Comparison of surface coverage values of tungsten-alumina catalysts determined by different methods

Apparent surface coverage (ASC) of a series of tungsten-alumina catalysts was determined by the electrophoretic migration method (EM). A linear increase in W coverage with increasing W loading (up to 13.1 wt.% W) was observed. The results were in close agreement with those obtained previously by ion scattering spectroscopy (ISS) and low temperature CO adsorption.     

Neighborhood Relationships of Widely Distributed and Irregularly Shaped Particles in Partially Dewatered Filter Cakes

A more thorough understanding of the properties of bulk material structures in solid–liquid separation processes is essential to understand better and optimize industrially established processes, such as cake filtration, whose process outcome is mainly dependent on the properties of the bulk material structure. Here, changes of bulk properties like porosity and permeability can originate from local variations in particle size, especially for non-spherical particles. In this study, we mix self-similar fractions of crushed, irregularly shaped Al₂O₃ particles (20 to 90 µm and 55 to 300 µm) to bimodal distributions. These mixtures vary in volume fraction of fines (0, 20, 30, 40, 50, 60 and 100 vol.%). The self-similarity of both systems serves the improved parameter correlation in the case of multimodal distributed particle systems. We use nondestructive 3D X-ray microscopy to capture the filter cake microstructure directly after mechanical dewatering, whereby we give particular attention to packing structure and particle–particle relationships (porosity, coordination number, particle size and corresponding hydraulic isolated liquid areas). Our results reveal widely varying distributions of local porosity and particle contact points. An average coordination number (here 5.84 to 6.04) is no longer a sufficient measure to describe the significant bulk porosity variation (in our case, 40 and 49%). Therefore, the explanation of the correlation is provided on a discrete particle level. While individual particles?<?90 µm had only two or three contacts, others?>?100 µm took up to 25. Due to this higher local coordination number, the liquid load of corresponding particles (liquid volume/particle volume) after mechanical dewatering increases from 0.48 to 1.47.

     

Über Glasbildung und Eigenschaften von Chalkogenidsystemen. XXVIII. Zur Bindungsenergie der Si?Si- und Ge?Ge-Bindung in den Verbindungen Na6Si2X6 und Na6Ge2X6 (X = S,Se)

About Glas Formation and Properties of Chalcogenide Systems. XXVIII. On Bonding Energies of Si? Si and Ge? Ge Bonds in Na₆Si₂X₆ and Na₆Ge₂X₆ (X = S, Se) Potentiometric titration of 0.01 molar solutions of Na₆Si₂S₆, Na₆Si₂Se₆, Na₆Ge₂S₆, and Na₆Ge₂Se₆ in methanol with bromine yields the thermodynamic data of the reactions which take place under scission of the Si—Si or Ge—Ge bonds, respectively. The bonding energies of these homonuclear bonds are estimated and compared with data from the literature.     

Novel processing tools for automated doppler picture veocimetry (DPV) evaluation

A unique technique, the Doppler Picture Velocimetry (DPV), for measuring and visualizing velocities especially in hypersonic gas flows is presented. By means of a Michelson interferometer (MI) the Doppler shifted light scattered by tracers is transformed into an image showing Fizeau fringes. The image fringe distribution provides information on the Doppler frequency shift which is related to the velocity of the particles crossing a light sheet plane. To overcome former disadvantages of DPV, the optical set-up as well as the processing scheme have been improved significantly. Two schemes have been tested in recent times for fringe processing: 1) an alternative process, the Least Square Estimators (LES) and 2) an algorithm based on a technique using Fast Fourier Transformations (FFT) to examine the DPV images in the frequency domain. The new DPV algorithms now allow an automated calculation of the velocity profiles from the Doppler pictures without manual fringe tracing as it had to be done in the past. Both methods are compared by means of Mach 6 flows around a wedge and a sphere produced in the ISL high energy shock tunnel STA. TiO₂ particles are illuminated by a laser light sheet which was perpendicularly arranged to the main flow direction. Light observation via the MI from the side (90° to illumination) informs on the vertically oriented velocity through the DPV images.     

Multistep scattering in the 160 MeV208Pb(α, α′) reaction

New experimental data has been obtained for the²⁰⁸Pb(α, α′) reaction induced by 160 MeV alpha particles, for inelastic scattering to forward angles. We use these data to investigate the applicability of the multistep scattering theory of Feshbach, Kerman, and Koonin for describing this reaction. The mechanism we study, following the work of Gadioli et al. [1], is of the incident alpha particle remaining intact throughout the scattering process, exciting nucleon particle-hole pairs through multistep process. We conclude that this mechanism, combined with compound nucleus decay at low emission energies, can account for much of the observed data. However, there are indications that other processes also contribute at energies above the compound nucleus emission regime, and we outline future theoretical analyses that are needed.     

Nano-Particles by Wet Chemical Processing in Commercial Applications

Nano-sized materials produced by wet chemical processing have a wide range of industrial applications. For example, a solution of monodisperse SiO₂-particles for single-layer anti-reflection coating on glass was developed. Although being porous, the anti-reflection coating shows excellent mechanical stability which is sufficient for commercial applications. The coating sol is used to produce cover glass with high transmission for solar energy systems, e.g. photovoltaic modules.Nano-sized materials made by sol–gel processes are not limited to niche applications. Inorganic metal oxide coatings on thin mica platelets are the basis for pearl lustre pigments. The inorganic layers, consisting of titanium dioxide or iron oxides, are obtained by a wet chemical procedure. The well-defined layer thickness, varying from 50 to 300 nm, determines the optical properties of the pearlescent pigment. By using synthetic SiO₂ platelets instead of natural mica, impressive angle-dependant colour effects can be achieved. Synthetic SiO₂ platelets are also produced by a sol–gel coating technique.Special spherical silica particles made by a wet chemical processing are used in cosmetic applications. The size distribution determines the skin feeling of the formulation. In addition, specific colour or anti-wrinkle effects can be achieved.     

Synthetic studies on palytoxin. Stereocontrolled,practical synthesis of the C.101–C.115 segment

A stereocontrolled and practical synthetic route to the acetal $\text{2a}$, a degradation product of palytoxin, in optically active form is described.