Formation of apatite oxynitrides by the reaction between apatite-type oxide ion conductors, La8+xSr2-x(Si/Ge)6O26+x/2, and ammonia

Following growing interest in the use of ammonia as a fuel in Solid Oxide Fuel Cells (SOFCs), we have investigated the possible reaction between the apatite silicate/germanate electrolytes, La8+xSr2-x(Si/Ge)6O26+x/2, and NH3 gas. We examine how the composition of the apatite phase affects the reaction with ammonia. For the silicate series, the results showed a small degree of N incorporation at 600○C, while at higher temperatures (800○C), substantial N incorporation was observed. For the germanate series, partial decomposition was observed after heating in ammonia at 800○C, while at the lower temperature (600○C), significant N incorporation was observed. For both series, the N content in the resulting apatite oxynitride was shown to increase with increasing interstitial oxide ion content (x) in the starting oxide. The results suggest that the driving force for the nitridation process is to remove the interstitial anion content, such that for the silicates the total anion (O+N) content in the oxynitrides approximates to 26.0, the value for an anion stoichiometric apatite. For the germanates, lower total anion contents are observed in some cases, consistent with the ability of the germanates to accommodate anion vacancies. The removal of the mobile interstitial oxide ions on nitridation suggests problems with the use of apatite-type electrolytes in SOFCs utilising NH3 at elevated temperatures

Synthesis, crystallization and characterization of diastereomeric salts formed by ephedrine and malic acid in water

A screening of crystallization conditions for the diastereomeric salts formed by L/D-malic acid and a common resolving agent, L-Ephedrine, in water is reported. So far, 7 different forms of salts with 1:1 and 2:1 stoichiometries were successfully crystallized, including one previously reported 1:1 LL salt. All new salts were characterized by differential scanning calorimetry, thermogravimetric and elemental analysis, infrared spectroscopy, solid-state NMR and powder XRD. 1:1 stoichiometry favours anhydrate formation while 2:1 stoichiometry tends to give monohydrate forms. Two monohydrates dehydrate on heating to produce anhydrous salts. A 2:1 LD trihydrate was discovered by vapor sorption experiments and is stable only at high relative humidity (>50%). Differences in stoichiometry and hydrate formation during salt crystallization, leading to differences in physicochemical properties could have a significant impact on resolution conditions and outcome

Fluorine-19 solid state NMR Investigation of Regiodefective Semicrystalline poly(vinylidenefluoride)

Solid-state F-19 NMR has been applied to poly(vinylidenefluoride) to investigate, inter alia, the location of the reverse units. The application of relaxation filters in pulse sequences revealed fundamental differences relating to the domain structure of PVDF. A T-1p(F) spin-lock experiment gave a spectrum of the crystalline phase along with some intensity from signals associated with reverse units. The proximity of reverse units to the amorphous and crystalline domains was further investigated by T-1p(F)-filtered radio frequency driven recoupling (RFDR) and spin-diffusion experiments. The results showed the majority of reverse units to be relatively mobile (i.e. amorphous). However, weak RFDR cross-peaks were detected which suggest the presence of some reverse units in relatively rigid domains. A signal arising from a highly mobile site was detected at delta(F) = -115 ppm by a delayed acquisition experiment and is tentatively assigned to -CH2CF2H end-groups. (C) 2002 Elsevier Science Ltd. All rights reserved.</p