3 research outputs found
Ignition and Combustion Characteristics of Nanoaluminum with Copper Oxide Nanoparticles of Differing Oxidation State
The
importance of the oxidation state of an oxidizer and its impact
on gaseous oxygen and total gas production in nanocomposite thermite
combustion was investigated by probing the reaction and ignition properties
of aluminum nanoparticles (Al-NPs) with both cupric oxide (CuO) and
cuprous oxide (Cu<sub>2</sub>O) nanoparticles. The gas release and
ignition behavior of these materials were tested with >10<sup>5</sup> K/s temperature jump (T-jump) heating pulses in a high temporal
resolution time-of-flight mass spectrometer (ToF-MS) as well as in
an argon environment. Reactivity was tested using a constant volume
combustion cell with simultaneous pressure and optical measurements.
A variety of Cu<sub>2</sub>O particle sizes ranging from 200 to 1500
nm were synthesized and found to release oxygen at ā¼1200 K,
which is higher than the values found for a variety of CuO particle
sizes (ā¼1000 K). Both oxides were found to ignite around 1000
K, which implies a consistent ignition mechanism for both through
a condensed phase pathway. The higher oxidation state (CuO) thermites
were found to react faster and produce higher pressures by several
orders of magnitude, which implies that gaseous species play a critical
role in the combustion process. Differences in reactivity between
argon and vacuum environments and the use of Cu diluent to simulate
Cu<sub>2</sub>O suggest that it is the intermediate product gas, O<sub>2</sub>, that plays the most significant role in combustion as an
enabler of heat transfer and a secondary oxidizer. The lack of any
oxidizer size dependence on ignition is suggestive of rapid sintering
that wipes out the effect of enhanced interfacial contact area for
smaller oxidizers
On-Demand and Location Selective Particle Assembly via Electrophoretic Deposition for Fabricating Structures with Particle-to-Particle Precision
Programmable positioning of 2 Ī¼m
polystyrene (PS) beads with
single particle precision and location selective, āon-demandā,
particle deposition was demonstrated by utilizing patterned electrodes
and electrophoretic deposition (EPD). An electrode with differently
sized hole patterns, from 0.5 to 5 Ī¼m, was used to illustrate
the discriminatory particle deposition events based on the voltage
and particle-to-hole size ratio. With decreasing patterned hole size,
a larger electric field was required for a particle deposition event
to occur in that hole. For the 5 Ī¼m hole, particle deposition
began to occur at 10 V/cm where as an electric field of 15 V/cm was
required for particles to begin depositing in the 2 Ī¼m holes.
The likelihood of particle depositions continued to increase for smaller
sized holes as the electric field increased. Eventually, a monolayer
of particles began to form at approximately 20 V/cm. In essence, a
voltage threshold was found for each hole pattern of different sizes,
allowing fine adjustments in pattern hole size and voltage to control
when a particle deposition event took place, even with the patterns
on the same electrode. This phenomenon opens a route toward controlled,
multimaterial deposition and assembly onto substrates without repatterning
of the electrode or complicated surface modification of the particles.
An analytical approach using the theories for electrophoresis and
dielectrophoresis found the former to be the dominating force for
depositing a particle into a patterned hole. Ebeam lithography was
used to pattern spherical holes in precise configurations onto electrode
surfaces, where each hole accompanied a polystyrene (PS) particle
placement and attachment during EPD. The versatility of e-beam lithography
was utilized to create arbitrary pattern configurations to fabricate
particle assemblies of limitless configurations, enabling fabrication
of unique materials assemblies and interfaces
Ultralight Conductive Silver Nanowire Aerogels
Low-density
metal foams have many potential applications in electronics,
energy storage, catalytic supports, fuel cells, sensors, and medical
devices. Here, we report a new method for fabricating ultralight,
conductive silver aerogel monoliths with predictable densities using
silver nanowires. Silver nanowire building blocks were prepared by
polyol synthesis and purified by selective precipitation. Silver aerogels
were produced by freeze-casting nanowire aqueous suspensions followed
by thermal sintering to weld the nanowire junctions. As-prepared silver
aerogels have unique anisotropic microporous structures, with density
precisely controlled by the nanowire concentration, down to 4.8 mg/cm<sup>3</sup> and an electrical conductivity up to 51āÆ000 S/m. Mechanical
studies show that silver nanowire aerogels exhibit āelastic
stiffeningā behavior with a Youngās modulus up to 16āÆ800
Pa