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[en] Transport and recombination have been studied in samples of hydrogenated amorphous silicon through measurements of photocurrent transients in the nanosecond to millisecond time regimes. Both sample configurations suitable for time-of-flight measurements and configurations appropriate for the usual photoconductivity measurements have been employed. In principle, analysis of the experiments together permits the separation of current decreases with time caused by time-dependent mobilities from those caused by carrier loss due to deep trapping. The former involves carrier trapping which is temporary on the time scale of the experiment; the latter, trapping which removes carriers permanently, on the same time scale. The occurrence of the latter carrier loss is checked through integration of the current transient to obtain the total collected charge, with the applied electric field as a parameter
[en] This work aims to evaluate the tribological performance of the newly synthesized silane surface treated crab, periwinkle and scallop shell powders in the epoxy modified Phenolic Friction Composites (FCs). The raw and silane treated shell powders are synthesized and characterized for its morphology, element composition and crystal properties. FCs are fabricated with the raw and silane surface treated shell powders using compression moulding process. The tribological performances of the shell powder based brake pads are studied based on IS 2742 standard. The performance of the samples is evaluated and ranked based on Extension Evaluation Method (EEM) considering 11 tribological parameters. The silane treated scallop shell based FC exhibited the best overall tribological performance and expressed as the weighted average dependent degree in EEM. (paper)
[en] Highlights: • We investigate SiH bond activation of SiH4 by Be atoms. • Excited Be(1P:2s12p1) atoms insert one SiH bond spontaneously. • HBeSiH3 rearranged to HBe(μ-H)3Si upon photolysis. • 3c-2e bond was formed in HBe(μ-H)3Si through hydrogen bridged bond. Laser-ablated beryllium atoms have been reacted with silane molecules during condensation in excess neon and argon at 4 K. Absorptions due to HBeSiH3 and HBe(μ-H)3Si were observed and identified on the basis of isotopic IR spectroscopy, deuterium substitution with SiD4, and quantum chemical frequency calculations. The observed results show excited Be atom (1P1:2s12p1) can insert into SiH bond spontaneously and the insertion product rearranges to HBe(μ-H)3Si upon photolysis. The electron localization function (ELF) analysis suggests that 3c-2e hydrogen bridge bond (BeHSi) was formed by the donation of electrons for SiH σ bond to the empty p orbital of Be atom for HBe(μ-H)3Si molecule, which shows much difference from CH bond complexes.
[en] The preparation of sizeable quantities of luminescent Si nanoparticles (Si-np) with controlled morphology is a challenging task. Here, we describe two strategies aiming at size reduction of the Si-np produced in a laser-assisted silane pyrolysis reactor without detrimental effects on the process yield and on the nanoparticle structural and compositional properties. The first method is based on the addition of a sensitizer gas to dilute silane and consequently reduce the nucleation centres density without decreasing the reaction temperature. The second consists in the introduction of a collector at a variable distance from the irradiated region to freeze the particle growth and decrease the inter-particle sintering probability. We report on the characterization of the produced Si-np, and we show that by combining the two methods, we are able to prepare 4 nm crystalline core size nanoparticles with a productivity of 1 g per hour. We also describe the enhancement effect of the wet-chemical oxidation processes on the luminescence emission intensity of the Si-np.
[en] Highlights: • Preparation of high performance biobased hemp fiber polybenzoxazine composites. • Silane coupling agent treated HF composite has highest thermal stability. • Excellent mechanical properties on the silane coupling agent treatment. • Slightly higher Tg and stiffness for silane composite than the alkali treated composites. • The lower fiber/matrix effectiveness coefficient C was observed for silane composite.
[en] Complete text of publication follows. In this paper the influence of halloysite structure on the properties of melt-prepared polymer nanocomposites have been studied. Intercalation of halloysite (HLS) carried out in solution as well as by dry mechanochemical method has been investigated by vibrational spectroscopic techniques. Except of currently used modifiers (alkylamines, silanes), an intensive study of organo-clay nanocomplexes (with potassium-acetate, urea, formamide and acetamide) has been investigated and new structural models (as well as reaction pathways) were proposed. It was found that modification of halloysite by alkylamines as well as silanes did not lead to intercalated structure of halloysite. Mechanochemical treatment with urea, however, resulted in an intensive intercalation of halloysite. Surface activation of the mineral has been achieved by the thermal treatment of the complex. The impact of the intercalated structure of halloysite was confirmed by improving mechanical properties, as well as by reduction of flammability of PP/halloysite nanocomposites. The investigation of the structure of polymer nanocomposites based on intercalated halloysite confirmed considerable reduction of particle size and high degree of filler exfoliation. The achieved results confirmed that there is a potential for future utilisation of natural halloysites for production of exfoliated polymer nanocomposites with outstanding end use properties.
[en] Complete text of publication follows. A classical hydride generation atomic absorption spectrometry flow system consists of a reaction coil, a stripping coil, a gas liquid separator (GLS) and a heated quartz T-tube atomizer. There have been some studies for determination of Ag by using this classical hydride generation system; however, only mg L-1 levels could be determined. In this study, three types of gas-liquid separators, namely, U-shape, cylindrical and a novel large volume device were used. It was possible to determine Ag in ng mL-1 level when stripping coil was eliminated from the system. The calibration plot was linear in the range of 50 to 500 ng mL-1 using a U-shape GLS. The 3s limit of detection (LOD) is 29 ng mL-1 and characteristic concentration value, C0, were found to be 15.3 ng mL-1. The similar set-up was used also with a cylindrical GLS; it was observed that the efficiency of this GLS is about 10 fold higher than the U-shape GLS; linear working range was 5.0 to 50 ng mL-1. LOD (3s) and C0 values were found to be 3.0 ng mL-1 and 2.9 ng mL-1, respectively. In order to minimize the memory effects, a 10% (v/v) solution of dichlorodimethylsilane in toluene was used to silanize both gas liquid separators to deactivate their internal surfaces. In addition to these studies, a novel large volume GLS was used. In this device 15.0 mL of mixed acidic analyte solution and NaBH4 were placed. Argon gas was passed through this mixture for 90 seconds and formed volatile analyte species were sent to a W-coil trap heated at an optimized temperature. The calibration plot was linear between 0.10 and 0.75 ng mL-1; the LOD (3s) and C0 were found to be 0.049 ng mL-1 and 0.050 ng mL-1, respectively.
[en] This thesis fits into the general pattern of the studies carried out by CEA/DEN on the future nuclear systems. The actions proposed in this context consist in synthesizing organo mineral solids from molecular precursors and to implant actinides from a solution to form a primary phase and then to transform this phase into a mineral solid in order to form a secondary phase by an appropriated treatment. The obtained material could be used as raw material for fuel preparation or as incineration target. The retained precursors to contribute to the primary phase are of poly-silanes or poly-carbo-silanes type. At first, these retained polymers have been synthesized. At the present time, two different considered methods are studied in order to obtain polymers with a control porosity and to be able to implant actinides. These synthesis methods are presented in this work. (O.M.)
[en] Polyamidoamine dendrimer was synthesized on the surface of amino silane modified magnetite nanoparticles. After coating of streptavidin to these dendrimer-modified magnetite nanoparticles, an up to 3.4 times higher amount of streptavidin (SA) was measured compared to magnetite nanoparticles modified with only amino silane. The biotin-binding capacity of SA thus increased after dendrimer modification