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Protecting troops with nanoceramics
The U.S. Army Research Laboratory dedicated a 5-year program to advanced metals
and ceramics for armor and anti-armor applications. To provide greater protection against
blunt trauma and higher velocity ammunition than can be provided by a standalone soft
ballistic vest, hard body armor was developed. It includes a rigid facing comprising ce-
ramic inserts, steel or titanium panels, and a ballistic fabric backing.
In hard armor with ce-
ramic inserts, the projectile’s
kinetic energy is absorbed
and dissipated in localized
shattering of the ceramic tile
and blunting of the bullet ma-
terial during impact. Armor
ceramics are critical for
weight reduction in current
and future military and civil-
ian applications. Realizing the
full potential of armor ceram-
ics requires an understanding of how the structure of armor-ceramic materials, at several
length scales, affects the inherent ballistic performance and its variability among identical
components.
Carbon nanotubes (CNTs) are being considered as a reinforcing material to enhance
the mechanical properties of ceramics, particularly fracture toughness, which is likely to
improve their resistance against multiple bullets. Recent studies show that CNTs in ce-
ramics like alumina and silicon carbide can have a strong influence on microstructure,
fracture mode, and mechanical properties. An improvement of up to 94% in fracture
toughness was observed when 4 vol.% of CNTs are added to alumina. .
Graphene ribbons highly conductive at room temperature
An international team including researchers from the French National Centre for Sci-
entific Research (CNRS), Université de Lorraine, the SOLEIL synchrotron facility, all in
France, Georgia Institute of Technology, Atlanta, Oak Ridge National Laboratory, Tenn.,
and Université de Leibniz, Germany, produced graphene ribbons in which electrons move
freely. The team devised a novel way of synthesizing such ribbons, and demonstrated their
exceptional electrical conductivity at room temperature. The nanoribbons hold great
promise for next-generation electronics, say researchers.
The team synthesized 1D graphene from silicon carbide and was able to obtain
graphene ribbons of very high structural quality, made of an extremely narrow sheet of
carbon only 40 nm wide. In order to obtain ribbons with regular edges, nanometer-deep
steps were etched into the silicon carbide, producing graphene ribbons directly on the
sidewalls of the steps. .
ADVANCED MATERIALS & PROCESSES • APRIL 2014 18
NANOTECHNOLOGY
briefs
Researchers at Seoul National
University, Korea, found that
nanoscale 3D objects such as
freestanding nanowalls can be
constructed using additive
manufacturing. Even without the
motion of the substrate, nanojets
are spontaneously laid down and
piled to yield nanowalls. A thin
metal line on an insulating plate
focuses the electrical field,
suppressing the instability of the
electrical nanojets. To stack fibers
in a controlled fashion, the fiber
deposit is manipulated to attract
rather than repel the incoming
nanojets by quickly draining the
electrical charge. A nanowall that
lines the ground is formed, which
implies that various freestanding
structures can be created in a
desired shape. .
Stephen Goodnick, professor at
Arizona State University, Phoenix,
gave a talk on nanoelectronics
advances that could increase
performance of solar energy
systems at the 2014 annual
meeting of the American
Association for the
Advancement of Science (AAAS),
Chicago, in February. Innovations
driven by nanoelectronics research
enable photovoltaic technology to
significantly improve the ability to
convert sunlight and heat into
electric power. New types of
nanostructure-based devices can
facilitate production of photovoltaic
solar cells that achieve better
energy-conversion efficiency.
Stephen Goodnick, 480/965-9572,
,
Conceptual drawing of an
electronic circuit comprised
of interconnected graphene
nanoribbons (black atoms)
that are epitaxially grown
on steps etched in silicon
carbide (yellow atoms).
Electrons (blue) travel
ballistically along the ribbon
and then from one ribbon
to the next via the metal
contacts. Electron flow is
modulated by electrostatic
gates. Courtesy of John
Hankinson/Georgia Institute
of Technology.
Researchers at Karlsruhe Institute of Technology, Germany, and
Carnegie Mellon University, Pittsburgh, developed the first ad-
hesive tape that not only adheres to a surface as reliably as the
toes of a gecko, but also has similar self-cleaning properties. Elas-
tic microhairs of variable size were used and, instead of dirt parti-
cles, micrometer-sized glass spheres were distributed on a smooth
plate. An artificial adhesive tape covered by microhairs was
pressed onto the plate, shifted, and lifted off. When the diameter of
the spheres exceeded that of the microhairs, the adhesive force
disappeared after the first contact. After eight to 10 test cycles,
however, the gecko-inspired adhesive tape reached 80 to 100% of
its original power again. , .