Mohammad Ali Fahimipour
7/29/2013
Strong but light: the new generation of metals
A recent breakthrough in the field of material science has created a new metal that may have a
tremendous impact on the world. The metal is an ultralow-density material that has all of the
strengths of chemically similar compounds, while being significantly lighter. Engineers designed
this material by applying architectural ideas used to create strong lightweight building, such as
the Eiffel Tower. As a result of this design, the micro-lattice metals are extremely light and as
strong as bulkier metals. The material is manufactured from a periodic array of hollow nickel
phosphorous tubes. The tubes are approximately one thousand times thinner than a single strand
of human hair, which is the reason that micro-lattice metals are almost entirely composed of air.
This metal is currently being limited by the means in which it is produced, as there is no reliable
method to produce it in large scales. Researchers at the University of California Irvine are
currently working on overcoming this problem and investigating its possible applications.
Introduction
There is no doubt that humans could not have made any significant progress in
agriculture, architecture, or transportation without the discovery of metals. With that
being said, it cannot be neglected that each of the naturally existing metals has positive
and negative characteristics associated with it, which makes them not very flexible for
use in today’s advanced society. To increase the capabilities of different metals,
engineers and scientists have constantly tried to alter the nature of metals in a way that
enhances their positive characteristics while eliminating the negative ones. Changing
the chemical properties by combining different materials with metals was one of the
earliest techniques used to improve metals; however, improving one property has
always impacted the other in a negative way. This trade-off is a problem that is slowing
down the advancement of a number of technologies.
A new method for strengthening the properties is being researched by material
scientists. They are experimenting with new ways of designing the structure of each
metallic compound in order to improve the characteristics. Specifically, engineers at the
University of California Irvine UCI), CalTech and HRL laboratories have used some
architectural techniques to fabricate new metals in ways that would decrease their
weight while maintaining their strength [1]. These techniques resulted in the
development of an extremely strong lightweight metal, named micro-lattice nickel. Due
to the micro-lattice nickel being both strong and light, it has the potential to revolutionize
the aerospace, marine, and automotive industries. In 2012 Popular Mechanics
Magazine declared micro-lattice nickel as one of the “10 World-Changing Innovations”
[2]. This advanced metal is created by connecting thin fibers that are formed by microlattice nickel phosphorous tubes. The tubes are made up of ninety nine percent air and
are approximately one thousand times thinner than a single strand of human hair [1].
The density of micro-lattice nickel was approximated to be 0.9 mg/cm3 that placed this
metal in the category of ultralow-density materials [3] (Fig. 1).
1 Figure 1. A clever demonstration of the lightweight nature of micro-lattice nickel [1].
Background
Low-density materials such as micro-lattice metals are significant due to their
cellular architecture (the spatial configuration of solid and voids) and their strength.
These materials are categorized in different regimes and the lightest of which is known
as ultralow regime with the density below 10 mg/cm3. Currently, there exist no more
than five types of materials that fall in the ultralow regime. Some examples of materials
from the ultralow regime are: metallic foams with a density of about 10 mg/cm3, carbon
nanotube aerogels with a density of 4 mg/cm3, and silica aerogels with a density of
approximately 1 mg/cm3. Micro-lattice metals with the density of 0.9 mg/cm3 possess
the lowest value of density among solids. Due to their unique properties, ultralowdensity materials are widely applicable in different industries, such as aerospace and
automobile. Some of their common applications are, but not limited to, thermal
insulation, acoustic absorption, and shock or vibration damping [3].
It is important to understand that the source of strength for these low-density
materials comes from their “random cell structure” and not their chemical formulas. The
idea of the “random cellular architecture” of low-density materials and micro-lattice
metals can be easily understood by using the structure of the Eiffel Tower as a model.
The Eiffel Tower’s structure demonstrates a hierarchy featured by the difference in the
size of the structural holes. This random size difference is the architectural inspiration
2 behind the design of most of the low-density materials that results in many beneficial
properties. However, the improvement to strength and density can cause some negative
side effects, such as a decrease in conductive efficiency. What differs micro-lattice
metals from other ultralow-density materials is their “ordered hollow-tube structure”. This
new design substantially improves the low-density materials’ properties and makes their
good characteristics competitive with that of bulkier materials. In the next section, the
method through which the lightest and strongest metal has been created will be
explained [3].
Synthesis
The structure of micro-lattice nickel is made of a “periodic array of hollow tubes
that connect at nodes, forming an octahedral unit cell without any lattice member in the
basal plane” [3] (Fig 2).
Figure 2. Synthetic process of micro-lattice nickel [3]
To fabricate such a sophisticated structure (shown in Fig 2), the
HRL/Caltech/UCI research team started with preparing a polymer template. For
constructing the template a reservoir full of UV-curable resin, a perforated mask, and an
ultraviolet (UV) laser were required. The procedure started by covering the reservoir by
the mask and exposing it to UV light. As the light passed though the holes of the mask,
3 the resin gradually solidified. While the resin was solidifying, under each hole of the
mask, a light beam, just like an optical fiber, got trapped and created a thin polymer
fiber along the path of the light. To form the three dimension lattice structure, multiple
fibers were interconnected by using multiple light beams to produce the polymer fibers.
Then a technique called electro-less nickel-plating (EN) was performed on the polymer
template, which coated the polymers with a thin layer of nickel (other metals can be
used, however nickel was chosen due to the ease in which it can be fabricated [1]).
Finally, the coated polymer was etched out to create the porous structure of microlattice nickel [3].
Properties
The micro-lattice metals’ structure can be separated into “three levels of hierarchy” [3].
