On the occurrence and role of SnO2, SnS and FeSn2 in coal hydroliquefaction experiments using tin-based catalysts

Mössbauer Spectroscopy, X-Ray Diffraction and Electron Microscopy were applied to the study of solid residues of coal hydroliquefaction, for which tin-based catalysts were used. In the general case hydroliquefaction runs were performed in the presence of added sulphur and of finely dispersed SnO₂ as a catalyst precursor. The only observed tin species were SnO₂ and SnS, the former with percentages higher than expected from XRD, due to its large f factor, the latter as a symmetric doublet, which suggests that any asymmetry should be ascribed to small particle sizes rather than to structure. When the S content was only that of coal and the catalyst precursor β-Sn, FeSn₂ occurred together with Sn sulfides and oxides, while no β-Sn was detected. The main catalytic role is ascribed to SnS.     

Direct determination of calcium,copper, iron,magnesium, manganese and zinc in amniotic fluid samples using inductively coupled plasma-atomic emission spectrometry

An inductively coupled plasma-atomic emission spectrometric method is reported for the determination of calcium, copper, iron, manganese, magnesium and zinc. Samples are introduced directly when a sheath gas device is used. An external calibration procedure is used. The standards are prepared in a matrix composed of 0.5% (w/v) albumin and 0.76% (w/v) sodium chloride. The procedure was evaluated with a standard reference material (NBS SRM 909 Human Serum); all the values obtained are in agreement with the certified values. Results obtained for the determination of zinc, calcium, magnesium, copper, iron and manganese in amniotic fluid samples are reported.     

The cyano nitronyl nitroxide radical: experimental and theoretical evidence for the fourth case of the McConnell-I mechanism

The nitronyl nitroxide 2-cyano-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide (1) crystallises in the tetragonal P42(1)m space group with a=7.4050(7), c=8.649(1) A. In the crystal the molecules form layers parallel to the ab plane in which they are orthogonal to each other. In the layers there are close contacts, 2.953(2) A, between the NO groups and the bridging carbon atoms of the O-N-C-N-O fragment of neighbouring radicals. The calculated spin density shows a positive population mainly and equally localised on the NO groups and small but significant negative spin densities on the bridging carbon atom and the cyano nitrogen. Absorption spectra show temperature-dependent transitions related to the magnetic behaviour. The temperature dependence of the magnetic susceptibility in the range 2-300 K reveals that couplings between the radicals are antiferromagnetic, and is interpreted by considering a two-dimensional square array of spin S=1/2 antiferromagnetically coupled (J=-10 cm(-1) and g=2.01). This is interpreted as an exchange coupling through close contact between positive and negative spin densities in orthogonal orbitals on oxygen and carbon atoms, respectively.     

A Mössbauer spectroscopic study of cobalt-iron molybdates

Fe _x Co_1–x MoO₄ compounds prepared by coprecipitation were studied by XRD, electrical conductivity and mainly by absorption and emission Mössbauer spectroscopy. FeMoO₄ and CoMoO₄ samples were shown to contain Fe³⁺ and Co³⁺, respectively, in solid solution. Three kinds of Fe _x Co_1–x MoO₄ solids can be described. Forx0.16: one has a -Co(Fe²⁺, Fe³⁺)MoO₄ solid solution. For 0.17x0.25: one has the same solid solution with its surface rich in Fe³⁺. Forx0.26: one has the same solid solution with only bulk Fe³⁺, and ferric molybdate. Studies of reduction by hydrogen and of catalytic reaction of mechanical mixtures of CoMoO₄ and ferric molybdate support these statements.     

