Materials Performance

NOV 2017

Materials Performance is the world's most widely circulated magazine dedicated to corrosion prevention and control. MP provides information about the latest corrosion control technologies and practical applications for every industry and environment.

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67 NACE INTERNATIONAL: VOL. 56, NO. 11 MATERIALS PERFORMANCE NOVEMBER 2017 moted crevice corrosion, while high con- c e n t ra t i o n s of C l – p r o m o t e d g e n e ra l corrosion outside the crevice. SO 4 2– ions by themselves seemed to induce crevice cor- rosion, and the crevices gradually became wider with increasing SO 4 2– concentrations. CO 3 2– ions by themselves tended to passiv- at e th e sur fa c e and inhi bit ed cre v i c e corrosion. The presence of low concentrations of Cl – in SO 4 2– solutions promoted crevice cor- rosion , and a synergistic ef fect existed between them. When the concentration of Cl – was higher, the corrosion behavior of copper in the Cl – /SO 4 2– mixed solutions fol- lowed the same mechanism as in unmixed Cl – solutions. CO 3 2– had an inhibiting influence on the crevice corrosion of copper ; it partially or TABLE 2. STATISTICAL RESULTS OF CREVICE CORROSION IN DIFFERENT ION SOLUTIONS Solutions Ions Ion Concentration Multipliers Crevice Corrosion Observed Average Crevice Depth (mm) Maximum Crevice Depth (mm) Solution I Cl – 1 yes 0.016 0.032 10 no — — 30 no — — Solution II SO 4 2– 1 yes 0.017 0.043 10 yes 0.022 0.043 30 yes 0.024 0.047 Solution III CO 3 2– 1 no — — 10 no — — 30 no — — Solution IV Cl – /SO 4 2– 1-1 yes 0.020 0.036 1-30 yes 0.044 0.098 30-1 no — — 30-30 no — — Solution V Cl – /CO 3 2– 1-1 yes 0.017 0.041 1-30 no — — 30-1 no — — 30-30 yes 0.023 0.056 Solution VI SO 4 2– /CO 3 2– 1-1 no — — 1-30 no — — 30-1 no — — 30-30 no — — Solution VII Cl – /SO 4 2– /CO 3 2– 1-1-1 yes 0.010 0.024 1-30-30 no — — 30-1-30 yes 0.012 0.055 30-30-1 no — — completely counteracted the aggressive effects of Cl – and SO 4 2– . These results strongly indicated the occurrence of a competitive adsorption process between inhibiting and aggressive ions. If the concentration of CO 3 2– were greater and CO 3 2– adsorption domi- nated, then crevice corrosion attack was not obser ved on the copper surface. If the adsorption of Cl – or SO 4 2– was greater, then crevice corrosion occurred. Conclusions The presences of Cl – and SO 4 2– pro- moted the corrosion process of copper, while CO 3 2– exhibited a suppressive effect. When the concentration of Cl – in solu- tion was low, crevice corrosion was pro- moted. The addition of SO 4 2– increased the promotion of crevice corrosion. When the concentration of Cl – was high, most of the copper corrosion occurred through active matrix dissolution outside of the crevice. CO 3 2– caused surface passivation of the cop- per and had an inhibiting effect against crevice corrosion from Cl – and SO 4 2– , but the protective effect depended on the con- centrations of each ion. Acknowledgment T h i s w o rk w a s su p p o r t e d b y t h e National Natural Science Foundation of China (No. 51271024). References 1 M. Drogowska, L. Brossard, H. Ménard, "In- fluence of Anions on the Passivity Behavior of Copper in Alkaline Solutions," Surf. Coat. Tech. 34, 4 (1988): p. 383. Continued on page 68 Effects of Anions on Crevice Corrosion of Copper

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