1Cr13钢在氯化钠溶液中闭塞区的化学和电化学变化及加速腐蚀效应

利用模拟闭塞电池测出“1Cr3钢/Cl~-”体系闭塞区不同阶段的化学变化,并在不同阶段的模拟闭塞区溶液中测1Cr13钢的腐蚀串和极化曲线等,绘制出描述该体系闭塞电池腐蚀行为的实验电位/pH图。由“腐蚀率/pH”曲线和电位/pH图都表明该体系存在一个闭塞电池加速腐蚀的临界pH值。约为3.7。当闭塞区溶液的pH值降到临界值以下时,1Cr13钢孔底或缝尖的腐蚀率骤增。其原因是闭塞区内发生了“钝态/活态”转变,并开始放氢反应。     

45CrNiMoV低合金高强钢在氯化物溶液中闭塞区化学状态的研究

采用模拟闭塞电池研究45CrNiMoV低合金高强钢在NaCl溶液中闭塞区内化学状态的变化.     

Ⅱ.外部电位和缝内电位及溶液pH的关系

本文系利用作者设计的模拟腐蚀裂缝并能承受拉应力的闭塞电池,以研究Crl8Ni9Ti奥氏体不锈钢在0.5NNaCl溶液中(40℃)模拟的缝隙(闭塞区)中电位及pH随外部试件极化时的变化.发现这个体系的缝隙腐蚀(或应力腐蚀)临界电位约为-0.10至-0.20V SCE 当外部试件极化到临界电位区,闭塞区内腐蚀微小,pH不变化.当极化到临界电位以上(+0.20V以下),闭塞区内电位最终稳定在-0.10至-0.13V SCE,即保持在自由腐蚀电位(或临界电位)范围之内,但阳极极化使闭塞区通过的电流增大,促进了金属阳极溶解,金属离子水解使溶液pH下降到2—3.5之间,闭塞区由钝态变为活态.腐蚀加速.当外部试件极化到临界电位以下,闭塞区内电位与外部极化电位基本相等,一般稍正,闭塞区内处于钝态,溶液pH增大到碱性.但如极化电位下降到放氢平衡线以下,则可能产生氢脆.当闭塞区试件受拉应力(0.90_y)时,在阳极极化下,闭塞区电位变得更负,溶液pH下降也较大些.在阴极极化下应力对闭塞区的电位及pH均无影响.由于了解了缝内电位和腐蚀程度随外部电位变化的情况,所以可以通过外部极化以控制缝内电位,达到保护的目的.也可以由外部电位的变化来探测缝内腐蚀是否可能发生.     

No_3~-对OCr18Ni9Ti钢在NaCl溶液中闭塞区腐蚀的抑制作用及其机理

采用模拟闭塞区溶液研究NO_3~-对氯化钠溶液中0Cr18Ni9Ti钢的缓蚀作用及机理。结果表明,随着(NO_3~-)_(bulk)(主体溶液中NO_3~-的浓度)增高,闭塞区内金属的腐蚀速率减小,腐蚀电位向正方向移动。50℃时,若[NO_3~-]_(bulk)≥0.025或90℃时[NO_3~-]_(bulk)≥0.2M,闭塞区内金属由活态转变为钝态。当50℃、[NO_3~-]_(bulk)≥0.3M或90℃、[NO_3~-]_(bulk)≥0.5M时,其动电位极化曲线上的钝化区增宽、致钝电流密度和维钝电流密度变小,缓蚀率高达90％以上。因此,在主体溶液中加入适量NO_3~-能导致闭塞区钝化,从而对孔蚀、缝隙腐蚀及应力腐蚀破裂起缓蚀作用。     

INVESTIGATION ON ELECTROCHEMISTRY INSIDE STRESS CORROSION CRACKS OR PITS

Techniques are developed for studying the mechanism of localized corrosion and protectivemeasures against such corrosion are suggested.The pH values and composition of the occluded sol-ution at different propagation stages are determined.Measurements of the critical pH value and cor-rosion rate inside the occluded cells are conducted.Potential-pH diagrams depicting kinetic andthermodynamic behaviors of occluded cell corrosion are being established.The mechanism of inhibi-tion of pitting and stress corrosion cracking have also been investigated.     

