Organically capped metal nanoparticles are an attractive alternative to more conventional oxide-passivated materials, due to the lower reaction temperatures and the possibility of tuning the organic coating. Sonochemical methods have been used to produce small (∼5 nm average size) air-stable aluminum nanoparticles capped with oleic acid. In order to understand the nature of the metal−organic bonding in the nanoparticles, we have used FTIR, XPS, and TOFMS−TPD techniques to study the organic passivation layer and its desorption at elevated temperatures. In the present case we find that the organic layer appears to be attached via Al−O−C bonds with the C atom formerly involved in the carboxylic acid functional group.
All solid Li-ion batteries display high stability and longevity but are hampered by the poor conductivity of most solid electrolytes. The influence of applied electrical fields during sintering on microstructure and electronic properties of lithium aluminum titanium phosphate (Li 1.3 Al 0.3 Ti 1.7 (PO 4 ) 3 , LATP) electrolyte material was investigated by sintering LATP pellets under DC voltages of 0 V, 2 V, 10 V, and 20 V, followed by characterization via scanning electron microscopy (SEM) and impedance spectroscopy. The application of a DC voltage increased the relative density to a maximum of 95.5%. However, unlike reports on other material systems such as zirconia, a high DC voltage induced rather than restrained abnormal grain growth. Resistivity increased with applied voltage from 2.1 kΩ·cm at 0 V to 7.8 kΩ·cm at 20 V, which was attributed to the high faceting and poor grain to grain contact of the grains sintered under 10 V and 20 V.
Aluminum nanoparticles have been a subject of active investigation in recent years because of their potential to enhance the energy content of energetic materials. The associated kinetics of the chemical reaction and energy release are, in many cases, governed by the properties of the passivation layer protecting the particle rather than those of the underlying metal core. The passivation layer of Al particles is typically an oxide shell several nanometers thick, but other possibilities are now available. We have previously developed synthesis routes to produce air-stable Al nanoparticles that are capped by oleic acid. In the present study, we examine the chemical dynamics of these materials in ammonium nitrate and ammonium perchlorate matrices. For comparison, the analogous experiments were also performed on samples using traditional oxide-protected particles. Reactions are initiated by a 20 μs IR laser pulse and then probed via time-of-flight mass spectrometry of the evolved gases and by emission spectroscopy of the flame. In both ammonium nitrate and ammonium perchlorate matrices, the organically passivated nanoparticles are found to be significantly more reactive and are able to access some reaction pathways unavailable to oxide-protected particles.
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