07238 Spectroscopic Evaluation of Corrosion Products on the Turret of the American Civil War Ironclad, USS Monitor

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Product Number: 51300-07238-SG

ISBN: 07238 2007 SG

Author: D. C. Cook, M. J. Shaw, E. Schindelholz, B. L. Bramfitt, S. J. Lawrence, R. C. Nester

Publication Date: 2007

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Spectroscopic analysis of artifacts from the American Civil War ironclad, USS Monitor, has been undertaken in order to determine the present state of degradation of the objects, and to identify foreign compounds that will require removal during the stages of conservation. Metallic artifacts consisting of wrought iron from the rotating gun turret have been studied by a variety of analytical techniques to determine the effect of long-term exposure to salt, and the anaerobic environment of the deep ocean. Mössbauer spectroscopy, and X-ray diffraction have been used to identify the corrosion products, concretion, and marine sediments attached to the turret when it was recovered in 2002, and subsequently during storage. Optical microscopy and Electron-Probe Micro-Analysis have been used to characterize the wrought iron morphology, and to locate and map the chlorine and other potentially detrimental elements in the iron. While submerged in the ocean, the corrosion of the turret has resulted in a thin coating of the reduced iron oxide, Corrosion Magnetite, which, when covered or incorporated with marine concretions, appears stable, and offers the wrought iron protection from accelerated corrosion often observed following recovery of metal artifacts from the ocean. However, if the concretion is breached and the rust or metal is exposed to air, further and immediate oxidation of the metal and existing rust occurs, and is believed to be detrimental to conservation processes. Elemental Xray mapping by Wavelength Dispersive Spectroscopy shows that during ocean submersion, chloride ions diffuse deep into the inclusions in the wrought iron, where they are trapped and become responsible for significant and continued corrosion. Once exposed to air and dried, the trapped chlorides have a detrimental effect on the longevity of the artifact.