Characteristics of mimetite(Pb-5(AsO4)(3)Cl)-pyromorphite(Pb-5(PO4)(3)Cl) corrosion products on Han Dynasty bronzes from Chongqing, China

摘要

Eight bronze samples from tombs near the Yangtze River were analyzed by optical microscope, Raman spec troscope, SEM-EDS and EPMA. The results showed the presence of rarely reported corrosion products of the mimetite-pyromorphite series. The mimetite-pyromorphite series on these archaeological bronzes were observe in a variety of colors, and the typical Raman spectra can be classified into three types, strong peaks o Pb-5(AsO4)(3)Cl with weak peaks of Pb-5(PO4)(3)Cl, equivalent peaks of Pb-5(AsO4)(3)Cl and Pb-5(PO4)(3)Cl, and strom peaks of Pb-5(PO4)(3)Cl with weak peaks of Pb-5(AsO4)(3)Cl. The distribution of the mimetite-pyromorphite phases the patinas does not appear to be systematic, they are found not only on the surface of bronze artefacts, but also in the middle of bronzes through cross-section analysis. The molar ratio As/As + P in the corrosion product varies between 0 and 1.0 means that the mimetite-pyromorphite series exist between Pb-5(PO4)(3)Cl and (Pb-5(AsO4)(3)Cl. It is possible that the formation of mimetite-pyromorphite has some relationship with the specia burial environment of sites nearby river or ocean.