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本文研究了AISI304不锈钢在25℃的1NH_2SO_4+0.5NNaCl溶液中,当电位正于击穿电位时发生小孔腐蚀的特征。用动电位扫描法测定孔蚀击穿电位时,发现击穿电位与扫描速度的立方根呈线性关系。当电位正于E_b时,给定电位下的孔密度起初随时间而增加,然而当电流密度达到10mA/cm~2时,它趋于一个稳态值,称之为稳定态孔密度(S.S.D.P.);小孔的最大深度的平均值随时间呈线性增加,而且其平均增长速度V_(dp)(mm/min)与(E-E_b)(mV)之间的关系为:logV_(dp)=-7.5+2.89log(E-E_b);电流密度J随时间t的变化在电位正于E_b时遵循下列方程式:logJ=a+blogt,电流密度低于和高于10mA/cm~2时,所得到的b值是不相同的,这可能反映了腐蚀过程有差别。基于所得结果,建议对不锈钢的砘化膜耐小孔腐蚀的性能可依据E_b值、给定电位下的S.S.D.P.,V_(dp)以及在给定的(E-E_b)时的斜率b值来作较全面的评估。

The characteristics of pitting corrosion above breakdown potential E_b are studied for AISI 304 stainless steel in the solution of 1NH_2SO_4+0.5NNaCl at 25℃. In potentiodynamic study, a linear relationship between E_b and cubic root of potential scanning rate is found. The actual value of E_b is obtained by extrapolation of the scanning rate to zero. It is about +596mV(SHE) for given conditions. Results also show that, at constant potential above E_b, the pit density first increases with time and tends afterwards to a steady state density of pits (S. S. D. P.)which is reached at a current density of 10mA/cm~2. The average deepening spewed of pits Vdp(mm/min) increases with(E-E_b) (mV) according to the equation:logVdp=-7.5+2.89log(E-E_b) The time dependence of courrent density at constant potential above E_b follows the equation:logJ=a+blogt The values of slope b are different for current densities below and above 10mA/cm~2, confirming the change in corrosion processes. It is suggested that, the resistance of passivating layers to pitting corrosion can be evaluated by E_b as well as S. S. D. P., Vdp and b at a given value of (E-E_b).