SM2FE17-NITRIDE-BASED PERMANENT-MAGNETS PRODUCED BY THE HYDROGENATION DECOMPOSITION DESORPTION RECOMBINATION (HDDR) PROCESS

The hydrogenation-decomposition-desorption-recombination (HDDR) process in conjunction with nitrogenation has been employed to produce Sm2Fe17-nitride-based permanent magnets. The HDDR process has been studied in terms of the reaction characteristics, the phases present and the development of the magnetic properties at the different stages involved in the process. On heating under hydrogen gas, the Sm2Fe17 phase begins to absorb hydrogen at a temperature of about 185-degrees-C and up to 250-degrees-C, where the hydrogen concentration reaches a maximum value of about 2.4 H atoms per mole of Sm2Fe17. Subsequently, interstitial hydrogen desorption occurs gradually up to a temperature of 510-degrees-C (SM2Fe17H0.1), where a massive absorption of hydrogen takes place owing to the decomposition of the Sm2Fe17H0.1 into Sm hydride + alpha-Fe. Additional beat treatment of the ''Sm hydride + alpha-Fe'' mixture at temperatures of about 725-degrees-C or above under vacuum or argon gas flow causes the simultaneous desorption of the Sm hydride (forming Sm + H-2) and recombination of Sm + alpha-Fe to form microcrystalline grains of the Sm2Fe17 phase. Subsequent nitrogenation at about 450-degrees-C produces Sm2Fe17-nitride which exhibits an intrinsic coercivity of 8.2 kOe, a Curie temperature of 470-degrees-C and a maximum energy product of about 14 MG Oe.