摘要
对青铜器腐蚀机理的研究是对其进行保护修复的重要前提,在过去的数十年间,与铜和铅的腐蚀产物相比,文物保护领域对于锡腐蚀产物的认识和研究是相对缺乏且零散的.本文回顾了不同领域在锡腐蚀产物发展过程、特点以及表征方法等方面的研究成果.青铜器中锡腐蚀后一般首先形成复杂的水合氧化物(SnOx·nH2O),随后在氧化性条件下进一步氧化脱水,向锡石(SnO2)转变,但由于此转变过程漫长而复杂,导致了锡腐蚀产物具有低结晶度、高电阻率、离子交换等特殊性质.通过梳理X射线衍射分析技术、拉曼光谱以及X射线光电子能谱以及其他分析方法在青铜器锡腐蚀产物表征中的应用进一步探讨了锡腐蚀产物的性质.最后,本文在回顾不同环境下的锡腐蚀产物的研究成果的基础上,介绍并比较了不同环境下青铜器的腐蚀模型.
Abstract
The study of the mechanism of corrosion of ancient bronze is an important prerequisite for its conservation and restoration.Over the past few decades,compared with the corrosion products of copper and lead,the understanding and research on tin corrosion products in the field of cultural relic conservation have been relatively insufficient and unsystematic.This article reviews research achievements in the formation process,as well as characteristics and characterization methods for tin corrosion products in different fields.We first summarize the transformation process of tin-formed corrosion products.Generally,the bivalent hydrated oxide SnO·nH2O is formed first after the corrosion of tin in bronze,and the tetravalent oxide SnO2·nH2O is partially formed under oxidizing conditions,resulting in a complex hydrated oxide-SnOx·nH2O.Then cassiterite(SnO2)is formed after further oxidization and dehydration.Due to the long and complex dehydration process in the natural environment,the tin corrosion products show an amorphous-nanocrystalline gel state externally.We then review some special properties of tin corrosion products.The first property is that the crystallinity is low-it is often difficult for the methods commonly used for cultural relic analysis(such as XRD and Raman spectrometry)to collect signals of tin corrosion products in bronze,or the signals are weak,mainly because they are in the transition stage from being amorphous to crystalline.The second property is in-situ deposition-copper and lead in bronze often migrate outwards after corrosion,while tin is corroded and deposits in situ,which is also the reason why some bronze objects suffer from severe corrosion,but the"tin rich patina"can retain the original state of the objects.The third property is high electrical resistivity-the formation and deposition of tin corrosion products can polarize the original anode and inhibit the corrosion of the anode metal matrix;however,the corrosion product film on bronze is not uniform and dense.The fourth property is the ability to exchange ions-the order in which tin corrosion products adsorb cations in alkaline environments is Al3+＞Ba2+＞Na+,and the order in which anions are adsorbed in weakly acidic environments is PO43-＞Br-＞Cl-.This may provide an explanation for the deposition of elements such as Fe and Al in the"tin rich patina"and the pyromorphite in the rust layer of bronze in Sichuan and Chongqing regions.The fifth property is the overlapping lattice structure with the Cu-Sn δ phase boundary,which can inhibit the corrosion of tin corrosion products and copper on the Cu-Sn δ phase boundary,thereby inhibiting the corrosion of metals-this coincidence can well explain the local corrosion resistance phenomenon of Heiqigu copper mirrors and mercury bronze mirrors.Subsequently,we review the application of XRD,Raman spectrometry,XPS and other analytical methods in the characterization of tin corrosion products in bronze,verifying their low crystallinity.This also reflects the shift in understanding of tin corrosion products in bronze from early tin dioxide to hydrated oxides with partial amorphous characteristics and an approximate cassiterite structure.Finally,based on a review of the research results of tin corrosion products in different environments,this article introduces and compares the corrosion models of bronze in different environments.In the atmospheric environment,outdoor bronze exhibits the deposition of cuprous oxide and tin corrosion products on the surface,and divalent copper corrosion products migrate to lower areas under the influence of rainwater erosion.In the oxygen-rich marine environment,tin in bronze often forms hydrated oxides containing chlorine in the early stages of corrosion,and then undergoes dechlorination and dehydration to transform into hydroxycassiterite and tin dioxide.In anaerobic marine mud zones,bronze is mainly affected by sulfate reducing bacteria to form sulfides of copper and tin.In the soil environment,"chloride corrosion"damages the substrate of bronze in the form of inward invasion of chloride ions,causing cyclic corrosion called"bronze disease"and forming powdery rust,and"chloride-free corrosion"occurs in the form of cation diffusion.Under specific conditions,Cu in the substrate continuously passes through the tin corrosion layer and flows outwards,causing the bronze strength to decrease and become"fragile".
基金项目
中国-希腊文物保护技术"一带一路"联合实验室建设与联合研究(2020YFE0204600)
万方数据