Laboratory-Grown Tubes Mimic Naturally Occurring Structures

Rust can be more than a formless powder and under certain conditions can even aggregate into organic-like structures. Layers of various iron oxides cover the surface of what had been a charged and bubbling electrode n a solution of dissolved iron and ammonium salts. The tubular formations grew around bubbles of gas generated by electrically driven reactions.

By sheer accident, researchers have discovered a laboratory method for artificially creating tube-like structures highly similar to those created naturally as soda straws in caves and chimneys at hydrothermal vents. The one-inch-high iron-oxide tubes shown above were made in the laboratory by immersing a pair of electrodes in a solution containing a mixture of water, ammonium, iron, and sulfates. Turning on the current for an hour or two created the structures, which the researchers have dubbed "ferrotubes." Using a video camera with a highly magnifying macroscopic lens, the researchers have obtained detailed information about the growth of natural tubes, which can take hundreds or even thousands of years to form.

Magnetite, green rust and other iron oxides precipitate over the surface of a negatively charged electrode. At certain sites, the material forms tubes around bubbles of gas produced by electrically driven reactions occurring on the surface. The tubes grow because every emerging bubble reacts with the surrounding solution and lays down a ring of new material.

Thanks to David A.Stone, University of Arizona, for supplying the images and captions.

Reported by: Stone and Goldstein, Proceedings of the National Academy of Sciences, 29 July 2004.

University of Arizona news release with more details and video

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