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41.
C. Kinowski S. Turrell M. Bouazaoui B. Capoen J. M. Nedelec L. L. Hench 《Journal of Sol-Gel Science and Technology》2004,32(1-3):345-348
Doped and undoped 50 Å porous silica xerogels were heat-treated at various annealing temperatures ranging from 800°C to 1150°C. The heating was performed in air for 1 hour at each temperature. Raman spectroscopy was used to follow the structural changes occurring at various stages of the gel-to-glass transformation, as well as to investigate the effects of metal ions on the densification of these nanoporous silica xerogels. Raman data and density measurements showed that while densification is completely achieved at 1050°C for undoped xerogels, it occurs at 950°C for Ag+-doped samples. On the other hand, Ce3 + doping was found to slow down the densification process, with complete densification occurring at 1100°C. 相似文献
42.
B. G. Turrell 《Hyperfine Interactions》2001,133(1-4):95-103
Low temperature nuclear orientation (LTNO) and nuclear magnetic resonance on oriented nuclei (NMRON) can be utilized to investigate the magnetic properties of solids, and are especially useful when high sensitivity is required, for example in the study of small or dilute systems. Spins of stable isotopes can also be studied using NMR thermally detected by NO (NMR-TDNO) of the radioactive nuclei. An effect of nuclear spin coupling in ordered magnets is frequency pulling of the abundant spins, and this has been investigated in the quasi-2-dimensional ferromagnet 54Mn–Mn(COOCH3)24H2O by comparing the NMRON of the dilute radioactive nuclei with the NMR-TDNO of the abundant host nuclei. A structure in the spectra is observed that is yet to be explained. Recent LTNO experiments on magnetic multilayers are described. Experiments implanting radioactive ions into insulating magnets show that the implanted nuclei experience sizeable hyperfine fields, and this may be useful for probing magnetic materials that are difficult to dope by conventional means. 相似文献
43.
Berrier E Courtheoux L Bouazaoui M Capoen B Turrell S 《Physical chemistry chemical physics : PCCP》2010,12(43):14477-14484
It is shown how the properties of a porous silica xerogel prepared using a classical sol-gel synthesis can be fine-tuned by a minor modification of the composition. The addition of a doping cation (Cu(2+), Ca(2+), Na(+)) in trace quantities in the silica sol was found to exert a dramatic effect at all stages of material preparation. An investigation of both liquid and solid phases is presented, making it possible to highlight strong correlations. The time-resolved speciation of Si-containing moieties in the sol was found to be an indication of the structuration of the gel, which was reflected by the porosity and by the molecular structure of the resulting porous material. Based on a careful comparison of several slightly doped silica gels, a model is proposed which makes it possible to predict the structure and the texture of a silica gel from data recorded early in the liquid phase. 相似文献
44.
Katarzyna Raulin Sylvia Turrell Bruno Capoen Christophe Kinowski Van Thi Thanh Tran Mohamed Bouazaoui Odile Cristini 《Journal of Raman spectroscopy : JRS》2011,42(6):1366-1372
A new technique of UV irradiation has been used for the first time to create microstructures of CdS nanoparticles in bulk xerogels. Porous silica matrices, which were first soaked in a solution containing CdS precursors, were subjected to irradiation using a nanopulsed ArF laser with a wavelength of 193 nm and a repetition rate of 10 Hz. Resonant micro‐Raman spectra, recorded using the 325‐nm line of a He‐Cd laser (with a continuous power less than 0.5 mW so as to avoid the thermal formation of nanoparticles) made it possible to identify CdS nanoparticles within the inscribed yellow zones and also to estimate the average particle size (3.6 to 8.0 nm, depending on the number of UV pulses used). The emission of CdS particles embedded in the silica matrix under excitation at 351.1 nm was studied by photoluminescence spectroscopy. It was then possible to show the effect of the number of pulses on the electronic structure of the nanocrystals. Finally, Raman spectra were used to monitor the structural changes in the silica matrix caused by the irradiation. It was found that the pulsed UVirradiation resulted in a local densification of the matrix, which was compensated for by a depolymerization process of the Si O Si network. In spite of this pulsed irradiation and the resulting structural depolymerization, no apparent ablation or cracking of the samples was observed. Copyright © 2010 John Wiley & Sons, Ltd. 相似文献
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48.
George Turrell 《Chemical physics》1974,3(3):473-481
The model of solute— solvent interaction based on dipole-induced-dipole forces (Kirkwood-Bauer-Magat) has been generalized, yielding an expression for the energy as a function of solute position and orientalion within a spherical cavity in a dielectric medium. An analogous relation has been derived for the dispersion energy. Barriers to rotation of the solute molecule and shifts in its vibrational frequency are calculated as functions of cavity radius and eccentricity for the case of dilute solutions of HCl in CCl4. It is found that the effect of dispersion forces on the vibrational frequency of HCl is two-to-three times more important than the traditional dipole-induced-dipole contribution. 相似文献
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50.
Pulsed NMRON, CW NMRON and thermal NMR-NO methods have been utilized to study54Mn-MnCl2 · 4H2O. The54Mn spin-lattice relaxation timeT
1 in zero applied field has been measured between 35 and 90 mK in the antiferromagnetic phase. Above 65 mK the dominant relaxation
mechanism is a Raman process with the electronic magnons, but at lower temperatures a direct process takes over. NMRON has
been observed for the first time in the paramagnetic phase, and a line width of 300 kHz, with both homogeneous and inhomogeneous
contributions, is observed. In the antiferromagnetic phase the line width is 35 kHz, and there are also homogeneous and inhomogeneous
contributions. The dependence ofT
1 for the54Mn spins on field and temperature was studied in the paramagnetic phase. AT
1 minimum centred atB
0=2.64 T was observed. The hyperfine parameter <54
AS>/h=−513.6(3) MHz in the paramagnetic phase, and comparison with the value in the antiferromagnetic phase gives 0.013(1) for
the zero point spin deviation. 相似文献