三种缓蚀性阴离子对碳钢在NaHCO_3-NaCl溶液中点蚀的抑制作用

EFFECTS OF THREE ANIONS ON PIT PROPAGATION OF MILD STEEL IN NaHCO_3-NaCl SOLUTIONS

利用动电位扫描法、恒电流模拟闭塞电池研究了MoO2 -4、Cr2 O2 -7、PO3 -4等 3种阴离子对A3 钢在NaHCO3 -NaCl溶液中点蚀形核和点蚀发展的影响以及作用机理 .结果表明 ,MoO2 -4和PO3 -4都对小孔形核和发展起到抑制作用 ,而Cr2 O2 -7仅对小孔形核起到抑制作用 ,对小孔生长则起到促进作用 .进一步的研究表明 ,造成这种差别的主要原因是它们在蚀孔闭塞区内对溶液 pH的影响是不一样的 .MoO2 -4和PO3 -4进入闭塞区后 ,能提高 pH ,抑制了阴极过程 ;而Cr2 O2 -7使 pH下降 ,促进了阴极过程 .

The effects of molybdate,phosphate and dichromate anions on pit propagation of mild steel in NaHCO 3-NaCl solution were investigated by electrochemical measurements.MoO 2- 4 and PO 3- 4 ions suppressed both pit nucleation and propagation.Cr 2O 2- 7 ion suppressed pit nucleation,but stimulated pit growth.The further study showed that the different effects of the three anions on pit propagation could be explained by their effects on pH value within pits.The pH value increased after adding molybdate or phosphate in the pit simulated solution as a result of polymerization of MoO 2- 4 or the hydrolysis of PO 3- 4,while pH value decreased after adding dichromate anions due to hydrolysis of Fe 3+ and Cr 3+ which were the products of oxide-reducing reactions between Cr 2O 2- 7 and Fe 2+ ions.