ABSTRACT

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 X-ray 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.

INTRODUCTION

USS Monitor was the first ironclad warship to be constructed in the United States. Built in 1862, it was rushed into battle in Hampton Roads, Virginia where the infamous Civil War battle with the iron covered Confederate frigate, CSS Virginia, was waged on March 9, 1862. Built in only 147 days, USS Monitor was 173 feet in length and 41 feet wide. Its flat deck was armor plated with 1-inch thick wrought iron, and the waterline armor consisted of 5 layers of 1-inch wrought iron plates bolted together. Although outfitted with only two very large 11" Dahlgren guns, the revolutionary design of USS Monitor centered on the gun turret that could be rotated through 360 degrees in 10 minutes. The cylindrical turret was 20 feet in diameter, 9 feet high, and weighed 120 tons. It was constructed using 8 layers of 1-inch wrought iron plate bolted together. History records the 4-hour battle between the two ironclads in Hampton Roads as fierce and at close range. Although struck often, neither ship sustained serious damage, due to their protective armor, thus ending the era of wooden fighting ships. CSS Virginia was eventually scuttled in Hampton Roads, Virginia, and USS Monitor sank in a storm off Cape Hatteras, North Carolina, on December 31, 1862. Lost at sea were 16 of the 56 sailors on board.

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