Metal hydride synthesis through reactive milling of metals with solid acids in a planetary ball mill

In this paper we report on a new type of synthesis of calcium hydride through reactive milling under an argon atmosphere. Therefore we have used two different protic acids (phosphoric acid and phenylphosphonic acid) which are solid at room temperature and have milled them together with calcium. For the synthesis calcium had two functions: It shall work as reduction agent and as reaction partner for the hydride formation. The received product has been characterised by XRD measurements. Using phenylphosphonic acid and calcium as reactants, calcium hydride could be synthesised as the only crystalline reaction product with a crystallite size of 20 nm. A similar reaction using magnesium could not be realised.

► Ball milling metals with solid acids yields metal hydrides.
► Calcium hydride synthesis from calcium and phenylphosphonic acid in a ball mill.
► Importance of redox potentials and acid's tendency to polycondensation.