Reactions in the SrH2-Al-H2 system

The reactions in SrH2-Al-H2 system were studied by hydrogenation/dehydrogenation of the 2SrH2 + Al mixture prepared by ball milling of Sr2Al alloy under hydrogen. It was found that SrH2 and Al can react with hydrogen to form Sr2AlH7 at 553 K when the hydrogen pressure is above 2.93 MPa and this reaction is reversible. The enthalpy change for the formation of Sr2AlH7 from SrH2 + Al + H2 is about −51 kJ/mol H2. When the hydrogen pressure is below 1.76 MPa and the temperature is 553 K, however, SrH2 reacts with Al to form SrAl4 and H2 with an enthalpy change of 48 kJ/mol H2. This reaction is irreversible under the present experimental condition. Similarly, Sr2AlH7 also decomposes into SrH2, SrAl4 and H2 when the hydrogen pressure is below the equilibrium pressure of the irreversible reaction.