Preparation and hydrogen storage properties of nanostructured Mg-Ni BCC alloys

Nanostructured Mg-Ni system alloys - Mg₉₀Ni₁₀, Mg₈₀Ni₂₀, Mg₆₇Ni₃₃ (Mg₂Ni), Mg₆₀Ni₄₀, Mg₅₀Ni₅₀, Mg₄₀N₆₀, Mg₃₃Ni₆₇ (MgNi₂) and Mg₃₀Ni₇₀ were prepared by mechanical alloying (MA) method. Body centered cubic (BCC) structure is obtained in Mg₆₀Ni₄₀, Mg₅₀Ni₅₀, Mg₄₀N₆₀ and Mg₃₃Ni₆₇ composition alloys after the milling. Mg₃₀Ni₇₀ alloy shows face centered cubic (FCC) structure. The BCC and FCC structures are confirmed by electron diffraction patterns of the samples. From the X-ray diffraction (XRD) patterns and transmission electron microscope (TEM) image observation results, the crystallite size of the alloys is calculated into nanometer scale. Hydrogen absorption kinetics and storage properties of these alloys were studied by hydrogen absorption rate and pressure-composition isotherm (PCT) measurements at 373 K. Mg₅₀Ni₅₀ BCC alloy shows the best kinetics and absorption efficiency among these Mg-Ni system alloys. It can absorb 1.85 mass% hydrogen at 373 K in a hydrogen pressure up to 7 MPa without any activation process.