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Kinetic Analyisis of LiAlSiO4 Formation from Ll-exchanged Zeolite A by Time-resolved Synchrotron Powder Diffraction

Thermal transformation of |Li|-LTA was followed by in situ, time-resolved synchrotron X-ray powder diffraction [1]. The powder diffraction experiment was carried out in non-isothermal mode, using transmission geometry with capillary sample and an imaging plate detector. The |Li|-LTA was heated linearly, from 30 oC to 1000 oC, using different heating rates ( 0.0417o/s, 0.1667o/s and 0.333o/s). A great amount of the |Li|-LTA was transformed into an amorphous aluminosilicate phase at about 820 oC. At about 790 oC, a new crystalline phase of β -eucryptite was started to crystallize from the amorphous phase. Kinetics of non-isothermal amorphization of |Li|-LTA and crystallization of β -eucryptite are analyzed by the changes of the rate constants during heating. Apparent activation energies of the amorphization of |Li|-LTA and crystallization of β -eucryptite are determined and kinetic equations for the mentioned processes are derived {; ; 2]. The kinetic orders, n = 3/2 for the amorphization of |Li|-LTA and n = 1/2 for crystallization of β -eucryptite indicate that in accordance with the Kolmogorov-Johnson-Mehl-Avrami-Evans (KJMAE) [3-6] model of solid-state transformation processes the non-isothermal amorphization of |Li|-LTA takes place by a thermally-induced formation of short-range ordered aluminosilicate subunits and their diffusion-limited agglomeration into X-ray amorphous agglomerates, and non-isothermal crystallization of β -eucryptite takes place by homogeneous nucleation of β -eucryptite and diffusion-limited, one-dimensional growth of nuclei (crystals).

Lithium aluminosilicate; Formation; Kinetic analysis; Time-resolved synchrotron powder diffraction

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