A microscopic sample of the researchers’ ‘metallic wood’. Image: University of Pennsylvania
By building a material from the atom up, engineers are able to create incredible things such as a ‘metallic wood’ as strong as titanium.
As an element, titanium has become the lifeblood of many engineering endeavours thanks to its immense strength and significantly lower weight than steel. This has seen it used in aerospace and marine industries, as well as nuclear waste storage.
However, a team of UK and US engineers set out to improve upon the natural element by building something entirely new at an atomic level. Publishing their findings in Scientific Reports, the researchers revealed the construction of a sheet of nickel with nanoscale pores and an incredible strength-to-weight ratio.
This intrinsic design has resulted in a ‘metallic wood’ that is as strong as titanium, but up to five times lighter.
Explaining the concept further, the researchers said that just as the porosity of wood grain serves the biological function of transporting energy, the empty space in the researchers’ metallic wood could be infused with other materials. By infusing it with anode and cathode materials, the material could serve a double purpose, such as a prosthetic leg that’s also a battery.
Metallic wood foil on a plastic backing. Image: University of Pennsylvania
Pushing the theoretical maximum
“The reason we call it metallic wood is not just its density, which is about that of wood, but its cellular nature,” said James Pikul of the University of Pennsylvania.
“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.”
These struts are only 10 nanometres in width – equivalent to 100 nickel atoms across – and are substantially larger than any that have come before it.
“We’ve known that going smaller gets you stronger for some time, but people haven’t been able to make these structures with strong materials that are big enough that you’d be able to do something useful,” Pikul said. “Most examples made from strong materials have been about the size of a small flea, but with our approach we can make metallic wood samples that are 400 times larger.”
Because roughly 70pc of the resulting material is empty space, this nickel-based metallic wood’s density is extremely low in relation to its strength. With a density on par with water’s, a brick of the material would float.
The next big challenge for the researchers is to find a way to produce it on a commercial scale as the infrastructure to make it is currently limited. Once they master this, they can build it much larger to subject it to tests, such as seeing whether it would dent like metal or shatter like glass.
