The possibility of increasing the solid-state reaction rate of MgH2 with Si by modifying the mixture preparation method and adding chemical compounds or elements, such as niobium pentafluoride (NbF5), nano-titanium (IV) oxide (TiO2), nano-chromium (III) oxide Cr2O3, yttrium, and nano- and microsized nickel, was investigated. The results show that changing the milling parameters of the MgH2 and Si mixture in a planetary ball mill greatly affects the rate of direct reaction between them and allows the reaction to take place at temperatures as low as 200 degrees C with an equilibrium pressure over 1 bar. Moreover, all additives significantly enhanced the reaction speed. The reaction pathway was found to be different for decomposition in a hydrogen vacuum and pressures of several bars. Reactions of the powders investigated did not occur at temperatures below 150 degrees C. (C) 2009 Professor T. Nejat Veziroglu. Published by Elsevier Ltd. All rights reserved.