The profiles of X-ray diffraction patterns have been examined for several powder samples of δ-TiCl3, obtained by mechanical activation of γ-TiCl3 and presenting different catalytic activities in the Ziegler-Natta stereospecific polymerization of propylene to isotactic polypropylene. Particular attention has been paid to the δ-TiCl3 samples showing the best catalytic properties. On the basis of a previous investigation by Allegra, a mathematical treatment has been developed and a disorder function has been elaborated taking into account, in calculating the profiles of the X-ray diffraction intensities, not only the disorder effects but also the sizes of the δ-TiCl3 crystallites. The selected experimental pattern (δ-TiCl3, highly activated) has been well reproduced in this way and fitted by overlapping the calculated spectra of two disordered forms, labelled ϵ1 and ϵ2, which differ in the relative amounts cubic and hexagonal sequences of the Cl-Ti-Cl layers constituting the violet forms of TiCl3. The best fit was achieved by introducing into the calculations crystallite sizes of about 70 Å. The results of the structural investigation are also discussed in terms of activity of the δ-TiCl3 based catalyst for the stereospecific polymerization of propylene.

A crystallographic study of disorder in titanium trichloride, a component of Ziegler-Natta catalysts for stereospecific polymerization

ZANNETTI, ROBERTO;MARIGO, ANTONIO;
1980

Abstract

The profiles of X-ray diffraction patterns have been examined for several powder samples of δ-TiCl3, obtained by mechanical activation of γ-TiCl3 and presenting different catalytic activities in the Ziegler-Natta stereospecific polymerization of propylene to isotactic polypropylene. Particular attention has been paid to the δ-TiCl3 samples showing the best catalytic properties. On the basis of a previous investigation by Allegra, a mathematical treatment has been developed and a disorder function has been elaborated taking into account, in calculating the profiles of the X-ray diffraction intensities, not only the disorder effects but also the sizes of the δ-TiCl3 crystallites. The selected experimental pattern (δ-TiCl3, highly activated) has been well reproduced in this way and fitted by overlapping the calculated spectra of two disordered forms, labelled ϵ1 and ϵ2, which differ in the relative amounts cubic and hexagonal sequences of the Cl-Ti-Cl layers constituting the violet forms of TiCl3. The best fit was achieved by introducing into the calculations crystallite sizes of about 70 Å. The results of the structural investigation are also discussed in terms of activity of the δ-TiCl3 based catalyst for the stereospecific polymerization of propylene.
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Utilizza questo identificativo per citare o creare un link a questo documento: http://hdl.handle.net/11577/2497131
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