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1.
Materials from the Mn(0.5−x)CaxTi2(PO4)3 (0≤x≤0.50) solid solution were obtained by solid-state reaction in air at 1000 °C. Selected compositions were investigated by powder X-ray diffraction analysis, 31P nuclear magnetic resonance (NMR) spectroscopy and electrochemical lithium intercalation. The structure of all samples determined by Rietveld analysis is of the Nasicon type with the R
space group. Mn2+/Ca2+ ions occupy only the M1 sites in the Ti2(PO4)3 framework. The divalent cations are ordered in one of two M1 sites, except for the Mn0.50Ti2(PO4)3 phase, where a small departure from the ideal order is observed by XRD and 31P MAS NMR. The electrochemical behaviour of Mn0.50Ti2(PO4)3 and Mn(0.5−x)CaxTi2(PO4)3 phases was characterised in Li cells. Two Li ions can be inserted without altering the Ti2(PO4)3 framework. In the 0≤y≤2 range, the OCV curves of Li//LiyMn0.50Ti2(PO4)3 cells show two main potential plateaus at 2.90 and 2.50–2.30 V. Comparison between the OCV curves of Li//Li(1+y)Ti2(PO4)3 and Li//LiyMn0.50Ti2(PO4)3 shows that the intercalation occurs first in the unoccupied M1 site of Mn0.50Ti2(PO4)3 at 2.90 V and then, for compositions y>0.50, at the M2 site (2.50–2.30 V voltage range). The effect of calcium substitution in Mn0.50Ti2(PO4)3 on the lithium intercalation is also discussed from a structural and kinetic viewpoint. In all systems, the lithium intercalation is associated with a redistribution of the divalent cation over all M1 sites. In the case of Mn0.50Ti2(PO4)3, the stability of Mn2+ either in an octahedral or tetrahedral environment facilitates cationic migration. 相似文献
2.
J. V. Sinisterra M. E. Borredon Z. Mouloungui M. Delmas A. Gaset 《Reaction Kinetics and Catalysis Letters》1985,29(1):41-47
The nature of adsorbed sulfonium and phosphonate ylids on a new barium hydroxide catalyst (C-200) is analyzed by IR. The catalytic activity of C-200 in solid-liquid phase transfer conditions is explained by these IR studies.
(C-200) . C-200 - .相似文献
3.
The simultaneous determination of major impurities present in Antarctic snow and ice at ng g? (ppb) concentrations by ion chromatography is described. Calibration data are presented for ammonium, sodium, potassium, chloride, nitrate and sulphate ions. Special attention is paid to the different ways of removing field contamination from ice and snow cores and suitable equipment is described. The results provide evidence against the validity of published sets of concentration data for nitrogen-containing compounds (NO?3 and NH+4 in Antarctic snow, and demonstrate a crucial contamination problem in the determination of ammonium ions. 相似文献
4.
Cremer GA Bureaud N Lelièvre D Piller V Piller F Delmas A 《Chemistry (Weinheim an der Bergstrasse, Germany)》2004,10(24):6353-6360
Our goal was to develop mimics of MUC1, highly immunogenic to induce an efficient immune response against the tumor-associated form of MUC1, and sufficiently different from the natural antigen to bypass the tolerance barrier in humans. With the aim of obtaining a well-defined peptide construct as a means of evoking the precise immune responses required in immunotherapy, we synthesized artificial mimics of the MUC1 protein composed of two MUC1 repeat units of inverse orientation and a universal T-helper epitope. To synthesize these heteromeric peptide constructs, we followed a convergent approach using chemoselective ligation based on oxime chemistry. A stem peptide was first synthesized bearing two orthogonally masked aldehydes. After successive deprotection, two oxime bonds can be specifically generated. The proposed strategy proved to be concise and robust, and allowed the synthesis of the tri-branched protein in a very satisfactory yield. The different constructs were tested for their ability to generate antibodies able to recognize the MUC1 protein. 相似文献
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Antonopoulos A Hardouin J Favetta P Helbert W Delmas AF Lafosse M 《Rapid communications in mass spectrometry : RCM》2005,19(16):2217-2226
Enzymatically digested oligosaccharides of kappa-, iota- and hybrid iota/nu-carrageenans were analysed using matrix-assisted laser desorption/ionisation time-of-flight mass spectrometry in the negative-ion mode. nor-Harmane was used as matrix. Depending on the stock concentration and the laser intensity applied, the oligosaccharides exhibited losses of sulphate units (neutralised by the Na+ ion, and thus non-stable), leaving the primary backbone structure in most cases with only the deprotonated sulphate groups (carrying the negative charge, stable). This meant that kappa- and iota-oligosaccharides could not be easily distinguished from one another since they share the same primary backbone structure. However, for the hybrid iota/nu-oligosaccharides the primary backbone structure could be identified since the nu-carrageenan repeating unit differs from that of the kappa/iota-carrageenan unit. For all types of oligosaccharides, the results indicated cleavage of an anhydrogalactose unit from the non-reducing end. Specifically, for the hybrid oligosaccharides of iota/nu-carrageenans, this type of fragmentation means that the nu-carrageenan unit is not positioned on the non-reducing end of the hybrid oligosaccharides. Dehydration reactions, and exchange reactions of Na+ with K+ and Ca2+, were also observed. 相似文献
8.
There is a need to know, before dismantling nuclear plants, how the induced radioactivity is distributed in concrete. Computer
codes are used to predict such a distribution, by applying input data like, among others, the chemical composition of the
material. Biological shield concretes with particularly high boron or barium concentrations had to be analyzed. Instrumental
neutron activation analysis is not able to determine all elements, thus, additional techniques are required, like ICP-MS and
ICP-AES. The respective performances of these techniques are discussed. For INAA, the thermal neutron self-shielding was empirically
corrected by using comparisons between thermal neutron activation (TNAA), epithermal and fast neutron activation (ENAA), ICP-AES
and ICP-MS measurements. 相似文献
9.
Na5Nb05 and Na5Ta05 Phases. Crystal Structure of Na5NbO5 New ternary oxides of formulas Na5NbO5 and Na5TaO5 have been prepared. They crystallize in the monoclinic system (space group C2/c). The crystal structure of Na5NbO5 has been determined. It derives from a NaCl-type structure by ordering of the cations and of the oxygen vacancies in the anionic sublattice, the corresponding formula being Na5/6Nb1/6O5/6□1/6. Sodium and niobium have a distorted square-pyramidal surrounding. 相似文献