Phase transformations in the La1−xNdxNi3.5Al1.5–H2 (x = 0.1 and 0.2) system

Interactions in the La1−xNdxNi3.5Al1.5-Н2 (x = 0.1 and 0.2) system was studied from room temperature up to 950 °C at the initial hydrogen pressure of 5 MPa through differential thermal (DTA) and X-ray phase analyses. Heating two-phase alloys (x = 0.1 and 0.2) in hydrogen results in their disproportionation (at 530 and 560 °С, respectively) and the formation of NiAl and unidentified amorphous products. The single-phase La0.9Nd0.1Ni3.5Al1.5 alloy decomposes in hydrogen at 900 °С into a hydride of rare-earth metals and an Ni3Al intermetallic; traces of NiAl and hydride of a phase of the CaCu5-type structure have also been observed. Heating the disproportionated samples in vacuum to 520–550 °С leads to their recombination into a homogenized phase with a CaCu5-type structure. In other words, the increase of neodymium content shifts the reaction equilibrium of La1−xNdxNi3.5Al1.5 alloys with hydrogen towards recombination.