Chemical Stability and Hydrogen Reaction Behavior of SmCo 2:17-Type Permanent Magnets

Herein, the reaction behavior and chemical stability of two commercially available SmCo 2:17-type sintered magnets with nominal composition of Sm23.75Co48.67FebalCu4.91Zr2.37 and Sm24.95Co48.80FebalCu4.46Zr2.68 (wt%) are investigated. The magnets are placed in a hydrogen atmosphere with systematically varied pressure, exposure time, and temperature ranging from 1-11 bar, 2-10 d, and 25-500 degrees C, respectively. Hydrogen content, magnetic properties, microstructure, and lattice constants are characterized in detail. It is found that for short exposure times like 2 d an activation temperature of 120 degrees C is necessary to initiate the reaction and to increase the amount of hydrogen in the Sm-Co material. Hydrogen absorption starts at lower temperatures with longer exposure times. An increase in exposure time, temperature, or pressure leads to a higher hydrogen content and a decrease in remanence B-r, energy product (BH)(max), and coercivity H-cB. Lattice expansion, estimated by X-ray diffraction analysis, correlates with the increasing amount of hydrogen in the Sm-Co magnets. With respect to all varied parameters under investigation, the exposure temperature has the highest impact on the observed property changes followed by reaction time and H-2 pressure.