HUNTING FREE AND BOUND CHLORIDE IN THE WROUGHT IRON RIVETS FROM THE AMERICAN CIVIL WAR SUBMARINE H. L. HUNLEY
N�STOR G. GONZ�LEZ, PHILIPPE DE VIVI�S, MICHAEL J. DREWS, & PAUL MARDIKIAN
ABSTRACT—The Confederate submarine H. L. Hunley, built in 1863, was successfully recovered in August 2000 after nearly 140 years of immersion in the Atlantic Ocean. One of the most significant challenges faced in the Hunley's stabilization and conservation will be the effective removal of chloride from the corrosion products present on the surface of the submarine. This article addresses the issue of the presence of free and bound chloride in the metal shavings retained when the rivets were removed, by drilling, from the Hunley's hull prior to the excavation of the interior. Before the extraction and digestion studies on the shavings, one of the rivets that had been stored in tap water since its removal was sectioned, and the sectioned surface was characterized using scanning electron microscopy and energy dispersive x-ray analysis. Rivet shavings that were stored dry, in tap water, and in sodium hydroxide made up with tap water after removal were extracted with deionized water, sodium carbonate, and sodium hydroxide solutions for up to two weeks. The total amount of chloride present in each sample was determined using nitric acid digestion. It was found that the shavings stored dry and in tap water contained very similar quantities of total chloride. It was also found that the shavings stored in caustic solution contained significantly less chloride than the other two sets of samples. For all of the shaving samples, it was found that a significant quantity of chloride (> 500 ppm) remained in the corrosion products after extraction, suggesting the presence of some form of bound or occluded chloride ion.
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4. SUMMARY AND CONCLUSIONS
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