Decomposition reactions of trinitrobutane.

International audienceThe mackinawite mineral was prepared as a carbon steel corrosion product in sulfidogenic waters at 90 degrees C after 2 months. The tetragonal crystal structure of the material was confirmed by Rietveld refinement of X-ray diffraction (XRD) data, and vibrational modes were analysed by micro-Raman spectroscopy. Despite a large number of studies on the formation and the stability of tetragonal mackinawite, the interpretation of the Raman spectra remains uncertain. In the present study, we report on the first calculation of the Raman-active vibrational modes of mackinawite using Density Functional Perturbation Theory and direct methods with BLYP + dispersion correction. Based on the comparison between calculated and experimental results, the four fundamental vibrational modes were assigned as 228 cm(-1) (B-1g), 246 cm(-1) (E-g), 373 cm(-1) (A(1g)) and 402 cm(-1) (E-g)

An investigation of the pressure induced phase transition from the scheelite phase (I41/a,Z = 4) to the fergusonite-like phase (I 2/a,Z = 4) and to the LaTaO4 phase (P 21/c,Z = 4) of LiYF4 is presented. Employing density functional theory (DFT) within the generalized gradient approximation, the structures were relaxed for a pressure range of 0–20 GPa without imposed symmetry. The influence of pressure on the lattice vibrational spectrum of the scheelite phase (I41/a,Z = 4) was evaluated using the direct approach, i.e. using force constants calculated from atomic displacements. This work tends to confirm the transformations . At 20 GPa, a P 21/c structure with a pentacoordinated lithium cation is found to be the most stable phase. This structure is compatible with a transition driven by a Bg zone-centre soft optic mode linked to a soft acoustic mode along the [] direction as observed from the evolution of the phonon dispersion curves as a function of pressure.

Carbon nanotube-based poly(methyl methacrylate) and polyamide-6 nanocomposites have been investigated using various techniques within the framework of the NANOFEU project. Scanning transmission electron microscopy was used to characterize morphologies of composites, while fire properties were studied using cone calorimeter and pyrolysis combustion flow microcalorimeter. The study focused particularly on composition and microstructure of gaseous and aerosol products. Morphology of ultrafine particles released from the combustion of nanocomposites was studied using cascade impactor and atomic force microscopy. Fire behaviour has been interpreted in relation with the degradation mechanisms specifically induced by the presence of carbon nanotubes.

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We report the structural properties, infrared (IR) and Raman spectra, dipole moment, polarisability, hardness and chemical potential of the trans and cis configurations of 4-hydroxyazobenzene calculated using the B3LYP functionals. All calculations were performed with the following basis sets: 6-31G, 6-31++G, 6-31G(d,p), 6-31++G(d,p), 6-31G(2d,2p), 6-31++G(2d,2p) and 6-311++G(2d,2p). We observed that 6-31++G(d,p) gives similar results to 6-311++G(2d,2p). Consequently, SVWN and PW91 methods were also used in association with 6-31++G(d,p) to test the influence of the different models of exchange and correlation functionals. A planar structure was obtained for all the optimised trans configuration structures. In both isomers, the presence of the hydroxyl group leads to an asymmetry in certain structural parameters. From these results, two IR or Raman active frequencies can be used to easily distinguish trans and cis configurations. The trans configuration was found to be more stable than the cis configuration by 67 +/- 2 kJ mol(-1) at 0 K. The difference of the dipole moment between trans and cis for 4-hydroxyazobenzene was found to be lower than for trans and cis azobenzene.

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