3232 XXXI International Mineral Processing Congress 2024 Proceedings/Washington, DC/Sep 29–Oct 3
quarter of the thickness of the magnet, which corresponds
to an approximately 90 vol% conversion of the magnet.
X-ray diffraction on a pulverized, slow cooled magnet
showed major peaks that correspond to Co, Co0.7Fe0.3,
SmFeO3, and Sm2Co17 as shown in Figure 3. No oxides
of Co were observed. It is unclear from the XRD pat-
tern whether Sm2O3 is present in the oxidized magnets.
The second most intense peak for Sm2O3 at 2θ =32.7°
was observed in the XRD pattern, but the main peak for
Sm2O3 at 2θ =28.2° was absent (Martin and McCarthy
1991). SmFeO3 has a major peak at 32.7 ° and its other
peaks match well with minor peaks in the XRD pattern
suggesting that SmFeO3 and not Sm2O3 formed during
the oxidation (Kharko et al. 2014). While SmCo magnets
are mostly Sm and Co, Fe is added in small quantities to
alter the magnets properties, so the presence of this phase
and the Co0.7Fe0.3 phase are believable (Ojima et al. 1977).
Furthermore, the equilibrium pO2 for Fe/FeO is lower than
Co/CoO at 800 °C, so it is conceivable that some of the
Fe oxidized and reacted with the samarium oxide to form
SmFeO3 (Barin and Platzki 1995 Kharko et al. 2013).
The magnets largely retained their shape, darkening
and swelling slightly but, otherwise, remained in one piece.
No evidence of microcracking was seen in the quenched
magnets using an optical microscope. Both the quenched
and slow cooled-magnets developed macroscopic cracks in
the oxide layer which extended from the edges of the mag-
net to the unoxidized core however, these appear to have
occurred before cooling, as evident by the circular oxida-
tion front at the tip of the crack in Figure 4. Additionally,
some edges of the oxidized magnets did not crack as shown
in Figure 5. Some porosity was seen in the treated magnets,
but this was also present in the as-received magnets.
Grinding the magnets with the ring and puck gave the
particle size distributions shown in Figure 6. The quenched
Figure 3. X-ray powder diffraction pattern of the slow cooled oxidized magnets indicating the presence of Co, Co
0.7 Fe
0.3 ,
SmFeO
3 ,and Sm
2 Co
17 (Swanson et al. 1966 Baker 1997 Kharko et al. 2014 Yan et al. 2009)
Figure 4. Cross section of a quenched, oxidized magnet
showing a crack in the oxidized layer
quarter of the thickness of the magnet, which corresponds
to an approximately 90 vol% conversion of the magnet.
X-ray diffraction on a pulverized, slow cooled magnet
showed major peaks that correspond to Co, Co0.7Fe0.3,
SmFeO3, and Sm2Co17 as shown in Figure 3. No oxides
of Co were observed. It is unclear from the XRD pat-
tern whether Sm2O3 is present in the oxidized magnets.
The second most intense peak for Sm2O3 at 2θ =32.7°
was observed in the XRD pattern, but the main peak for
Sm2O3 at 2θ =28.2° was absent (Martin and McCarthy
1991). SmFeO3 has a major peak at 32.7 ° and its other
peaks match well with minor peaks in the XRD pattern
suggesting that SmFeO3 and not Sm2O3 formed during
the oxidation (Kharko et al. 2014). While SmCo magnets
are mostly Sm and Co, Fe is added in small quantities to
alter the magnets properties, so the presence of this phase
and the Co0.7Fe0.3 phase are believable (Ojima et al. 1977).
Furthermore, the equilibrium pO2 for Fe/FeO is lower than
Co/CoO at 800 °C, so it is conceivable that some of the
Fe oxidized and reacted with the samarium oxide to form
SmFeO3 (Barin and Platzki 1995 Kharko et al. 2013).
The magnets largely retained their shape, darkening
and swelling slightly but, otherwise, remained in one piece.
No evidence of microcracking was seen in the quenched
magnets using an optical microscope. Both the quenched
and slow cooled-magnets developed macroscopic cracks in
the oxide layer which extended from the edges of the mag-
net to the unoxidized core however, these appear to have
occurred before cooling, as evident by the circular oxida-
tion front at the tip of the crack in Figure 4. Additionally,
some edges of the oxidized magnets did not crack as shown
in Figure 5. Some porosity was seen in the treated magnets,
but this was also present in the as-received magnets.
Grinding the magnets with the ring and puck gave the
particle size distributions shown in Figure 6. The quenched
Figure 3. X-ray powder diffraction pattern of the slow cooled oxidized magnets indicating the presence of Co, Co
0.7 Fe
0.3 ,
SmFeO
3 ,and Sm
2 Co
17 (Swanson et al. 1966 Baker 1997 Kharko et al. 2014 Yan et al. 2009)
Figure 4. Cross section of a quenched, oxidized magnet
showing a crack in the oxidized layer