Abstract
Freshly precipitated alumina gel consists of very small particles (amorphous to XRD) that are agglomerated into larger particles (∼12 μm). When those particles are abruptly transferred into a solution at a pH equal or greater than 7 and at a temperature greater than 65 °C, an aging process occurs. The experiments performed in this work indicate that there are two mechanisms in the aging process, structural rearrangement and Ostwald ripening. The two mechanisms occur simultaneously, but their kinetics are very different. In the first period (i.e., the first 5 min of aging), the structural rearrangement mechanism is very rapid and governs the aging of the alumina (the particles undergo a dramatic water loss), whereas in the second period, the structural rearrangement is almost finished, and Ostwald ripening controls the aging process. The influence of the aging conditions (temperature, pH, and salt solution concentration) on the particle size distribution, crystallite size, crystallinity, specific surface a...
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