研究了2008年南京长干寺出土的北宋七宝阿育王塔鎏金银基体及其腐蚀产物成分,并根据银基体成分按传统工艺自行冶炼、加工出模拟的银试样.用电化学、OM、XRD、XRF、SEM-EDS技术研究并比较了银试样在不同浓度Na2S溶液中的腐蚀电位与电流、腐蚀产物成分、形貌、晶粒度等.结果表明,Na2S浓度由20 mg/L升高到5.0× 104 mg/L (5％ Na2S)时,自腐蚀电位Ecorr负移0.70V,自腐蚀电流密度Icorr从0.274 μA/cm2升高至1.056 μA/cm2,腐蚀倾向和速度大幅度增加.在20 mg/L Na2S溶液中-0.31 V～1.8 V范围内极化,银试样始终处于活化溶解状态.在5％ Na2S溶液中,腐蚀活化区电流密度从1.056 μA/cm2迅速升高至1.56× 104μA/cm2,并以较大的腐蚀电流密度(约1.56× 104 μA/cm2)进入钝化区并维持钝态;分别在20 mg/L和5％ Na2S溶液中活化区恒电位+0.3V、-0.8 V极化不同时间后,腐蚀产物主要为Ag2S.随着Na2S溶液浓度的增大,试样表面S2-腐蚀活性中心增多,Ag2S晶体成核速率增大,而腐蚀产物的晶粒度则由20 μm减小到1.86～5.10 nm.
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