Influence of functional nanoparticles on the photostability of polymer materials: Recent progress and further applications

The photochemical behaviour of polymer–nanoparticles/nanocomposites has been studied depending on the geometry of the nanofiller and an overview of the studies reported in the last decade is tentatively given. Depending on their functionality, nanoparticles can impact the durability of the nanocomposite materials under light irradiation. The behaviour to UV-light exposure in presence of oxygen of various types of nanocomposites with clays, LDH and carbon nanotubes has been investigated and recent progress on the influence of functional nanoparticles on the polymer photodegradation is reported. The influence of photocatalytic (ZnO and TiO₂) nanoparticles and phosphors on the photooxidation of the polymeric matrix and the durability of the material properties are characterized. From a general point of view, the stabilization strategy of polymer nanocomposites must be adapted depending on the nanofiller.     

Antimatter and matter production in heavy ion collisions at CERN (The NEWMASS experiment NA52)

Besides the dedicated search for strangelets NA52 measures light (anti)particle and (anti)nuclei production over a wide range of rapidity. Compared to previous runs the statistics has been increased in the 1998 run by more than one order of magnitude for negatively charged objects at different spectrometer rigidities. Together with previous data taking at a rigidity of ?20 GeV/c we obtained $10^6 \bar p, 10^3 \bar d$ and two $\overline {^3 He} $ without centrality requirements. We measured nuclei and antinuclei (p, d, $\bar p,\bar d$ ) near midrapidity covering an impact parameter range of b ～ 2–12 fm. Our results strongly indicate that nuclei and antinuclei are mainly produced via the coalescence mechanism. However, the centrality dependence of the antibaryon to baryon ratios shows that antibaryons are diminished due to annihilation and breakup reactions in the hadron dense environment. The volume of the particle source extracted from coalescence models agrees with results from pion interferometry for an expanding source. The chemical and thermal freeze-out of nuclei and antinuclei appear to coincide with each other and with the thermal freeze-out of hadrons.     

Experimental evidence of energy pumping in acousticsMise en évidence expérimentale de pompage énergétique en acoustique

This Note presents an experimental vibro-acoustic set-up that aims to reproduce the energy pumping phenomenon between an acoustic medium and an essentially nonlinear oscillator. It shows a one-way irreversible transfer of energy between the first acoustic mode in a tube and a thin visco-elastic membrane. To cite this article: B. Cochelin et al., C. R. Mecanique 334 (2006).     

NGR study of pyrrhotites obtained in coal hydroliquefaction

Iron Mössbauer spectroscopy has been performed on 38 residues of hydroliquefaction of the French bituminous Freyming coal, without and with added iron based catalysts. 56 to 94 % of the area of each spectrum was occupied by 2, 3, 4 or 5 sextets of Fe_1?xS, either at 295 K or at 78 K or at 4 K. Values of H at 295 K are proposed: 299, 283, 268, 254, 242 and 228 kOe, ±3 kOe, associated with δ(α-Fe)=0.72±0.02 mm/s. The vacancies responsible for the values of H are likely to be randomly distributed. The best accuracy on the relative intensities cannot ensure a precise determination of the overall stoichiometry, so that a better knowledge of the samples is given by the distribution of the Fe sites.     

Dynamic mechanical properties of epoxy resin/epoxidized rubber blends: Effect of phase separated rubber

The dynamic mechanical properties of blends of diglycidyl ether of bisphenol-A-based epoxy resin and internally epoxidized polybutadiene rubber have been studied. It is shown that the influence of the composition of the continuous phase and of the dispersed phase can be studied not only from the variations of the glass transition temperature but also from the changes in the apparent enthalpy of activation associated with this transition. As the initial rubber content increases, the composition of the dispersed phase remains practically constant while more rubber is able to dissolve in the continuous phase. Analysis of the rubbery plateau region reveals that the shear modulus of the blends is not much affected by the presence of dissolved rubber in the continuous phase but strongly depends on the volume fraction of dispersed phase. This volume fraction can be obtained from the relative drop in shear modulus after modeling the results with the Kerner equation. The results compares well with independent measurements by scanning electron microscopy. © 1994 John Wiley & Sons, Inc.