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Abstract  

We investigated the features of the glass transition relaxation of two room temperature ionic liquids using DSC. An important observation was that the heat capacity jump, that is the signature of the glass transition relaxation, shows a particularly strong value in this type of new and promising materials, candidates for a range of applications. This suggests a high degree of molecular mobility in the supercooled liquid state. The study of the influence of the heating rate on the temperature location of the glass transition signal, allowed the determination of the activation energy at the glass transition temperature, and the calculation of the fragility index of these two ionic glass-formers. It was concluded that this kind of materials belong to the class of relatively strong glass-forming systems.

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Abstract  

Three different room temperature ionic liquids (RTILs) namely protonated betaine bis(trifluromethylsulfonyl)imide ([Hbet][Tf2N]), N-butyl-N-methylpyrrolidinium bis(trifluromethylsulfonyl)imide (BMPyTf2N) and N-methyl-N-propylpiperidinium bis(trifluromethylsulfonyl)imide (MPPiTf2N) were synthesized and characterized by CHNS analysis, NMR and FTIR spectroscopy. Heat capacity measurements and thermogravimetric analysis of these RTILs were carried out and the results are reported in this paper.

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Abstract  

Lithium assisted electrochemical reduction of U3O8 in the room temperature ionic liquid (RTIL), N-methyl-N-propylpiperidinium bis(trifluoromethylsulfonyl)imide (MPPiNTf2), was studied to explore the feasibility of using RTILs for direct electrochemical reduction of uranium oxide at near ambient temperature. The electrochemical behavior of Li+ in MPPiNTf2 at stainless steel electrode was investigated by cyclic voltammetry and chronoamperometry. The cyclic voltammogram of LiNTf2 in MPPiNTf2 at 373 K consisted of a surge in cathodic current occurring at a potential of −2.8 V (vs. Fc/Fc+) due to the reduction of Li(I) to metallic form. The nucleation phenomenon observed in the voltammogram was investigated by chronoamperometry. Electrodeposition of metallic lithium on U3O8 particles contained in a stainless steel (SS) basket was carried out to examine the feasibility of reducing U3O8 to metallic form. The results are discussed in this paper.

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Journal of Thermal Analysis and Calorimetry
Authors: Claudia Stefan, Daniel Lemordant, Philippe Biensan, Clémence Siret, and Bénédicte Claude-Montigny

Abstract  

A series of N-alkyl-N-alkyl′-pyrrolidinium-bis(trifluoromethanesulfonyl) imide (TFSI) room temperature ionic liquids (RTILs) has been investigated by means of thermogravimetric analysis (TG), differential scanning calorimetry, FT-IR spectroscopy, and X-ray diffraction analysis. These compounds exhibit a thermal stability up to 548–573 K. The mass loss starting temperature, T ml, falls in a narrow range of temperatures: 578–594 K. FT-IR spectra, performed before and after 24 h isothermal experiments at 553 and 573 K, have confirmed their great thermal stability. Below the ambient temperature, these compounds exhibit a complex behavior. N-methyl-N-propyl-pyrrolidinium-TFSI is the sole liquid which crystallizes without forming any amorphous phase even after quenching in liquid nitrogen. Its crystalline phase has a melting point, T m, of 283 ± 1 K. When the amorphous solid is heated, the N-butyl-N-ethyl-pyrrolidinium-TFSI presents a glass transition temperature, T g, at 186 K followed by a cold crystallization, T cc, at 225 K, and a final T m at 262 K. The N-butyl-N-methyl-pyrrolidinium-TFSI exhibits a T g between 186 and 181 K, its cold crystallization leading to two different solid phases. Solid phase I has a melting point T I,m = 252 K and phase II, T II,m = 262 K. When the amorphous phase is obtained at a cooling rate of 10 K/min, its T cc is 204 K, and a metastable solid phase (III) is obtained which transforms into the phase II at 226 K. However, when the sample is quenched, the amorphous phase transforms into phase II at T cc = 217 K and phase I at 239 K. P15-TFSI exhibits the most complicated pattern as, on cooling, it leads to both a crystallized phase at 237 K and an amorphous phase at 191 K. On heating, after a T g at 186 K and a T cc at 217 K, two solid–solid phase transitions are observed at 239 K and 270 K, the final T m being 279 K.

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Introduction Room Temperature Ionic Liquids (RTILs) are a class of organic molten electrolytes which are liquids around room temperature [ 1 ]. They have specific properties such as negligible vapour pressures, high ionic

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–polytungstates [ 7 ], superoxides [ 8 ] and so on. However, the extractants are usually volatile organic compounds (VOCs), which are flammable, leading to further environmental and safety concerns. RTILs have been wildly used as environmentally benign

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and 43% ee% for α-methylstyrene. It would be of interest if we could shorten the reaction time and improve the enantioselectivity of the asymmetric reaction without the use of volatile organic solvent. Room temperature ionic liquids (RTILs) are

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