Analytical electron microscopy of SmFeTaN

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www2.ijs.si/goran/
Analytical electron microscopy of SmFeTaN based
permanent-magnet materials
Goran Draic, Paul McGuiness, Kristina uek,
Spomenka Kobe
Joef 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
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basics of HDDR process
Sm Fe Ta cast alloy HDDR hydrogen
absorption desorption disproportionation recombina
tion fine-grained material high coercivity
Sm2Fe17 lt--H2--gt SmH2 Fe
Question What is the reason for the shift of the
temperature of hydrogenation?
Chemical composition of phases changes during
consecutive HDDR process
Hypothesis
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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
magnetic material, powder samples, small grains,
presence of nano precipitates, peak overlapping,
low concentration (below 2 atom)
Expected problems
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instruments methods
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
TEM EDXS standards quantification
Sample preparation
Gatan dimpler Baltec ion mill
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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
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microstructure
Cast alloy (SmFe) a- Fe SmFe2 Sm2Fe17
Cast alloy Ta Ta3Fe7 SmFe2 Sm2Fe17
Sm2Fe17
Ta precipitate
SmFe2(3) precipitate
HDDR (Ta) Ta3Fe7 SmFe2 Sm2Fe17
Cast HDDR
Large amount of very fine precipitates could
interfere with the analyses.
Ta3Fe7, SmFe2 precipitates
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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
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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.