PHASE EQUILIBRIUM AND HYDROGEN ABSORPTION OF LaNis-LaCus SYSTEM

X-ray diffraction and thermal analyses were used to study the phase equilibrium relationships in the pseudo-binary system LaNi_5-LaCu_5. The system is of a continuous solid solution. The melting point and the amount of hydrogen absorbed decrease as well as the lattice parameters and the stability of the intermetallic hydrides increase with the increase of Cu content. It was determined that LaNi_(5-x)Cu_xH_n is independent compound in the LaNi_(5-x)Cu_x-H_2 system.The absorption and desorption of hydrogen in the LaNi_(5-x)Cu_x-H_2 system is not a homogeneous and continuous process of hydrogen dissolving in alloy, but is the formation of hydride through hydrogenation of the intermetallic compounds LaNi_(5-x)Cu_x by way of one unit cell by another. The atomic radius of both La and Ni (or Cu) are compressed separately in the alloys LaNi_(5-x_Cu_x, especially in the basal planes perpendicular to the principal axis. This compression phenomenon disappears as soon as the hydrides form.