Engineers at University of Pennsylvania have built a nickel sheet that is comprised of nanoscale pores making it as strong as titanium but up to five times lighter. The porous material's composition and its self-assembly process makes it similar to wood. The porosity allows for infusing of energy transporting materials that could turn the metal into a battery. The team's research was recently published in Nature Scientific Reports.
"The reason we call it metallic wood is not just its density, which is about that of wood, but its cellular nature. Cellular materials are porous; 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,” says study lead James Pikul, Associate Professor in the Department of Mechanical and Applied Mechanics at Penn Engineering. “Our structure is similar,” he says. “We have areas that are thick and dense with strong metal struts, and areas that are porous with air gaps. We’re just operating at the length scales where the strength of struts approaches the theoretical maximum.”
From the University of Pennsylvania Engineering article: "Pikul’s method starts with tiny plastic spheres, a few hundred nanometers 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, the same technique that adds a thin layer of chrome to a hubcap, the researchers then infiltrate the plastic spheres with nickel. Once the nickel is in place, the plastic spheres are dissolved with a solvent, leaving an open network of metallic struts."
Read more about the titanium strength metallic wood at University of Pennsylvania.