Insitu corrosion investigations on Delhi iron pillar

Abstract

For the first time, insitu corrosion investigations were carried out over the 1600 years old Delhi iron pillar to understand the corrosion aspects of the pillar and the scales developed over the surface. The study clearly indicated the heterogeneity of the Pillar with respect to corrosion behaviour. The polished surfaces at selected locations from base to crown of the pillar corroded in similar manner, and there was no significant variation in their corrosion behaviour. The scale developed over the pillar showed passive behaviour and depending on the location, variations were noticed in their polarization behaviour. The passivation current density measured from the polarization curves indicated the differences in the passivability of the scales, and the scale developed at the top of the pillar showed better passivation nature. XRD of the rust scale from two locations of the pillar showed mostly the presence of α-FeOOH, γ-FeOOH and γ-Fe₂O₃. Laser Raman Spectroscopy of the rust also supported the above findings.