碘离子迁入裂缝的规律及其对闭塞电池腐蚀的影响

MIGRATION OF I^- INTO CRACKS AND ITS EFFECTS ON OCCLUDED CELL CORROSION

一、前言氯离子是导致奥氏体不锈钢发生应力腐蚀破裂和孔蚀的特性离子。它从主体溶液迁入闭塞区已被许多作者的实验所证实。我们以前的工作证明Cl^-的迁入量与通过闭塞区的电量成直线关系,Cl^-增浓是促进闭塞区合金溶解的因素之一。I^-和Cl^-同属卤族离子,但据报道将I^-加入含Cl^-的体系对奥氏体不锈钢的应力腐蚀破裂具有抑制作用。显然探明特性离子(如Cl^-、I^-等)的作用有益于认识局部腐蚀的机理。本工作研究I^-的迁移规律以及对闭塞电池腐蚀的影响。二、实验方法 1.闭塞电池不同阶段的溶液成份测定——模拟闭塞电池实验采用文献[3]所用的方法,测量0.5mol/L NaCl溶液中加入0～0.3mol/L NaI后304不锈钢模拟裂缝不同阶段的溶液成份,进而了解I^-对缝内化学和电化学状态的影响。在“

Simulated occluded cell(0C) was used to study the chemical and electrochemical changes within stress corrosion cracks for the system sensitized AISI304 steel/Cl^- with addition of different concentrations of I^-. The respective number of equivalents of migrated I^- as well as Cl^- was proportional to the quantity of electricity passing through the occluded cell. The ratio of migration rate of Cl^-/I^- was the same as that of the concentrations of those ions in bulk solution. The pH value inside occluded cell was independent of I^- migration, but the occcluded potential moved more positively than that without I^-. It was shown by potentiostatie weight loss method using simulated occluded solutions with different I^- concentrations that the migation of I^- from outside inhibited the occluded cell corrosion. The inhibition efficiency of 0C was more than 98％ when the concentration of I^- in bulk solution was only 0.01mol/L. So the iodide was an effective inhibitor of stress corrosion cracking for austenitic stainless steel in chloride solutions.