Imagine holding styrofoam in your hand. It's lightweight, right?
Now imagine holding something 200 times lighter. Yes, researchers have created the world's lightest material -- the ultralight metallic microlattices.
What exactly is it? Well, it's actually 99.99% air and .01% nickel phosphorous. The material is made up of connected hollow tubes that contain only a few hundred atoms in their walls.
I recently had the chance to speak with two members from the team, Alan Jacobsen and Bill Carter from HRL Laboratories, who collaborated with researchers from UC Irvine, and CalTech to create the material.
So, what's their secret? Imagine the Eiffel Tower -- it has structural hierarchy. When you step back and look at it, it looks like a truss structure (kind of like a bridge, but a tower). If you zoom into each of the pieces of the tower, those pieces (called struts) are each made of trusses themselves. If you zoom in further, you can see that each strut is also made up of trusses. The Eiffel Tower is essentially a truss of truss of trusses! This is mechanically efficient -- the trusses allow you to take out a lot of material that isn't bearing load in the structural element.
The ultralight metallic microlattices use this same strategy. There is essentially a network of elements and if you zoom in on those elements, you will find that there are tubes. Why tubes instead of rods? Well, if you have two pieces of material that have the same length and same mass, but one's a rod and the other's a tube, then the tube is going to be a lot more stiffer to bend than the rod.
Other light materials, such as aerogels, have a random structure. Although this can be beneficial in terms of high surface area and gas flow restriction, these materials have drawbacks in stiffness and strength. Carter mentions that there seems to be a lot of extra material in aerogels that isn't connected mechanically. Even though aerogels are lightweight, they are poor in stiffness and strength. Researchers in the past have tried to create stronger and stiffer materials, but quickly realized that they needed to sacrifice density. Carter, Jacobsen, and their colleagues were looking at ways you can order materials by using lattice structures. Although the team had to give up some properties with the ultralight metallic microlattices, such as high surface area, they were able to create a lightweight, stiff material.
Why did they choose nickel? It's because nickel is straightforward to use and easier for fabrication. Carter and Jacobsen state that their lab has also experimented with other materials such as electroplated metals, ceramics, oxides, silica, and other polymers -- all these materials can create the hollow tube architecture needed for the microlattice. Carter states, "if we can go to other materials, then we will start getting more interesting properties." The team also mentioned other interesting methods they could use, such as slurry coating and then burning out polymers.
Now, what we've all been waiting for -- where can we use this material? Carter and Jacobsen assert that their research is still in the early stages, but they predict there will be applications in many fields, including medicine and energy. The ultralight metallic microlattices can be also used in batteries. It works similar to the way nickel metal hydride batteries are made -- we start out with a 3-D electrical conductor that is made of nickel, and then add the active material in the battery, which allows us to make very cheap, very thick electrodes in the battery. On the other hand, lithium ion batteries are promising, but they don't have the wonderful, 3-D electrode that the nickel metal hydride battery has. Carter notes that one could go down this road with the ultralight metallic microlattices. It would make batteries cheaper to produce, and material that doesn't contribute to energy storage inside the battery can be minimized.
Why has nobody done this before? It's because they didn't have a cost effective method. But, with the microlattices, we now might be able to have better batteries.
The ultralight metallic microlattices also have great use in energy absorption. The future of vehicle technologies is going to be towards lighter weight for fuel efficiency. A lightweight vehicle doesn't take too much energy to accelerate and decelerate. However, we are looking for materials that will be lightweight without compromising the effectiveness of the vehicle. People want to be in a vehicle that feels stable and comfortable. These microlattices could be useful in application to provide both a structural and energy absorption function.
Jacobsen mentions that the material can be mass-produced at competitive market prices.
Previously, nanotech or nanoscale phenomenon has been limited to particles and thin films. Now with the ultralight metallic microlattices, there's a new tool that we can use -- taking a thin tube and coating on the micromatrix to make a useful, 3-D material.
Folks, sturdy and lightweight are now synonymous.