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Elemential managanese and aluminum powders were mechan- ical
alloyed by high ball milling of centrifugal tpye argon
atomosphere. Amorphous Mn sub x Al sub 1-x powders were pre-
pared in the concentration range of 0.4 .ltoreq. X .ltoreq. 0.9
and the Mn sub 5 Al sub 8 phase appeared behore amorphiz-
ation. the enthalpies of mixing was calculated for these amor-
phous powders and the effect of enthalpies on the reaction rate
of amorphization was also discussed. Manganses concentration
was 70-72 wt% in the Mn-Al binary alloy system. the .tau. phase
was the only ferromagnetic phase. Elemental manganese (70.5
wt%) and aluminum (29.5 wt%) powder would be enough mixed (for
composing powder of Mn sub 0.55 Al sub 0.45), then these mixed
powders were milled used by mechan- ical alloying method for
10-150 hour and the milling time of 50 hour was found best.
Accoding to this optimal condition, we add- ed elemential
carbon (0.2-2.0 wt%) powders to the Mn sub 0.55 Al sub 0.45
powders. After 50 hour milling, the mechanically alloy- ed
powders was compact into a disk of 6 mm diameter and 1 mm
thickness under a pressure of 780 MPa. The disks were sealed in
quartz tubes under vaccum (10E-2 Torr) and annealed at 450-650
degree C for 0.5-5 hour, then quenched in water order to obtain
the .tau. phase. When the different carbon content of 50 hour
milled Mn sub 0.55 Al sub 0.45 powder annealed at 450-650
degree C for 0.5-5 h, A maximum value of the saturation
magnetization 78 emu per gram was obtained, for adding 0.6 wt%
of carbon and anneaded at 600 degree C for 2.5 hour. The
coercivity increased with increasing carbon concentration
(0.2-2.0 wt%) and its value was 1400-2000 Oe.
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