The Experts below are selected from a list of 306 Experts worldwide ranked by ideXlab platform
Kevin J Smith - One of the best experts on this subject based on the ideXlab platform.
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hydrodesulfurization of dibenzothiophene over exfoliated mos2 catalyst
Catalysis Today, 2006Co-Authors: Kevin J SmithAbstract:Abstract The activity of exfoliated MoS2 in hydrodesulfurization of dibenzothiophene (DBT) was compared to crystalline MoS2, molybdenum naphthenate (MoNaph) derived MoS2 and ammonium heptamolybdate (AHM) derived MoS2. The prepared catalysts had significantly different morphologies, as described by the Crystallite stack height and slab length, measured by both XRD and TEM. These data were used to estimate the fraction of rim and edge sites in the Crystallites. The DBT turnover frequency (TOF) was highest on the exfoliated MoS2, whereas the selectivity for hydrogenolysis and hydrogenation reactions was shown to correlate with the fraction of rim or edge sites. Selectivity for hydrogenolysis increased as the fraction of edge sites increased.
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hydrodesulfurization of dibenzothiophene over exfoliated mos2 catalyst
Catalysis Today, 2006Co-Authors: Ching Thian Tye, Kevin J SmithAbstract:Abstract The activity of exfoliated MoS2 in hydrodesulfurization of dibenzothiophene (DBT) was compared to crystalline MoS2, molybdenum naphthenate (MoNaph) derived MoS2 and ammonium heptamolybdate (AHM) derived MoS2. The prepared catalysts had significantly different morphologies, as described by the Crystallite stack height and slab length, measured by both XRD and TEM. These data were used to estimate the fraction of rim and edge sites in the Crystallites. The DBT turnover frequency (TOF) was highest on the exfoliated MoS2, whereas the selectivity for hydrogenolysis and hydrogenation reactions was shown to correlate with the fraction of rim or edge sites. Selectivity for hydrogenolysis increased as the fraction of edge sites increased.
Joo Youl Huh - One of the best experts on this subject based on the ideXlab platform.
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mechanism for the formation of ag Crystallites in the ag thick film contacts of crystalline si solar cells
Solar Energy Materials and Solar Cells, 2009Co-Authors: Kyoung Kook Hong, Sung Bi Cho, Ji Weo Jeong, Jae Sung You, Joo Youl HuhAbstract:Abstract This study examined the interfacial reactions between various Ag pastes and (100) Si wafers with and without an SiN x layer during firing at 800 °C for extended times in order to better understand the mechanism for the formation of Ag Crystallites in Ag thick-film contacts of crystalline Si solar cells. The results showed that, in contrast to the model proposed previously, the Ag Crystallites were formed by a direct reaction between Ag + ions dissolved in the glass frit and the Si wafer without an aid of liquid-Pb formation. The redox reactions between PbO and Si as well as between PbO and SiN x were suppressed by adding a few weight percent of Ag powder into the glass frit. The size and distribution of the inverted pyramidal Ag Crystallites formed at the glass/Si interface were found to depend critically on the PbO content in the glass frit. The role of PbO in Ag Crystallite formation was discussed in terms of the solubility of Ag and the viscosity of the glass frit at the firing temperature.
Benoît Duchemin - One of the best experts on this subject based on the ideXlab platform.
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Size, shape, orientation and crystallinity of cellulose I_β by X-ray powder diffraction using a free spreadsheet program
Cellulose, 2017Co-Authors: Benoît DucheminAbstract:X-ray powder diffraction is one of the most commonly used methods in cellulose science. This technique is used to identify the cellulose allomorphs, their crystallinity, and the size of their Crystallites. In this paper, a novel model is introduced that implicitly takes into account the shape and size of cellulose I_β Crystallites in the interpretation of powder diffractograms. Because of the limited amount of data in cellulose powder patterns, this model focuses on a small number of adjustable parameters. The method hypothesizes that cellulose I_β Crystallites are straight crystalline rods with superelliptical cross-sections. This superellipse is a parametric curve that can, for example, describe various Crystallite shapes as rectangles or ellipses. Additionally, preferred orientation along the (0 0 1) crystallographic planes can be modelled using the March–Dollase approach. The simulated background has a semi-empirical form. An initial model comprised cellulose I_β Crystallites and the amorphous background. A second model comprised a biphasic distribution of Crystallites and the same amorphous background. In this second model, large cellulose I_β Crystallites coexisted with more slender Crystallites, usually less than 20 Å in lateral size. Cellulose IV_I nanocrystals were selected as a modeling construct to represent these small and distorted forms of native cellulose. Both models produced simulations in excellent agreement with the experimental measurements.
