Hydrogen generating reaction between sodium borohydride, NaBH4, and magnesium hydroxide, Mg(OH)(2) (brucite), was studied. Reaction rate was found to depend on the degree of reactants homogenization and/or their particle size. Kinetic of the reaction was studied in isothermal approach in the temperature range of 240-360 degrees C. It is shown that the reaction obeys 2D diffusion mechanism and its activation energy is 155.9 kJ/mol. Powder XRD analysis and Raman spectroscopy reveal that mechanically activated mixture of NaBH4 and Mg(OH)(2) reacts yielding MgO as the only crystalline phase in the temperature range of 240-318 degrees C. At higher temperatures a new crystalline tetragonal phase of as yet undetermined composition is developed. (C) 2007 International Association for Hydrogen Energy. Published by Elsevier Ltd. All rights reserved.