Researchers Build Aluminum Tubes That Cannot Be Sunk
The Swedish warship Vasa sailed on August 10, 1628, from Stockholm on its maiden voyage in front of large crowds, carrying 64 bronze-coated cannons and hundreds of carved statues. But after only 1,300 meters, a light gust tipped it over, water rushed in through the gun ports, and the ship and its passengers sank. The wreck was raised 333 years later and preserved for study. A new study now asks whether that disaster could have been prevented by choosing different materials.
Researchers note that buoyancy depends mainly on density, the amount of mass packed into a given volume. That is why oil floats on water while sand and many plastics sink. Iron is about eight times denser than water, yet ships made from it usually float because their hulls trap large volumes of air, making the average density lower than water.
Scientists at the University of Rochester in New York say they have now shown that even a large metal structure can be made impossible to sink. In a paper published in Advanced Functional Materials, they described water-repellent aluminum tubes with a nanoscale and microscale porous structure that gives the metal enormous surface area. When submerged, the pores keep water out of the larger cavities in the material, trap air against tiny surface protrusions, and force water away. The pores were created through etching, a controlled chemical process that removes surface layers.
To strengthen the design, the researchers added a divider in the middle of each tube, so an air bubble stays in place even when the tube is held vertically. They say that even if the tubes are pierced with many holes, they still will not sink, because air remains stuck to the surface at the microscopic level and keeps the overall density below that of water. The team took inspiration from the diving bell spider, Argyroneta aquatica, which traps air bubbles on its body and builds an underwater shelter around them.
The researchers say the tubes could be linked into a raft-like array to form a base for advanced vessels, though it is not yet clear whether such craft could move through water like existing ships. They also suggest the structure could be used to harvest energy from ocean waves and surf.
