Role of copper in tarnishing process of silver alloys in sulphide media

作     者：J.ORTíZ-CORONA F.J.RODRíGUEZ-GóMEZ J. ORTíZ-CORONA;F. J. RODRíGUEZ-GóMEZ

作者机构：Departamento de Ingeniería MetalúrgicaFacultad de QuímicaUniversidad Nacional Autónoma de México 

出 版 物：《Transactions of Nonferrous Metals Society of China》 (中国有色金属学报（英文版）)

年 卷 期：2019年第29卷第12期

页      面：2646-2657页

核心收录：

学科分类：0806[工学-冶金工程] 08[工学] 0818[工学-地质资源与地质工程] 0815[工学-水利工程] 0805[工学-材料科学与工程（可授工学、理学学位）] 080502[工学-材料学] 0813[工学-建筑学] 0703[理学-化学] 0814[工学-土木工程] 0702[理学-物理学] 

基　　金：CONACyT for their support:scholarship to JOC 45653 and the Basic Science Projects 239938 LANCIC CONACyT LN 232619,260779 and 271614 the Chemistry School at UNAM for the financial support given for this work through the Program for Research and Graduate Studies Sponsorship(PAIP) 

主　　题：silver conservation and restoration tarnishing electrochemical impedance spectroscopy silver alloys corrosion mechanism 

摘      要：Silver and silver alloys usually tarnish,which causes some changes in their aesthetic appearance and electrical properties,due to their exposure to sulphide environments(H2S),and this is a problem in the field of corrosion and conservation of cultural heritage metallic *** this study,the role of copper content in the tarnishing process of 0.925,0.800 and 0.720 silver alloys in a 0.07 vol.%ammonium sulphide solution for different immersion periods was analyzed by electrochemical impedance spectroscopy(EIS)and scanning electron microscopy(SEM).The polarisation curves showed that the copper content and sulphide increased the corrosion current density and delayed the passivation of silver *** impedance spectra collected at the open circuit potential(OCP)showed a single capacitive,incomplete and depressed loop,indicating that the charge transfer resistance decreased as the copper content increased in the *** contrast,the double-layer capacitance increased as the copper content *** SEM-EDS analysis confirmed that the copper-rich phase in the silver alloys was selectively dissolved due to the preference of S to react with Cu,resulting in a localised attack,thus delaying the formation of a passive film.A marked localised attack was observed in alloys with lower copper *** mechanism for the tarnishing of silver alloys in sulphide media was dependent on the nature of the alloy and the greater affinity of copper for *** dissolution of Ag and Cu to form corrosion products was proposed as the rate determining step.