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Copper structure shown here is a precursor material
for explosive compounds used in military detonators. The copper
structure can be formed on chips, then converted to an explosive
compound. The compound is being used to improve US Navy detonator
devices.
Foto by
Gary Meek
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�An ability to tailor the porosity and
structural integrity of the explosive precursor material is a
combination we�ve never had before,� said Jason Nadler, a GTRI
research engineer. �We can start with the Navy�s requirements for the
material and design structures that are able to meet those
requirements. We can have an integrated design tool able to develop a
whole range of explosive precursors on different size scales.�
Nadler uses a variety of templates, including microspheres and woven
fabrics, to create regular patterns in copper oxide paste whose
viscosity is controlled by the addition of polymers. He then
thermochemically removes the template and converts the resulting
copper oxide structures to pure metal, retaining the patterns imparted
by the template. The size of the pores can be controlled by using
different templates and by varying the processing conditions.
So far, he�s made copper structures with channel sizes as small as a
few microns � with structural components that have nanoscale pores.
Based on feedback from the Navy scientists, Nadler can tweak the
structures to help optimize the overall device � known as a fuze �
which controls when and where a munition will explode.
�We are now able to link structural characteristics to performance,�
Nadler noted. �We can produce a technically advanced material that can
be tailored to the thermodynamics and kinetics that are needed using
modeling techniques.�
Beyond the fabrication techniques, Nadler developed characterization
and modeling techniques to help understand and control the fabrication
process for the unique copper structures, which may also have
commercial applications.
The copper precursor developed in GTRI is a significant improvement
over the copper foam material that Indian Head had previously been
evaluating. Produced with a sintered powder process, the foam was
fragile and non-uniform, meaning Navy scientists couldn�t precisely
predict reliability or how much explosive would be created in each
micro-detonator.
�GTRI has been able to provide us with material that has
well-controlled and well-known characteristics,� said Michael Beggans,
a scientist in the Energetics Technology Department of the Indian Head
Division of the Naval Surface Warfare Center. �Having this material
allows us to determine the amount of explosive that can be formed in
the MEMS fuze. The size of that charge also determines the size and
operation of the other components.�
The research will lead to a detonator with enhanced capabilities. �The
long-term goal of the MEMS Fuze program is to produce a low-cost,
highly-reliable detonator with built-in safe and arm capabilities in
an extremely small package that would allow the smallest weapons in
the Navy to be as safe and reliable as the largest,� Beggans explained.
Reducing the size of the fuze is part of a long-term strategy toward
smarter weapons intended to reduce the risk of collateral damage. That
will be possible, in part, because hundreds of fuzes, each about a
centimeter square, can be fabricated simultaneously using techniques
developed by the microelectronics industry.
�Today, everything is becoming smaller, consuming less power and
offering more functionality,� Beggans added. �When you hear that a
weapon is �smart,� it�s really all about the fuze. The fuze is �smart�
in that it knows the exact environment that the weapon needs to be in,
and detonates it at the right time. The MEMS fuze would provide
�smart� functionality in medium-caliber and sub-munitions, improving
results and reducing collateral damage.�
Development and implementation of the new fuze will also have
environmental and safety benefits.
�Practical implementation of this technology will enable the military
to reduce the quantity of sensitive primary explosives in each weapon
by at least two orders of magnitude,� said Gerald R. Laib, senior
explosives applications scientist at Indian Head and inventor of the
MEMS Fuze concept. �This development will also vastly reduce the use
of toxic heavy metals and waste products, and increase the safety of
weapon production by removing the need for handling bulk quantities of
sensitive primary explosives.�
The next step will be for Indian Head to integrate all the components
of the fuze into the smallest possible package � and then begin
producing the device in large quantities.
A specialist in metallic and ceramic cellular materials, Nadler said
the challenge of the project was creating structures porous enough to
be chemically converted in a consistent way � while retaining
sufficient mechanical strength to withstand processing and remain
stable in finished devices.
�The ability to design things on multiple size scales at the same time
is very important,� he added. �Designing materials on the nano-scale,
micron-scale and even the millimeter-scale simultaneously as a system
is very powerful and challenging. When these different length scales
are available, a whole new world of capabilities opens up.�
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