New metallic wood has the strength of titanium and the density of water
Researchers at the University of Pennsylvania, the University of Illinois, the University of Cambridge, and Middle East Technical University in Ankara, Turkey, engineered a sheet of nickel with nanoscale pores that make the material as strong as titanium but up to five times lighter.
Titanium is a popular metal for making anything from high-performance golf clubs to airplane wings. The material is as strong as steel, but twice as light. The properties of the material largely depend on the way a metal’s atoms are stacked. However, due to random defects that arise during the manufacturing process, titanium is only a fraction as strong as it could theoretically be.
The material the researchers designed is similar to wood. Not just because of its density, but also because of wood’s cellular nature. “Cellular materials are porous,” James Pikul, who led the study, says, “if you look at wood grain, that’s what you’re seeing — parts that are thick and dense and made to hold the structure, and parts that are porous and made to support biological functions, like transport to and from cells.”
The structure of the metallic wood is similar. The material has areas that are thick and dense with strong metal struts and areas that are porous with air gaps. The struts are around 10 nanometres wide. The method of making the material starts with tiny plastic sphere, which are just a few hundred nanometres in diameter, suspended in water. When the water is slowly evaporated, the spheres settle and stack like cannonballs, providing an orderly, crystalline framework. Using electroplating, a thin layer of nickel is added to infiltrate the plastic spheres. Once the nickel is in place, the spheres are dissolved using a solvent, leaving an open network of struts.
Because roughly 70 per cent of the material consists of air, the metallic wood’s density is extremely low, low enough to stay afloat on water. The pores in the metallic wood could be infused with other materials. For instance, by infusing the material with anode and cathode materials, it could also serve as a battery.
Photos: University of Pennsylvania, University of Illinois, University of Cambridge, and Middle East Technical University