The biggest element is the unit cell, then the hollow tube, and finally the wall of the
hollow tubes. By controlling and changing each of those elements, the properties (for
example, density and stiffness) of the resulting micro-lattice metal can be modified [3].
As it was previously mentioned, the unique structure of micro-lattice metals resulted in
their great strength. But how strong can a featherweight metal be? This question was
answered by a series of compression tests. Through the first cycle of the experiments, a
block of micro-lattice nickel was compressed to 50 percent of its volume. After removing
the load from the block, it was observed that the metal recovered its original volume and
shape almost entirely. Therefore, micro-lattice metals proved that it takes a great
amount of force before they go through permanent deformations. This experiment
showed the micro-lattice metals’ high strength and stiffness [3].
The above experiment demonstrated not only the strength of the substance, but also its
high level of resilience. After the load was removed from block, the micro-lattice metal
recovered very rapidly. This property could have great applications in the automobile
industry that are going to be discussed in the following section [3].
Applications
The material science division at UCI is investigating the possible applications of
micro-lattice metals in several fields. They are looking into the way in which it can be
used in impact protection, aerospace engineering, acoustic damping, and automotive
engineering [4]. One example of where such a light and strong metal could make an
immediate impact is in the aerospace industry. In fact, Boeing, as one of the biggest
companies in the industry of aerospace, is one of the sponsors of micro-lattice metal’s
project. This shows the crucial role that this metal could play in the aerospace industry.
It is not hard to imagine that a significant drop in the weight of airplanes can result in
less fuel consumption. The result of this improvement in fuel efficiency would be
4 comparable to the difference from the Boeing 787 and Airbus 350A. The difference
between these two airplanes is the amount of some light material that was incorporated
in them. This difference is only three percent, and, yet the Airbus 350A consumes
twenty five percent less fuel despite still using material much heavier than the innovative
micro-lattice [5].
This metal could also have a substantial impact on the automotive industry. Glen
Daehn, a researcher at Ohio State University, reports for every ten percent in weight
reduction a seven percent improvement in fuel economy could be created. When this is
applied to the millions of vehicles on the roads it becomes a monumental amount of
savings. Anthony Luscher, another researcher at Ohio State University believes that in
the future all vehicles will be made up of these lightweight composite materials.
Additionally he believes that the use of these materials will go beyond cars and planes,
reaching to every form of transportation such as bikes, boats, and trains [6].
While the light nature of micro-lattice metals can help to produce energy efficient
cars without reducing their sizes, their ability to absorb a great amount of stress without
going through permanent deformation can also greatly contribute to the automobile
industry. For instance, if micro-lattice metals were incorporated in the body of cars, their
great resilience could make the cars resistant to accidents. In other words, using microlattice metals in the body of cars could cut from the amount fuel they burn and, at the
same time, add to their safety [4].
Issues
Since the micro-lattice metals are relatively new, they still require more research to
reach their maximum capabilities and become available for widespread use. Some
modifications in the cellular properties such as cell size or tube diameter can result in
exceptionally high strength and stiffness [7]. These types of changes must be made
relative to the field where the micro-lattice metals are going to be used. However, the
greatest challenge that is stopping the micro-lattice metals from being used more is the
limitations in their production. Although the production of these materials in small scales
is relatively easy, scaling up this production is difficult. A method for scaling up the
production of these materials must be discovered before they can become widely used.
The fusing of different materials with different properties such as metals (nickel) and
nonmetals (polymers) is a necessary step in the production of the lightweight structures,
yet it is a complex and often extremely difficult task. This is currently being worked on at
the Ohio State University, and appears to be the only obstacle stopping the lightweight
materials from living up to their potential as revolutionary materials [6].
Conclusion:
The micro-lattice material, created by the University of California Irvine, CalTech and
HRL Laboratories has the potential to greatly enhance a wide range of scientific fields.
5 This material is extremely light, thin, and durable while being composed of almost
entirely air. This material offers superior strength in comparison to heavier metals, while
being several orders of magnitude lighter. With this combination of benefits, the microlattice metal can lead to significant savings to consumers by reducing travel expenses,
while also improving safety. The development of this lightweight micro-lattice metal is a
promising sign that advancements in engineering are leading towards a more ecofriendly environmental age of technology.
6 References:
[1] B. Liggett. (2011, December 29). Scientists Develop World’s Lightest Metal, 100x Lighter
than Styrofoam. [Online]. Available: http://fuel-­‐efficient-­‐vehicles.org/energy-­‐news/?p=1127 [2] R. Sterling. (2012, October 29). The World’s Lightest Material. [Online]. Available:
http://www.boeing.com/Features/2012/10/bds_hrl_10_29_12.html
[3] T.A. Schaedler et al. (2011, November 18). Ultralight Metallic Microlattices. [Online].
Available: http://www.sciencemag.org.libproxy.usc.edu/content/334/6058/962.full
[4] K. Hall-Geisler. Micro-lattice Metal: The future of lightweight cars? [Online]. Available:
http://auto.howstuffworks.com/fuel-efficiency/vehicles/micro-lattice-metal.htm
[5] Change in the air. (2011, September 3). [Online].
Available: http://www.economist.com/node/21527035
[6] IIEglobal. (2012, September 28). Lightweight Metal-Based Vehicle Structures. [Online].
Available: http://www.youtube.com/watch?v=670-ofQobe8
[7] HRL's breakthrough development of ultralight microlattice materials recognized. (2012,
October 5). [Online]. Available: http://phys.org/news/2012-10-hrl-breakthrough-ultralightmicrolattice-materials.html
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