青铜文物腐蚀过程的模拟研究

SIMULATION STUDY ON THE CORROSION PROCESSES OF UNEARTHED BRONZE RELICS

采用地球化学模式程序EQ3/6,研究了青铜器蚀变过程.模拟结果表明,在土壤中常见的Eh和pH及研究区的年平均温度条件下,溶液中铜离子的含量达到一定的浓度时,可以生成赤铜矿(当Cu≈0.0016 mol/L)、孔雀石及黑铜矿(当Cu≈0.0079mol/L)等次生矿物,溶液中Cu的存在形式也发生了变化,即CuCO3(aq)所占的比例不断减小,而Cu2+和CuOH+的含量则相继增高,且Cu2+的增幅大于CuOH+.青铜制品中的Cu在不同的Eh和pH条件下腐蚀的产物是不同的.在研究的Eh(-0.2 V^0.7 V)和pH值(5~9.5)范围内,赤铜矿的形成不受氧化—还原电位及酸碱度变化的影响;孔雀石和黑铜矿形成于较高pH值(>7)和较高的氧化—还原电位(>0.2 V)条件;而辉铜矿则形成于较低的pH值(<7)和较低的Eh(<0.2 V)条件.水-青铜器相互作用的模拟研究结果表明,在作用过程中将依次生成赤铜矿、孔雀石、黑铜矿、白铅矿、锡石及在合金内层残留的自然Cu、Pb和Zn.在这一过程中溶液中Cu和Pb的含量逐渐降低,但Zn的行为则与Cu、Pb相反,即随着合金的溶解在溶液中的含量增加了.在上述模拟结果基础上,建立了青铜器腐蚀的化学作用过程,即青铜器的腐蚀大致可分为两个阶段:第一阶段生成黑铜矿和孔雀石,第二阶段生成白铅矿和锡石等矿物.上述模拟研究结果与现有的测定结果相吻合,同时还揭示了现有的常规研究所不能揭示的腐蚀过程,由此说明不仅可以应用地球化学模式程序来研究青铜器的腐蚀产物,还可以揭示青铜类文物的腐蚀过程及机理.

Modeling study of corrosion processes of unearthed bronze relics was preformed by EQ3/6, a software package for geochemical modeling of aqueous system. It was revealed that： cuprite, malachite and tenorite are the three main kinds of copper- hearing minerals which would be supersaturated when Cu concentration in the solution is high enough（higher than 0. 0016 mol/L, 0. 0079 mol/L separately） under the study conditions. Copper exists in the solution mainly as the species of CuCO3 （aq）, Cu^2＋ and CuOH^＋. The corresponding content of CuCO3（aq） would be decreased following the deposition of the copper- bearing minerals, nevertheless, Cu^2＋ and CuOH ＋ would be increased. The species of Cu and the saturation index of the copper - bearing minerals would be greatly affected by the Eh and pH values of the solution. Cuprite is supersaturated in the studied Eh and pH condition（Eh = -0.2 V～0.7 V, pH = 5～9.5）. Malachite and tenorite are supersaturated under the conditions E h 〉0.2 V, pH〉7, while chalcocite is supersaturated under the condition of pHi7 and Eh〈0.2 V. Waterbronze interaction has been revealed that cuprite, malachite, tenorite, cerussite, cassiterite, copper, lead and tin would be formed in a sequence from the early stage to the later stage of the reaction. The simulation calculation also showed the different behavior between Cu and Zn. It has demonstrated that Cu was leached off easily and the corresponding content in outer corrosion layer is lower than the interior layer, but Sn is just contrary. It is believed the corrosion processes of bronze could be divided into two stages： at the first stage, cuprite, malachite and tenorite were formed;cassiterite, cerussite and relic copper, lead and tin were formed in the second stage, which can be found in the outer layer of bronze. The simulation result not only fixed the natural corrosion products, but revealed the corrosion processes also which we could not understand by routine methods. So the geochemical modeling study can be used to simulate the bronze corrosion product and its corrosion processes also.