Rearrangement/Fragmentation Reactions of Oligosilanes with Aluminum Chloride

Reinvestigation of the Lewis acid catalyzed rearrangement of some open-chain permethyloligosilanes with the Al(Fe)Cl(3) catalyst system exhibited several cases of additional reactivity: namely, a fragmentation/cyclization reaction. Introduction of (trimethylsilyl)methyl substituents into the oligosilane substrates strongly facilitated this reaction, yielding cyclic or bicyclic carbacyclosilanes. Investigations concerning the composition of the catalyst system indicated that the incorporation of about 0.1% FeCl(3) into the AlCl(3) lattice provided an effective catalyst.     

Canadian Field Soils I. Mineral Composition by XRD/XRF Measurements

Forty Canadian soils were laboratory tested for the presence of quartz and other minerals using X-ray diffraction/X-ray fluorescence techniques. On average, the highest quartz content was observed in soil samples from sites in Nova Scotia followed by Prince Edward Island sites, whereas soil sample from British Columbia sites had the lowest quartz content. The second most abundant mineral was albite that mainly occurred in soil samples from Ontario and Quebec sites. Illite was the third most abundant and prevailed in soils mainly from British Columbia and New Brunswick sites. Soil samples from British Columbia sites had the highest combined clay and silt content and were composed of illite, albite, kaolinite, and chlorite. The lowest clay content was found in the samples from the Quebec sites. The highest microcline (a potassium feldspar) content was observed in Quebec, Ontario, and Prince Edward Island sites. In contrast to other provinces, samples from Quebec and Ontario sites also included amphibole. Soil samples from Saskatchewan and Manitoba sites also comprised carbonates, i.e., calcite and dolomite. Iron oxides (e.g., goethite) were present in all soils, except the Quebec sites, but their occurrence was rather insignificant.     

Rheotens-mastercurves and drawability of polymer melts

In a Rheotens experiment, the tensile force needed for elongation of an extruded filament is measured as a function of the draw ratio. For thermo-rheologically simple polymer melts, the existence of Rheotens-mastercurves is proven. Rheotens-mastercurves are invariant with respect to changes in melt temperature. Also, for polymer melts with different average molar masses, but similar molar mass distribution and branching structure, Rheotens-mastercurves are invariant to changes in the average molar mass. It is shown, by testing several polyethylenes with different molar mass distribution and different long-chain branching, that Rheotens-mastercurves allow a direct and quantitative assessment of the drawability of polymer melts under actual processing conditions, i.e. under the action of a constant tensile force and including the effects of the rheological prehistory in the extrusion die.     

The significance of microcomposites as experimental models

This paper demonstrates the usefulness of careful experimental work with model composite materials, such as thin polymeric films in which single fibers are accurately positioned, in at least two respects: to assess the validity of a theory for a given physical property, and to accurately probe the effects of various parameters on the behavior of composites. Working with such model composites has obvious advantages, such as the full control of experimental parameters, the possibility of introducing perturbative effects in a controlled way, and the possibility of verifying theoretical models in the range of low fiber content. Indeed, macroscopic composite materials contain various types of defects and perturbative effects, such as fiber misalignment or slack, fiber-poor regions, voids, etc., which bias any quantitative assessment of mechanical and physical properties, and preclude the accurate verification of theoretical schemes. One difficulty in working with microcomposite models, also recalled here, is the need for an appropriate “scaling-up” procedure to the level of macroscopic composites.     

Donorsubstituierte 2,4-Diazacyclopentadienone und indigoide 1,3,5,7-Tetraazafulvalene

Donor Substituted 2,4-Diazacyclopentadienones and Indigoid 1,3,5,7-Tetraazafulvalenes Hydrolysis of tris(diethylamino)imidazolylium chloride gives rise to 2,5-bis-diethyl-amino-4H-imidazolin-4-one; thiolysis leads, depending on conditions, to 2,5-bis-diethylamino-4H-imidazolin-4-thione or potassium 2,6-bis-diethylamino-1,3,5,7-tetraazafulvalene-4,8-dithiolate. The latter can be protonated to form green 2,6-bis(dimethylamino)-3,4,7,8-tetrahydro-1,3,5,7-tetraaza-fulvalen-4,8-dithione, a new indigoid compound, and alkylated to give blue 2,6-bis-diethylamino-4,8-bis-alkylthio-1,3,5,7-tetraazafulvalenes. Treatment of 2,5-bis-diethylamino-4H-imidazolin-4-thione with copper furnishes 2,6,4,8-tetrakis-diethylamino-1,3,5,7-tetraazafulvalene. – Oxidation of 2,6-bis-dimethylamino-3,4,7,8-tetrahydro-1,3,5,7-tetraazafulvalen-4,8-dithione gives rise to (2,2′-bis-diethylamino-4,4′-bi(4H-imidazol)-5,5′-dithione, corresponding to dehydroindigo, and reduction leads to a colorless compound, corresponding to leucoindigo.     

The radioecology of the grapevine. 2. Effects of the nuclear reactor accident in Chernobyl on the radioactivity in the soil, leaves, grapes and wine

Natural (tritium, 14C, 40K, 226Ra) and man-made radionuclides (90Sr, 134Cs, 137Cs) were determined in soil (top 30 cm), vine leaves, grapes and wine in eight locations of the most important viticultural regions in the Federal Republic of Germany. The results obtained in 1983-1985 have been published previously. Part II of this study presents results obtained in 1986 and 1987, i.e. after the reactor accident at Chernobyl in the Soviet Union. The mean content of 137Cs before (after) Chernobyl was 4 (9) Bq/kg dry matter in soil, 0.07 (3) Bq/kg fresh matter in leaves, 0.02 (0.4) Bq/kg in grapes, and 0.008 (0.9) Bq/L in wine. As compared with 1986, distinctly lower levels were found in leaves, grapes and wine in 1987. In 1986 the content of 134Cs was about half that of 137Cs. Owing to its shorter half-life, 134Cs was below the detection limit in many of the 1987 samples. Transfer factors such as from soil to leaves and from soil to grapes for caesium agreed well in 1983-1985 and 1987, but showed considerable deviations in 1986, due to the ubiquitous contamination of the environment. Results of 90Sr determinations confirmed other reports showing this radionuclide to be a very minor contributor to the total radioactivity released at Chernobyl. No effect of the reactor accident on levels of the other radionuclides was detected.     

Hydrogen microscopy – Distribution of hydrogen in buckled niobium hydrogen thin films

Hydrogen absorption in thin metal films clamped to rigid substrates results in mechanical stress that changes the hydrogen's chemical potential by Δμ_H(σ) = −1.124σ kJ/mol_H for σ measured in [GPa]. In this paper we show that local stress relaxation by the detachment of niobium hydrogen thin films from the substrate affects the chemical potential on the local scale: using coincident proton–proton scattering at a proton microprobe, the hydrogen concentration is determined with μm resolution, revealing that hydrogen is not homogenously distributed in the film. The local hydrogen solubility of the film changes with its local stress state, mapping the buckled film fraction. In niobium hydrogen thin films loaded up to nominal concentrations in the two-phase coexistence region, the clamped film fraction remains in the solid solution phase, while the buckles represent the hydride phase. These results are compared to a simple model taking the stress impact on the chemical potential into account.