Thermogravimetric data for the decomposition of diaspore have been obtained under nonisothermal conditions. A model-free isoconversional method is used to yield dependency of the activation energy on the extent of conversion for experiments. Reaction model of the Sestak-Berggren equation is identified by Malek and Mitsuhashi method. The parameter of the model SB(m, n) and the pre-exponential factor (A) are calculated. (C) 2004 Elsevier B.V. All rights reserved.