S.W. Wang et al.: Densification of Al O3 powder using spark plasma sintering
2
IV. CONCLUSIONS
3. K. Matsugi, T. Hatayama, and O. Yanagisawa, J. Jpn. Inst. Met.
9, 740 (1995).
. S.H. Risbud, C.H. Shan, A.K. Mukherjee, J.S. Bow, and R.A.
Holl, J. Mater. Res. 10, 237 (1995).
5
From the experimental results mentioned above, some
conclusions are drawn as follows:
4
(
1) SPS was effective in the preparation of fine-
5. T. Nishimura, M. Mitomo, H. Hirotsuru, and M. Kawahara,
J. Mater. Sci. Lett. 14, 1046 (1995).
grained, nearly fully dense Al O ceramics from the
2
3
6
7
. S.H. Risbud and C.H. Shan, Mater. Lett. 20, 149 (1994).
. C.H. Shan, S.H. Risbud, K. Yamazaki, and K. Shoda, Mater. Sci.
Eng. B 26, 55 (1994).
powder with a smaller particle size by employing a high
heating rate. However, rapid sintering of SPS by a high
heating rate did not work so well when the particle size
of the starting powder was too large (e.g., 21.4 m)
because its driving force for densification was low.
8. M. Yoshimura, T. Ohji, M. Sando, Y-H. Choa, T. Sekino, and
K. Niihara, Mater. Lett. 38, 18 (1999).
9
. L. Gao, H.Z. Wang, J.S. Hong, H. Miyamoto, K. Miyamoto, S.D.
De La Torre, and Y. Nishikawa, in Proc. of the 2nd Inter. Symp.
On the Science of Engineering Ceramics (EnCera’98), edited by
K. Niihara, T. Sekino, E. Yasuda, and T. Sasa (Osaka, Japan,
1998), p. 401.
(2) Abnormal grain growth was found in an Al O3
2
sample when a slower heating rate was applied during the
SPS process, prohibiting further densification of the
sample, similar to the case of pressureless sintering or hot
pressing.
10. M. Omori, A. Okubo, K. Gilhwan, and Y. Hirai, J. Mater. Syn.
Proc. 5, 279 (1997).
1
1. Y.S. Kang, K. Noda, L.D. Chen, S. Moriya, and M. Niino, in Joint
ASME, ASCE & SES Summer Meeting (McNU’97) (Northwestern
University, Evanston, IL, 1997), p. 414.
(3) Microstructure inhomogeneity, that is, the edge
was denser than the inside of the sample, appeared in
the sample sintered at 1550 °C for a short holding time
12. M. Omori and Hirai, New Ceram. 7, 27 (1994).
(
10 min). When the holding time was 30 min, the inside
13. M. Orihashi, Y. Noda, L.D. Chen, Y.S. Kang, A. Moro, and
T. Hirai, in Proc. 4th Int. Symp. on Functional Gradient Materi-
als, edited by I. Shiota and Y. Miyamoto (AIST Tsukuba Research
Center, Tsukuba, Japan, 1996), p. 569.
could be sintered almost as dense as the edge of the
sample. This result suggested that Al O powder was
2
2
heated by the heat from the graphite mold and punches.
It also implied that optimization of the SPS process with
regard to the starting powder, sample size, heating rate,
holding time, and mechanical pressure is necessary for
preparation of Al O or other nonmetallic materials with
a homogeneous microstructure.
4) Rapid sintering was ascribed to the efficient heat
transfer, because the graphite mold and punches were the
heating elements, and to application of a high heating
rate in SPS.
1
4. Y. Ishiyama, in Proc. of 1993 Powder Metallurgy World Con-
gress, edited by Y. Bando and K. Kosuge (Japan Society of Pow-
der and Powder Metallurgy, Kyoto, Japan, 1993), p. 931.
1
1
5. M. Tokita, J. Soc. Powder Technol. Jpn. 30, 790 (1993).
6. S.H. Risbud, J.R. Groza, and M.J. Kim, Philos. Mag. B 69, 525
2
3
(1994).
1
7. M. Omori, J. Jpn. Soc. Powder Powder Metall. 45, 1055 (1998).
(
18. Y. Kinemuchi, H. Funakoshi, and K. Ishizaki, J. Ceram. Soc. Jpn.
106, 535 (1998).
1
2
2
2
9. H. Tomino, H. Watanabe, and Y. Kondo, J. Jpn. Soc. Powder
Powder Metall. 44, 974 (1997).
0. S. Sumi, Y. Mizutani, and M. Yoneya, J. Jpn. Soc. Powder Pow-
der Metall. 45, 153 (1998).
1. S.W. Wang, L.D. Chen, Y.S. Kang, M. Niino, and T. Hirai, Mater.
Res. Bull. (in press).
2. W.D. Kingery, H.K, Bowen, and D.R. Uhlmann, Introduction to
Ceramics, 2nd ed. (Wiley-Interscience, New York, 1976).
3. M.P. Harmer and R.J. Brook, J. Br. Ceram. Soc. 80, 147 (1981).
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ACKNOWLEDGMENTS
The authors are grateful to Dr. M. Omori (IMR, To-
hoku University, Sendai, Japan) for his helpful discus-
sions. This research was partially funded by the Ministry
of Education, Science, and Culture of Japan under a
Grant-in-Aid for Scientific Research on Priority Areas
2
2
25. D-J. Chen and M.J. Mayo, J. Am. Ceram. Soc. 79, 906 (1996).
2
6. Huesup Song and R.L. Coble, J. Am. Ceram. Soc. 73, 2077
1990).
7. T. Koyama, A. Nishiyama, and K. Niihara, J. Mater. Sci. 28, 5952
1993).
(No. 08243102).
(
2
(
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