Investigation on lead corrosion products in sea water and in neutral saline solutions

摘要

AbstractA method was developed to characterize and quality lead corrosion products in sea water and in saline neutral solutions.This method is based on selective dissolution of various compounds, using suitable reagents (methanol, glycine, potassium nitrate etc.) and on subsequent chemical analysis of the various dissolved elements.The findings are then verified by X‐ray diffractometer analysis.This method was used for an examination of the corrosion products adhering to a lead plate of a Roman ship wrecked in the Gulf of Toulon about two thousand years ago. The following corrosion products were determined:documentclass{article}pagestyle{empty}begin{document}$$ {rm PbCl}_{{rm 2}^{rm - } } {rm Pb}_2 {rm Cl}_3 {rm OH} - 3{rm PbCO}_3 cdot 2{rm Pb(OH)}_2 cdot {rm H}_2 {rm O} - {rm Pb}_2 {rm O}_{3^ - ,} ,{rm Pb}_4 {rm O}_3 {rm SO}_4 cdot {rm n},{rm H}_2 {rm O} - {rm Pb}_{rm x} {rm S}_{{rm y},} {rm or},{rm PbS}. $$end{document}These products were compared with those obtained on sea water immersed lead specimen.In the latter case, the products were the following:documentclass{article}pagestyle{empty}begin{document}$$ {rm PbCl}_{2^ - } {rm PbCO}_3 cdot {rm PbCl}_{2^ - } {rm Pb}_3 ({rm CO}_3)_2 ({rm OH})_{2^ - } {rm PbO} - {rm Pb}_{rm 2} {rm O}_3 . $$end{document}The difference between the two test specimen is deemed to be due to the known formation caused by bacterial fouling processes (desulfovibrio desulfuricans) of hydrogen sulphide in marine sediments which, by altering the pH value, also alter the equilibrium of the CO3−−‐HCO3−‐CO2‐SO4−−HSO4−systems thus affecting the differentiated formation of the corrosion products.Lead, despite its improved corrosion resistance in various environments as compared with other normally used metals (e.g. iron), is not so commonly employed because of its poor mechanical properties (deformation, grain coarsening, brittleness 1, etc.) so that it is only used for certain structures like pipings or coverings (roofs, chemical vats etc.) not exposed to strong mechanical stresses.These applications were common even in ancient times, when the Romans already covered their hulls with lead plates because they did not corrode easily and