In-situ X-ray diffraction study on MlNi_(3.75)Co_(0.75)Mn_(0.3)Al_(0.2) during electrochemical hydriding-dehydriding process

摘要

Phase transformations and lattice expansions of MlNi_(3.75)Co_(0.75)Mn_(0.3)Al_(0.2) during the electrochemical hydriding-dehydriding process were investigated using in-situ X-ray diffraction. An intermediate hydride gamma phase between the hydrogen solid solution a phase and fully hydrided beta phase can he observed during the cycling. The formation of gamma phase is related to the diffusion of hydrogen in the crystal grains. The lower the charge rate is, the higher the content of gamma phase is. The phase transformations during the hydriding-dehydriding process can be described as alpha reversible alpha+ gamma +beta reversible beta reversible gamma +alpha reversible alpha. The lattice expansion from alpha to beta is discrete, while that from gamma to beta is continuous. The formation of gamma phase can reduce the discrete lattice expansion from alpha to beta by 30 percent.