  This work aims at investigating the effect that the energy transferred during
powder-to-wall collisions in a milling process without grinding media entails
on solid-gas reactions. For this purpose, the synthesis of Mg(BH$_4$)$_2$ from
MgB$_2$ in a pressurized hydrogen atmosphere was chosen as a model reaction.
MgB$_2$ was milled under a broad set of milling parameters (i.e. milling times
and rotation regimes) and the obtained product thoroughly characterized. By
proving the partial formation of Mg(BH$_4$)$_2$, the results of this
investigation indicate that the energy transferred to the powder bed by the
powder particles colliding with the chamber wall during milling is not
negligible, in particular when the milling process is protracted for a long
period.