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Ultrastructure of cellulose Crystallites in flax textile fibres
Cellulose, 2012Co-Authors: Benoît Duchemin, Anthony Thuault, Aurélie Vicente, Baptiste Rigaud, Christian FernandezAbstract:Seven varieties of flax ( Linum usitatissimum ) fibres were analyzed in order to gain a deeper insight into the morphological features of the crystalline assembly. Different spectroscopic techniques and a chemical bleaching process were used to provide an accurate description of the lateral arrangement of the polysaccharide chains within the fibre cell wall. The flax fibres were analyzed in their natural state and after an extraction treatment of the non-crystalline components such as hemicelluloses, pectins and phenolics. The chemical bleaching process consisted of a Soxhlet extraction in toluene, a sodium chlorite treatment and an alkaline extraction of the residual hemicelluloses. Solid-state ^13C nuclear magnetic resonance (NMR) confirmed the sequential removal of the non-cellulosic components from the flax cell wall. Both wide-angle X-ray diffraction (WAXD) and solid-state ^13C NMR provided measures of the Crystallite thicknesses and overall crystallinities before and after treatment. The existence of non-cellulosic highly ordered paracrystalline domains was also evidenced by proton spin relaxation time calculation. Whereas the overall crystallinity determined by WAXD decreased after treatment, the cellulose crystallinity calculated with the help of the solid-state ^13C NMR slightly increased. This is explained by the difference in chemical selectivity between these two techniques and by the paracrystalline state of both hemicelluloses and pectins. Strong adhesion between cellulose Crystallites, hemicelluloses and pectins in the fibres was evidenced by low spin–spin relaxation times and by an increase in Crystallite thickness after bleaching. A simple model is proposed that describes the rearrangement of the macromolecules during the bleaching process.
Johannes Ganster - One of the best experts on this subject based on the ideXlab platform.
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Structure‐Property Relationships in Extruded Starch, 1 Supermolecular Structure of Pea Amylose and Extruded Pea Amylose
Macromolecular Materials and Engineering, 2001Co-Authors: Ernst Walenta, Hans-peter Fink, Peter Weigel, Johannes GansterAbstract:Separated amyloses with different molecular weight distributions were obtained enzymatically from wrinkled pea starch and processed in a multi-zone twin-screw extruder. The crystalline polymorphs, crystanllinity and Crystallite dimensions of amylose (unbranched molecular starch component) and films extruded from it were investigated by wide-angle X-ray scattering. The starting amylose materials exhibit a crystalline V A structure with rather large Crystallites (9-25nm) and a degree of crystallinity ranging between 30 and 40%, depending on the history of the amylose sample. The extruded films, on the other hand, recrystallized in the B-type with a slightly higher degree of crystallinity and significantly smaller Crystallite dimensions (3-7 nm). In one case, V H -type crystals were observed. The mechanical properties of the extruded materials were determined in tensile tests. The amylose with the highest molar mass produces films with the highest mechanical performance. As compared with cellulose or synthetic polymer films, the mechanical properties of the amylose films appear to be fundamentally limited by the lack of preferred molecular orientation.
Kyoung Kook Hong - One of the best experts on this subject based on the ideXlab platform.
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mechanism for the formation of ag Crystallites in the ag thick film contacts of crystalline si solar cells
Solar Energy Materials and Solar Cells, 2009Co-Authors: Kyoung Kook Hong, Sung Bi Cho, Ji Weo Jeong, Jae Sung You, Joo Youl HuhAbstract:Abstract This study examined the interfacial reactions between various Ag pastes and (100) Si wafers with and without an SiN x layer during firing at 800 °C for extended times in order to better understand the mechanism for the formation of Ag Crystallites in Ag thick-film contacts of crystalline Si solar cells. The results showed that, in contrast to the model proposed previously, the Ag Crystallites were formed by a direct reaction between Ag + ions dissolved in the glass frit and the Si wafer without an aid of liquid-Pb formation. The redox reactions between PbO and Si as well as between PbO and SiN x were suppressed by adding a few weight percent of Ag powder into the glass frit. The size and distribution of the inverted pyramidal Ag Crystallites formed at the glass/Si interface were found to depend critically on the PbO content in the glass frit. The role of PbO in Ag Crystallite formation was discussed in terms of the solubility of Ag and the viscosity of the glass frit at the firing temperature.