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Analytical electron microscopy of SmFeTaN based permanent-magnet materials

www2.ijs.si/~goran/. Analytical electron microscopy of SmFeTaN based permanent-magnet materials. Goran Dražič , Paul McGuiness, Kristina Žužek, Spomenka Kobe. Jožef Stefan Institute, Ljubljana, Slovenia. I J S. Keywords. high-energy permanent magnets bonded magnets HDDR SmFeN.

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Analytical electron microscopy of SmFeTaN based permanent-magnet materials

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  1. www2.ijs.si/~goran/ Analytical electron microscopy of SmFeTaN based permanent-magnet materials • Goran Dražič, • Paul McGuiness, Kristina Žužek, Spomenka Kobe Jožef Stefan Institute, Ljubljana, Slovenia I J S Keywords high-energy permanent magnets bonded magnets HDDR SmFeN material methods analytical electron microscopy energy dispersive X-ray spect. Story Using quant. EDXS the solubility of Ta in Sm2Fe17 phase was determined and specific phenomena during the preparation of the material explained

  2. Mass Flow Controller H2 Furnace Ar Gass mixer Vacuum N2 PC basics of HDDR process Sm + Fe + Ta cast alloy HDDR hydrogen absorption desorption disproportionation recombination fine-grained material high coercivity Sm2Fe17 <--H2--> SmH2 + Fe Question: What is the reason for the shift of the temperature of hydrogenation? Hypothesis: Chemical composition of phases changes during consecutive HDDR process

  3. chemical analysis of Sm-Fe-Ta Samples Method powder particles with size of several mm, consisting of 50 - 100 nm sized grains of main magnetic phase (Sm2Fe17) Analytical Electron Microscopy (TEM-EDXS) Sample preparation (TEM) powder hydrophobization mixing of powders pressing & heating solid disk Powder embedded in phenol-formaldehyde resin, grinding, dimpling, ion erosion Expected problems magnetic material, powder samples, small grains, presence of nano precipitates, peak overlapping, low concentration (below 2 atom%)

  4. instruments & methods TEM EDXS standards quantification Jeol 2000 FX transmission electron microscope Link AN-10000 system (UTW Si(Li)) Ta3Fe7 phase (cast with Ta) for Ta Sm2Fe17 phase (cast without Ta) for Sm Cliff-Lorimer method with absorption corrections Sample preparation Gatan dimpler Baltec ion mill

  5. quantitative TEM-EDXS analysis Optimisation of parameters beam diameter acquisition time choice of standards Corrections Absorption Fluorescence a compromise between spatial resolution, statistical error and specimen drift collecting time: 300s I Ta ~ 5000 cnts (3%) el. beam: 20-30 nm Standards: Ta3Fe7 Sm2Fe17 from cast Sample thickness: contamination spots Analytical conditions 5 min spectrum acquisition time, 20nm beam size, foil thickness 100+/-20 nm, absorption corrections

  6. Sm2Fe17 Ta precipitates SmFe2(3) microstructure Cast alloy (Sm&Fe) a- Fe SmFe2 Sm2Fe17 Cast alloy + Ta Ta3Fe7 SmFe2 Sm2Fe17 Sm2Fe17 Ta precipitate SmFe2(3) precipitate HDDR (Ta) Ta3Fe7 SmFe2 Sm2Fe17 Cast HDDR Ta3Fe7, SmFe2precipitates Large amount of very fine precipitates could interfere with the analyses.

  7. results Cast alloy (Ta) Ta at.% rel. s Ta3Fe7(standard) 29.60 +/- 1.7% Sm2Fe17 (Ta) 2.03 +/- 4.5% HDDR Sm2Fe17 (Ta) 1.23 +/- 11.9% Sm2Fe17 (Ta)1.20 +/- 6.0% (after corr.) a - Sm2Fe17 (Ta) b - SmFe2 (Ta) c - Ta3Fe7 “Correction” due to precipitates 20% of points with highest Ta concentration were discarded

  8. conclusions Analytical point of view Material preparation point of view Optimising the analytical parameters, the precision of measurements were improved, and the difference in the amount of Ta in hard magnetic phase was determined with enough confidence. The shift in the temperature of hydrogenation could be ascribed to the difference in chemical composition of the Sm2Fe17 phase.

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