In Situ Laser Raman Spectroelectrochemical Study of the Corrosion of lead in Dilute Na2S04 Solution at High Temperature

The h igh temperature corrosion and pass ivat ion behav ior of a lead electrode in a 100 ppm Na2SO4 solut ion was exam-ined by in situ laser Raman spectroscopy and cyclic vo l tammetry. The exper imenta l observat ions were compared with the thermodynamic predict ions of the temperature-dependent Pourba ix d i gram for lead in aqueous sulfate solution. At open-c i rcui t condi t ion and room temperature, the compos i t ion of the corrosion film was found to be 3PbOPbSO4H20. The latter compos i t ion is stabi l ized relative to PbSO4 by an elevated local pH at the electrode surface wh ich accompanies the reduct ion of d issolved oxygen at open circuit. At h igher temperatures only PbOPbSO4 and PbSO4 were observed at open circuit. By correlat ing the temperature dependence of the cyclic vo l tammetry wi th the Pourba ix diagram, the PbSO4 cor-ros ion film was found to be a more effective pass ivator than the PbOPbSO4 film. In this report, we present the application of an in situ Raman probe of corrosion films on metals to include mea-surements in high temperature aqueous solutions. The identification of passivating films at elevated temperature can be useful in understanding corrosion mechan isms. We have examined the corrosion and passivation behavior of