The H. L. Hunley
Found on the ocean floor nearly 140 years after its mission, the Hunley submarine has provided historians a unique glimpse back in time. Carefully moved to the Warren Lasch Conservation Laboratory, the submarine has revealed to researchers much about civil war era technology, as well as dramatic insight into the lives of those who manned her. Driven by the challenge of studying such a large, complex, and historically valuable artifact, the conservation team has continually expanded the boundaries of proven scientific techniques and procedures. Their job is all the more challenging since the submarine is only protected from rapid deterioration by a cocoon of concretion that formed while it was submerged and by the expertise of the conservation team at the Lasch Center. This quest for the best ways to study and preserve all of the submarine’s materials—glass, rubber, wood and metal—led to the involvement of Clemson material scientist, Dr. Michael Drews.
Starting in spring 2002, Dr. Drews began to use his considerable expertise to understand and analyze the state of the submarine’s metal hull and other components. Submerged for so long, the wrought and cast iron body of the submarine is infused with salt, or chlorides. Until the salt is removed, exposure to air will rapidly cause the metal to corrode and rust. To date, the only treatment to remove the chlorides from large and complex artifacts has been to soak the affected metals in alkaline solutions over a period of years, sometimes also using electrolysis to aid the process. Dr. Drews' experience with subcritical and supercritical fluid reactions led him to explore this alternate option for preserving the Hunley.
Subcritical and supercritical chemical reactions depend on applying heat and pressure to a fluid within a reaction vessel. Analogous to using a pressure-cooker, the higher temperatures and pressures allow for both quicker reaction times and sometimes facilitate chemical changes that can not be done at ordinary temperatures and pressures. To date, the study of Hunley wrought iron hull rivets and pieces of a cast iron artillery shell show that this approach has promise. These ordinary materials from the 1800s, treated through this new process, and carefully examined using state of the art instrumental methods such as micro-Raman spectroscopy, x-ray diffraction and electron microprobe analysis, are the focus of advanced scientific inquiry that has broad applications. First, the results will aid in preservation of the Hunley and other important historical metal objects from marine or even terrestrial sites. Second, these treatment and testing techniques may eventually have commercial application in many anti-corrosion situations. In the meantime, the examination provides a one-of-a-kind learning experience for students, with a course for undergraduate summer interns in the planning, and opportunities for Clemson-sponsored graduate student research.
Dr. Drews remarks, “Anytime you have the opportunity to study what was amazing advanced technology in its time, as well as reflect on the fact that you are preserving an instance of bravery, courage and incredible dedication, you have to realize that this is a once-in-a-lifetime experience.”
The research was featured on S.C. ETVs The Big Picture in August 2008, to commemorate the eighth anniversary of the Hunley submarines recovery 136 years after it sank in the Atlantic Ocean - click here to view the YouTube videos.
For more information on the Clemson Conservation Center’s H.L. Hunley Project: