Aging of Precipitated Amorphous Alumina Gel

• Published in: Industrial & engineering chemistry research Vol. 41; no. 24; pp. 6059 - 6069
• Main Authors: Rousseaux, J. M, Weisbecker, P, Muhr, H, Plasari, E
• Format: Journal Article
• Language: English
• Published: Washington, DC American Chemical Society 27-11-2002
• Subjects: Chemistry; Cross-disciplinary physics: materials science; rheology; Exact sciences and technology; Growth from solutions; Inorganic chemistry and origins of life; Kinetics and mechanism of reactions; Materials science; Methods of crystal growth; physics of crystal growth; Physics; Aluminium Hydroxides; Inorganic compounds; Chemical precipitation; Moisture; Specific surface area; Aluminium Hydroxides oxides; Crystallinity; XRD; Experimental study; TGA; Kinetic model; Aluminium Oxides; Particle size distribution; Ostwald ripening; Aging; Crystal growth from solutions; Structure modification; Kinetics; Semiempirical method; Porosity; Alumina
• ISSN: 0888-5885; 1520-5045
• DOI: 10.1021/ie000053p

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 area, total pore volume, and total water content is investigated, and the mechanisms of ripening are elucidated. The kinetics of Ostwald ripening are well quantified by a semiempirical equation that can be used for practical purposes.