Mud battery stops marine rust
Electricity from microbes could shield ships and rigs.
Ships, buoys, oil rigs and other ocean-bound steel objects can be protected from rust by plugging them into the seabed, says a team of Argentinian researchers.
The scientists have turned marine mud into a battery that can suppress corrosion by charging up stainless steel. The energy is free, clean and everlasting.
Stainless steel, which contains chromium, is much more resistant to corrosion than is ordinary steel. But in seawater it quickly acquires a layer of microbes and algae. These microbes' electrochemical reactions slowly erode the metal.
Supplying the steel surface with electrons, which gives it a negative charge, suppresses this process. At present, these electrons usually come from a sacrificial metal, which is eaten away instead of the steel and must be replaced periodically.
Juan Pablo Busalmen at the National University of Mar del Plata and his colleagues realized that microbial batteries made by inserting electrodes into ocean sediments would be an ideal source of electrons.
Stick in the mud
Microbes pull electrons from sulphide mineral particles in the mud, and use them in metabolic reactions that release energy.
The electrons are eventually dumped onto an 'electron acceptor' normally oxygen. But in the microbial battery they are shunted onto an electrode. The resulting electrical current is tiny but that is all that's needed.
Researchers have previously sought to use these microbial fuel cells to power devices such as instruments for environmental monitoring. "People have looked at using them to create electricity", says Bruce Logan, a specialist in this technology at Pennsylvania State University, University Park. "But using them for corrosion protection seems new."
The Argentinian team tested sediment's ability to protect steel in a laboratory mock-up of the seabed. Seawater and sediment were collected off Mar del Plata, a fishing port south of Buenos Aires.
The battery electrodes were rods of graphite, which the researchers simply stuck in the mud. They wired them up to plates of stainless steel partly immersed in water.
Plates lacking any corrosion protection became heavily pitted after about four months. Those hooked up to the biobattery showed no signs of corrosion, the team reports in Environmental Science and Technology1.
Once installed, the researchers say, the anti-corrosion system "should need minimal maintenance with a very low cost."
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- Orfei L. H., et al. Environ. Sci. Technol., 40 . 6473 - 6478 (2006).