Corrosion of Submerged Artifacts and the Conservation of the USS Monitor

Abstract

The USS Monitor, the first ironclad warship to be constructed in the United States, was built in 1862 to serve in the American Civil War. It took part in the infamous battle of Hampton Roads, Virginia with the iron covered Confederate frigate, CSS Virginia. The USS Monitor eventually sank at sea in a storm in 1862, and following its discovery in 1973 many important pieces have been recovered. In order to evaluate the extent of degradation of the iron artifacts due to prolonged seawater submersion, a spectroscopic study of the corrosion products and marine sediments attached to the artifacts has begun, with some of the early findings being reported in this document. It has been determined that under anaerobic, aqueous and high chloride exposure, the predominant rust component formed on the wrought iron artifacts was Corrosion Magnetite, an unstable compound whose Mossbauer signature is different to that of the pure, natural and synthetic forms. The Corrosion Magnetite changed with time of exposure in air, with its oxidation forming non‐stoichiometric maghemite. No akaganeite was detected in the anaerobically formed rust, but was identified if the iron artifact was allowed to dry in air. This is an important finding for archaeologists since formation of akaganeite indicates significant effort may be required to remove the insoluble chlorides from an artifact. Analysis of some ocean sediments trapped between wrought iron plates has shown that the pH is low, and the composition is mainly calcite and siderite, with the latter forming as a result of the rusting iron. The sulfur content was high at 1.5 weight percent, indicating the potential presence of microbial activity. Rusticles formed on iron surfaces of the USS Monitor have been identified as a solid outer casing of siderite, lepidocrocite and goethite, and a liquidous inner core of unstable Corrosion Magnetite having a low pH of about 3.