HYDROGENATION OF SM2FE17

The characteristics of the reaction between Sm2Fe17 and H-2 have been studied by means of isochorothermal analysis, X-ray diffraction and thermomagnetic analysis. Sm2Fe17 begins to absorb hydrogen at about 185-degrees-C. At 250-degrees-C the hydrogen content reaches the maximum value of 2.4 atoms of hydrogen per mole of Sm2Fe17. Subsequent cooling to room temperature causes an increase in the hydrogen concentration up to the value of 5 H atoms per mole of Sm2Fe17. Above 250-degrees-C the Sm2Fe17 hydride begins to desorb hydrogen and its composition becomes Sm2Fe17H0.1 at about 500-degrees-C. The Sm2Fe17 hydride desorbs and absorbs hydrogen reversibly in the temperature range between 25 and 500-degrees-C. At about 510-degrees-C the hydride begins to decompose into Sm hydride and alpha-Fe. The decomposition reaction is accompanied by massive hydrogen absorption. The Sm2Fe17 hydride has the rhombohedral crystal structure (the same as the parent compound) with a 3.4% expanded lattice with parameters a = 8.667 angstrom and c = 12.520 angstrom. The stresses introduced by the lattice expansion cause crack formation along the Sm2Fe17 grain boundaries and the samples become friable. The Curie temperature and saturation magnetization are 280-degrees-C and 159 e.m.u. g-1 for Sm2Fe17H5 as compared with 135-degrees-C and 116 e.m.u. g-1 for Sm2Fe17. For both Sm2Fe17 and Sm2Fe17 hydride the easy direction of magnetization is perpendicular to the c direction in the rhombohedral structure.