Kinetic study of the thermal decomposition of cobalt(III) oxyhydroxide

Abstract

The kinetics of thermal decomposition of CoOOH have been studied by analysis of isothermal weight loss data under vacuum. The comparison of linear correlation coefficients of different kinetic expressions applied to these data does not allow an understanding of the mechanism, even when significance tests are performed (t test). A single value of the activation energy (193 kJ tool -t) is obtained from the Arrhenius plots, and is relatively independent of the choice of rate law. On the other hand, a change in the mechanism of formation of Co304 with temperature cannot be inferred from analysis of isothermal data. Thus, the statement of some authors that from formal kinetics it is possible to distinguish the proton and electron transfers involved in the transformation appears unacceptable.A few years ago, Avramov [1, 2] stated that it is possible to distinguish the two physico~:hemical processes involved in the thermal decomposition of CoOOH from kinetic analysis of the isothermal weight loss data. The first process is a proton transfer between two hydroxyl groups, and the second is an electron transfer from an oxide ion to a Co(Ill) ion. The resulting reaction is endothermic in nature, and has the stoichiometry:12 CoOOH --->4 Co304 + 6 H20 + 02( 1) in which oxygen and water are released simultaneously. According to Avramov, the contracting area rate law proved applicable and two values of activation energy were reported 145 and 79 kJ mol-1, below and above 280 ~ respectively. However, the experimental conditions used in his study (static air atmosphere and a large amount of sample: lg) are not the most appropriate for this reaction, which involves gaseous products. Special control is necessary to prevent the development of a gas layer around the solid. Ir this way, the effect of the partial pressure of the evolved gas on the equilibrium decomposition temperature and the problems related to its diffusion should be minimized.

Thermal decomposition of [Co(NH3)6]Cl3

“…In the fourth stage, Co304 is transformed to CoO, which is in agreement with the literature data [16,21]. In the fourth stage, Co304 is transformed to CoO, which is in agreement with the literature data [16,21].…”

Polytypic transformations during the thermal decomposition of cobalt hydroxide and cobalt hydroxynitrate

“…Nanocrystalline cobalt hydroxide platelets were prepared by the hydrothermal treatment technique in presence of amines and polyvinylpyrrolidine [14,15]. There are several reports on the thermal decomposition studies of cobalt hydroxide, cobalt oxyhydroxide and cobalt based layered double hydroxides in relation to texture, morphology by electron diffraction, X-ray diffraction, Raman spectroscopy and X-ray photoelectron spectroscopy [16][17][18][19]. The above studies on thermal decomposition of cobalt hydroxide and cobalt oxyhydroxide do not characterize the intermediate phases formed during the decomposition process.…”