，在2．0g／LNaCl、0．67g／L（NH4）2sSO4、2．3g／LNH4Cl混合溶液中，不锈钢表面形成稳定致密的钝化膜的典型特征．此钝化膜的电阻远小于腐蚀反应极化电阻．即使在形成良好的钝化膜的情况下，不锈钢所表现出的优良的抗腐蚀性能主要是由于金属表面活性点的钝化，而非钝化膜对离子导电或者对反应物／产物的扩散过程的阻隔作用．

CORROSION BEHAVIOR OF 304 STAINLESS STEEL IN NaCl-(NH4)2SO4-NH4Cl SOLUTIONS

The corrosion behaviors of 304 stainless steel(304SS) in 3%NaCl solution and in mixed solution of 2.0 g/L NaCl+0.67g/L(NH4)2SO4+2.3 g/L NH4Cl were investigated using polarisation curve and electrochemical impedance spectroscopy(EIS) methods.304SS maintained its good passive state after immersed in the mixed solution for 750 h.Its average corrosion current density in this medium was determined to be of 0.056 mA/cm2.It was found from EIS studies that in 3%NaCl solution,304SS exhibited a pitting corrosion behavior of bare metal with a thin passive film;while in the mixed solution,it showed a more typical feature of stable and complete passive film.The ohmic resistance of this passive film was much smaller than the charge transfer resistance of corrosion reaction.The good anti-corrosion performance of 304SS could be mainly attributed to the inactivation of surface site rather than to the barrier effect of the passive film against the ionic conductance or against the diffusion of reactants /products.