THERMODYNAMIC AND STRUCTURAL-CHANGES OF VARIOUS INTERMETALLIC COMPOUNDS DURING EXTENDED CYCLING IN CLOSED SYSTEMS

The application-relevant AB(5)-type intermetallic compounds LmNi(4.85) Sn(0.15), LmNi(4.49)Co(0.1)Mn(0.205)Al(0.205) and LmNi(4.08)Mn(0.62)Al (0.1)Co(0.2) underwent about 90 000 thermally induced hydrogen absorpt ion-desorption cycles in closed systems at different cycling temperatu res and pressures. Depending on the individual rates of decay, regener ation procedures were carried out several times. After the half time a nd after the end of cycling additional experimental techniques were em ployed in order to determine possible structural and stoichiometric ch anges. Among these X-ray powder diffractometry, magnetization, scannin g electron microscopy including EDX and thermal desorption spectroscop y were utilized. Besides the degradation behaviour of each material, n ew results are presented about the degradation phenomena (structural c hanges, disproportionation) and a comparison is given of various regen eration procedures.