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.