a new take on the idea:
A new material is tested to cut the weight of ships by 30 percent. For an average sized freight vessel with a capacity of 7000 m³ this corresponds to a weight reduction of more than 1000 tons. Researchers from Fraunhofer Institute for Machine Tools and Forming Technology in Chemnitz, Germany, have experimented with an aluminum powder that foams when heated up (Jan '11)
The new material is lighter than water and has a high stiffness. Within seconds a cube made from aluminum starts to inflate into the shape of a sponge under the impact of heat. The secret of this reaction lies in the compounds of the new material. The metal is a mixture of aluminum and titanium hydride powder, which acts as a blowing agent just like yeast makes dough rise.
The aim of the researchers from the EU research project CREATING was to find a processing method to build large aluminum foam sandwich plates. These compounds could eventually replace steel plates of a vessel. To form such sandwich compounds, the powder is initially pressed into bars. The bars are then placed between two steel sheets and heated in an oven. At a temperature of more than 650° Celsius the new material expands and bonds with the steel sheets without the help of any adhesives.
Consider the implications for aero industries too. I wonder about the possibilities of foaming a metal with helium...