Thermal dehydration kinetics of a rare earth hydroxide, Gd(OH)3

✍ Scribed by Chengkang Chang; Dali Mao

• Book ID: 102925971
• Publisher: John Wiley and Sons
• Year: 2006
• Tongue: English
• Weight: 788 KB
• Volume: 39
• Category: Article
• ISSN: 0538-8066
• DOI: 10.1002/kin.20221

✦ Synopsis

Abstract

This paper reports the synthesis, characterization, and dehydration kinetics of a rare earth hydroxide, Gd(OH)~3~. Uniform rod‐like Gd(OH)~3~ powder was prepared by a colloidal hydrothermal method. The powder thus obtained dehydrated into its oxide form in a two‐step process, where crystalline GdOOH was obtained as the intermediate phase. Crystal structure study revealed a monoclinic structure for GdOOH, with space group P2/1__m__ and lattice parameters a = 6.0633, b = 3.7107, c = 4.3266, and β = 108.669. The first‐step dehydration follows the F2 mechanism, while the second step follows the F1 model, indicating that both the steps are controlled by nucleation/growth mechanism. The activation energy E~a~ and frequency factor A are 231±12 kJ/mol and 2.08 × 1018 s^−1^ for the first step and 496 ± 32 kJ/mol and 7.88 × 10^33^ s^−1^ for the second step, respectively. Such high activation energy calculated from the experimental data can be ascribed to the high bonding energy of GdO bond, and the difference in activation energy for the two steps is due to the change in the bond length of hexagonal Gd(OH)~3~ and monoclinic GdOOH. © 2006 Wiley Periodicals, Inc. Int J Chem Kinet 39: 75–81, 2007