模拟宋代银制品在NaCl溶液中的腐蚀行为研究

Corrosion Behavior of Simulated Song Dynasty Silver Product in NaCl Solution

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和腐蚀产物成分，并根据银基体成分自行冶炼、加工出模拟的银试样。用电化学、XRD、XRF、SEM．EDS技术研究并比较了银试样在不同浓度NaCl环境中的腐蚀电位与电流，腐蚀产物成分、形貌、尺寸等。结果表明：NaCl浓度由较小的0．1％（质量分数，下同）升高到较大的3．5％时，自腐蚀电位φe负移47．5mV，自腐蚀电流密度i。升高0．0015μA／cm^2，腐蚀热力学倾向和动力学速度没有大幅度增加。腐蚀活化区电流密度迅速升高，致钝电流密度ip为ie的7．2×10^3-7．6×100倍，钝化区的银试样以71．2-308．8mm／a的腐蚀速率维持钝态。在0．1％、3．5％NaCl溶液中分别恒电位＋0．12VSCE极化不同时间后，腐蚀产物为AgCI，且基体发生了孔蚀，随着NaCl溶液浓度由0．1％增大到3．5％，试样表面c1。腐蚀活性中心增多，AgCl晶体生长速度增大，生成的颗粒尺寸由1-2gm减小到100nm；腐蚀产物层的颜色逐渐由灰白色变为黑色；在0．1％NaCl中可清晰观察到AgCl颗粒主要为棱柱状五面体结构，且随着极化时间延长，颗粒逐渐长大。

Chemical composition and corrosion product of the Northern Song Dynasty Emperor Asoka Pagoda substrate were studied for the first time since it was unearthed from the Changgan Temple underground palace of Nanjing in 2008. Silver samples based on the composition of the Pagoda substrate were simulated by the traditional smelting and processing technique by authors. The corrosion potential, the corrosion current of silver samples and the composition, the morphology and the size of corrosion products in NaCl corrosion medium of different concentrations were examined and compared with each other by means of electrochemical technique, XRD, XRF, SEM and EDS. The results show that the concentration increase of the NaCl solutions from lower 0.1 wt% to higher 3.5 wt% leads to the increase of the corrosion current density ic by 0.0015 gA/cm2 and the corrosion potential tpc is shifted towards less noble values by 47.5 mV. So the increasement of corrosion thermodynamical inclination and the kinetic rate are not great. Current density of the corrosion active region is increased rapidly. The initial passivity current density ip is 7.2×10^3-7.6×10^4 times as much as the ic. Silver samples in the corrosion passive region maintain the passivation with the corrosion rate about 71.2-308.8 mm/a. Corrosion products are AgCl and pitting corrosion occurs after ＋0.12 VSCE constant potential polarized time intervals in 0.1% and 3.5% NaCl solution. The amount of active corrosion sites and the growth rate of AgC1 crystals on the silver sample surface are increased with the increase of the NaCI concentrations from 0.1% to 3.5%, and the size of AgC1 crystals is reduced from 1-2 ktm to 100 nm. The color of corrosion product layers turns from grayish white to black. The prism-like pentahedron structure of AgC1 crystals is clearly observed in 0.1% NaCl solution, and the size of AgCl particles becomes bigger with the polarization time increasing