Scientists to study third way of conserving Confederate sub

CHARLESTON, S.C. -- Scientists studying both traditional electrolysis and cutting-edge cold plasma technology also will investigate a third way to preserve the Confederate submarine H.L. Hunley, the first sub in history to sink an enemy warship.

During the next year, scientists will experiment to see if supercritical fluids may prove the best choice for conserving the sub that sank with its crew of eight in February 1864, after sinking the Union blockade ship Housatonic.

The Hunley was raised off Charleston's coast two years ago and brought to a conservation lab at the old Charleston Navy Base.

"We're working on setting up some experiments to explore using super- and subcritical fluids to remove corrosive salts," said Michael Drews, the materials scientist who heads the Clemson University research team helping with the Hunley conservation.

Like liquid and gas

Supercritical fluids -- in this case the fluid would be water -- take on the characteristics of both a gas and a liquid under intense heat and pressure and have unique dissolving characteristics, Drews said.

They are used in a number of commercial applications, including decaffeinating coffee and in processing hops for brewing beer. But they've never been used to preserve maritime artifacts, Drews said.

The traditional method of conserving large marine artifacts, and one that takes years to complete, has been electrolysis in which an electrical current removes corrosive salts from metal artifacts in water.

However, the electrical field often doesn't penetrate behind pieces bolted or riveted together as would be needed with the Hunley, scientists say.

In cold plasma reduction, hydrogen gas is blown over the artifact in a sealed container and the plasma formed pulls out the impurities as a gas.

Both cold plasma and supercritical fluids, if they work on the sub, could mean the Hunley might go on museum display years sooner than using electrolysis, which could take about seven years, scientists say.

"It has the potential for significantly reducing the time it would take to treat the Hunley," Drews said.

Scientists will use small pieces from the boiler of a paddle steamer that sank off Australia in 1880 to test the various methods, he said.

Tests in December

The cold plasma tests will be conducted at a lab in France while equipment from Clemson will be brought to the Hunley lab in December for the fluids tests.

"We're hoping the time frame in the pressure container will be short, under a day if we're lucky and, if we're really lucky, a matter of hours," Drews said. "If we're not lucky, it may not work at all."

If the experiments are successful and a decision is made to use cold plasma or the fluids, a larger pressurized container would have to be built.

It would be possible, Drews said, to build a container large enough for the entire submarine. But whether that's done will depend on the cost.

"Yes, you could build a container that would treat the whole thing and it would cost you X dollars," he said.

The alternative might be a smaller, less expensive chamber in which smaller pieces of the sub could be treated. "It would depend on how much you want to take it apart," Drews said.