1,720,983 research outputs found
The crystal structure of α-TiCl3 and the reticular disorder introduced by ball-milling
No full textBy X-ray powder diffraction methods the crystal structures of α-TiCl3 and of the products obtained by dry ball-milling activation of this form were studied. TiCl3 microcrystals show initially a structural disorder in the positions of titanium atoms and the successive mechanical activation introduces into the structure some stacking faults, mainly associated to ±60° rotations of the triple layers Cl[BOND]Ti[BOND]Cl. The structural investigation has been carried out by an accurate fit of observed X-ray patterns to those calculated in correspondence of structures containing well-defined disordered sequences and of likewise well-defined crystallite sizes. Like γ-TiCl3 and MgCl2, α-TiCl3 is very sensitive to mechanical activation, which improves the performances of these three compounds when they are employed as catalysts, or supports for catalysts, in Ziegler-Natta polymerization processes
The evaluation of the degree of crystallinity in polymers: a comparison between different methods.
No full textLayer-lattices in Ziegler–Natta catalysts
No full textSome layered inorganic compounds of interest in old and new polymerization processes by Ziegler-Natta stereospecific catalysis have been studied. The results are reported of an investigation concerning the crystallographic disorder phenomena in α-TiCl3, VCl3, FeCl3, ball-milled α-MgCl2, β-MgCl2, and in a new catalytic system produced according to some recent trends in the field. Best fits are reported of the experimental x-ray diffraction patterns with patterns calculated for a theoretical model that accounts for structural disorder; the different fits indicate that disorder phenomena due to stacking faults are rather frequent in the examined compounds. The catalytic systems are more and more dispersed, and the maximum of dispersion in heterogeneous systems is reached for the recently proposed formulations
A study of the lamellar thickness distribution in 1-butene, 4-methyl-1-pentene and 1-hexene LLDPE by small and wide angle X-ray scattering and transmission electron microscopy
No full textThree samples were examined of commercial linear low-density polyethylene, containing different comonomers (1-butene, 4-methyl-1-pentene and 1-hexene) and having comparable molecular weight and branching amount. An analysis was carried out by transmission electron microscopy and small- and wide-angle X-ray scattering. The thicknesses were determined of the polymer lamellae, as well as their distributions and the morphology of the crystalline phase. Moreover, small-angle X-ray scattering experimental spectra were analyzed by a fit with the profiles calculated from some theoretical distribution models of the lamellar thickness. The mathematical evaluation of small angle X-ray scattering patterns and the analysis by transmission electron microscopy have provided crystallinity values which were compared with those obtained by wide angle X-ray scattering in order to obtain information on the organization in lamellar stacks. The fitting method has also provided lamellar thickness values comparable to the transmission electron microscopy data
Un dispositivo per l'indagine strutturale mediante diffrazione dei raggi x di campioni policristallini che si deteriorano all'aria
No full textDeterminazione di tracce di mercurio in sedimenti mediante spettrofotometria per assorbimento atomico
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