ABSTRACT
Selective regulation of stability and density via isomerism is a promising strategy for developing energetic materials. In this work, we selectively introduced dinitromethyl groups at different positions of 4-nitro-1,2,3-triazole. The regional heterogeneity endows a high crystal density by virtue of the dense packing; on the other hand, it changes the charge distribution in the molecule, and reinforces the hydrogen bonding interactions, all of which stabilize the material. The resulting compounds exhibit excellent detonation properties and impact sensitivity that are comparable to those of HMX (Dv = 9250 m s-1 and IS = 10 J).
ABSTRACT
A method involving a vibrating hot wire is proposed for measuring the viscosity and thermal conductivity of liquids. A platinum wire is bent into a semicircular shape and immersed in the sample liquid in the presence of a static magnetic field. Alternating current is then applied to the wire, causing it to vibrate and generate heat. At low frequency, the frequency response of the vibration is used to calculate the viscosity. At high frequency, the vibration amplitude of the wire is less than the molecular free path, and the thermal conductivity of the sample is obtained from the temperature dependence of the resistance. The proposed method is validated using water, toluene, anhydrous ethanol, and ethanediol as the test samples. The measurement uncertainty is estimated to be 1.5% (k = 1) for thermal conductivity and 0.7% (k = 2) for viscosity.
ABSTRACT
The electrical resistivity of suspended polycrystalline gold nanofilms with different lengths has been measured over the temperature range of 2 K to 340 K, which dramatically increases compared with bulk gold and slightly increases with length. Classical size effect theories considering surface and grain boundary scatterings cannot explain the increased film resistivity, especially the temperature dependence of resistivity, over the whole temperature range. Considering the fact that the reduction of the coordination number of atoms at the surface and the interface leads to a decrease of the phonon spectrum frequency and consequently affects the surface phonon spectrum, the electron-phonon interaction as a relatively independent surface effect is taken into account. The theoretical predictions and the experimental measured film resistivity match very well over the whole temperature range and the extracted surface Debye temperature decreases significantly compared to the bulk value, which illustrates the essential role of enhanced surface electron-phonon interactions on the electrical transport of the present gold nanofilms.
