HYDROGEN ABSORPTION IN AN ICOSAHEDRAL ZNMGY ALLOY

Hydrogen adsorption in a stable icosahedral (i) Zn50Mg42Y8 alloy has b een studied by X-ray diffraction, transmission electron microscopy and differential scanning calorimetry. The i-phase decomposed to a hexago nal Zn2Mg Laves phase, YH3 and MgH2 after hydrogenation under 3 MPa hy drogen pressure at 573 K for 259.2 ks. Two stages of hydrogenation for the i-phase were identified; i-ZnMgY+xH(2)-->i-ZnMgYH2x in the initia l stage and then i-ZnMgYH2x+H-2-->Zn2Mg+YH2+MgH2. DSC curve of the ful ly hydrogenated (3 MPa, 573 K, 259.2 ks) sample revealed an endothermi c peak around 730 K corresponding to the hydrogen desorption. The tran sformations between the icosahedral and crystalline phases due to hydr ogen absorption and desorption are reversible.