The influence of the kinetics of the hydrogenation of Nd–Fe–B alloys on hydrogen distribution in the alloy phases

Abstract

We present results of experiments on hydrogenation of Nd 16Fe 75.8B 8.2 controlled by two parameters: the amount of hydrogen and the rate of feeding the sample with hydrogen at low pressures. By proper combination of these parameters four different schemes for the hydrogenation process were generated: (1) selective hydrogenation of the Nd-rich phase, (2) hydrogenation of the Nd-rich phase followed by diffusion of hydrogen into the Nd 2Fe 14B phase, (3) simultaneous partial hydrogenation of both phases, (4) simultaneous complete hydrogenation of both phases. For the first two cases the results of measurements of equilibrium pressure versus hydrogen concentration at room temperature are presented in the form of a p– c diagram with three phase regions: (1) Nd+NdH y +Nd 2Fe 14B, (2) NdH y +Nd 2Fe 14B+Nd 2Fe 14BH x<2.7 , (3) NdH y +Nd 2Fe 14BH x>2.7