Scientists have created a new material they call “metallic wood” that is as strong as titanium while being lighter than aluminum. The process for fabricating this material is modeled after the way nature creates the gemstone opal. Opals are formed from microscopic spheres of a substance called silica. However, the metallic wood is an inverse opal because the spheres in the material dissolve away. The best part is, just like opals do, the wood radiates a rainbow of colors when held at certain angles, as the microscopic pores are just the right size to interfere with the wavelengths of visible light.
The material itself contains no actual wood. They call it metallic wood because of its wood-like properties. It is porous – full of air spaces in between billions of miniature struts of nickel – and light enough to float in water. The material looks like honeycomb or a sponge magnified thousands of times under a microscope. “It’s like a scaffold,” said the leader of the study James Pikul, Assistant Professor in the Department of Mechanical Engineering and Applied Mechanics at Penn Engineering.
So, you can call it inverse opal, or you can call it metallic wood, but whatever its name is, it may be what the smartphones and cars of the future are made of.
How It’s Made:
- They begin with billions of tiny plastic spheres suspended in a small vial of water.
- Next, they insert a substrate — a strip of glass-like material that conducts electricity — and heat the water. As the water evaporates, the spheres settle on the strip in an orderly pattern, stacking themselves almost like a pyramid of oranges in a grocery-store display.
- Then they “electroplate” the spheres with nickel, meaning they place the strip coated with spheres into a solution of nickel ions, then applying an electrical current, causing the nickel to coat the surfaces of the plastic balls.
- Lastly, a solvent is added to dissolve away the plastic and what’s left is a porous scaffold of nickel.
How is it strong if it is so porous you may be wondering? The magic lies in the small size of the nickel struts. While large pieces of conventional metal tend to have defects occasionally – gaps at the atomic level decreasing their strength – the small samples of the metallic wood didn’t because such defects rose to the surface and disappeared, explained Pikul. Laboratory tests showed that it has a compressive strength on par with titanium. The study was published in the journal Scientific Reports.
So far, the engineers have just made small squares about the size of a postage stamp of the material. It takes the Penn team about a whole day to make the small square too. Now, if they can figure out how to scale up the production and scale down the time it takes for production, the material will be perfect for a wide range of applications, primarily automotive manufacture. Or, the pores can be filled with other substances, such as the chemicals needed to make a lightweight rechargeable battery, Pikul said. It could even be used in architecture. The possibilities are endless really.