1Cr13钢在氯化钠溶液中闭塞区的化学和电化学变化及加速腐蚀效应

利用模拟闭塞电池测出“1Cr3钢/Cl~-”体系闭塞区不同阶段的化学变化,并在不同阶段的模拟闭塞区溶液中测1Cr13钢的腐蚀串和极化曲线等,绘制出描述该体系闭塞电池腐蚀行为的实验电位/pH图。由“腐蚀率/pH”曲线和电位/pH图都表明该体系存在一个闭塞电池加速腐蚀的临界pH值。约为3.7。当闭塞区溶液的pH值降到临界值以下时,1Cr13钢孔底或缝尖的腐蚀率骤增。其原因是闭塞区内发生了“钝态/活态”转变,并开始放氢反应。     

腐蚀与防腐的现代概念

<正> 腐蚀学(或称腐蚀与腐蚀控制学)是一门新兴的科学。它的主要目的就是控制腐蚀对人类的危害。腐蚀危害究竟有多大呢?据统计,在每年生产的每十吨钢铁中,有一吨腐蚀成为铁锈,有三吨已制成的设备因腐蚀而报废。从现代概念来看,金属损失造成的危害还不过是腐蚀总危害中的一小部分。例     

用电位/pH图解释Ⅰ~-对闭塞电池腐蚀的抑制作用及机理

用电位/pH图解释Ⅰ~-对闭塞电池腐蚀的抑制作用及机理刘幼平,王丹,左景伊(北京化工学院应用化学系,北京100013)发表于《北京化工学院学报》,1991;18(3):63.获中国腐蚀与防护学会第三届全国青年腐蚀科技论文讲评会优秀奖刘幼平,男,副教授,中国腐蚀与防护学会青年工作委员会委员.1965年出生,7”2年就学北京化工学院,获硕士学位,并留校工作.从事局部腐蚀和应力腐蚀破裂机理及防护方法的研究,两次获国家教育委员会科技进步奖门则8年....     

INVESTIGATION OF CHEMICAL AND ELECTROCHEMICAL CHANGES WITHIN CORROSION CRACKS——Ⅰ.Interrelations between Currents,C1~- migration and pH values

A simulated occluded corrosion cell was used to study the changes within corrosion cracks or crev-ices of 1Crl8Ni9Ti austenitic stainless steel in NaCI solution.As anodic currents passed through thecell,a series of changes took place,the most important of which were pH fall and CI-migration.Itwas found that the pH fall is proportional to current density and duration of current flowing,consequentlyit is a function of the quantity of electricity passing the occluded anode.The pH in the occluded cellmight be negative value when current density was 3.5mA/cm~2 after 168 hours.Meanwhile the CI-migratedinto occluded cell increased the CI-concentration 18 times as much as the original concentration.A linear relationship existed between CI-migration in g-equivalents per cm~2 of anode area and currentdensity,and also a linear relation existed between CI-migration per hour and current intensity.Conse-quently,the number of equivalents of CI-migration into crack tip was proportional to the quantity ofelectricity passing through it.It was interesting to discover that for each faraday passed almost always1/2 g-equivalent of CI-migrated into the occluded cell.This relationship did not change whatever werethe concentration of bulk solution,current density,temperature,and time elapsed.Two empirical for-mulas regarding the relationship between pH and Cr~3 dissolution or Cl-migration respectively werederived based on the relationships between quantity of electricity passed and other variables found in thepresent experiments.     

材料的环境破裂

环境破坏——腐蚀金属材料在自然或人为的环境中会发生破坏性的变化,有机材料(如塑料、橡胶、木材等)也能发生类似的破坏。材料的环境破坏就是腐蚀的定义。腐蚀通常是一种自发过程,对于金属来说,它由不稳定的元素态变为稳定的化合物态,伴随着自由能量的释放,金属腐蚀正好与冶金过程相反,如下所示: 显然,腐蚀造成了下列重大危害:1)浪费大量金属资源;2)损耗大量能源;3)引起设备损坏,生产停顿,污染及各类事故;4)阻碍新技术的发展等。据美国国会组织的调查,1975年美国全