Hydrogen decrepitation as a highly efficient and excellent crushing method is widely used in the preparation of NdFeB magnets [1] . However, this method still exist many difficulties in the industrial preparation for 2:17 type SmCo alloys owing to high hydrogen pressure . Our previous work [2] has reported 2:17 type SmCo alloys occur HD at room temperature and hydrogen pressure of 0 .3 MPa and has shown that Fe atom improved hydrogenation decrepitation ability of alloys by improving hydrogen-absorbing ability of 1:7 phase . But the mechanism that Fe improve hydrogen-absorbing ability of the 1:7 phase still need further study . In addition, subsequent degassing behaviour of alloys have been studied by using DSC . The alloy compositions in this study are Sm(Co bal Fe x Cu 0 .053 Zr 0 .02 ) 7 .84 (x=0 .2,0 .3,0 .4,0 .5) alloy . Fig .1(a) shows that the alloy with x=0 .2 was not decrepitated for extremely low hydrogen absorption while the alloys with x=0 .3,0 .4 and 0 .5 are decrepitated after absorbing more than 0 .15 wt% hydrogen at room temperature and hydrogen pressure of 0 .4 MPa . It can be seen that hydrogenation ability for the alloys is obviously improved with increasing Fe content . DSC curves for dehydrogenation of alloys are showed in Fig .1(b) . It can be seen that x≥0 .3 alloys exhibit endothermic peak except alloy with x=0 .2 . Kwon [3] and Zakotnik [4] both show that dehydrogenation temperature of 2:17 type SmCo alloys is 200 0C . According to XRD showed in Fig .1(c), the main phase in alloys is 1:7 phase and some alloys also consist of 2:7 phase and 1:5 phase . So it seems that the endothermic peaks occurred at about 2000C and 160 0C could be dehydrogenation temperature of 1:7 phase and of 2:7 phase, respectively . XRD results show that the peaks of 1:7 phase for the hydrogenated alloys with x=0 .3, 0 .4 and 0 .5 occur at lower angles which indicate that the unit cells have expanded after absorbing hydrogen without a change in the crystal structure . The same results can also be obtained from the lattice parameters of 1:7 phase for alloys showed in Fig .2 . Firstly, H 2 molecule is absorbed on the surface of alloys, which is called physical adsorption . Then H 2 molecule is broken into H atom when activation energy is offered, which is called chemical adsorption . H atom absorbed on the surface will enter into lattice gap and diffuse toward the inside of alloys . In the end, the hydride is produced in the form of solid solution . It can be seen that a, c and V of 1:7 phase for alloys increase with increasing Fe content because the atomic radius of Fe is larger than that of Co, which indicate H atoms can more easily enter into lattice gap . In addition, electronegativity of Fe atom is 1 .83, lower than that of Co atom(1 .88) . It is known that electronegativity of H atom is 2 .20 . The greater electronegativity difference for two atom, The easier combination between two atom . So the addition of Fe atom lead to decreasing of activation energy and is conductive to chemical adsorption . Thus, the imp...
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