The influence of different additives on the solid-state reaction of magnesium hydride (MgH2) with Si

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 °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 °C.