Some observations on corrosion resistance of ancient Delhi Iron Pillar and present time Adivasi Iron made by primitive methods

Abstract

This paper outlines the results of metallurgical examination of the ancient Delhi Iron Pillar and the Adivasi iron smelted by primitive methods in tribal Indian villages. Such metallurgical examination has covered chemical, metallographic, physical and X-ray diffraction studies apart from atmospheric corrosion-resistance exposure tests and salt-spray attack etc. Current investigations on the subject at the National Metallurgical Laboratory, particularly the long-term atmospheric tests, will take some time for arriving at definite conclusions on the complex subject of corrosion-resistance of ancient iron structures, even though valuable light and data on the mechanisms by which the latter have withstood ravages of corrosion, have meanwhile been obtained. One of the main conclusions arrived at which appears to provide adequate explanation for high corrosion-resistance of the Delhi Iron Pillar is related to the mode of smelting and fabrication of the latter, particularly the trapping of slag and sponge iron during smelting and their intimate kneading with each other during subsequent forging operations. The three dimensional inter-mixture of slag, oxides etc and their envelopes within and around the metal, would afford considerable corrosion-resistance by drastically reducing the breakdown areas where corrosion attacks could be initiated. Corrosion-resistance of the ancient Delhi Iron Pillar appears basically to be related to that of Adivasi iron with its improved corrosion-resistance in corrosion tests conducted so far. When it is borne in mind that even 800 years old beams at the Sun-Temple of Konark, situated on the sea coast, are still in an excellent state of preservation, the hypothesis that the dry climate of Delhi would have materially contributed towards improved corrosion-resistance of the Delhi Iron Pillar would hardly appear tenable. (Mr. A.K. Lahiri, Senior Scientific Officer; Dr. T. Banerjee, Dy. Director; Dr. B.R. Nijhawan, Director, National Metallurgical Laboratory, Jamshedpur)