S. Okada et al. / Journal of Alloys and Compounds 317–318 (2001) 315–319
319
4
. Conclusion
In this investigation crystals of manganese silicides
Mn Si , MnSi, and Mn Si were prepared from a high
5
3
27 47
temperature flux method using copper, tin or lead as fluxes.
From copper flux, only the two silicides MnSi and Mn Si
5
3
were formed. Crystals of other phases were smaller, and
not sufficiently large for property measurements. From tin
and lead fluxes, the three silicides Mn Si , MnSi, and
5
3
Mn Si crystals were prepared. The largest crystals were
2
7
47
those of Mn Si and MnSi as obtained from tin flux. These
5
3
crystals were of mm size. The oxidation sets in at
relatively high temperature for MnSi, namely at 10608C.
As-grown manganese silicide crystals were used for mea-
surements of Vickers microhardness and electrical resistiv-
ity. In this study, the electrical resistance of Mn Si and
5
3
MnSi crystals were found to be an order of magnitude
higher than earlier reported, based on sintered bodies [3].
The microhardness values of Mn Si are somewhat lower
5
3
than the value of MnSi. The microhardness values of the
compounds seem to be related to its crystal structure.
Acknowledgements
The authors would like to thank Dr. K. Iizumi, Miss T.
Tsuchiya and Mr. F. Matsukawa of Tokyo Institute of
Polytechnics, and Dr. L.-E. Tergenius of Uppsala Universi-
ty for their help in the experiments.
Fig. 3. TG-DTA curves of Mn Si , MnSi, and Mn27Si47 crystals heated
5
3
in air.
References
to identify any oxidation products by XRD. MnSi (cubic
system) shows high oxidation resistivity, while Mn Si
2
7
47
[
1] B. Aronsson, T. Lundstr o¨ m, S. Rundqvist, in: Borides, Silicides and
Phosphides, Methuen, London, 1965, p. 1.
(
tetragonal system) and Mn Si (hexagonal system) show
5 3
low oxidation resistivity. The resistivity towards oxidation
seems to be related to crystal structure and thermodynamic
stability. However, a large exothermic peak of the DTA
curve was found at about 11758C for Mn Si , and three
[2] P. Peshev, M. Khristov, G. Gyurov, J. Less-Common Metals 153
(
1989) 15.
[3] G .V . Samsonov, I.M. Vinitskii, in: Handbook of Refractory Com-
pounds, IFI/Plenum, New York, 1980, p. 136.
5
3
[
[
4] P.F. Wieser, W.D. Forgeng, Trans. AIME 230 (1964) 1675.
5] T.B. Massalski, in: 2nd Edition, Binary Alloy Diagrams, Vol. l, The
Material Information Society, ASM International, Ohio, 1990, p.
1588.
small endothermic peaks of the DTA curve were found at
about 10238C, 11258C and 11768C for Mn Si . The
2
7
47
following oxidation products were identified for Mn Si as
5
3
well as Mn Si , namely crystalline MnSiO (triclinic),
[6] S. Okada, T. Atoda, Nippon Kagaku Kaishi 5 (1983) 746, in
Japanese.
2
7
47
3
MnO (cubic), g-Mn O (tetragonal) and SiO (tetragonal).
2
3
2
[
[
[
7] S. Okada, K. Kudou, M. Miyamoto, Y. Hikichi, Nippon Kagaku
For Mn Si this leads to the following total formula:
5
3
Kaishi 12 (1991) 1612, in Japanese.
8] S. Okada, K. Kudou, T. Lundstr o¨ m, in: Proceedings of the Sixth
International Conference on Ferrite (ICF 6), 1992, p. 389.
9] S. Okada, K. Okita, K. Hamano, T. Lundstr o¨ m, High Temp. Mater.
Processes 13 (1994) 311.
Mn Si 1 6O → MnSiO 1 2MnO 1 g-Mn O 1 2SiO
2
5
3
2
3
2
3
The observed weight gain of about 30% at 12008C (Fig.
) corresponds to a transformation of |50% by volume of
3
[
10] S. Okada, T. Atoda, I. Higashi, Y. Takahashi, J. Less-Common
Metals 113 (1985) 331.
11] S. Okada, K. Iizumi, K. Kudaka, T. Shishido, T. Fukuda, in: 9th
Cimtec-World Forum on New Materials Symposium VII — Innova-
tive Materials in Advanced Energy Technologies, Vol. 24, 1999, p.
the Mn Si crystals. This reaction is probably exothermic.
5
3
[
The occurrence of three small endothermic peaks in the
DTA curve of Mn Si is probably associated with partial
2
7
47
melting of the MnSi22x phase. However, the phase rela-
tionships (Mn Si , Mn Si , Mn Si , and Mn Si )
6
35.
1
1
19
15 26
26 45
27 47
[12] T.B. Massalski (Ed.), Binary Phase Diagrams, American Society of
Metals, Metals Park, OH, USA, 1986, p. 1588.
and the corresponding part of the phase diagram [12] are
not well known and conclusions are uncertain.