HYDROGENATION AND NITROGENATION OF SMFE2

The characteristics of the reactions between SmFe2 and H-2 or N2 were studied by isochorothermal analysis, X-ray diffraction and thermomagnetic analysis. Under hydrogen pressures of below 150 kPa, SmFe2 absorbs hydrogen instantaneously and exothermically at temperatures of between 120 and 160-degrees-C. When hydrogenation occurs in an ''excess of hydrogen gas'', the reaction products are dependent on the maximum hydrogenation temperature: unreacted SmFe2, SmFe2 hydride, amorphous (Sm,Fe2) hydride, Sm hydride and alpha-Fe. When hydrogenation occurs in a ''deficient hydrogen gas'' atmosphere, Sm2Fe17, SmFe3 and Sm are also found in the reaction products, depending on the maximum hydrogenation temperature. The amorphous (SmFe2) hydride begins to decompose into an Sm-poorer amorphous (Sm,Fe2) hydride and Sm hydride immediately after its formation. At about 325 -degrees-C, alpha-Fe also begins to crystallize and the composition of the amorphous phase varies continuously. The Curie temperatures of SmFe2, SmFe2 hydride and amorphous (Sm,Fe2) hydride are 683 K, 110 K and 348-508 K (depending on the metal composition and hydrogen content) respectively. On heating under vacuum, the amorphous (Sm,Fe2) hydride begins to lose hydrogen at temperatures of between 160 and 200-degrees-C with simultaneous decomposition into Sm hydride and an Sm-poorer amorphous phase. The reaction of SmFe2 powder with N2 begins at about 250-degrees-C with the formation of SmN, alpha-Fe and Sm. At high temperatures (950-degrees-C), only SmN and alpha-Fe exist. When bulk SmFe2 is used instead of powder, the reaction is not complete (even at 950-degrees-C) and SmFe3 begins to appear. No interstitial SmFe2 nitride was formed at any temperature.