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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。
In this paper, the corrosion behavior of small holes in AISI 304 stainless steel in 1NH_2SO_4 + 0.5NNaCl solution at 25 ℃ was investigated. Pitting potentials were measured by potentiodynamic scanning, and it was found that there was a linear relationship between the breakdown potential and the cubic root of scanning velocity. The hole density at a given potential initially increases with time when the potential is at E_b, but tends to a steady-state value when the current density reaches 10 mA / cm2, which is called the steady state hole density (SSDP) ; The average value of the maximum depth of the pores increases linearly with time, and the relationship between the average growth rate V dp (mm / min) and (E-E_b) (mV) is: logV dp = 7.5 + 2.89 log (E-E_b); Current density J varies with time t The following equation is valid for a positive potential at E_b: logJ = a + blogt, at current densities below and above 10 mA / cm ~ The b value is not the same, which may reflect the difference between the corrosion process. Based on the results obtained, it is suggested that the corrosion resistance of stainless steel to small holes be improved based on the E_b value, the SSDP at a given potential, the Vp (dp), and the slope b at a given (E-E_b) A more comprehensive assessment.