汉代五铢钱币腐蚀特性研究

THE CHARACTERIZATION OF ANCIENT CHINESE WU ZHU COIN OF HAN DYNASTY AND ITS CORROSION MECHANISM

用光学显微镜、X-射线衍射及扫描电镜能谱等方法,研究了五铢钱币的化学组成及表面腐蚀特点。通过对模拟青铜样片进行锈蚀产生条件及腐蚀特征的分析,研究了铜币的腐蚀机理。研究表明,尽管不同钱币表面上的化学元素含量差异较大,但钱币基体的元素含量约为Cu 82%～86%,Sn 2%～4%,Pb 7%～11%,属于青铜材料。Fe、Si和Al的含量较低。钱币腐蚀产物以多种形式附着在铜币表面,淡绿色的粉状腐蚀产物主要为Cu2(OH)3Cl(绿铜矿),致密的绿色腐蚀产物主要为Cu3(CO3)2(OH)2(蓝铜矿),坚硬致密的墨绿色突出结状物为Cu2(OH)2CO3(孔雀石),土绿色锈蚀为铜锈与铁锈的混合物,锈层较厚。模拟腐蚀研究表明,Cl-、O2、H2O及酸性条件共存是五铢钱币腐蚀的主要因素。

This paper presents the joint research aimed at collecting technical information through an scientific examinations carried out on WuZhu coins from the largest mint site in the Chinese history. Optical microscopy （OM）, scanning electron microscopy coupled with energy-dispersive X-ray analysis （SEM-EDX） as well as X- ray diffraction （XRD） have been used for both characterizing the elementary composition,morphology and corrosion products of coins.The analytical results revealed that the coin was made of bronze;the elementary composition is in good agreement with the information gathered through the historical survey. At the same time, the patina of coin was analyzed in this paper, mainly containing Cu2（OH）3Cl, Cu2（OH）3Cl, Cu3（CO3）2（OH）2, Cu2（OH）2CO3, CuO2 and some other minerals. The main corrosion products were azurite （2CuCO3·Cu（OH）2, blue appearance ）, malachite （CuCO3·Cu（OH）2, dark green color）, dioptase （CuCl2·3Cu（OH）2, CuCl2·Cu（OH）2, dark green color）, cerusite （PbCO3） and others. Meanwhile, the artificial corrosion displayed that Cl-, O2, H2O were the most important factors for the erosion of WuZhu coin.