No, that's not a sponge. It's a piece of metal that's light enough to float. Researchers at New York University, who invented the substance, say it's also strong enough to build boats with.
This metal is called a syntactic foam. It's a magnesium alloy riddled with hollow silicon carbide spheres, a bit like metallic Swiss cheese. Though it's slightly lighter than water, it's strong enough to withstand pressures of 25,000 pounds (11 tonnes) per square inch (about ten times the pressure you’d feel one mile deep in the ocean).
Many modern boats are already built out of metal, so what’s the big deal? Consider that a square chunk of steel won’t float; boats are shaped the way they are so that their hulls will displace enough water to make the boat buoyant. But materials scientist Nikhil Gupta's syntactic foam is lighter than water, so it floats on its own. Ship designers using the new material would still have to reckon with the weight of crew, cargo, and onboard systems, but the hull itself would no longer weigh the ship down.
Gupta told Vice that the new material will be ready for production in about three years, and he expects to see the first Navy prototypes around that time. He published his work in the current issue of the International Journal of Impact Engineering.
Syntactic foam isn’t a new idea. Since the 1960s, polymer foams filled with glass or ceramic spheres have been used in buoys, submersibles, and some aerospace applications. Metal syntactic foams are more recent. One of the most common is aluminium foam filled with ceramic spheres, but engineers have also developed magnesium, steel, and titanium foams. Not only are these foams lighter than a solid block of the metal, they’re also better at absorbing impact energy, which is a useful trait in something like a warship hull.
Image: NYU via Science 2.0