Ultralight Micromaterials: The Example of Microlattice

Materials science conjures up the building blocks of every vision of a Brave New World. We became used to miraculous materials such as aerogels, carbon aerogels, or black and white graphene – the world’s first 2-D material – that are easily predicted to become foundations of substantial game-changing applications. One of them is ultralight metallic microlattice, a structure developed by  HRL Laboratories and commissioned by DARPA.
One hundred times lighter than obsolete styrofoam, yet capable of withstanding the loads in aerospace technology, microlattice consists of 99.99% air. The rest is nickel of 100 nm thickness forming tubes 1/1000 times thinner than a human hair. The material can be balanced on a dandelion blossom without damaging its delicate structure. It is an ultralight (<10 mg/cc) material in a 3D open cellular structure, somewhat – vaguely – similar to bone structure. So it is at the same time, relatively speaking, ultrastrong.
Proof of concept for this stuff has been around since 2011. It is, of course, notoriously difficult to manufacture in large quantities. It is done by employing a template created by self—propagating polymer waveguide prototyping that is coated by electroless nickel plating (nickel-phosphorus alloy) before the template is etched away, leaving a microlattice of interconnected hollow rods. The reason why the dandelion blossom holds up so well is because the material’s density is ≤ 0.9 mg/cc (by comparison: silica aerogels have a density of 1.0 mg/cc while aerographite is claimed to be only 0.2 mg/cc and also has remarkable mechanical, electrical and optical properties as a nanowall built out of carbon nanotube material that is extremely robust under strong deformations, with applications especially in electrodes. Microlattice also has strong elastomeric properties and recovers almost completely (98%) from compression exceeding 50% strain and absorbs energy similarly to elastomers. Classical Humpty-Dumpty experiments have shown an egg packed in microlattice to survive a 25-floor undamaged – without having been wrapped in a substantial quantity of material. Now the process needs to be brought out of the lab and into commercial applications that hold immense promise:
The value of structural components is determined by weight and energy absorption. Fuel efficiency of any vehicle, especially in aerospace, is determined by the same, which explains Boeing’s interest as well as that of GM and Raytheon. It may also serve applications from thermal insulation to battery electrodes to catalyst support, to acoustic, vibration, and shock energy damping. Generally speaking, its main purpose may be in structural reinforcement and heat transfer, and there is speculation that the scope of its potential uses may render microlattice technology “one of the most significant inventions in history” comparable to lasers and LCD screens.
Manufacture is similar to photolithography by employing a two-dimensional mask that defines the structure of the initial template where a self-forming waveguide process permits formation of templates for large, free-standing and scalable 3D lattice structures in 10-100 seconds rather than hours as in traditional stereolithography, the technology used in 3D printing. The template is coated by electroless nickel plating, but the process is not restricted to nickel. Micro-truss nanocrystalline nickel hybrids were first explored in 2008 by testing optimal strut geometry in uniaxial compression.

1 comment: