采用恒电位计时电流法研究了304不锈钢在0.5mol/L NaCl介质中孔蚀发展过程及缓蚀剂对孔蚀发展的抑制作用,同时用原子吸收光谱(AAS)测定合金各组分元素的溶解量。结果表明:304不锈钢蚀孔内,铬元素以三价,铁、镍和锰以二价离子形式溶解,缓蚀剂PD不改变各元素溶解的价态。极化电位对孔蚀自催化效应有显著影响。哌啶对304不锈钢的孔蚀发展过程有良好的缓蚀作用。PD对各合金元素存在“选择性抑制”效应,降低了各元素的溶解速度,弱化孔蚀自催化效应。PD增强孔内沉积层阻力,促使蚀孔向发展速度较慢的类型转变。根据孔蚀发展动力学模型,讨论了PD的缓蚀机制。
The pitting growth for 304 stainless steel in 0.5mol/L NaCl and its inhibition by piperidine(PD) were investigated by means of atomic absorption spectrometry(AAS) and pitting current-time curve measurements under potentiostatic condition. According to AAS data, Fe, Ni and Mn in pits dissolved into ions in form of divalence, and Cr in form of trivalence both in the presence and absence of PD. The ratios by which each component element of 304 stainless steel dissolved played a very important role in pitting self-propagation process. The self-propagation effect decreased with downward shift of the dissolution ratio of Cr because the decrease in pH in pits could be ascribed mainly to the hydrolysis of Cr3+. PD inhibited 304 stainless steel from pitting growth by decreasing the total amount of dissolved ions and the dissolution ratio of Cr. On the basis of pitting growth kinetics, the influence of PD on the type of pit configuration was analysed. The results showed that the addition of PD turned the pits into those with slower development rate. The possible inhibition mechanism on pitting development was also discussed.
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